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pressure load by air expansion in cube

Posted 3 juil. 2024, 00:01 UTC−4 Fluid & Heat, Structural Mechanics Version 6.1 4 Replies

Hyeontak Kim

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Hello,

I'm new to COMSOL and I'm trying to make a model of cube filled with air. When the cube is heated, so does the air. But the volume of air is constant(=cube), the pressure of the air will increase with increasing temperature. I want to calculate the stress the cube receives due to the increased pressure. So I chose the physics of "Heat transfer in solids and fluids" and "Structure mechanics". I set the heat flux on the top surface of the cube, and set the boundary load on the inner surface of the cube in function(p=po*T/T0). Unfortunatley, it doesn't work but I wonder the way I chose is correct. And I want to ask you about another way to simulate my model.

Thanks

4 Replies Last Post 4 juil. 2024, 20:05 UTC−4

Jeff Hiller COMSOL Employee

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Posted: 6 days ago

Updated: 6 days ago

Hello Hyeontak,

If you want to capture how the air pressure is affected by the (presumably small) change in the volume occupied by the air due to the deformation of the cube, without including the space occupied by the air in your geometry, consider using the method based on Gauss's theorem (a.k.a. the divergence theorem), which is discussed in this Discussion Forum thread and this blog post.

If not, things are simpler. Your idea of applying a pressure on the internal boundaries of the cube is correct although I would remove the volume occupied by the air from the model and use a "Heat Transfer in Solids" physics interface. I would imagine that the temperature of the air can be considered uniform within the cavity and equal to the temperature of the inner walls of the container, so I would use that temperature in the formula for the pressure on the inner walls.

Other than that, make sure that you have sufficient constraints to remove all 6 rigid body motions, and you should be all set.

Best,

Jeff

-------------------
Jeff Hiller

Hyeontak Kim

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Posted: 6 days ago

Updated: 6 days ago

Hello Hyeontak,

If you want to capture how the air pressure is affected by the (presumably small) change in the volume occupied by the air due to the deformation of the cube, without including the space occupied by the air in your geometry, consider using the method based on Gauss's theorem (a.k.a. the divergence theorem), which is discussed in this Discussion Forum thread and this blog post.

If not, things are simpler. Your idea of applying a pressure on the internal boundaries of the cube is correct although I would remove the volume occupied by the air from the model and use a "Heat Transfer in Solids" physics interface. I would imagine that the temperature of the air can be considered uniform within the cavity and equal to the temperature of the inner walls of the container, so I would use that temperature in the formula for the pressure on the inner walls.

Other than that, make sure that you have sufficient constraints to remove all 6 rigid body motions, and you should be all set.

Best,

Jeff

Hello Jeff, I'm so appreciate for your apply.

I think that I would better simulate my model step by step. As you said, I would make constraints to remove all 6 rigid body motions. I didn't do that at first, and the resulting graphics position was weird every time with error. Also, it looks much easier to remove the aire in the cube and use a "Heat Transfer in Solids" physics. But I wonder which boundary of the cube should be set in the constraint. In real experiment, the cube is hanged and doesn't attached to any surfaces. Which constraint is proper for my model?

Someday, I want to consider the effects of cube deformation, change of air pressure and interaction between those. I'm sure that blog post you recommended will be helpful for my model.

Thank you very much, Jeff.

Best,

Hyeontak Kim

>Hello Hyeontak, > >If you want to capture how the air pressure is affected by the (presumably small) change in the volume occupied by the air due to the deformation of the cube, without including the space occupied by the air in your geometry, consider using the method based on Gauss's theorem (a.k.a. the divergence theorem), which is discussed in [this Discussion Forum thread](https://www.comsol.com/forum/thread/317481/how-to-calculate-the-volume-of-a-hole-inside-an-axisymmetric-2d-domain?last=2023-01-25T14:54:09Z) and [this blog post](https://www.comsol.com/blogs/computing-controlling-volume-cavity). > >If not, things are simpler. Your idea of applying a pressure on the internal boundaries of the cube is correct although I would remove the volume occupied by the air from the model and use a "Heat Transfer in Solids" physics interface. I would imagine that the temperature of the air can be considered uniform within the cavity and equal to the temperature of the inner walls of the container, so I would use that temperature in the formula for the pressure on the inner walls. > >Other than that, make sure that you have sufficient constraints to remove all 6 rigid body motions, and you should be all set. > >Best, > >Jeff Hello Jeff, I'm so appreciate for your apply. I think that I would better simulate my model step by step. As you said, I would make constraints to remove all 6 rigid body motions. I didn't do that at first, and the resulting graphics position was weird every time with error. Also, it looks much easier to remove the aire in the cube and use a "Heat Transfer in Solids" physics. But I wonder which boundary of the cube should be set in the constraint. In real experiment, the cube is hanged and doesn't attached to any surfaces. Which constraint is proper for my model? Someday, I want to consider the effects of cube deformation, change of air pressure and interaction between those. I'm sure that blog post you recommended will be helpful for my model. Thank you very much, Jeff. Best, Hyeontak Kim

Ed Gonzalez COMSOL Employee

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Posted: 5 days ago

Hi, Since version 6.2 you can add "enclosed cavities" inside solid domains, thus simplifying the workflow, see Fluid Filled Cavities under https://www.comsol.com/release/6.2/structural-mechanics-module .

Hyeontak Kim

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Posted: 5 days ago

Hi, Since version 6.2 you can add "enclosed cavities" inside solid domains, thus simplifying the workflow, see Fluid Filled Cavities under https://www.comsol.com/release/6.2/structural-mechanics-module .

Hi, Gonzalez. Thanks for your advice! I'll try that feature after update my COMSOL to version 6.2 :)

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pressure load by air expansion in cube

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