resistance test in wave conditions

[jehardiman]

Originally Posted by Leo Lazauskas

I've read dozens of books and chapters on turbulence and its causes over the last 25 years, but I can't remember the Lugt one specifically.
Remind me - does he devote a section or two to negative eddy viscosity flows in Nature?

Not sure what you mean by "negative eddy", but is has a lot on natural viscious mixing due to things like density layers, jet flows, and falling objects.

I've tried to find a way of introducing repeatable turbulence in a towing tank, but I suspect it's a hopeless cause.

Isn't "repeatable turbulence" an oxymoron? ....I mean if it is repeatable isn't it by definition a "vibration" no matter how long the period, i.e. a step function happens once and only once.....after that it is a periodic function....

[Leo Lazauskas]

Originally Posted by jehardiman

Isn't "repeatable turbulence" an oxymoron? ....I mean if it is repeatable isn't it by definition a "vibration" no matter how long the period, i.e. a step function happens once and only once.....after that it is a periodic function....

Yes it is, but I can't think of a better term for it.
Maybe turbulence within a given fixed range of intensity would have been better.

[DCockey]

Or repeatable as far as the relevant probability statistics are concerned.

Vibrations are generally considered to repeat with one or more fixed periods/frequencies. Of course if enough frequencies are considered any reasonable continuous but random function can be approximated to the desired level of accuracy.

[jehardiman]

Originally Posted by DCockey

Of course if enough frequencies are considered any reasonable continuous but random function can be approximated to the desired level of accuracy.

Uncertainity actually, lol

I spent a lot of time wallowing around in that tar pit trying to predict peak motions and loads in waves...I wouldn't advise it. Better to use stoichastic spectral analysis and then walk away knowing you did your best.

[Leo Lazauskas]

Originally Posted by jehardiman

Uncertainity actually, lol

Uncertainty actually, pedantic lol

All I want is a way of producing reasonably consistent large values of the horizontal and vertical eddy viscosity in a tank.
Maybe I should use a tar pit.

[jehardiman]

Originally Posted by Leo Lazauskas

Uncertainty actually, pedantic lol

To paraphrase Fermi "If I could have spelt better, I would have been a writer." I blame the English school system where I learned my colours.

[DCockey]

Originally Posted by jehardiman

Uncertainity actually, lol

I spent a lot of time wallowing around in that tar pit trying to predict peak motions and loads in waves...I wouldn't advise it. Better to use stoichastic spectral analysis and then walk away knowing you did your best.

Agree. I was commenting on the theory, not what is a reasonable approach.