Time and Amplitude in ABAQUS

I am recently using the dynamic analysis in Abaqus, so I decided to summarize the understanding of time and amplitude in it so that I can refer to this article later if needed.

Time

  • Step Time: the time period in *STEP definition.
  • Total Time: the sum of all the Step Time.
  • Natural time: actual time that one thing takes.
  • The time in Abaqus/Standard does not have any actual meaning, it can be understood as the relative time.
  • The time in Abaqus/Explicit is the actual time, that is the time that loads applied on the structure.

Amplitude definition

  • Select Step time for time that is measured from the beginning of each step.
  • Select Total time for total time accumulated over all non-perturbation analysis steps.

An example in ABAQUS

A steel frame loaded with one point load with the value 10, the Step time and Amplitude definition with Tubular is listed in the following table. The results of time and force are also listed.

Time in ABAQUS 1

The Point Load – Step time curve of the last circumstance is illustrated below. The point load is applied up to  5 times the defined load to structure instantly, the curve at point (0.01, 50.5) is just the 0.01 times the  defined load plus the  5 times the defined load.

Time in ABAQUS 2

It can be concluded that:

  1. Abaqus always analyzes the structure to the end of the step time.
  2. The time in Amplitude definition is the same meaning with step time and only the role of it is to definite the curve of applied force with the step time. 
  3. If you didn’t define the time before or after the time in Amplitude definition, the amplitude is considered the same with the closest time.

The conclusions accord with the explanation in Abaqus Analysis User’s Guide.

About the unit of time

You can use the International System of Units and the units derived from them for all the structure, that is

  • Length:               m                         (meter)
  • Mass:                  kg                        (kilogram) 
  • Time:                  s                           (second)
  • Force:                 N = kg*m/s2        (Nowton)
  • Pressure:           Pa = N/m2              (Pascal) 
  • Energy/Work:  J = N*m            (Joule)
  • Angle:                rad = m*m-1        (Radian)

If you set some units associated with time as a unit different from International Unit, then the unit of time in your analysis is the unite derived from your unites. (individual understanding)

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