Bodies are the only modeling elements that explicitly capture mass and inertia
effects.
The following three types of bodies are available in
MotionSolve:
- Body_Point
- Use this three degree of freedom element when the moment of inertia of the
component is negligible, but its mass is significant.
- Body_Rigid
- Use this six degree of freedom element when both mass and inertia are
significant, and the deformations are negligible.
- Body_Flexible
- Use this element when the component deformation has a significant effect on
system dynamics or when component stresses are of interest. The deformation
of a flexible body in MotionSolve can be modeled
using the following bodies:
- Linear flexible body
- This method uses linear superposition of modes computed using
the Component Mode Synthesis (CMS) method. Several variants of
CMS exist, each attempting to accurately capture the
deformations and boundary conditions with a minimum number of
modes. A CMS-based flexible body contributes degrees of freedom
equal to the number of CMS modes in addition to the six degrees
of freedom associated with the rigid body motion. This body is
able to handle small or linear deformations only.
- For MotionSolve 12.0 and above, the
efficiency of component mode synthesis methods in OptiStruct for generating modal
flex-bodies has been significantly improved. Speed improvements
in excess of 8 times have been observed when performing
component model synthesis for large systems such as the
Body-In-White (BIW) component for automobiles. This applies to
both the Craig-Bampton and the Craig-Change methods. The
Craig-Bampton method is much faster for problems with a large
number of interface nodes (ASET DOF). The Craig-Chang method is
dramatically faster when the AMSES or AMLS eigenvalue methods in
OptiStruct are used.
- Flexbody component and assembly information is transferred from
HyperMesh via OptiStruct and MotionSolve to HyperView. Flexbody component and
assembly information is written to the MotionSolve output H3D file. This enables
visibility of flexbodies to be controlled by components or
assemblies in HyperView.
- Nodal velocities and accelerations are written to the MotionSolve H3D output file. This allows
velocities and accelerations to be visualized in HyperView.
-
MotionSolve allows you to specify an
environment variable to define a set of paths to search for
flexbody (Flex_H3D) files, improving the search mechanism. This
provides a centralized repository of flexbodies that can be
easily used by models located on various areas of your computer.
To use this feature, specify the environment variable
MS_H3DFILE_DIR and point it to a list of the desired search
folders separated by the ";" delimiter.
mspost searches for the flex H3D (with
the relative path, if specified), at the following locations (in
order) until it is found:
- Input file folder
- Each folder location in the list specified by the
MS_H3DFILE_DIR environment variable
- For MotionSolve 12.0 and above, H3D
files contain a new shell thickness attribute. This additional
piece of information is used to calculate fatigue or damage of
shell structures such as automotive bodies or automobile
doors.
- Non-Linear Finite Element (NLFE) body
- This method uses the "Absolute Nodal Coordinate Formulation" to
obtain a fully non-linear finite element representation of the
flexible component. As the name suggests, this body is defined
with respect to the global frame and does not have a local part
reference frame like the linear flexible body. Each flexible
component can be made up of several finite elements that
represent flexibility in the component. Similar to traditional
finite elements, this flexibility is determined by the geometric
and material data specified for the elements. The NLFE body
allows you to model geometric non-linearity (large deformations)
as well as material non-linearity (hyper-elastic materials like
rubber). Current support for the NLFE body is limited to BEAM
and CABLE elements only. These elements are useful in modeling
long, slender structures.
- Since this representation is fully non-linear, no reduction
analysis (like CMS) is required to create this body - the body
can be created and modified entirely within MotionView without the need for any FE
solver based pre-processing. For more information on the NLFE
body, refer to the Body_Flexible modeling
component.
- Like the linear flexible body, the component and assembly
information for an NLFE body is written to the H3D animation
file. The animation H3D also contains stress, strain and
displacement information that can be visualized in HyperView. The BEAM and CABLE elements
within an NLFE body are represented as solid elements in
HyperView to aid in visualizing
the stresses, strains and displacements. Unlike traditional line
elements, the BEAM element's cross section can be deformed which
can also be visualized in HyperView.
In addition, it is also possible to define a planar body possessing only three degrees of
freedom. This can be specified using Reference_2DCluster and
Subsystem_Planar elements.
