Volkswagen (VW) AG uses NEC SX-5 Supercomputers for Crash simulation

VW is moving to a new strategy to develop and build cars. Using existing platforms is cheaper and faster than beginning from scratch. A new car is the combination of a given platform with an individual exterior and form. Now the time from the decision "go" up to the real production is reduced to 36 months. With the idea of concurrent engineering a virtual prototype has to be built within the first nine month. This is based on a digital mock-up. After this timeframe all the functionality and properties of the new car are known. VW uses CAE to prove all these elements.

Crash Simulations

Dr. Richter presented different crashes, the frontal on a rigid wall or half of a barrier, the side, offset and rear impacts. There are specific German and European Union rules, rules for the United States, tests for automotive magazines or associations. In Germany the insurances use the so called Danner-Crash with only 15 km/h speed to check the repair costs of a little hit. Then the car is classified and the owner has to pay a specific fee depending on those costs.

VW installed the supercomputer NEC SX-5, which is the successor of the "old" SX-3 and the next generation SX-4. Thus VW has a long experience in using NEC vector processors. In total they have 12 processors in three computer complexes. Each processor has a peak performance of 4 GFlop/s, which would result in 47 GFlop/s Linpack performance. VW runs mainly PAMCRASH on them. The turnaround time of a crash simulation is constant since years, 10 hours - over night. With faster machines the engineers use a finer grid and therefore get better results, approaching reality. Dr. Bernd Richter told us that a computer model is compromise between accuracy and quality of results and responsetime. Thus the engineer has to abstract his model. His team benchmarked other systems too and choose the NEC SX-5 because of the performance in specific applications, for example crash. He mentioned that the turn-around time, including CPU and I/O and other elements has been improved by a factor of 3 on the SX-5 compared to the SX-4 - although the peak performance is only a factor of two. SGI workstations are used for model set-up and postprocessing of the results. For High end graphics output (virtual reality) special SGI computers are used.

But VW is not only concentrating on vector processors but uses Hewlett-Packard N-class machines (40 RISC processors) for scalar applications also part of the equipment in the super computer centre. They are dedicated for other computations, e.g.. NASTRAN applications, CFD (Computational Fluid Dynamics).

Showing half of a Passat, assuming symmetry, five years ago, the model had had 15 000 finite elements. Three years later VW processed 82 000 elements. Nowadays a compatibility crash has two components, the pushed car - 160 000 elements - and the bumping car - 94 000 elements.

An extremely time-consuming task is the computation of the airbag sensoric. A model of the platform only, e.g. of the Golf A4 - the actually sold Golf, consists of 664.000 elements and needs a turn-around time of 3.5 days. The standard crash platform consists of 63.500 elements only.

Simulations are not sufficient, therefore about 300 to 400 VW cars are crashed in reality. The results are compared with the numerical simulation. Sometimes the cars are selected randomly out of the usual production.