The acoustic tools widely used in borehole well logging and being developed in borehole acoustic reflection imaging do not have the function of azimuthal measurement due to a symmetric source, so they can not be used ...The acoustic tools widely used in borehole well logging and being developed in borehole acoustic reflection imaging do not have the function of azimuthal measurement due to a symmetric source, so they can not be used to evaluate the azimuthal character of borehole formation. In this paper, a 3D finite difference method was used to simulate the acoustic fields in a fluid-filled borehole generated by a traditional monopole source and a phased arc array. Acoustic waveforms were presented for both cases. The analysis of the simulated waveforms showed that different from the monopole source, the acoustic energy generated by the phased arc array transmitter mainly radiated to the borehole in a narrow azimuthal range, which was the key technique to implement azimuthal acoustic well logging. Similar to the monopole source, the waveforms generated by the phased arc array in the fluid-filled borehole also contain compressional （P） waves and shear （S） waves refracted along the borehole, which is the theoretical foundation of phased arc array acoustic well logging.展开更多
The phenomena of polarization rotation induced by self-modulation in semiconductor optical amplifier (SOA) are analyzed theoretically. The relationship between polarization parameters and gain as well as phase is obta...The phenomena of polarization rotation induced by self-modulation in semiconductor optical amplifier (SOA) are analyzed theoretically. The relationship between polarization parameters and gain as well as phase is obtained by the correlation parameter of ellipse polarization and SOA nonlinearity polarization rotation theory. The experiment employs polarizer drive by walking electromotor and power meter, the light power of 360 degree is measured. The transformation law of output polarization power components is found for obvious polarization rotation in the selected coordinate axes based on connection of polarization state in difference axes. Using this law make the manipulation easily on getting ideal polarization state. It can offer a fine method to realize all-optical switch and other logic elements in experiment. This work is of great significance for the applications of SOA nonlinear polarization rotation at high-speed all-optical signal processing and all-optical logic gate.展开更多
Based on the two-dimensional(2D)three-component first-order velocity-stress equation,the high order staggered mesh finite difference numerical simulation method was used to simulate the elastic and viscoelastic tilted...Based on the two-dimensional(2D)three-component first-order velocity-stress equation,the high order staggered mesh finite difference numerical simulation method was used to simulate the elastic and viscoelastic tilted transversely isotropic(TTI)media.The perfect matched layer(PML)absorption boundary condition was selected to eliminate the boundary effect.The results show that:(①)Under the condition of fixed elastic parameters of elastic TTI medium,when the polarization angle and azimuth are 60°and 45°respectively,the degree of shear wave splitting is significantly greater than the angle of 0°;②The influence of viscoelasticity on TTI medium is mainly reflected in the amplitude.If the quality factor decreases,the attenuation of the seismic wave amplitude increases,causing the waveform to become wider and distorted.If the quality factor increases,the viscoelastic medium becomes closer to elastic medium;③For TTI medium with different polarization angle and azimuth angle in the upper and lower layers,the shear wave can multiple splits at the interface of medium.The symmetry of seismograms is affected by the polarization angle and azimuth angle of TTI medium;④Viscoelasticity has a great influence on reflected wave,transmitted wave and converted wave in the low-velocity model.When the viscoelasticity is strong,the weaker waves may not be shown.展开更多
The existing research results show that a fixed single station must conduct three consecutive frequency shift measurements and obtain the target’s moving speed by constructing two frequency difference equations. This...The existing research results show that a fixed single station must conduct three consecutive frequency shift measurements and obtain the target’s moving speed by constructing two frequency difference equations. This article proposes a new method that requires only two consecutive measurements. While using the azimuth measurement to obtain the angular difference between two radial distances, it also conducts two consecutive Doppler frequency shift measurements at the same target azimuth. On the basis of this measurement, a frequency difference equation is first constructed and solved jointly with the Doppler frequency shift equation. By eliminating the velocity variable and using the measured angular difference to obtain the target’s lead angle, the target’s velocity can be solved by using the Doppler frequency shift equation again. The new method avoids the condition that the target must move equidistantly, which not only provides an achievable method for engineering applications but also lays a good foundation for further exploring the use of steady-state signals to achieve passive positioning.展开更多
针对大方位失准角捷联惯性导航系统误差模型非线性的特点,利用基于迭代测量更新的中心差分卡尔曼滤波(iterated central difference Kalman filter,ICDKF)方法进行初始对准。与传统的非线性扩展卡尔曼滤波相比,ICDKF不仅能够提高滤波精...针对大方位失准角捷联惯性导航系统误差模型非线性的特点,利用基于迭代测量更新的中心差分卡尔曼滤波(iterated central difference Kalman filter,ICDKF)方法进行初始对准。与传统的非线性扩展卡尔曼滤波相比,ICDKF不仅能够提高滤波精度,而且不需要模型的具体解析形式,避免了复杂的雅可比矩阵的推导;同时ICDKF通过迭代测量更新,提高了目前存在的中心差分卡尔曼滤波的估计精度。仿真结果进一步表明ICDKF算法的可行性与优越性,能够满足初始对准的要求。展开更多
基金supported by the National Natural ScienceFoundation of China(Grant Nos.10534040,40574049 and 40874097)the Research Fund for the Doctoral Programof Higher Education(Grant No.20070425028)the Foundation of State Key Laboratory of Petroleum Resourceand Prospecting,China University of Petroleum(Grant No.PRPDX2008-08).
