Wrong results with negative compliance
Altair EmployeeHello all,
I'm trying to simulate some load cases of a car chassis. It should later be used for a topology optimization, so that I start with the design space.
I started with one side, mirrored it and delete the coincident nodes. The blue beams are stiff (very high elastic modulus) and connected with ball joints (coincident nodes). Those beams are connected to the chassis with RBE3 elements (free around the x-axis).
I realise that the mesh is not the best, but it's just for testing the suspension.
i got the following warnings (using HM 2017 and optistruct):
*** WARNING # 5629
In static load case 2,
The magnitude of Residual Energy Ratio, 1.83121e+006, is large (larger than 10%).
The results for this subcase may not be correct.
*** WARNING # 312
In static load case 2
the compliance is negative or large -316.526.
Optimization/buckling analysis cannot be performed.
due to possible rigid body mode.
Subcase: 2
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Label x-force y-force z-force x-moment y-moment z-moment
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Sum-App. 0.000E+00 0.000E+00 1.000E+04 1.416E+07 -1.743E+07 0.000E+00
Sum-SPCF 3.630E+04 -2.914E+04 4.500E+03 -2.370E+07 -1.162E+07 -1.056E+08
I don't understand, why I get a the following displacements (scale factor 1000). Moreover, the displacements are not symmetrical, although the forces are applied symmetrically.
@Prakash Pagadala: I uploaded the file 'Suspension_Beams': I would really appreciate your help.
<?xml version="1.0" encoding="UTF-8"?>
<?xml version="1.0" encoding="UTF-8"?>
Answers
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If the model is properly setup but still the compliance is large, then add the following PARAM card. PFA screenshot from help.
PARAM, HGHCMPOK
<?xml version="1.0" encoding="UTF-8"?>
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Thank you Rahul, but I think I made a mistake in the model setup.
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