针对旋转机械故障振动信号的降噪问题,提出一种基于短时Fourier变换(short time Fourier transform,简称STFT)时频谱系数收缩的信号降噪方法。先将信号进行STFT,得到其时频谱。由于谱系数为复数,故根据模值大小进行谱系数收缩,并利用步...针对旋转机械故障振动信号的降噪问题,提出一种基于短时Fourier变换(short time Fourier transform,简称STFT)时频谱系数收缩的信号降噪方法。先将信号进行STFT,得到其时频谱。由于谱系数为复数,故根据模值大小进行谱系数收缩,并利用步长迭代算法在0到谱系数最大模值的区间内估计最优阈值。迭代运算过程中,首先,分别采用基本的硬阈值函数和软阈值函数进行系数收缩;然后,以改进风险函数为阈值评价标准,估计最优阈值;最后,利用最优阈值重新进行谱系数收缩,对得到的新谱进行STFT逆变换,重构降噪后的时域信号。仿真信号与试验数据的处理结果表明,利用所估计的最优阈值,STFT时频谱系数硬、软阈值函数收缩方法均能够实现噪声混合信号的降噪。展开更多
针对现有认知无线网络功率控制算法在离散功率空间内无法收敛的问题,提出一种定步长功率控制算法。在离散功率空间内,将认知用户的目标信干扰比(signal to interference plus noise ratio,SINR)由具体的目标数值扩展为目标窗口。为了最...针对现有认知无线网络功率控制算法在离散功率空间内无法收敛的问题,提出一种定步长功率控制算法。在离散功率空间内,将认知用户的目标信干扰比(signal to interference plus noise ratio,SINR)由具体的目标数值扩展为目标窗口。为了最大化系统容量,在满足系统约束条件的前提下,建立了滑动窗口机制。通过认知用户总干扰与干扰温度域上下限的比较,动态调整中值SINR,从而实现目标窗口的滑动。对于确定的目标窗口,采用定步长迭代算法进行发射功率的调整。仿真实验表明,算法达到了预期效果,并取得与最优算法相近的系统性能。展开更多
As structure buckling problems easily arise when supercavitating projectiles operate with high underwater velocity, it is necessary to perform structure buckling reliability analysis. Now it is widely known that proba...As structure buckling problems easily arise when supercavitating projectiles operate with high underwater velocity, it is necessary to perform structure buckling reliability analysis. Now it is widely known that probabilistic and non-probabilistic uncertain information exists in engineering analysis. Based on reliability comprehensive index of multi-ellipsoid convex set, probabilistic uncertain information is added and transferred into non-probabilistic interval variable. The hybrid reliability is calculated by a combined method of modified limit step length iteration algorithm(MLSLIA) and Monte-Carlo method. The results of engineering examples show that the convergence of MLSLIA is better than that of limit step length iteration algorithm(LSLIA). Structure buckling hybrid reliability increases with the increase of ratio of base diameter to cavitator diameter, and decreases with the increase of initial launch velocity. Also the changes of uncertain degree of projectile velocity and cavitator drag coefficient affect structure buckling hybrid reliability index obviously. Therefore, uncertain degree of projectile velocity and cavitator drag coefficient should be controlled in project for high structure buckling reliability.展开更多
The method of nonlinear finite element reliability analysis (FERA) of slope stability using the technique of slip surface stress analysis (SSA) is studied. The limit state function that can consider the direction of s...The method of nonlinear finite element reliability analysis (FERA) of slope stability using the technique of slip surface stress analysis (SSA) is studied. The limit state function that can consider the direction of slip surface is given, and the formula-tions of FERA based on incremental tangent stiffness method and modified Aitken accelerating algorithm are developed. The limited step length iteration method (LSLIM) is adopted to calculate the reliability index. The nonlinear FERA code using the SSA technique is developed and the main flow chart is illustrated. Numerical examples are used to demonstrate the efficiency and robustness of this method. It is found that the accelerating convergence algorithm proposed in this study proves to be very efficient for it can reduce the iteration number greatly, and LSLIM is also efficient for it can assure the convergence of the iteration of the reliability index.展开更多
文摘针对旋转机械故障振动信号的降噪问题,提出一种基于短时Fourier变换(short time Fourier transform,简称STFT)时频谱系数收缩的信号降噪方法。先将信号进行STFT,得到其时频谱。由于谱系数为复数,故根据模值大小进行谱系数收缩,并利用步长迭代算法在0到谱系数最大模值的区间内估计最优阈值。迭代运算过程中,首先,分别采用基本的硬阈值函数和软阈值函数进行系数收缩;然后,以改进风险函数为阈值评价标准,估计最优阈值;最后,利用最优阈值重新进行谱系数收缩,对得到的新谱进行STFT逆变换,重构降噪后的时域信号。仿真信号与试验数据的处理结果表明,利用所估计的最优阈值,STFT时频谱系数硬、软阈值函数收缩方法均能够实现噪声混合信号的降噪。
文摘针对现有认知无线网络功率控制算法在离散功率空间内无法收敛的问题,提出一种定步长功率控制算法。在离散功率空间内,将认知用户的目标信干扰比(signal to interference plus noise ratio,SINR)由具体的目标数值扩展为目标窗口。为了最大化系统容量,在满足系统约束条件的前提下,建立了滑动窗口机制。通过认知用户总干扰与干扰温度域上下限的比较,动态调整中值SINR,从而实现目标窗口的滑动。对于确定的目标窗口,采用定步长迭代算法进行发射功率的调整。仿真实验表明,算法达到了预期效果,并取得与最优算法相近的系统性能。
基金the National Natural Science Foundation of China(No.51305421)the National Defense Technology Basis Research Project(No.JSZL2014130B005)the Development of Science and Technology Project of Jilin Province(No.20140520137JH)
文摘As structure buckling problems easily arise when supercavitating projectiles operate with high underwater velocity, it is necessary to perform structure buckling reliability analysis. Now it is widely known that probabilistic and non-probabilistic uncertain information exists in engineering analysis. Based on reliability comprehensive index of multi-ellipsoid convex set, probabilistic uncertain information is added and transferred into non-probabilistic interval variable. The hybrid reliability is calculated by a combined method of modified limit step length iteration algorithm(MLSLIA) and Monte-Carlo method. The results of engineering examples show that the convergence of MLSLIA is better than that of limit step length iteration algorithm(LSLIA). Structure buckling hybrid reliability increases with the increase of ratio of base diameter to cavitator diameter, and decreases with the increase of initial launch velocity. Also the changes of uncertain degree of projectile velocity and cavitator drag coefficient affect structure buckling hybrid reliability index obviously. Therefore, uncertain degree of projectile velocity and cavitator drag coefficient should be controlled in project for high structure buckling reliability.
基金supported by the National Natural Science Foundation of China (No. 50748033)the Specific Foundation for PhD of Hefei University of Technology (No. 2007GDBJ044), China
文摘The method of nonlinear finite element reliability analysis (FERA) of slope stability using the technique of slip surface stress analysis (SSA) is studied. The limit state function that can consider the direction of slip surface is given, and the formula-tions of FERA based on incremental tangent stiffness method and modified Aitken accelerating algorithm are developed. The limited step length iteration method (LSLIM) is adopted to calculate the reliability index. The nonlinear FERA code using the SSA technique is developed and the main flow chart is illustrated. Numerical examples are used to demonstrate the efficiency and robustness of this method. It is found that the accelerating convergence algorithm proposed in this study proves to be very efficient for it can reduce the iteration number greatly, and LSLIM is also efficient for it can assure the convergence of the iteration of the reliability index.
