Deformable Bodies

The Modes dialog lists the modes information in the flexible body and allows you to select/deselect the modes to include during the solution. It can also be used to set modal damping.

The Modes dialog is available in the MotionSolve or Adams solver mode.

modes_flexbody

Deformable Body - Modes dialog (MotionSolve)

modes_dialog_example_adams_mv

Deformable Body - Modes dialog (Adams)

Use

Check on or off to select/deselect a mode. The first 6 modes with near zero frequencies are deselected by default, as they are rigid body modes of the flexbody and are not required (since MotionSolve or Adams will already compute this via the local part reference frame).

Index

The index number of the mode information contained in the flexbody .h3d file.

Frequency

The frequency value of the mode in 1/time_unit; where time_unit refers to the unit of time of the model.

Damping Type

The method of damping ratio specification.

Default Damping

Sets the default damping ratio which is:

•	0.01 for frequency<100 Hz

•	0.1 for 100<frequency<1000 Hz

•	1.0 for frequency>1000 Hz

CRatio Damping

Set a real value as the damping ratio. See Comment 2 below.

CRatio Expression Damping

Set the damping ratio as a solver expression. See Comment 3 below.

User Function Damping

Set the damping ratio based on a user subroutine. See Comment 4 below.

Damping Ratio

The damping ratio (fraction of critical damping) associated with the mode. The values in this column depend on Damping Type selected.

Geometric Stiffness

MotionSolve Only - Use this option to activate/deactivate the geometric stiffness block. See Comment 5 below.

DMODE

ADAMS Only - Specify the displacement initial condition of the modal generalized coordinates for a particular mode.

VMODE

ADAMS Only - Specify the time rate of change of change of the modal generalized coordinates.

MEXACT

ADAMS Only - Set this option if the modal coordinates should not be changed during the initial condition analysis.

All Geostiff Modes

MotionSolve Only - Activate geometric stiffness data for all modes.

No Geostiff Modes

MotionSolve Only - Deactivate geometric stiffness data for all modes.

Comments

Eliminating modes might help gain performance, however it can potentially cause a loss in accuracy of the solution. Therefore, it is not advisable to deselect a mode from the flexible body. Please see the MotionSolve or Adams manual for more information on these solvers with regards to mode selection. It is recommended that you review the mode shapes by loading the flexbody .h3d into HyperView, in order to help identify any problems with the modes that resulted from an error in the finite element model and to better understand the deformation of each mode shape.

2.	When using CRatio Damping, MotionView can only specify a single damping value for all modes, this means that different damping cannot be specified for individual modes. To specify different damping values by mode, see the other damping options.

3.	The solver attribute FXFREQ can be used with the CRatio Expression Damping type to define the damping ratio, which is a function of frequency. For example, STEP(FXFREQ,0,0.01,100,0.2).

When using the User Function Damping type, a USER expression must be provided that passes parameters to the subroutine. The graphical user interface currently does not have a provision to define the library (dll/so) and function name. A workaround for this is to provide the library name in the solver execution command line.

Geometric stiffening data is available in the flexible H3d for each mode. If geometric stiffening is being used in a solution, deactivating data for certain modes that have negligible contribution to geometric stiffening may speed up the solution. By default all geostiff data is selected and is recommended, therefore deactivating any data should be done with caution.

Deformable Bodies - Modes

Deformable Bodies - Modes

Deformable Bodies - Modes

Comments