Nonlinear behaviors of a free-floating body in waves were experimentally investigated in the present study. The experiments were carried out for 6 different wave heights and 6 different wave periods to cover a relativ...Nonlinear behaviors of a free-floating body in waves were experimentally investigated in the present study. The experiments were carried out for 6 different wave heights and 6 different wave periods to cover a relatively wide range of wave nonlinearities. A charge-coupled device （CCD） camera was used to capture the real-time motion of the floating body. The measurement data show that the sway, heave and roll motions of the floating body are all harmonic oscillations while the equilibrium position of the sway motion drifts in the wave direction. The drift speed is proportional to wave steepness when the size of the floating body is comparable to the wavelength, while it is proportional to the square of wave steepness when the floating body is relatively small. In addition, the drift motion leads to a slightly longer oscillation period of the floating body than the wave period of nonlinear wave and the discrepancy increases with the increment of wave steepness.展开更多
Complex phenomena such as prolongedly undamped ultra-low frequency oscillation(ULFO)and eigenmode re-excitation are observed in the simulations of hydroelectric power systems.Emphases are put on nonlinearities and mod...Complex phenomena such as prolongedly undamped ultra-low frequency oscillation(ULFO)and eigenmode re-excitation are observed in the simulations of hydroelectric power systems.Emphases are put on nonlinearities and mode interactions,which cannot be analyzed by traditional eigen-analysis methods.In order to investigate the mechanism of the evolvement of the nonlinear dynamic process in ULFO,this paper proposes a method to analyze the mode interactions quantificationally.First,a disturbed trajectory is decoupled into a set of time-varying components.Second,transfer matrices of eigenmodes are extracted along the trajectory.Third,consecutive sequences of eigenvalues and trajectories of components are formed by a proposed technique.Based on the decoupled components and transfer matrices,the mechanisms of mode interactions and inheritance relationships between eigenmodes are analyzed.The causes and developments of the above complex phenomena are revealed by the proposed method in a test two-machine system.Meanwhile,the accuracy of the eigenmode matching technique is verified in the New England system.展开更多
The effects of pressure oscillation on aerodynamic characteristics in an aero-engine combustor are investigated. A combustor test rig is designed to simulate the pressure drop characteristics of a practical annular co...The effects of pressure oscillation on aerodynamic characteristics in an aero-engine combustor are investigated. A combustor test rig is designed to simulate the pressure drop characteristics of a practical annular combustor. The pressure drop characteristics are firstly measured under atmosphere condition with non-reacting flow(or cold flow), and the air mass flow proportion of each component(dome/liner) are obtained;these properties are base lines for comparison with combustion state. The combustion tests are then carried out under conditions of inlet temperature 340–450 K, fuel air ratio 0.010–0.028. The stability map and the oscillation frequencies are obtained in the tests, the results show that pressure oscillation amplitude increases with the increase of fuel air ratio. Phase trajectory reconstruction is applied to classify the pressure oscillation motion;there are three motions captured in the tests including: ‘‘disk", ‘‘ring" and ‘‘cluster". The pressure drops across the dome under strong pressure oscillation are distinctly divergent from the cold flow, and the changes of pressure drops are mainly affected by pressure oscillation amplitude, but is less influenced by pressure oscillation motion nor oscillation frequencies. Based on the mass flow conservation, the reduction of effective flow area of combustor under strong pressure oscillation is demonstrated. Liner wall temperatures are analyzed through Multiple Linear Regression(MLR)method to estimate the reduction of the air mass flow proportion of the liner cooling under strong pressure oscillation. Finally, the air mass flow proportions of each component under strong pressure oscillation are estimated, the results show that the pressure oscillation motion also has influence on air mass flow proportion.展开更多
