Engineering design is… the process of devising a system, component or process to meet needs a decision-making process in which science and mathematics are applied to convert resources to meet objectives establishing objectives & criteria, synthesis, analysis, construction, testing, and evaluation

Problem Characteristics Engineering Problem Problem statement incomplete, ambiguous No readily identifiable closure Solutions neither unique nor compact Solution needs integration of many specialties Science Problem Succinct problem statement Identifiable closure Unique solution Problem defined and solved with specialized knowledge

Engineering Design Creativity Open-ended problems Use design theory and methods Formulate design problem statements and specifications Consider alternative solutions Consider feasibility

Engineering Design Process Backup Chart 1. Identify a need 2. Establish design criteria and constraints 3. Evaluate alternatives 4. Build prototype 5. Test/evaluate against design criteria 6. Analyze, redesign, retest 7. Communicate the design

The Engineering Design Process

Design is an Iterative Process Begins with a recognition of need for a product, service, or system During the idea phase encourage a wide variety of solutions through brainstorming, literature search, and talking to users Best solutions are selected for further refinement Models or prototypes are made and problems that arise may require new ideas to solve and a return to an earlier stage in the process Finally drawings are released to manufacturing for production

Engineering Design Process Customer Need or Opportunity Implementation of Optimal Design Evaluation of Designs/ Selection of Optimal Design Development of Alternative Designs Data & Information Collection Problem Definition/ Specifications Source: Accrediting Board For Engineering and Technology

Primary Design Features 1. Meets a need, has a “customer” 2. Design criteria and constraints 3. Evaluate alternatives (systems or components) 4. Build prototype (figuratively) 5. Test/evaluate against test plans (criteria) 6. Analyze, “tweak” ( ), redesign (  ), retest 7. Project book: record, analyses, decisions, specs

Criteria & Constraints “Design criteria are requirements you specify for your design that will be used to make decisions about how to build the product” Aesthetics Geometry Physical Features Performance Inputs-Outputs Use Environment Usability Reliability

Some Design Constraints Cost Time Knowledge Legal, ethical Physical: size, weight, power, durability Natural, topography, climate, resources Company practices

Evaluate Alternatives Needs best stated as function, not form Likely to find good alternatives for cheapest, fastest, lightest, and encourage discovery Research should reveal what has been done Improve on what has been done Play alternatives off criteria and constraints Brainstorming helps

Best Design Choose best design that meets criteria Demonstrate tradeoff analyses (among criteria and constraints) are high quality Cost (lifecycle) is always consideration Resist overbuilding; drives complexity, cost, time, resources A quality design meets customers expectations!

Prototype Prototype is implementation of chosen design alternative It is a proof of design, production and suitability Prototypes are often cost prohibitive: Models and simulations may suffice Quality design does not include redesigning a lot of prototypes

Test and Redesign

Documentation Project data book A complete record All key decisions Good drawings Test plans Results Conclusions Things learned

Archimedes' Principle Any object completely or partially submerged in a fluid is buoyed up by a force whose magnitude is equal to the weight of the fluid displaced by the object.

Buoyancy and Archimedes’ Principle For a floating object, the fraction that is submerged is given by the ratio of the object’s density to that of the fluid.

Bernoulli’s Equation A fluid can also change its height. By looking at the work done as it moves, we find: This is Bernoulli’s equation. One thing it tells us is that as the speed goes up, the pressure goes down.

Concept of Drag Drag is the resistive force exerted on a moving body in a fluid medium It does not attempt to turn the object, simply to slow it down It is a function of the speed of the body, the size (and shape) of the body, and the fluid through which it is moving

Drag Force The drag force due to a fluid acting on an object can be found by: F D = ½ ρ C D V 2 A where: F D = drag force (N) C D = drag coefficient (no units) V = velocity of object (m/s) A = projected area (m 2 ) ρ = density of air (kg/m 3 ) {1.2 kg/m 3 }