We developed a modified stochastic finite-fault method for estimating strong ground motions.An adjustment to the dynamic corner frequency was introduced,which accounted for the effect of the location of the subfault r...We developed a modified stochastic finite-fault method for estimating strong ground motions.An adjustment to the dynamic corner frequency was introduced,which accounted for the effect of the location of the subfault relative to the hypocenter and rupture propagation direction,to account for the influence of the rupture propagation direction on the subfault dynamic corner frequency.By comparing the peak ground acceleration(PGA),pseudo-absolute response spectra acceleration(PSA,damping ratio of 5%),and duration,the results of the modified and existing methods were compared,demonstrating that our proposed adjustment to the dynamic corner frequency can accurately reflect the rupture directivity effect.We applied our modified method to simulate near-field strong motions within 150 km of the 2008 MW7.9 Wenchuan earthquake rupture.Our modified method performed well over a broad period range,particularly at 0.04-4 s.The total deviations of the stochastic finite-fault method(EXSIM)and the modified EXSIM were 0.1676 and 0.1494,respectively.The modified method can effectively account for the influence of the rupture propagation direction and provide more realistic ground motion estimations for earthquake disaster mitigation.展开更多
Based on the concept of the constitutive relation error along with the residuals of both the origin and the dual problems, a goal-oriented error estimation method with extended degrees of freedom is developed. It lead...Based on the concept of the constitutive relation error along with the residuals of both the origin and the dual problems, a goal-oriented error estimation method with extended degrees of freedom is developed. It leads to the high quality locM error bounds in the problem of the direct-solution steady-state dynamic analysis with a frequency-domain finite element, which involves the enrichments with plural variable basis functions. The solution of the steady-state dynamic procedure calculates the harmonic response directly in terms of the physical degrees of freedom in the model, which uses the mass, damping, and stiffness matrices of the system. A three-dimensional finite element example is carried out to illustrate the computational procedures.展开更多
An approach for joint direction of arrival(DOA) angle and frequency estimation for a linear array is investigated in this paper. Specifically, we make the utmost of the autocorrelation and cross-correlation informatio...An approach for joint direction of arrival(DOA) angle and frequency estimation for a linear array is investigated in this paper. Specifically, we make the utmost of the autocorrelation and cross-correlation information to propose an extended DOAmatrix(EDOAM) method. Subsequently, we obtain the autopaired angle and frequency estimates by the eigenvalues and the corresponding eigenvectors of the novel DOA matrix. Furthermore, the proposed method surpasses the DOA-matrix method which partly ignores the autocorrelation and cross-correlation information. Finally, the proposed method works well for both uniform and non-uniform linear arrays. The simulation consequences indicate the superiority of our proposed approach.展开更多
An efficient method to track the carrier frequency which is recommended to use in low earth orbit(LEO) direct-sequence spread-spectrum(DS/SS) communication system is given. The carrier frequency drifts quicker in LEO ...An efficient method to track the carrier frequency which is recommended to use in low earth orbit(LEO) direct-sequence spread-spectrum(DS/SS) communication system is given. The carrier frequency drifts quicker in LEO DS/SS communication system, its tracking problem becomes much more important especially in digital receiver with the limits of physical shape and power. Under the condition of coarse carrier frequency synchronization, a digital tracking method based on least square method(LSM) is proved to be a quick, simple and efficient method. Numerical results and charts are given.展开更多
为了提升分布式传感器场景下对于宽带辐射源的定位效果,本文提出了一种基于到达时间差(Time Difference Of Arrival,TDOA)的多频率聚焦与融合的相干辐射源直接定位(Direct Position Determination,DPD)方法 .首先,对衰减系数未知的传感...为了提升分布式传感器场景下对于宽带辐射源的定位效果,本文提出了一种基于到达时间差(Time Difference Of Arrival,TDOA)的多频率聚焦与融合的相干辐射源直接定位(Direct Position Determination,DPD)方法 .首先,对衰减系数未知的传感器时域接收信号进行预处理,进行数据分段和频域变换,将宽带信号转化成若干个多快拍窄带频域信号;其次,根据最佳聚焦矩阵构造准则,构造聚焦矩阵,将各频率对应的信号聚焦到中心频率附近频谱能量最大的聚焦频率,得到聚焦后的接收数据;然后,根据子空间正交性建立关于辐射源位置的最小化代价函数,融合多个聚焦后的代价函数解决衰减系数未知的问题;最后,结合拉格朗日乘子法,通过网格点上代价函数值的谱峰搜索得到宽带辐射源的估计位置.所提方法可以在衰减系数未知的情况下实现相干辐射源的高精度定位,仿真和实际测试结果表明本文所提方法的有效性,在信噪比大于0 dB的四节点多径定位场景中,所提方法的定位性能较其他时差直接定位性能提升了30%以上.展开更多
For the proportional directional valve controlled by two proportional solenoids, the normal control method(NCM) energizes only one solenoid at a time. The performance of the valve is greatly influenced by the nonlinea...For the proportional directional valve controlled by two proportional solenoids, the normal control method(NCM) energizes only one solenoid at a time. The performance of the valve is greatly influenced by the nonlinearity of the proportional solenoid, such as dead zone and low force gain with a small current, and this effect cannot be eliminated by a simple dead-zone current compensation. To avoid this disadvantage, we propose the differential control method(DCM). By employing DCM, the controller outputs differential signals to simultaneously energize both solenoids of the proportional valve, and the operating point is found by analyzing the force output of the two solenoids to make a minimum variation of the current force gain. The comparisons of the valve response characteristics are made between NCM and DCM by nonlinear dynamic simulation and experiments. Simulation and experimental results show that by using DCM, the frequency response of the valve is greatly enhanced, especially when the input is small, which means that the dynamic characteristics of the proportional valve are improved.展开更多
文摘We developed a modified stochastic finite-fault method for estimating strong ground motions.An adjustment to the dynamic corner frequency was introduced,which accounted for the effect of the location of the subfault relative to the hypocenter and rupture propagation direction,to account for the influence of the rupture propagation direction on the subfault dynamic corner frequency.By comparing the peak ground acceleration(PGA),pseudo-absolute response spectra acceleration(PSA,damping ratio of 5%),and duration,the results of the modified and existing methods were compared,demonstrating that our proposed adjustment to the dynamic corner frequency can accurately reflect the rupture directivity effect.We applied our modified method to simulate near-field strong motions within 150 km of the 2008 MW7.9 Wenchuan earthquake rupture.Our modified method performed well over a broad period range,particularly at 0.04-4 s.The total deviations of the stochastic finite-fault method(EXSIM)and the modified EXSIM were 0.1676 and 0.1494,respectively.The modified method can effectively account for the influence of the rupture propagation direction and provide more realistic ground motion estimations for earthquake disaster mitigation.
