How to get data from RIGID BODY?

[ME3D]

Hello All,

I'm trying to get a reaction force especially Moment forces from RIGID BODIES.

I have several RIGID BODIES that rotates their axis.

I found that reaction forces from RIGID BODIES could get from RCFORC.

But, It only get me an output from Contact.

(I tried BNDOUT, etc..)

So, is there any way to get Moment force from RIGID BODY at the Center of Axis, which rotates it self.

Regards,

ME 

[James Kennedy]

Dear ME3D,

 

See if the following is of some help.

 

Reaction and moment forces from rigid bodies in LS-DYNA

In LS-DYNA, you can analyze the reaction and moment forces acting on rigid bodies, which are commonly used to represent stiff components or tooling in simulations where deformation is negligible. 

Here's how to obtain this information

1.      Defining Rigid Bodies: Rigid bodies are typically defined using *MAT_RIGID or *CONSTRAINED_NODAL_RIGID_BODY.

2.      Constraints and Boundary Conditions:

·         To obtain reaction forces associated with boundary conditions, use the *DATABASE_BNDOUT keyword.

·         If using Single Point Constraints (SPCs) with *BOUNDARY_SPC, the reaction forces from the SPCs can be extracted using the *DATABASE_SPCFORC keyword. These reaction forces will be equal in magnitude and opposite in direction to the applied external forces at the constrained nodes.

3.      Contact Forces:

·         For contact interactions between rigid bodies or between rigid and deformable bodies, use *DATABASE_RCFORC to output the resultant contact forces.

·         In the case of single surface contact, you may also need *CONTACT_FORCE_TRANSDUCER_(option) to extract resultant contact forces.

·         Note that the raw contact force output can be noisy and may require averaging over time for more meaningful results.

4.      Rigid Body Output:

·         LS-DYNA allows direct output of rigid body response using the *DATABASE_RBDOUT keyword. This file contains the history data for the rigid body, including its translational and rotational motion, and potentially the associated forces and moments if defined to be output.

5.      Outputting Rotational Information:

·         Rotational information for rigid bodies can be directly output as history data (nodal velocities, accelerations, displacements) in the global coordinate system.

·         Alternatively, if you're analyzing a deformable body containing solid elements, you can define a small rigid patch within it using *CONSTRAINED_NODAL_RIGID_BODY to output the rotations of that specific region to the RBDOUT file. 

In summary

By using the appropriate *DATABASE keywords, you can extract the reaction forces and moments associated with boundary conditions, contact interactions, and the overall rigid body motion in LS-DYNA simulations. Remember to consult the LS-DYNA user manuals for specific details on keyword usage and options. 

 

Sincerely,

James M. Kennedy

KBS2 Inc.

August 5, 2025

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[Özgür Yalçın]

Hi,

Did you tried to SPC2BND ---> 1 from control_output keyword before trying to read forces bndout ? You have to change this line to read forces from bndout

5 Ağu 2025 Sal 07:35 tarihinde ME3D <dqq...@gmail.com> şunu yazdı:

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