Model files are composed of many different parts, or entities. MotionView allows you to change the display attributes of each entity in a graphic. Visual properties such as shading, color, and
mesh lines can be assigned using the Graphic Entity Attributes panel.
The System/Assembly panel allows you to add new systems and assemblies to your model, modify attachments, and set
initial conditions and options for systems and assemblies.
The Command Sets panel allows you to create command sets for the solver-command file. The command sets for a model are
order dependent, since they define the contents of the solver command file.
Use the Deformable Surfaces tool to create and edit deformable surfaces. These entities can change shape during the simulation
and can be used with advanced joints and contacts.
In a multibody system, a rigid body is an ideal representation of solid body/part of fixed size and shape in which
deformation is insignificant or neglected, or in other words, the distance between any two points of a rigid body
remains unchanged (irrespective of the external forces acting on it). A rigid body will have six degrees of freedom
(DOF) and therefore every additional rigid body in a multibody system adds an additional six DOF to the system.
Deformable bodies in multibody systems are those that can be used to model elastic deformation of the bodies of the
system. The deformable body connects to its neighboring elements/bodies through interface nodes. The deformable body
consists of reduced stiffness and mass matrices, which can be obtained in various ways. Two popular methods for the
same are: Craig-Bampton Method and Craig-Chang Method.
The point mass body is a reduced version of the six DOF rigid body. It only has three translational DOFs, therefore
the point mass body has mass but no inertia properties. The position of a point mass is defined by a center of mass
point. By default, the orientation of the point mass is set to be the same as the Global Coordinate System (which
never changes during simulation). The purpose of a point mass entity is to add additional representative weight
to another body, for example the mass of a driver on a seat.
NLFE stands for Non Linear Finite Elements. The NLFE implementation in MotionView/MotionSolve is based on Absolute Nodal Coordinate Formulation or ANCF. In this approach, only absolute coordinates and global
slopes are used to define the element nodal coordinates without the need for using infinitesimal or finite rotations.
In complex multi-body simulations, flexible bodies are needed to improve model fidelity. In cases where the deformations
and rotations are expected to be large and/or exceed linear assumptions, NLFE becomes a necessity.
Use the Advanced Joints tool to create and edit a set of special constraints called higher pair joints. Typically, these are constraints
that involve a curve or surface on at least one of the two bodies.
Use the Fields tool to create a compliant connection between two bodies where stiffness or damping in one direction can be a function
of displacement in another direction
Use the Variables tool to create solver variables that can be used to create an algebraic expression of state variables, as well as
other solver variables. This can then be referenced in function expressions throughout the solver input file.
Use the Arrays tool to create solver arrays and set solver array data. Solver array types include X array, Y array, U array, IC
array, Plant Input array, and Plant Output array.
Use the Strings tool to create a solver string and set solver string data. A solver string provides a string that can be accessed
within the model, for example, to pass into a user subroutine.
Use the Diff Equations tool to set solver differential equations. These equations can be used to add additional states to the mechanical
system being modeled.
NLFE stands for Non Linear Finite Elements. The NLFE implementation in MotionView/MotionSolve is based on Absolute Nodal Coordinate Formulation or ANCF. In this approach, only absolute coordinates and global
slopes are used to define the element nodal coordinates without the need for using infinitesimal or finite rotations.
In complex multi-body simulations, flexible bodies are needed to improve model fidelity. In cases where the deformations
and rotations are expected to be large and/or exceed linear assumptions, NLFE becomes a necessity.
Generating Position and Gradients for Loaded Configuration
The following process can be used to generate a CSV file
containing the position and gradients for loaded configuration, which can then be
imported and saved into a MotionView model.
Start with the NLFE Body in a No Load configuration and apply Force/Motion to
load the NLFE Body as needed.
Include the MotionSolve Save command to save the states of the model into an
XML file (herein referred as “saved state XML”) after the Simulate command. A
template that writes into the solver command section can be used in MotionView.
Figure 1.
Solve the model. From the MotionView Run panel, use the Scripted simulation
option.
Figure 2.
Use a python script “NLFE_generate_loaded_csv.py” available in the Hyperworks
install (install_location/utility/mbd/NLFE) to extract the final loaded state of
the NLFE Body and save it into a CSV file. The python executable “python.exe”
(if not installed separately) can also be found in the Hyperworks install
(install_location/hw/python\python27\win64).
Figure 3.
The script will prompt you to open the saved state XML file and also
provide a CSV file name to save the position and gradients information.Figure 4.
Once the CSV file is saved, import it into MotionView using the Import Points
option available in the Loaded View of the NLFE Connectivity tab.
Figure 5.
Upon importing the loaded configuration, the display of the NLFE Body in
graphics area would change. The NLFE Body loaded configuration gets the
prominent display with solid implicit graphics while the no load configuration
will be shown in a wireframe featured mode. Figure 6.