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modelling of this mathematical equation

Posted Nov 12, 2011, 11:05 p.m. EST Studies & Solvers Version 4.2a 10 Replies

Ramandeep Saluja
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i want to implement mathematical equation for my model but i am not able to find any tutorial for it .so plz help.

dT/dt=k1/b(k2x-T(1+k2/k1)+A+bdx/dt).

in this T is the input i.e force and x is the elongation i.e output...rest all are constants.i was trying implementing this equation as ODE .
10 Replies Last Post Feb 14, 2013, 10:29 a.m. EST
Francois Gregoire
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Posted: 1 decade ago Nov 13, 2011, 11:36 a.m. EST
you should use a PDE Interface, either Coefficient or General Form PDE.

the right side of your equation will be the source term f, see the documentation.
you should use a PDE Interface, either Coefficient or General Form PDE. the right side of your equation will be the source term f, see the documentation.
Ramandeep Saluja
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Posted: 1 decade ago Nov 15, 2011, 10:28 p.m. EST
but right side of my equation has dx/dt which is also a function of time ...every time its showing error about that variable is undefined.because i have only 1 equation .where how can i define that variable
but right side of my equation has dx/dt which is also a function of time ...every time its showing error about that variable is undefined.because i have only 1 equation .where how can i define that variable
Krishnachaitanya S
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Posted: 1 decade ago Nov 16, 2011, 1:00 a.m. EST
I suppose u can impliment it as Xt on right side in the coefficent value f along with other variables and values ..
I suppose u can impliment it as Xt on right side in the coefficent value f along with other variables and values ..
Francois Gregoire
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Posted: 1 decade ago Nov 16, 2011, 1:53 p.m. EST
You want to solve for T or for x???
You want to solve for T or for x???
Ramandeep Saluja
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Posted: 1 decade ago Nov 16, 2011, 10:26 p.m. EST
T is my tension produced in the muscle and X is the elongation produced due to that tension ..i want to calculate 'X' i.e elongation in the muscle .
T is my tension produced in the muscle and X is the elongation produced due to that tension ..i want to calculate 'X' i.e elongation in the muscle .
Muhammad Mohsin Rehman
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Posted: 1 decade ago Dec 19, 2011, 2:13 a.m. EST
Hi Ramandeep,

Have you implemented your equation in COMSOL sussessfully?

Thanks.
Hi Ramandeep, Have you implemented your equation in COMSOL sussessfully? Thanks.
Ramandeep Saluja
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Posted: 1 decade ago Jan 9, 2012, 11:15 a.m. EST
sir

no its showing error everytime as time dependent solver....unknown function.....but i have mentioned each and every parameter.i think i am missing some step.can u plz guide.


details

i need to calculate x that is elongation produced in the muscle wrt force applied.i have used cylindrical geometry and meshed .materials i have mentioned is of viscoelastic material.then i m using coefficient form of PDE .
sir no its showing error everytime as time dependent solver....unknown function.....but i have mentioned each and every parameter.i think i am missing some step.can u plz guide. details i need to calculate x that is elongation produced in the muscle wrt force applied.i have used cylindrical geometry and meshed .materials i have mentioned is of viscoelastic material.then i m using coefficient form of PDE .
Francois Gregoire
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Posted: 1 decade ago Jan 9, 2012, 1:21 p.m. EST
Hi Ramandeep,

In the coefficient form PDE interface documentation, u is the dependent variable. Have you set up your equation in a way that your T is the dependent variable u in the doc?

You have to write your equation in a way that your dependent variable X is the u in the documentation. The terms with T will be in the source term f of the documentation.
Hi Ramandeep, In the coefficient form PDE interface documentation, u is the dependent variable. Have you set up your equation in a way that your T is the dependent variable u in the doc? You have to write your equation in a way that your dependent variable X is the u in the documentation. The terms with T will be in the source term f of the documentation.
Sirimala Chandrashekhar
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Posted: 1 decade ago Feb 14, 2013, 9:47 a.m. EST
you're refering to a documentation right ? where can I find this documentation ?
you're refering to a documentation right ? where can I find this documentation ?
Francois Gregoire
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Posted: 1 decade ago Feb 14, 2013, 10:29 a.m. EST
I'm working with Comsol 4.2a, the documentation I'm referring to is:

COMSOL Multiphysics User's Guide
Chapter 15: Equation-Based Modeling
Section: Coefficient Form PDE
I'm working with Comsol 4.2a, the documentation I'm referring to is: COMSOL Multiphysics User's Guide Chapter 15: Equation-Based Modeling Section: Coefficient Form PDE

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