NVSAGE - Noise & Vibration Bulletin - March 2014 Vol.049

VOL 049 March 2014

©NV Dynamics 2014 | all rights reserved

IN THIS ISSUE

Foreword

Metro Vibration tests and predictions

Vibration caused by Bit Extraction process

Discussion Board

Noise and Vibration in various Domains – Part 1

Fact File

Therapy using Whole Body Vibration

World’s Fastest Bird - Peregrine Falcon

All rights reserved NV Dynamics 2014 www.nvdynamics.com

Dear Customer

Chennai Metro assigned us the task of testing, validating and predicting the vibrations at their underground sections of the

metro track.

To elaborate, this is the first of its kind assignment being carried out by any Indian Metro rail; that is, to conduct simulated

force injection tests at tunnel locations and determine the transfer characteristics of the ground mass and Vibration response

at target surface locations above the ground.

In all, 4 test locations at 2 tunnel stretches were identified; the Vibration responses were measured at 6 points for each test

location. The typical test methodology as defined both by FTA guidelines and DIN 4150 were followed; a known mass from a

pre-defined height was dropped on to the target tunnel floor location, both the injected force and the Vibration response at

the point of dropping weight were recorded, further, synchronized Vibration response were measured and recorded from the

target locations above the ground surface.

Combining the test inputs and parameters of STRATA, distance of the dwellings from the Vibration source and such other

values required for the prediction of Vibration as per DIN 4150-1, data of predicted Vibration values are computed. To

improve upon the credibility of the predicted data, actual Vibration data from comparable Metro Train operations are used for

calculating the transfer loss, based on the findings, Vibration mitigation plans are worked out.

Upon implementation of the vibration mitigation plans, validation studies will be conducted.

One of leading companies in the business of construction and mining tools has put in place, methods to recycle the carbide

bits from the mining heads after they are used for the operational cycle. The methodlogy to extract the bits (buttons) from the

mining head involves heating the bits to a high temperature and using high impact pneumatic hammer; the bits (buttons) will

be ejected from their mouting.

However, the above process induces high levels of Noise and Vibration which are beyond both the human comfort limits and

legal limits. NV Dynamics carried out a complete study on the Noise and Vibration response of the bit extraction process;

detailed mitigation plan including some of process modifications are worked out to reduce the Noise & Vibration both at its

source and surroundings.

Warm Regards

Krishna Balamuralikrishna@nvdynamics.com

NVSAGE - Noise & Vibration Bulletin - March 2014 Vol.049

Foreword

NOISE AND VIBRATION IN VARIOUS DOMAINS: Part 1

NVSAGE - Noise & Vibration Bulletin - March 2014 Vol.049

Discussion Board

Discussion Board

Noise, Vibration and Harshness (NVH), is the study and optimization of the noise and vibration

characteristics for improving the performance and quality of the product / system. Noise, vibration,

harshness (NVH) and acoustic analysis have been implemented in various domains such as

aerospace, automotive, transportation, manufacturing, processing, construction & civil structures and

many other industries.

This edition will discuss about the Noise and Vibration application in Aerospace Engineering / Industry.

There are many causes of airplane vibration, including landing gear extension and retraction, extension

of speed brakes, free play in movable surfaces, and system malfunctions. Flight crews need to

understand the causes and effects of general airplane vibrations such that appropriate actions need to

be taken to maintain flight safety and further prevent excessive wear or airframe damage.

In addition to this, valuable inputs from the flight crew regarding any in-service events will facilitate

troubleshooting and maintenance activities.

