Angle between an Element and a Vector |
 
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Angle between an Element and a Vector |
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The second type of Angles output is the angle between an element you identify and a vector that you also define. In order to define a vector, you associate a name or label with the vector, input the vector components in the global axes, and identify the node at which the vector is located. This node can be either a node of the structure finite element discretisation or a so-called auxiliary node. The significance of this last input is as follows. The vector components you input give the vector orientation at the undisplaced or initial position of the node. As the node displaces subsequently (either statically or dynamically), the rotations at the node are also applied to the vector so that the vector orientation changes with the motion of the node. In this way you can find the angle between an element and, say, a vector at an auxiliary node which is located on a floating vessel, and which is translating and rotating with that vessel. This allows you, for example, to find the true angle between the last element on a riser coming into a vessel connection and the static hang-off angle of that riser. The output in this case is again the true or actual angle between the element and the vector, in the plane formed by both of these. Mathematically, the angle is again the arc-cosine of the dot product of (i) a unit vector directed from first-specified to second-specified node of the element, and (ii) a unit vector in the instantaneous direction of the vector you specified. Again, this angle will be in the range 0° to 180°.
•*TIMETRACE is used to request the creation of timetrace plots. Specifically, TYPE=ELEMENT_VECTOR_ANGLE is used to request a timetrace of the angle between an element and a vector.
•*PARA ANGLE AXIS is used to request summary output of the angle between an element and either a vector or an axis system.