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how can i create a transient analysis ?

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Old   December 4, 2007, 09:44
Default how can i create a transient analysis ?
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i would like to have a FSI 2way where the input will change pressure from 10 bar to 100 and then to 2000. the transient analysis will take 1 second , from the beginning the pressure will be 0 bar then until 0.3 second it will increase to 10 bar and it will stay there until 0.6 second, at the 0.6 the pressure will increase to reach the 2000 bar at second 1.

any help how to do the expressions?

thanks in advance
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Old   December 4, 2007, 15:15
Default Re: how can i create a transient analysis ?
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where do you plan to implement this transient pressure effect ? i.e. at inlet/outlet?

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Old   December 4, 2007, 16:40
Default Re: how can i create a transient analysis ?------W
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You can either create an expression for the changes using step functions, or create a 1D function in Pre with the values and use this for your boundary condtion. The 1D function will interpolate between points, so you may need to put two points close together to get a sharp change at 0.3 and 0.6 seconds (i.e. 0 [bar] at .29 [s] and 10 [bar] at 0.3 [s]. The step function would look like this:

Pinlet = 10 [bar] * step((t-0.2999 [s])/1[s]) + (2000 [bar] - 10 [bar]) * step((t-0.5999 [s])/1[s])

The step() function takes a non-dimensional argument (hence dividing by 1 [s]) and evalues to 0 if the operand is negative, 0.5 if it is equal to zero, and 1 if it is positive.

Just be careful about having sudden changes in pressure like this. It's actually quite non-physical, so using the 1D function and leaving a little more time between pressure increments may yield better results.

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