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## Postprocessing in cyclindrical coordinates

Posted Feb 6, 2013, 3:50 PM EST Heat Transfer & Phase Change, Structural Mechanics & Thermal Stresses Version 4.3a 12 Replies

I am doing a plane strain analysis of a pipe with a crack in it.

I would like to get the stress components in the cyclindridcal coordinate system (radial, hoop stress) rather than in the cartesian coordinate system (x & y stress components).

There seems to be do obvcious way of doing this.

Is there anyone who can suggest something?

Thanks,

--

Arthur Rupel

This is the way to do it:

1. Add a cylindrical coordinate system with suitable axis directions under Definitions.

2. Select that system in the Linear Elastic feature.

3. Solve

4. Plot local stress tensor components ("Stress tensor, local coordinate system")

Regards,

Henrik

There is no problem in defining the cyc coord in definitions. However I cannot find anyway of stating this with the material properties that I am using. This is not a linear elastic material.

Thanks

Arthur Rupel

You still have a Linear Elastic node (where you set Young's Modulus etc.) to which Plasticity is a sub-node in the model tree. In Linear Elastic there is a coordinate system setting even if the plasticity is isotropic.

Regards,

Henrik

In the linear elastic option, the only coordinate system allowed in the global. There does not seem to be a way of changing this.

When I try to plot r, theta stresses in the cyclindrical system, all I get are the x & y stresses-even in the changed local system.

There has to be a way for results to see that I want cyclindrical stresses, but I cannot find it.

Thanks,

--

Arthur Rupel

When you define user coordinate systems, COMSOL defines the transformation matrix, and its inverse, so you can use these also directly (see the doc) COMSOL remains in the Cartesian x,y,z coordinate system, so you need to apply these transforms manually to the Results section, f you need to map back

--

Good luck

Ivar

I defined the cyclindrical coordinate system in definitions.

In the linear elastic option, the only coordinate system allowed in the global. There does not seem to be a way of changing this.

The reason is that only coordinate systems which belong to the material frame can be selected for the material definition. So if you change the setting in the coordinate system from Spatial to Material, then it will show up.

Regards,

Henrik

This may be something other people should note.

--

Arthur Rupel

Hi,

This is the way to do it:

1. Add a cylindrical coordinate system with suitable axis directions under Definitions.

2. Select that system in the Linear Elastic feature.

3. Solve

4. Plot local stress tensor components ("Stress tensor, local coordinate system")

Regards,

Henrik

About the fourth step "Plot local stress tensor components ("Stress tensor, local coordinate system")", I got a question: when I choose the "Stress tensor(Spatial)", I got the same plots compare with the "Stress tensor, local coordinate system". But "Stress tensor(Spatial)" seems to be defined according to the Cartesian coordinate system. How can I get the stress tensor of Cylindrical system component?

Thanks,

Fan shuyu

Hi,

This is the way to do it:

1. Add a cylindrical coordinate system with suitable axis directions under Definitions.

2. Select that system in the Linear Elastic feature.

3. Solve

4. Plot local stress tensor components ("Stress tensor, local coordinate system")

Regards,

Henrik

About the fourth step "Plot local stress tensor components ("Stress tensor, local coordinate system")", I got a question: when I choose the "Stress tensor(Spatial)", I got the same plots compare with the "Stress tensor, local coordinate system". But "Stress tensor(Spatial)" seems to be defined according to the Cartesian coordinate system. How can I get the stress tensor of Cylindrical system component?

Thanks,

Fan shuyu

Hi,

The "Stress tensor(Spatial)" is as you say oriented along the global Cartesian coordinate system, whereas the "Stress tensor, local coordinate system" has orientations determined by the coordinate system selection in the Linear Elastic node.

Note that "Step 3: Solve" is not strictly necessary if the material is isotropic, and you just want to change the display directions for "Stress tensor, local coordinate system". It is then sufficient to instead do an "Update solution" for the study.

Regards,

Henrik

Fan shuyu

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