Help with torque calculation of underwater rotating disk?

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Discussion Overview

The discussion revolves around calculating the torque required to rotate an underwater disk setup at a constant speed of 100 rpm. The scenario includes considerations of the disk's dimensions, weight, and the influence of water on the torque calculation. Participants explore the implications of water dynamics and the potential need for simulations.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested, Mathematical reasoning

Main Points Raised

  • One participant describes a disk with specific dimensions and weight, seeking to calculate the torque needed for rotation in water.
  • Another participant suggests that simulations may be necessary for accurate torque estimates due to the influence of the rotating disk on the water level.
  • A question is raised about the feasibility of calculating torque under the assumption that the water level remains constant during the process.
  • Some participants indicate that while estimates can be made, they may be problematic without simulations.
  • A separate participant introduces a different disk setup and requests assistance in selecting a DC motor for rotation, indicating a need for specifications.
  • One participant asks for additional details about the setup, such as a sketch and the size of the water basin, to provide better guidance on estimating torque.

Areas of Agreement / Disagreement

Participants express differing views on the necessity of simulations for accurate torque calculations, with some suggesting that estimates can be made while others caution about their reliability without simulation support. The discussion remains unresolved regarding the best approach to calculate the required torque.

Contextual Notes

Participants note the potential complications arising from the interaction between the rotating disk and the water, including the water/air boundary and the effects of water dynamics on torque calculations. There is also mention of missing details that could affect the estimates, such as the size of the water basin and what lies beneath the disk.

Who May Find This Useful

This discussion may be useful for individuals interested in fluid dynamics, mechanical engineering, or those working on projects involving rotating systems in aquatic environments.

IamDev
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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.
 
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.
 
Is it possible to calculate required torque if we consider that water level will be constant during the whole process?
 
It is possible to get some estimates, but I think without a simulation all those estimates will be problematic.
 
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?
 
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?
 

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