Bracket

This section presents one way to model brackets in AquaSim. Other solutions may be applied but is not covered by this tutorial.

The floater pipes, brackets and railing are components that will be exposed to axial forces, shear forces and bending moments. Therefore, they are modelled as component type Beams. Beams are in AquaSim based on drawing elements connected with two nodes: node A and node B. Each element in AquaSim has its own local coordinate system, this is illustrated in the figure below. The local x-axis runs from node A to B, and y- and z-direction is perpendicular to this. You should have this in mind to later in this tutorial.

The stiffness of beam element is given by the element length and cross-sectional properties. So, since the stiffness is not solely given by the modelled geometry, one will need to make use of excentre elements to bind together the different structural components of the bracket. The chosen solution is presented in the figure below.

Accounting motion of bracket

The brackets should be able to slide, or be restrained, with respect to the floater pipes. How much the bracket should move is dependent on friction between the floater pipe and the bracket. To account for this, the motions must be determined with respect to local coordinate system of the element. This can be resolved in several ways, for example:

• with the use of the element decorator Roller,
• or with the use of the element decorator Hinge. This tutorial demonstrates the use of Hinge. This enables the user to define which local degrees of freedom to be free or restrained. In addition, you can add friction with the use of damping. Hinges are available for beam elements and is found by right click on an element > Elements > Hinge.

AquaEdit

Load Moving-Bracket.amodel that comes with this tutorial in AquaEdit.

The model shows a conventional floating collar in PE modelled in a frame mooring configuration. This model is finished with Hinge on the brackets.   In the figure below you can see a section of how the floater pipes and brackets are modelled, and where the hinges are placed.

Recall the stoppers, preventing the bracket from moving, is situated on the same side as the railing. Have this in mind when we in the next section should investigate the properties of the hinges.