CHAPTER 1

INTRODUCTION & PROBLEM FORMULATION

1.1 Problem formulation

As this dissertation work is based on Finite Element Analysis, so it is required that a

component on which analysis is to be done should have practical application and result of

experimental analysis could be compared with FE analysis results for validation. The

component chosen for this purpose is a Tail Lamp of a bike which finds widespread

applications in all vehicles.

The availability of the design of Tail Lamp is made possible due to the kind assistance

of Altair-Design Tech, New Delhi. The CAD model of Tail lamp has been generated in

CATIA.

The main objective in Tail Lamp is to restrict the temperature of a device within its

permissible range under worst operating conditions. The temperature can be kept within the

permissible range by mounting the device on a heat sink which conducts the heat away from

the junction of the device thereby keeping the temperature to a safe limit. As tail lamp is

subjected to heat generated by the bulb which leads to thermal stresses in components of tail

lamp so a coupled thermal and structural heat conduction linear static analysis of heat sink has

been carried out. The main objective of this dissertation work is to perform the Finite Element

Analysis of Heat Sink of a Tail Lamp so as to determine the maximum deflection, temperature,

stress distribution and its location in the tail lamp. The temperature, displacement and thermal

stress contours have been plotted and patterns are studied. The results are compared and

verified with available experimental and standard results.

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1.2 Introduction

Auto lights are very important, because they enhance visibility on the road and keep the driver

and the passengers’ safe especially in driving through poorly lit areas. There are many types of

lights used in vehicle; each has its own vital function and specific location in the vehicle.

The lighting system of a motor vehicle consists of lighting and signaling devices mounted or

integrated to the front, sides and rear of the vehicle. The purpose of this system is to provide

illumination for the driver to operate the vehicle safely after dark, to increase the conspicuity of

the vehicle, and to display information about the vehicle's presence, position, size, direction of

travel, and driver's intentions regarding direction and speed of travel.

1.3 Types of lamps

1.3.1 Forward illumination- Headlamps

Forward illumination is provided by high and low beam headlamps, which may be augmented

by auxiliary fog lamps, driving lamps, and/or cornering lamps.

Dipped beam

Dipped-beam (also called low, passing, or meeting beam) headlamps provide a light

distribution to give adequate forward and lateral illumination without blinding other road users

with excessive glare. This beam is specified for use whenever other vehicles are present ahead.

The international ECE Regulations for headlamps specify a beam with a sharp, asymmetric

cutoff preventing significant amounts of light from being cast into the eyes of drivers of

preceding or oncoming vehicle.

Main beam

Main-beam (also called high, driving, or full beam) headlamps provide an intense, centre-

weighted distribution of light with no particular control of glare. Therefore, they are only

suitable for use when alone on the road, as the glare they produce will dazzle other drivers.

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Rallye and off-road lamps

Vehicles used in rallying, off-roading, or at very high speeds often have extra lamps to broaden

and extend the field of illumination in front of the vehicle. On off-road vehicles in particular,

these additional lamps are sometimes mounted along with forward-facing lights on a bar above

the roof, which protects them from road hazards and raises the beams allowing for a greater

projection of light forward.

Front fog lamps

Front fog lamps provide a wide, bar-shaped beam of light with a sharp cutoff at the top, and are

generally aimed and mounted low. They may be either white or selective yellow as shown in

fig. 1.1. They are intended for use at low speed to increase the illumination directed towards the

road surface and verges in conditions of poor visibility due to rain, fog, dust or snow. As such,

they are often most effectively used in place of dipped-beam headlamps, reducing the glare

back from fog or falling snow, although the legality varies by jurisdiction of using front fog

lamps without low beam headlamps.

Fig 1.1 A pair of yellow fog lamps

Cornering lamps

On some models, white cornering lamps provide extra lateral illumination in the direction of an

intended turn or lane change. These are actuated in conjunction with the turn signals, though

they burn steadily, and they may also be wired to illuminate when the vehicle is shifted into

reverse gear.

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Spot lights

Police cars, emergency vehicles, and those competing in road rallies are sometimes equipped

with an auxiliary lamp, sometimes called an alley light, in a swivel-mounted housing attached

to one or both a-pillars, directable by a handle protruding through the pillar into the vehicle.

Front position lamps (parking lamps)

Nighttime standing-vehicle conspicuity to the front is provided by front position lamps, known

as parking lamps or parking lights and front sidelights as shown in fig. 1.2. These are not the

same as the sidemarker lights described below. The front position lamps may emit white or

amber light

Fig. 1.2 Parking lamps

Since the late 1960s, front position lamps have been required to remain illuminated

even when the headlamps are on, to maintain the visual signature of a dual-track vehicle to

oncoming drivers in the event of headlamp burnout With the vehicle's ignition switched off, the

operator may activate a low-intensity light at the front (white or amber) and rear (red) on either

the left or the right side of the car. This function is used when parking in narrow unlit streets to

provide parked-vehicle conspicuity to approaching drivers.

Daytime running lamps

Some countries permit or require vehicles to be equipped with daytime running lamps (DRL).

These may be functionally-dedicated lamps, or the function may be provided by e.g. the low

beam or high beam headlamps, the front turn signals, or the front fog lamps, depending on local

regulations.

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Fig. 1.3 LED daytime running lights

In ECE Regulations, a functionally-dedicated DRL must emit white light as shown in

fig. 1.3 with an intensity of at least 400 candelas on axis and no more than 1200 candelas in any

direction.

Sidemarker lights

Fig. 1.4 Amber rear sidemarker

Side-facing devices make the vehicle's presence, position and direction of travel clearly visible

from oblique angles as shown in fig. 1.4. The lights are wired so as to illuminate whenever the

vehicles' parking and tail lamps are on, including when the headlamps are being used.

Turn signals

Fig. 1.5 Vehicle with front turn signal and side repeater illuminated

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Turn signals — formally called directional indicators or directional signals, and informally

known as "directionals", "blinkers", "indicators" or "flashers" — are signal lights mounted near

the left and right front and rear corners of a vehicle, and sometimes on the sides as shown in

fig. 1.5, used to indicate to other drivers that the operator intends a lateral change of position

(turn or lane change).

1.3.2 Rear position lamps (Tail Lamps)

The taillight, also known as tail lamp, rear lamp or stop lamp, is found at the rear end of the

vehicle. It usually emits red light when the brake is stepped on, thereby warning the vehicle at

the back that the vehicle would stop. This gives the driver of the following vehicle time to slow

down so as not to bump into the preceding vehicle. Tail lamps consist of lens and frames called

the tail lamp bezel or tail light frame. They are mounted on the rear fender, thus they are also

called rear lamps. Tail light or tail lamp is a lighting system that is part of the vehicle usually

mounted at the rear of the vehicle. This group of lights on one mounting is consisting of

different lights with different function.

The signal lights or the turn lights are part of the tail light. As a regulatory standard, the

turn lights are colored yellow. This is used to indicate whether the vehicle is turning left or

right. These same set of lights are also used during emergency, as a hazard. The reverse lights

are another set of lights that are part of the tail light assembly. This light is used to illuminate

the rear of the vehicle when backing up. The reverse lights are automatically turned on when

the driver puts the vehicle in the reverse shift. These lights have the highest illumination among

the set of lights but not as bright as the head light.

Another part of the tail light system is the park light. The park light is also used as the

brake light. It has the largest part on the tail light assembly which automatically turns on when

the driver hits the brake or if the headlight is turned on. The park light signals the drivers

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behind the presence of other vehicle at night. The park light is also used during foggy and rainy

weather as an early warning to the vehicle at the rear.

From signal lights, park lights, brake lights, and reverse lights, the whole tail light

assembly is very important in every vehicle. With each function to perform the tail light is

standard to every vehicle on the road. Without it, drivers cannot detect whether there are

presence of other vehicles around him.

The tail lamp mainly consists of four parts as shown in figure 1.6.

Body

Heat sink

Reflector

Lens

Body of tail lamp protects the whole assembly from damage. Heat sink is used to

restrict the temperature of a device within its permissible range under worst operating

conditions thereby prolonging the life and usefulness of the lamps. Reflectors perform the very

important function of gathering the light emitted by the lamp and then directing it as required.

Reflector distributes the energy evenly in intended directions.

The plastic covering the taillight is called taillight lens, which may come in various shades.

Most vintage cars have glass tail light covers, which also come in several colors matching the

car giving it a monochromatic effect. These specialty lenses enhance the cars style while

adding safety to the driver and the passengers. Some have wire covering fixed over the lenses

for protection and added tough and trendy look. Latest models of cars use clear bulbs and red

reflector instead of clear rear lamps that use red taillight bulb. Mostly owners replace OEM tail

lamps with specialty taillights to achieve -Euro look. There are the so-called Euro Altezza tail

lights that use clear or smoked lens over red or amber lamps to provide a sporty and modern

look. Altezza tail lights were first used by Toyota’s Altezza sedan model marketed in Europe. It

became popular that the name was used to refer to these taillights, also known as Euro Tails.

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Night time vehicle conspicuity to the rear is provided by rear position lamps (also called

taillamps or tail lamps, taillights or tail lights). These are required to produce only red light, and

to be wired such that they are lit whenever the front position lamps are illuminated including

when the headlamps are on. Rear position lamps may be combined with the vehicle's brake

lamps, or separate from them. In combined-function installations, the lamps produce brighter

red light for the brake lamp function, and dimmer red light for the rear position lamp function.

The tail and brake light functions may be produced separately and/or by a dual-intensity lamp.

Regulations worldwide stipulate minimum intensity ratios between the bright (brake) and dim

(tail) modes, so that a vehicle displaying rear position lamps will not be mistakenly interpreted

as showing brake lamps, and vice versa.

Rear fog lamps

Fig. 1.7 Rear fog lamps in the bumper of a European-spec Chevrolet Corvette

In Europe and other countries adhering to ECE Regulation, vehicles must be equipped with one

or two bright red "rear fog lamps" (or "fog taillamps") as shown in fig. 1.7, which serve as

high-intensity rear position lamps to be energized by the driver in conditions of poor visibility

to enhance vehicle conspicuity from the rear. The allowable range of intensity for a rear fog

lamp is 150 to 300 candelas. Most jurisdictions permit rear fog lamps to be installed either

singly or in pairs. If a single rear fog is fitted, most jurisdictions require it to be located at or to

the driver's side of the vehicle's centerline whichever side is the prevailing driver's side in the

country in which the vehicle is registered. This is to maximize the sight line of following

drivers to the rear fog lamp. If two rear fog lamps are fitted, they must be symmetrical with

respect to the vehicle's centerline.

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Stop lamps (brake lamps)

Red steady-burning rear lights, brighter than the rear position lamps, are activated when the

driver applies the vehicle's brakes. These are called brake lights or stop lamps. They are

required to be fitted in multiples of two, symmetrically at the left and right edges of the rear of

every vehicle. The range of acceptable intensity for a brake lamp containing one light source

(e.g. bulb) is 60 to 300 candelas.

Centre High Mount Stop Lamp (CHMSL)

Fig. 1.8 Centre High Mount Stop Lamp

The CHMSL is intended to provide a deceleration warning to following drivers whose view of

the vehicle's left and right stop lamps is blocked by interceding vehicles. It also helps to

disambiguate brake vs. turn signal messages, where red rear turn signals identical in appearance

to break lamps are permitted, and also can provide a redundant brake signal in the event of a

brake lamp malfunction. The CHMSL is required to illuminate steadily; it is not permitted to

flash except in certain cases under severe braking. On passenger cars, the CHMSL may be

placed above the back glass, affixed to the vehicle's interior just inside the back glass as shown

in fig. 1.8 or it may be integrated into the vehicle's deck lid or into a spoiler.

Reversing lamps

To provide illumination to the rear when backing up, and to warn adjacent vehicle operators

and pedestrians of a vehicle's rearward motion, each vehicle must be equipped with at least one

rear-mounted, rear-facing reversing lamp (or "backup light") as shown in fig. 1.9.

