# Flex_Body

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

Flex_Body

## Description

The Body_Flexible 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: 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. Four major variations of the linearly flexible body are available.
• Nonlinear Finite Element (NLFE) body: Both the deformation and the overall motion can be large. This is fully nonlinear finite element representation of the flexible body.

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

## 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
vx Double (None) Yes FD Only
vy Double (None) Yes FD Only
vz Double (None) Yes FD Only
wx Double (None) Yes FD Only
wy Double (None) Yes FD Only
wz Double (None) Yes FD Only
vm Reference ("Marker")   Yes
wm Reference ("Marker")   Yes
cratio Function ()
routine Routine ()
script Script ()
rigidified Bool ()
mtx_file String () Yes
h3d_file String () Yes

## Usage

The linear Flex_Body implementation is available in four different variants.
#1. Linearly flexible body without user defined damping
Flex_Body (mtx_file=string, optional_arguments)

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

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

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

## Attributes

Linearly flexible body without user-defined damping
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.
Linearly flexible body with damping in a MotionSolve expression
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.
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.
The cratio attribute is mandatory.
cratio must evaluate to value ≥ 0
Linearly flexible body with user-defined damping in a compiled subroutine
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.
cratio
String containing a valid MotionSolve user expression.
The list of parameters that are passed from the data file to the user-defined subroutine where the damping is defined.
The cratio attribute is mandatory.
routine
String
Specifies an alternative name for the user 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
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.
cratio
String containing a valid MotionSolve user expression.
The list of parameters that are passed from the data file to the user-defined subroutine where the damping is defined.
The cratio attribute is mandatory.
routine
Pointer to a callable function in Python.
An example is: 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.
id
Integer
Specifies the element identification number. This number must be unique among all the Flex_Body objects in the model.
This attribute is optional. MotionSolve will automatically create an ID when one is not specified.
Range of values: id > 0
label
String
Specifies the name of the Flex_Body object.
This attribute is optional. When not specified, MotionSolve will create a label for you.
qg
A Location object or a list of 3 doubles.
Specifies the coordinates of local part reference Marker. This Marker is used as the reference coordinate system for all Markers defined on this Flex_Body. It also defines the location of 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, i.e. (0, 0, 0).
reuler
A list of 3 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 Flex_Body. It also defines the orientation of 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), i.e. the local part reference Marker has the same orientation as the global coordinate system.
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 Flex_Body is fully constrained and you are not interested in the constraint forces, then mass and inertia need not to be specified. When these are not specified, you must not specify CM.
Note: In order 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.
mass
Specifies the mass of the Flex_Body object.
The attribute mass is optional. If a Flex_Body is fully constrained and you are not interested in the constraint forces, then mass needs not to be specified.
When not specified, mass is set to zero.
Valid range of values: mass ≥ 0.0
ip
List of 3 doubles or a list of 6 doubles.
Specifies the mass moments of inertia matrix for the Flex_Body 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 Flex_Body is fully constrained and you are not interested in the constraint forces, then ip need not 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 Flex_Body.
When not specified vm defaults to Global coordinate system.
vx vy vz
Double
Specifies the initial translational velocity of the Flex_Body along the x-, y- and z-axes of the VM marker.
The vx, vy, vz attributes are optional.
• When not specified, MotionSolve will perform an internal computation to ensure that all Part velocities are consistent with the first time derivative of the constraints.
• When specified, MotionSolve will try 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.
wm
Reference to a Marker.
Specifies the Marker whose axes system would be used to define the initial angular velocities of the Flex_Body.
When not specified it defaults to Flex_Body CM coordinate system.
wx wy wz
Double
Specifies the initial angular velocity of the Flex_Body about the x-, y- and z-axes of the WM marker.
The wx, wy, wz attributes are optional.
• When not specified, MotionSolve will perform an internal computation to ensure that all Part velocities are consistent with the first time derivative of the constraints.
• When specified, MotionSolve will try 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.
h3d_file
String
Specifies the name of the H3D file that contains all the 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 Flex_Body as a rigid body. Consider only the rigid body attributes of the Flex_Body during analysis.
• False means treat the Flex_Body as a flexible body during analysis.
This flag is optional. The default is False.

## Example

The first example below demonstrates the one possible specification of the FLEX_BODY.
Flex_Body (label="Boom", qg=[0,5,0], mtx_file="11", h3d_file="../../flex_h3d/beam.h3d",cratio=0.0)
The second example below demonstrates the specification of the FLEX_BODY where damping is specified using expression.
Flex_Body (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 below demonstrates the specification of the FLEX_BODY where damping is specified using user defined subroutine (DMPSUB).
Flex_Body (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 below demonstrates how to rigidify a FLEX_BODY.
Flex_Body (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.))")