Affected by the nonlinear time-varying factors due to fault scenarios,protection relaying,and control measures,the dynamic behaviors of a power system may be significantly different from the results of previous method...Affected by the nonlinear time-varying factors due to fault scenarios,protection relaying,and control measures,the dynamic behaviors of a power system may be significantly different from the results of previous methods.In order to analyze the oscillation characteristics of complex power systems more accurately and suppress the low frequency oscillation more effectively,this paper improves the trajectory section eigenvalue method.Firstly,the time response of a system is obtained by numerical simulation in a given fault scenario.Secondly,the algebraic variables are substituted to the differential equations along the trajectory.Thus,the original time-varying differential-algebraic equations are approximated by a set of linear ordinary differential equations,which can be updated along the trajectory.On this basis,this paper proposes a method to extract instantaneous features of the oscillation from the micro perspective.The non-equilibrium points with strong nonlinearity or critical eigenmodes are identified by the proposed method.The simulation test results of the IEEE 3-machine 9-bus system and the New England system illustrate the validity of the proposed method.展开更多
The intraseasonal oscillation(ISO) of the South China Sea(SCS, 105-120°E, 5-20°N) convection and its influences on the genesis and track of the western North Pacific(WNP) tropical cyclones(TCs) were explored...The intraseasonal oscillation(ISO) of the South China Sea(SCS, 105-120°E, 5-20°N) convection and its influences on the genesis and track of the western North Pacific(WNP) tropical cyclones(TCs) were explored, based on the daily average of NCEP/NCAR reanalysis data, the OLR data and the western North Pacific tropical cyclone best-track data from 1979 to 2008. The mechanism of the influences of ISO on TC movement and the corresponding large-scale circulation were discussed by a trajectory model. It was found as follows.(1) During the SCS summer monsoon, the SCS convection exhibits the ISO features with active phases alternating with inactive phases. The monsoon circulation patterns are significantly different during these two phases. When the SCS convection is active(inactive), the SCS-WNP monsoon trough stretches eastward(retreats westward) due to the activity(inactivity) of SCS monsoon, and the WNP subtropical high retreats eastward(stretches westward), which enhances(suppresses) the monsoon circulation.(2) The amount of TC genesis in the active phase is much more than that in the inactive phase. A majority of TCs form west of 135 °E during the active phases but east of 135 °E in the inactive phases.(3) The TCs entering the area west of 135 °E and south of 25 °N would move straight into the SCS in the active phase, or recurve northward in the inactive phase.(4) Simulation results show that the steering flow associated with the active(inactive)phases is in favor of straight-moving(recurving) TCs. Meanwhile, the impacts of the locations of TC genesis on the characteristics of TC track cannot be ignored. TCs that occurred father westward are more likely to move straight into the SCS region.展开更多
田路分割是农机轨迹语义分割模型的重要任务之一,其目的是将轨迹自动分割为田间作业轨迹和道路行驶轨迹。田路分割模型的参数是影响其分割准确性及精度的关键因素,传统的参数选择方法效率较低且难以获得较好的方案,限制了模型的分割性...田路分割是农机轨迹语义分割模型的重要任务之一,其目的是将轨迹自动分割为田间作业轨迹和道路行驶轨迹。田路分割模型的参数是影响其分割准确性及精度的关键因素,传统的参数选择方法效率较低且难以获得较好的方案,限制了模型的分割性能。因此,该研究选用基于方向分布的田路分割模型(Field-Road Trajectory Segmentation Based on Direction Distribution,BDFRTS),尝试从参数优化的角度研究模型的性能提升,提出的方法主要包括两个方面,首先建立了一种基于元启发式算法(Metaheuristic Algorithms,MA)的田路分割模型参数优化解决方案;其次,在黏菌算法(Slime Mould Algorithm,SMA)的基础上提出了一种改进的多元振荡黏菌算法(Multiplex Oscillation Slime Mould Algorithm,MOSMA)求解参数优化方案以更好地提高模型的分割性能。MOSMA分别提出一种动态引导策略与多元振荡策略强化了黏菌的振荡收缩反应及细胞质的流动过程,进而增强了算法的优化能力。为验证所提参数优化方法的有效性,将博创联动提供的中国农机在2021年9月底—10月中下旬进行水稻收割的作业轨迹作为数据集开展试验。试验结果表明,该研究所提方法有效地提升了田路分割模型的准确性和性能。MOSMA-BDFRTS分割模型在10组高密度轨迹中的平均准确率相比网格搜索田路分割模型、粒子群田路分割模型分别提高了25和28个百分点;在10组低密度轨迹中分割的平均准确率分别提高了17和14个百分点。该研究可为田路分割技术提供合理的性能优化方案,也为农业机械运动轨迹分割技术的效率研究提供参考依据。展开更多
基金financially supported by the National Natural Science Foundation of China(Grant No.11272079)the National Basic Research Program of China(973 Program,Grant No.2011CB013702)
文摘Nonlinear behaviors of a free-floating body in waves were experimentally investigated in the present study. The experiments were carried out for 6 different wave heights and 6 different wave periods to cover a relatively wide range of wave nonlinearities. A charge-coupled device （CCD） camera was used to capture the real-time motion of the floating body. The measurement data show that the sway, heave and roll motions of the floating body are all harmonic oscillations while the equilibrium position of the sway motion drifts in the wave direction. The drift speed is proportional to wave steepness when the size of the floating body is comparable to the wavelength, while it is proportional to the square of wave steepness when the floating body is relatively small. In addition, the drift motion leads to a slightly longer oscillation period of the floating body than the wave period of nonlinear wave and the discrepancy increases with the increment of wave steepness.
