ENG 201 Lecture, Spring 2012

3-0 CHAPTER 3 Introduction to Engineering Design 3-1 Design process • Recognize the need for a product or service • Define and understand the problem completely • Do preliminary research and preparation • Conceptualize ideas for possible solutions (create a time plan) • Synthesize the findings (perform simulations, verify materials, standards and codes, do calculations) • Evaluate good ideas in more detail (verify all calculations, investigate to remove uncertainties, create working models, in order to select the best alternative) • Optimize solutions to arrive at the best possible solution • Present the final solution 3-2 Design process: 1. Recognize the need for a product or service • Keep an open eye around for: – A product, if optimized, would improve the quality of life/ pleasure of people – A service that can be improved or created • A general rule: whenever there is a complaint about a service, a product, a task that is too difficult, a situation too dangerous,… right there is the opportunity for the engineer 3-3 Design process: 2. Define and understand the problem completely • This is the most important step in any design process: you need it in order to end up with a product or service that fulfils the demand. • To completely understand the problem, you have to ask many questions: – The price the client is willing to pay – The restrictions of dimensions, type of material – How much time can they wait for the product to be finished? • For complex problems, engineers often divide the problem into smaller tasks. You will then have to understand your part and how it fits in the whole project 3-4 Design process: 3. Do preliminary research and preparation • In other words, collect all useful information: – What product available is closest to the proposed need? Its advantages/disadvantages for my client? – What are the parts that are already available and what remains for me to create? • Places to search: internet, other engineers and companies. 3-5 Design process: 4. Conceptualize ideas for possible solutions (create a time plan) • Without performing any detailed analysis, you need to come up with some possible ways for solving the problem: – Develop several alternative solutions – Do not rule out any reasonable working concept, but verify that it is worth considering, that is if it is likely to work – Identify the components of the system, if it is complex • Budget your time: prepare your time plan for completing your project 3-6 Design process: 5. Synthesize the findings • Narrowing down the alternatives into the best (2 or 3 at most) – Perform calculations – Run computer models – Consult pertinent codes and standards – Find out how the product is going to be fabricated 3-7 Design process: 6. Evaluate good ideas in more detail • Analyze the problem in more detail (1 alternative): – Identify critical design parameters and verify their influence – Verify all calculations – Perform experimental investigation to verify uncertainties in the analysis – Create and test working models – Work out fully how the product is to be fabricated – In order to choose the best alternative. 3-8 Design process: 7. Optimize solutions to arrive at the best possible solution • Improve the chosen alternative: – It is based on a criterion: cost, strength, size, weight, reliability, noise, performance,… – Examples include optimizing the weight without jeopardizing the strength (an aluminum ladder) • Note that optimizing individual components of a system does not necessarily lead to an optimized system, for example in a refrigerator, optimizing the compressor, evaporator and condenser does not have to lead to an optimal fridge 3-9 Design process: Optimize solutions to arrive at the best possible solution 3-10 Design process: Optimization – an example • Read example 3.1 – p.44 3-11 Design process: Optimization – an example – Aim: purchase storage tanks for my company – Constraints: • Budget = 1680$ • Total surface area available = 90ft2 – Objective (or optimization) function : maximize storage capacity – Manufacturer A: 120$ / tank of capacity 16ft3; require 7.5ft2 of floor space – Manufacturer B: 240$ / tank of capacity 24ft3; require 10ft2 of floor space 3-12 Design process: Optimization – an example • Write the requirements mathematically: – Let x1 be the number of tanks I will buy from manufacturer1 and x2 those from manufacturer2 – Maximize: Z = 16 x1 + 24 x2 (total volume) – Subject to the following constraints: – 120 x1 + 240 x2 ≤ 1680 – 7.5 x1 + 10x2 ≤ 90 – x1 ≥ 0 – x2 ≥ 0 3-13 3-14 3-15 Design process: 8. Present the final solution • Communicate your solution / findings to your customer/ boss • Learn the written, oral and software methods to correctly communicate • Note that presentations can be also required as progress reports during the execution of the project 3-16 Engineering economics • Engineers never design a product without considering the economic side: – Products have to be cost effective in order to: • be sold at an affordable price / or a price accepted by the market and • Make profits 3-17 Material selection • To select a material suitable for a specific application, you should ask yourself questions such as: – How strong it is when subjected to a load? – How much will it expand when temperature changes? – How expensive is it? – Would it dissipate heat effectively? – Is it toxic to the body? – How would it resist mechanical shock and fatigue? – …. And many more, depending on the specific application. 3-18 Material selection – material properties • Electrical resistivity: – it is the measure of resistance to electric flow. Ceramics and plastics have a high value; metals have a low value • Density: – It is a measure of how compact a material is for a given volume • Modulus of Elasticity (Young’s modulus): – It is a measure of how easily a material will stretch when pulled or shorten when pushed 3-19 Material selection – material properties • Modulus of rigidity: – It is a measure of how easily a material can be twisted or sheared (the resistance to shear deformation) • Tensile strength: – Also called ultimate strength, is the maximum tensile load a material can carry without failure. • Compression strength: – It is the maximum compressive load a material can carry without failure 3-20 Material selection – material properties • Modulus of resilience: – It is a mechanical property of a material that shows how good the material is in absorbing mechanical energy without going through any permanent damage • Modulus of toughness: – It indicates the ability of a material to handle overloading before it fractures • Strength to weight ratio: – It is the strength of a material (either yield or ultimate) with respect to its weight 3-21 Material selection – material properties • Thermal expansion: – It is the coefficient of change in length