engineering design is… the process of devising a system, component or process to meet needs a...
TRANSCRIPT
Engineering design is…
the process of devising a system, component or process to meet needsa decision-making process in which science and mathematics are applied to convert resources to meet objectivesestablishing 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 ProcessBackup Chart
1. Identify a need2. Establish design criteria and
constraints3. Evaluate alternatives4. Build prototype 5. Test/evaluate against design criteria6. Analyze, redesign, retest7. Communicate the design
The Engineering Design Process
Design is an Iterative ProcessBegins with a recognition of need for a product, service, or systemDuring the idea phase encourage a wide variety of solutions through brainstorming, literature search, and talking to usersBest 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 processFinally drawings are released to manufacturing for production
Engineering Design Process
Customer Needor Opportunity
Implementation ofOptimal Design
Evaluation of Designs/Selection of Optimal Design
Development ofAlternative Designs
Data & InformationCollection
Problem Definition/Specifications
Source: Accrediting Board For Engineering and Technology
Primary Design Features
1. Meets a need, has a “customer”2. Design criteria and constraints3. Evaluate alternatives (systems or
components)4. Build prototype (figuratively)5. Test/evaluate against test plans (criteria)6. Analyze, “tweak” (), redesign (),
retest7. 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
CostTimeKnowledgeLegal, ethical Physical: size, weight, power, durabilityNatural, topography, climate, resourcesCompany practices
Evaluate Alternatives
Needs best stated as function, not formLikely to find good alternatives for cheapest, fastest, lightest, and encourage discoveryResearch should reveal what has been doneImprove on what has been donePlay alternatives off criteria and constraintsBrainstorming helps
Best Design
Choose best design that meets criteriaDemonstrate tradeoff analyses (among criteria and constraints) are high qualityCost (lifecycle) is always considerationResist overbuilding; drives complexity, cost, time, resourcesA quality design meets customers expectations!
Prototype
Prototype is implementation of chosen design alternativeIt is a proof of design, production and suitabilityPrototypes are often cost prohibitive: Models and simulations may sufficeQuality design does not include redesigning a lot of prototypes
Test and Redesign
Documentation
Project data bookA 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 mediumIt does not attempt to turn the object, simply to slow it downIt 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:
FD = ½ ρ CDV2A
where: FD = drag force (N)
CD = drag coefficient (no units)
V = velocity of object (m/s)A = projected area (m2)ρ = density of air (kg/m3) {1.2
kg/m3}