They are electrical circuits controlled by switches to produce regulated outputs despite the load disturbances and power supply irregularities.
China Academy of Railway Sciences has studied on China's three main track irregularity power spectrums, and put forward the fitting function of the track irregularity power spectrum of the three main lines.
Furthermore, by contrasting Beijing Subway with national rail line, a proper function research has been done about track irregularity of Beijing Subway and the characteristics of track irregularity power spectral.
First, number theory method (NTM) with 2N-dimensional vectors for the stochastic harmonic function (SHF) of rail irregularity power spectrum density was adopted to determine the representative points of spatial frequencies and phases to generate the random rail irregularity samples, and the non-stationary rail irregularity samples were modulated with the slowly varying function.
It reflects the frequency distribution of the track vertical irregularity power spectrum density on the shaft of the power spectrum diagram.
In 1980s, according to six speed and track state level [2] based on the FRA Division of American Track Safety Standard, the U.S. laid down the track irregularity power spectrum.
According to the fitting curve of Beijing Subway and national railway, Beijing Subway irregularity power spectrum curve is mostly above the national railway.
China began the research in 1960s 1970s, Changsha Railway Institute and the Academy of Railway Sciences used the "Inertia Reference Method" [3] to measure the track irregularity, combined with ground testing and Inspection Car tracking and other different methods to analyze the track irregularity power spectrum.
In addition, based on the maximum entropy principle, the spectrum of track irregularity power spectral density which is short for PSD has been drawn using MATLAB and fitted by using a nonlinear least squares method.
Subway track irregularity power spectrum frequency is obviously increased in the curve amplitude between 0.5 and 1.0 Hz, indicating the need for better rail rolling technology and rail welding technology.