基金supported by the Program of State Grid Corporation of China“Theoretical BasisAlgorithmand Application of Trajectory Eigenvalue Method”
文摘Complex phenomena such as prolongedly undamped ultra-low frequency oscillation(ULFO)and eigenmode re-excitation are observed in the simulations of hydroelectric power systems.Emphases are put on nonlinearities and mode interactions,which cannot be analyzed by traditional eigen-analysis methods.In order to investigate the mechanism of the evolvement of the nonlinear dynamic process in ULFO,this paper proposes a method to analyze the mode interactions quantificationally.First,a disturbed trajectory is decoupled into a set of time-varying components.Second,transfer matrices of eigenmodes are extracted along the trajectory.Third,consecutive sequences of eigenvalues and trajectories of components are formed by a proposed technique.Based on the decoupled components and transfer matrices,the mechanisms of mode interactions and inheritance relationships between eigenmodes are analyzed.The causes and developments of the above complex phenomena are revealed by the proposed method in a test two-machine system.Meanwhile,the accuracy of the eigenmode matching technique is verified in the New England system.
文摘The effects of pressure oscillation on aerodynamic characteristics in an aero-engine combustor are investigated. A combustor test rig is designed to simulate the pressure drop characteristics of a practical annular combustor. The pressure drop characteristics are firstly measured under atmosphere condition with non-reacting flow(or cold flow), and the air mass flow proportion of each component(dome/liner) are obtained;these properties are base lines for comparison with combustion state. The combustion tests are then carried out under conditions of inlet temperature 340–450 K, fuel air ratio 0.010–0.028. The stability map and the oscillation frequencies are obtained in the tests, the results show that pressure oscillation amplitude increases with the increase of fuel air ratio. Phase trajectory reconstruction is applied to classify the pressure oscillation motion;there are three motions captured in the tests including: ‘‘disk", ‘‘ring" and ‘‘cluster". The pressure drops across the dome under strong pressure oscillation are distinctly divergent from the cold flow, and the changes of pressure drops are mainly affected by pressure oscillation amplitude, but is less influenced by pressure oscillation motion nor oscillation frequencies. Based on the mass flow conservation, the reduction of effective flow area of combustor under strong pressure oscillation is demonstrated. Liner wall temperatures are analyzed through Multiple Linear Regression(MLR)method to estimate the reduction of the air mass flow proportion of the liner cooling under strong pressure oscillation. Finally, the air mass flow proportions of each component under strong pressure oscillation are estimated, the results show that the pressure oscillation motion also has influence on air mass flow proportion.
基金supported by Science and Technology Program of State Grid Corporation of China(Theoretical Basis,Algorithm and Application of Trajectory Eigenvalue Method).
