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Concurrent Design and Thoughts on 'Flows'

John Parry

John Parry

Posted Nov 17, 2009
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Electrical engineers often talk about a ‘design flow’, which Wikipedia defines as ‘the explicit combination of electronic design automation tools to accomplish the design of an integrated circuit.’ I heard the term a lot when making presentations at the Solutions Expos in the last few weeks. To someone with a background in fluid dynamics, flow means something rather different, but what electronic engineers are seeking to achieve is the seamless linking of a set of tools so that the data flows smoothly between them.

This got me thinking about the overall design process as being analogous to a ‘flow’ and how to get the product design to flow smoothly from concept through to finished product. People that know me know I just love analogies, so I thought I’d share this one with you.

Imagine a product design as being an object, and the design process a fluid through which it passes. We want our object to pass smoothly though our fluid without disturbing it, so the flow recovers quickly. This is a somewhat unscientific description of laminar flow.

We want our design to pass smoothly and quickly through from concept to finished product without creating ‘turbulence’ which has affects the process downstream. In turbulent flow, which we don’t want, the flow rips apart as it passes over the object causing eddies of different length scales which continue far downstream until the flow eventually recovers. Bigger eddies have the most energy and continue to break up to form smaller eddies that eventually die away as heat far downstream of the object.

Turbulence in the design process is just like turbulence in fluid flow – unpredictable, chaotic and hard to get rid of. It’s the unexpected design rework that’s required to make a poorly performing product perform acceptably. The bigger the issues the harder they are to fix, so like the larger turbulence eddies they take longer to dissipate, causing unforeseen delays to the schedule. Yet these issues have to be detected and fixed if the product is to ship. To avoid this we need a fluent (meaning flowing in a smooth and graceful way) product design, analogous to laminar flow.

So we have fluent design as a concept, and a way to visualize it is. How do we achieve it?

To pass both smoothly and quickly through a fluid, an object must be both the right shape i.e. aerodynamic – see the images below.

airfoil-cylinder

For our product design to pass smoothly through our design process it must also have the right ‘shape’, meaning that it must be proven to work acceptably well before details have been committed to in either mechanical or electrical CAD systems and the design ‘solidifies’. If our design solidifies before it has the right shape it will cause turbulence downstream in our design process.

Achieving fluent product design therefore requires upfront analysis of the product’s functional performance. For example building a thermal model of the entire electronics enclosure at the concept design stage to check the cooling strategy is viable, or checking the acceptability of the pressure drop vs. flow rate characteristics of a valve before other details of its mechanical design are considered.

Design, by its nature involves changing the shape of a product, and is often a trade-off between competing requirements – light and strong for example. The shape of our product will change as the design is elaborated, so fluent product design requires more than just upfront analysis. It requires continual use of analysis tools right from the start of the design process to check the performance impact of any design changes.

To be efficient, these analyses have to be performed by the designers making the design changes. It’s not something that can be achieved by ad hoc simulations performed in response to problems found late in the design. Being embedded within the mechanical CAD environment, FloEFD is the ideal CFD tool for designers, enabling them to perform analyses concurrently with their design changes without ever having to leave their MCAD software. There’s even a FREE Demo and Trial version available.

Our product design should then flow through our design process from start to finish without introducing any significant turbulence – costly and time-consuming redesign later in the design flow when the product design has solidified and is hard to change. The result is a first prototype that meets all its performance specs.

So there we have it. FloEFD enables concurrent fluent design, or CFD enables CFD perhaps? :)

If you found this interesting take a look at the CIMdata report on CFD for Mechanical Design Engineers “A Paradigm Shift for Better Design” which describes the value of earlier use of CFD. 

Dr J, Hampton Court

Upfront, Concurrent Design, Design Flow, CFD, Flow Behavior, Fluid Dynamics, Design Process, FloEFD

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About John Parry

John ParryI started my career in the consultancy group at CHAM Ltd., using PHOENICS for a variety of CFD applications. From the consultancy group I moved into support, helping customers debug models, and figuring out how to model new applications. That broadened into delivering training courses and creating training material. I was invited to join Flomerics when it started in 1989 to head up Customer Services, and I jumped at the chance to work for a startup. After a few years supporting customers using FloTHERM I moved across into research, developing thermofluid models of common electronic parts, like fans and IC packages, later managing the DELPHI and SEED projects. More recently I worked with Flomerics’ Finance Director on the acquisition of MicReD, helping to integrate MicReD’s business into Flomerics Group which was great fun. Since Flomerics acquired Nika, I’ve been responsible for promoting the FloEFD suite in education, and moved into marketing. I now work as part of the Mechanical Analysis Division’s Corporate Marketing group, responsible for ElectronicsCooling Magazine and the division’s Higher Education Program. Expertise: I’m a chemical engineer by training and did a PhD in reactor design before getting involved with CFD more than 25 years ago. Visit John Parry’s Blog

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