Solid object falling in water tank simulation

cassini83 · June 11, 2014, 19:00

Hello fellow CFD experts,
I need your help setting up this simulation in CFX. From the physical standpoint, the scenario is somewhat straight forward. The scenario goes as follows:
A stationary tank with water (like a glass of water) is subject to a solid object moving through (translation domain for the solid) from the top surface of the water to the bottom of the tank. After the solid is pushed to the bottom of the tank, it is left to interact with the fluid (and assuming its density is less than the liquid) one shall see the solid float to the surface.
The goal of the simulation is to visualize the transient fluid velocity profiles created as a result of the moving object. Ideally, I would like to estimate how long it takes for the water to get back to zero velocity (equilibrium) after one cycle (pushing the solid to the bottom of the tank and letting go of it and reach the surface).
This is obviously a transient simulation, with several domains (stationary and moving). Also, buoyancy would have to be enabled.
Any suggestions as to how to approach this setup would be greatly appreciated. After the simulation is setup, the ultimate goal is to optimize the shape of the solid object in order to "maximize" the time it takes for the water to get back to zero velocity.
Thanks!

aspsarv · August 7, 2021, 21:44

Hi every one,

I would like also to let me know about how to model a solid object dropping into a Tank.

Thanks
Arnold.

ghorrocks · August 8, 2021, 18:06

If you model this in a stationary reference frame then the water is stationary and the body moves relative to it. This can be done using immersed solids or a rigid body solver. But this is a hard way of doing it as you will need a very large and fine mesh.

The easiest way of doing it is to model the body in a frame of reference fixed on the body. Then do a series of simulations with the fluid moving over the body at different velocities. This gives you a drag versus speed curve, and you can use a simple ODE (ordinary differential equation) solver to then predict what this drag versus speed curve makes the body motion.

The easy way of doing it will work as long as you don't have complex motion (eg the body zig-zags or spirals as it moves) or the transients at start up or stopping are not important.

Gert-Jan · August 9, 2021, 17:05

I would opt for Overset Meshing in Fluent, which is more accurate than immersed solids in CFX.

June 11, 2014, 19:00	Solid object falling in water tank simulation	#1
cassini83 New Member Alberto Join Date: Jun 2014 Posts: 2 Rep Power: 0	Hello fellow CFD experts, I need your help setting up this simulation in CFX. From the physical standpoint, the scenario is somewhat straight forward. The scenario goes as follows: A stationary tank with water (like a glass of water) is subject to a solid object moving through (translation domain for the solid) from the top surface of the water to the bottom of the tank. After the solid is pushed to the bottom of the tank, it is left to interact with the fluid (and assuming its density is less than the liquid) one shall see the solid float to the surface. The goal of the simulation is to visualize the transient fluid velocity profiles created as a result of the moving object. Ideally, I would like to estimate how long it takes for the water to get back to zero velocity (equilibrium) after one cycle (pushing the solid to the bottom of the tank and letting go of it and reach the surface). This is obviously a transient simulation, with several domains (stationary and moving). Also, buoyancy would have to be enabled. Any suggestions as to how to approach this setup would be greatly appreciated. After the simulation is setup, the ultimate goal is to optimize the shape of the solid object in order to "maximize" the time it takes for the water to get back to zero velocity. Thanks! Last edited by cassini83; June 11, 2014 at 22:18.

August 7, 2021, 21:44	Modelling A solid particle dropping into a Tank	#2
aspsarv New Member Arnold Join Date: Aug 2021 Posts: 2 Rep Power: 0	Hi every one, I would like also to let me know about how to model a solid object dropping into a Tank. Thanks Arnold.

August 8, 2021, 18:06		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	If you model this in a stationary reference frame then the water is stationary and the body moves relative to it. This can be done using immersed solids or a rigid body solver. But this is a hard way of doing it as you will need a very large and fine mesh. The easiest way of doing it is to model the body in a frame of reference fixed on the body. Then do a series of simulations with the fluid moving over the body at different velocities. This gives you a drag versus speed curve, and you can use a simple ODE (ordinary differential equation) solver to then predict what this drag versus speed curve makes the body motion. The easy way of doing it will work as long as you don't have complex motion (eg the body zig-zags or spirals as it moves) or the transients at start up or stopping are not important. aero_head likes this. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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August 9, 2021, 17:05		#4
Gert-Jan Senior Member Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,827 Rep Power: 27	I would opt for Overset Meshing in Fluent, which is more accurate than immersed solids in CFX.