Role of Dynamic Multibody Simulation in Design of Race Cars

[hkazami]

Hey guys,

I always think that the main reason of using a dynamic multibody tool like Adams is to estimate the dynamic loads of the chassis components during some driving events (ex. riding on curbs), so that those components can be optimised in finite element tools, while some kinematic tools (OptimumK or the suspension analysis of Adams) will help defining the kinematic points of the suspension.

But a chassis engineer told me that in their team no one is really using dynamic multibody simulation, what they do is just measuring forces in all suspension linkages of the car of last year, calculating the contact patch force, and feed it back to finite element software. And for the performance analysis they have another in-house quasi-static lap time simulation tool.

Does anyone know that if it is the general case in motorsport? What role do dynamic multibody tools play in the design phase of race cars? Looking forward to your opinions and comments

hkazami

[dynatune]

In the hay days (1995 to 2005) of using multibody dynamik tools like ADAMS every team did put quite a lot of effort in this. I know this for a fact since I was heavily involved in it myself. Certainly ADAMS was used as a kinematic and elastokinematic tool for layout of suspensions and it provided a lot of new insights and was being used to cover weaknesses in the data logging of those days. Typically loadcases were defined with ADAMS due to lack of better. One of the greater problems was the amount of data needed to create and validate a model and many of those data had to come also from FE programs. Beyond that since there are no real bushes in an F1 car many deformations are structural and would have to be modeled in a similar way to FE. So why do it twice ?. The other of the greater problems that ADAMS or similar programs faced was the immense use of CPU time to do laptime simulation with full blown (300 DoF) models. For instance on some top state of the art workstations a simulated lap of SPA Francorchamps took a whole working day. In fact in those day I used all 50 licenses of an OEM to run a decent number of simulations during the night, nevertheless I think the problem is clear and to my understanding it has not changed significantly. Beyond that many FE tools have now incorporated non-linear modules so a great deal of suspension characteristics can be calculated with those.
Then one final observation, but I could be wrong on it, there is almost no hardcore formation on ADAMS in the sense that the older generation was used to calculate with "elementary tools" and could enhance their skill and experience world with ADAMS to new horizons, where as nowadays many young engineers seem to start with ADAMS without even knowing the equations for a bicycle model. Knowing the booby traps in ADAMS, inexperience and complexity can be a very dangerous cocktail.

Cheers,
dynatune, http://www.dynatune-xl.com

[hkazami]

Hi dynatune,

Thanks a lot for your aspect! I know that in multibody simulation one can also include flexible bodies which are reduced or simplified in modal space (Modal Neutral File), is this what you mean by those data coming from FE programs? Isn't it more efficient to analyse the stress states and then optimise the geometry directly in MBS with the simplified flexible bodies, since MBS is still faster than FEA? Or is it just too simplified and not precise enough? And do you mean that in FE tools now one can also investigate anti's, bump steers etc.?

Well, I also know quite a few people who can use Adams quite well, without knowing what they're actually doing and what the results mean. You're absolutely right, but actually it happens everywhere if you rely on your CAE too heavily

hkazami