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Concept Evaluation & Selection

UC Berkeley, ME Dept.

Concept Selection (Evaluation)

Concept selection is one of the most critical decision-making exercises in a product development.

To make decisions effectively, one must basically carry out two steps.

- Minimize the possibility of misrepresenting a solution that may be effective.

Engineer is not familiar with the technology.

- Fully consider the different ramifications of a decision.

For example, not considering the costumer’s need

may lead to the product failing in the marketplace.

UC Berkeley, ME Dept.

Concept Selection

- Design Evaluations

Occurs at all phases of product evaluation, from concept to detailed design phases. Structured decision-making methods are needed.

- Quality of Information

Low quality of information - how well each alternative design would meet criterion cannot be fully understood.

High quality of information - The alternative solutions are well understood.

UC Berkeley, ME Dept.

Estimating Technical Feasibility

What separates a skilled engineer from a novice is the ability to effectively estimate.

Estimating skill depends on familiarity with dimensional units and familiarity of different values along the dimensions.

Example: let’s consider a book

When asked to estimate the thickness, all will have little trouble.

When asked to estimate the weight of the book, most will have little trouble.

When asked to estimate the energy released if the book is burned, many do have trouble.

UC Berkeley, ME Dept.

Energy is not directly perceived, we cannot visualize 1 J or 100 J. Energy is a derived unit of directly perceived units.

Estimating Technical Feasibility- Perceived Dimensional Units

Size and weight are directly perceived, we

can see the difference between 1 cm and 1 m.

- Engineers should become familiar with the derived units by associating them to known units. 2000 Watts is 3 hp, lawnmower engine.

UC Berkeley, ME Dept.

Some Reference Values

Length, SI system (English system)

Human hair thickness

30 x 10-6 m (.0012 in.)

Book cover thickness

2 mm (.08 in.)

Person’s height

2 m (6’-7”)

Width of a small town

5 km (8 mile)

San Jose to LA

700 km (435 miles)

Earth to Moon

3.84 x 109 m (2.4 x 106 miles)

UC Berkeley, ME Dept.

Some Reference Values

Velocity, SI system (English system)

Speed of tide rising from low to high

0.1 mm/s (.004 in/s)

1 mm/s (.04 in/s)

Tip speed of a wrist watch minute hand

Walking speed

1.5 m/s (3.35 mi/h)

Highway speed

30 m/s (67 mi/h)

Jetliner speed

250 m/s (560 mi/h)

1 km/s (.62 mi/s)

3 times the speed of sound

Voyager 1 traveling in space

17 km/s (10 mi/s)

Speed of light in vacuum

3 x 108 m/s (670 x 106 mi/h)

UC Berkeley, ME Dept.

Acceleration , SI system (English system)

Some Reference ValuesFast car

3 m/s2 (118 in/ s2)

Hard braking car

7 m/s2(275 in/ s2)

Earth gravity at sea level

9.81 m/s2 (32.2 ft/ s2)

Humans blackout

40 m/s2(4 g-force)

- Belly flopping in water from 10 m diving board, causing broken bones

100 m/s2 (10 g-force)

Head-on car collision occupant acceleration

10,000 m/s2(2730 ft/ s2)

Bullet fired from a rifle

60,000 m/s2 (16,400 ft/ s2)

Centrifugal acceleration of light trapped in a black hole

2 x 1013 m/s2 (550 x 1013 ft/s2)

UC Berkeley, ME Dept.

Force, SI system (English system)

Some Reference ValuesAttraction between electron and proton in hydrogen

0.08 μ N (.018 μ lb.)

Weight of piece of paper

0.04 N (.14 ounce)

Weight of small apple

1 N (.22 lb.)

Finger force for appliance

7 N (1.6 lb.)

Weight of bag of potatoes

100 N (22.5 lb.)

Weight of two small people

1.5 kN (337 lb.)

Thrust of Boeing 747

1 MN (224, 820 lb.)

Space shuttle thrust

0.2 GN (45 million lbs.)

UC Berkeley, ME Dept.

Some Reference Values

Mass - kg (lb.)

1” x 1” piece of paper

40 x 10-6 kg

Grape

10 g

Penny

3 g

Average person

70 kg (150 lb.)

Mid-size car

1300 kg (2,800 lb.)

Elephant

5000 kg (11,000 lb.)

747 fully loaded

300,000 kg (660,000 lb.)

Ocean liner

107 x 106 kg (235 x 106 lb.)

UC Berkeley, ME Dept.

Some Reference Values

Pressure, SI system (English system)

Moon surface

0.13 x 10-9 MPa (1.88 x 10-8 psi)

0.8 x 10-8 MPa (1.16 x 10-6 psi)

Mars atmosphere

16 x 10-3 MPa (2.32 psi)

Blood pressure

1 MPa (145 psi)

25 ft under water

Engine compression pressure

1.3 MPa (188 psi)

Pressure to create a diamond

5,000 MPa (725 ksi)

Center of Earth

0.40 x 106 MPa (58 million psi)

Center of the Sun

20 x 109 MPa (2.9x 1012 psi)

UC Berkeley, ME Dept.

