Increasing degrees of freedom(DOFs)is a useful way to raise the power capture efficiency of oscillating wave energy converters.Thus,this study proposes a buoy with three DOFs,which are surge,heave,and pitch.The hydrod...Increasing degrees of freedom(DOFs)is a useful way to raise the power capture efficiency of oscillating wave energy converters.Thus,this study proposes a buoy with three DOFs,which are surge,heave,and pitch.The hydrodynamic performance and power capture efficiency of the buoy is physically modeled.Amplitudes of unidirectional and coupled motions are compared to analyze the interaction effect between freedoms under conditions with and without power take-off damping.The capture width ratio and corresponding growth rates are also calculated.Results show that the buoy makes a periodic sinusoidal(or approximate)movement in every DOF.Coupling effect can cause an increase in the amplitude in one DOF and a decrease in the amplitudes of the others.This phenomenon shows that the kinematic energy of the buoy redistributes to all DOFs compared with the unidirectional conditions.Adding DOFs can improve the power absorption of the buoy in most cases,but the number of DOFs is not the more the better.展开更多
Modal parameter identification is a mature technology.However,there are some challenges in its practical applications such as the identification of vibration systems involving closely spaced modes and intensive noise ...Modal parameter identification is a mature technology.However,there are some challenges in its practical applications such as the identification of vibration systems involving closely spaced modes and intensive noise contamination.This paper proposes a new time-frequency method based on intrinsic chirp component decomposition(ICCD)to address these issues.In this method,a redundant Fourier model is used to ameliorate border distortions and improve the accuracy of signal reconstruction.The effectiveness and accuracy of the proposed method are illustrated using three examples:a cantilever beam structure with intensive noise contamination or environmental interference,a four-degree-of-freedom structure with two closely spaced modes,and an impact test on a cantilever rectangular plate.By comparison with the identification method based on the empirical wavelet transform(EWT),it is shown that the presented method is effective,even in a high-noise environment,and the dynamic characteristics of closely spaced modes are accurately determined.展开更多
A class of two-degree-of-freedom systems in resonance with an external, parametric excitation is investigated, the existence of the periodic solutions locked to Omega is proved by the use of the method of multiple sca...A class of two-degree-of-freedom systems in resonance with an external, parametric excitation is investigated, the existence of the periodic solutions locked to Omega is proved by the use of the method of multiple scales. This systems can be transformed into the systems of Wiggins under some conditions. A calculating formula which determines the existence of homoclinic orbits of the systems is given.展开更多
场地-城市相互作用(site-city interaction,SCI)效应会显著改变场地地震波场分布及建筑反应,基于SCI效应理论计算研究方法的发展现状,发挥谱元(spectral element,SE)法可快速高效求解三维地震波场传播和多自由度(multi-degree of freedo...场地-城市相互作用(site-city interaction,SCI)效应会显著改变场地地震波场分布及建筑反应,基于SCI效应理论计算研究方法的发展现状,发挥谱元(spectral element,SE)法可快速高效求解三维地震波场传播和多自由度(multi-degree of freedom,MDOF)模型计算量小且可同时模拟大量建筑的优势,同时,结合频率波数域(frequency wave number analysis,FK)方法,以等效地震荷载的方式施加地震波场,建立了FK-SE-MDOF耦合方法,实现了SE-MDOF耦合模型中多种波型(P波、SV波和SH波)的斜入射输入,解决了当前三维SCI效应研究方法中未能同时考虑建筑非线性、频谱特性、地震波波型及入射角度影响的问题。首先对方法原理进行了介绍;然后,通过与振动台试验的对比,验证了方法的正确性;进而,采用该方法建立理想场地-城市建筑群相互作用耦合模型,主要探讨了入射角度和地震波波型对SCI效应的影响,得到了一些有益结论。该方法较为真实地反映SCI效应影响的同时,可反映建筑基础轮廓对地震波场的影响,适用于需考虑建筑轮廓信息的社区尺度SCI效应研究,可为城市规划、抗震设计、风险评估以及震后救援等工作提供定量指导。展开更多
