Difference between part_x_form and part.CM results when contact forces are present?

mohsin.khan over 2 years ago

Accelerations with Adams_postprocessor/object/body/CM_acceleration

Accelerations with Adams_postprocessor/Result Sets/part_xform/ACCZ

are different for dynamic simulation with contact forces present in the model.

Can anyone help me with this odd behviour ?

Can anyone tell me how part_xform measures result and which marker it considers ?

0 Jesper Slattengren over 2 years ago

Of course it is. They are different points. The XFORM describes the motion of the LPRF (Local Part Reference Frame). This is the global location of the part (right click on the part and select 'Info' and loc for location and orientation). Very often the LPRF is located at global origin, this will always be the case if you created your part by drag and drop geometries instead of explicitly creating he part through the command navigator.
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0 mohsin.khan over 2 years ago

But will that affect its measure. As CM_acceleration also measures same way, there should not be any difference in their measure. But I am getting different outputs from these two adams/postprocessor outputs, especially when I am taking contacts.
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0 Henrik.Skovbjerg over 2 years ago

If the part is both rotating and translating, then the translational accelerations in the two different points will be different.
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0 mohsin.khan over 2 years ago

Hi @Jesper Slattengren thank you for your answer. But can we change LPRF location after creating part ?
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0 Henrik.Skovbjerg over 2 years ago

Right-click the part, select "Modify" and under "Category" select "Name and Position"

The location and orientation you enter here is for the LPRF.

Note that all markers on the part will move with the part if not otherwise parameterized. This means that you can break joints and forces by doing this kind of move.
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0 Martin Kieltsch over 2 years ago

How about good old requests ?

Using pre-defined stuff always sucks. With requests, you can specify your own measurement channels.

You wouldn't have to change anything on the part except adding some markers at user-specified locations.

Then create a request "give me DX/Y/Z or ACCX/Y/Z for this exact point vs. ground.origo or any other user-chosen reference" and the job is done.

Changing this Marker after creation is easy. In A/Car you usually create the marker and parametrize it to a hardpoint (point in A/View). When changing the point, the marker changes the location, too.

The part itself is not affected, unless it's not parametrized, too.
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