Boat Design Forums  |  Boat Design Directory  |  Boat Design Gallery  |  Boat Design Book Store  |  Thanks to Our Site Sponsors

Go Back   Boat Design Forums > Design > Software
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read Most Recent Posts Gallery Images Search

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 11-02-2012, 10:58 AM
Murdock86 Murdock86 is offline
Junior Member
 
Join Date: Oct 2012
Rep: 26 Posts: 11
Location: Netherlands
Understanding Rhino from a MultiSurf POV

Hello to all boat designers on a lovely Friday afternoon!

I am fairly familiar with AeroHydro's powerful tool Multisurf for WAMIT and have been using it for a few months now. We just got a new Rhinoceres license and my mates plan to use it to read GHS data files.

My interest is in exploring the other (deeper) features of Rhino. Does it perform a hydrostatic analysis comparable to the level of Multisurf? Some popular opinions I get are that Multisurf is numerically more reliable than Maxsurf, Rhino or any other modelling tool out there. If that is untrue, I stand to be corrected.

Is there anyone who has used both modelling softwares and can make a comparison of sorts? Plan to dig my teeth into Rhino over the next week and see how it fits in the 'bigger picture'! Thanks in advance, folks.
Reply With Quote


  #2  
Old 11-05-2012, 03:11 PM
Joe Petrich Joe Petrich is offline
Designer
 
Join Date: Jun 2008
Rep: 141 Posts: 165
Location: PNW
Rhino alone only has rudimentary hydrostatic capabilities. There are plug-ins for Rhino, most notably Orca3d, which provide better hydrostatics and marine functionality. I'm sorry but I have no experience in the other programs you mention so I cannot give you a reliable comparison. What I can say is that our firm has used Rhino and Orca3d for years and have experienced no problems with accuracy.
Reply With Quote
  #3  
Old 11-05-2012, 05:02 PM
DCockey DCockey is offline
Senior Member
 
Join Date: Oct 2009
Rep: 1399 Posts: 2,970
Location: SE Michigan
Rhino uses double precision for floating point calculations which is yields around 14 significant digits for math accuracy. But many geometry calculations require iteration and the accuracy of those calculations will depend on the tolerances set in DoucmentProperties under Units. The default values are usually too coarse for me so I reset them to my preferences. If I'm working on a small boat in inches then I usually set the Absolute tolerance to .001 units. For a small boat in feet I usually use .0001 units. I use .01 or .001 percent for Relative tolerance and .1 or .01 degrees for Angle tolerance.
__________________
David Cockey
Reply With Quote
  #4  
Old 11-05-2012, 05:39 PM
DCockey DCockey is offline
Senior Member
 
Join Date: Oct 2009
Rep: 1399 Posts: 2,970
Location: SE Michigan
Claims have been made by John Letcher that the way MultiSurf works with geometry is inherently superior to "NURBS" modelers such as Rhino. For instance Letcher has argued, correctly, that the exact solution to the intersection of two NURBS surfaces in general is not a NURBS curve, and representing it by a NURBS curve is an approximation. But are the results from MultiSurf any better in reality? I have not done a direct comparison but I have gone through the MultiSurf users manual. As far as I can determine from the manual arbitrary surfaces and curves are usually modeled using a form of NURBS. The curve resulting from the intersection of two arbitrary surfaces in MultiSurf appears to be a NURBS type curve which only approximates the intersection rather than fiting it exactly. This is the same situation as in Rhino. I don't recall if the accuracy of that approximation can be set by the user in MultiSurf but it can be set by the user in Rhino.
__________________
David Cockey
Reply With Quote
  #5  
Old 12-06-2012, 08:44 AM
Murdock86 Murdock86 is offline
Junior Member
 
Join Date: Oct 2012
Rep: 26 Posts: 11
Location: Netherlands
Quote:
Originally Posted by DCockey View Post
I don't recall if the accuracy of that approximation can be set by the user in MultiSurf but it can be set by the user in Rhino.
In a broad way, one can. When solving for a MultiSurf modelled object in WAMIT, there is a choice between FAST and ACCURATE modes of evaluation. From what I understand, the accuracy is good enough to opt for a "FAST" mode of evaluation every single time.

Thanks, David and everyone else for answers. As I explore Rhino more, hopefully, I'd be able to share some of my insights (in terms of comparison with MultiSurf and applications) with you folks on here :-)
Reply With Quote
  #6  
Old 12-06-2012, 10:43 AM
CWTeebs CWTeebs is offline
AnomalyGenerator
 
Join Date: Apr 2011
Rep: 171 Posts: 224
Location: Maine
Mr. Cockey and I had a robust conversation about the tenets of Rhino versus Multisurf (see link below).

I will say that if you've mastered Multisurf it'll take you about a half hour to become a zen buddhist in Rhino.

I'm currently working on a fatigue analysis project which requires both a solid structural FEA model and a hydrodynamic surface model. I've been having trouble creating the latter in Rhino (via lofting the outer contours) and quite literally just loaded it into Multisurf to see if I might have better luck (wish I was well versed in MSurf).