with respect to a change in temperature • Thermal conductivity: – It is a coefficient indicating how good a material can transfer heat • Heat capacity: – It represents how well a material can store heat, defined by the amount of thermal energy required to raise 1kg of the material 1oC 3-22 Material selection – material properties • Viscosity: – It represents how easily a given fluid can flow. The higher the value of viscosity, the more resistance the fluid offers to flow • Vapor pressure: – Under same conditions, fluids with high vapor pressure evaporate faster than fluids with low vapor pressure • Bulk modulus of compressibility: – This modulus represents how easily can one reduce the volume of a fluid when the pressure is increased 3-23 Team work – common traits of a good team • All the team members must understand and accept the goals of the assigned project, which should be clear and realistic • Made up of individuals with complementary expertise • Have a good leader • Team environment should promote openness, respect, and honesty • Team needs and goals come before individual needs and goals 3-24 Common traits of a good team – cont. A good team should have all or some of the following role-individuals: • The organizer: experienced and confident, coordinator, good at clarifying goals and advancing decision making • The creator: comes up with new ideas, helps team develop ideas further • The gatherer: enthusiastic, good at developing contacts, looking for possibilities • The motivator: energetic, confident, good at finding ways around obstacles, good at making objective decisions • The evaluator: someone capable of understanding the complete scope of the project and at judging outcomes correctly • The team worker: someone who tries to get everyone come together • The solver: reliable and decisive, can turn concepts into practical solutions • The finisher: the time keeper, keeps track of the schedule and pushes the team to finish its assignment on time 3-25 Conflict resolution Several possibilities: • Compromise solution for the sake of group unity • Compromising a team member • Collaborative “conflict resolution” approach (treating the conflict as a new project) 3-26 Project Schedule - an example 3-27 Evaluating alternatives • After narrowing down the design into a few workable concepts, it is customary to use an evaluation table to decide on the better solution. This is done by: – Defining the design criterions – Assigning an importance level, I, to each – Then giving a rate, R, for every design with respect to each design criterion – The design having the highest weighed sum, ∑(IxR), is chosen as best 3-28 Evaluating alternatives - example 3-29 3-30 Protecting intellectual property • Patent: protects the right to make, use or sell the new invention (design: 14 years; utility: 17 years) • Trademark/Service mark: word or symbol used to distinguish a certain product • Copyright: protects intellectual published and unpublished work for author’s lifetime plus 70 years. 3-31 Why do we need standards and codes? • To ensure safety (drinking water, electrical devices,…) • To ensure uniformity (of units, sizes,…) 3-32 Examples of Standards and Codes organizations in the US • ANSI - American National Standards Institute: it assists qualified groups with the development of standards • ASTM – American Society for Testing and Materials: it publishes standards and test procedures that are considered authoritative technical guidelines for product safety, reliability and uniformity • NFPA – National Fire Protection Association: it provides codes and standards to reduce the burden of fire. • UL – Underwriters Laboratories: a collection of laboratories that perform product safety tests and certifications 3-33 Examples of International Standards and Codes organizations • ISO – International Standardization Organization: a federation of national standards from various countries – develops standards that can be used by all countries • CE standards (Communité Européenne): it provides a single set of safety and environmental standards that are used throughout the European union 3-34 3-35 3-36 3-37 Specific examples of standards and codes in the US • Of particular importance, the standards of drinking water and the air that we breathe • Those standards are set by the EPA – Environmental Protection Agency 3-38 Drinking water standards in the US • EPA sets the maximum level of contamination in the water that is still considered safe to drink • It sets 2 levels: 1. MCGL: maximum contamination goal level 2. MCL: maximum contamination level – MCGL = maximum level of contaminant that causes no known harmful effects – MCL = levels of contaminants that are legally enforceable (MCGL levels are not always attainable because of economic or technical reasons) 3-39 3-40 3-41 Outdoor air quality standards in the US • Sources of outdoor air pollution classified into 3 broad categories: – Stationary sources: ex: power plants, factories, dry cleaners,… – Mobile sources: ex: cars, buses, trucks planes trains,… – Natural sources: ex: windblown dust, volcanic eruptions,… 3-42 Outdoor air quality standards in the US • The EPA sets standards for the 6 major air pollutants: – carbon monoxide (CO) – Lead (Pb) – Nitrogen dioxide (NO2) – Ozone (O3) – Sulfur dioxide (SO2) – Particular matter, PM 3-43 Risks of outdoor air pollution • Bad effect to health, especially for children • Climate effects: it triggers global warming 3-44 Inside air quality (IAQ) standards in the US The indoor level of pollutants may be 2 to 5 times higher than outdoor levels • According to EPA, some common health symptoms caused by poor indoor air quality (called SBS, sick building syndromes) are: – Headache, fatigue and shortness of breath – Sinus congestion, coughing and sneezing – Eye, nose, throat and skin irritation – Dizziness and nausea Some of these symptoms may also be caused by factors other than pollution, like stress and health problems. 3-45 3-46 3-47 Sources of indoor air pollution • HVAC systems • Building tight, weakly aerated houses for heating purposes • Using more synthetic materials in buildings • Using more chemical pollutants: perticides, cleaning detergents 3-48 Methods to manage contaminants • Source elimination or removal, ex: not allowing indoor smoking, while designing a building, avoiding placing the outdoor air intake near dumpsters or other pollution sources • Source substitution, ex: use gentle cleaning products instead of ones that give off harmful vapors • Proper ventilation, ex: install and control exhaust fans in restrooms • Exposure control, ex: cleaning the surfaces in detergents on a Friday afternoon, leaving a weekend for the evacuation of fumes before anyone breathes them • Air cleaning. It means removing harmful particulate and gazes from the air as it passes through some cleaning system