Ship, Boat, and Yacht Design

Hi

It's about more than just the surface area.

You need to add the cross-section shapes and Re (to find the drag coefficient) to calculate the forces. Potentially also the velocity profile (given that it is a rowing motion it will likely be some kind of a sinusoidal function).

Could you please explain it more for me.. I am a computer engineer and have little information about CFD and need to design such a project.

Ok, CFD is a different beast than a cold analytical calculation.

So do you need to calculate this analytically or with a FEM? (the approach is usually different)

I saw your question here as well: https://grabcad.com/groups/cfd-and-fea/discussions/rowing-motion-in-solidworks

I think we can consolidate the topics - assuming you are asking about the same thing.

I googled 'labrid fin' but got no useful results - can you explain which fin that is please?

Ok sir , first of all I would like to express my thanks and grateful for your time...

I designed my model which consist of pectoral fin of robotic fish.. my fin is quarter moon like shape.That means it has two surface areas say A and B as I explained in the first post.

Now I would like to study the hydrodynamic forces acting on it

Iam really lost with these equations plus CFD analysis..

Many thanks again for you sir..

If you want to calculate this via a CFD you will probably need to do a transient simulation with an adaptive mesh.

Although, perhaps you could get away without the letter. If you are using Solidworks Flowsimulation, set the simulation as time dependent, and set the velocity of the fluid as a function of time. This function of course is determined by your mechanism.

It will probably take you a few tries before you get decently accurate results, so you should do at least preliminary hand calculations to know when you are in the ballpark.

For the sake of simplicity and clarity i will make a few assumptions:

1. The fins move only forward/backward, no up/down motion or rotation

2. velocity is low enough that there is no cavitation

3. you do not need highly accurate results - as if you do, even standard CFD will likely be inadequate, and you will need your own optimized version

4. The power stroke produces only trust

5. The recovery stroke produces only drag

You will calculate both '4.' and '5.' with the general aerodynamic drag equation:

Drag = 0.5 * velocity^2 * Fluid_density * Planar_area * Drag_coefficient

'Planar_area' is the cross-section area of the fin as seen perpendicual to the flow.

You can find C shape 'Drag_coefficient here (if this is your shape):

https://qph.fs.quoracdn.net/main-qimg-ba2b9a5bffd1671cc925925b68ce9ca7.webp

Since your fins do not move at a constant speed, calculate the average thrust recursively or integrate it.

You will need to modify the results you get with an efficiency coefficient. Unfortunately this one is a bit tricky as it depends on the overall shape of your fin.

It is usually determined empirically, so this might be though to get.

A few years ago i saw a collection of efficiency coefficients for multiple animals' "propulsion systems" online, ask Mr. G., perhaps it is still available.

Alternatively i can try to help you estimate it but i am probably out of my league there.

This is very kind of you sir

you helped me so much and I will start to do my calculations right now ...

may I ask one more question regarding thrust calculation.

Do I have to calculate GG --> Force or GG--> Force (z) as z is my flow direction?

I know that the total thrust is the integration of thrust generated at each time instant over the surface area but how to calculate this integration in solidworks?

Again I would like to express my thanks for you sir.