The Structure Selection tree object enables the definition of interacting structures, in addition to any structures that you want to exclude for this particular analysis. It also enables the structure order to be changed.

Structures can be selected graphically (use the Ctrl key to select more than one) for inclusion in a group or to be excluded from the analysis. To include structures in a group, click on an Interacting Structure Groups field. To exclude structures from the analysis, click on the Structures to Exclude field. Select the structures in the model, then click the Apply button. The selected structures will be listed in the field. If a structure is excluded, then it will automatically be removed from any groups and the structure order. A structure may only be included in one interacting structure group.

By default, when Aqwa is first started all parts are considered to be hydrodynamically interacting and are included in the analysis. Note, however, that if a part is made up entirely of non-diffracting elements (for example, completely above the water surface or consisting of Morison elements only), then the part is not considered as interacting and is excluded from the list of Interacting Structure Groups. If a part is subsequently suppressed, it cannot be used in the analysis, and is automatically excluded in the Structure Selection.

Once you have defined your groups of interacting structures, you can optionally lock the motions of the structures by applying a Motion Lock to the relevant group. The RAOs calculated for the structures in the locked interacting group are then consistent with the RAOs of an equivalent single structure. This is particularly useful for the estimation of splitting forces and moments on a structure in a time domain Hydrodynamic Response calculation. This is achieved in the time domain analysis by including a joint between each of the bodies in the interacting group to output such forces/moments.

If a structure has been removed from the analysis and you want to add it back in, you must reselect the set of Structures to Exclude. If you want all structures to be included in the analysis, you may click on the field next to Structures to Exclude then click Apply with no structures selected.

The Aqwa solver requires that a group of interacting structures be consecutively ordered for the analysis. Modifying the interacting groups will automatically update the order of structures in the Aqwa analysis, and this will be reflected in the Structure Ordering section of the Details panel.