Optimization of the dynamic stiffness of the seismic vibrator

Abstract

Due to the sweep excitation of the vibrator, the dynamic stiffness of the seismic vibrator has an enormous influence on the performance of the vibroseis system and the accuracy of the output signal. In order to improve the dynamic stiffness of the vibrator, an optimization strategy is presented to improve the weak link which is defined by dynamic analysis of the vibrator. The weak link is the weakest part, which brings about the resonance, and the weak link in different excitation frequencies is identified by dynamic stiffness analysis in this method. A modified finite element model with reaction mass is built; harmonic response analysis and modal analysis are employed to find out the weak link of the vibrator, which indicates that the supporting column is the weakest component. Sensitivity analysis is used to determine the optimization parameters of the supporting column. Response surface model developed from a parametric finite element model is used to establish the objective function, and the mass is the constraint condition. The optimization problem is solved by particle swarm optimization, and the dynamic stiffness of the optimized vibrator is calculated by harmonic response model. Results show that compared with the original model, the natural frequency of the optimized vibrator is increased by 6.63% and the resonance peak is decreased by 9.00%.

Modal characteristics and phase response of vibrator under excitation of sweep frequency

“…Although two methods are used, the abrupt change/jumping frequencies of the phase are basically the same as the natural frequencies obtained from the modal analysis, which confirms the correctness and accuracy of the two methods. Besides, the previous papers 16,17 didn’t reflect the phase changes at natural frequencies, but our method shows the influence of the resonance on phase response. In the field exploration process, because the sweep frequency does not continue to operate at the natural frequency, so the resonance response may not be very large, or the structure may not have a complete phase change, but the response near the natural frequency is greater than that far away from the natural frequency, and has been verified in field tests.…”

“…If R b (1) and R r (1) are the solutions in which v 1 is substituted into equation (17), and R b (2) and R r (2) are the solutions in which v 2 is substituted into equation 17, the following solutions can be obtained:…”

“…Obviously, R r = R b = 0 is the solution satisfying equation (17), but this means that the vibration system is at rest. If vibrations exist, the values of R r and R b cannot always be equal to zero.…”

“…However, a static model cannot accurately describe the response of the vibrator. Huang et al 17 optimized the dynamic stiffness of the seismic vibrator with harmonic response model. The results showed that this method can improve natural frequency of the vibrator and reduce the resonance peak.…”

Nonlinear 3D finite element analysis of a shear-wave vibrator-ground interaction system

“…Thus, the finite element analysis comes into light as an efficient tool to simulate the dynamics of the vibrator-ground system. As an example, Wei et al and Huang et al proposed a finite element model for a p-wave vibrator located on an elastic ground column [21][22][23]. By using this model, they studied the response of the vibrator with different excitation frequencies and soil properties.…”