AMPLITUDE and STEP times

[gyom]

Dear forum members:

I would like to use AMPLITUDE command to define the "cyclic thermal loading". To simplify, let's assume that the range of the temperatures (daily basis) is between 0C and 15C. Note that I use degree centigrade to be consistent with SI units. My question is:
(a) How do I define the 'time' in my AMPLITUDE command?
(b) In STEP, the maximum time step was 1.0. Is there any relationship between AMPLITUDE 'time' and step 'time' mentione above? Should I use the same number (i.e., 1.0), or different number (i.e., 8hoursx3600s).

Thank you for your help.

gyom.

 

[bassmanjax]

Hi

Look at section 27.1.2 of the ABAQUS Users Manual - most of what you need to know is in there.

There is an option on the *AMPLITUDE keyword to define time in either step time or total time - TIME=STEP TIME and is the default. TIME=TOTAL TIME uses the total analysis time which is useful if you want an amplitude to span a number of steps. The time in the *AMPLITUDE definition needs be consistent with the time units in the analysis.

For example, if you want to increase the temperature linearly from 0-15 deg C over 1 hour, your amplitude curve would be;

*AMPLITUDE
0,0,3600,15

In your step definition, the step time would be 3600 seconds. This assumes that SI units are used for the material thermal properties and hence seconds are the unit of choice for time.

Regards

Martin

 

[bassmanjax]

Just to add to the above...

In an amplitude definition, the driven values are scaled. I have defined a curve that goes from 0 to 15, which means that on my thermal step, I would apply a temperature load of 1 deg C. This would then give a thermal load of 0 deg C at time t=0s (0 * 1 deg C) and a load of 15 deg C (1 * 15 deg C) at time t=3600s.

You could equally define a curve;

*AMPLITUDE
0,0,3600,1

and then define your temperature load as 15 deg C - the result would be the same.

Regards

Martin

 

[gyom]

Hi Martin (bassmanjax):

Thank you very much for your insightful comments and hints.

Regards,

gyom