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Define a function like Linear elastic-perfectly plastic behavior.

Posted 3 mar 2013, 11:10 GMT-5 Materials Version 4.3 4 Replies

Mahmood Mamivand
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How can I define a load which increase linearly up to time t0 and then stay fix by time.
I defined something like "F*(rm1(t<t0)+step1(t))" which step function location is time t0. the only section which I do not know if it works or not is the Ramp section. I want a ramp function which goes from 0 to 1 in time domain of 0 and t0 and after t0 ramp function become zero.
4 Replies Last Post 4 mar 2013, 10:13 GMT-5
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 3 mar 2013, 12:24 GMT-5
Hi

you could combine a ramp1() with cut-off at 1 and slope 1/t0 and a step1() (from 1 to 0 at t0) and adapt the transition regions to make it nicely smooth.

Then check your time stepping to intermediate and assure enough time steps during the ramp, and at the turn down from 0 to 1 (you can combine several range(,,) 'es

--
Good luck
Ivar
Hi you could combine a ramp1() with cut-off at 1 and slope 1/t0 and a step1() (from 1 to 0 at t0) and adapt the transition regions to make it nicely smooth. Then check your time stepping to intermediate and assure enough time steps during the ramp, and at the turn down from 0 to 1 (you can combine several range(,,) 'es -- Good luck Ivar
Mahmood Mamivand
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Posted: 1 decade ago 3 mar 2013, 12:46 GMT-5
Thank you Ivar
Does my definition for ramp with cut of at t0 is correct? (ramp1(t<t0))
Thanks
Mahmood
Thank you Ivar Does my definition for ramp with cut of at t0 is correct? (ramp1(t
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 3 mar 2013, 14:46 GMT-5
Hi

I would suggest NOT to use Booleans as these make sharp non-continuous transitions and then the solver has issues how to handle these. If you are in v4 check all the tabs and features of the Definitions Functions ramp1(...) you define the slope as 1/t0 (t0 is a Parameter you have defined ) and you limit at "1" (check on) and then you adjust the ansition times. Use the "plot" button to llok at the shape. You then call it with F0*ramp(t[1/s]) where F0 is a Parameter wit the amplitude of the ramp

--
Good luck
Ivar
Hi I would suggest NOT to use Booleans as these make sharp non-continuous transitions and then the solver has issues how to handle these. If you are in v4 check all the tabs and features of the Definitions Functions ramp1(...) you define the slope as 1/t0 (t0 is a Parameter you have defined ) and you limit at "1" (check on) and then you adjust the ansition times. Use the "plot" button to llok at the shape. You then call it with F0*ramp(t[1/s]) where F0 is a Parameter wit the amplitude of the ramp -- Good luck Ivar
Mahmood Mamivand
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Posted: 1 decade ago 4 mar 2013, 10:13 GMT-5
Thank you so much.
Thank you so much.

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