MultiSurf
MultiSurf is a parametric surface modelling program used for developing linesplans. Included in the software is the Hydro module, used for hydrostatic calculations.
Contents
Manuals and Training
Digital
- see \Home\Manuls\MultiSurf
- see Tips
- see Instructional Videos
Paper
- MultiSurf Tutorials
- MultiSurf User's Manual
- Working with components
- Advanced Modeling
Breaklines
Correspondence with Reinhard Siegel 04-02-2007.
The root of the problem are the breaklines in the developable surfaces (devsurf). Those lines are drawn in bold fashion. For details about breakpoints and breaklines please see the MultiSurf program help and user documentation. See also the command "breaklines" that reports curve breaks and surface breaks.
It is not my practice to avoid those breaklines at all. For me, most important is the wanted shape of the devsurf. If by small alterations of the supporting curves a breakline can be avoided, I will accept the change. But if the changes would lead to a considerable different shape than the intended one, I do not care about those breaklines of a devsurf.
Breaklines in a devsurf can indicate an unfairness in the surface. Even if both supporting curves of the devsurf may be fair, the devsurf may show an unwanted shape. This is often the case, when a series of rulings run into a single point on one curve at a forward position, and on the other curve at a more aftward position. Then waterlines, stations etc. are ugly.
As an example please see the attached model 2lines.ms2. A Developable Surface and a Ruled Surface are spanned between two twisted lines. The contour, that cuts the devsurf, has a knuckle.
If the rulings are distributed in an unharmonic fashion along a devsurf, one should check waterlines, stations, etc. It is not always the case, that contours are ugly, but it might occur.
So, if the breaklines do not indicate such a problematic area, I leave them aside. If the devsurf needs to be export via Iges, then I follow these steps (boat.ms2 should be the file name of the model, that is worked on):
1. Export the Iges file from model boat.ms2 2. Open a new model in MultiSurf 3. Import the iges file in the new model and check the result.
If the appearance is not ok, than I do the following:
4. Create a Fitted Surface for the devsurf in model boat.ms2. Set the v-degree to 1 (because the surface is straight in the direction of the rulings). Set log-tolerance to 0 (this refers to your model, with units in mm).
5. In boat.ms2 check the result of the fitting via Tools/ Measure/ Clearance.
6. Save the Fitted Surface as Iges.
7. Import it into a new model, check the appearance.
8. If there is a fold (as it is in your model on the top of the bow, move control points. For this, show the net of the surface; this gives guidance about the order of control points.
9. Export Iges from this model.
Attached please find the models topside.ms2 and bottom.ms2, that were processed in this way.
The forefoot of the bottom is an example for ommiting a breakline. In your model, both chine and fairbody curve end in the same point. It would make no difference in shape, if the fairbody curve would end at point MC5_CL. Then the forward edge of the bottom would not be degenerated, but it would be straight (from MC5_CL to MC5_chine). This would remove the breakline and the fold, that shows now in the Iges exported surface.
In the attached model model-10-rs.ms2 I did this change.
Exporting and accuracy
A correspondence with Reinhard Siegel from 05-07-2007.
Under Tools/ Options/ Performance there is the "divisions multiplier". This is a number, by which all t-divisions of curves and snakes and all u and v-divisions of surfaces is globally multiplied.
So, when you are exporting data increase it accordingly. Please note, that there is no gain in accurracy, when you increase the divisions of a SubSurface to, say 8x16 in u and v, but keep the basis surface to a 8x4 divisions. Coordination of divisions is important.
My rule of thumb for elongated bodys like boats and ships is for the design stage:
- all curves (snakes), which are longer than half the overall length: 8x8
- all surfaces, which are longer than half the overall length: 8x8 in longitudinal direction, 8x4 transverse
- the master curves of a lofted surface has the same division as the the surface in the direction of the master curves (for example, the demo model: 8x4 for all mcs, and u= 8x4 (because u is in the direction of the mcs, v=8x8, because it is in the longitudinal direction).
Multisurf export
Use the correct settings for a precise export of the model.
Settings
- Decimal places (options):
- 4 when model units are (m)
- 1 when model units are (mm)
- Division multiplier (options):
- 3 (2 if 3 is not working)
- Export 3D to Rhino in iges format (*.igs)
- Save mode: Accurate
Support
Support inquiries can be send to:
- AeroHydro support staff (support@aerohydro.com)
- the European distributor (ReinhardSiegel@compuserve.com)
