Time-Frequency Characteristics of Fluctuating Pressure on the Bottom of the Stilling Basin with Step-Down Floor Based on Hilbert–Huang Transform

Table 1

Common signal processing methods.

Method	Merit	Defect
Fast Fourier transform	Complete theory and mature method	(1) Unable to extract local features from data
		(2) Not suitable for nonlinear and nonstationary data
		(3) Predetermined basis function
		(4) Fourier spectrum can only approximately reflect the actual situation
Wavelet transform	(1) Complete theory; methods mature	(1) Not suitable for nonlinear data
	(2) Nonstationary signals can be processed	(2) Need to define base functions in advance
	(3) Simultaneous energy-time-frequency information	(3) Intrawave frequency modulation cannot be given
	(4) Interwave frequency modulation can be given
Hilbert–Huang transform	(1) No requirements for data stability and nonlinearity	Incomplete theory belongs to empirical method
	(2) EMD decomposition does not require presupposition basis function
	(3) Simultaneous energy-time-frequency information
	(4) Instantaneous frequency has physical meaning and can reflect local characteristics of signal more accurately
	(5) Marginal spectra accurately reflect the actual situation