Learning Forum

[javat33489]

Hi all.

I have a material question.

My task is a cylinder, it is filled with a finely dispersed medium of 1-3 mm, with a filling density of 900 kg/m3. I do the calculation in static analysis. Gravity will be used to push the medium against the walls of the cylinder.

I want to pass water material and use like this:

to what extent is this acceptable?

[peteroznewman]

Fluent can compute the flow of water through porous media.

[javat33489]

My task is not in FLUENT. I'm solving a problem in static analysis! My goal is to examine the cylinder.

[peteroznewman]

Will the water fill the tank or simply flow through the particles? 

If the water fills the tank, the water will be a larger load than the dry particles. You can simulate the stress in the tank caused be being filled with water using a Hydrostatic Pressure load on the inner surfaces of the tank up to the free surface of the water.

To consider the load caused by particles, you have to know the angle of repose of the material.

The angle also depends on whether the material is dry or wet.

Ansys has a Geomechanical material model called Mohr-Coulomb that is used to model soil.

Ansys Explicit Dynamics can have materials defined by spherical particles that can flow like sand.

https://youtu.be/SIkRUv39SoI

[javat33489]

You can simulate the stress in the tank caused be being filled with water using a Hydrostatic Pressure load on the inner surfaces of the tank up to the free surface of the water.

Yes, that's what I need. The water won't flow, I just need to consider the load from it and its weight in the vertical tank. I cannot set a simple pressure, because it is evenly distributed over the surface.

[peteroznewman]

[javat33489]

Exactly!

I completely forgot about it!

Thank you very much!

[javat33489]

When using a hydrostatic pressure tool, will the weight from the water fill also be transferred to the structure?

[peteroznewman]

The pressure from the water is transferred to the structure.

In my example above, I have water to a depth of 0.06 m and the pressure is 587.42 N/m^2 at that depth. Let's assume the bottom of the tank has an area of 1 m^2 so the volume is 0.06 m^3. Multiply that by the density of water and you get the mass of water. Multiply the mass of water by the acceleration of gravity and you get the force of the water pushing down on the bottom of the tank, which is 587.42 N.  That is the weight of the water. Divide that by the area, and you get the pressure that was calculated.

[javat33489]

The pressure from the water is transferred to the structure.

I understood it.

The mass of water will not be taken into account? How to set the mass of water that will act on the inner surface of the reservoir? Will you have to manually calculate the internal volume of the tank, calculate the mass and set the force on the entire internal surface that the water touches?

[peteroznewman]

The image below is the line-by-line computation of the mass of water causing a pressure on the bottom of the tank that the hydrostatic pressure load will apply to the bottom of the tank.

The legs of the tank will see the downward force from the pressure on the bottom of the tank as if there were water in the tank. The Force is the Weight of the water. That is included in the model unless you don't create a bottom surface for the tank. If there is no bottom surface on the tank, there will be no downward force.

[javat33489]

The Force is the Weight of the water. That is included in the model

Thanks, this is what I need, in addition to pressure, to take into account the weight of water when deciding, as if there is water in the tank.

Outside, a wind load acts on the tank, and it is necessary to make a calculation taking into account the filling with water (of course, the weight and pressure of the water inside must be taken into account) and without water.

[peteroznewman]

You don't apply a force in addition to the hydrostatic pressure. You only apply the hydrostatic pressure load to the bottom and sides of the tank to represent the forces the water puts on the tank. The hydrostatic pressure creates a downward force by acting on the surface area of the bottom of the tank.

For the wind load, you could compute the pressure on the sides of the tank from a CFD simulation in Fluent, or you could look up standards that civil engineers use for wind loads on buildings.

[javat33489]

You don't apply a force in addition to the hydrostatic pressure. You only apply the hydrostatic pressure load to the bottom and sides of the tank to represent the forces the water puts on the tank. The hydrostatic pressure creates a downward force by acting on the surface area of the bottom of the tank.

This will be enough for me. I asked about the weight of the water, because an empty tank is less stable and a full one is more stable due to weight. Therefore, I asked if the weight of the water will take into account the instrument-hydrostatic pressure.

[peteroznewman]

If you were to do a Modal analysis and a Harmonic Response analysis to study the structural dynamics of the tank, then you would need to represent the mass of the water, but in a Static Structural analysis, you don’t need the mass of the water to calculate the stress in the tank walls and structure legs, only the forces caused by the hydrostatic pressure.

[javat33489]

Okay, thanks a lot for the replies!