Some Reference Values

Power (watts)

Ant crawling up the wall at 1 cm/s

33 μW (4.4 x 10-8 hp)

LED

40 mW

Small flashlight

10 W

Household light bulb

40, 60, 100 W

Household appliance

100-1000 W

Small lawnmower engine

2000 W (2.7 hp)

Electrical power to a small town

1 MW

Electrical power plant

1 GW

UC Berkeley, ME Dept.

Some Reference Values

Energy (Joules)

Moving 5 g snail

0.45 μJ kinetic energy

Bee in flight

2 mJ kinetic energy

Small apple falling 1 m

1 J kinetic energy (8.85 lb-in)

90 mile/hr fast ball

114 J kinetic energy (1000 lb-in)

- Energy extracted from a AA and D size battery

1 kJ and 80 kJ

Car traveling at 60 mph

1 MJ kinetic energy (9 x 106 lb-in)

Car battery

5 MJ

USS Nimitz, 91,400 tons, traveling at 30 knots

9.9 GJ kinetic energy (88 x 109 lb-in)

UC Berkeley, ME Dept.

Estimation

The estimation process should be used to eliminate concepts that are not technically feasible.

- Imagine the concept to estimate
- Construct a simple model
- Use the model to provide a comparison with a known quantity
- Judge whether the estimated quantity compares with the known quantity

UC Berkeley, ME Dept.

Example – can crusher

Alternate concept – dropping a weight on the can

Imagine the concept: flow of energy

Simple model: F = (mass)(acceleration) + weight

Known quantity: 200 lb of force needed to crush the can (from a simple crush test)

Choose 30 lb weight, and calculate the height needed to exert 200 lbs to crush the can 5 inches.

V 2 = 2gH, a = V 2/2S, F = WH/S + W = 200, Height = 28.33 “

Judge: is the height practical?

UC Berkeley, ME Dept.

Concept Selection (Evaluation)

- Technology Readiness Assessment

If a technology is to be used as part of a product design, it must be mature enough that its use is a design issue, not a research issue.

- GO/NO-GO screening

Each concept must be compared to the customer requirements in an absolute fashion. Each customer need must be transformed into a question to be addressed to each concept. The questions should be answerable as either yes or maybe (go), or no (no-go). This evaluation will weed out concepts quickly and will help generate new ideas.

UC Berkeley, ME Dept.

Concept Selection

- Based on the Decision-Matrix (Pugh’s method)

The method is very effective for comparing concepts that are not refined enough for direct comparison with the engineering requirements.

UC Berkeley, ME Dept.

Concept Selection – Pugh’s Method

The method is an iterative evaluation that tests the completeness and understanding of requirements, quickly identifies the strongest concept.

The method is most effective if each member of the design team performs it independently. The results of the comparison will usually lead to repetition of the method, with iteration continued until the team reaches a consensus.

- Step 1 – Select the Criteria for Comparison

The list of criteria must be developed from the customer needs and engineering specifications. All team members should contribute in making the list. The list then should be debated until consensus is reached.

UC Berkeley, ME Dept.

Concept Selection – Pugh’s Method

- Step 2 – Select the Concepts to be Compared

These alternatives should be those that proceed from the concept generation. It is important that all the concepts to be compared be at the same level of abstraction.

- Step 3 – Generate the Score

A favorite concept should be selected as a datum. All other designs are compared to it relative to each customer needs. For each comparison, the concept being evaluated is judged to be either better than (“+” score), about the same (“s” score), or worse than the datum (“-” score).

UC Berkeley, ME Dept.

Concept Selection – Pugh’s Method

- Step 4 – Compute the total score

Three scores are generated, the number of plus scores, the number of minus scores and the total.

If a concept has a good overall score or a high “+” score, it is important to notice what strengths it exhibits, that is, which criteria it meets better than datum. Same for “-” score.

If most concepts get the same score on a certain criterion, examine that criterion closely. More knowledge may have to be developed in the area of the criterion. Or, it may be ambiguous, is interpreted differently by different members.

UC Berkeley, ME Dept.

Bike Splashguard Concepts

UC Berkeley, ME Dept.

Pugh’s Method – Example

Bike splashguard

Initial decision matrix

Best overall score, design II (5), should be used as a datum concept for the next step.

Concepts IV and V are rated as next best designs.

UC Berkeley, ME Dept.

Pugh’s Method – Example

Bike splashguard attachment subsystem

Initial decision matrix

UC Berkeley, ME Dept.

Summary

- Estimation is a critical skill to develop and can help in quickly eliminating weak concepts
- The feasibility of the concepts is based on the design team’s knowledge. It is often necessary to augment this knowledge with research and development of simple models.
- In order for a technology to be used in a product, it must be ready.
- A go/no-go screening based on customer needs helps to eliminate some of the concepts quickly.
- The decision matrix (Pugh’s method) provides means of comparing and evaluating concepts. The method gives insight into strong and weak areas of the concepts.

UC Berkeley, ME Dept.

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