I am currently working on a little project regarding cfd calculations on fish. I have only just begun and i would therefor like to ask for any information on the subject. I am planning to write a new or modify an existing code. I would therefore be interested in codes that I could start from. The code will be incompressible, transient, inviscid at first (viscosity later), moving grid, and preferably written in fortran. nay help, suggestions, hints on the matter are appreciated.

(1). What kind of fish? (2). How do you model the fish geometry, especially when the fish is moving?

What kind of fish? Any somewhat common fish will do, bass, cod, herring etc They all more or less have the same topology. Modelling the fish should not be so difficult. one grid with maximun deflection in one, say x direction, and then a second one with maximum deflection in the -x direction. Then I will interpolate between the two to account for the fish moving it's tail. Possibly I need to use some grids in between as well.

Martin

(1). Well, that's a mechanical fish. (2). I have noticed that the fish open and close the mouth at roughly one second a time, to get needed the water and oxygen. (2). Why not just use three rectangular plates to simulate the fish motion. In that way, you can simplify the modeling work. With two hinges, you can position the plates at any angles to simulate its motion. (it's not going to have the mouth anyway.)

Simplifications are always made, no? And it is the propelling motion I am interested in, and I am quite sure that the flow through the fish is not all to involed in that. Besides, I want to have the possibility to use different deflections on the fish's tail.

Martin

(1). In that case, 3D Studio Max is probably a good software to model the fish and animation. (2). I have used the software since early 90's, and I think it can model quite complex geometry.

Check

H. Liu & K. Kawachi, "A Numerical Study of Undulatory Swimming," J. Comp. Phys., Vol. 155, pp 223-247, 1999.

Adrin Gharakhani

Here is an article in Annual reviews in Fluid Mechanics 32(1)33. (2000)

Hydrodynamics of Fishlike Swimming

================================================== ==== http://fluid.annualreviews.org/cgi/c...eabstract=fish+motion&searchid=QID_NOT_SET&stored_search=&FIRSTI NDEX=&journalcode=fluid

================================================== ==== these may or may not be of interest...

http://web.mit.edu/afs/athena.mit.ed...ects/fish.html

http://www.cee.hw.ac.uk/~sfakios/html/swim.htm

http://www.csuchico.edu/~pmaslin/ichthy/loco2.html

(1). Thank you for the websites information on fish motion.

Hello;

Meldon Wolfgang's PhD thesis (mentioned in the Annual Review article) presents 3-d unsteady results for a swimming fish. I believe he modified PMARC to do the calculations. I've also been modifying PMARC for modeling flow about morphing bodies and it seems to work pretty well for my stuff.

Regards,

R

Bass, cod, herring?! You should model a high performance fish! I suggest a tuna as the geometry is relatively simple. Some guys at MIT have done research on a robotic tuna that you may want to find out about.

High performace fish? Well, they all use the same principles, and once I can model one, I can do all. I have looked at the stuff MIT have done and I must say I like it. Does anyone know what code they used? But to begin I will probably invent a fish. If anyone have a meshed fish (structured hex) I would be most grateful.

Martin

If I remember correctly, the MIT people (like most others) used an inviscid model and the vortex-panel approach. Actually, if you do a simple literature search you'll see most analyses, beginning by Lighthill all the way until very recently, use a thin (curved) plate model and "shed" vorticity at the tail. For this work, the original/inviscid vortex panel method probably works best if the interest is the long wake behind the fish (or a school of fish). In many respects, to first order, flow over a fish is similar to flow over a wing in the sense that there is little/no massive separation. Fish is smarter, though, as it can use the shed vorticity to propel forward.

Adrin Gharakhani

Martin, lighten up man I was joking! The MIT work to which I was refering was some experimental work that was done with a robotic tuna in a water tank. If I remember correctly the robot was called Charlie.

Irony is hard to catch over the computer.

Martin

Hence the smiley face or should I use the wry face :-?

Heh heh