Through a higher-order boundary element method based on NURBS （Non-uniform Rational B-splines）, the calculation of second-order low-frequency forces and slow drift motions is conducted for floating bodies. In the fl...Through a higher-order boundary element method based on NURBS （Non-uniform Rational B-splines）, the calculation of second-order low-frequency forces and slow drift motions is conducted for floating bodies. In the floating body＇s inner domain, an auxiliary equation is obtained by applying a Green function which satisfies the solid surface condition. Then, the auxiliary equation and the velocity potential equation are combined in the fluid domain to remove the solid angle coefficient and the singularity of the double layer potentials in the integral equation. Thus, a new velocity potential integral equation is obtained. The new equation is extended to the inner domain to reheve the irregular frequency effects; on the basis of the order analysis, the comparison is made about the contribution of all integral terms with the result in the second-order tow-frequency problem; the higher-order boundary element method based on NURBS is apphed to calculate the geometric position and velocity potentials; the slow drift motions are calculated by the spectrum analysis method. Removing the solid angle coefficient can apply NURBS technology to the hydrodynamic calculation of floating bodies with complex surfaces, and the extended boundary integral method can reduce the irregular frequency effects. Order analysis shows that free surface integral can be neglected, and the numerical results can also prove the correctness of order analysis. The results of second-order low-frequency forces and slow drift motions and the comparison with the results from references show that the application of the NURBS technology to the second-order low-frequency problem is of high efficiency and credible results.展开更多
A structure consisting of a spiral piezoelectric transducer and a concentrated mass is proposed as a low-frequency piezoelectric power harvester. A theoretical model is developed for the system from the theory of piez...A structure consisting of a spiral piezoelectric transducer and a concentrated mass is proposed as a low-frequency piezoelectric power harvester. A theoretical model is developed for the system from the theory of piezoelectricity. An analysis is performed to demonstrate the low-frequency nature of the system. Other basic characteristics of the power harvester including the output power, voltage, and efficiency are also calculated and examined.展开更多
We propose a quantum nondemolition measurement of the collective motional energy of two trapped ions for the first time.It is based on the excitation of the two ions by two lasers with appropriate frequencies and ampl...We propose a quantum nondemolition measurement of the collective motional energy of two trapped ions for the first time.It is based on the excitation of the two ions by two lasers with appropriate frequencies and amplitudes.The scheme also provides a new possibility of preparing vibrational Fock states and laser cooling.展开更多
After decades of theoretical studies,the rich phase states of active matter and cluster kinetic processes are still of research interest.How to efficiently calculate the dynamical processes under their complex conditi...After decades of theoretical studies,the rich phase states of active matter and cluster kinetic processes are still of research interest.How to efficiently calculate the dynamical processes under their complex conditions becomes an open problem.Recently,machine learning methods have been proposed to predict the degree of coherence of active matter systems.In this way,the phase transition process of the system is quantified and studied.In this paper,we use graph network as a powerful model to determine the evolution of active matter with variable individual velocities solely based on the initial position and state of the particles.The graph network accurately predicts the order parameters of the system in different scale models with different individual velocities,noise and density to effectively evaluate the effect of diverse condition.Compared with the classical physical deduction method,we demonstrate that graph network prediction is excellent,which could save significantly computing resources and time.In addition to active matter,our method can be applied widely to other large-scale physical systems.展开更多
The two characteristics of near-fault ground motions, i.e., the forward directivity effect and permanent displacement effect, result in long period and large velocity pulse in the velocity time history and large step ...The two characteristics of near-fault ground motions, i.e., the forward directivity effect and permanent displacement effect, result in long period and large velocity pulse in the velocity time history and large step pulse in the displacement time history. Considering the two effects, a simple expression of continuous function for equivalent velocity pulse time history is presented in this paper. The equivalent pulse model, in which the pulse period, peak velocity and pulse shape are described by five parameters, is highly advantageous to fit and simulate the pulse-type velocity time history. The equivalent pulse model comprises only one low-frequency component while the high-frequency component of a pulse-type earthquake record cannot be considered. Based on 28 records of 11 earthquakes, the pulse frequency of pulse-type records is generally less than 1 Hz. Therefore the low-frequency component and high-frequency component are simulated respectively and combined them together to generate a pulse-type ground motion.展开更多