Understanding the possible sources of Vibration and the information needed to isolate/correct Vibration

problems requires knowledge of the following:

1. Types of Vibration and Noise in Airplanes.

2. Causes of Airplane vibration.

3. Detection of Airplane vibration.

4. Flight crew response.

5. Maintenance troubleshooting.

The major Vibrations generated by an aircraft are random in nature which can be due to Buffet or

Flutter. Buffet is a form of vibration usually caused by aerodynamic excitation and can be felt during the

extension of speed brakes or during air turbulence. Flutter is an unstable condition in which unsteady

aerodynamics excite the natural frequencies of the structure over which the air flows (Ex: wings, rudder,

etc.). The resulting vibrations can grow to huge magnitude that may result in failure of the structure.

http://www.youtube.com/watch?v=GzvA9tHNTyg

Noise is an air borne vibration and is ideally audible. When the Vibration is random, the noise heard is

unpleasant / confused. When the Vibration is harmonic, the result is tone like, typically of the kind heard

from a musical instrument.

NVSAGE - Noise & Vibration Bulletin - March 2014 Vol.049

Whole Body Vibration Therapy

Fact File

The causes for Noise and Vibration in an Aircraft can be either due to the normal operation of the

aircraft (take off & landing, engine vibrations, etc.) or due to any abnormal activity (mechanical failure,

improper maintenance, etc.).

Each airplane / aircraft has a unique signature of normal vibration. This is a consequence of mass

distribution and structural stiffness that results in vibrations at certain frequencies. When external

forces act on the aircraft, such as normal airflow over the surfaces (fuselage, wings, rudder etc.), it

results in very-low-level vibrations. Typically, this is perceived as background noise. More noticeable,

but also normal, is the reaction of the airplane to turbulent air, in which the magnitude of the vibration

may be larger and is clearly felt. Engine operation at some speeds may result in increased Vibrations

because of resonance and transmits these vibrations throughout the airframe.

The vibration may be intermittent or steady with a distinct frequency, or it may be a more random type.

When the onset of abnormal vibration can be associated with a previous action or event, the source

may be obvious. However, some vibrations initially are rather subtle and require diagnostic procedures

to determine their probable causes.

The effects of airplane vibration range from passenger and crew discomfort to flight safety issues.

Appropriate flight crew response, involves operating the flight in a manner that avoids continued

vibration and recording information that will assist in identifying the cause of the vibration. Crew’s

understanding of airplane vibration and response procedures is important because it can prevent

prolonged exposures to NVH events that may cause airframe damage and proper awareness can

provide valuable information to facilitate maintenance troubleshooting. In all cases, without doubt, pre-

flight safety takes precedence over any post in-flight analysis of Vibration.

Abnormal Vibrations usually is related to one or more of the following

causes:

Engine rotor imbalance, Malfunction of Mechanical equipments and

Airflow disturbances acting over doors or control surfaces that have

excessive wear and excessive clearance. Abnormal vibration rarely is

caused by a structural failure or an unstable power control system.

NVSAGE - Noise & Vibration Bulletin - March 2014 Vol.049

Whole Body Vibration Therapy

See: Highest and longest bridges in the world .

World’s Fastest Bird – Peregrine Falcon

A pivotal machine running on a low frequency (12 Hz and under) would be mainly used for physiotherapy applications.

The two factors Amplitude and frequency determine the effect of vibration upon the body. Different tissues in the body will respond to different frequencies. For instance, research has shown that the collagen (protein) which makes up the cartilage of your joints and the discs between the bones of the spine responds to a slow pulse of 4 Hertz (four pulses per second).

The muscles respond best to frequencies between 30 and 50 Hertz, and the ideal frequency window for stimulating bone growth is 30 Hertz.

The Peregrine Falcon is the fastest flying bird only when diving or "stooping" as it's called in aviation and thus is subject to controversy as the leader of the world's fastest "flyers".

Its horizontal flying speed is between 80 to 90 kilometres per hour (50 to 60 mph). Although the often quoted diving speed of Peregrine Falcons is as high as 89-157 meters/sec (200-350 mph) the accuracy of this speed is unknown because the speed of a diving falcon is difficult to measure.

All inputs and copyrights duly acknowledged

The required instrumentation is complex, and the dive of a falcon is a brief, rare event that takes place at unpredictable places and times.

The botanical name is Falcon Peregrines This is an endangered species and the estimated population of this bird is approximately 1,200,000 around the world.