A water tank subjected to frame motion

khabdullah3 · August 7, 2022, 03:39

Hi,
I am simulating a water tank subjected to discontinous velocity. At the point of discontinuity a pressure surge is seen in "area weighted average Max pressure" curve then it stablizes. I just want to know that is this term corrwcr or not.
Example:
Velocity changes at 10secs (linear Velocity profile is used)
At 9.995 pressure is 5000Pa
At 10.005 pressure is 5500 Pa
At 10 pressure is 120 KPa

Miya97 · August 7, 2022, 05:03

Which CFD software do you use?

khabdullah3 · August 7, 2022, 05:21

I am using ansys fluent

agd · August 8, 2022, 10:23

Are you familiar with the impulse-momentum form of Newton's 2nd law? You have a momentum change when the velocity changes - if the change is very rapid then you can easily generate an impulsive type force. A better way to think of it is that you would need to apply a large impulse to generate the observed or desired change in velocity. But fundamentally you have the impulse I = (Mass)x(Velocity2 - Velocity1). The impulse is the integral of the applied force over the time applied, so for your case it could be approximated as 0.5*(Timestep)*(120000 Pa - 5000 Pa)*(Area of application). I don't know your setup, so that's as far as I can go. But you should be able to work out the rest.

August 7, 2022, 03:39	A water tank subjected to frame motion	#1
khabdullah3 New Member Abdullah Join Date: Aug 2022 Posts: 2 Rep Power: 0	Hi, I am simulating a water tank subjected to discontinous velocity. At the point of discontinuity a pressure surge is seen in "area weighted average Max pressure" curve then it stablizes. I just want to know that is this term corrwcr or not. Example: Velocity changes at 10secs (linear Velocity profile is used) At 9.995 pressure is 5000Pa At 10.005 pressure is 5500 Pa At 10 pressure is 120 KPa

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August 7, 2022, 05:03		#2
Miya97 New Member Join Date: Aug 2022 Posts: 1 Rep Power: 0	Which CFD software do you use?

August 7, 2022, 05:21		#3
khabdullah3 New Member Abdullah Join Date: Aug 2022 Posts: 2 Rep Power: 0	I am using ansys fluent

August 8, 2022, 10:23		#4
agd Senior Member Join Date: Jul 2009 Posts: 351 Rep Power: 18	Are you familiar with the impulse-momentum form of Newton's 2nd law? You have a momentum change when the velocity changes - if the change is very rapid then you can easily generate an impulsive type force. A better way to think of it is that you would need to apply a large impulse to generate the observed or desired change in velocity. But fundamentally you have the impulse I = (Mass)x(Velocity2 - Velocity1). The impulse is the integral of the applied force over the time applied, so for your case it could be approximated as 0.5(Timestep)(120000 Pa - 5000 Pa)*(Area of application). I don't know your setup, so that's as far as I can go. But you should be able to work out the rest.