FlexBody

Model ElementFlexBody defines a flexible body object in MotionSolve. This entity has mass and inertia properties, like a rigid body. In addition, it has flexibility properties that allow it to deform under loads.

Class Name

FlexBody

Description

The FlexBody operates in 3D space where it can simultaneously undergo large overall motion as well as deformation. MotionSolve supports two kinds of flexible bodies:

Linearly flexible body based on Component Mode Synthesis (CMS): The deformation is small, but the overall motion is large. Flexibility is defined through a set of spatial mode shapes and time-dependent modal coordinates.
Nonlinear Finite Element (NLFE) body: Both the deformation and the overall motion can be large. This is a fully nonlinear finite element representation of the flexible body.

The Python interface, however, only supports the linearly flexible body (CMS).

Attribute Summary

Name	Property	Modifiable by command?	Designable?
id	Int ()
label	Str ()	Yes
qg	Location ([0,0,0])		FD Only
reuler	Angles ([0,0,0])		FD Only
mass	Double ()	Yes	FD Only
cm	Location ([])		Yes
ip	Ips ()	Yes	FD Only
vm	Reference ("Marker")		Yes
vx	Double (None)	Yes	FD Only
vy	Double (None)	Yes	FD Only
vz	Double (None)	Yes	FD Only
wm	Reference ("Marker")		Yes
wx	Double (None)	Yes	FD Only
wy	Double (None)	Yes	FD Only
wz	Double (None)	Yes	FD Only
cratio	Function ()
routine	Routine ()
script	Script ()
rigidified	Bool ()
mtx_file	String ()	Yes
h3d_file	String ()	Yes
lset_file	String ()
max_num_cnt_loadset	Int (Unspecified)

Usage

The linear FlexBody implementation is available in four different variants.

#1. Linearly flexible body without user defined damping
FlexBody (mtx_file=string, optional_arguments)

#2. Linearly flexible body with damping in a MotionSolve expression
FlexBody (mtx_file=string, cratio=expressionString, optional_arguments)

#3. Linearly flexible body with user defined damping in a compiled user-subroutine
FlexBody (mtx_file=string, cratio=userString, routine=string, optional_arguments)

#4. Linearly flexible body with user defined damping in a Python/Matlab/OML function
FlexBody (mtx_file=string, cratio=userString, routine=functionPointer, optional_arguments)

Attributes

id

Integer

Specifies the element identification number. This number must be unique among all the FlexBody objects in the model.

This attribute is optional. MotionSolve automatically creates an ID when one is not specified.

Range of values: id > 0.

label

String

Specifies the name of the FlexBody object.

This attribute is optional. When not specified, MotionSolve creates a label for you.

qg

A Location object or a list of three doubles.

Specifies the coordinates of a local part reference Marker. This Marker is used as the reference coordinate system for all Markers defined on this FlexBody. It also defines the location of the finite element global coordinate with respect to the MBS global coordinate system.

The qg attribute is optional.

When not specified, it is assumed to be coincident with the global origin. That is, (0, 0, 0).

reuler

A list of three doubles.

Specifies the body-fixed 3-1-3 Euler angles of the local part reference Marker with respect to the global coordinate system. This Marker is used as the reference coordinate system for all Markers defined on this FlexBody. It also defines the orientation of the finite element global coordinate with respect to the MBS global coordinate system.

The reuler attribute is optional.

When not specified, it is assumed to be (0,0,0). That is, the local part reference Marker has the same orientation as the global coordinate system.

mass

Specifies the mass of the FlexBody object.

The attribute mass is optional. If a FlexBody is fully constrained and you are not interested in the constraint forces, then mass does not need to be specified.

When not specified, mass is set to zero.

Valid range of values: mass ≥ 0.0

cm

Reference to a Marker.

Specifies the Marker that is located at the center-of-mass of the PART.

The attribute cm is optional. If a FlexBody is fully constrained and you are not interested in the constraint forces, then mass and inertia do not need to be specified. When these are not specified, you must not specify cm.

Note: To remove circular references, the body is created in two steps. First, the body is defined without a cm marker. Then, the cm attribute is explicitly defined.

ip

List of three doubles or a list of six doubles.

Specifies the mass moments of the inertia matrix for the FlexBody about the x, y, z-axes of the cm marker.

The ip attribute is optional. When not specified, it is assumed to be the zero matrix. If a FlexBody is fully constrained and you are not interested in the constraint forces, then ip does not need to be specified.

You may choose to specify only the diagonal entries [Ixx, Iyy, Izz] or the full matrix [Ixx, Iyy, Izz, Ixy, Ixz, Iyz] in the order shown.

When specified:

Inertia_xx ≥ 0
Inertia_yy ≥ 0
Inertia_zz ≤ 0

vm

Reference to a Marker.

Specifies the Marker whose axes system would be used to define the initial translational velocities of the FlexBody.

