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Doubt regarding compliance matrix calculation error in suspension analysis

I have read online help regarding this matter and understand that whenever we perform a standard event (for eg Suspension Analysis-----> Steering, which I am trying on one of the projects), the compliance matrix is calculated for every Joint and then various elements of this matrix are used for calculating different requests such as Ride rate, ride steer and a number of other parameters. The model which I have built has a number of idealized constraints (Convel, spherical, revoulte, fixed joints in the steering template). I have tried to replace as many fixed joints in the suspension templates as possible with bushes to see if it worked, but the problem still persists. There are also no redundant constraints in the model. I have also double checked the communicators that I have used and ensured that none of the parts are inadvertently connected to the ground. without the matrix, none of the requests which use this matrix are being calculated. The model I am trying to simulate is that of a tandem axle front suspension with bell-crank equalizing links and twin steering. I have also taken a look at the same assembly from the shared truck database. There seem to be quite a lot of idealized constraints in that model, but still there seems to be no issue when I simulate a similar steering event using that model. Can anybody suggest any corrections I may be able to incorporate into my model to make it work?
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  • If you keep in mind what the compliance matrix does, then the errors are kind of self explaining.
     
    In suspension analysis you enter the number of steps and ADAMS "pauses" in between each of these quasi-static steps.
    Here the wheel is excited by a small force of "1" and the small "reactions" of the wheel displacements are stored as the "compliance matrix". If that worked, ADAMS is calculating derived results like steering axis or roll center from these compliance results and export that to the req/res files for the last step.
    So if you for example use a motion driven maneuver on the wheel center, the suspension cannot travel up/down and some of the compliance matrix results don't make sense.
    Another possibility is that you have a completely kinematic suspension without bushings, nrods or flex-bodies. If that mechanism is in one position you can apply infinite forces and it wouldn't move - thus the compliance matrix is zero in those directions.
     
    If you carefully read the errors, it's exactly what they're saying.
    The solution was already proposed: If you for example think you need a revolute joint, then replace it by stiff bushing in x/y/z that has a low rotational stiffness around az.
     
Reply
  • If you keep in mind what the compliance matrix does, then the errors are kind of self explaining.
     
    In suspension analysis you enter the number of steps and ADAMS "pauses" in between each of these quasi-static steps.
    Here the wheel is excited by a small force of "1" and the small "reactions" of the wheel displacements are stored as the "compliance matrix". If that worked, ADAMS is calculating derived results like steering axis or roll center from these compliance results and export that to the req/res files for the last step.
    So if you for example use a motion driven maneuver on the wheel center, the suspension cannot travel up/down and some of the compliance matrix results don't make sense.
    Another possibility is that you have a completely kinematic suspension without bushings, nrods or flex-bodies. If that mechanism is in one position you can apply infinite forces and it wouldn't move - thus the compliance matrix is zero in those directions.
     
    If you carefully read the errors, it's exactly what they're saying.
    The solution was already proposed: If you for example think you need a revolute joint, then replace it by stiff bushing in x/y/z that has a low rotational stiffness around az.
     
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