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Can we model this creep in COMSOL?

Posted Oct 7, 2013, 8:23 a.m. EDT Heat Transfer & Phase Change, Materials, Structural Mechanics 4 Replies

Anuj Kumar Deo
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I am having a pressurized cylinder with a temperature variation along the length which is increasing with time. I want to include the creep equations as in the attached file. There is an integration term in the equation. All the elements do not reach 1123 K at the same time, plz advice how to do it?

Warm Regards

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4 Replies Last Post Oct 7, 2013, 11:59 p.m. EDT
Nagi Elabbasi Facebook Reality Labs
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Posted: 1 decade ago Oct 7, 2013, 9:13 a.m. EDT
Dear Anuj,

It’s not a built in creep model obviously, but you should be able to implement it as a User defined creep expression. The difficulty is in the time integral part in the denominator of the second creep term. It’s only a function of temperature and time so if the temperature is predefined you can predefine that integral as well. If not then you should setup that equation as an ODE that COMSOL solves for simultaneously with the other solution variables, and use that equation in the user defined creep expression.

Nagi Elabbasi
Veryst Engineering
Dear Anuj, It’s not a built in creep model obviously, but you should be able to implement it as a User defined creep expression. The difficulty is in the time integral part in the denominator of the second creep term. It’s only a function of temperature and time so if the temperature is predefined you can predefine that integral as well. If not then you should setup that equation as an ODE that COMSOL solves for simultaneously with the other solution variables, and use that equation in the user defined creep expression. Nagi Elabbasi Veryst Engineering
Anuj Kumar Deo
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Posted: 1 decade ago Oct 7, 2013, 12:27 p.m. EDT
Dear Nagi,

Thanks for the prompt reply.
As all the elements are not going to reach temperature = 1123 K at one time, won't it be true that we need to know the history of each element?
In programming (such as fortran) we can make a counter so that as soon as an element temperature reaches 1123 K, it will calculate the integral term also (here the integral is t-t1 or dt multiplied by other constants,) and keep on adding for each small time step.

I don't know how to do that here in COMSOL. Could you plz give some hints or refer me to some examples?

Warm Regards
Anuj
Dear Nagi, Thanks for the prompt reply. As all the elements are not going to reach temperature = 1123 K at one time, won't it be true that we need to know the history of each element? In programming (such as fortran) we can make a counter so that as soon as an element temperature reaches 1123 K, it will calculate the integral term also (here the integral is t-t1 or dt multiplied by other constants,) and keep on adding for each small time step. I don't know how to do that here in COMSOL. Could you plz give some hints or refer me to some examples? Warm Regards Anuj
Nagi Elabbasi Facebook Reality Labs
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Posted: 1 decade ago Oct 7, 2013, 2:17 p.m. EDT
Dear Anuj,

There is no “counter” option in COMSOL as far as I know. However, you can setup a domain level differential equation for that variable as I described earlier. That way COMSOL will have a value for that variable at each point in the material. You will find a lot of COMSOL material on how to do this if you search for Equation Based Modeling, including this recent webinar: www.comsol.com/video/equation-based-modeling-custom-simulations-comsol-multiphysics .

Nagi Elabbasi
Veryst Engineering
Dear Anuj, There is no “counter” option in COMSOL as far as I know. However, you can setup a domain level differential equation for that variable as I described earlier. That way COMSOL will have a value for that variable at each point in the material. You will find a lot of COMSOL material on how to do this if you search for Equation Based Modeling, including this recent webinar: http://www.comsol.com/video/equation-based-modeling-custom-simulations-comsol-multiphysics . Nagi Elabbasi Veryst Engineering
Anuj Kumar Deo
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Posted: 1 decade ago Oct 7, 2013, 11:59 p.m. EDT
Thank you Nagi,

I will do that.

Warm Regards
Thank you Nagi, I will do that. Warm Regards

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