Model Element

Class Name

Nforce

Description

Nforce defines a force and torque acting between many markers.  The force and the torque can only be linear functions of the relative displacement and velocity of the various markers.

Attribute Summary

Usage

Nforce (j=objMarker, imarkers=list, kmatrix=objMatrix, optional_attributes)

Attribute Description

j

Reference to an existing Marker object

Specifies the Marker that is the reference coordinate system for Nforce. All inputs such as stiffness and damping matrices and forces are measured in j. Relative displacements, velocities and force vectors are computed in this coordinate system.

The j attribute is mandatory.

imarkers

List of existing Marker objects

Specifies the list of IMARKERS between which the NFORCE is applied.

The imarkers attribute is mandatory.

kmatrix

Reference to an existing Matrix object

Specifies the MATRIX element which contains the stiffness matrix.  This is an 6N*6N matrix, where N is the number of I markers.

The kmatrix attribute is mandatory.

kmatrix should be positive semi-definite. This means for any deformation Δ, the matrix product ΔT[kmatrix]Δ ≥ 0.

id

Integer

Specifies the element identification number.  This number must be unique among all the Nforce 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 Nforce object.

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

cratio

Double

Defines a damping scale factor.  If this is specified, the damping matrix is calculated as C = cratio * K.

The cratio attribute is optional.

cratio ≥ 0

The default value for Cratio = 0

Note: cratio and cmatrix are mutually exclusive. You may specify neither or only one of these.

cmatrix

Reference to an existing Matrix object

Specifies the MATRIX element that contains the damping matrix. This is a 6N*6N matrix, where N is the number of I markers.

The cmatrix attribute is optional.

Default is a zero matrix.

When specified, cmatrix should be positive semi-definite. This means for any deformation velocity v, the matrix product vT[cmatrix]v ≥ 0.

Note: cratio and cmatrix are mutually exclusive. You may specify neither or only one of these.

force

Reference to an existing Matrix object

Specifies the 6N*1 MATRIX element which contains the preload values for each pair of markers between which the NFORCE is applied. N is the number of IMARKERS.

The force attribute is optional.

Default is a zero matrix.

length

Reference to an existing Matrix object

Specifies the 3N*1 MATRIX element which contains the length values for each pair of markers between which the NFORCE is applied. N is the number of IMARKERS.

The force attribute is optional.

When omitted, the imarkers are taken to be at their reference locations. This means that at the input configuration, all deformations are computed as zero.

active

Bool

Select one from True or False.

The attribute active is optional. When not specified, active defaults to True

Comments

See Force_MultiPoint

Example

The example below shows how the NFORCE element may be defined.

# Define the necessary markers

m10  = Marker (body=p10, qp=[1.4,3.1,1.61], zp=[1.5,3.1,1.61])

m101 = Marker (body=p11, qp=[-4.4, 9.3, 5.31])

m102 = Marker (body=p12, qp=[8.14, 2.01, 1.11])

m103 = Marker (body=p13, qp=[0.0, 4.56,2.02])

# Define the Nforce

nfo1 = Nforce (label="Truss", j=m10, imarkers=[m101,m102,m103], kmatrix=mat11, cratio=0.01)