| As a simple and safe excitation source widely used in shallow seismic exploration,the excitation results of hammer source are mainly determined by the hammer and the base plate that used.Usually,the base plate is made of different materials such as aluminum alloy,chemicals(plastics)or iron to adapt to different working conditions.In this paper,we first studied the excitation principles of hammer source and made the conclusion that the excitation results of hammer sources are determined by the mass of the hammer,the impact velocity,the size and materials of the base plate.By using the software ANSYS/LS-DYNA,we numerically simulated the whole process of the hammer source excitation to the formation of the seismic wavelet,based on finite element methods,and then calculated and analyzed the wavelet.We used the Mises yield criterion to find the boundary of plastic zone and analyzed the same node in elastic region.First from the angle of excitation parameters,we carried out numerical simulations of the seismic excitation with different parameters in soil and rock medium and analyzed their different impact on the wavelet.On that basis,from the angle of lithologic characters,we studied source excitation parameters changing in different mediums and simulated different parameter combinations.Finally,we found the relative optimal parameter combinations in different conditions.The mediums involved are:loess,clay,sandstone,limestone.We found that the influence of hammer source parameters to wavelets is not the same in different mediums.In soil,using a base plate is better than not using one,but the size of base plate has little influence.The mass of hammer and the material of the base plate.have great influences on wavelets.In rock medium,the use of base plate has little influence while the mass of hammer,the size and material of the base plate have a great impact.In the end,we gave a relative optimal hammer source parameter combination according to different targets in different conditions... |
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