Structure - Attachments
The yoke provides a rigid connection between the main structure body and any attached line or cable. You have the option to specify the properties of a yoke in the Yoke dialog. Your structure does not have to include a yoke.
The yoke is connected to the structure at the distance along the structure length that is specified in the Pivot Axial Offset input. It can also be placed above the structure centreline using the Pivot Vertical Offset input (follows same convention as the structure COG Vertical Offset input). In such scenarios a rigid mass less beam element maintains a connection between the yoke and the structure centreline. The free rotation angle is defined in terms of positive and negative rotations about an axis perpendicular to the structure, accommodating non-symmetrical free rotational boundaries. While the angle between the yoke and the structure is within the specified free rotation angle, the common end behaves as a one-dimensional hinge. Outside this range, the rotation of the yoke is restricted by a high rotational resistance.
The yoke itself is modelled using a rigid beam element, with the specified Weight in Air and Weight in Water used to compute total mass and buoyancy. This mass and buoyancy can be uniformly distributed along the yoke by leaving the COG Axial Offset blank otherwise they are applied as point loads in a similar fashion to the structure when its COG offsets are specified. The yoke COG Axial Offset measures the distance along the yoke centreline from its start point to the point where the COG element connects to the yoke. The yoke COG Vertical Offset represents the in-plane displacement of the COG node with respect to the yoke centreline. Given that the yoke and its attachments are generally orientated vertically the sign convention for the yoke COG Vertical Offset is different to that of the structure. If the line or cable attached to the yoke has a start point with a smaller global X coordinate than the end point then a positive yoke COG Vertical Offset will place the COG node on the left of the yoke centreline (as measured in elevation view). The opposite is true if the line or cable start point has a larger X coordinate. The yoke COG Lateral Offset corresponds to the horizontal distance between the yoke centreline and the COG node as measured in side view (out-of-plane displacement). This offset input follows the same convention as the corresponding structure input.
It is also possible to offset any attached line or cable from the yoke centreline using the Connection Vertical Offset and Connection Lateral Offset inputs. Theses offsets and the associated rigid connection element are similar to that of the yoke COG.
Note that the various conventions for the different offset inputs can lead to confusion and so it is recommended that all offset inputs, whether they are for the structure or the yoke, are visually checked for correctness using the Cable Solution animation on the Results tab of the Analysis component. Sample screenshots of a representative Cable Solution animation are provided in the two figures below.
These figures show an elevation view of a typical 1st End PLET model where the mud mat is positioned directly above the seabed prior to lay down. The first figure depicts the various components of the model, whereas the second focuses purely on the Structure component and outlines the various offset inputs that were required to create it. Please note that all offset inputs in this model, except for the vertical offsets from pipe, represent positive values.
Sample Animation of 1st End PLET Model
Offset Inputs for Sample 1st End PLET Model