# Help with torque calculation of underwater rotating disk?

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1. Mar 31, 2015

### IamDev

Hello Guys,

I have a disk of diameter of 150mm and thickness of 10mm which is rotating at the constant speed of 100rpm. The disk is inside water which is approximately 4-5 cm below the surface. Disk is horizontal (parallel to the water surface). Disk is attached with the shaft of the motor. At the upper surface of the disk there is a circular ring of outside diameter of 80mm and inside diameter of 70mm and height is 20mm.
I need to calculate the torque required to rotate this whole setup at 100rpm.
The weight of this setup is approximately about 1kg and the water is still at the surface.

2. Apr 5, 2015

### Greg Bernhardt

Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?

3. Apr 5, 2015

### Staff: Mentor

In general, those things need simulations to get some numerical estimates. The water level will get influenced by the rotating disk, so you have to consider the water/air boundary as well. There are software packages that can model it, but expect some work to get the simulations running.

4. Apr 7, 2015

### IamDev

Is it possible to calculate required torque if we consider that water level will be constant during the whole process?

5. Apr 7, 2015

### Staff: Mentor

It is possible to get some estimates, but I think without a simulation all those estimates will be problematic.

6. Apr 8, 2015

### IamDev

Okay, I have a disk of 8 cm radius and 4 cm thickness and I have to rotate the disk at constant speed of 100 rpm. I need to buy a DC motor to rotate the disk but I am unable to short out the specification of DC motor. Can you help me please?

7. Apr 8, 2015

### Staff: Mentor

Well, it is possible to get some order of magnitude estimate. Do you have a sketch of the setup? How large is the water basin? What is below the disk?