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Fig. 1.9 Illuminated reversing lamps

These are currently required to produce white light by U.S. and international ECE regulations.

However, some countries have at various times permitted amber reversing lamps.

Rear registration plate lamp

The rear registration plate is illuminated by a white lamp designed to light the surface of the

plate without creating white light directly visible to the rear of the vehicle; it must be

illuminated whenever the position lamps are lit.

Rear overtake lights

Until about the 1970s in France, Spain, and possibly other countries, many commercial vehicles

had a green light mounted on the rear offside. This could be operated by the driver to indicate

that it was safe for the following vehicle to overtake.

Emergency warning devices-Hazard flashers

Also called "hazards", "hazard warning flashers", "4-way flashers", or simply "flashers".

International regulations require vehicles to be equipped with a control which, when activated,

flashes the left and right directional signals, front and rear, all at the same time and in phase.

This function is meant to be used to indicate a hazard such as a vehicle stopped in or alongside

moving traffic, a disabled vehicle, an exceptionally slow-moving vehicle (including, for

example, trucks climbing steep grades on Canadian expressways), or the presence of

stopped/slow moving traffic ahead on a high speed road. Some people are known to use them

in severe fog conditions, or simply when the vehicle has become a traffic hazard.

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Emergency Braking Display

Mercedes-Benz, Volvo, and BMW have released vehicles equipped with brake lamps having a

standard appearance when the driver brakes normally, and a unique appearance when the driver

applies the brakes rapidly and severely, as for example in an emergency. Mercedes' concept is

to flash the brake lamps rapidly under heavy deceleration, Volvo makes the brake lamps

brighter, and BMW uses "Adaptive Brake Lights" - brake lamps that use the normal brake

light, plus illuminating the normal rear running lamps to the same high intensity under a panic

stop.

The Volkswagen Group of manufacturers (VW, Audi, Seat & Skoda) also have a system on all

newer models that will turn on the hazard flasher under braking conditions hard enough to

activate the Emergency Brake Assist or ABS.

An experimental study at the University of Toronto has tested brake lights which

gradually and continuously grow in illuminated area with increasing vehicle deceleration rate

(i.e., increasing brake application pressure).

The idea behind such emergency-braking indicator systems is to catch following

drivers' attention with special urgency. However, there remains considerable debate over

whether the system offers a measurable increase in safety performance. To date, studies of

vehicles in service have not shown any significant such improvement.

1.4 History and development of Tail Lamps

How would one react if he saw an automobile without any taillight parts fitted to its rear?  He

would obviously conclude that the car or truck has not been completely manufactured yet. Now

go back to the 1900's or the 1910's. Such a vehicle would have been the norm then. The first

two decades of automobile history did not have auto tail lights fitted in each and every car. The

idea of informing other car drivers on the road about the presence of the car using an auto tail

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light was yet to become important.  It was only when the roads were paved and cars started

going faster with more powerful engines did this idea catch on.

Even then, the auto tail light was nothing more than a safety accessory that was

unavoidable. People often viewed the automotive tail light as unnecessary expense.  That is the

reason why cars often were fitted with just one tail light until the 1930's. Budget cars did not

come with tail lights on both sides. One had to buy the other part and get it fitted into the car

separately. The factory designed taillight was usually fitted to the left and this was enough to

comply with the safety norms existing then. The position of the tail light was no different than

the position of the passenger side view mirror today.  Its presence was an unnecessary expense

and was preferred only as an accessory to make the vehicle look different. Throughout the

1930's, budget vehicles came with just one tail light. The fact that the Great Depression had left

very little money in the hands of the ordinary man did not help either. The end of the 1930's

saw the beginning of the World War. Automobile manufacturers practically ceased to build

automobiles for civilians.

The entire industry was geared towards the war effort.  However, the condition and

status of the taillight improved in the 1950's when the automobile manufacturing industry

boomed.  As people had more money to spend, installing a pair of taillights became very

common. Soon, it became the standard norm and single tail light vehicles ceased to be

manufactured. Traffic safety regulations made it mandatory for a pair of tail lights to be fitted

in all vehicles and this was the final nail in the coffin. Over the years, the number of parts used

in tail lights has undergone numerous changes.  The earliest tail light was nothing more than a

metal plate with the electric socket fitted to it.  The bulb was fitted to the assembly and was

wired to the engine of the vehicle. Even the slightest bump would crash the glass and render the

taillight useless. Glass covers were then used to protect the bulb.  However, vibrations made it

very difficult to hold the glass properly in its place.  Toughened glass reduced the intensity of

the light but this was considered an acceptable compromise. The invention of plastic lenses

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made it easier to make taillight assemblies that were lighter, less prone to damage and easier

and cheaper to replace.

CHAPTER 2

LITERATURE REVIEW

There is a vast amount of literature related to Finite Element Analysis. Many research

publications, journals, reference manuals, newspaper articles, handbooks, books are available

of national and international editions dealing with basic concepts of FEA. Many other

publications indicate the success story of implementation of FEA on various components. The

literature review presented here considers the major development in implementation of FEA.

Pramote Dechaumphai and Wiroj Lim [1] presented the Finite element analysis procedures

for predicting temperature response and associated deformation including thermal stresses of

heated products. Finite element computer programs that can be used on standard personal

computers have been developed. The capabilities of the finite element method and the

computer programs are evaluated by the examples of: (l) heat transfer in amplifier fins, and (2)

thermal stress in an engine piston. Results from these examples demonstrate the efficiency of

the method for the analysis of heated products that have complex geometries.

William I. Moore et. al. [2] has developed a code which has the capability to perform

coupled specular radiation and fluid flow analysis using a ray tracing method. The code has

been applied to automotive lamp thermal analysis to accurately predict lamp surface

temperatures resulting from radiation and natural convection heating. The results have been

successfully correlated with empirical data using an infrared thermal imaging camera. The code

predictions were consistently within ±10% of measurements. The code can be applied to large

FEA models of unstructured three-dimensional meshes with four-node tetrahedral elements.

The ADINA-F Computational Fluid Dynamics code can now be used to perform thermal

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validation of automotive lamps for a wide variety of large and complex lamp designs. This

capability can significantly reduce design costs and expensive prototyping.

Chung-Yi Chu et. al. [3] have described that the heat source from cold cathode

fluorescent lamps (CCFLs) in the backlight module of a TFT-LCD TV causes the cell assembly

to warpage. The extruding phenomenon, appearing between the cell and its bezel, leads to

defects in display of the TFT-LCD TV. The study successfully simulates and predicts the

process by finite element analysis (FEA), computational fluid dynamics (CFD), and structure

heat transfer. Authors have shown the efficient experimental verification which uses kinds of

physical sensors to measure the temperature variation and thermal stresses on the surface of

LCD-TV cell. The achievements and techniques can be employed to analyze and design the

geometric parameters of different components in LCD-TV modules for product optimization.

J.M.M. Sousa et. al. [4] presented detailed measurements of wall temperatures and

fluid flow velocities inside an automotive headlight with venting apertures. Thermocouples

have been used to characterize the temperature distributions in the walls of the reflectors under

transient and steady operating conditions. Quantification of the markedly three-dimensional

flow field inside the headlight cavities has been achieved through the use of laser-Doppler

velocimetry for the latter condition only. Significant thermal stratification occurs in the

headlight cavities. The regime corresponding to steady operating conditions is characterized by

the development of a vortex-dominated flow. The interaction of the main vortex flow with the

stream of colder fluid entering the enclosed volume through the venting aperture contributes

significantly to increase the complexity of the basic flow pattern. Globally, the results have

improved the understanding of the temperature loads and fluid flow phenomena inside a

modern automotive headlight.

Piyapong Premvaranon et. al. [5] proposed an application of CAE technology in

automotive lighting design. Firstly, the thermal performance of a simple lighting system,

similar to automotive forward projector was predicted by using a finite element analysis. The

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multiphysics analysis was employed to account for heat transfer mechanism and thermal

deformation in the lighting system. Next, the beam pattern and irradiance of the lighting system

was predicted by using a ray tracing method. The beam shift due to the thermal deformation of

reflector and lens was also presented. The finite element thermal model for a lighting system

was built to predict the thermal behavior due to conduction, convection and heat radiation

within the lamp. The temperature distribution on reflector, lens and enclosed air were

calculated by coupling the fluid flow and heat transfer analysis. With the same thermal model,

the thermal deformation of reflector and lens was predicted by using the thermal distribution

result as a thermal load for structural analysis. The thermal results can be used as a guideline

for material selection or venting design of the lamp.

Lucas V. Fornace [6] investigated & utilized the Computer Aided Engineering (CAE)

topology optimization software in the analysis & design of the 2006 UC San Diego Formula

SAE vehicle as a means to determine the optimum material distribution within a component for

a given set of loading and boundary conditions. Rear suspension bell crank component using

modern topology optimization techniques was designed and compares the end product to that

of the 2005 model bell crank component. A hydraulic load cell system was created to simulate

the vehicle suspension forces and was used to physically test the original and optimized parts to

failure. Through the use of Altair OptiStruct® topology optimization software, a weight

savings of 24.3% coupled with an increase in yield strength of 29.7% was realized in the

optimized design of the 2006 bell crank.

Joseph Bielecki et. al. [7] described two methods of determining the junction

temperature of automotive lamp direct and indirect. Both are based on temperature

measurements, but the indirect method also requires a thermal resistance specified by the

manufacturer. A computer model for a typical plate finned heat sink design for a high power

automotive lamp was experimentally calibrated. Design of experiment analysis was performed

using a 3 level 3 input factor full factorial test matrix. The factors were defined as an active

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heat sink surface area, convection coefficient correlated to an airflow, and environment

temperature. Maintaining Tj of the lamp below its temperature limit by being able to measure

Tj directly, designing adequate heat sinks for the most stringent standard test environment, and

guarding the device from other heat sources in the lamp can be addressed by applying the

techniques in this study.

X. Luo et. al. [8] carried out thermal analysis of an 80 W street lamp. Sixteen

thermocouples were used to measure the temperatures at 16 different positions of the street

lamp. The results demonstrated that the temperature of the frame and the heat sink of the 80 W

street lamp remained stable at about 42C after several hours of lighting at a room temperature

of 11C, and the bulk material resistance of the heat sink could be neglected. Numerical

simulation was also used to analyse the temperature distribution of the lamp. The reliability of

the numerical model was proven by a comparison of simulation results with the experimental

data. Through simulations and the corresponding analyses it was found that the tested 80 W

LED street lamp would have poor reliability at an environment temperature of 45C.

Devender Kumar and Amit Kumar [9] carried out Finite Element Analysis of Rear Engine

Semi Floor (RESLF) city bus body structure with actual design considerations and loading

conditions. The CAD model of the bus body structure has been generated which has been

exported to hypermesh for preprocessing. FE model has been solved using Radioss Linear. The

Vonmises stress and displacement contours have been generated. It was observed that stresses

and displacements have been found within prescribed limits and structure could withstand the

load under the given conditions.

Vinod Chaudhari and Chandrakant Naiktari [10] has explained that reducing

design cycle time by using state of art CAE software is no longer sufficient to meet design

community productivity requirements. Also learning curve of getting familiar with new

release of CAE software often create hurdle for reduction in design cycle time. The design

community needs to customize CAE software like HyperMesh and standardize in-house

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design processes to improve productivity dramatically and reduce learning time of CAE

software to zero. A method to build automated shell meshing for complex surface model

using HyperMesh is presented to reduce meshing time.