In the process of crowd movement,pedestrians are often affected by their neighbors.In order to describe the consistency of adjacent individuals and collectivity of a group,this paper learns from the rules of the flock...In the process of crowd movement,pedestrians are often affected by their neighbors.In order to describe the consistency of adjacent individuals and collectivity of a group,this paper learns from the rules of the flocking behavior,such as segregation,alignment and cohesion,and proposes a method for crowd motion simulation based on the Boids model and social force model.Firstly,the perception area of individuals is divided into zone of segregation,alignment and cohesion.Secondly,the interactive force among individuals is calculated based upon the zone information,velocity vector and the group information.The interactive force among individuals is the synthesis of three forces:the repulsion force to avoid collisions,the alignment force to keep consistent with the velocity direction,and the attractive force to get close to the members of group.In segregation and alignment areas,the repulsion force and alignment force among pedestrians are limited by visual field factors.Finally,the interactive force among individuals,the driving force of destination and the repulsion force of obstacles work together to drive the behavior of crowd motion.The simulation results show that the proposed method can not only effectively simulate the interactive behavior between adjacent individuals but also the collective behavior of group.展开更多
基于实验室设备自主开发了一套320 kV锥束工业CT成像系统。首先设计了基于运动控制卡的六轴机械扫描平台,并将其与320 kV射线机、平板探测器结合搭建了锥束CT成像系统的硬件。其次,利用平板探测器和运动控制卡的动态链接库开发锥束CT投...基于实验室设备自主开发了一套320 kV锥束工业CT成像系统。首先设计了基于运动控制卡的六轴机械扫描平台,并将其与320 kV射线机、平板探测器结合搭建了锥束CT成像系统的硬件。其次,利用平板探测器和运动控制卡的动态链接库开发锥束CT投影数据采集软件和重建软件,自主开发FDK算法并基于CUDA架构实现FDK算法的GPU加速。最后,采用阻尼器对锥束CT成像系统进行测试。结果表明,整个系统运行稳定,可以获得高质量的CT重建图像,且重建效果与VG STUDIO MAX 3.4软件的重建效果一致。展开更多
Collective motion is one of the most fascinating phenomena and mainly caused by the interactions between individuals. Physical-barriers, as the particular facilities which divide the crowd into different lanes, greatl...Collective motion is one of the most fascinating phenomena and mainly caused by the interactions between individuals. Physical-barriers, as the particular facilities which divide the crowd into different lanes, greatly affect the measurement of such interactions. In this paper we propose the physical-barrier detection based collective motion analysis (PDCMA) approach. The main idea is that the interaction between spatially adjacent pedestrians actually does not exist if they are separated by the physical-barrier. Firstly, the physical-barriers are extracted by two-stage clustering. The scene is automatically divided into several motion regions. Secondly, local region collectiveness is calculated to represent the interactions between pedestrians in each region. Finally, extensive evaluations use the three typical methods, i.e., the PDCMA, the Collectiveness, and the average normalized Velocity, to show the efficiency and efficacy of our approach in the scenes with and without physical barriers. Moreover, several escalator scenes are selected as the typical physical-barrier test scenes to demonstrate the performance of our approach. Compared with the current collective motion analysis methods, our approach better adapts to the scenes with physical barriers.展开更多
文摘Through a higher-order boundary element method based on NURBS （Non-uniform Rational B-splines）, the calculation of second-order low-frequency forces and slow drift motions is conducted for floating bodies. In the floating body＇s inner domain, an auxiliary equation is obtained by applying a Green function which satisfies the solid surface condition. Then, the auxiliary equation and the velocity potential equation are combined in the fluid domain to remove the solid angle coefficient and the singularity of the double layer potentials in the integral equation. Thus, a new velocity potential integral equation is obtained. The new equation is extended to the inner domain to reheve the irregular frequency effects; on the basis of the order analysis, the comparison is made about the contribution of all integral terms with the result in the second-order tow-frequency problem; the higher-order boundary element method based on NURBS is apphed to calculate the geometric position and velocity potentials; the slow drift motions are calculated by the spectrum analysis method. Removing the solid angle coefficient can apply NURBS technology to the hydrodynamic calculation of floating bodies with complex surfaces, and the extended boundary integral method can reduce the irregular frequency effects. Order analysis shows that free surface integral can be neglected, and the numerical results can also prove the correctness of order analysis. The results of second-order low-frequency forces and slow drift motions and the comparison with the results from references show that the application of the NURBS technology to the second-order low-frequency problem is of high efficiency and credible results.
基金supported by the National Natural Science Foundation of China(Nos.10932004 and 11272127)
文摘A structure consisting of a spiral piezoelectric transducer and a concentrated mass is proposed as a low-frequency piezoelectric power harvester. A theoretical model is developed for the system from the theory of piezoelectricity. An analysis is performed to demonstrate the low-frequency nature of the system. Other basic characteristics of the power harvester including the output power, voltage, and efficiency are also calculated and examined.
文摘We propose a quantum nondemolition measurement of the collective motional energy of two trapped ions for the first time.It is based on the excitation of the two ions by two lasers with appropriate frequencies and amplitudes.The scheme also provides a new possibility of preparing vibrational Fock states and laser cooling.
