The Four Phases of the Engineering Design Process (EDP)Many engineering students are taught the Engineering Design Process(EDP) early in their engineering coursework, so we review it here and introduce the details of systems engineering later. The EDP is actually contained within the Systems Engineering process model - you can see it on the bottom half of the Vee Chart - for the purpose of designing the parts, components and subsystems.Typically the EDP is applied to the design of a new consumer product, or redesign of an old product, to the design of a single component or a subsystem of a larger system. The process is sparked by the recognition and identification of a need for that product, which itself could require a significant effort. When incorporated in a SE effort, the need (and requirements and architectural design) is supplied by the Systems Engineering effort to that point in time. The four phases of the EDP are listed below [1]. To explain the process, an example design problem based on the need for a mousetrap that wont kill the mouse is used for illustration. The EDP can be applied to simple projects (such as the design of a welded lap joint) or relatively uncomplicated systems such as the design of consumer products.

Phase 1. Project Definition and Planning Phase. Amission objectiveis stated (The objective is to create an inexpensive mousetrap that does not kill or harm the mouse). The primary tasks are identified with objectives for each, teams are formed, costs and schedules to meet the objectives are estimated, deliverables and reviews are planned, all followed by the first design review.Phase 2. Requirements Definition and Engineering Specifications. The goal of this phase is to understand the problem and establishcustomer requirementsandengineering specifications.The customers are identified and their requirements on the design carefully phrased (e.g., the mousetrap must be reusable, inexpensive, safe to humans and doesnt kill the mouse). Requirements may befunctional requirements(requirements on what the design must be able to do),performance requirements(how well a function must be performed),physical requirements(e.g. space, weight, physical properties),reliability requirements(how long it must last), etc.Engineering specificationsare requirement-like statements which possess target or required measures, are created by engineers and are derived from customer requirements. Engineering carefully review customer requirements and translate them to quantifiable measurements. For example, 1) the mousetrap shall cost less than 20 cents to make, 2) it shall fit in a 3x3x3 box, 3) it can be opened and closed 50 times without breaking. What some engineers and organizations call engineering specifications, others might term these same statements requirements, so the terminology is not rigid. At a design review the requirements and engineering specifications are presented to management for approval.

