MARINTEK VERES: catamaran seakeeping calculations

I am looking for somebody who is running the Marintek VERES code (or similar) that can calculate seakeeping characteristics of a high speed catamaran (FnL = 1.0).

Typically this requires a 2.5D strip theory calculation.

I need the following parameters calculated for :

• Motions (pitch, heave and roll) for two loading conditions and 4 speeds, 16 wave headings. Roll being the tough one to do accurately.
• motion sickness index calculatiom
• added ressitance in waves, 1 loading condition, 4 speeds

Can anybody help?

 

VERES generally requires model testing for greater accuracy at higher Fn.

Why not contact Marintek directly, or some design house that uses the software?

This isn't cheap micky-mouse software and I doubt anyone will give you such results for free.

 

VERES gives pretty good results accross a wide range of Froude numbers for catamarans and does nto need model test validation unless the wetdeck is slamming.

Of course I am not expecting such results for free:!: I have contacted Marintek already but as you likely know, Norway is not the cheapest place to get any engineering services. The point of my post was to find out who else is running the software and can give me a quotation for the work.

 

Indeed it does. But for greater accuracy, especially in roll, model tests are often used (better added mass, stiffness and damping coeff's) to obtain the improved accuracy at the higher Fn's.

Indeed. Much like here

I know Austal use this software...but the strength of the Aussie dollar wont help there much perhaps?

 

It has been my experience that VERES often over-predicts the pitch motions of catamaran-hulled vessels; I have numerous examples of that, the most recent from 2007, in which case the pitch motions were over-predicted, relative to the model test results, by 30-40%. That over-prediction did not degrade the accuracy of the predicted vertical accelerations too badly though..so the habitability results are still useful.

I've seen too little correlation between VERES results and measured roll motions to even be able to comment on that from own experience.

 

How accurate are model tests compared to full-size tests?

 

As you well know..that depends on a huge number of factors. But my observations of the tendency of VERES to overpredict cat pitch are over about a 15-20 year period (ever since the boys in Trondheim first started using their new simulation) and correlation with numerous model tests and full scale trials.

While all such are fraught with many dangers for the accuracy of the results...Gauss alone suggests strongly that, were the pitch prediction and comparative data error random in nature, that the predictions would be both high and low.

Of course all model tests that I've done correlated so well with the full-scale final results that you would swear I cheated.

 

Thanks, Bill.
I wasn't trying to be facetious or disingenuous.
I thought viscosity might affect the roll of small models.

Just like CFD!

Leo.

 

There are damping terms in VERES that can be tweaked to bring the simulation results in to very good agreement with model test data. Once that agreement is in hand (and assuming you trust the model test data), its off to the races and you can generate a vast number of assesment points far more cheaply with VERES than in a model tank. Especially those at oblique wave headings.

I used, for years, a multi hull motions simulation program similar in many ways to VERES; SEAKP, developed originally for the USN beginning back in the 70s. It was sufficiently refined and adjusted over the years that by the late 80s the results were so accurate you really would think we cheated. In fact, seakeeping and habitability performance guarantees would be predicated on the results. IT would not handle SWATH..but it did a superb job of predicting catamaran and SES motions in any manner of seaway you wanted to specifiy.

I would like to get my hands on that program again but it may be "lost to eternity", at least as far as USN's custody goes.

 

Was it based on SMP (The Ship Motion Program) originally developed
for monohulls by Tuck, Salvesen and Faltinsen?
Tuck certainly didn't have anything to do with the multihull or SES
codes, as he was totally bored with ship motions by the 1980's.

 

No. The SEAKP program development was part of the original USN 2k/3KSES programs and started back in the early 70s. Navy "property" and written in Fortran, I was involved in the first complete rewrite that ported then original main-fram/mini-frame code (with card stack craft data and run control inputs!) over to run on a PC. (Circa 1987?). Then the USN funded further development of the code..backed with a good deal of model test correlation..to extend the capabilities and range of hull variations it would handle. By about 1990, it was a nice tool and heavily validated, and Navy continued some level of developement and code support funding up until about 1993.

