Prescribing Motion to a Rigidbody with Respect to a Local System
LS-DYNA2
l...@schwer.net
On first reading your request does not make sense. Can you provide an illustration of such a deformable body prescribed rotation.
To move/rotate a deformable body requires the application of force of displacement. This will deform the body, I.e. change the center of gravity (motion). How do you predict this change is center of motion to accommodate your prescribed path?
Possibly, you could make one element near the center of motion rigid, and prescribe that element’s motion. --len
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James Kennedy
Dear User,
2.4 Constraints and Rigid Bodies
Avoid the use of *CONSTRAINED_NODE_SET unless nodes in the node set are coincident.
To rigidly connect two or more deformable, non-coincident nodes, use *CONSTRAINED_NODAL_
RIGID_BODY instead of *CONSTRAINED_NODE_SET so that nonphysical resistance to rotation
is not imposed. A rigid body can be defined in LS-DYNA in several ways:
• A part that references *MAT_RIGID is a rigid body.
• A set of nodes referenced by *CONSTRAINED_NODAL_RIGID_BODY forms a rigid body.
• A node or set of nodes referenced by *CONSTRAINED_EXTRA_NODES is added to or becomes
a rigid body.
Rigid bodies are subject to certain rules of modeling to which deformable bodies are not. For example:
• With few exceptions, *CONSTRAINED_OPTION cannot be applied to any element or part that is
rigid or to any node that is included in a rigid body. The exceptions are * CONSTRAINED_RIGID_
BODIES, * CONSTRAINED_JOINT, and * CONSTRAINED_LAGRANGE_IN_SOLID (if penalty-
based coupling is used).
• Constraint-based contact algorithms, predominately used in LS-DYNA in tied (not tiebreak) contact
types, cannot be used on rigid bodies.
• Prescribed motion cannot be applied to more than one node of a rigid body. The preferred method of
prescribing motion to a rigid body is via
*BOUNDARY_PRESCRIBED_MOTION_RIGID in which the motion is defined with respect to the
center-of-mass of the rigid body.
• Though nodal single-point-constraints (*BOUNDARY_SPC) on nodes of rigid bodies will internally
tbe converted by LS-DYNA into an equivalent set of constraints on the rigid body’s center-of-mass, the
preferred method of constraining rigid body motion is via Card 2 of *MAT_RIGID, or if the rigid body
is defined as a nodal rigid body, via
*CONSTRAINED_NODAL_RIGID_BODY_SPC. *BOUNDARY_PRESCRIBED_MOTION_
RIGID would be another acceptable means of constraining a rigid body (velocity or displacement could
be prescribed as zero). The mesh of rigid bodies should generally be no coarser than that of a deformable
body, unless the rigid body’s motion is fully constrained and/or prescribed, or unless the mass properties
are specified directly via *PART_INERTIA. Because mass is lumped at the nodes, a coarse mesh will
often give highly inaccurate inertia values.
Sincerely,
James M. Kennedy
KBS2 Inc.
May 12, 2023
From: LS-DYNA2 [mailto:ls-d...@googlegroups.com]
Sent: Friday, May 12, 2023 8:49 AM
To: LS-DYNA2 <ls-d...@googlegroups.com>
Subject: [LS-DYNA2] Prescribing Motion to a Rigidbody with Respect to a Local System
Dear all,
From what I know, in LS Dyna, there is an option to prescribe a motion to a rigidbody along a local coordinate system using Boundary_Prescribed_Motion_Rigid_Local. However, for my work, I would like to rotate a deformable body along a local coordinate system. Do you know if there is possible with LS-Dyna?
Thank you for any suggestions!
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