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Regarding the generation of loaded super elements in Hypermesh

I want to create a super unit for multi-body dynamics students, with a concentrated force of 1000N in the middle of the super unit and two end holes as hinge points with multi-body dynamics. I am a bit confused now. Under the CMSMETH card, should I choose Preload or LoadSET? If Preload is chosen, will SPCID be based on ASET geometry, or will two additional SPCs be created in RBE2? I feel like I can't quite understand the help document CMSMETH. Another question is whether the generated super unit in Motionview is subjected to a gravity field, or does it need to be added with a gravity field during the generation of the super unit?

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Accepted answers

Giorgio

Hello Jin1,

you must use PRELOAD and use the SPC set who you likes and the related load set ID. These loads/constrains are used to evaluate the egenmodes, the ASET can be different and are used to evaluate the constrained/interface modes.

Gravity (and any other kind of acceleration/internal force) is applied by MotionSolve (for that are important the egenmodes).

Tell me why is not clear the documentation:

CMSMETH

Flexible Body Generation

Best regards

Giorgio

Hello Jin1,

PRELOAD has effects on the stiffness matrix and then is used for the CMS process when you need to take in accountthis effect

Prestressed Linear Analysis

Tipically, for the flexbody preparation, this is used when on the component there are internal forces, like enforced connection, to take in account and change the response of the component inside the multibody mechanism. This is not visible on the flexible body, but the modes take in account the effects.

LOADSET is used to reduce the static loads into a proper mode. In fact, each loadset, adding an additional mode who can be activated, when is used into the multibody system, through the modal force statement

Force: FlexModal

The constraints used for this load, are the ASET.

Tipically, the loadset is used when you have complex loads to activate on the flex body, like aerodinalic loads, on a wing, who are distributed on the flexible body and are activated by the state (velocity) of the flex body inside the mechanism. The LOADSET in general is defined as a unit force/pressure on the structure and through the modal force, can be modulated/scaled as you need.

In your case, the force to apply on the structure, can be applied inside the multibody, by defining a force but the point of application on the structure must be an interface node (so you have defined the ASET over the 2 ASET of the constraints), or you can define a LOADSET and then is not needed the interface node to apply the fiorce, but to activate the force, you need to define the FlexModal statement.

Tell me if is more clear.

Have a good day.

Giorgio

All comments

Jin1

sorry， I typed the wrong word, it should be a super element. I typed it as a super unit

Giorgio

Hello Jin1,

Gravity (and any other kind of acceleration/internal force) is applied by MotionSolve (for that are important the egenmodes).

Tell me why is not clear the documentation:

CMSMETH

Flexible Body Generation

Best regards

Giorgio

Jin1

hello, Thank you for your answer. According to your response, can I understand it this way? If I need to generate a loaded super Element, then I should add an additional SPC, and ASET should be used as a connection point for multibody dynamics, without needing to be referenced in CMSMETH's preload.
I am confused about the help document because there is a loadset field under PRELOAD, which is used for static load condition aggregation. This may give me some confusion. Is it for static aggregation or is it using static load condition as prestress for dynamic aggregation? If it is dynamic condensation, isn't it duplicated with the preload field?

Giorgio

Hello Jin1,

PRELOAD has effects on the stiffness matrix and then is used for the CMS process when you need to take in accountthis effect

Prestressed Linear Analysis

Force: FlexModal

The constraints used for this load, are the ASET.

Tell me if is more clear.

Have a good day.

Giorgio

Jin1

Thank you again for your reply. I feel that I have understood what you said and the help document. Let me clarify if I misunderstood: Preload is equivalent to introducing prestress, which only affects the reduced stiffness of the flexible body, but the load that causes prestress is not transmitted to Motionview; LoadSET affects the mode and also condenses the static load into the H3D file, adding an additional static condensation condition. Motionview activates this static load through FlexModal. Can I understand it this way? In addition, I would like to ask you another question, how to speed up the calculation in Motionsolve? Is it by increasing the number of CPU cores or by relying on the CPU's clock speed?