Which Uni?

Thanks for that.

Where are the longest towing tanks? IIRC, David Taylor Basinin the USA had one almost 1km long. Is there anything else to rival that in the UK or elsewhere?

 

I can't see the need for a 1km tank personally, but of course everything is "bigger" in US?!

UK tanks listed here:
http://www.marine.gov.uk/tanks.htm

The 270m at Haslar is now the largest left in the UK i believe.

 

I have read that long tanks are needed for some tests in shallowish water because it is difficult to reach a steady state near the critical Froude number.

 

Not entirely sure i understand what you're referring to, since go to:
http://www.boatdesign.net/forums/boat-design/wave-pattern-question-28667.html
post #3.

It is just a function of depth.

We have tank tested in tanks significantly less than 1km...for shallow water analysis.

 

Thanks. I know about depth effects. One of my supervisors gave me a paper from a conference in Korea that shows the problem. He reckons that even 1km is sometimes not long enough to get a truly steady-state solution.

I only have a hard copy but there is an abstract at the IWWWFB website.
http://www.iwwwfb.org/Abstracts/iwwwfb23/iwwwfb23_09.pdf

 

But he hasn't really defined what he means by steady state, other than theory predicts otherwise; he is also assuming or rather saying the sidewalls interfere with the 'theoretical', hence 'sees' a problem, nor quantified the "error". Other than an observation.

However, in shallow water, the energy is far more important than wave profile.

 

I agree with you, AH. That is just one of many papers I am ploughing during the first few months. There are some terrible experimental results for surface effect ship models and hovercraft travelling near Fcrit where the model seems to shudder its way down the tank.

I agree too that the effect of boundary layers on the bottom of tanks and the sidewalls is an issue that should be better quantified.

I haven't picked an exact thesis topic yet but I am very interested in what people believe they are testing and what is actually being measured. I am also interested in the faith some naval architects and engineers place in dubious experiments. There have been some amusing disasters such as the "Hughes Line" for ship skin friction. Although it is nearly complete bs it is still sometimes used to cast doubt on other work. A more recent example is the Princeton superpipe experiments that had to be corrected for a variety of over-looked factors.

Thanks for your help.

(I tried to give you some "rep" points but I am too low level.)

 

Jenny

You need to be careful with some of your "assumptions", and make sure that you are following a path that you are interested in, rather than being surreptitiously lead, by a tutor.

Take the Hughes line for instance. All frictional lines have been debated and almost always the conclusion,from academics is that it is "poor science". Ok, well...please define the hull roughness of a ship for me mathematically, all the ribs in the surface the circular marks left by the grinder and the paint brush etc......oh and while at it, how about the roughness of a GRP boat then an ally and steel, and one that has had excellent workmanship and then another with poor workmanship etc etc.....the point being, 'fudge factors' etc may not sit well with academics (I know because i sit on both sides of the fence, so to speak). But to a practising naval architect whom has a contract, all that is of concern is the end result, but a consistent and quantitative result. If fudge factors are required, then so long as said fudge factors are "consistent" then it justifies the means. It is for academics to establish what lies behind the fudge factors.

My personal point of view is that one will never establish exactly skin friction. Owing to the infinite variables that affect friction. However, just like a mathematical model to represent the 'random' sea surface was unthinkable some 30~40 years ago, we can describe the sea with a high degree of accuracy, even though not 100% perfect.

So, it is one thing to say the Hughes line is BS, but it is quite another to say why and explain with significant confidence what should replace it or the ITTC for instance.

Practising Naval Architects, like myself, are very interested in cutting edge science. But, we must remain focused on the objective....designing boats and being able to use the data quantitatively, not qualitatively.

I recently came across the Toms Effect. This is akin to what Einstein discovered about light. The Toms effects shows that at low Rn's, fish use the concept that particles of water are both 'waves' and 'particles' and work in 'packets'. This has now been proven. Very interesting subject.

Thanks for the though about rep points. the thought and engaging debate is praise and pleasure enough

Nice to see an open and enquirying mind on the forum.

 

(Written in haste as I am going away for a couple of weeks.)

1. The Hughes line was fatally flawed because the experiments contained spurious edge effects. This was not just a head-in-the-clouds academic issue. Results were corrected for those effects relatively quickly but the old results and line are still used by some people too lazy to keep up with the research. (That was

2. I agree with you on the matter of skin friction and roughness. Some people are now claiming that there will never be definitive experiments even for the simple flat plate case for high Reynolds numbers. I saw a recent proposal for experiments on a 10m plate but that was abandoned because of insurmountable technical problems and a realisation that they would not be conclusive anyway.

3. I'm too old to let others pick my thesis topics. I only study for enjoyment so it's not to enhance career prospects.

 

Enjoy your few weeks away...wherever it may be

What areas do interest you, what "gets you going", so to speak?

 

any one can share how is the quality of MSC in Marine Technology in NTNU ?
Norwegian University of Science and Technology (NTNU)
www.ntnu.no/english