When not specified vm defaults to the global coordinate system.

vx vy vz

Double

Specifies the initial translational velocity of the FlexBody along the x-, y- and z-axes of the vm marker.

The vx, vy, and vz attributes are optional.

When not specified, MotionSolve performs an internal computation to ensure that all Part velocities are consistent with the first-time derivative of the constraints.
When specified, MotionSolve tries to maintain the value specified as it performs the internal computation to ensure that all Part velocities are consistent with the first-time derivative of the constraints.

wm

Reference to a Marker.

Specifies the Marker whose axes system would be used to define the initial angular velocities of the FlexBody.

When not specified, it defaults to the FlexBody cm coordinate system.

wx wy wz

Double

Specifies the initial angular velocity of the FlexBody about the x-, y- and z-axes of the wm marker.

The wx, wy, and wz attributes are optional.

When not specified, MotionSolve performs an internal computation to ensure that all Part velocities are consistent with the first-time derivative of the constraints.
When specified, MotionSolve tries to maintain the value specified as it perform the internal computation to ensure that all Part velocities are consistent with the first-time derivative of the constraints.

mtx_file

String

Specifies the name of the MTX file that contains the CMS representation for the flexible body.

The mtx_file attribute is mandatory.

h3d_file

String

Specifies the name of the H3D file that contains all nodes in the finite element mesh.

The h3d_file attribute is optional.

This file is needed only for creating an animation file; the solver does not use it for analysis.

rigidified

Boolean

A Boolean that allows you to convert the flexible body to a rigid body. Specify either True or False.

True means treat the FlexBody as a rigid body. Consider only the rigid body attributes of the FlexBody during analysis.
False means treat the FlexBody as a flexible body during analysis.

This flag is optional. The default is False.

lset_file

String

Instructs MotionSolve to write loadsets for grid nodes that get into contact, and stores them in the specified file.

The lset_file attribute is optional.

This file can be used to enhance the CMS analysis during flexbody creation. lset_file requires h3d_file to be defined.

max_num_cnt_loadset

Integer

Defines the maximum number of loadsets to be written out if lset_file is set. The number of loadsets improves the enrichment for FlexBody, but also decreases computational efficiency. This attribute is optional. By default, MotionSolve automatically calculates an appropriate number of loadsets.

max_num_cnt_loadset > 0

Linearly flexible body with user-defined damping as a MotionSolve expression:

cratio: String containing a valid MotionSolve expression.; Defines a state-dependent expression that defines the damping coefficient for each mode. Any valid run-time MotionSolve expression can be provided as input.; cratio must evaluate to value ≥ 0

Linearly flexible body with user-defined damping in a compiled subroutine:

cratio

String containing a valid MotionSolve user-written subroutine.

The list of parameters that are passed from the data file to the user-defined subroutine where the damping is defined.

routine

String

Specifies an alternative name for the user-written subroutine. The name consists of two pieces of information, separated by "::". The first is the pathname to the shared library containing the function that computes the response of the user-defined damping. The second is the name of the function in the shared library that does the computation.

An example is: routine="/staff/Altair/engine.dll::myDamping".

"/staff/Altair/ engine.dll is the DLL.
"myDamping" is the function within this DLL that performs the calculations.

The attribute routine is optional.

When not specified, routine defaults to DMPSUB.

Linearly flexible body with user-defined damping in a Python function:

cratio

String containing a valid MotionSolve user-written subroutine.

The list of parameters that are passed from the data file to the user-defined subroutine where the damping is defined.

routine

Pointer to a callable function in Python.

For example: routine=myDamping.

myDamping is a Python function or method that can be called from wherever the model resides.

The attribute routine is optional.

When not specified, routine defaults to DMPSUB.

Example

The first example demonstrates the one possible specification of the FlexBody.

FlexBody (label="Boom", qg=[0,5,0], mtx_file="11", h3d_file="../../flex_h3d/beam.h3d",cratio=0.0)

The second example demonstrates the specification of the FlexBody, where damping is specified using an expression.

FlexBody (qg=[10,12,0], mtx_file="30102", h3d_file="../../flex_h3d/beam.h3d",cratio ="IF(FXFREQ-100:0.01,0.1,IF(FXFREQ-1000:0.1,1.,1.))")

The third example demonstrates the specification of the FlexBody, where damping is specified using a user-defined subroutine (DMPSUB).

FlexBody (qg=[10,12,0], mtx_file="30102", h3d_file="../../flex_h3d/beam.h3d",cratio="USER(0.01,100,0.1,1000,1)")

The fourth example demonstrates how to rigidify a FlexBody.

FlexBody (qg=[10,12,0], mtx_file="30102", h3d_file="../../flex_h3d/beam.h3d",rigidified=True, cratio="IF(FXFREQ-100:0.01,0.1,IF(FXFREQ-1000:0.1,1.,1.))")

Comments

See Properties for an explanation about what properties are, why they are used, and how you can extend them.
For a more detailed explanation of FlexBody, see Body: Flexible.