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Surface Wrapping Technology for Industrial CAE
Posted Thu March 13, 2008 @04:25PM
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Geometry Stephen Ferguson, Joel Davison and Jon Lewin
CD-adapco

Dealing with the consequences of ‘dirty’ or complicated CAD data has long been the biggest bottleneck in the CAE process and, until recently, was the single largest obstacle preventing the routine implementation of numerical simulation early in the industrial design process.

Although the route from CAD model to CAE solution has been much improved in recent years, with the introduction of better translators and CAD-embedded CAE simulation technology, there still exists a significant group of problems where CAD geometries are too big or complex to be handled easily.


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These problems typically involve large assemblies of complex CAD parts, many of which contain more detail than is strictly necessary for the CAE calculation. Estimates from the automotive industry1 suggest that as much as 80% of the simulation effort spent in a typical CAE project is taken up in generating the computational model, the lion’s share of which is surface preparation and repair.

In response to this, CD-adapco has invested heavily in developing an automatic geometry repair tool which utilises ‘surface wrapping’ technology. Now in its third generation, this approach has delivered the following demonstrable business benefits to our customers:

  1. A significant reduction in the time required to produce simulation results from complex or poor-quality geometric data. In some cases users have been able to reduce their model creation times from weeks to just a few hours.
  2. Increased productivity, as highly qualified engineers are able to spend more time concentrating on engineering analysis rather than menial geometry preparation and repair.
  3. More accurate simulation results. CAE models are able to represent the full complexity of the actual component geometry and do not require geometric simplification in order to facilitate meshing.
  4. Rapid turn-around times increases the viability of performing multiple simulations early in the design cycle, increasing the degree of design optimization

What type of CAE simulation is the Surface Wrapper good for?
The surface wrapper is suitable for FEA, CFD, crash, or any other type of analyses for which a high quality triangulated surface is a necessary prerequisite for producing a simulation ready mesh. As the examples below demonstrate, surface wrapping technology is being employed to improve the CAE process of industry giants, such as the Mercedes Benz Car Group and as way of making simulation a viable part of the product development process in smaller companies that are relatively new to CAE.

How does the Surface Wrapper Work?
From a user’s point of view, surface wrapping is an entirely automatic process. Using a simple GUI, the user first imports the geometry, sets a representative ‘base-size’ (that determines the level of feature resolution in the final surface), and hits the “surface wrap” button. The surface wrapper is guaranteed to return a closed manifold surface.

Behind the scenes, the Surface Wrapper works by ‘shrink-wrapping’ a high-quality triangulated surface mesh onto the geometry, closing holes in the geometry and joining disconnected and overlapping surfaces. The surface wrapper quickly calculates the wetted surface of the geometry, automatically discarding surfaces that are outside the calculation-domain, instantly eliminating unnecessary detail.

Although the emphasis of the surface wrapper is on fully automatic repair, the tool is also fully customizable, allowing users to specify the level of resolution on a surface-by-surface basis if necessary, or using volume regions to specify larger areas of refinement. All size specifications are relative to a global base size, so that once set up, the wrapped surface can be fine tuned by just altering a single parameter.

Importantly the surface wrapper respects the fidelity of the original surface. Unlike other surface-wrappers, CD-adapco’s wrapper automatically respects the sharp edges and corners of the original model, as well as any other “feature curves” that the user chooses to prescribe.

How long does it take?
The exact time to perform a wrap depends on how complex the geometry is, what level of surface refinement is required and how much computing power is available. A complicated structure such as an offshore oil platform or automotive underhood can usually be wrapped within an hour. In most cases surface wrapping takes just a few minutes using a simple desktop PC.

What constitutes ‘dirty’ CAD?
The surface wrapper is useful for dealing with many different instances of ‘dirty’ or ‘overcomplicated’ CAD:

  1. Any complex collection of CAD parts, such as an automotive underhood that needs to be combined into a single surface for meshing. Early in the design process, before packaging issues have been resolved, individual components often do not fit together perfectly, as they would in the final configuration, meaning that their volumes overlap or surfaces potentially interfere with each other.
  2. A fully detailed CAD part that requires too much detail for CAE analysis, and which needs to be de-featured prior to constructing a computational mesh suitable for analysis.
  3. A CAD part that contains internal (or external geometrical details) that are not relevant to the CAE simulation and need to be discarded (such as engine internals when conducting an underhood thermal management simulation).
  4. An assembly of parts configured for manufacture, so containing gaps where fixtures (welds, screws, rivets etc) are to be placed. Without closure these gaps are likely to prevent meshing or can lead to features significantly smaller than the domain of interest.

Conclusion
Surface wrapping is a fully automatic method for preparing assemblies of complex CAD parts and other ‘dirty CAD’ for meshing. Now in its third generation, CD-adapco’s surface wrapper requires only modest computer resources and minimal user training.

Deployed early in the design process, surface wrapping can deliver significant benefits in terms of productivity and increase in both the quality and viability of CAE analysis.

motorcycle
Motorcycle geometry wrapped in a surface mesh.

 

oil rig
Offshore oil rig geometry wrapped in a surface mesh.

aircraft
Passenger aircraft geometry wrapped in a surface mesh.

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