R. Sandhya Rani and Kanchan Bag [11] described the validation of Dumper body

design through Finite Element Analysis. The preliminary design was carried out as per Telcon

standards and modeling was done using standard CAD tools.For FEA, meshing was performed

using Hypermesh. Linear static analysis was carried out for various load cases and all stress

results are found to be within safe limit. However, slight modification in design was done to

reduce cost and weight without compromising functional requirements. Linear static analysis

was performed with the same load cases and in order to find out the reliability of the body and

to investigate mechanical failures Drop/Impact test analysis was performed

Thomas Luce et. al. [12] have described that the first series cars with LED

frontlighting are already on the roads, and further projects using HB LEDs for forward lighting

are under development. A pseudo standard of the optical system for these headlamps seems to

be the projector type. However, contrary to the situation for Halogen and Xenon systems, the

lower temperature levels in LED headlamps permit the use of alternative lens materials.

Thermoplastics allow for cost effective production of highly customized lenses, exhibiting

significant weight advantages over glass lenses. This becomes even more important, if multi-

lens approaches are applied for adaptive LED headlamps. Benefits, challenges and ways for

further development of thermoplastic lenses in automotive headlamps have been discussed.

Author proved that even for Xenon applications, injection molded silicone lenses could be an

interesting alternative to conventional glass projector lenses, allowing for a styling freedom similar

to thermoplastic lenses.

K.F. Kwok et. al. [13] studied the high power Light Emitted diode (LED) and the heat

distribution of the heat sink. Thermal design examines by using the thermal analysis. They

provide an analysis of the thermal design of the heat sink that is amounted with LEDs. The

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work started form single LED and examined its thermal behavior and analysis its prediction of

the thermal point. The analysis provides an analytical study of the thermal data for a heat sink

unit under the fabrication of the LED.

William I. Moore et. al. [14] described the advance in automotive lamp designs result

in a more compact, aerodynamic packaging and the use of less expensive plastic materials for

the lens and housing. The smaller packaging and lower melting point of plastics have increased

the need for a predictive tool for simulating the lamp temperature rise under operating

conditions. The modeling of lamps requires sophisticated analysis tools incorporating

computational fluid dynamics and specular radiation. These tools use a finite element method

to solve a system of non-linear equations for velocity, pressure and temperature. In addition to

the non-linearity, the complex parabolic shape of the lamp reflector and lens requires very

powerful mesh generation capability in order to produce an adequately refined mesh.

MSC/PATRAN has become a common pre/post-processor for many analysis codes because of

the open CAE environment, advanced meshing capability, ease of applying loads and boundary

conditions and effective post-processing capability for displaying results.

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CHAPTER 3

INTRODUCTION TO CAE AND ITS TOOLS

3.1 Introduction

Computer-aided technologies are a broad term describing the use of computer technology to aid

in the design, analysis, and manufacture of products.

Computer Aided Engineering is Computer Aided technology for supporting engineers

in tasks such as analysis, simulation, design, manufacture, planning, diagnosis and repair.

Software tools that have been developed for providing support to these activities are considered

CAE tools. CAE tools are being used, for example, to analyze the robustness and performance

of components and assemblies. It encompasses simulation, validation and optimization of

products and manufacturing tools. In the future, CAE system will be major providers of

information to help support design teams in decision making.

CAE embraces the application of computers from preliminary design (CAD) through

production (CAM). Computer Aided Design, which is usually associated with computerized

drafting applications, also includes such diverse application programs such as those for

calculating the dimensional stack-ups due to tolerances, ergonomic studies with virtual people

and design optimization. Computer Aided Analysis includes finite element and finite difference

method for solving the partial differential equations governing solid mechanics, fluid

mechanics and heat transfer, but it also includes diverse program for specialized analyses such

as rigid body dynamics and control system modeling.

Computer aided manufacturing (CAM) includes programs for generating the

instructions for computer numerically controlled (CNC) machining to production and process

scheduling and inventory control. Recently, manufactures have been asked to design their

products for eventual recycling, and this aspect of engineering will undoubtedly fall under the 20

umbrella of CAE, but as of yet it doesn’t have its own acronym. Studies say that any design

engineer can save approx. 30% of time and cost by CAE tools.

Areas covered by CAE tools:

Stress analyses on components and assemblies using FEA (Finite Element Analyses)

Thermal and fluid flow analyses by Computational fluid dynamics (CFD)

Kinematics

Mechanical Event Simulation (MES)

Analyses tools for process simulation for operations such as casting , molding , and die

press forming

Optimization of the product or process

In general, there are three phases in any Computer Aided Engineering task:

Pre-processing – defining the model and environmental factors to be applied to it.

Analyses solver

Post-processing of results

3.2 Application Area

Aerospace

Automobiles

Metal Forming

Sheet Metal Forming

Drop testing

Can and shipping container design

Electronic component design

Glass forming

Plastic, mold and blow forming

Biomedical

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Metal cutting

Earthquake engineering

Failure analyses

Sports equipments

Civil engineering

3.3 CAE and Process Management

The various activities that make up Computer Aided Engineering are an essential part of the

product design cycle to speed up the design cycle, to ensure that the products designed are of

higher quality, and to reduce cost of the final product. Broadly, the tasks the designer has to

carry out, exists in two categories the first is model creation, while the second covers reporting

and interpretation of results.

Regardless of the category, many of the tasks are tedious, requiring a considerable

attention to detail. One way to improve a model is to use a checklist: element quality checks are

an excellent example of checklists. But suppose as a result of oversight or of ignorance, the

checklist has not been applied? Even worse, suppose the designer has neglected to report any

assumptions in the model and suppose the violation of these assumptions can lead to disaster:

Clearly, the potential impact of CAE errors can be very high.

Other Computer Aided Technologies are:-

The term CAD/CAM (computer-aided design and computer-aided manufacturing) is also

often used in the context of a software tool covering a number of engineering functions as

shown in fig 3.1.

22

Computer-aided architectural design (CAAD)

Computer-aided design and drafting (CADD)

Computer-aided drafting (CAD)

Computer-aided electrical and electronic design (ECAD)

Computer-aided industrial design (CAID)

Computer aided engineering (CAE)

Knowledge-Based Engineering (KBE)

Manufacturing Process Management (MPM)

Manufacturing process planning (MPP)

Manufacturing resource planning (MRP)

Product data management (PDM)

Product lifecycle management (PLM)

Reverse engineering (RE)

Fig – 3.1 Various Computer Aided Technologies

23

3.4. Computer Aided Analysis (CAA)

Computer Aided Analysis (CAA) is a technique by which approximate solution of a numerical

problem can be carried out. Computer Aided Analysis includes finite element analysis for

solving the partial differential equations governing solid mechanics, fluid mechanics, and heat

transfer, but it also includes diverse programs for specialized analysis such as rigid body

dynamics and control system modeling. The two most widely used methods in computer aided

analysis are Finite Element methods and Finite Difference method. The later are used mainly

for problems in Computational Fluid Dynamics (CFD), while the former is used in a wide

range of applications.

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CHAPTER-4

INTRODUCTION TO CAE SOFTWARE

4.1 List of available CAE Software

For the purpose of CAD model generation and Finite Element Analysis there are many

software packages available in the market [15]. List of such software and name of company

providing the software is given in Table- 4.1

S.NO. Software Company

1. Abaqus Dassault System

2. Abaqus Explicit Dassault System

3. Adams MSC software Corporation

4. Ansys Ansys,Ins

5. CASTFLOW Walkingtone Engg, Inc

6. CATIA Dassault System

7. CFX Ansys,Ins

8. FE-safe Safe Technology Ltd

9. Fluent Ansys,Ins

10. Unigraphics UGS-SIEMENS

11. Star-CD CD-adapco

12. Ls-dyna Liver more softwareTech. Group

13. MATLAB The Mathworks

14. Motion-solve Altair Engg. Inc.

15. MSC Fatigue MSC software Corporation

16. MSC Nastran MSC software Corporation

17. NX-Ideas SIEMENS-UGS

18. NX-Nastran SIEMENS-UGS

25

19. Optistruct Altair Engg. Inc.

20. Pam crash ESE Group

21. Radioss Altair Engg. Inc.

22. Solid WORKS 3D Vision Technologies

23. Batchmesher Altair Engg. Inc.

24. Hyperview Player Altair Engg. Inc.

25. HyperMesh Altair Engg. Inc.

26. Hypergraph Altair Engg. Inc.

27. Hypercrash Altair Engg. Inc.

Table- 4.1 Software and their provider companies

From all of the above software’s we have used Altair Hyperworks 9.0

Altair Hyperworks 9.0 package consists of:

(1) Altair Hypermesh (6) Altair Optistruct

(2) Altair Hyperview (7) Altair Hyperstudy

(3) Altair Motion Solve (8) Altair Data Manager

(4) Altair Batchmesher (9) Altair Assembler

(5) Altair Radioss

4.2 Altair HyperWorks

HyperWorks [16] is an enterprise simulation solution for rapid design exploration and decision-

making.  As one of the most comprehensive CAE solutions in the industry, HyperWorks

provides a tightly integrated suite of best-in-class tools for modeling, analysis, optimization,

visualization, reporting, and performance data management, Altair HyperWorks is one of the

26

leading softwares used in the industry with the broadest interoperability to commercial CAD

and CAE solutions.

4.2.1 System Requirements

The following are the system requirements to ensure the smooth running of Hypermesh on

system:

• System unit: An Intel Pentium 4 or AMD 64, running Microsoft 2000 Professional Edition,

Windows XP 32-bit, or Windows XP x64.

• Memory: 512 MB of RAM is the minimum requirement for all applications. However, for 64-

bit systems, 1 GB of RAM is the minimum requirement.

• Disk drive: 2.2 GB Disk Drive space (Minimum recommended size).

• A DVD drive is required for the program installation.

• Graphics adapter: Graphics card compatible with the supported operating systems, capable of

supporting 1024x768 High Color (16-bit), and a 17-inch monitor compatible with this type of

graphics card.

4.2.2 HyperWorks 9.0 applications:

Hypermesh Finite Element Pre and Post Processor

HyperCrash Finite element pre-processor for crash analysis

MotionView Multi-body dynamics pre- and post-processor

RADIOSS Finite element solver for the analysis of linear and

Non-linear structures, fluids and fluid-structure interactions

OptiStruct Finite element and multi-body dynamics based design and

Optimization software

HyperView High performance finite element and mechanical system

Post-processor, engineering plotter and data analysis tool

HyperView Player Plug-in and stand-alone utility to share and visualize 3-D

27

CAE models and results

HyperGraph Engineering plotter and data analysis too

HyperGraph 3D Engineering 3-D plotter and data analysis tool

HyperStudy Integrated optimization, DOE, and robustness engine

HyperStudyDSS Design support system for evaluation, exploration and Optimization

Data Manager A solution that organizes, manages, and stores CAE and

test data throughout the product design cycle.

Process Manager Process automation tool for HyperWorks and third party Software

4.3 Pre-Processor-HyperMesh 9.0

Altair HyperMesh is a high-performance finite element pre- and post-processor for major finite

element solvers, which allows engineers to analyze design conditions in a highly interactive

and visual environment. HyperMesh’s user-interface is easy to learn and supports the direct use

of CAD geometry and existing finite element models, providing robust interoperability and

efficiency. Advanced automation tools within HyperMesh allow users to optimize meshes from

a set of quality criteria, change existing meshes through morphing, and generate mid-surfaces

from models of varying thickness.

4.4 Solvers

4.4.1 RADIOSS

RADIOSS is Finite Element software which allows mechanical, structure, fluid, or fluid-

structure interaction problems resolution, under dynamic or static solicitations. The structures

can be subjected to large strains, large displacements, and large rotations by using the materials

non-linear behaviors.

RADIOSS is well suited to the simulation of rapid dynamic phenomena, such as the

study of hyper-velocity impacts in space, and is also used for simulating shocks and crash in

the automobile, aeronautics, rail, and marine industries.

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RADIOSS provides small and large deformation finite element, multi-body dynamics,

and sheet metal stamping analysis.

4.4.2 Altair OptiStruct 9.0

Altair OptiStruct is a finite element and multi-body dynamics software. OptiStruct can be used

to design, analyze and optimize structures and mechanical systems. Altair Optistruct 9.0 can be

used for solving FEA problems as well as Optimization problems.

