Calculating the Force of Moving Water: Vehicle Hydrodynamic Drag Equation

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Discussion Overview

The discussion revolves around calculating the force exerted by moving water on a vehicle, specifically focusing on hydrodynamic drag when driving upstream. Participants explore theoretical equations and parameters relevant to this scenario, including water depth, speed, density, and the vehicle's surface area.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant inquires about an equation to calculate the resistive force a vehicle would encounter in moving water, suggesting that parameters like water depth, speed, density, and surface area are important.
  • Another participant proposes a formula for hydrodynamic drag: F = Apv², where p is the density of water, v is the velocity of water, and A is the surface area.
  • A subsequent participant questions whether the same equation used for aerodynamic drag can be applied to hydrodynamic drag, noting that the coefficient of drag would need to be specific to the vehicle's interaction with water.
  • The aerodynamic drag formula is presented as F = 0.5PV²Cdf, with a clarification that P would represent water density instead of air density.

Areas of Agreement / Disagreement

Participants express differing views on the applicability of aerodynamic drag equations to hydrodynamic scenarios, indicating that multiple competing perspectives exist regarding the use of coefficients and parameters.

Contextual Notes

Participants do not reach a consensus on the equivalence of aerodynamic and hydrodynamic drag equations, and there are assumptions regarding the coefficient of drag that remain unaddressed.

Ideologue
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Does anyone know of an equation I may use to calculate the force of moving water? I am trying to theoretically workout the resistive force a vehicle would meet if it were to drive upstream (hydrodynamic drag).

I am assuming the main parameters such an equation would include are water depth, water speed, water density and the surface area of the exposed parts of the vehicle such as the portion of its tyres submerged in the stream.

Thanks.
 
Last edited:
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Force=v*rate of change of mass
F=Apv^2, where p = density of water, v=velocity of water, A=surface area
 
Thank you very much, Harmony.
 
I am wondering now if it is possible to use exactly the same equation for calculating aerodynamic drag as is used for calculating hydrodynamic drag?

Instead of using a figure for air density, a figure for water density is employed. The coefficient of drag remains the same.

What do you think?

Aerodynamic drag is: F = 0.5PV²Cdf

Where:

P = air density
V = velocity
Cd = coefficient of drag
f = frontal areaEdit: Of course the coefficient of drag would be specific to the part of the vehicle subjected to the flowing water.
 

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