CADfix provides sound basis for acoustic analysis
The current proliferation of integrated desktop modelling and analysis systems signals an acceptance among the engineering community of the importance of predictive performance calculations as early as possible in the design cycle. The aim is for it to become routine for designers to run finite element analysis (FEA) on every component they create, checking for optimum performance according to fit and function specifications. For straightforward stresses in single parts and simple assemblies this makes perfect sense, but more complex situations require specialist analysis expertise, and this is where companies like Advanced Analysis Ltd (AAL) come into their own.
AAL, now part of Lotus, is a specialist agency offering design and analysis consultancy services to automotive component manufacturers in the UK and abroad. Its customer list reads like a Who's Who of car and motorcycle OEMs and first tier suppliers. Ninety percent of AAL's work involves some form of thermal, mechanical, fluid or acoustic analysis, so it comes as no surprise that CADfix is a potent weapon in its armoury. What makes AAL's case slightly unusual is the different ways which it has found to use CADfix's powerful data handling capabilities.
"Our clients use so many different CAD systems that we could not afford to standardise on just one. CADfix means that we have a reliable means of addressing this problem," explains Richard Tyrrell, AAL's Managing Director. "But we pride ourselves on the innovative use of the tools we have at our disposal, and we were looking for new ways of harnessing the power of CADfix the minute we got it out of the box."
Transfer system
CADfix provides a comprehensive range of automatic and interactive tools for
correcting errors and inconsistencies that arise when solid and surface
modelling geometry is transferred from one application to another. Such
problems stem from the inherent complexity of defining 3D forms: even 'neutral'
file formats such as IGES can be seen as little more than a set of guidelines
which different systems interpret in different ways. A slight variation in
tolerance between one application and another, for example, can mean the
difference between neighbouring surfaces flowing smoothly together or being
separated by tiny unwanted gaps.
"It's a rare day when we get an IGES file through that we can process with no corrections," says Tyrrell. "Some of this is down to our customers' different CAD systems, but there are also problems in the way the modellers themselves are being used. A CAD user who really understands where the priorities lie in analysis is likely to provide us with a far cleaner model than one who doesn't.
"It's not that the designers are making mistakes," he adds. "It's more a question of poor drafting practice. Parts that have been extensively reworked, for example, can come with lots of residual baggage which can be easily overlooked in modellers but will play havoc in a less forgiving environment like FEA where all geometry is broken down into tiny individual elements."
AAL is not in the position of insisting that its customers' designers be retrained in the principles of FEA, so this issue of model quality is one that's unlikely to go away. Fortunately, this is exactly the kind of situation for which CADfix was designed. "Our team are all professional engineering analysts, and the last thing we want them to be doing is unnecessary data rework," says Matthew Woods, Senior Engineer at AAL. "Without CADfix that is exactly what we'd have to do. In some cases CADfix has meant a 50 percent time improvement. It's been a life saver."
Reverse is the trend
Beyond what may be considered the standard use for CADfix - translating and
repairing customers' data - AAL is now beginning to use it as the basis for a
reverse engineering service.
AAL has been receiving more and more requests for reverse engineering services, typically from foundries who have been making the same engine block for years but have never actually had an engineering drawing, let alone a CAD model. Retrieving geometric data in the form of point clouds is easy enough - either through touch probes or non-contact 3D laser scanners - but the real challenge is to transform this raw data into CAD- or FEA-style data. AAL has found a route that uses CADfix to maximise surface control and therefore flexibility.
The first stage is a conversion from point cloud to triangulated STL format - AAL has written its own code for this transformation. "CADfix really comes into its own at the next stage," says Tyrrell. "STL files can be a messy breed, but in CADfix we can process them really quickly. And because we know exactly what the data is going to be used for - typically, we'll be performing FEA or acoustic analysis - we can restrict ourselves to transforming just the relevant data. Without the control over the reverse engineering process that CADfix gives us, we would not have this invaluable flexibility."
As well as this 'traditional' reverse engineering, AAL is also increasingly asked to work backwards from previously generated FE meshes. Once again, CADfix makes this possible. "Surprisingly often, customers come to us for analysis without CAD geometry despite having legacy data - meshes and results - from previous analysis projects," explains Tyrrell. "We use so many different analysis techniques - each with a different meshing requirement - that the chances of being able to use the old mesh directly are all but zero. With CADfix we can take mesh data and use the surface borders and node positions to regenerate IGES style data that can be remeshed as required.
"Acoustic analysis is a classic case in point," he adds. "To determine noise levels radiated by a car engine, for instance, we need a surface mesh of boundary elements of approximately 20mm in size. Often, the starting point for this will be a solid FE mesh of 4mm or 5mm elements. We can quickly isolate the skin geometry from the FE mesh and, via CADfix, use this as the basis for the new boundary elements."
Massive time savings
This ability to isolate and manipulate specific geometric regions has added up
to some massive time savings at AAL. Without CADfix there would be no option
but to recreate the entire geometry and from scratch and then go ahead and mesh
it. For a complex cylinder assembly, Woods estimates that this is three or four
days' work. "But really we are only interested in about 15 percent of the data
for boundary element work," he says. "In CADfix we can go from FE mesh or CAD
model to fully defined BE mesh in just a couple of hours."
Richard Tyrrell sums up the importance of CADfix for AAL. "People come to us because they want to know whether their designs will work - and if not why not," he says. "For us to give meaningful answers to such questions and to suggest improvements and adjustments that are going to help in design optimisation we need to dedicate all of our time to complex engineering calculations. Without CADfix this would be impossible - we'd spend far too much time either editing messy CAD files or remodelling from scratch.
"Put simply," he concludes. "CADfix allows us to do the job that we're paid for."
Note to editors: FEGS Limited was founded in 1978 by Dr Geoff Butlin and is an established name in CAE software, particularly in the areas of CAD data exchange and pre- and post-processing for finite element analysis. CADfix is the fruit of FEGS's ongoing R&D in data exchange over the past 18 years. FEGS is a wholly owned subsidiary of Ohio-based International TechneGroup Incorporated (ITI).
ITI is the world's leading supplier of product data interoperability solutions, providing CAD/CAM/CAE and product data management (PDM) users and vendors with proven product data interoperability solutions. Headquartered in Milford, Ohio, ITI has representation throughout North America, Europe and Asia.
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