Finite Elements Analysis capabilities of Optistruct

Different solution sequences are available for the analysis of structures and structural

components. Basic analysis features include:

Linear static analysis

Normal modes analysis

Linear buckling analysis

Frequency response analysis using the direct or modal method

Transient response analysis using the direct or modal method

Transient response analysis based on the Fourier method using direct or modal

frequency response analysis

Non-linear gap analysis

Structural Design and Optimization capabilities

Structural design tools include topology, topography, and free-size optimization.  Sizing, shape

and free shape optimization are available for structural optimization. In the formulation of

design and optimization problems, the following responses can be applied as the objective or as

constraints:  compliance, frequency, volume, mass, moment of inertia, center of gravity,

displacement, velocity, acceleration, buckling factor, stress, strain, composite failure, force,

synthetic response, and external (user defined) functions.  Static, inertia relief, nonlinear gap,

normal modes, buckling, and frequency response solutions can be included in a multi-

29

disciplinary optimization setup. Topology, topography, size, and shape optimization are the

three types of Optimization Methods used in Altair Optistruct 9.0 .These three can be combined

for the solution of a general problem.

Topology Optimization

Topology optimization generates an optimized material distribution for a set of loads and

constraints within a given design space.  The design space can be defined using shell or solid

elements, or both.  The classical topology optimization set up solving the minimum compliance

problem, as well as the dual formulation with multiple constraints are available.  Constraints on

Von Mises stress and buckling factor are available with limitations. 

Topography Optimization

Topography optimization generates an optimized distribution of shape based reinforcements

such as stamped beads in shell structures.  The problem set up is simply done by defining the

design region, the maximum bead depth and the draw angle.  OptiStruct automatically provides

the design variable creation and optimization control.  Manufacturing constraints can be

imposed using symmetry planes, pattern grouping, and pattern repetition. 

 Size and Shape Optimization

General size and shape optimization problems can be solved.  Variables can be assigned to

perturbation vectors, which control the shape of the model.  Variables can also be assigned to

properties, which control the thickness, area, moments of inertia, stiffness, and non-structural

mass of elements in the model.  All of the variables supported by OptiStruct can be assigned

using Altair HyperMesh. 

4.5 Post-processors and Data Analyzers

30

Altair HyperView

HyperView enables to visualize data interactively as well as capture and standardize post-

processing activities using process automation features. HyperView also saves 3-D animation

results in Altair's compact H3D format so as to can visualize and share CAE results within a 3D

web environment using Altair HyperView Player.

CHAPTER 5

31

FINITE ELEMENT ANALYSIS (FEA/FEM)

5. 1 Introduction

The finite element method is a numerical method for solving engineering and mathematical

physics problems. The typical use of this method is to solve the problems in the field of stress

analysis, heat transfer, fluid flow, and mass transfer and electromagnetic. This method can able

to solve physical problems involving complicated geometrics, loadings and material properties

which cannot be solved by analytical method. In this method, the domain in which the analysis

to be carried out is divided into smaller bodies or unit called as finite elements.

The properties of each type of finite element is obtained and assembled together and

solved as whole to get solution. Based on application, the problems are classified into structural

and nonstructural problems. Finite Element Analysis (or other numerical analysis),

development of structures must be based on hand calculations only. For complex structures, the

simplifying assumptions required to make any calculations possible can lead to a conservative

and heavy design. A considerable factor of ignorance can remain as to whether the structure

will be adequate for all design loads.

In structural problems, displacement at each nodal point is obtained. Using these

displacement solutions, stress and strain in each element are determined.

Similarly, the non-structural problems, a temperature or fluid property at each nodal point is/are

obtained. Using these nodal values, properties like heat flux, fluid flow etc., for each element is

determined. Since large computations are to be carried out, this method requires high-speed

computation facility with large memory. Finite element method (FEM) and Finite element

analysis (FEA) are both one and same term. But term FEA is more popular in industries while

FEM is famous at universities.

5.2 Brief history

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The finite element method used today was developed to its present state very recently.

According to Zinckiewicz [17], the development is occurred along two major paths, one in

mathematics and other in engineering; somewhere in between these two paths are variational

and weighted residual methods. Both of which requires trial functions to effect a solution. The

use of these functions data is sent back to almost 250 years. These trial functions are assumed

based on physical intuition and they are applied globally to get the solution for the problem.

The use of trial functions is neither considered as development in pure mathematical field nor

in engineering field.

In a paper by Gauss in 1795, trial functions were used in what is now called as the

method of weighted residuals. Later, Rayleigh used these functions in variational method in

1870 and by Ritz in 1909. In a landmark paper in 1915; Galerkin introduced a particular type of

weighted residual method which is called by his name as “Galerkin weighted residual method”.

In 1943, Courant introduced piecewise trial functions which are now called as shape functions.

These shape functions are applied in a smaller region (i.e. at element level) instead of applying

it globally which is made him to solve the real world problems. In the early 1940’s, aircraft

engineers were developing and using analysis method called force matrix method which is

recognized as early form of finite element method. In this method, the nodal unknowns are

forces not the displacements. When the displacements of each node are taken as unknown, the

method is called as “St method”.

In a paper in 1960, Clough first introduced the term “Finite element”. In 1965, Zinekiwicz

and Cheung applied FEM, to solve the non-structural problems. Szabo & Leo showed how the

weighted residual method, particularly the Galerkin method could be used in non-structural

problem analysis. However, the present day FEM does not have its roots in any discipline.

Mathematicians are trying to improve the mathematical background of FEM, while the

engineers are interesting in applications where FEM can be used. In most branches of

33

engineering, these developments have made the FEM as one of the most powerful numerical

solution method.

5.3 Finite Element Method (FEM)

Finite Element method (FEM) simulates a physical part or assembly’s behavior by dividing the

geometry of the part into a number of elements of standard shapes, applying loads and

constraints, then calculating variables of interest – deflection, stresses, temperature, pressures

etc. The behavior of an individual element is usually described by a relatively simple set of

equations. Just as the set of elements would be joined together to build the whole structure, the

equation describing the behaviors of the individuals elements are joined into a set of equations

that describe the behaviors of the whole structure.

FEM is

- A numerical method

- Mathematical representation of actual problem

- Approximate method

Definition of FEM is hidden in the world itself. Basic theme is to make calculation at

only limited number of points and then interpolate the result for entire domain (surface &

volume).

Finite- any continuous object has finite degree of freedom & it’s just not possible to solve in

this format. Finite Element Method reduces degree of freedom from infinite to finite with the

help of discretization i.e. (nodes & elements).

Element- all the calculations are made at limited number of points known as nodes. Entity

joining nodes and forming a specific shape such as quadrilateral or triangular etc. is known as

Element. To get value of variable (say displacement) at where between the calculation points,

interpolation function (as per the shape of element) is used.

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Method- There are three methods to solve any engineering problem. Finite Element Analysis

belongs to numerical method category.

A Finite Element program takes the elements one has defined, lists the equations for

each unknown value, puts them together as a matrix equation, and then solves all these for the

values of the unknown parameters [18].

The equilibrium equation is of the form:

[K] [u] = [f]

Since it’s analogous to the equations of spring deflection, K is often called stiffness matrix,

u is called the deformation vector, and f is called the load vector. K is a square matrix, with one

row and column for each unknown variable in the problem definition. If there are 100 nodes in

a model, and each node has 6 unknowns, then stiffness matrix would be 600 X 600. u and f are

each column-matrix which has 1 column and 600 rows.

5.4 Finite Difference Method (FDM)

In this approach, there are no elements – the discrete points are referred to as grid points or

grids some analyses program call for “Structured “ grids the numbering of and positioning of

grid points must follow specific patterns. Other analyses programs are less stringent in their

requirements unstructured grids or blocks are supported. It is used in fluid flow analysis.

5.5 Comparison of FEM and FDM

The major difference between FEM and FDM are:

The most altercative feature of finite difference is that it can be very easy to implement.

There are reasons to consider the mathematical foundation of the finite element

approximation more sound, for instance, because the quality of the approximation

between grid points is poor in FDM.

35

The quality of a FEM approximation is often higher than in the corresponding FDM

approach, but this is extremely problem dependent and several examples to the contrary

can be provided.

5.6 Basic Concept of FEM

The basic concept of FEM is that the structure to be analyzed is considered as an assemblage of

discrete pieces called “Elements”, which are connected together at a finite number of points

(or) nodes. The finite element is a geometrically simplified representation of a small part of the

physical structure.

Concept:

1. Divide the domain in which analysis is to be carried out.

2. Isolating one of the elements from each type and get the property of them.

3. Assembling the finite elements to get the property of whole domain.

Example: Determination of the area of a circle using the areas of triangles

Finite-element discretization [17]:

First the continuous region (i.e. the circle) is represented as a collection of a Finite number ‘n’

of sub regions say triangles. This is called discretization of the domain by triangles. Each sub

region is called as an “element”. Consider the two methods of discretizing of circle with

triangular elements as shown in fig. 5.1.

Fig - 5.1 Two methods of discretizing circle with triangular elements

36

Element equation:

From each method of discretization, Isolate one of the elements and get the property (i.e., areas

of triangle fig. 5.2 & 5.3.)

Assembly of elements and solution:

The approximate area of the circle is obtained by adding all areas of triangles; this process is

called assembly of the element.

Total area = Sum of the area of individual elements.

37

Convergence and error estimate:

The error in the approximation is equal to each difference between the area of the sector and

that of the triangle as shown in fig. 5.4.

Fig 5.4 Elemental Error

The error estimate for an element in type 1 and 2 are given by:

Total error (global error) is given by multiplying e1 or e2 by n

38

We now show that E1 and E2 tend to zero as n tends to infinity.

5.7 FEM Procedure

The following steps summarize the finite element procedure:

Fig – 5.5 Procedure of FEM39

5.8 Practical FEM through FEA Softwares/FEA Tools

In FEA softwares, the general process of finite element method is divided into three main

phases, preprocessing, solution, and post processing. There are a lot of softwares used for these

three phases. Some software such as ANSYS and ABAQUS are used for all the three phases

and some software used different softwares for these three phases. E.g. in Altair Hyperworks,

Hypermesh which is one of the best pre processing tool is used as Pre Processor and

Otpsitruct/RADIOSS are used as Solvers and then after solution Hypermesh and HyperView

are used for Post Processing.

Similarly for solution in MSC Nastran, MSC Patran is used as pre processor and Post

processor. In Femap with Nx Nastran , Femap is used as Pre- processor and Post-processor and

Nx Nastran is used as Solver.

Preprocessing

The preprocessing is a program that processes the input data to produce the output that is used

as input to the subsequent phase (solution).Here HyperMesh is used as a Pre-Processor.

Following are the input data that needs to be given to the preprocessor:

1. Type of analysis (structural or thermal, static or dynamic, and linear or nonlinear)

2. Element type.

3. Real constraints.

4. Material properties.

5. Geometric model.

6. Meshed model.

7. Loadings and boundary conditions.

The input data will be preprocessed for the output data and preprocessor will generate the data

files automatically with the help of users. These data files will be used by the subsequent phase.

40

Solution

Solution phase is completely automatic. The FEA software generates the element matrices,

computes nodal values and derivatives, and stores the result data in files. Optistruct and

RADIOSS are used as Solver in this problem. These files are further used by the subsequent

phase as for this purpose (postprocessor) to review and analyze the results through the graphic

display and tabular listings.

Post processing

The output from the solution phase (result data files) is in the numerical form and consists of

nodal values of the field variable and its derivatives. For example, in structural analysis, the

output is nodal displacement and stress in the elements. The postprocessor processes the result

data and displays them in graphical form to check or analyze the result. The graphical output

gives the detailed information about the required result data. The postprocessor phase is

automatic and generates the graphical output in the form specified by the user. HyperMesh and

HyperView are used for Post-Processing in this problem.