针对在机器人辅助头颈部手术中双机械臂进行牵拉易产生碰撞且对目标软组织造成损伤问题,文中基于传统Informed-RRT*(Informed-Rapidly Exploring Random Tree*)路径规划算法叠加引力场降低路径搜索的盲目性。为优化传统Informed-RRT*路...针对在机器人辅助头颈部手术中双机械臂进行牵拉易产生碰撞且对目标软组织造成损伤问题,文中基于传统Informed-RRT*(Informed-Rapidly Exploring Random Tree*)路径规划算法叠加引力场降低路径搜索的盲目性。为优化传统Informed-RRT*路径规划算法存在导向性差和效率低等缺点,引入回归滤波机制避免搜索陷入局部最优,对步长进行动态调节。同时,优化了规划路径,采用冗余节点剔除策略,去除了冗余节点,提高了路径的平滑性。基于双机械臂碰撞检测方法和改进Informed-RRT*算法对双臂协调路径规划方法进行了研究。通过仿真实验可知,与原有算法相比,所提算法的迭代时间降低了72.76%,迭代次数降低了46.39%,平均路径长度约缩短6%,节点数约减少45%,验证了改进规划算法的有效性。展开更多
Hyperentangled Bell states analysis(HBSA)is an essential building block for certain hyper-parallel quantum information processing.We propose a complete and deterministic HBSA scheme encoded in spatial and polarization...Hyperentangled Bell states analysis(HBSA)is an essential building block for certain hyper-parallel quantum information processing.We propose a complete and deterministic HBSA scheme encoded in spatial and polarization degrees of freedom(DOFs)of two-photon system assisted by a fixed frequency-based entanglement and a time interval DOF.The parity information the spatial-based and polarization-based hyper-entanglement can be distinguished by the distinct time intervals of the photon pairs,and the phase information can be distinguished by the detection signature.Compared with previous schemes,the number of the auxiliary entanglements is reduced from two to one by introducing time interval DOF.Moreover,the additional frequency and time interval DOFs suffer less from the collective channel noise.展开更多
基金the support of the National Key R&D Program of China (No. 2018YFB1501900)the National Natural Science Fund of China (No. 41706100)+3 种基金the Shandong Provincial Natural Science Key Basic Program (No. ZR2017ZA 0202)the Special Projects for Marine Renewable Energy (No. GHME2016YY02)the Shandong Provincial Key Laboratory of Ocean Engineeringthe Qingdao Municipal Key Laboratory of Ocean Renewable Energy
文摘Increasing degrees of freedom(DOFs)is a useful way to raise the power capture efficiency of oscillating wave energy converters.Thus,this study proposes a buoy with three DOFs,which are surge,heave,and pitch.The hydrodynamic performance and power capture efficiency of the buoy is physically modeled.Amplitudes of unidirectional and coupled motions are compared to analyze the interaction effect between freedoms under conditions with and without power take-off damping.The capture width ratio and corresponding growth rates are also calculated.Results show that the buoy makes a periodic sinusoidal(or approximate)movement in every DOF.Coupling effect can cause an increase in the amplitude in one DOF and a decrease in the amplitudes of the others.This phenomenon shows that the kinematic energy of the buoy redistributes to all DOFs compared with the unidirectional conditions.Adding DOFs can improve the power absorption of the buoy in most cases,but the number of DOFs is not the more the better.
基金Project supported by the National Natural Science Foundation of China(Nos.11702170,11320011,and 11802279)the China Postdoctoral Science Foundation(No.2016M601585)
文摘Modal parameter identification is a mature technology.However,there are some challenges in its practical applications such as the identification of vibration systems involving closely spaced modes and intensive noise contamination.This paper proposes a new time-frequency method based on intrinsic chirp component decomposition(ICCD)to address these issues.In this method,a redundant Fourier model is used to ameliorate border distortions and improve the accuracy of signal reconstruction.The effectiveness and accuracy of the proposed method are illustrated using three examples:a cantilever beam structure with intensive noise contamination or environmental interference,a four-degree-of-freedom structure with two closely spaced modes,and an impact test on a cantilever rectangular plate.By comparison with the identification method based on the empirical wavelet transform(EWT),it is shown that the presented method is effective,even in a high-noise environment,and the dynamic characteristics of closely spaced modes are accurately determined.
