A description of a TriMesh surface is given in the Surface Types in Maxsurf section on page 80.

 View a video that will show you how a random set of marker data is made suitable for a TriMesh surface.

Before you can generate a TriMesh it is necessary to order the markers. You can do this marker ordering in many ways, but there is a particular work order which generally seems to work quite well:

1.      Generating a Grid from Markers

2.      Group Markers by Stations

3.      Delete Duplicate Markers

4.      Sort Marker Stations (automatic sorting)

5.      Re-order Selected Markers (manual sorting)

You may have to delete spurious markers that for example do not form a complete station from bottom to deck edge. Also see other commands in the Marker Menu that may be of use.

After ordering your marker data, you may generate a TriMesh:

Ø  Markers | Generate Trimesh Surface

This brings up the following dialog:

Mirror surface about centreline

This will mirror the surface generated from the markers across the transverse centreline of the model. Tick this box if you have defined just one half of the vessel. If you have defined markers for both port and starboard halves of the vessel then leave this option un-ticked.

Delete large triangles

This option is useful if the vessel has a bulbous bow. If this is the case then there will be large triangles generated on the centreline between the top of the bulb and the bow above the bulb. These triangles will only affect wetted surface area calculations but if desired, they can be detected and deleted. You can specify how large the triangles are allowed to be before they are deleted – this is done by specifying the number of standard deviations from the mean edge length.

Notes:

§   The Generate TriMesh command works on the selected markers.

§   Maxsurf can only generate one TriMesh surface.

§   No other NURB surfaces with Surface Use “Hull” may exist, only surfaces with Surface Use “Internal Structure” are allowed.

§   A TriMesh surface cannot be trimmed with regular NURB surfaces.

§   A TriMesh surface can be saved as a .msd file and read directly into Hydromax, Seakeeper and Hullspeed for analysis. For Hydromax tanks and compartments, additional NURB internal structure surfaces should be defined.

A TriMesh surface can be rendered in Perspective view. The colour of the rendered TriMesh panels is dependent on their orientation in the model.

When “Show all Markers” and “Connect Marker Stations” is selected from the Display | Markers menu, the individual TriMesh panels may be displayed in all four view Windows.

Just like for NURB surfaces you can display all regular contours on a TriMesh surface.

You can not hide a TriMesh, but you can easily delete and re-generate the TriMesh as long as the markers position and the marker’s order remains the same.

Unwanted duplicate markers

In most cases duplicate markers cause problems. For instance in this catamaran models, duplicate markers on the sharp corner cause the corner detection algorithm to fail. However in some cases duplicate markers are required. To delete duplicates from a range of markers, simply select the range of markers with the selection box and choose Markers | Remove duplicate markers. If no markers are selected duplicates from the entire marker list will be deleted

Duplicate markers causing corner detection to fail

Delete duplicate markers in the corner region of these sections:

Select the markers from which you want to delete duplicates

Duplicate markers removed: corner detection now works correctly

Connections appear between non-consecutive sections

In some cases if you insert markers graphically, although they are inserted into the correct section (ie given the correct station index, they may be in the wrong order in the marker table). This is easily solved with the Markers | Group Markers by Station command which will reorganise the marker table so that the markers will be grouped by station index. The order of the actual markers on a given section will not be changed. For this to work correctly it is imperative that the section grid spacing is monotonic.

In the example below, an extra station was added – these markers were appended to the end of the Marker table, out of sequence, hence the TriMesh is trying to connect the sections in the wrong order.

Before adding new section

After adding section, markers are out of sequence because added to the end of the Marker table

After Markers | Group Markers by Station -
markers appear in the correct order in the Marker table

An unwanted hole appears in the TriMesh surface

Generally it is desirable to remove unusually large triangles from the trimesh – this enables bulbous bows and yachts with fin-keels and bulbs to be defined (not to mention multihulls). However if the marker spacing is very irregular, valid triangles that should not be removed are removed resulting in unwanted holes in the surface:

There are two solutions to fix this problem:

a)   When generating the trim mesh surface either increase the size of acceptable triangle sizes or turn off the “Delete large triangles from surface” option:

b)   Insert an extra section of markers that dissects the hole in the surface (this will create triangles that have edges that lie within the acceptable range).