5.9 Key Assumptions in FEA

There are four basic assumptions that affect the quality of the solution and must be considered

for finite element analysis. These assumptions are not comprehensive, but cover a wide variety

of situations applicable to the problem. Moreover, by no means, do all the following

assumptions apply to all the situations. So, make sure to use only those assumptions that apply

to the analysis under consideration.

.Assumptions Related to Geometry

1. Displacement values will be small so that a linear solution is valid.

2. Stress behavior outside the area of interest is not important, so the geometric simplifications

in those areas will not affect the outcome.

3. Only internal fillets in the area of interest will be included in the solution.

41

4. Local behavior at the corners, joints, and intersection of geometries is of primary interest;

therefore no special modeling of these areas is required.

5. Decorative external features will be assumed insignificant for the stiffness and performance

of the part and will be omitted from the model.

6. The variation in mass due to the suppressed features is negligible.

Assumptions Related to Material Properties

1. Material properties will remain in the linear region and nonlinear behavior of the material

property cannot be accepted. For example, it is understood that either the stress levels

exceeding the yield point or excessive displacement will cause a component failure.

2. Material properties are not affected by the load rate.

3. The component is free from surface imperfections that can produce stress risers.

4. All simulations will assume room temperature, unless otherwise specified.

5. The effects of relative humidity or water absorption on material used will be neglected.

6. No compensation will be made to account for the effect of chemicals, corrosives, wears or

other factors that may have an impact on the long term structural integrity.

Assumptions Related to Boundary Conditions

1. Displacements will be small so that the magnitude, orientation, and distribution of the load

remain constant throughout the process of deformation.

2. Frictional loss in the system is considered to be negligible.

3. All interfacing components will be assumed rigid.

4. The portion of the structure being studied is assumed a separate part from the rest of the

system, therefore so that any reaction or input from the adjacent features is neglected.

42

5.10 Sources of Errors in FEA

1. The model contains fundamental flaws: parts missing not connected, or details are

inappropriate

2. The model may not properly represent the structure as built, or recorded in the engineering

drawings

3. The loads or boundary conditions may not represented properly

4. Failure to consider that a particular type of analysis was needed

5. Experience of the analyst inappropriate to the task at hand plus inadequate errors in applying

design codes

6. Computer is too small and slow to use fine meshing, run nonlinear analysis, and review

results in sufficient detail.

5.11 Advantages and Disadvantages of FEA

Advantages of FEM:

I. Irregular geometries can be modeled more accurately and easily.

2. Implementation of any type of boundary conditions is very easy.

3. With very little effort, heterogeneous and anisotropic materials can be modeled.

4. Any type of loading can be handled.

5. The element sizes can be varied throughout the model. Wherever it is necessary, we can use

fine meshes.

6. Whether the problem is linear or non linear, the basics (i.e. steps followed/implemented) of

FEA remain same.

7. Altering the element model with different loads, boundary conditions and other changes on

the model can be done easily.

43

Disadvantages:

1. FEA softwares are costlier.

2. Output result will vary considerably, when the body is modeled with fine mesh when

compared to body modeled with course mesh.

3. Before using an element for a problem, we should know about its capabilities and nature,

because no single element is available for all applications.

4. Even though the FEA softwares are user friendly but they are not relatively easier for use.

5.12 Applications of FEA [18]

The FEA can be used to analyze both the structural and non-structural problems.

(a) Types of structural problems.

(i) Stress analysis

a). Linear Analysis-Fig. 5.6

Fig 5.6 Linear Analysis

Example: Linear Analysis: - Plate with hole subjected to inplane loads.

Commonly used softwares: Nastran, Ansys, Abaqus, I-deas NX, Radioss, Cosmos, UG, Pro-

Mechanica, Catia etc.

44

b). Non-linear analysis- Fig. 5.7.

Fig.

Fig. 5.7 Non Linearity Analysis

Material Non-linearity - Machine element members are subjected to stress more than elastic

limit as shown in fig. 5.8.

Fig 5.8 – Material Non-Linearity

Geometrical non-linearity: - Thin shell structure is subjected axial or torsional loads. Though

component is within the elastic limit but due to very large length even small force causes large

deformation.

Both material and geometrical non-linearity: - Thin shell structures are subjected to mechanical

loading with high temperature creep effect. Commonly used softwares: Abaqus, Nastran,

Ansys, Marc, Radioss, LS Dyna etc

45

(ii) Eigen Buckling Analysis: Example: Connecting rod subjected to axial compression. This

analysis can be used to determine mode shape of buckling load and its critical loads.

Commonly used softwares: Nastran, Ansys, Abaqus

(iii) Dynamic Analysis-Fig. 5.9.

Fig 5.9 Types of Dynamic Analysis

Example: Beams subjected to different types of loading. This analysis can be used to determine

the mode shape of vibration with its natural frequencies.

Commonly used softwares: Nastran, Ansys, Abaqus, Matlab, I-deas NX, Radioss etc.

(b) Types of non-structural problems

(i) Heat Transfer Analysis:

Thermal Analysis- Fig. 5.10

Fig 5.10 Modes of heat transfer analysis46

Linear: - Steady state thermal analysis on composite wall.

Non-linear:- Thermal Analysis with anisotropic materials.

The heat transfer problem can be further classified as Steady state (time independent) and

Transient (time dependent)

Practical applications: Engine, radiator, exhaust system, heat exchangers, power plants, satellite

design etc. Commonly used softwares: Ansys, Nastran, Abaqus, I-deas NX etc.

(ii) Fluid-flow Analysis:

Computational Fluid Dynamics (CFD) is a branch of Fluid mechanics which uses Numerical

Methods to analyse fluid dynamics problems. It is based on Navies-Strokes equation (Mass

Momentum and Energy conservation equations)

Example: Fluid flow through pipes or channel.

(iii) Electromagnetic Analysis:

Example: Modeling of electromagnetic field of motor.

Recently FEM is used in Bio-Mechanical Engineering field. For example, stress analysis on

human parts like bones, joints, skull, tooth etc.

(iv) Fatigue Analysis

Calculations for life of the structure when subjected to repetitive load.

S- N curve (alternating stress vs. cycles) or E - N (alternating strain vs. reversals) is the base for

fatigue calculations (like a - E diagram for static analysis) as shown in fig. 5.11.

Fig 5.11 – S N Curve for fatigue analysis

47

(v) Noise Vibration and Harshness Analysis (NVH)

Practical applications: Computing the sound pressure levels is of utmost importance to

automobile, aeroplane and aerospace designers as customers always prefer a low noise level

Computing the response at the driver’s feet (brake pedal), mirror mounts, steering column and

seats plays a crucial role as the driver must be comfortable.

Commonly used softwares: Sysnoise, LMS — Virtual Lab, Matlab etc.

48

CHAPTER 6

FE MODELING METHODOLOGY

There are three steps in software based Finite Element Analysis-

1) Preprocessing

2) Proprocessing

3) Post processing

FE Modeling Methodology-Pre processing- The first step in preprocessing is to prepare a

CAD Model of Tail Lamp. CAD modeling of the complete Tail Lamp is generated using

CATIA software [19]. CATIA is having special tools in generative surface design to construct

typical surfaces, which are later on converted into solid. Solid models of all parts of the

structure are the assembled to make a complete structure. The process of assembly is very

much analogous to general process of fabricating structure while real production. CAD model

of our problem consists of four parts, which are assembled together in assembly design to make

a complete Tail Lamp model. The CAD model of Tail Lamp used for analysis is shown in Fig.

6.1

Fig 6.1-CAD Model of Tail lamp in CATIA

49

The CAD model has been prepared from various 2D drawing. After preparing the Tail

Lamp FE Model is generated in Hypermesh. Step by step procedure of preparing Finite

Element model is given in this chapter.

6.1 Importing the CAD Model

The model used in this dissertation is prepared in IGES (Initial Graphics Exchange

Specification) format which is compatible with all CAD software. After importing the CAD file

into Hypermesh, it is then saved in form of .hm format (say Tail Lamp.hm as shown in fig. 6.2)

until the FE model is not completed.

Fig 6.2-.Hm Model of Tail Lamp in Hypermesh

6.2 Geometry Visualization and Geometry Cleanup

Geometry can be imported into HyperMesh from many sources. A number of HyperMesh

functions rely on having surfaces properly connected, especially the automesh panel. So after

importing the CAD data, the first step is geometry cleanup. Geometry cleanup tools are used to

restore proper surface connectivity to part geometry [20]. The Geometry panel contains tools

50

Reflector

Heat Sink

Body

Lens

like quick edit, edge edit, point edit, autocleanup etc. which help in preparing surface geometry

for meshing. Geometry cleanup is one of the most time consuming task in the project. Meshing

quality depends very much on the quality of geometry. According to FEA engineers around one

fourth of the total time of a project should be utilized in studying and editing the geometry

before doing meshing, For example if the time allotted for a project is sixteen hours then four-

five hours should be spent in geometry editing and cleanup and properly understanding the

geometry Before starting the job geometry should be carefully checked for'

Duplicate surfaces

Small fillets

Scar lines

Beads

Intersection of components

Small Holes

The benefits of repairing CAD are:

Correcting any errors in the geometry from import

Creating the simplified part needed for the analysis

Ensuring proper connectivity of mesh

Obtaining a desirable mesh pattern and quality

6.3 Symmetry Check

After geometry visualization and check it is found out whether there is any symmetry

in the model or not. A structure possesses symmetry if its components are arranged in

a periodic or reflective manner.

Types of Symmetry:

Reflective (mirror, bilateral) symmetry

Rotational (cyclic) symmetry

51

Axisymmetry

Translational symmetry

Applications of the symmetry properties:

Reducing the size of the problems (save CPU time, disk space, post processing

effort, etc.)

Simplifying the modeling task

In Tail lamp model there is reflective symmetry in two components i.e. Heat sink and

reflector as shown in fig. 6.3. The model is symmetrical about XY plane. So this

symmetry can save a lot of time in meshing because we have to mesh only half part

of these two components & similar meshing can be reflected on other half.

Fig 6.3 Symmetrical components i.e. Heat sink and Reflector

6.4 Geometry Preparation or Simplification

Then after the first task that most analysts are faced with is that of preparing the geometry for

analysis. This involves the task of removal of features, extraction of mid-surfaces, changing the

shape of a part in order to simplify the geometry. Certain details of the shape, such as small

holes or blends, may simply not be necessary for the analysis being performed. Depending on

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the analysis, certain details in the geometry may be ignored as shown in fig. 6.4. This may

depend on:

• Importance of the part in the overall assembly

• Location of the feature relative to the area of interest in the analysis

• Size of the feature vs. the average size of the mesh being used

Fig. 6.4 Surface after Geometry simplification

When these details are removed, the analysis can run more efficiently. Additionally,

mesh quality is often improved as well. Changing the geometry to match the desired shape can

also allow a mesh to be created more quickly. Figure 6.5 shows the Tail Lamp model after

geometry simplification. If we compare this model with the previous one as shown in figure 6.1

we can observe that all the complex features like thread, projected ribs, fillets etc. have been

removed that were considered too small to be captured by the desired element size of 2(defined

later). The model is now represented in a much simpler form that suits the analysis that will be

performed.

Fig 6.5 Tail Lamp after Geometry Simplification

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6.5 Refining Topology to Achieve a Quality Mesh

“Topology refinement” is modifying topology in order to obtain a quality mesh [21]. Once a set

of surfaces has been obtained that accurately reflects the intended shape for the analysis, further

geometry cleanup may still be necessary. Topological details of the geometry may affect the

quality of the mesh created from the surfaces. These details may not reflect any major feature

of the part’s shape, and can be removed without concern. When modifying the topology affects

the shape of the surfaces, a compromise must be made between the part shape and the element

quality necessary for the analysis. Other times, adding topological features that do not change

the shape of the part may actually help create a better quality mesh as shown in fig. 6.6.

