Learning Forum

[Laure]

Hello Ansys community,
I am creating a 3D model in DesignModeler. The model comprises a cuboid (tank) with a thin cylinder (heat source) inside the cuboid. First, I drew the shorter face of the cuboid and extruded it. Then, I drew a circle inside the rectangle and extruded it to create the thin cylinder (I selected "Slice material" on the operation tap). Since the cylinder needs to be 1 m from the centre of the cuboid, I used the "Translate" option to move the cylinder in the Z direction. I am attaching an image of the model for clarification.
In Mechanical, I created the mesh, assigned BC, and heat flux to the cylinder. When I run the simulation, there is not heat transfer from the cylinder to cuboid. However, if I leave the cylinder in the centre of the cuboid (no translation) heat transfer works ok. 
Could you please guide me on the correct way to build the thin cylinder inside the cuboid? Thanks in advance.

[NickFL]

What you have to be sure to have is an interface between the cylinder and the cuboid. In the computer these can occupy the same volume, but physically they cannot. My approach would be as follows:
1. Draw the rectangle and create the cubes.
2. Draw cirlce (or rectangle if you want to use revolve) and create the cylinders.
3. Use a Boolean operation to cut the cylinder from the cuboid.
4. (if you want a congruent mesh) Put them in a multibody part.

Using the above approach, Mechanical should pick up the contact between the bodies. If not you can create the contacts manually.

[Laure]

Thank you NickFL,

I reckon that using Extrude or Boolean operations can both do the cut and create the interfaces (using the "slide" option in extrude and "substract" in boolean). The problem is when I want to move the cylinder to the desired position inside the cuboid. Yesterday, I created a new plane at the position where the cylinder should be located and it worked. However, if I need to include more cylinders in other positions, I may need to add as many planes as cylinders are required. So the task will become quite repetitive.

Wonder if there is another way to add sub-bodies in specificic positions (not at the centre of the XY plane) inside a main body?

  

[peteroznewman]

Laure, if the cylinders are in a rectangular or circular pattern, then Create > Pattern can take one cylinder and make as many copies as there are in the pattern.  As NickFL said, use a Boolean to subtract the pattern from the tank and finish up selecting all the bodies and Form New Part.

[Laure]

Hi all.
Thank you Peter. I will try this today.
I just generated my first mesh I got an error regarding size limit. I am using the student version 2022 R2 and according to the version features the maximum number of elements allowed to this version is 128 K. In my mesh I have 123,720 elements and 36,304 nodes. Do I have to consider the sum of elements and nodes in this limit?

Thanks in advance.

 

[NickFL]

Based on my understanding, it will be limited by the number of nodes in Mechanical and in Fluent I believe it is the elements. I have a Research license so I cannot test it out myself. My understanding was false.

 

[peteroznewman]

Hi Laure, the Student license limit of 128K is based on the highest node or element number in the Mechanical model. This includes elements that are created automatically for you such as Contact elements, so it is not just the elements you can see in the mesh. Sometimes, there is a gap in the element numbering so the Statistics on the number of elements in the model is a smaller number than the highest element number. You can insert a Numbering(?) object under the Mesh and force it to renumber the mesh to eliminate gaps.

In Fluent, the Student license limit is 512K nodes or cells. Fluent can compute heat transfer for solids as well as fluids, but it's a whole different interface.

[Laure]

Thanks Peter / NickFL,

I may need then to migrate my model to Fluent since I will need to increase the model size later, so the number of elements will be higher if I keep the same resolution.

[peteroznewman]

Hi Laure, if your geometry, loads and boundary conditions have a plane of symmetry, you can cut your model size in half.

[Laure]

Hi Peter,
I will start the simulation using constant properties (e.g., density and thermal conductivity of soil), but later I will need to input a cuboid of heterogeneous properties (btw, no idea how to input such a cuboid!!!), so the element of symmetry won’t work. Thanks anyway.