Model Element

Description

The Constraint_PTdCV element constrains a fixed point on a body to slide along a curve that passes through the origins of a specified set of markers.  These markers may belong to different bodies.  As the markers move in space, the curve is calculated at every time step using CUBIC spline interpolation through the marker origins.  Hence, the curve deforms as the markers move about.

This constraint is useful for simulating connection between a point on a body and a slender, flexible element such as a cable.  For example, a ski chair-lift.

Format

<Constraint_PTdCV

    id                  = "integer"

  [ label               = "string" ]

    i_marker_id         = "integer"

    ref_dcurve_id       = "integer"

/>

Attributes

id

Element identification number, (integer>0).  This number is unique among all Constraint_PTdCV elements.

label

The name of the Constraint_PTdCV element.

i_marker_id

Specifies a Reference_Marker whose origin defines the point that is constrained to move along the deformable curve.

ref_dcurve_id

Specifies the deformable curve used to define the Constraint_PTdCV element.

Comments

If the current u value goes out of this range, MotionSolve will hold the u value at the boundary until the point falls back in range of the deformable curve.  However, this may lead to incorrect results.  You are encouraged to check the results for correctness in such a situation.  For more information, please refer to the Reference_DeformCurve model element.

Example

The following example demonstrates the use of the Constraint_PTdCV element, along with the Reference_DeformCurve and Post_Graphic elements.

Application of the Constraint_PTdCV element

The figure above shows five slender, bar-shaped rigid bodies constrained to a ground body, represented by the blue horizontal bar graphic, by translational joints with axes along the Z direction.  The bodies are connected to ground by linear spring-dampers.

A deformable curve is defined to pass through seven markers shown in the figure.  Five of these markers are located at the lower tips of the rigid bodies.  Two of these markers are located at either end of the ground body.  The deformable curve is defined using the Reference_DeformCurve element as follows:

<Reference_DeformCurve

    id                  = "1"

    end_type_left       = "NATURAL"

    end_type_right      = "NATURAL"    

    num_marker_id       = "7">

30101120 30102061 30103071 30104081 30105091 30106101 30101130

</Reference_DeformCurve>

<Post_Graphic

    id                  = "500000"

    type                = "DeformCurve"

    curve_id            = "1"

    nseg                = "100"

 />

A small spherical body, shown with a yellow sphere, is constrained to slide along the deformable curve as follows:

  <Constraint_PTdCV

      id                  = "1"

      i_marker_id         = "30107060"

      ref_dcurve_id       = "1"

  />

Transient simulation of this system shows the changing shape of the deformable curve, as the sphere slides back and forth under gravity.

Model Element

Description

PTDCV defines a constraint of a point to a deformed curve.  This is an instance of a higher pair constraint.

Declaration

def PTDCV(id, LABEL=””, I= , DCURVE= ):

Attributes

id

Element identification number (integer>0).  This number is unique among all PTDCV elements.

LABEL

The name of the PTDCV element.

I

Defines the marker ID of the point.

DCURVE

Defines the ID of the deformed curve.

Comments

See Constraint_PTDCV

Example

The example below shows a definition of a PTDCV.

PTDCV(1, I=30107060, DCURVE=1)