Slender tube element. The STUB element differs from the TUBE element in the following respects:
STUB elements permit tubes of non-circular cross-section to be modeled, by allowing the tube properties (diameter, drag coefficient, and added mass coefficient) to be specified in two directions at right angles.
Longer lengths of tube can be input, as the program automatically subdivides STUB elements into sections of shorter length for integration purposes.
STUB elements should only be employed if the mean diameter is small compared to the length.
The local axis of the element runs from Node 1 to Node 2 (origin at Node 1). The perpendicular from Node 3 to the local X-axis, together with the local X-axis itself, defines the XZ-plane, and hence the Z-axis. The local Y-axis forms a right-handed set.
If any Z parameter for a STUB is omitted or set to zero it will default to the equivalent Y value.
If the STUB area is omitted or set to zero, the program will assume a circular cross-section if diameter Y and diameter Z are equal. If they are unequal, the cross-section is assumed to be rectangular and area will be set to the rectangular cross-sectional area. The area for the STUB element is used to calculate the displaced mass per unit length and buoyancy force. It is also used to calculate the Froude-Krylov force and default added mass. The area for the STUB element is used in the calculation of defaults for drag and added mass coefficients. Although the program will accept any value for area, warnings are issued if the value is greater than 1.05 * rectangular area or less than 0.95 * circular area.