Based on the mathematical analysis of band transmission signal coherent detection theory and mud pressure DPSK signal modulation process, by establishing the coherent detection mathematical model of mud pressure DPSK signal, this paper studies the practicability of broadband mud pressure DPSK signal coherent detection. By analyzing the noise impact on input signal parameter of demodulation system, based on probabilistic statistics theory and coherent demodulation mathematical model, the bit error rate and antinoise ability of mud pressure DPSK signal is studied. Theoretical analysis and numerical simulation indicate that, by adding arc cosine and derivation segment to basic demodulation process, the coherent demodulation effect of mud pressure DPSK signal is satisfied, but the demodulation process is more complex than conventional communication system. Theoretical analysis shows that mud pressure DPSK signal has the same theatrical bit error rate as conventional communication binary phase shift keying (2PSK) signal, but due to the difference of signal demodulation means, the reconstruction of rotary valve control pulse will be affected seriously by the derivate of vertical component of the noise within frequency band, causing that the antinoise ability of mud pressure DPSK signal demodulation system is far lower than 2PSK signal system, and numerical calculation shows that the actual bit error rate is far higher than latter; so under the condition of large carrier frequency, to obtain relative small actual bit error rate and relative larger information transmission rate, the mud pressure DPSK signal input signal-to-noise ratio should be raised as far as possible.

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The load characteristic analysis of permanent magnet synchronous generator is presented. An internal impedance mathematic model of the generator was built with phasor analysis method for analyzing the relationship between exterior voltage characteristic or voltage regulation rate, active power and armature reactance. The research results demonstrated that the internal impedance of generator has both current and power factor angle negative feedback characteristic, which makes the voltage regulation rate be improved to a certain extent and the improved effect lying on both the direct-axis armature reactance under condition of an inductive load and the quadrature-axis armature reactance under resistive load. Additionally, an optimal range of the armature reactance being of less voltage regulation rate was determined according to numerical calculation and analysis. An experimental result based on the experimental measurement and data analysis of exterior voltage characteristic corresponds to the theoretical calculation demonstrated the correctness of the research model based upon the armature reaction analysis. Those can provide the theoretically guidance to the electromagnetic design of permanent magnet generator.

In the process of detecting leak hole in pipeline by intelligent pig with eddy current measuring method, the cut off effect of eddy current field in the closed cross section of leak hole in steel plate is weak due to geometric deformation of eddy current on the edge of the hole produced by destroyed drilling. As a result, the measured signal is very unobvious. Meanwhile, owing to the rough surface of steel plate, the periodic interference generated by movement of the detecting probe cannot be eliminated or be inhibited easily by conventional signal processing methods for its large amplitude and approximate frequency band with the leak hole signals, the signal to noise ratio (SNR) of measured signal is very low and the accurate identification of leak hole cannot be guaranteed. The wavelet transform, with characteristics of time-frequency localization and multiple scales, is a useful and effective method for identifying singularity of the signals and adapts to detect the transient signal or extract non-stationary information in the signals with strong periodic interference and noise. The reconstructing signal SNR will be increased greatly in eddy current detecting of leak hole in the pipeline with wavelet packet analysis of the signal by constructing the self-defined cost function based on maximum SNR to obtain optimal wavelet packet basis function. This ensures good detection and location of leak hole in the pipeline.

The primary energy losses of electric submersible pump (ESP) are waterpower loss and volumetric loss. Owing to the limit of current casting technique of the ESP impeller, some fractions of casting residua will be settled in the flow passage of impeller and cause local jam-up in the flow passage, which will increase additional waterpower loss and reduce the pump efficiency. Because of the complicated structure of ESP impeller, conventional nondestructive testing (NDT) is difficult to inspect the defects fast and efficiently. Fluid energy analysis method based on the boundary layer theory and the flow resistance theory analyzes the fluid kinetic energy loss caused by obstacles in the flow passage of impeller and the change of flow rate caused by the change of flow resistance. Based on the similarity principle of fluid movement, abnormal change of waterpower construction in flow passage of impeller can be reflected by measuring and analyzing the impact pressure change generated by flow rate of each flow passage using air as flow medium. The theoretic analysis and experimental results show that this method can identify the defective impeller quickly, efficiently and correctly and will be of some revelatory action on measuring the waterpower structure change of complicated impeller machinery with small size.