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# flex chassis(or body)

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## flex chassis(or body)

(OP)
Hello guys!
I built a rigid-flexible coupled vehicle model for handling and stability simulation. The flex part is the chassis(or the body).I carried out the following four simulation conditions for full-vehicle analyis:
(1)step steer;
(2)constant radius cornering;
(3)swept_sine steer for frequency scanning condition, whose frequency is increased by 0.08Hz from 0.01Hz to 3Hz;
(4)swept_sine steer for intermediate position steering condition at 0.2Hz;
The first two output curves are successful. But the output curves of the latter two conditions are not smooth,even the burr is very serious.
What are the possible reasons?
Thanks for your hands!

### RE: flex chassis(or body)

(OP)
Hi,@GregLocock
Thanks for your reply!
In Adams/Car, I have made the flex chassis rigid through the function key "Make Rigid". After I did these, the output curves of the swep_sine steer is successful. Only when the chassis is a flexible part, the output curve fluctuates greatly.

### RE: flex chassis(or body)

Good plots. It looks to me as though the model is having trouble in the steering, and is struggling to find straight ahead at t=0. Everything from t=3 onwards looks fine. Perhaps there is a build error in your flex model?

Have you closely examined the animation in the first few seconds? is something jiggling about?

You could try running straight line drive at the same speed and solver setting. If that shows similar problems at t=0 then it is a build problem. If it doesn't then I can't think of an obvious soultion.

Cheers

Greg Locock

New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

### RE: flex chassis(or body)

(OP)
Firstly, thanks for your replies!
After I swicthed the power steering assist off, the output curves were terrible and it took about three and a half hours to run the whole simulation. It is not the right way.
However, I found that if the quasi-static straight-line setup check box is checked, the output curves were correct. Is it proper to check the quasi-static straight-line check box when running swept-sine steer? After doing so, are the obtained curves credible? Can these output curves accurately represent the sinusoidal sweep condition?

### RE: flex chassis(or body)

Hmmm.

Select to perform a quasi-static prephase analysis before running the transient analysis on your full-vehicle assemblies.

For all cornering analyses, selecting this option causes Adams/Car to perform a SKID_PAD quasi-static analysis.

For all other analyses, selecting this option causes Adams/Car to perform a STRAIGHT (sometimes called ClearVision adjustment) analysis.

If you do not select this option, Adams/Car performs a SETTLE analysis.

For more information about the different quasi-static setup method keywords (such as SETTLE and STRAIGHT), see Structure of Event Files.

The problem with QS is that things like your shock absorbers don't get to play. it's not the end of the world but you will get different results to a true dynamic event. What it does is to set the car up in D'Alembert equilibrium for a given vehicle state equation, ie speed SWA and latacc. However reading Structure of Event Files suggests this may just be for the initial setup, as an alternative to Settle, which is what I'd regard as the default. So overlay no flex with settle and no flex with QS, if they are identical, including roll, and SWT, then you are safe to use QS flex.

I don't use Car, so these options are an unknown to me.

Cheers

Greg Locock

New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

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