Modeling Bodies

Bodies are the only modeling elements that explicitly capture mass and inertia effects. The following three types of bodies are available in MotionSolve:

1.	Body_Point - Use this three degree of freedom element when the moment of inertia of the component is negligible, but its mass is significant.

2.	Body_Rigid - Use this six degree of freedom element when both mass and inertia are significant, and the deformations are negligible.

3.	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.

Flex-body component and assembly information is transferred from HyperMesh via OptiStruct and MotionSolve to HyperView. Flex-body component and assembly information is written to the MotionSolve output H3D file. This enables visibility of flex-bodies 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 flex-body (Flex_H3D) files, improving the search mechanism. This provides a centralized repository of flex-bodies 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.