Theoretic Research On Simulated Modal Test And Analysis Of The Ultra-shallow Wave-shock Two-Phase Character

The paper introduces the theory of modal test and analysis(MTA) into the field of ultra-shallow seismic prospecting by elastic wave. Combined with the wave motion principle of shallow seismic exploration, mixed together with the shock response character of medium and structure and the dynamic response character of the wave propagation, the basic theory of the simulated modal test and analysis(SMTA) of the two-phase wave-shock character of ultra-shallow elastic wave by effective excitation was theoretically founded. From the view angle of system analysis, based on the definition of General Background of Geophysical Prospecting, synthesizing the prospecting instrument and equipment, methods, non-linear reversion theory and relevant contemporary techniques and the theory of digital signal and digital image processing, it made a somewhat comprehensive analysis on the method of SMTA and anomaly reversion and explanation, which has broken through those theory and method followed closely the heel of the traditional seismic survey and will lead new principle and technique for ultra-shallow elastic wave prospecting by SMTA methods.Firstly, the paper gives a brief introduction on the present research situation of the shallow to ultra-shallow seismic prospecting at home and broad. Systematic comparing and analysis is made between Geophysical exploration system and the theory of modal test and analysis, which shows the relationship of the two fields and the research situation of the relevant problems. The specific research goals are pointed out in the end of this chapter.Based on the theory of modal test and analysis, a systematical modal of mass-spring-damping was imported and the simulated modal test and analysis theory of the two-phase wave-shock character of ultra-shallow elastic wave by effective excitation was built up. Combined with the detailed theoretical analysis of the special modal character of directly arrived wave, Rayleigh surface wave, wave response of the thinning-out layered structure or other special structuresuch as cavities, it shows that the simulated modal test and analysis is a synthetic system. The main four classes of the system were also stated respectively.Associated with the practice of seismic prospecting, detailed analysis was given to related effective excitation and high-fidelity detecting of simulated signals in the third chapter. It contains wave-excited source introduction, effective excitation, the frequency character analysis of the ordinary transducer and the whole system and equipment for the signal collection.On the view of system analysis, the next chapter is focus on the discussing of the basic theory of General Background of Geophysical Prospecting and abnormal phenomena distinguishing. Based on the four classes of simulated modal test system, integrated with wavelet analysis and short-time Fourier transformation, the paper introduced the foundation problem of thin-sheet response analysis and simulated modal energy group analysis. Meanwhile, based on Radon transformation theory, the paper showed the basic principle of the technique of the simulated modal image distinguishing. Furthermore, by the construction of the mapping system in the processing and explanation of the simulated modal signal, the non-linear character of the simulated modal response and the necessary of building up a non-linear reversing system were stressed. In the end, the operating idea of leading BP artificial neural network into the practice of the simulated modal test and analysis was presented.Conclusion summarized not only the main contribution and the pioneering work in elastic wave prospecting and inspect, but also the defect in both theoretical research and technology research. The follow-up research items were forecasted in the end of this paper.