Fig-6.6 Topological refinement

Similar split surface and suppress operations are performed on Heat sink and Reflector to

produce quality mesh.

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6.6 Meshing

No. of Points - ∞ No. of Nodes = 8

DOF per point = 6 DOF per Node = 6

Total equations = ∞ Total equations = 48

Fig. 6.7 Meshing

Basic Theme of FEA is to make calculations only at limited number of points and then

interpolate the results for entire domain. Any continuous object has infinite degree of freedom

and it is not possible to solve the problem in this format. Finite element method reduces the

degree of freedom from infinite to finite with the help of discretisation i.e. meshing as shown in

fig. 6.7.

Element type can be decided on the base of

a) Geometry shape and size

b) Type of analysis

a) Geometry shape and size

Geometry shape and size are categorized as 1-D, 2-D and 3-D

1-D Meshing is used when one dimension is very large in comparison to other two dim. & is

created by connecting two nodes, software comes to know about only one out of 3 dimensions.

Remaining two dimensions i.e. area of c/s must be defined by the user as additional input data

& assigned to respective elements

Practical Example: Long shaft, rod, beam, column, spot welding, bolted joints, pin joints,

bearing modeling etc.

55

2-D Meshing is used when two dimensions are very large in comparison to third one.

Generally 2-d meshing is carried out on mid surface of the part. 2-d elements are planer just

like paper of this page. By creating 2-d element software comes to know 2 out of 3 required

dimensions. The third dimension i.e. thickness has to provided as an additional input data.

Practical example: Sheet metal parts, plastic components like instrument panels etc.

3-D Meshing is used when all the three dimension are comparable in all dimensions.

Practical example: Transmission casing, clutch, engine block.

b) Based on type of analysis:

Structural & fatigue analysis - Quad, hex elements are preferred over trias, tetras and pentas.

Crash and Non linear analysis - Priority to mesh flow lines and brick elements over tetrahedron.

Mould flow analysis - Triangular element are preferred over quadrilateral.

Dynamic analysis - When the geometry is border case as per above classification of 2-d & 3-d.

As all the three dimension of Tail Lamp are comparable so 3-D mesh & Tetra element is

preferred for meshing all the four components.

6.6.1 Element Type Options for 2D Shell Meshing

Different type of options for shell meshing:

1) Pure quad elements

2) Mixed mode

3) Equilateral triangle

4) Right Angle (R-tria)

Mixed mode is commonly preferred due to better mesh transition pattern (restriction: total tria

% <5). That’s why Tail lamp is first meshed with 2D mixed element.

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6.6.2 Element Length

The results of the analysis depend very much on the element size. As much as the element size

is reduced, results get close to the actual results. The judgment of element size is taken on the

basis of:

1) Based upon previous experience of similar type of problem or calculate the ratio of total

size of model to the size of element. Greater the ratio between sizes of model to the size

of element, more accurate will be the results.

2) Type of analysis: Linear static analysis could be easily carried out that too quiet fast

with high no of nodes and elements

3) Hardware configuration and graphics card capacity of available computer.

Therefore based upon the above points element length is taken as 2.

6.6.3 Meshing Techniques

2-D Meshing Technique

There are three techniques used for 2D mesh.

1) Automatic

2) Mapped(or interactive)

3) Manual

  AutomaticMapped(or interactive)

    Manual

Time required for meshing ↓~(Intermediate i.e. more than auto but less than

manual)↑

Geometry required √ √ XNo. of nodes and elements

generated↑ ~ ↓

User friendliness ↑ ~ ↓User's control over the mesh ↓ ~ ↑Structural mesh ( flow lines ) ↓ ~ ↑Experience or skill required ↓ ~ ↑

Patience ↓ ~ ↑Table 6.1 Comparison b/w various types of 2D mesh

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Based upon the above table we have selected Manual 2D mesh for meshing all the components.

There are lots of commands in manual meshing. But some of the main commands used for

meshing are spline, ruled, drag, line drag etc. Depending upon the needs automesh is also

utilized.

The automesh allows creating meshes or re-meshing existing meshing interactively or

automatically on surfaces or groups of elements. The sub-panels on the automesh panel can be

used to provide specific meshing parameters.

The size and bias options is used for meshing surfaces or re-meshing existing meshes

with a great deal of control over how the mesh is created. Fig. 6.8 shows the size & bias sub-

panel. Here we can adjust the element size and mesh style. Fig 6.9 shows the automeshing of a

surface using size and bias command having mixed element

Fig. 6.8 Automesh panel when Size and Bias subpanel is on

Fig 6.9 Automeshing of a surface using size and bias command having mixed element

In QI optimized meshing, the surfaces are meshed to optimize the quality index (QI) of

the elements generated. A criteria file can be provided or the quality index panel can be

updated with desired quality criteria. The surfaces are then meshed with algorithms that

58

Mixed element

produce the best quality index. The placement of the nodes on the surface is also optimized to

improve the QI.

The spline is used to create a shell mesh and/or surface. A mesh and surface can be

created using nodes, points, or lines. Spline function can be used to create a mesh without

surface, or a surface without a mesh. Lines or nodes can be picked in any order-. HyperMesh

determines the correct order when creating the mesh/surface. There is no limit on the number of

lines, points, or nodes when creating a spline surface. The disconnected entities can be

connected with straight lines and creates a spline surface and/or mesh within the boundary

formed by the chosen entities and the constructed lines. If the lines selected to create a spline

are edges of an adjoining surface, the software updates the edge topology to make them shared

edges, and considers the curvature of the adjoining surfaces when creating the spline surface.

The four lines in the fig.6.10are selected for creating mesh by using spline command.

Fig 6.10 Meshing of surface by using spline command

The ruled panel is used to create surfaces and/or meshes of plate elements from nodes,

lines, and/or line segments, in any combination. Nodes in the mesh being created are placed on

a surface created on a linear basis between the two sets of selected entities.

The line drag panel is used to create a two or three dimensional surface and mesh or

elements by dragging nodes, lines or elements along another line.

Each of the three methods presented on this panel (drag along vector, drag along line,

and spin) is a different means of creating mesh. One method can be used at a time.

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6.6.4 Meshing around holes

For better representation of hole geometry and smooth mesh flow lines, holes should be

modeled with even no. of elements (like6, 8, 12 etc.) as shown in fig. 5.11.

Fig 6.11 Meshing around hole of Heat sink

Figure 6.12 Tail lamp after 2-D mesh

Fig. 6.12 represents the Tail Lamp after 2D mesh using various commands of meshing

as described above.

6.6.5 3-D Meshing Technique-As all the three dimensions of Tail Lamp are comparable

so we have selected 3D tetramesh. There are two techniques for tetramesh.

1) Automatic mesh-This approach is limited to simple geometries and pre-requisite is error

free CAD model. It is very quick method but results in very high no. of nodes and elements.

There is no control on mesh flow lines and specific mesh pattern requirement.

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2) 2D (Tria) to 3d (Tetra)-Most commonly used method.

2D (Tria) to 3d (Tetra)-Meshing Technique is utilized to mesh all the components of Tail

Lamp. Mixed meshing (combination of quad & tria element) is carried out on all the outer

surface of the geometry, quad split to trias and converted to tetras.

Steps to convert 2D (Mixed) to 3d (Tetra)

1) Study the geometry

2) Mesh all the surfaces of model one by one to have smooth desired mesh flow pattern &

connectivity of one surface node with other surface.

3) Quality check for triangular elements (Min. tria angle>0.1, Jacobian>15 degree etc.)

4) Covert mixed element to Tetra elements as shown in fig. 6.13. Ensure that

geometry/mesh is close only then one can convert 2D mesh to 3D.

Figure 6.13 Tail lamp after 3-D mesh

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6.7 Quality checks [18]

After completing meshing part of the model, than quality check is performed to check the

quality of elements. Depending on the type of mesh, this can be done either semi-automatically

or manually.

Result quality α Element quality

Ideal shape for rectangular element - Square

Ideal shape for triangular element - Equilateral triangle

Different quality parameters like skew, aspect ratio, included angles, jacobian, stretch

etc. are the measures of how far a given element deviates from ideal shape. Square means all

angle 90° and equal sides, while equilateral triangle is all angles 60° and equal sides. Some of

the qualities checks are based on angles (like skew, included angles) while others on side ratios

& area (aspect, stretch). Following are general definitions of various quality checks:

Warp angle: Warp angle is out of plane angle. Warp angle is not applicable for triangular

elements. It is defined as angle between normal to two planes formed by splitting the quad

element along diagonals as shown in fig. 6.14. Max. angle out of two possibilities is reported as

warp angle.

Ideal value = 0 degree (Acceptable < 10°)

Fig 6.14 Wrap angle b/w normals of two plane of an element

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Aspect ratio: Ratio of longest side to the shortest side of an element or max. as shown in fig.

6.15. Element edge length/minimum element edge length.

Ideal value = 1 (Acceptable < 5)

Fig. 6.15 Aspect Ratio

Skew: Skew for quadrilateral element = 90° minus minimum angle between two lines joining

opposite mid-sides of the element (α) as shown in fig. 6.16. Skew for Triangular element = 90°

minus minimum angle between the lines from each node to the opposing mid-side and between

the two adjacent mid-sides at each node of the element.

Fig. 6.16 Skew

Jacobian: It is a scale factor arising because of transformation of co-ordinate system.

Ideal value= 1.0 (Acceptable> 0.6)

Distortion: Ideal value= 1.0(Acceptable> 0.6)

Distortion is defined as – (Jacobian)* Area Lcs /Area Gcs

LCS- Local Coordinate system

GCS - Global Coordinate system

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Included Angles:

Quad: Ideal value = 90 deg. (Acceptable= 45<θ<135)

Tria: Ideal value = 60 deg. (Acceptable= 20<θ<120)

% of Trias: Should be less than 5% of total number of elements.

Fig:-6.17 Quality Check panel

Same quality criterion has been done on tail lamp .Fig 6.17 shows the tail lamp quality

check index. Coloured elements are failed elements which can be edited by using various

commands in quality index panel such as swap edge, place node, element optimize and node

optimize to improve Component Q.I. Comp. Q.I. should be less than 100. The FE model

satisfy the quality criterion described above.

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Duplicate elements:

Mistakes during operations like reflect, translate etc, results in duplicate elements. These extra

duplicate elements do not cause any error during the analysis but increases stiffness of the

model and results in lesser displacement and stress.

Element free edges:

Any single quad element has 4 free edges.

Two elements

In this case middle edge is shared and no more free edge. For a real life FE model, free

edges should match with geometry outer/free edges. Additional free edges are an indication of

unconnected nodes as shown in fig. 6.18.

Fig. 6.18 White line indicates free edge & unconnected nodes

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Free edge & unconnected nodes

After maintaining the desired quality index, Tail Lamp is checked for free edges. As

long as there are free edges 2D mesh can’t be converted in to 3D mesh. Connectivity between

elements can be checked by using free edge command. If there is no connection between two

nodes then the results will not come accurately or the stress distribution is disturbed, so there

should be node to node connectivity between the various elements. So that the load will transfer

from node to node and we can obtain the results at every node

6.8 Rigid elements

Rigid elements function as rigid bodies; therefore they are also known as rigid bodies or

constraint elements. The RBE1 and RBE2 elements are rigid bodies connected to an arbitrary

number of grid points. Rigid element (node to node connection) has infinite stiffness and

transfers all the forces and moments or in other words dofs from one node to other as it is.

Rbar, Rigid, Rigid link are examples of rigid elements. RBE2 element distributes the force and

moment equally among all the connected nodes irrespective of position of force or moment

application.

Fig 6.19 RBE2 Element –Centre node independent (DOF-1234656)

RBE2 elements are used to simulate the bolt connection for heat sink and reflector at

four places. In order to represent the connection b/w body and reflector two RBE2 elements are

used as shown in figure 6.20.

