Abaqus Keywords Reference Guide  
How to find keyword examples

*SPECTRUM
Define or create a response spectrum.

This option is used to convert a dynamic event into a spectrum to be used in a *RESPONSE SPECTRUM analysis. You can define a spectrum using values of S as a function of frequency and damping or create a spectrum from a user-specified amplitude that describes a dynamic event.

Products: Abaqus/Standard  Abaqus/CAE  

Type: Model data

Level: Model  

Abaqus/CAE: Amplitude toolset; supported only for defining a spectrum.

References:


Defining a spectrum using values of S as a function of frequency and damping

Required parameter:

NAME

Set this parameter equal to a label that will be used to refer to the spectrum. This label is used to cross-reference a spectrum on the *RESPONSE SPECTRUM option.

Optional parameters:

G

Set this parameter equal to the value of the acceleration of gravity. This parameter is used only when TYPE=G is specified.

INPUT

Set this parameter equal to the name of the alternate input file containing the data lines for this option. See “Input syntax rules,” Section 1.2.1 of the Abaqus Analysis User's Guide, for the syntax of such file names. If this parameter is omitted, it is assumed that the data follow the keyword line.

TYPE

Set TYPE=DISPLACEMENT, TYPE=VELOCITY, or TYPE=ACCELERATION (default) to define the units in which the spectrum is defined.

Set TYPE=G to enter an acceleration spectrum in g-units. The parameter G then defines the gravitational acceleration.

Date lines to define a spectrum using values of S as a function of frequency and damping: 

First line:

  1. Magnitude of the spectrum.

  2. Frequency, in cycles per time, at which this magnitude is used.

  3. Associated damping, given as ratio of critical damping.

Repeat this data line as often as necessary to define the spectrum at all frequencies at each damping value.


Creating a spectrum from a user-specified amplitude

Required parameters:

CREATE

Use this parameter to invoke spectrum building from a dynamic event provided by the user specified amplitude.

AMPLITUDE

Set this parameter equal to an amplitude name that describes the dynamic event used to create the spectrum.

NAME

Set this parameter equal to a label that will be used to refer to this created spectrum. This label is used to cross-reference a spectrum on the *RESPONSE SPECTRUM option.

TIME INCREMENT

Set this parameter equal to the time increment for implicit time integration scheme used to build this spectrum.

Optional parameters:

G

Set this parameter equal to the value of the acceleration of gravity. This parameter is used when TYPE=G or EVENT TYPE=G is specified.

TYPE

Set TYPE=DISPLACEMENT, TYPE=VELOCITY, or TYPE=ACCELERATION (default) to define the units in which the spectrum is created.

Set TYPE=G to create an acceleration spectrum in g-units. The parameter G then defines the gravitational acceleration.

ABSOLUTE

This parameter is only relevant for acceleration spectrum. Use this parameter to request creation of absolute acceleration spectrum (default, if both ABSOLUTE and RELATIVE parameters are omitted).

RELATIVE

This parameter is only relevant for acceleration spectrum. Use this parameter to request creation of relative acceleration spectrum.

DAMPING GENERATE

Use this parameter to request generation of the list containing the fraction of critical damping for which spectra will be created.

EVENT TYPE

Set EVENT TYPE=DISPLACEMENT, EVENT TYPE=VELOCITY, or EVENT TYPE=ACCELERATION (default) to define the units in which the amplitude is defined.

Set EVENT TYPE=G to enter an acceleration amplitude in g-units. The parameter G then defines the gravitational acceleration.

FILE

Set this parameter equal to the name of the alternate output file containing the created spectrum data. Each line of this data file will contain magnitude of the spectrum, frequency, in cycles per time, at which this magnitude is used, and associated damping, given as ratio of critical damping. See “Input syntax rules,” Section 1.2.1 of the Abaqus Analysis User's Guide, for the syntax of such file names. If this parameter is omitted, it is assumed that the created spectrum can only be used in a subsequent response spectrum procedures of the same or restarted job.

Data lines to create a spectrum from a user-specified amplitude: 

First line:

  1. Lower limit of the frequency range, in cycles per time, at which the spectrum will start.

  2. Upper limit of the frequency range, in cycles per time, at which the spectrum will end.

  3. Total number of points in the frequency range at which the spectrum value is requested, including the end points. The minimum value is 2. If the value given is less than 2 (or omitted), the default value of 2 points is assumed.

Second line if the DAMPING GENERATE parameter is omitted:

  1. List of damping values (fraction of critical damping).

Second line if the DAMPING GENERATE parameter is included:

  1. Starting value of the fraction of critical damping.

  2. End value of the fraction of critical damping.

  3. Increment of the fraction of critical damping.