freqrespΒΆ

Purpose:

Compute frequency response of a known discrete time response.

Syntax:
[Freq, Resp] = freqresp(D, dt)
Description:

freqresp computes the frequency response of a discrete dynamic system.

  • D is the time history function.

  • dt is the sampling time increment, i.e., the time increment used in the time integration procedure.

  • Resp contains the computed response as a function of frequency.

  • Freq contains the corresponding frequencies.

Example:

The result can be visualized by:

plot(Freq, Resp)
xlabel('frequency (Hz)')

or:

semilogy(Freq, Resp)
xlabel('frequency (Hz)')

The dimension of Resp is the same as that of the original time history function.

Note

The time history function of a discrete system computed by direct integration often behaves in an unstructured manner. The reason for this is that the time history is a mixture of several participating eigenmodes at different eigenfrequencies. By using a Fourier transform, however, the response as a function of frequency can be computed efficiently. In particular, it is possible to identify the participating frequencies.