# Frequency Analysis

The DSHplus Frequency Spectrum (FFT), the DSHplus Frequency Analysis and the DSHplus Order Analysis are three core modules of the DSHplus Virtual Engineering Lab's postprocessing functionality.

The DSHplus Frequency Spectrum computes the representation of a time-domain signal in the frequency domain. The frequency spectrum can be generated via a Fourier transformation of the signal. Baron Jean Baptiste Fourier showed that any waveform that exists in the real world can be generated by adding up sine waves. A major use of the frequency domain is to resolve small signals at certain frequencies in the presence of large ones at other frequencies. The DSHplus Frequency Spectrum is integrated into the DSHplus online graphic. The frequency spectrum is computed immediately after the simulation run stopped.

The DSHplus Frequency Analysis Module computes the frequency response of a system. The transfer function is subsequently displayed in a Bode-diagram depicting amplitude and phase shift. There are two methods available to calculate the mean value of the spectrum the Root-Mean-Square method (RMS) and the Peak-Hold method. If the raw data are contaminated with noise the DSHplus Frequency Analysis Module offers different cross correlation functions in order to identify the usable signal and computes the coherence value of the two signals. By means of two boundary lines a data interval suitable for the calculation can be chosen. If the data is not periodic a weighting function - such as Hanning or Blackman Harris - can be assigned to improve the calculation.

By means of the parameter block size and percentage of the blocks overlap the DSHplus Frequency Analysis Module it able to perform a sliding window analysis of the data.

The calculated frequency data can be stored to a file, including also complex power spectrum values of input and output. The Bode-diagram can be printed or copied. Input or output of the frequency analysis may be any variable in the simulation model or measurement data that has been imported into DSHplus.

The DSHplus Order Analysis computes a spectrogram. The horizontal axis represents time or rpm, the vertical axis is frequency. The third dimension indicating the amplitude of a particular frequency at a particular time is represented by a color of each point in the image. As representation of the spectrogram a top view or a rotatable 3D surface is available. If the excitation is linear increasing with time, individual frequency orders can be extracted from the signal.