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VR

The VR function calculates the radial (separation) velocity of marker i with respect to marker j. The vector time derivative is taken in the reference frame of marker l. Markers j and l default to the global coordinate system if they are not specified.

Format

VR(i[,j][,l])

Arguments

 

i	The marker whose velocity is being measured.
j	The marker with respect to which the velociy is being measured. Set j = 0, while still specifying l, if you want j default to the global coordinate system.
l	The reference frame in which the time derivative of the displacement vector is taken. Set l = 0 or omit the argument if you want the time derivatives to be taken in the ground coordinate system (GCS).

Extended Definition

Mathematically, VR is calculated by projecting the velocity vector on a unit vector along the line of sight between i and j, as follows:

where:  

•	is the displacement of marker i with respect to the global origin.

•	is the displacement of marker j with respect to the global origin.

•	DM (i,j) is the distance between markers i and j.

As markers i and j separate from each other, VR is positive. VR is negative when markers i and j approach each other.

Examples

SFORCE/1, TRANSLATION, I=467, J=764
, FUNCTION=-10*VR(467,764)

This SFORCE statement defines a translational damper with a damping constant of 10.