A part is a group of geometric entities that form a ship or other structure that is to be analyzed in Aqwa. The name is read in from the geometry database and the graphical view will show the part; the appropriate structure will be highlighted when the part in the tree is selected. Each part will be assigned a structure number for the analysis. The parts can be included or excluded from the analysis using the Structure Selection.

For each imported part, a set of local structure axes is created. These axes are drawn at the part's center of gravity.

A number of options can be set for each part in the Details panel.

To help visualization, it is possible to show or hide specific parts using the Part Visibility option, while the Part Color option can be used to define the color of the surface bodies which make up each part. The Part Activity option is used to decide what structures are used in the analysis.

The Mass Properties section displays the Total Mass, the Center of Gravity X, Y, and Z, and the Moment of Inertia Ixx, Ixy, Ixz, Iyy, Iyz, and Izz for the Part. If the Part includes Internal Tanks, the Total Structural Mass and Total Internal Tank Mass will also be displayed; the Center of Gravity shown in the Details panel will be the combined center of gravity including the internal tank fluid. If the Part includes at least one Program Controlled Point Mass and the Mesh is not up-to-date, the Total Mass field will display Generate Mesh to Update and all other Mass Properties will be hidden.

If an internal lid is required to prevent irregular frequency problems then Generate Internal Lid can be set to Yes and it will be automatically generated during the Aqwa analysis. Note that an automatically generated lid will not be displayed. When Lid Element Size Definition is set to Program Controlled, the size of the internal lid elements will be set to the mean mesh size of the corresponding structure. Alternatively, the Lid Element Size can be defined manually by setting Lid Element Size Definition to Manual Definition.

A manually generated lid may also be used: create an appropriate plane surface as a Surface Body; set Structure Type to Abstract Geometry and Abstract Type to Internal Lid. If you have a structure with a Moonpool where large resonant waves may occur, then you can form an external lid using a predefined geometry Surface Body with Structure Type set to Abstract Geometry and Abstract Type to External Lid.

Hull drag loads may either be accounted for by defining a 6 x 6 matrix of Morison Hull Drag Coefficients, or by including a table of Current Force Coefficients. Where Morison Hull Drag Coefficients are used, the current velocity is always measured at the structure center of gravity. Where Current Force Coefficients are used, a Current Calculation Position should be defined, at which the current velocity is measured for the hull drag loading calculation. When the Current Calculation Position is set to At Fixed Depth, a constant Current Calculation Depth can be set. Alternatively, when the Current Calculation Position is set to Moves with Structure, the Current Calculation Position Definition can be switched between Vertex Selection and Manual Definition. If the position definition is set to Vertex Selection, you should select a Current Calculation Vertex from the geometry and (optionally) define a Vertex X, Y, and Z Offset. The Vertex X, Y, and Z Position will be read-only. If the position definition is set to Manual Definition, you should enter the Current Calculation X, Y, and Z Position directly.

By default the structure is set to be free to move. Alternatively, the whole structure can be fixed by setting Structure Fixity to Structure is Fixed in Place. Fixity primarily affects the results of a hydrodynamic diffraction analysis by affecting the structure's RAOs. It therefore also has an effect on a hydrodynamic time response result as the calculated drift forces depend on these RAOs. It is therefore necessary to impose the coherence between the setup of the two analyses by fixing the structure in the time response analysis. Since you can create joints to be used in a time response analysis, it is your responsibility to create a rigid joint when it is connected to a fixed point on any Part marked as Fixed in the Details dialog. Not doing so will result in an error when solving the time response analysis.

The Mass Multiplying Factor and Drag Multiplying Factor provide a way of modifying the added mass and drag coefficients defined for any Line Bodies (via their associated Beam Section objects) and Discs associated with this part. The Added Mass and Transverse Drag are multiplied by these factors after they have been calculated by Aqwa (the total coefficient applied for each quantity is the cumulative product of the factor specified by these settings with the factor specified for each Line Body or Disc). These factors may be used for parametric studies where the effects of Morison drag on Line Bodies and Discs are considered important (for example, simulating tests at model scale). These factors have no effect on any other object type in the part.

The Slam Multiplying Factor provides a way to enable the computation of slamming loads on Line Bodies. By default a factor of zero is specified which disables this computation. Any positive non-zero value will cause the program to compute the slam coefficient for each Line Body, based on the premise that the slam force is equal to the rate of change of the added mass tensor (with time) multiplied by the velocity. The resulting coefficient is then multiplied by this factor. This may be used for parametric studies where the effects of slamming loads on Line Bodies are considered important (for example, simulating tests at model scale).

Slamming loads can also be included for slender tube elements by setting the Slam Factor to a positive non-zero value, but the magnitude of the factor is immaterial in this case because a value of unity is always employed in the analysis.

In analyses containing a single structure only, you may calculate the (static or RAO-based) shear forces and bending moments acting on that structure under different wave load conditions. Such calculations require the Neutral Axis of the structure to be defined, which can be any one of the Fixed Reference Axes (FRA) as well as the position of this axis in the perpendicular plane. By default, the Neutral Axis is assumed to pass through the center of gravity (COG) of the structure. Changing Neutral Axis Position Definition from Through COG to Manual Definition allows you to define the position manually. For example, if Neutral Axis is set to Global X, you should also specify the positions Neutral Axis Y and Neutral Axis Z.

Submerged Structure Detection is Program Controlled by default, and Aqwa will detect the highest point (greatest Z coordinate) and check whether it is below the water level; alternatively this automatic detection can be overridden.

The Metacentric Heights can be overridden about both the global X (Override Calculated GMX = Yes) or Y (Override Calculated GMY = Yes) axes to modify the hydrostatic stiffness of the vessel. When these are overridden, Aqwa first calculates the hydrostatic stiffness matrix based only on the cut water plane and displaced volume properties. It then adjusts the second moments of area IXX, IYY and recalculates its associated properties, PHI (principal axis), GMX/GMY, BMX/BMY etc. to give the required GM values. The associated additional hydrostatic stiffness is calculated automatically and stored in the hydrodynamic database. If the GM value input is less than that based on the geometry alone, the resulting additional stiffness will be negative. This would be the case if ballast tanks were being modeled, making the structure less stable, statically.

You can remove any of these objects by right-clicking them in the tree and selecting Delete from the context menu.