Data: Mesh details

The mesh details page gives a spreadsheet summary, visible before running a calculation, of the calculation mesh that OrcaWave will use to solve the integral equations for your model. This report gives you details on how OrcaWave has loaded and manipulated the panels supplied in your mesh files. It may be useful for diagnosing errors or warnings raised during validation.

Panels

The panels sheet gives geometrical information for every panel in the calculation mesh – i.e. the location of its vertices, and some derived quantities. In the simplest possible case, panel vertices are an exact copy of coordinate data in the mesh file. However, there are many situations in which a panel can differ from the coordinate data in the mesh file. For example:

If one (or two) symmetry planes are present in the mesh file, some panels originate from reflected mesh file data.
All panels in the OrcaWave calculation mesh are planar. If your mesh file contains non-planar quadrilateral vertices, OrcaWave will either project them onto a common plane or divide the panel.
The position and orientation of a body, if non-zero, imply translation and rotation of panels.
Any body panels above the free surface are automatically removed by OrcaWave.
Any body panels that straddle the free surface are clipped by OrcaWave to remove the portion above the free surface. This process may introduce additional triangular panels: clipping a quadrilateral that has one vertex in $Z > 0$ would naturally produce a pentagonal panel, but OrcaWave only supports triangular and quadrilateral panels, so the pentagon is divided into two panels: one quadrilateral and one triangle.

Note:

You can see the dry body panels in the mesh view. They are not used in the calculation and do not appear in the mesh details.

The panel index column gives the unique index of each panel in the calculation mesh. You can view the same data by selecting panel indices in the mesh view. These panel indices are also used to identify specific panels in some validation messages, and to highlight panels in the mesh view.

The panel type column indicates whether a panel has been interpreted as part of a body surface $\SB$, or an interior free surface $\SI$ (for removing irregular frequency effects), or is part of a damping lid.

Tip:	You can also visually check panel types in the mesh view by setting distinctive colours for each type in the drawing data.

The bounding waterline index column indicates, for interior free surface panels, which waterline (if any) OrcaWave has detected that the panel belongs to. This data is important for removing irregular frequency effects in the source formulation.

The mesh file panel index column identifies the source data (in a mesh file) from which the panel is derived. Specifically, these are one-based indices into the panels that are imported from each mesh file. You can view the same data by selecting mesh file panel indices in the mesh view.

The aspect ratio column gives a metric for how long and slender a panel is. Several alternative definitions are possible. The definition used here is the square of the longest side divided by the panel area. Aspect ratio is not used by OrcaWave during the calculation - it is only used for the validation of mesh panels.

The projection length column gives a metric for how non-planar the vertices in the mesh file are. OrcaWave projects the vertices in the mesh file onto a common plane to create a planar panel. The value reported is the maximum distance by which a vertex is moved during this process.

Notes:	The projection length for all triangular panels is zero since any three vertices are co-planar.
	In all subsequent calculations OrcaWave uses the planar panel created by the projection process. Therefore a large projection length implies that the geometry in the mesh file is poorly represented in the calculation, and you should consider re-meshing the body or selecting the divide non-planar panels option.

Dipole panels

If relevant, a dipole panels sheet gives details of every dipole panel in the mesh. The same geometrical information is given as on the panels sheet.

Waterlines

The waterlines sheet gives details of every waterline OrcaWave has detected. This can be particularly useful for understanding and correcting validation messages related to body waterlines.

Tips:	Using the mesh view to highlight detected waterlines is often the easiest first step to take.
	If your mesh file contains non-planar panels, using the divide non-planar panels option may improve the detection of waterlines.

Using a combination of the mesh view and the waterline information in the mesh details, you can determine whether the correct number of waterlines have been detected and whether any waterline segments are missing.

If a segment is missing because a panel edge that should be part of a waterline has not been detected as such by OrcaWave, then you can try increasing the waterline Z calculation tolerance. However beware that using too large a value may cause other panel edges to be mistakenly classified as part of a waterline.
If the waterline segments are complete and the waterline is still reported as not closed, then you can try increasing the waterline gap calculation tolerance.

Tip:	If you need to increase either the waterline Z or the waterline gap calculation tolerance, the measuring tape tool can be useful for determining a value that is appropriate for your mesh.

Hydrostatics

The hydrostatic properties of each body are determined by a combination of mesh data and inertia data. The hydrostatics sheet gives the value of all such properties.

The same information is also given, after a calculation, in the hydrostatics results.

Control surface

If relevant, a control surface sheet gives details of every control surface panel. The same geometrical information is given as on the panels sheet.

Free surface panelled zone

If relevant, a free surface panelled zone sheet gives details of every panel in the free surface panelled zone of a full QTF calculation. The same geometrical information is given as on the panels sheet.