文摘The acoustic tools widely used in borehole well logging and being developed in borehole acoustic reflection imaging do not have the function of azimuthal measurement due to a symmetric source, so they can not be used to evaluate the azimuthal character of borehole formation. In this paper, a 3D finite difference method was used to simulate the acoustic fields in a fluid-filled borehole generated by a traditional monopole source and a phased arc array. Acoustic waveforms were presented for both cases. The analysis of the simulated waveforms showed that different from the monopole source, the acoustic energy generated by the phased arc array transmitter mainly radiated to the borehole in a narrow azimuthal range, which was the key technique to implement azimuthal acoustic well logging. Similar to the monopole source, the waveforms generated by the phased arc array in the fluid-filled borehole also contain compressional （P） waves and shear （S） waves refracted along the borehole, which is the theoretical foundation of phased arc array acoustic well logging.
文摘The phenomena of polarization rotation induced by self-modulation in semiconductor optical amplifier (SOA) are analyzed theoretically. The relationship between polarization parameters and gain as well as phase is obtained by the correlation parameter of ellipse polarization and SOA nonlinearity polarization rotation theory. The experiment employs polarizer drive by walking electromotor and power meter, the light power of 360 degree is measured. The transformation law of output polarization power components is found for obvious polarization rotation in the selected coordinate axes based on connection of polarization state in difference axes. Using this law make the manipulation easily on getting ideal polarization state. It can offer a fine method to realize all-optical switch and other logic elements in experiment. This work is of great significance for the applications of SOA nonlinear polarization rotation at high-speed all-optical signal processing and all-optical logic gate.
基金the National Natural Science Foundation of China(Nos.41974048,41574078,41604039,41604102)the Guangxi Natural Science Foundation of China(Nos.2018GXNSFAA138059,2016GXNSFBA380082 and 2018GXNSFBA050005)+1 种基金Guangxi Science and Technology Base and Talent Project(Gui Kc AD19110057)Guangxi High School Junior Teachers Foundation Funding for capacity improvement projects(No.2019KY0264).
文摘Based on the two-dimensional(2D)three-component first-order velocity-stress equation,the high order staggered mesh finite difference numerical simulation method was used to simulate the elastic and viscoelastic tilted transversely isotropic(TTI)media.The perfect matched layer(PML)absorption boundary condition was selected to eliminate the boundary effect.The results show that:(①)Under the condition of fixed elastic parameters of elastic TTI medium,when the polarization angle and azimuth are 60°and 45°respectively,the degree of shear wave splitting is significantly greater than the angle of 0°;②The influence of viscoelasticity on TTI medium is mainly reflected in the amplitude.If the quality factor decreases,the attenuation of the seismic wave amplitude increases,causing the waveform to become wider and distorted.If the quality factor increases,the viscoelastic medium becomes closer to elastic medium;③For TTI medium with different polarization angle and azimuth angle in the upper and lower layers,the shear wave can multiple splits at the interface of medium.The symmetry of seismograms is affected by the polarization angle and azimuth angle of TTI medium;④Viscoelasticity has a great influence on reflected wave,transmitted wave and converted wave in the low-velocity model.When the viscoelasticity is strong,the weaker waves may not be shown.
文摘The existing research results show that a fixed single station must conduct three consecutive frequency shift measurements and obtain the target’s moving speed by constructing two frequency difference equations. This article proposes a new method that requires only two consecutive measurements. While using the azimuth measurement to obtain the angular difference between two radial distances, it also conducts two consecutive Doppler frequency shift measurements at the same target azimuth. On the basis of this measurement, a frequency difference equation is first constructed and solved jointly with the Doppler frequency shift equation. By eliminating the velocity variable and using the measured angular difference to obtain the target’s lead angle, the target’s velocity can be solved by using the Doppler frequency shift equation again. The new method avoids the condition that the target must move equidistantly, which not only provides an achievable method for engineering applications but also lays a good foundation for further exploring the use of steady-state signals to achieve passive positioning.
文摘针对大方位失准角捷联惯性导航系统误差模型非线性的特点,利用基于迭代测量更新的中心差分卡尔曼滤波(iterated central difference Kalman filter,ICDKF)方法进行初始对准。与传统的非线性扩展卡尔曼滤波相比,ICDKF不仅能够提高滤波精度,而且不需要模型的具体解析形式,避免了复杂的雅可比矩阵的推导;同时ICDKF通过迭代测量更新,提高了目前存在的中心差分卡尔曼滤波的估计精度。仿真结果进一步表明ICDKF算法的可行性与优越性,能够满足初始对准的要求。