Here's the link to the discussion I mentioned above (see especially page 2):

MultiSurf & Rhino terminology, comparison & transitions??

Last edited by CWTeebs : 12-06-2012 at 10:45 AM. Reason: Grammar
Reply With Quote
  #7  
Old 12-06-2012, 12:02 PM
DCockey DCockey is offline
Senior Member
 
Join Date: Oct 2009
Rep: 1399 Posts: 2,970
Location: SE Michigan
Quote:
Originally Posted by CWTeebs View Post
Mr. Cockey and I had a robust conversation about the tenets of Rhino versus Multisurf (see link below).

I will say that if you've mastered Multisurf it'll take you about a half hour to become a zen buddhist in Rhino.
One challenge most people face in going from one software package to another is to start "thinking" in terms of how the new software works, not just translating commands, etc between the two. While not a MultiSurf user myself my estimate is that an experienced MultiSurf user could become familar enough with Rhino in a half hour to do useful work in Rhino, but that it would take considerably longer to master Rhino. Rhino does seem to have a reputation for being relatively easy for most people to learn though.

Quote:
Originally Posted by CWTeebs View Post
I'm currently working on a fatigue analysis project which requires both a solid structural FEA model and a hydrodynamic surface model. I've been having trouble creating the latter in Rhino (via lofting the outer contours) and quite literally just loaded it into Multisurf to see if I might have better luck (wish I was well versed in MSurf).

Here's the link to the discussion I mentioned above (see especially page 2):

MultiSurf & Rhino terminology, comparison & transitions??
I'm curious about the surface you are having trouble creating in Rhino by lofting the outer contours. Can you provide any more information?
__________________
David Cockey
Reply With Quote
  #8  
Old 12-07-2012, 11:08 PM
CWTeebs CWTeebs is offline
AnomalyGenerator
 
Join Date: Apr 2011
Rep: 171 Posts: 224
Location: Maine
Quote:
Originally Posted by DCockey
I'm curious about the surface you are having trouble creating in Rhino by lofting the outer contours. Can you provide any more information?
In my case it has more to do with the other tools I'm using and what the surfaces are used for.

It's a fairly large, high speed craft, the forward sections are sharp V-shaped, then there's the flat transition region, then the aft sections have the upward concavity from the shafts. I had trouble surfacing these transition regions together in a way in which the resulting geometry could be imported into ANSYS-Workbench and then meshed for hydrodynamic analysis in ANSYS-AQWA. The requirements are strict, so your incoming geometry needs to be a Catholic Saint or you don't stand a chance. I'm also severely limited by the fact that I don't know what I'm doing. A real drafter would have no problem with this.

As I understand it, the 'meshing' phase for WAMIT is straightforward as MultiSurf creates panels for the low order problem directly (Rhino also saves in GDF format, it would be interesting to compare the two). There's also that add-on for high-order WAMIT, but I'm not sure how that works (do you purchase it as a .DLL add-on for MultiSurf or something?)
Reply With Quote
  #9  
Old 12-08-2012, 02:08 AM
Ad Hoc Ad Hoc is offline
Naval Architect
 
Join Date: Oct 2008
Rep: 2285 Posts: 4,216
Location: Japan
Quote:
Originally Posted by CWTeebs View Post
The requirements are strict, so your incoming geometry needs to be a Catholic Saint or you don't stand a chance.


Sadly most are like this.

As a rule, I manually mesh; takes me longer, but i trust the results more too.

Quote:
Originally Posted by CWTeebs View Post
I'm also severely limited by the fact that I don't know what I'm doing.
What are you have trouble with...?
Reply With Quote
  #10  
Old 12-08-2012, 12:47 PM
CWTeebs CWTeebs is offline
AnomalyGenerator
 
Join Date: Apr 2011
Rep: 171 Posts: 224
Location: Maine
Quote:
Originally Posted by Ad Hoc View Post


Sadly most are like this.

As a rule, I manually mesh; takes me longer, but i trust the results more too.
I do recall you saying you require your engineers to manually edit the vertices in the AQWA input files. The fluoxetine industry thanks you. Okay, I'm being silly, a bad mesh can yield catastrophic results, especially when you're dealing with very large floating structures which, when they bump into other things, have a tendency to explode.