文摘After decades of theoretical studies,the rich phase states of active matter and cluster kinetic processes are still of research interest.How to efficiently calculate the dynamical processes under their complex conditions becomes an open problem.Recently,machine learning methods have been proposed to predict the degree of coherence of active matter systems.In this way,the phase transition process of the system is quantified and studied.In this paper,we use graph network as a powerful model to determine the evolution of active matter with variable individual velocities solely based on the initial position and state of the particles.The graph network accurately predicts the order parameters of the system in different scale models with different individual velocities,noise and density to effectively evaluate the effect of diverse condition.Compared with the classical physical deduction method,we demonstrate that graph network prediction is excellent,which could save significantly computing resources and time.In addition to active matter,our method can be applied widely to other large-scale physical systems.
基金National Natural Science Foundation of China (50478063)
文摘The two characteristics of near-fault ground motions, i.e., the forward directivity effect and permanent displacement effect, result in long period and large velocity pulse in the velocity time history and large step pulse in the displacement time history. Considering the two effects, a simple expression of continuous function for equivalent velocity pulse time history is presented in this paper. The equivalent pulse model, in which the pulse period, peak velocity and pulse shape are described by five parameters, is highly advantageous to fit and simulate the pulse-type velocity time history. The equivalent pulse model comprises only one low-frequency component while the high-frequency component of a pulse-type earthquake record cannot be considered. Based on 28 records of 11 earthquakes, the pulse frequency of pulse-type records is generally less than 1 Hz. Therefore the low-frequency component and high-frequency component are simulated respectively and combined them together to generate a pulse-type ground motion.
文摘In the process of crowd movement,pedestrians are often affected by their neighbors.In order to describe the consistency of adjacent individuals and collectivity of a group,this paper learns from the rules of the flocking behavior,such as segregation,alignment and cohesion,and proposes a method for crowd motion simulation based on the Boids model and social force model.Firstly,the perception area of individuals is divided into zone of segregation,alignment and cohesion.Secondly,the interactive force among individuals is calculated based upon the zone information,velocity vector and the group information.The interactive force among individuals is the synthesis of three forces:the repulsion force to avoid collisions,the alignment force to keep consistent with the velocity direction,and the attractive force to get close to the members of group.In segregation and alignment areas,the repulsion force and alignment force among pedestrians are limited by visual field factors.Finally,the interactive force among individuals,the driving force of destination and the repulsion force of obstacles work together to drive the behavior of crowd motion.The simulation results show that the proposed method can not only effectively simulate the interactive behavior between adjacent individuals but also the collective behavior of group.
文摘基于实验室设备自主开发了一套320 kV锥束工业CT成像系统。首先设计了基于运动控制卡的六轴机械扫描平台,并将其与320 kV射线机、平板探测器结合搭建了锥束CT成像系统的硬件。其次,利用平板探测器和运动控制卡的动态链接库开发锥束CT投影数据采集软件和重建软件,自主开发FDK算法并基于CUDA架构实现FDK算法的GPU加速。最后,采用阻尼器对锥束CT成像系统进行测试。结果表明,整个系统运行稳定,可以获得高质量的CT重建图像,且重建效果与VG STUDIO MAX 3.4软件的重建效果一致。
基金the National Key Research and Development Program of China (2016YFA0502300)the National Natural Science Foundation of China (Grant No. 61602175)+3 种基金Shanghai Municipal Commission of Economy and Informatization (150809)the Open Research Funding Program of KLGIS (KLGIS2015A05) and BUAA (BUAAVR- 15KF-03)the Fundamental Research Funds for the Central Universities (222201514331)Green Manufacturing System Integration Project of Ministry of Industry and Technology of China (9908000006).
文摘Collective motion is one of the most fascinating phenomena and mainly caused by the interactions between individuals. Physical-barriers, as the particular facilities which divide the crowd into different lanes, greatly affect the measurement of such interactions. In this paper we propose the physical-barrier detection based collective motion analysis (PDCMA) approach. The main idea is that the interaction between spatially adjacent pedestrians actually does not exist if they are separated by the physical-barrier. Firstly, the physical-barriers are extracted by two-stage clustering. The scene is automatically divided into several motion regions. Secondly, local region collectiveness is calculated to represent the interactions between pedestrians in each region. Finally, extensive evaluations use the three typical methods, i.e., the PDCMA, the Collectiveness, and the average normalized Velocity, to show the efficiency and efficacy of our approach in the scenes with and without physical barriers. Moreover, several escalator scenes are selected as the typical physical-barrier test scenes to demonstrate the performance of our approach. Compared with the current collective motion analysis methods, our approach better adapts to the scenes with physical barriers.
