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[FAQ]

The error is stemming from the keycard *CONSTRAINED_NODAL_RIGID_BODY, which is generated for remote points. I have the following comments/questions? 1.Try using mm, t, N as the Unit System in Mechanical. 2.Use the double precision solver: 3.Please make sure that part no. specified in the error is not repeated by opening it is LS-PrePost? 4.Constrained nodal rigid bodies are treated internally in LS-DYNA like a rigid body part, which uses the MAT_RIGID material model. A set of nodes is defined for each nodal rigid body definition with a minimum number of 2 nodes. Nodal rigid bodies with one node are deleted. So, to add a lumped mass or an inertia tensor to a single nodal point, use the respective keyword commands: *ELEMENT_MASS or *ELEMENT_INERTIA. 5.This error will occur if a nodal rigid body’s inertia is sufficiently small to where it could cause numerical instability in the rigid body subroutines. Generally, “too small for the accuracy of the computer” means that when certain quantities are computed using the inertias, (like an inverse), the numbers will result in an NaN. To resolve this issue, the user would’ve to investigate whether the rigid body is important to the simulation and if it is important, modify the model in some way to raise the inertia of the rigid body as suggested in the error message. Another option which might work is to set *CONTROL_RIGID, NORBIC=1. As noted in remarks section of this keyword in User’s Manual Vol. I, during initialization, the determinant of the rigid body inertia tensor is checked. If it falls below a tolerance value of 10^−30, LS-DYNA issues an error message and the calculation stops. In some rare cases (for example with an unfavorable system of units), such tiny values would still be valid. In this case, NORBIC should be set to 1 to circumvent the implied inertia check.