基金Project supported by the National Natural Science Foundation of China (No. 10876100)
文摘Based on the concept of the constitutive relation error along with the residuals of both the origin and the dual problems, a goal-oriented error estimation method with extended degrees of freedom is developed. It leads to the high quality locM error bounds in the problem of the direct-solution steady-state dynamic analysis with a frequency-domain finite element, which involves the enrichments with plural variable basis functions. The solution of the steady-state dynamic procedure calculates the harmonic response directly in terms of the physical degrees of freedom in the model, which uses the mass, damping, and stiffness matrices of the system. A three-dimensional finite element example is carried out to illustrate the computational procedures.
基金supported by the National Natural Science Foundation of China (61971217,61971218,61631020)Jiangsu Natural Science Foundation (BK20200444)+1 种基金Jiangsu Key Research and Development Project (BE2020101)the Fund of Sonar Technology Key Laboratory。
文摘An approach for joint direction of arrival(DOA) angle and frequency estimation for a linear array is investigated in this paper. Specifically, we make the utmost of the autocorrelation and cross-correlation information to propose an extended DOAmatrix(EDOAM) method. Subsequently, we obtain the autopaired angle and frequency estimates by the eigenvalues and the corresponding eigenvectors of the novel DOA matrix. Furthermore, the proposed method surpasses the DOA-matrix method which partly ignores the autocorrelation and cross-correlation information. Finally, the proposed method works well for both uniform and non-uniform linear arrays. The simulation consequences indicate the superiority of our proposed approach.
文摘An efficient method to track the carrier frequency which is recommended to use in low earth orbit(LEO) direct-sequence spread-spectrum(DS/SS) communication system is given. The carrier frequency drifts quicker in LEO DS/SS communication system, its tracking problem becomes much more important especially in digital receiver with the limits of physical shape and power. Under the condition of coarse carrier frequency synchronization, a digital tracking method based on least square method(LSM) is proved to be a quick, simple and efficient method. Numerical results and charts are given.
文摘为了提升分布式传感器场景下对于宽带辐射源的定位效果,本文提出了一种基于到达时间差(Time Difference Of Arrival,TDOA)的多频率聚焦与融合的相干辐射源直接定位(Direct Position Determination,DPD)方法 .首先,对衰减系数未知的传感器时域接收信号进行预处理,进行数据分段和频域变换,将宽带信号转化成若干个多快拍窄带频域信号;其次,根据最佳聚焦矩阵构造准则,构造聚焦矩阵,将各频率对应的信号聚焦到中心频率附近频谱能量最大的聚焦频率,得到聚焦后的接收数据;然后,根据子空间正交性建立关于辐射源位置的最小化代价函数,融合多个聚焦后的代价函数解决衰减系数未知的问题;最后,结合拉格朗日乘子法,通过网格点上代价函数值的谱峰搜索得到宽带辐射源的估计位置.所提方法可以在衰减系数未知的情况下实现相干辐射源的高精度定位,仿真和实际测试结果表明本文所提方法的有效性,在信噪比大于0 dB的四节点多径定位场景中,所提方法的定位性能较其他时差直接定位性能提升了30%以上.
基金Project supported by the National Natural Science Foundation of China(No.51221004)the Program for Zhejiang Leading Team of S&T Innovation(No.2010R50036)
文摘For the proportional directional valve controlled by two proportional solenoids, the normal control method(NCM) energizes only one solenoid at a time. The performance of the valve is greatly influenced by the nonlinearity of the proportional solenoid, such as dead zone and low force gain with a small current, and this effect cannot be eliminated by a simple dead-zone current compensation. To avoid this disadvantage, we propose the differential control method(DCM). By employing DCM, the controller outputs differential signals to simultaneously energize both solenoids of the proportional valve, and the operating point is found by analyzing the force output of the two solenoids to make a minimum variation of the current force gain. The comparisons of the valve response characteristics are made between NCM and DCM by nonlinear dynamic simulation and experiments. Simulation and experimental results show that by using DCM, the frequency response of the valve is greatly enhanced, especially when the input is small, which means that the dynamic characteristics of the proportional valve are improved.
