Add mass to rigid body (LS Dyna user profile in HM)
Using HyperMesh and the Radioss user profile it is possible to create a rigid body where the mass is dependent on the defined mass density of the material assigned to the rigid part and, also, to add mass using the RBODY card (thus, if an initial velocity is applied to the rigid part, the total kinetic energy is determined using 'mass + rho*volume').
I am wondering what the equivalent is in HM, using the LS-Dyna user profile. I understand defining the mass density in the MAT_RIGID keyword, but adding mass to a node (1D > mass > create > 'select node' > create) does not yield the same results as simply adding mass using the RBODY card for Radioss. I have confirmed this difference by first ensuring that the added mass is part of the rigid component and calculating the mass (Tool > mass calc > 'select component' > calculate). The expected total mass is provided (mass + rho*volume). Yet, when I run the .k file, the initial kinetic energy provided only takes 'rho*volume' into account and not also the added mass.
Is there any way (with the LS-Dyna user profile in HM) to add mass to a rigid component - or a node that is a part of the rigid component - without modifying the mass density of the material assigned to the rigid component?
I have attached a sample .k file which has mass + rho*volume = 0.5kg + 0.5kg = 1kg, but the initial kinetic energy listed during initialization is only 20.25 J. The initial velocity is 9 m/s, so I expect 0.5*1kg*(9m/s)^2 = 40.5 J.
Please let me know if you require any clarification of my question.
Thank you in advance for your time and any suggestions.
Answers
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Hello Autumn,
as a first hint, what you can try is to convert a RADIOSS model into Dyna:
- through the top menu Tools -> Convert -> Radioss to Dyna in the old interface
- through File -> Convert -> LS Dyna
This should generate a LS Dyna with a valid modeling for the non structural mass.
If you start from scratch, then you need to check with LS Dyna what is the recommended way to set it up. I'm a bit surprised that the added mass you used returns you the valid mass, but is not taken into account for Kinetic Energy computation. Maybe you need to check this point on LS Dyna forum.
Best Regards,
Michael
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Michael Herve_21439 said:
Hello Autumn,
as a first hint, what you can try is to convert a RADIOSS model into Dyna:
- through the top menu Tools -> Convert -> Radioss to Dyna in the old interface
- through File -> Convert -> LS Dyna
This should generate a LS Dyna with a valid modeling for the non structural mass.
If you start from scratch, then you need to check with LS Dyna what is the recommended way to set it up. I'm a bit surprised that the added mass you used returns you the valid mass, but is not taken into account for Kinetic Energy computation. Maybe you need to check this point on LS Dyna forum.
Best Regards,
Michael
Hi Michael,
Interestingly enough, I had obtained the .k file by converting a .rad file (using HyperCrash though, as the Tools > Convert > Radioss in HM only provides me with PamCrash and Optistruct options and nothing for LS-Dyna). However, I did do some edits to ensure it was actually able to be initialized and run through the LS-Dyna solver without error, so checking the unmodified, converted .k file reveals that perhaps I need to make use of the *CONSTRAINED_NODAL_RIGID_BODY_INERTIA keyword... hopefully this keyword works. I will provide an update if I figure it out.
Thank you for your tips!
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