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Time taken to reach steady state

Posted 11 sept. 2015, 05:55 UTC−4 3 Replies

Matt James
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Hi all,

I have a heat transfer problem, and I want to look at the transient development and then know how long it takes before it reaches steady state. Is there a way to tell Comsol to run until the steady state condition is met, or do I have to just let it run for an arbitrary time and then deduce when steady state was reached?

Thanks
3 Replies Last Post 5 oct. 2015, 16:48 UTC−4
Andrew Young COMSOL Employee

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Posted: 9 years ago 11 sept. 2015, 07:21 UTC−4

Hi all,

I have a heat transfer problem, and I want to look at the transient development and then know how long it takes before it reaches steady state. Is there a way to tell Comsol to run until the steady state condition is met, or do I have to just let it run for an arbitrary time and then deduce when steady state was reached?

Thanks


Hi Matt,

Thanks for posting in the Forum! COMSOL does indeed have a way to stop a time dependent solution when a certain criteria is reached, however you must first define what this condition is. To do this a number of tools may be required, and it is difficult to know which are needed without seeing your model file.

If you upload it via the "Attach File" button when replying, I can have a look and make the relevant changes for you? You can even send a simplified model if you have any IP sensitive geometries! This way you can see the steps needed and apply them to your current model.

Thanks,
Andrew
[QUOTE] Hi all, I have a heat transfer problem, and I want to look at the transient development and then know how long it takes before it reaches steady state. Is there a way to tell Comsol to run until the steady state condition is met, or do I have to just let it run for an arbitrary time and then deduce when steady state was reached? Thanks [/QUOTE] Hi Matt, Thanks for posting in the Forum! COMSOL does indeed have a way to stop a time dependent solution when a certain criteria is reached, however you must first define what this condition is. To do this a number of tools may be required, and it is difficult to know which are needed without seeing your model file. If you upload it via the "Attach File" button when replying, I can have a look and make the relevant changes for you? You can even send a simplified model if you have any IP sensitive geometries! This way you can see the steps needed and apply them to your current model. Thanks, Andrew
Matt James
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Posted: 9 years ago 1 oct. 2015, 07:12 UTC−4
Hi Andrew,

Thanks for the help. Unfortunately I'm not allowed to send anything from my end, the company says so. Basically imagine you have a uniform block that's heated at one end and is cooled by an air flow. Eventually it will reach a steady state, I just want to know how long that takes. I hope that makes sense.

Thanks,

Matt
Hi Andrew, Thanks for the help. Unfortunately I'm not allowed to send anything from my end, the company says so. Basically imagine you have a uniform block that's heated at one end and is cooled by an air flow. Eventually it will reach a steady state, I just want to know how long that takes. I hope that makes sense. Thanks, Matt
Andrew Young COMSOL Employee

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Posted: 9 years ago 5 oct. 2015, 16:48 UTC−4

Hi Andrew,

Thanks for the help. Unfortunately I'm not allowed to send anything from my end, the company says so. Basically imagine you have a uniform block that's heated at one end and is cooled by an air flow. Eventually it will reach a steady state, I just want to know how long that takes. I hope that makes sense.

Thanks,

Matt


Hi Matt,

It's hard to say the best way to set this up without a little more detail, or what you want to use as the definition for steady state (i.e. a metric and a tolerance/cut off value). Attached to this post is a simple demo (as you have described above) utilising a Domain Probe which will is set up in the Component 1 > Definitions node to monitor (and plot while solving - see the Study 1 > Step 1: Time Dependent node) a defined metric, the average temperature in the domain.

In this example of a block of material with arbitrary material properties has been set up in a time dependent study and used a Convective Heat Flux boundary condition to account for convective cooling while one boundary is maintained at the initial temperature. Note a heat transfer coefficient and external temperature have been defined for the Heat Flux boundary condition.

To interrupt a study but retain the solution calculated up to that point, you can click the "Stop" buttons found in the Progress tab of the Messages Window. You can use the Probe Plot 1 to determine when to do so.

If you are able to provide a more specific description of the problem, perhaps with a generic geometry and material properties (as in this example), I should be able to provide more relevant and specific advice. Are you able to construct a demo without exposing any commercially sensitive material? Let me know how you get on with this model in the meantime!

Regards,

Andrew
[QUOTE] Hi Andrew, Thanks for the help. Unfortunately I'm not allowed to send anything from my end, the company says so. Basically imagine you have a uniform block that's heated at one end and is cooled by an air flow. Eventually it will reach a steady state, I just want to know how long that takes. I hope that makes sense. Thanks, Matt [/QUOTE] Hi Matt, It's hard to say the best way to set this up without a little more detail, or what you want to use as the definition for steady state (i.e. a metric and a tolerance/cut off value). Attached to this post is a simple demo (as you have described above) utilising a [b]Domain Probe[/b] which will is set up in the [b]Component 1 > Definitions[/b] node to monitor (and plot while solving - see the Study 1 > Step 1: Time Dependent node) a defined metric, the average temperature in the domain. In this example of a block of material with arbitrary material properties has been set up in a time dependent study and used a [b]Convective Heat Flux[/b] boundary condition to account for convective cooling while one boundary is maintained at the initial temperature. Note a heat transfer coefficient and external temperature have been defined for the Heat Flux boundary condition. To interrupt a study but retain the solution calculated up to that point, you can click the "Stop" buttons found in the [i]Progress[/i] tab of the Messages Window. You can use the Probe Plot 1 to determine when to do so. If you are able to provide a more specific description of the problem, perhaps with a generic geometry and material properties (as in this example), I should be able to provide more relevant and specific advice. Are you able to construct a demo without exposing any commercially sensitive material? Let me know how you get on with this model in the meantime! Regards, Andrew

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