Phase 3. Concept Generation and Evaluation Phase (aka the Conceptual Design Phase). This phase is concerned with generating manyconceptsfrom ideas, comparing and evaluating those concepts, and choosing the best concept(s) to put forward. Ideas are generated by brainstorming (aka lateral thinking, in contrast with the step-by-step procedures required of most analytical engineering course homework problems). Concepts flow from these ideas. Aconceptis a developed idea that is believed to feasible (also known as afeasible alternative), that can be presented with enough detail so that it is possible to evaluate its behavior based on physical principles, and to show that it is feasible. The concepts are compared and evaluated and the best selected to put forward by comparing performance, cost, and/or other criteria in atradestudy. The concepts and the down selection process need to be communicated and documented. Initially, they may be hand-sketched and put in a design notebook, represented by a diagram, or a proof-of-concept prototype. A third design review normally follows. For the mousetrap example, one students concept consisted of a hardened toilet paper tube with a hinged and latched door on one end, and with a one-way entry door on the other end.The concept generation process does not have to be an unstructured mental exercise. The preferred approach is numbered below, and is analogous to the Marine Corp boot camp philosophy of tearing down the recruit (concept) in order to build him/her back up again in the Marine Corp image. Analogously, concept generation includes the following steps:1.Functional Analysisis the identification of the functions needed for a system, subsystem or component to fulfill goals and objectives. Thefunctionof an element is what that element must be able to do. A functional analysis is often insightful, since "form (i.e. the physical realization) follows from function". This forces understanding of what the product is supposed to do before Concept Generation as the next step. One popular technique (Functional Flow Block Diagram) connects blocks of functions diagrammatically to show function or task sequences and relationships. For the mousetrap example, functional blocks can be 1) entice mouse to enter, 2) enable mouse to easily enter, 3) prevent mouse from escaping, 4) safe transfer of mouse in mousetrap to release location, 5) safe release of mouse and 6) cleaning of mousetrap for reuse. The designer can then develop concepts and physical components that could satisfy each and every function.2.Concept Generationby such techniques as A) brainstorming, B) review of literature, patents, product information to spark new ideas or to use or modify existing products, and C) talking to experts in the field, the end user, or people who do (or will do) the maintenance, procurement, shipping, etc. of the end product. The mousetrap example might include interviews with pest exterminators or biologists specializing in mice and rodents.Steps 1 and 2 should be applied more than once to create several candidate concepts (also calledfeasible alternatives).3.Concept Evaluationto choose the best concept, by comparing and evaluating. The best concept is chosen for the Product Design Phase (Phase 4). The trade study is a tool of Concept Evaluation.Thetrade spaceof a trade study is the set of all feasible alternatives that were created at the end of Step 2 for evaluation in Step 3. The mousetrap case might have 2 door options (one or two closing doors), 3 bait options (none, replaceable, user supplied) and 4 actuation concepts (spring, electric sensor, hydraulic, mouse powered). These alone give a trade space of 24 possible concepts to impartially evaluate! Although all the steps are important, a trade space analysis during the concept evaluation (Step 3) is traditionally the place where small errors in judgment, or cutting corners to rush to the design phase, leadsto a non-optimizedsolution. Be sure you include the entire trade space of interest andknowwhy you have left any part out (e.g., not considering any mousetrap design that must be plugged into an electrical outlet since power is often not available in all locations where the trap is likely to be set). Too restrictive a trade space may lead to no solution or the same conclusion as before (i.e., the mouse must be held by a single metal bar released by a spring). Finally, the comparison process itself can be misleading if the full number of option permutations are not included or the metrics are too restrictive.Many techniques are available for comparing concepts and making a good decision. Sometimes metrics are available for concept evaluation. Sometimes decisions can often be quickly arrived at and agreed upon based on asking simple questions like: Whether the concept is physically realizable or not? Is the technology ready? Will it be too costly? Will it be safe? Can it be manufactured? Can a simple test be performed or small prototype built or a CAD model created to validate or invalidate the concept?But be careful! Such simple questions can easily lead to biased or predicted answers that favor one or another solution, because the answers are often gut reactions or experience driven. The decisions made here must be universal and logical. For example a mousetrap design that does not include an electrical power source is unlikely to work with electronic sensor initiation. Therefore that design can be legitimately eliminated from further consideration.Sometimes it is best to evaluate a concept by simply adding more detail, such as:1) draw parts and assemble in CAD making 3-D concept drawings and assemblies for review, 2) select and rough size components that are critical to performance such as motors, heat exchanges, control valves, linkages, sensors, actuators, etc., 3) browse catalogs and supplier websites, talk to sales engineers, 4) perform proof-of-concept physical testing to prove concept feasibility, build a small-scale model or prototype, build breadboard circuits, 4) perform simple engineering calculations (such as sizing linkages, cylinders for expected loads, heat exchanger sizing, motor horsepower requirements), 5) use software to simulate and assist in engineering analysis (e.g. MATLAB, Working Model, ModelCenter, Flames, FE software (ANSYS, Algor, NASTRAN)), Virtual Prototyping software (ADAMS)), circuit analysis (PSPICE)), 6) Rough cost analysis to make the prototype, the final product, or to mass produce if necessary. At the end of Phase 3 it is time for Conceptual Design Presentation/Report.Phase 4. Product Design Phase. Phase 3 ends with the best concept. Phase 4 evolves the chosen concept to a product, i.e. its final physical form. First there is the creation of theproduct design(or just called the "design"). A product design to most engineers is detailed documentation sufficient to manufacture and assemble the designed product (it should also include relevant operation, maintenance and disposal information as appropriate). This primarily implies providing detailed dimensioned drawings such that components can be made and assembled as the drawings specify (such as from drafts of 3-view dimensioned orthographic projections and assembly drawings, detailed electrical schematics, etc.). A design includes a completeBill of Materialsand cost analysis, along with the operating and assembly instructions. It also includes necessary engineering analysis so parts and components can be accurately dimensioned and sized so as not to fail. Now the design is submitted for approval, and if approved released for manufacturing. The physical products performance will be tested and compared to the engineering specifications and customer requirements and targets from Phase 2 requirements and engineering specifications. A test program could verify that requirements are met, that the mission objective can be performed, determine the effect of the environment on useful life, etc. At the end of Phase 4 it is time to present the Design Presentation/Report.It must be emphasized that the entire process is iterative within and across phases. For example, in Phase 3 a concept may fail to meet engineering specification after concept evaluation, so the steps of Phase 3 may begin again to create more concepts. At one time, this was not true and traditional EDP was thought of as a sequential process like Figure 3, with manufacturing the last step which started only when design was complete.Project DefinitionRequirements DefinitionConceptual DesignProduct DesignManufacturing

