Engineering Design Notes Conceptual Design

Engineering Design Notes III Conceptual Design

EE 498/499 Capstone Design ClassesKlipsch School of Electrical & Computer Engineering

Spring 2007 Design Notes III - Conceptual Design 2

Topics

Overview Definitions Conceptual Design Steps Activity Analysis Concept Generation Analysis and Feasibility Evaluation Methods Documentation


Overview

The Conceptual Design is the first part of the design process after the specifications have been determined.

This is to act as the intellectual exercise to generate ways accomplishing the actual design.

This step is successful if we have at least one feasible alternative to work with when we are done.

Specification

Establish functional requirementsDetermine design constraintsDetermine acceptance criteria

Generate Alternatives

Create alternative solutions to realize Specifications

Analyze Alternatives

How well do the alternative designs meet the Specifications

Evaluate Alternatives

Perform numeric comparison of the alternatives and the quality of their meeting Specifications

Fabrication specification for the best alternative

Redesign iteration

Feasible Alternatives

Design Process Version I


Definitions

What is the Conceptual Design process? It is the generation of design alternatives or Design Concepts and the supporting analysis to determine the feasibility of each alternative.

What is a Design Concept? It is a design alternative that includes at least one physical principle and one abstract embodiment.


Definitions

What is a physical principle? This is a natural law or effect that produces a useable method of modifying a signal or device to produce a functional output. For example, the photoelectric effect is a physical principle that produces a current in proportion to the intensity of the incident light.

An abstract embodiment is a diagram that shows the relative relationship between the actors in the design. It need not be to scale.


Definitions

Examples

BatteryChemical Storage

Energy Storage

Radio/modemLaser/detectorWiring harness

RFOpticalWire

Data Communications

Solar Cells

ReactorFurnace

Photoelectric EffectNuclear PowerCombustion

Energy Generation

Embodiment Method

Physical Principle

Design Element


Definitions

The Conceptual Design Diagram is A diagram with the Design Concept, Including the physical principles being used, and The abstract embodiment.

This is basically a block diagram or extended sketch with the necessary aspect labeled.

Note: systems usually need to have individual Conceptual Design Diagrams for the component subsystems rather than all-in-one diagrams.


Definitions

Example: Develop a Conceptual Design Diagram for a communications system composed of a modem, RF transmission unit, and antenna.

Note, actual components not specified at this level. Potential Physical Principles that can be considered:

RF, Optical, or Wire harness communications. Here, we consider the Conceptual Design Diagram

for the RF option. The RF embodiment is based on a RF unit and a modem. The following diagram shows the Concept.


Definitions

Communications Conceptual Design Diagram


Conceptual Design Steps

The proper Conceptual Design Process has the following stages: Activity Analysis: how will the design be used in

various stages such as normal use, battery recharging, disposal, start-up and shutdown, etc., as appropriate for the needs.

Generate Alternative Concepts: the design team uses various strategies to generate Concepts that should meet the design requirements.


Conceptual Design Steps

Conceptual Design Process (cont.) Analyze: use engineering analysis, simulation,

bench testing, etc. to verify that the design concept does work to meet the specifications.

Feasibility Test: does the design analysis indicate that the design concept will meet the specifications and actually can per executed.

Evaluate: determine which one or set of the feasible design concepts left are best (at least at the level we can tell at this time).


Activity Analysis

The Activity Analysis stage really is an exercise to determine how the design meeting the specifications is to be used in real life. This includes user activities and understanding the inputs and outputs (signals, power, etc.).

To do this activity, you will need to perform a functional decomposition and an I/O analysis.


Activity Analysis

The functional decomposition takes the design functional requirements and refines them respective subfunctions and sub-subfunctions.

The functions are not broken down by expected embodiments but by similar functions.


Activity Analysis

The I/O analysis looks at the control, data, and power signals coming into and out of a function.

This will become a basis for the designs Interface Control Document that specifies and documents all interface details.


Activity Analysis

Comms Example Functional Decomposition Antenna

Transmit Frequency Receive Frequency

RF unit Transmit Electronics Receive Electronics Computer Control

Set Frequencies Set Power

Modem unit Waveform Processing Computer Control

Set Baud rate Set comms parameters

Buffer data

Comms Example I/O Analysis Antenna

RF signal in RF signal out

RF Unit Computer interface RF signal in RF signal out Signal from modem in Signal to modem out Power

Modem unit Signal from RF in Signal to RF out Computer interface Power


Activity Analysis

Activity Analysis results: An assessment of which functions can be

combined A check-off to ensure that all required functions

are addressed An understanding of the required interfaces A possibility that the design requirements may

need to be reviewed and iterated upon to update them.


Concept Generation

The design team uses various strategies to generate Concepts that should meet the design requirements.

This is also sometimes called synthesis. Use brainstorming, past experience, similar

designs, Google searches, WAGs, sleeping on it, etc.

This process may take some time!


Analysis and Feasibility

Analyze: use engineering analysis, simulation, bench testing, etc. to verify that the design concept does work to meet the specifications.

Feasibility Test: does the design analysis indicate that the design concept will meet the specifications and actually can per executed.

From the analysis and testing, we should also eliminate those designs that cant be built, would cost too much, etc.


Evaluation Methods

Once the design concepts are generated and evaluated for feasibility, the surviving design concepts need to be evaluated to determine which one is best.

How does one define best? One common method is to use the criteria for the

design and weight the relative importance to determine best.

Note: the designers must be careful not to rig the weighting to make a favorite come out best.


Evaluation Methods

Weighted Evaluation Method: Select the evaluation criteria and place in column 1 of a

matrix. Importance weights are assigned to each criterion and

placed in column 2 of the matrix. The concepts to be evaluated are placed in subsequent

columns of the matrix. Each concept is rates against the criteria and a score of 0

to 4 is given. A 0 implies unsatisfactory performance while a 4 is implies very good performance.

Each score is multiplied by the weighting factor and the scores are summed. Highest weighted score wins.


Evaluation Methods

Example evaluation matrix. Notice, functional requirements are not included because it is

assumed that all design concepts meet the testable requirements. This is for the intangibles or more subjective criteria. Testable requirements with varying degrees of performance can also be included.

2.802.953.50100

0.3030.4040.20210Buffer Capacity

0.4530.6040.30215Cost

0.4020.6030.80420Mass

0.7530.7531.00425Physical Size

0.9030.6021.20430Operating current

Weighted RatingRating



Importance Weight (%)Criteria

Internal ModemDSP ModemExternal COTS Modem

Concept Alternatives


Documentation

At the end of the Conceptual Design stage, the following documents should be part of the design documentation, at a minimum: Operations Concept document Conceptual Design Diagram Function Decomposition I/O Analysis Design Analysis showing that Conceptual Design

meets requirements Design Evaluation matrix


Documentation

Additional documents that can be started at this stage include: Budgets: mass, size, link analysis, power, etc. Start considering how the various components will

be integrated and tested. Integration and test plans can be started.

Note, in some cases, these will be no more than outlines with placeholder sections to be developed further.

Documents

Engineering Design Notes Conceptual Design