Trimming Surfaces in Maxsurf

[Dick Sarre]

Hello
When trimming surfaces in Maxsurf Modeler (for example a skeg keel to a hull) two intersection edge lines are created, one for the hull and one for the skeg keel. The section lines of the hull/skeg keel at the intersection either overlap or are discontinuous. This is only visible when zooming right in to the trimmed intersection and the overlaps or 'open' sections are only in the order of a few mm. When looking at the sectional area curve, all is OK with no discontinuities. Is this normal? If not, what might be causing the problem? All surface penetrations are good and surfaces trim correctly, with the exception of the very small overlaps/discontinuities.
I need to use the model in Hydromax for stability calculations, so want to be sure that the model will be analysed correctly.
Thanks in advance for any assistance/clarification that anybody can offer.

 

[jehardiman]

It has to do with the way that the surfaces are trimmed. Maxsurf inserts a new boundary edge for each surface based upon the numerical model of the respective surface. Therefore the two boundary edges are not the same. What works is to choose/insert a boundary edge that is the same for both surfaces. Also important is to make sure that the direction of the new trimmed surface is the proper orientation.

Read here about Maxsurf NURBS and trimming.
Why We Use NURBS for Surface Modeling http://www.kastenmarine.com/why_NURBS.htm#:~:text=Maxsurf%20is%20a%20Direct%20(free,envelope%20for%20fairing%20and%20analysis.&text=Working%20with%20a%203D%20NURBS,a%202D%20or%203D%20spline.

 

[DCockey]

Comment based on experience in Rhino. I have no experience with Maxsurf.

In Rhino if you zoom for high magnification of a surface edge, partcularly a trimmed edge, in a shaded or "rendered" view there can be apparent gaps of the shaded surface along the edge of the surface. This is due to the coarseness of the display mesh. Wireframe display and will be accurate The underlying geometry used for calculations will be more accurate. In Rhino the user can adjust settings to refine the display mesh. I do not know if anything similar occurs in Maxsurf.

 

[Dick Sarre]

It has to do with the way that the surfaces are trimmed. Maxsurf inserts a new boundary edge for each surface based upon the numerical model of the respective surface. Therefore the two boundary edges are not the same. What works is to choose/insert a boundary edge that is the same for both surfaces. Also important is to make sure that the direction of the new trimmed surface is the proper orientation.

Read here about Maxsurf NURBS and trimming.
Why We Use NURBS for Surface Modeling http://www.kastenmarine.com/why_NURBS.htm#:~:text=Maxsurf%20is%20a%20Direct%20(free,envelope%20for%20fairing%20and%20analysis.&text=Working%20with%20a%203D%20NURBS,a%202D%20or%203D%20spline.

Thanks for your reply. How would you go about choosing or inserting a boundary edge and deleting the existing two boundary edges? I suppose, I just need to be sure that Maxsurf Stability will produce the correct results in spite of this anomaly.

 

[jehardiman]

Comment based on experience in Rhino. I have no experience with Maxsurf.

In Rhino if you zoom for high magnification of a surface edge, partcularly a trimmed edge, in a shaded or "rendered" view there can be apparent gaps of the shaded surface along the edge of the surface. This is due to the coarseness of the display mesh. Wireframe display and will be accurate The underlying geometry used for calculations will be more accurate. In Rhino the user can adjust settings to refine the display mesh. I do not know if anything similar occurs in Maxsurf.

That can also be a rendering issue from the mathematical surface to the displayed mesh. However, when actually generating the physical mesh polygons from NURBS surfaces, it is important to make sure all the edge nodes are co-incident.
Polygonal and NURBS Modeling: What’s The Difference? https://conceptartempire.com/polygonal-vs-nurbs/

 

[jehardiman]

Thanks for your reply. How would you go about choosing or inserting a boundary edge and deleting the existing two boundary edges? I suppose, I just need to be sure that Maxsurf Stability will produce the correct results in spite of this anomaly.

I believe that Maxsurf has a tolerance setting that will gather in "close" nodes and make them coincident. But it is up to you to assure that you set up the surface to generate the proper number of mesh nodes along the surface intersection to get them within this set tolerance.

 

[TANSL]

Maxsurf automatically fills the gaps between surfaces. If you want, we can verify your results with an application of mine that also makes those calculations. Send me the model of your boat and we will compare the results.

 

[jehardiman]

Maxsurf automatically fills the gaps between surfaces. If you want, we can verify your results with an application of mine that also makes those calculations. Send me the model of your boat and we will compare the results.

Since we used Maxsurf to generate meshes to feed other programs <WAMIT and custom codes>, I am unsure how good the handoff to Hydromax is. Making sure the polygons stitched correctly the first time was a huge time saver.

 

[Alexanov]

Intersections line of two surfaces presented by lines on each surface. Intersection lines can’t be exactly same. It depends from intersection precision.