Figure 3.Steps of Traditional EDP as a Sequential Process, Left to Right in FigureConcurrent EngineeringModern application of the EDP now can incorporateconcurrent engineering, which involves teams working simultaneously and interacting to affect the design, instead of sequentially (and independently) like Figure 3. In a corporate setting where concurrent engineering is applied everyone - including engineering, manufacturing, testing, marketing, finance and sales - should be involved, to some level, in all steps of the product life-cycle. For concurrent engineering to work effectively, teams must collaborate, trust and share details across boundaries of design teams and disciplines. The objective of concurrent engineering is to reduce the product development cycle time through a better integration of activities and processes. Parallelism is the prime concept in reducing design lead time [2].On a SE student project, subsystem teams will need to be involved and cooperating in all steps of the systems engineering design effort. Information is shared among all team members. Shared information is not just drawing and schematics, but also requirements, stakeholder expectations, mission objectives, interfaces between subsystems, concepts, etc.Parallelism for a SE project is also the simultaneous and synchronized design of the subsystems needed to make the system. For example a satellites power subsystem is being designed by one team at the same time as the payload subsystem by another team, and it is known that these subsystems will be interacting with each other in some way during operations. To guarantee a successful outcome there must be a synchronization of some activities and a Systems Engineer who is required to provide guidance in the form of interfacing requirements and an architectural design to both teams. Concurrent engineering is a cornerstone of systems engineering.Concurrent engineering in SE can lead to the rapid evolution of concepts and requirements and the avoidance of major mistakes or rework at the projects end. When concurrent engineering is practiced the design cycle is shortened because fewer design changes occur, they occur more frequently in the earlier formative design stages, and they occur less frequently later in the cycle (Figure 4). Concurrent engineering also reduces cost because design changes later in the process are more expensive than if they occur earlier. Locking in prematurely on an inadequately scrutinized design concept will lead to greater costs down the road from design changes and poor performance from patch fixes. Choosing to proceed with development based on a poor design concept can be an expensive mistake, since at least 80 percent of a vehicles life-cycle cost is locked in by the concept that is chosen (NASA/TP-2001-210992), (Figure 5).

Figure 4. Design Changes as a Function of Time from American and Japanese Automobiles (American Suppliers Institute)

Figure 5. 80% of Life-Cycle Costs is Determined by the Conceptual Design at End of Phase A.

The Phases of the Life CycleFigure 6. NASA Phases of the Systems Engineering Life-Cycle [2]In Figure 6 the life-cycle begins with phases associated with designing (theformulationphases) and includes Pre-Phases A through C. Phase B ends with a preliminary design of a single system, and marks a turning point in the process where significant resources and design effort will be required to complete the design and the remainder of the project phases. The design is completed in Phase C. The latter part of Phase C through Phase F are associated with realizing the physical product - so are calledimplementationphases - beginning with the procurement and fabrication, assembly of subsystems from components and parts, integration of subsystems to create the system, and continuing on through operations and onto phase-out.A typical student project could start at Pre-Phase A and end in Phase D with testing, although some projects will have a launch and operation at a student competition, for example. At the end of each phase can be a review as named in the Figure 6, where passing the review is a prerequisite to the next phase activities. Later sections describe the specific tasks the 11 Systems engineering Functions - that a student team must consider in each phase.

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