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Fig 6.20 RBE2 element joining the nodes on the periphery of hole & reflector to body

6.9 Collectors

The HyperMesh model is organized using “collectors”. Most entities in HyperMesh must be

placed in a collector. Each collector type holds a specific type of entity. There are many types

of collectors like component collector, material collector, property collector, load collector etc.

6.9.1 Component collector

After meshing, various component collectors are created. The meshes of the different surfaces

are put together in different component collectors.

E.g. the mesh created on the Heat Sink is placed in a collector named Heatsink_tetra.

Similarly other elements are placed in other collectors such as Body_tetra, Lens_tetra,

Reflector_tetra etc. Separate color is given to different collectors for easy recognition of mesh.

6.9.2 Material Collector

The next step after putting elements in various component collectors is to create material

collector and assigning the material to the elements. As there are four components of Tail lamp,

each having different material so create four material collectors i.e. ABS, Aluminium, Nylon-6

& Acrylic. While creating the material collector specify the card image as MAT1 & MAT4 and

specify properties corresponding to each material as shown in table 6.2.  MAT1 card is used to

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Rigid Element

define the isotropic structural material.  MAT4 card is for the constant thermal material.

MAT4 uses the same material ID as MAT1.

Material

Thermal coefficient

of expansion

Young’s modulus(N/mm2)

Density(tonne/mm3)Thermal

conductivity K(KW/mm c)

ABS 73.8E-6 m/mk

0.4X10^5 1.05E-09 0.78

Aluminium 22.2E-6 m/mk

1.1X10^5 2.70E-09 237

Nylon-6 85E-6 m/mk 0.75X10^5 1.16E-09 0.25

Acrylic 81E-6 m/mk 0.7X10^5 1.19E-09 0.2

Table 6.2 Material specification

The same numerical values have been taken as used in Tail Lamp industry.

6.9.3 Property collector

After creating material collectors, properties collectors are created. The various properties

collectors are named according to their material. E.g. ABS_solid, Aluminium_solid etc. Then

element type, card image and material are assigned to various property collectors. For the Tail

Lamp model element type is 3D, card image used is PSOLID and material is ABS, Aluminium

etc.

Once the material and property are defined, they need to be linked to the component.

Assign the component created in component collector to material in material collector. Link

Reflector_tetra to Abs_solid, Body_tetra to Nylon_solid, Heatsink_tetra to Aluminium &

Lens_tetra to Acrylic_solid. To check whether the property is assigned or not to all the

components we can check property table and component table in utility menu.

6.9.4 Load collector-Boundary Conditions

After creating property collector, load collector is created. Load collector is the collection of

boundary conditions i.e. different forces, pressure, velocity, supports, constraints and any other

condition required for complete analysis. Applying boundary condition is one of the most

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typical processes of analysis. A special care is required while assigning loads and constraints to

the elements. Boundary condition is of two types:

1. Element based boundary condition

2. Node based boundary condition

In element based boundary condition a group of elements is selected on which various

load is to be applied. Whereas in node based boundary condition nodes of mesh are selected for

applying loads and forces.

For analysis of the Tail lamp both boundary conditions are used. A bunch of nodes is

selected and surface elements are created. Then load is applied on this surface element which

distributes load equally on all the nodes of elements.

A load collector ‘Con’ is created & structural constraint ‘con’ is applied on the RBE2

element to fix the Heat sink on the ground. Two empty load collectors, ‘Heat’ and ‘Heat flux’,

have been created. The thermal boundary conditions and heat flux will be applied on the model

and saved in heat and heat flux respectively. Assign different color to each load collector for

easy recoganization. Fig. 6.21 shows the various load collectors created for analysis of Tail

Lamp.

Fig 6.21 Component, property, material etc. collector

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Structural & Thermal Constraints

The Tail Lamp is constrained at four positions around the bolt. Set ‘Con’ as the current load

collector & in constraint panel select the centre (calculated) node of RBE2 element located at

centre of each bolt. These nodes are constrained as shown in fig.6.22. All the six degree of

freedom is constrained. This applies structural constraints to the selected nodal set. Similarly

apply the thermal constraint to the nodes around the bolt area in Heat load collector as shown in

fig. 6.23.

Fig. 6.22 Structural constraint at centre node of RBE2 Element

Fig 6.23 Thermal constraint around holes

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Detailed view

6.10 CHBDYE Surface Elements

After applying the constraint to model heat flux is applied on the surface of the heat sink.

Hence the surface elements CHBDYE for defining heat transfer boundaries must be created

first. From the analysis panel create the ‘Heat transfer’ surface elements Then type and face are

defined on which heat flux to be applied. For the Tail Lamp model type is Conduction, face

defined is slot face on heatsink. This adds the CHBDYE surface elements on all the solid

elements, as shown in Figure 6.24.

Fig.6.24 CHBDY Surface element

6.11 Heat flux on surface elements

The uniform heat flux into CHBDYE elements will be defined with QBDY1 entries. Heat flux

applied to CHBDY elements is calculated as [22]:-

Heat flux=Q=KA (Ts-Ta)/L

Where K-Thermal conductivity=237W/mk

Ts-Surface temp. Of Heat sink

Ta-Atmospheric temp.

(Ts-Ta) = 150 (Given data)

L-Thickness=2.3 mm = 0.0023m

A-Area on which heat flux is applied=432 mm2 = 0.00043264 m2

Q= {237 X .00043264 X (150)}.0023 = 6687 W

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CHBDY elements

This load is applied on this CHBDY element which distributes load equally on all the nodes of

elements.

No. of nodes on CHBDY elements=121

Heat Flux on each node= Total Discharge/No. of nodes

Heat Flux on each node = 6687/121

= 56w

So apply a flux of 56 w on each node of CHBDY element in heat flux load collector as shown

in fig. 6.25.

Fig. 6.25 Heat flux of 56 w on surface elements

6.12 Heat transfer load step

A RADIOSS steady state heat conduction loadstep is created which refers the thermal

boundary conditions in the load collector ‘heat’ and the heat flux in the load collector ‘heat

flux’. The gradient, flux, and temperature output for the heat transfer analysis are selected in

load steps panel.

72

6.13 Structure load step

To perform a coupled thermal/structural analysis, the heat transfer subcase is referred by a

structural subcase by ‘Temp’. Displacement and stress output are selected in the loadstep

information.

73

CHAPTER 7

ANAL YSIS

7.1 Linear Static Analysis

While the pre-processing and post-processing phases of the finite element method are

interactive and time-consuming for the analyst, the solution is often a batch process, and is

demanding of computer resource. The governing equations are assembled into matrix form and

are solved numerically. The assembly process depends not only on the type of analysis (e.g.

Static or dynamic), but also on the model element types and properties, material properties and

boundary conditions. In the case of a linear static structural analysis, the assembled equation is

of the form

[K] [u] = [F],

Where K is the system stiffness matrix,

u is the nodal degree of freedom (dof) displacement vector,

F is the applied nodal load vector

To appreciate this equation, one must begin with the underlying elasticity theory. The

strain-displacement relation may be introduced into the stress-strain relation to express stress in

terms of displacement. Under the assumption of compatibility, the differential equations of

equilibrium in concert with the boundary conditions then determine a unique displacement field

solution, which in turn determines the strain and stress fields. The chances of directly solving

these equations are slim to none for anything but the most trivial geometries, hence the need for

approximate numerical techniques presents itself For the FEA of Tail Lamp the case chosen is

linear static. This analysis is used when the response of the body is linear, and there is no

variation with time. In stress analysis, model is appropriate when operating within elastic

region (stress strain curve is linear) and when the deformations are small and load do not vary

with time. It is the simplest and most commonly used type of analysis.

74

Linear means straight line, σ = t.E is equation of straight line (y = m x) passing through

origin. "E" Elastic Modulus is slope of the curve & is a constant. In real life after crossing yield

point material follows non liner curve but software follows same straight line as shown in fig

5.6. Component brake into two separate pieces after crossing ultimate stress but software based

analysis never show failure in this fashion. It shows single unbroken part with red color zone at

the location of failure. Analyst has to conclude whether the component is safe or failed by

comparing the maximum stress value with yield or ultimate stress.

There are two conditions for static analysis

1) Force is static i.e. no variation with respect to time (deadweight) dF/dt = 0 as shown

in fig. 7.1.

Fig 7.1 Static Force

2) Equilibrium condition - forces ∑ (Fx. Fy, Fz) and Moments ∑ (Mx, My, Mz) = O. FE

model fulfils this condition at each and every node, For complete model summation of

external forces and moment is equal to reaction forces and moments.

7.2 Thermal Analysis

Heat transfer is defined as energy in transit. Analysis of a system using the laws of heat transfer

is named as Thermal Analysis. Heat transfer is a branch of thermodynamics which deals with

rate of heat transfer between two or more equilibrium states of a system.

Thermal analysis is investigation of the part or a system, to calculate heat transfer rate and

temperature distribution. Different approaches for thermal analysis are,

75

1) Theoretical (Analytical)

2) Experimental

3) Numerical

4) Graphical

Why thermal analysis?

To understand the physical phenomenon either natural or manmade & most important to

control them. Theoretical approach of thermal analysis is applicable to simple geometries

(exact solution). Experimental approach is limited by the time, cost and uncertainty in

measuring the property data ( e.g. pressure, temperature, velocity) due to complexity of

geometry, induced errors( Instrumental, human) and environmental disturbance. Numerical

approach is probably the best approach i.e. using the present high end hardware & software

computational support &validated computer codes. The forth approach, using graphical

techniques is a history & now outdated.

7.2.1 Conduction Heat Transfer

The transfer of heat is normally from a high temperature object to a lower temperature object

[18]. Conduction heat transfer is observed in all types of phases i.e. solid, liquid & gas. In

solids it is due to lattice vibration (translational & rotational) & mainly due to free electrons.

Hence pure metals like copper, aluminium are good conductors of electricity and also good

thermal conductors. But, the surprising thing is, sometimes a bad conductor of electricity can

be a very good conductor of heat (e.g. Diamond - used in special cutting tool). In liquids,

conduction is due to molecular movement & in gases due to molecular collisions.

Fourier's law governs conduction heat transfer. Fourier proved by experiments, that heat

transfer rate is proportional to area, temperature difference and inversely proportional to

thickness.

Q = -k A * [dT / dX]

76

Where

Q= Heat transfer rate (W)

A=Area (m2)

dT = Temperature differential (ºC/K/ ºR)

dX = Thickness (m)

k= Thermal conductivity (W/m K)

The bracketed term is called as temperature gradient; it’s been assigned with negative sign, as

the temperature gradient vector is in opposite direction of heat flow as shown in fig. 7.2..

Fig. 7.2 The net heat transfer is in the direction of negative of the temperature gradient

The direction of heat transfer will be opposite to temperature gradient, since net energy

transfer will be from high temperature to low. This direction of maximum heat transfer will be

perpendicular to the equal-temperature surfaces surrounding a source of heat.

Conduction heat transfer is significant in solids. Any heat transfer problem obeys the

first law of thermodynamics (Energy is conserved) & to satisfy this, we have to apply boundary

conditions, (e.g. known temperature, heat flux, heat source/generation, convective like known

heat transfer coefficient or radiation).

7.3 Preparing for analysis

Once the mesh is ready, additional data is specified - the properties of the materials used , the

thickness or cross sectional properties of shell or beam elements, the conditions on the

boundaries ( restraints, loads or excitations), initial conditions, data for the specific solution

algorithm to be employed, kind of output required for text and graphics records, and so on.

77

After doing this, the data is turned over to solution program for the next phase -solving.

Data is often returned out in the form of a text file, which is referred to as a deck. Each line of

the text in the deck is commonly referred to as a card.

A card image is the format followed by the analysis program to interpret the text on the

line. The procedure of building the finite element model is sometimes referred to as FEM-short

for finite element modeling.

7.4 Proprocessing

The model created in the earlier steps is now taken up for solution - the computer program

reads the data, calculates matrix entries, solves the matrix equation and writes the data out for

interpretation.

