How to do modal transient with force as a base excitation

I was trying to do truck frame modal transient analysis. Full vehicle (truck ) model with base force excitation at wheel center. since it is force a input i dont understand where to apply the constraint. if spc not applied then model travels with large displacment which is illogical.

Please suggest some solution on this

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0 Don.Graff over 6 years ago

Hi Rajendra,

Rigid body modes would not really influence the elemental responses (FORCE, STRESS, etc) as these responses are based on the relative motion anyway.

When you do NOT include any rigid body modes, the displacements, velocities, and accelerations obtained are relative to the overall motion of the structure and are not absolute response quantities. When you DO include rigid body modes, you then additionally have the overall motion of the structure acting as a rigid body, which can influence the absolute displacement, velocity and acceleration responses.

In my experience, people rarely look at the displacement results when rigid body motion is included, but sometimes will look at accelerations. It is not uncommon to run the analysis twice, once with rigid body modes included, and once without for the data recovery of accelerations and element results, respectively.

Regards,

Don
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0 Don.Graff over 6 years ago

Hi Rajendra,

Rigid body modes would not really influence the elemental responses (FORCE, STRESS, etc) as these responses are based on the relative motion anyway.

When you do NOT include any rigid body modes, the displacements, velocities, and accelerations obtained are relative to the overall motion of the structure and are not absolute response quantities. When you DO include rigid body modes, you then additionally have the overall motion of the structure acting as a rigid body, which can influence the absolute displacement, velocity and acceleration responses.

In my experience, people rarely look at the displacement results when rigid body motion is included, but sometimes will look at accelerations. It is not uncommon to run the analysis twice, once with rigid body modes included, and once without for the data recovery of accelerations and element results, respectively.

Regards,

Don
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