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Combining different variables into one
Posted 09.07.2013, 04:38 GMT-4 Low-Frequency Electromagnetics, Heat Transfer & Phase Change Version 4.3b 1 Reply
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Hello all, i am quite new in the COMSOL world so i dont know all the possibilities that go with it and i would like to know if somebody can tell me how to combine expressions for different time steps in time dependent problems into one.
for example i want to use a smoothed step function from 0 to t1 and then from t1 to t2 a cosine function, so similar like the IF and ELSEIF operators in MATLAB. so again, form 0 to t1 i need to use one expression and from t2 to t3 another.
thank you in advance :)
for example i want to use a smoothed step function from 0 to t1 and then from t1 to t2 a cosine function, so similar like the IF and ELSEIF operators in MATLAB. so again, form 0 to t1 i need to use one expression and from t2 to t3 another.
thank you in advance :)
1 Reply Last Post 11.07.2013, 04:22 GMT-4
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Posted:
1 decade ago
Hi,
You can use an "if" function directly in COMSOL when defining a variable, material property, or PDE coefficient, for example:
if(t<t1,step1(t),cos(t))
means that COMSOL will use step1(t) (a smoothed step function that you have added to the model) from the simulation start time up until t1 and then switch to cos(t) (the cosine function, which is a built-in mathematical function). t1 is typically defined as a parameter.
You can also use a Boolean expression:
step1(t)*(t<t1)+cos(t)*(t>=t1)
which is equivalent, and can be expanded to additional "time segments." You may want to call the functions using t[1/s] to make the input unitless.
Best regards,
Magnus Ringh, COMSOL
You can use an "if" function directly in COMSOL when defining a variable, material property, or PDE coefficient, for example:
if(t<t1,step1(t),cos(t))
means that COMSOL will use step1(t) (a smoothed step function that you have added to the model) from the simulation start time up until t1 and then switch to cos(t) (the cosine function, which is a built-in mathematical function). t1 is typically defined as a parameter.
You can also use a Boolean expression:
step1(t)*(t<t1)+cos(t)*(t>=t1)
which is equivalent, and can be expanded to additional "time segments." You may want to call the functions using t[1/s] to make the input unitless.
Best regards,
Magnus Ringh, COMSOL