v1.0 - SEP Step 4 - Preliminary Design

Added by Jeremy Wright over 11 years ago

We're not quite to this step yet, but I want to make sure I fully understand what we'll need to do. J and/or Greg, could you briefly outline what you envisioned for this step when you first outlined the SEP for Shepard? How do we know when to stop on the preliminary design and start on the detailed design?

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RE: v1.0 - SEP Step 4 - Preliminary Design - Added by Greg Moran over 11 years ago

Preliminary design - brainstorming of all the possible solutions to each component/element, then picking the best option
Detailed design - In depth analysis and prediction/simulation of expected system performance based on interactions of each componemt.

Longer answer: That's a really good question, and the answer is usually best informed by experience. However I can try and describe the preliminary design process and how that differs from the detailed design process.

During preliminary design, the trade space is expanded and additional information is collected. For each section of the block diagram, a list of possible solutions should be developed and compared. For example, with the "Load cell" block, the designers should collect a list of possible equipment that meets the system requirements like being NIST certified. Then they pick a load cell off the list that best meets all the requirements and values of the project. Similarly for each of the other blocks this same process (collection of possible solutions and selection of one) is repeated. The preliminary design review (PDR) is a way to thoroughly review the available options and discuss the rationale for selecting the components that were chosen. This is sometimes referred to as "Powerpoint engineering" because of the use of briefing slides to show the design as opposed to using more technical methods.

The detailed design process is different due to the additional evaluation of the chosen design. After the PDR is complete, the lower level details and component interactions are discussed. Also, i like to try and predict the performance of the system to manage expectations of the customer. Even though this is before the formal "build phase" it is appropriate to use mock-ups, models, simulations, or prototypes to better evaluate the system. The culmination of the detailled design is a Critical Design Review (CDR) which should thoroughly describe the predicted (or simulated) performance of the system. CAD files or other visualization tools can be used to communicate the design and assembly of the structural components. Other software products can also be used to show predicted performance (but I cant think of any specific examples off the top of my head).

Hope that answers your question. Let me know if I can clarify any of these ideas further.