文摘A class of two-degree-of-freedom systems in resonance with an external, parametric excitation is investigated, the existence of the periodic solutions locked to Omega is proved by the use of the method of multiple scales. This systems can be transformed into the systems of Wiggins under some conditions. A calculating formula which determines the existence of homoclinic orbits of the systems is given.
文摘场地-城市相互作用(site-city interaction,SCI)效应会显著改变场地地震波场分布及建筑反应,基于SCI效应理论计算研究方法的发展现状,发挥谱元(spectral element,SE)法可快速高效求解三维地震波场传播和多自由度(multi-degree of freedom,MDOF)模型计算量小且可同时模拟大量建筑的优势,同时,结合频率波数域(frequency wave number analysis,FK)方法,以等效地震荷载的方式施加地震波场,建立了FK-SE-MDOF耦合方法,实现了SE-MDOF耦合模型中多种波型(P波、SV波和SH波)的斜入射输入,解决了当前三维SCI效应研究方法中未能同时考虑建筑非线性、频谱特性、地震波波型及入射角度影响的问题。首先对方法原理进行了介绍;然后,通过与振动台试验的对比,验证了方法的正确性;进而,采用该方法建立理想场地-城市建筑群相互作用耦合模型,主要探讨了入射角度和地震波波型对SCI效应的影响,得到了一些有益结论。该方法较为真实地反映SCI效应影响的同时,可反映建筑基础轮廓对地震波场的影响,适用于需考虑建筑轮廓信息的社区尺度SCI效应研究,可为城市规划、抗震设计、风险评估以及震后救援等工作提供定量指导。
文摘针对在机器人辅助头颈部手术中双机械臂进行牵拉易产生碰撞且对目标软组织造成损伤问题,文中基于传统Informed-RRT*(Informed-Rapidly Exploring Random Tree*)路径规划算法叠加引力场降低路径搜索的盲目性。为优化传统Informed-RRT*路径规划算法存在导向性差和效率低等缺点,引入回归滤波机制避免搜索陷入局部最优,对步长进行动态调节。同时,优化了规划路径,采用冗余节点剔除策略,去除了冗余节点,提高了路径的平滑性。基于双机械臂碰撞检测方法和改进Informed-RRT*算法对双臂协调路径规划方法进行了研究。通过仿真实验可知,与原有算法相比,所提算法的迭代时间降低了72.76%,迭代次数降低了46.39%,平均路径长度约缩短6%,节点数约减少45%,验证了改进规划算法的有效性。
基金This work was supported by the National Natural Science Foundation of China under Grant No.11604012the Fundamental Research Funds for the Central Universities under Grant No.FRF-TP-19-011A3+2 种基金the National Natural Science Foundation of China under Contract 61901420the Shanxi Province Science Foundation for Youths under Contract No.201901D211235the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi under Contract No.2019L0507。
文摘Hyperentangled Bell states analysis(HBSA)is an essential building block for certain hyper-parallel quantum information processing.We propose a complete and deterministic HBSA scheme encoded in spatial and polarization degrees of freedom(DOFs)of two-photon system assisted by a fixed frequency-based entanglement and a time interval DOF.The parity information the spatial-based and polarization-based hyper-entanglement can be distinguished by the distinct time intervals of the photon pairs,and the phase information can be distinguished by the detection signature.Compared with previous schemes,the number of the auxiliary entanglements is reduced from two to one by introducing time interval DOF.Moreover,the additional frequency and time interval DOFs suffer less from the collective channel noise.
