Force: Multi-Point

Model ElementForce_MultiPoint defines a force and torque acting between many Reference_Markers.

Description

The force and the torque can only be linear functions of the relative displacement and velocity of the various Reference_Markers.

Format

< Force_MultiPoint
     id                = "integer"
     ref_marker_id     = "integer"
     kmtx_id           = "integer"  
  [{ cmtx_id           = "integer"
|    cratio            = "real"  
  }]
   [ preload_mtx_id    = "integer" ]   
   [ length_mtx_id     = "integer" ]     
     n_i_marker        = "integer"  >
 integer1   integer1   … integerN   
</Force_MultiPoint >

Attributes

id: Element identification number (integer>0). This number is unique among all Force_MultiPoint elements and uniquely identifies the element.
ref_marker_id: Specifies the Reference_Marker which serves as the reference frame in which relative velocities are computed. The components of the relative displacement, relative velocity and force vectors are resolved in the coordinate system specified by ref_marker_id.
kmtx_id: Specifies the Reference_Matrix element which contains the stiffness matrix. This is a 6N*6N matrix, where N is the number of I Reference_Markers.; This is a required parameter.
cmtx_id: Specifies the Reference_Matrix element which contains the damping matrix. This is a 6N*6N matrix, where N is the number of I Reference_Markers.; This parameter is optional. Default is a zero matrix.
cratio: Defines a damping scale factor. If this is specified, the damping matrix is calculated as C = cratio * K.; This parameter is optional. Default is zero.
preload_mtx_id: Specifies the 6N*1 Reference_Matrix element which contains the preload values for each pair of markers between which the Force_MultiPoint is applied. N is the number of I Reference_Markers.; This parameter is optional. Default is a zero matrix.
length_mtx_id: Specifies the 3N*1 Reference_Matrix element which contains the reference length values for each pair of markers between which the Force_MultiPoint is applied. N is the number of I Reference_Markers.; This parameter is optional. When omitted, the I Reference_Markers are taken to be at their reference locations.
n_i_marker: Specifies the number of I Reference_Marker elements between which the Force_MultiPoint is applied. If there are N such markers, then N integers specifying their IDs must follow.

Example

The following is an implementation of a Force_MultiPoint element between three markers with ids 101 through 103. The reference marker has an id of 10. The stiffness matrix is specified using the Reference_Matrix with id 11. The damping ratio is specified as 0.05. The preload and length matrices are not specified.

<Force_MultiPoint
     id                  = "1"
     ref_marker_id       = "10"
     kmtx_id             = "11"
     cratio              = "0.05"
     n_i_marker          = "3">
     101 102 103
</Force_MultiPoint>

Comments

The Force_MultiPoint element is used to implement a linear force acting between N Reference_Markers, similar to finite element models.
MotionSolve computes the reaction forces and torques acting on the Reference_Marker specified using ref_marker_id.
The NFORCE function may be used to output the forces and torques generated by the Force_MultiPoint element. The components of these vectors are resolved in the coordinate system specified by ref_marker_id.