And there it stopped.

SEAKP was used extensively and almost exclusively to suppport the air cushion systems design tasks and the seakeeping performance assessments of both the RNoN MCMV and MTB (Skjold) programs. But it was also the tool used to design the first active catamaran stabilization systems and predict their performance in a seaway. Incats, Westamaran, Batservice, etc..many cats were evaluated.

We later developed a monohull program too..but it was not a derivative of the SEAKP baseline at all. In fact, "We" is not really correct; Dr. Higdon developed the monohull program for us and I had nothing to do with that one at all. (He of SWATH simulation and control fame..and my mentor)

 

Thanks for the potted history, Bill.

I am doing a little work on SES with split cushions. Was the program able to
handle multiple cushions at different pressures?

 

No, Leo, it was not. We had a separate stand-alone simulation program that was created just for that purpose. That in-house program modeled the cushion as up to eight volumes and included the ability to insert "midcushion seals" with various characteristics defined by the user. Longitudinal and lateral cushion acoustic modes as well as longitudinal hull structural bending modes were fully modeled. We had also developed a fairly robust model for the stern seal dynamics but never completed the integration of that; teh development of much more stable stern seal geometries rather "late in the game" had removed the urgency.

That "finite-volume vertical-plan motions" FVVPM simulation only handled head seas; it was primarily - almost exclusively, in fact - a tool used to develop the advanced filters for SES ride control systems and predict their performance. That result would then be "ported" over to the much more capable and flexible SEAKP simulation; the SEAKP not modeling the often very performance-limiting (gain limiting) effects of things like acoustic mode instabilities. That technique served us very well for many years in getting the real-world air cushion ride systems to work well.

What you are after, I suspect, the effects of different cushion pressures in different cushion volumes on cushion drag and wave formation, was "not even thunk of yet" back when the FVVPM program was in regular use. Further, the drag prediction was rather crude; drag not being of any interest as a predicted parameter from that simulation.

So you and Lawry are, yet again, way out there and all alone doing it. Good luck!

By the way..Loheed invented a new mid-cushion seal geometry that is far more effective as a mid-cushion barrier seal than any of the bag-finger seals that have been used in that role up to this point in model tests. We finally got to test his innovative midcushion seal design back in 2007/2008 on the HSSL 55' LOA free-running model. Unfortunately..the model testing proram was exceedingly short due to funds running out at the end of the progrm.

 

Nice of you to mention us in the same breath, but Lawry
is a long way ahead of my work. He has funding, testing
facilities, and esteeemed colleagues. I have a grant from
the dole office, and work in my pyjamas

The last work I did was to put up some wave patterns of SES
with compartmented cushions at:
http://www.cyberiad.net/wakeses.htm

I also validated my programs against the tank tests
conducted by Lawry et al.
I'm not interested in finite width, so I only used cuts
well away from the walls.
See attached short note to myself and some friends.

None of that is of engineering interest, unfortunately.
Wish Rick the best with his invention.
Like him I too have been trawling through patents to see if
anyone else had the same idea for reducing wear on the front
skirts. Some time during the exercise I realised I was
straying into engineering and stopped dead in my tracks.
As one of your wiser philosophers once said:
"A man's got to know his limitations".

 

It's all quite an interesting mix of potentially large strides in achieving some remarkably efficient high-speed transport, this extremely high L/B SES with divided air cushion.

As far as I know, USN has no intention to spend another nickel on further testing or development of the HSSL Sea Train SES concept(s) that turned out (from all the model testing and analyses completed to date, including Lawry's) to be so promising. We seen no real interest from the commercial sector either; the recent CCDOT study in to advanced short-sea shipping platforms apparently did not even consider the HSSL Sea Train in their mix.

So Rick's new mid-cushion seal may never see life at full scale.