文摘Affected by the nonlinear time-varying factors due to fault scenarios,protection relaying,and control measures,the dynamic behaviors of a power system may be significantly different from the results of previous methods.In order to analyze the oscillation characteristics of complex power systems more accurately and suppress the low frequency oscillation more effectively,this paper improves the trajectory section eigenvalue method.Firstly,the time response of a system is obtained by numerical simulation in a given fault scenario.Secondly,the algebraic variables are substituted to the differential equations along the trajectory.Thus,the original time-varying differential-algebraic equations are approximated by a set of linear ordinary differential equations,which can be updated along the trajectory.On this basis,this paper proposes a method to extract instantaneous features of the oscillation from the micro perspective.The non-equilibrium points with strong nonlinearity or critical eigenmodes are identified by the proposed method.The simulation test results of the IEEE 3-machine 9-bus system and the New England system illustrate the validity of the proposed method.
基金National Basic Research Program of China(2015CB953904)National Natural Science Foundation of China(41575081)+1 种基金Startup Foundation for Introducing Talent of NUIST(2015r035)Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)
文摘The intraseasonal oscillation(ISO) of the South China Sea(SCS, 105-120°E, 5-20°N) convection and its influences on the genesis and track of the western North Pacific(WNP) tropical cyclones(TCs) were explored, based on the daily average of NCEP/NCAR reanalysis data, the OLR data and the western North Pacific tropical cyclone best-track data from 1979 to 2008. The mechanism of the influences of ISO on TC movement and the corresponding large-scale circulation were discussed by a trajectory model. It was found as follows.(1) During the SCS summer monsoon, the SCS convection exhibits the ISO features with active phases alternating with inactive phases. The monsoon circulation patterns are significantly different during these two phases. When the SCS convection is active(inactive), the SCS-WNP monsoon trough stretches eastward(retreats westward) due to the activity(inactivity) of SCS monsoon, and the WNP subtropical high retreats eastward(stretches westward), which enhances(suppresses) the monsoon circulation.(2) The amount of TC genesis in the active phase is much more than that in the inactive phase. A majority of TCs form west of 135 °E during the active phases but east of 135 °E in the inactive phases.(3) The TCs entering the area west of 135 °E and south of 25 °N would move straight into the SCS in the active phase, or recurve northward in the inactive phase.(4) Simulation results show that the steering flow associated with the active(inactive)phases is in favor of straight-moving(recurving) TCs. Meanwhile, the impacts of the locations of TC genesis on the characteristics of TC track cannot be ignored. TCs that occurred father westward are more likely to move straight into the SCS region.
文摘田路分割是农机轨迹语义分割模型的重要任务之一,其目的是将轨迹自动分割为田间作业轨迹和道路行驶轨迹。田路分割模型的参数是影响其分割准确性及精度的关键因素,传统的参数选择方法效率较低且难以获得较好的方案,限制了模型的分割性能。因此,该研究选用基于方向分布的田路分割模型(Field-Road Trajectory Segmentation Based on Direction Distribution,BDFRTS),尝试从参数优化的角度研究模型的性能提升,提出的方法主要包括两个方面,首先建立了一种基于元启发式算法(Metaheuristic Algorithms,MA)的田路分割模型参数优化解决方案;其次,在黏菌算法(Slime Mould Algorithm,SMA)的基础上提出了一种改进的多元振荡黏菌算法(Multiplex Oscillation Slime Mould Algorithm,MOSMA)求解参数优化方案以更好地提高模型的分割性能。MOSMA分别提出一种动态引导策略与多元振荡策略强化了黏菌的振荡收缩反应及细胞质的流动过程,进而增强了算法的优化能力。为验证所提参数优化方法的有效性,将博创联动提供的中国农机在2021年9月底—10月中下旬进行水稻收割的作业轨迹作为数据集开展试验。试验结果表明,该研究所提方法有效地提升了田路分割模型的准确性和性能。MOSMA-BDFRTS分割模型在10组高密度轨迹中的平均准确率相比网格搜索田路分割模型、粒子群田路分割模型分别提高了25和28个百分点;在10组低密度轨迹中分割的平均准确率分别提高了17和14个百分点。该研究可为田路分割技术提供合理的性能优化方案,也为农业机械运动轨迹分割技术的效率研究提供参考依据。
