Data: Mesh file formats

OrcaWave can load panel mesh data from files of the following formats:

WAMIT .gdf

OrcaWave supports low-order .gdf files. The full specification for the format can be found in the WAMIT user manual.

Quadrilateral panel vertex coordinates are listed in order (a triangular panel is represented by a repeated vertex), with the ordering of the vertices implying the orientation of the panel normal. WAMIT and OrcaWave share the same convention for the orientation of normal vectors on body surfaces and control surfaces:

• Panels on a body surface $\SB$ must have vertices ordered in an anticlockwise sense when viewed from outside the body, or equivalently in a clockwise sense when viewed from inside the body.
• Panels on a control surface must have vertices ordered in an anticlockwise sense when viewed from outside the control volume, or equivalently in a clockwise sense when viewed from inside.

Vertices may be ordered in either sense in OrcaWave for the following types of panels:

• Panels on the interior free surface of a body $S_I$ (as used for irregular frequency removal)
• Panels on a damping lid
• Panels in the free surface panelled zone of a QTF calculation

WAMIT .fdf

The file specification is similar to the .gdf (see the WAMIT user manual) but vertices only have two coordinates since the .fdf only describes panels on the free surface. OrcaWave accepts an .fdf for a damping lid or the free surface panelled zone of a QTF calculation.

Panel vertex coordinates may be ordered in either sense.

WAMIT .csf

OrcaWave supports low-order .csf files for control surfaces. The file specification is almost identical to the .gdf (see the WAMIT user manual).

• The file should contain panels for the submerged part of the control surface $\SCsub$ and, if the body is not completely submerged, the free surface part $\SCfre$.
• Panels on a control surface must have vertices ordered in an anticlockwise sense when viewed from outside the control volume, or equivalently in a clockwise sense when viewed from inside.

Aqwa .dat

OrcaWave only supports the import of explicitly defined nodes. Generated nodes are not supported. The OFFSET data record is supported.

OrcaWave imports quadrilateral panels (QPPL) and triangular panels (TPPL). Other element types are ignored. If the mesh file defines multiple structures, OrcaWave will import the panels for the specified body number.

Aqwa requires that panels below the waterline are marked with the DIFF indicator. All such panels (wet panels) are imported. Optionally, you can specify that panels above the waterline (dry panels) are also imported.

Hydrostar .hst

The file contains a list of nodes (COORDINATES) followed by a list of node numbers (PANEL) defining the four vertices of each panel. A triangular panel is represented by repeating a vertex. The ordering of the vertices implies the orientation of the panel normal, following the same conventions as the WAMIT .gdf above.

If multiple bodies are defined (NBBODY > 1), OrcaWave will import the panels for the specified body number. Optionally, you can specify that visualisation panels (dry panels) defined by NUMFPONT are also imported.

Sesam .fem

OrcaWave reads nodes and elements defined by GCOORD and GELMNT1 data types, respectively. Flat quadrilateral thin shell elements (ELTYP=24) and flat triangular thin shell elements (ELTYP=25) are read. All other element types are ignored.

Nemoh .dat

The full specification for the format can be found on the Nemoh website.

The file contains an ordered list of nodes followed by a list of integers specifying which four nodes are the vertices of each panel. A triangular panel is represented by repeating a vertex. The ordering of the vertices implies the orientation of the panel normal, following the same conventions as the WAMIT .gdf above.

Gmsh .msh

The format is fully documented on Gmsh website.

OrcaWave has support for version 4 ASCII format files. Parametric nodes are not supported. First order triangular (elementType=2) and quadrilateral (elementType=3) elements are imported. All other elements are ignored.

Wavefront .obj

Descriptions for Wavefront .obj file can be found in a variety of places:

• Wikipedia
• http://paulbourke.net/dataformats/obj/
• Wavefront OBJ file format (Library of Congress)

OrcaWave imports vertices and faces, as specified by the v and f commands, respectively. All other information in the file is ignored.

There is no standard convention for axis systems used by .obj files. OrcaWave assumes that the .obj file vertices are specified using the same axis system as OrcaWave itself uses. If your .obj file is not compatible with this assumption, then you may need to re-export the file from your meshing tool having changed the relevant export options.