Quote:
What are you have trouble with...?
The only unresolved issue I have is at the transom. It changes direction in every plane, I'll probably have to mesh it manually. Or hire you to mesh it manually for me
Reply With Quote
  #11  
Old 12-08-2012, 02:20 PM
SukiSolo SukiSolo is offline
Senior Member
 
Join Date: Dec 2012
Rep: 117 Posts: 299
Location: Hampshire UK
As a long time Rhino user, Pro-E aned SW too, I have had problems with Iges files from some marine hull modellers. On a 4m boat the sheerline has been up to 1.5mm out. Rhino has excellent tools for 'solving' surfaces properly. The curves are king, they are the key element to fairness if modelling inside Rhino.
I don't know about Multisurf but have used Maxsurf. For more general modelling Rhino is far superior and surface tools will show you tangency problems with even Pro-E exported surfaces. Deviations of 0.001 to 0.0001mm if that tolerance is important to you. Personally I model at 0.0001 or 0.001mm and pretty tight angular tolerances. You can always ease off later. CNC only cuts to 0.1mm.
Amazed if you do not have the tools in Rhino to 'fix' a file. Nearly always it's just knowing the full capabilities of the tools in it. You also have lots of other file formats - STEP (worlds 2nd best translator) etc in the package. Sometimes these are more reliable ways into other packages, if supported.

I am suspicious of 'lofting the contours' which would seem to be inocuous.
Have you checked the curves? - how many control points/knots etc. Have you edited them? Are they out by 0.0001mm? unfair? kinked?. Mostly a very mild edit will give you good results. Is the geometry from single or double precision software? What tolerance ar the original curves?
Sometimes the first way you try to create something is not the right way and it is worth persevering with one or more further ways. Rhino is a very powerful tool but to get the best from it does take a little learning.
Curves are the key in Rhino. Good curves give good geometry.
Reply With Quote
  #12  
Old 12-08-2012, 03:06 PM
CWTeebs CWTeebs is offline
AnomalyGenerator
 
Join Date: Apr 2011
Rep: 171 Posts: 224
Location: Maine
Quote:
Originally Posted by SukiSolo
how many control points/knots etc. Have you edited them?
I'm not good at doing that in Rhino, any pointers?. I think manually editing the control points so they line up appropriately is the better way to handle the transition regions mentioned above. What I typically do is either connect or explode the curves and then vary the number of control points and tolerance until I get what I want.

EDIT:
Quote:
Originally Posted by SukiSolo
Is the geometry from single or double precision software?
Boiled down from SolidWorks by an associate firm. The curves are immaculate and highly professional actually.
Reply With Quote
  #13  
Old 12-09-2012, 06:09 AM
SukiSolo SukiSolo is offline
Senior Member
 
Join Date: Dec 2012
Rep: 117 Posts: 299
Location: Hampshire UK
Normally I tend to use rebuild curve - look at the number of points and see which type - interpolate through/interpolate etc. Aim for the simplest type ie Type 3 NURB spline or even simpler, Type 2 is a true radius. Simplify to the absolute minimum the number of points. Rhino also requires a point at the end of a lofted surface to create say an end bulge. Sometimes a rail sweep is a better option than lofting. With double chined hulls I have done better with a 2 rail sweep than loft. If you rebuild a curve within less than 0.1mm it really won't affect the integrity of the model. In the past I have reduced some curves by 70% of their control points, surfaces to. Make sure you use preview and examine the variation encountered.

It is also possible that the curves you need are not in the SW file. They may need to be extensions and then trimmed - it is very hard without seeing the geometry. They may need to be created, Project curve? curve curve intersect? Maybe some untrimmed solid shape from SW for model purposes only would help. Like tangent draft surfaces when modelling mould taper. This type of stuff is needed in Pro-E too.

Solid Works is fine. BTW Rhino surfaces go into SW parametrically as an operation and can be worked on and deplaced as a feature in SW. Rhino has been a Gold partner to SW since the earliest days as it has always had better surface creation tools. SW is a lot better these days and Rhino has progressed too. The NURB 'engine' in Rhino is from Integrity Ware.
Reply With Quote
  #14  
Old 12-12-2012, 08:37 PM
DCockey DCockey is offline
Senior Member
 
Join Date: Oct 2009
Rep: 1399 Posts: 2,970
Location: SE Michigan
So what did I say in this thread which annoyed someone?
__________________
David Cockey
Reply With Quote


  #15  
Old 12-12-2012, 09:27 PM
CWTeebs CWTeebs is offline
AnomalyGenerator
 
Join Date: Apr 2011
Rep: 171 Posts: 224
Location: Maine
Quote:
So what did I say in this thread which annoyed someone?
I personally miss the days when your follow up posts were accompanied with an offer for a no-strings-attached hug.
Reply With Quote
Reply



Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
MultiSurf & Rhino terminology, comparison & transitions?? DCockey Software 18 04-09-2012 07:17 PM
Rhino Rhino Rhino (hull thickness, offset surface, and unrolldvp for cnc cutting) metin_mehel Software 11 10-11-2011 01:10 AM
...Two Multisurf questions... kalada Software 6 02-02-2009 10:39 AM
Stations in Multisurf: help!! Akeswins Software 0 12-11-2005 12:34 PM
MultiSurf questions... Guest Software 2 04-22-2003 03:49 PM


All times are GMT -4. The time now is 05:37 AM.


Powered by: vBulletin Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Web Site Design and Content Copyright ©1999 - 2014 Boat Design Net