Defining Nodes in Terms of Cables |
 
|
Defining Nodes in Terms of Cables |
|
Two methods were noted earlier for defining nodal locations in terms of cables, denoted (iii) directly in terms of distance along a cable, and (iv) generated along a cable. It is in fact these facilities which are the purpose of using cables in the first place.
The first of these facilities is largely self-explanatory, and requires three data inputs, namely the node number, the number of the cable on which it is located, and the required distance along the cable, which is measured from the specified cable start node.
The generation option permits nodes to be uniformly distributed between two nodes on a particular cable. The user inputs in this case are the cable number, the first node number, the last node number, and the increment for assigning node numbers to the generated nodes (which defaults to a value of 1). The first and last nodes are not necessarily the cable start and end nodes, but if they are not, their location must be defined directly using the method just discussed.
The operation of both of these facilities, and indeed of the whole cable pre-static step, is illustrated below. Here a steep wave riser is defined in terms of 3 cables, a lower catenary from Nodes 1 to 15, a section with buoyancy modules attached extending from Nodes 15 to 34, and an upper catenary from Nodes 34 to 71. The coordinates of four cable end nodes (1, 15, 34 and 71) are required inputs for this riser. Of these, two are exact locations (Nodes 1 and 71), since boundary conditions will be applied here. On the other hand, the exact locations of Nodes 15 and 34 are a function of the unknown static structure configuration, and so can be specified only as approximate locations which satisfy the conditions discussed in the previous section.
Defining Nodes In Terms Of Cables