This task is CPU intensive, and is often called processing. Most of the time, very little

interaction from the user is required. In some cases, the analyst periodically monitors the result

to check that they are indeed on the right track. If the solution seems to be evolving in an

unexpected direction, the analyst can stop the solver and modify the model, thereby saving

valuable time.

The analysis of tail lamp produces different type of data files having different type of

information .dat file obtained from solver [23] gives the information and result such as:

• Number of elements in the model

• Number of nodes

• Memory used for analysis

• Time taken for analysis

• Volume of the model

• Weight of the model

• Animated file of the displacement

• Finite element file

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7.5 Post Processing

After the program has evaluated the results, we have to examine and interprets the result which

in our case has been done in Hyperview [24]. Different data files and the graphic visualization

are available at that helps in looking for errors or improvements in design such as:

• Displacement contours in X, Y and Z direction

• Resultant displacement contours

• Von Misses stress contours

• Temperature distribution contour

• Element Temperature gradient

• Element flux

79

CHAPTER 8

RESULTS AND DISCUSSION

This chapter deals with the results of coupled thermal and structural heat conduction linear

static analysis of the Tail Lamp of a bike. The results include temp gradient, thermal stress and

displacement contours for a calculated flux. The post processing has been done in Radioss

Linear which can read the .hm files written as output from Hypermesh. The elapsed time is the

time taken by software to convert the model from .hm file to .fem file. Maximum memory used

gives the information about the memory used during pre-processing. Maximum disk space used

gives the information about the amount of space used by temporary files for preprocessing.

Shading and wireframe options, animation options and contour colours are used to study, and

compare the results. The output file .out gives the detail about total number of nodes, element

type, total number of degree of freedom, load and boundary information, and material and

property information.

The FEA results of the Tail Lamp have been compared with available experimental and

standard results for validation. For this purpose all experimental as well as FEA results are

organized in the tabular form which shows the variation among the various parameters. The

sample result file generated which gives all the information related to FE analysis of Tail

Lamp. The analysis has also been shown.

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8.1 Result File************************************************************************** **** **** RADIOSS 9.0 **** **** Finite Element Analysis Software **** from Altair Engineering, Inc. **** **** **** Windows XP Professional SP2 (Build 2600) SUNNY-8A705A651 **** 2 CPU: Intel(R) Pentium(R) 4 CPU 3.00GHz **** CPU speed 3000 MHz **** 648 MB RAM, 2441 MB swap **** **** Build tag: 0413758_5333O90_Ci3242M-000 14000 **************************************************************************** COPYRIGHT (C) 1996-2008 Altair Engineering, Inc. **** All Rights Reserved. Copyright notice does not imply publication. **** Contains trade secrets of Altair Engineering, Inc. **** Decompilation or disassembly of this software strictly prohibited. **************************************************************************

*** OptiStruct defaults set from: install config file: C:\Altair\hw9.0/hwsolvers/hwsolver.cfg

INFORMATION # 742 The dependent rotational d.o.f. of this rigid element is removed. RBE2 element id = 162605 independent grid id = 61553 a dependent grid id = 36941 This is because there is no need to constrain the rotational d.o.f. of any of the dependent grids.

INFORMATION # 742 The dependent rotational d.o.f. of this rigid element is removed. RBE2 element id = 162606 independent grid id = 61554 a dependent grid id = 36668 This is because there is no need to constrain the rotational d.o.f. of any of the dependent grids.

INFORMATION # 742 The dependent rotational d.o.f. of this rigid element is removed. RBE2 element id = 162607 independent grid id = 61556 a dependent grid id = 32021 This is because there is no need to constrain the rotational d.o.f. of any of the dependent grids.

INFORMATION # 743 The total number of rigid elements, whose rotational dependent d.o.f. are removed because there is no need to constrain those d.o.f., is 6

************************************************************************

81

OPTIMIZATION FILE AND PARAMETER INFORMATION :---------------------------------------------

Optimization parameters from : C:/Documents and Settings/sunny/Desktop/86 ass4 loadstep2.fem FEM model file : C:/Documents and Settings/sunny/Desktop/86 ass4 loadstep2.fem Output files prefix : C:/Documents and Settings/sunny/Desktop/86 ass4 loadstep2

************************************************************************

************************************************************************

FINITE ELEMENT MODEL DATA INFORMATION :---------------------------------------

Total # of Grids (Structural) : 25900 Total # of Elements : 76833 Total # of Rigid Elements : 6 Total # of Rigid Element Constraints : 975 Total # of Degrees of Freedom : 78693 Total # of Non-zero Stiffness Terms : 1348014

Element Type Information ------------------------

CTETRA Elements : 76833

Load and Boundary Information -----------------------------

FORCE Sets : 2 SPC Sets : 2

Material and Property Information ---------------------------------

PSOLID Cards : 4 MAT1 Cards : 4 MAT4 Cards : 4

************************************************************************

************************************************************************

OPTIMIZATION PROBLEM PARAMETERS :---------------------------------

NO DESIGN MATERIAL OR DESIGN VARIABLES FOUND : ANALYSIS ONLY

---------------------- Load Subcase Summary : ----------------------

---------- -------- -------- --------------

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Subcase ID SPC ID FORCE ID Weight = w(i) ---------- -------- -------- -------------- 2 1 0 1.000 ---------- -------- -------- --------------

------------------------------- Heat Transfer Subcase Summary : -------------------------------

---------- -------- -------- Subcase ID SPC ID LOAD ID ---------- -------- -------- 1 2 3 ---------- -------- --------

--------------------------- Design Parameters Summary : ---------------------------

Run Type : Analysis Only Scratch file directory : ./ Free space: 2305 MB Number of CPU processors : 1

************************************************************************

************************************************************************

MEMORY ESTIMATION INFORMATION :-------------------------------

Solver Type is: Sparse-Matrix Solver Current Memory (RAM) : 179 MB Estimated Minimum Memory (RAM) for Out of Core Solution : 52 MB Recommended Memory (RAM) for Out of Core Solution : 57 MB Recommended Memory (RAM) for In-Core Solution : 179 MB DISK SPACE ESTIMATION INFORMATION :-----------------------------------

Estimated Disk Space for Output Data Files : 12 MB Estimated Scratch Disk Space for In-Core Solution : 40 MB Estimated Scratch Disk Space for Out of Core Solution : 212 MB

************************************************************************

BEGINNING ANALYSIS SOLUTION ....

************************************************************************

ANALYSIS RESULTS :------------------

Element Quality Check Summary

83

----------------------------- Total # of elements that exceeded recommended range (warning) = 61

(Scratch disk space usage for starting iteration = 33 MB)(Running in-core solution)

Volume = 1.06995E+05 Mass = 1.37969E-04

Subcase Compliance 2 5.602406E+01

************************************************************************PROGRAM STOPPED FOR ANALYSIS ONLY.

************************************************************************

RESOURCE USAGE INFORMATION--------------------------

MAXIMUM MEMORY USED 179 MB MAXIMUM DISK SPACE USED 45 MB

************************************************************************

************************************************************************

COMPUTE TIME INFORMATION------------------------

EXECUTION STARTED Wed Jun 30 21:29:41 2010 EXECUTION COMPLETED Wed Jun 30 21:30:07 2010 ELAPSED TIME 00:00:25 CPU TIME 00:00:14

************************************************************************

***** END OF REPORT *****

RADIOSS 9.0 Report

Problem submitted Wed Jun 30 21:31:02 2010

Input file C:/Documents and Settings/sunny/Desktop/86 ass4 loadstep2.fem

Problem summary

• Problem parameters: C:/Documents and Settings/sunny/Desktop/86 ass4

loadstep2.fem

• Finite element model: C:/Documents and Settings/sunny/Desktop/86 ass4

loadstep2.fem

• Output files prefix: 86 ass4 loadstep2

84

Finite element model information

Number of nodes: 25900

Number of elements: 76833

Number of rigid elements: 6

Number of rigid element constraints: 975

Number of degrees of freedom: 78693

Number of non-zero stiffness terms: 1348014

• Elements

Number of TETRA elements: 76833

• Loads and boundaries

Number of FORCE sets: 2

Number of SPC sets: 2

• Materials and properties

Number of PSOLID cards: 4

Number of MAT1 cards: 4

Subcases & loadcases information

• Static subcases

Subcase ID SPC ID Force ID Weight

________________________________________

2 1 0 1.00

Results summary

Subcase 2 - Structure

• Maximum displacement is 0.122E-01 at grid 7889.

• Maximum 3-D element stress is 41.0 in element 50471.Temperature Contour

85

8.2 Temperature Contours

The figure 8.1 shows temperature distribution in the heat sink of the tail lamp. It is observed

from the temperature contours that temperature is decreasing towards fixed end of the Heat

sink. The maximum temperature observed is 22.7ºC at the centre of the heat sink as per

expectations.

86

8.3 Element Temperature Gradient Contours

The figure 8.2 shows element temperature gradient in the heat sink. The maximum element

temperature gradient observed is 1.5 ºC/mm at the location of the heat sink where thickness of

the heat sink changes. This location is critical for observation of thermal stresses.

87

8.4 Element Flux Contours

The figure 8.3 shows element flux in the heat sink. The maximum element flux observed is

357.5 W/mm2. The element flux pattern is similar to element temperature gradient pattern

because flux and temperature gradient have direct relationship. As temperature gradient

increase, flux also increases as per the below relation:

[Q/A] α [dT/dX]

88

8.5 Displacement Contours

With the same thermal model, the deformation of reflector and heat sink is also predicted by

using the thermal distribution result as a thermal load for the structural analysis. The figure 8.4

shows displacement contours of the heat sink and reflector. The maximum deformation

observed is 0.012mm in the heat sink at the free end. The deformation observed is very less

which indicates that there is no chance of warpage of the Tail Lamp.

89

8.6 Thermal Stress Contours

With the same thermal model, the thermal stress of reflector and heat sink is also predicted by

using the thermal distribution result as a thermal load for the structural analysis. The figure 8.5

shows Thermal stress contour of the heat sink and reflector. The maximum stress observed is

37 N/mm2 in the heat sink which is well below the yield stress (45 N/mm2 for Aluminium).

90

8.7 Comparison of FEA Results

To validate the analysis, the results have been compared with the available experimental and

standard results. As the experimental results were available [8] for the street light of 80W lamp,

the same FE analysis has been carried out for the load of 80 W. The maximum temperature

observed in this trial is 32ºC, which is well below the experimental and FEA results of 42ºC for

80 W lamp. The thermal stress and displacement comparison also validate the FE analysis of

the tail lamp. The results of the present analysis are better than experimental results of street

lamp for the same load because of the efficient design of the tail lamp than a street lamp. The

results of the comparison have been depicted in tabular form in table 9.1.

Sr. No. Parameters Experimental Results FEA Results Variation

1 Temperature 42ºcelcius 32ºcelcius 23%

2 DisplacementBy observation -No warpage

0.012mm (negligible)

Nil

3 Thermal Stress 45 N/mm2 37 N/mm2 17%

Table 8.1 Comparison of Experimental and FEA Results

91

CHAPTER 9

CONCLUSION

1. The maximum temperature observed in FE Analysis of the tail lamp is 22.7ºC for the

load of 56 W.

2. The maximum element temperature gradient is 1.5 ºC/mm.

3. The maximum element flux observed is 357.5 W/mm2.

4. The maximum deformation is 0.012mm which is negligible and harmless.

5. The maximum stress for the heat sink is 37 N/mm2 which is below the yield stress for

Aluminium.

6. The results are well in agreement with the similar available experimental results.

92

CHAPTER 10

SCOPE FOR FUTURE WORK

1. The design can be further improved by installing fins so as to have better heat

dissipation.

2. Once the thermal stress is further reduced, optimization of the reflector and heat sink

can be performed to save the material and reduce cost.

3. CFD analysis can also be performed to validate the results.

93