AX
The AX function returns the rotational displacement (in radians) of marker i about the x-axis of marker j, and accounts for angle wrapping.
Marker j defaults to the global coordinate system if it is not specified. This value is computed as follows: assume that rotations about the other two axes (y- and z-axes) of marker j are zero. Then, AX is the angle between the two y-axes (or the two z-axes). AX is measured in a counter-clockwise sense from the y-axis of marker J to the y-axis of marker I (see the figure below).
Measurement of AX
Format
AX(i[,j])
Arguments
i | The marker whose rotations are being sought. |
j | The marker whose coordinate system is used as a reference to calculate the rotations of marker i. When j is not specified, Adams Solver (C++) defaults to the global coordinate system. |
Extended Definition
Mathematically, AX is calculated as:
where:
■
is the z-axis of marker i
is the z-axis of marker i■
is the y-azis of marker j
is the y-azis of marker j■
is the z-axis of marker j
is the z-axis of marker jTip: | If you want to change the AX function so it does not account for angle wrapping, use the MOD function. For example, use the function: (MOD(AX(2,1) + PI, 2 * PI) - PI The MOD function achieves the cyclic effect and the +PI and -PI shift the curve accordingly. |
Caution: | For large rotations (greater than 10 degrees) about the y-axis or z-axis on Marker j, the AX function becomes increasingly non-physical. Moreover, AX is undefined when both arguments to ATAN2 are zero. This occurs when the z-axis of marker i is orthogonal to the plane defined by the y and z-axis of the j marker. |
Examples
GFORCE/1, I=21, JFLOAT=31, RM=41
, FX=-20*AX(43,32)
, FX=-20*AX(43,32)
This GFORCE statement applies a force at the origin of Marker 21 along the x-axis of Marker 41. The reaction force is on floating Marker 31. The floating Marker 31 can belong to another part but its location is always the same as Marker 21.
The value of the force is -20 times the angle between the y axes of Markers 43 and 32. The angle is measured in a counterclockwise sense from the y-axis of Marker 32 to the y-axis of Marker 43.
The value of the force is -20 times the angle between the y axes of Markers 43 and 32. The angle is measured in a counterclockwise sense from the y-axis of Marker 32 to the y-axis of Marker 43.
See other Displacement measures available.