The problem of track control is studied for a class of strict-feedback stochastic nonlinear systems in which unknown virtual control gain function is the main feature.First,the so-called stochastic LaSalle theory is e...The problem of track control is studied for a class of strict-feedback stochastic nonlinear systems in which unknown virtual control gain function is the main feature.First,the so-called stochastic LaSalle theory is extended to some extent,and accordingly,the results of global ultimate boundedness for stochastic nonlinear systems are developed.Next,a new design scheme of fuzzy adaptive control is proposed.The advantage of it is that it does not require priori knowledge of virtual control gain function sign,which is usually demanded in many designs.At the same time,the track performance of closed-loop systems is improved by adaptive modifying the estimated error upper bound.By theoretical analysis,the signals of closed-loop systems are globally ultimately bounded in probability and the track error converges to a small residual set around the origin in 4th-power expectation.展开更多
The stiffness reduction is studied in detail of compact W-Shapes （wide-flange steel shapes） that results from yielding of the cross-section due to uniaxial bending and axial compression. Three-dimensional m-p-τ su...The stiffness reduction is studied in detail of compact W-Shapes （wide-flange steel shapes） that results from yielding of the cross-section due to uniaxial bending and axial compression. Three-dimensional m-p-τ surface plots developed from detailed fiber element models of a W8x31 are used to develop a generalized material model for direct implementation in the virtual work method. A portal steel frame is used to illustrate the virtual work method with the nonlinear material model in a first-order, inelastic analysis implementation and in a second-order, inelastic analysis condition. The nonlinear modeling capabilities of MASTAN2 are used to verify the accuracy of the virtual work results and are found to be in very close agreement.展开更多
We uncover the virtual monopoles underlying the nontrivial phases of the one-dimensional nonlinear excitations of rogue waves by extending the Dirac magnetic monopole theory to a complex plane. We find that the densit...We uncover the virtual monopoles underlying the nontrivial phases of the one-dimensional nonlinear excitations of rogue waves by extending the Dirac magnetic monopole theory to a complex plane. We find that the density zeros of the nonlinear waves on the extended complex plane constitute the virtual monopole fields with a quantized flux of elementary π. We then explain the exotic properties of rogue waves by means of a virtual monopole collision mechanism and find that the maximum amplitude amplification ratio and multiple phase steps of the high-order rogue waves are closely related to the number of their contained monopoles. These results open a new avenue for studying topological properties of nonlinear waves and provide an alternative way to understand their dynamics.展开更多
无刷直流电机(Brushless DC Motor,简称BLDCM)凭借高功率密度、高效能以及低维护费用等优势,在工业自动化、航空航天、电力巡检等多个领域被广泛采用[1]。不过,受其自身独特结构的制约,电机在运转过程中会产生以齿槽转矩为主导的非线性...无刷直流电机(Brushless DC Motor,简称BLDCM)凭借高功率密度、高效能以及低维护费用等优势,在工业自动化、航空航天、电力巡检等多个领域被广泛采用[1]。不过,受其自身独特结构的制约,电机在运转过程中会产生以齿槽转矩为主导的非线性干扰,这极大地阻碍了系统模型的精准辨识,进而对高性能控制算法的研发与应用造成限制。通过深入剖析了无刷直流电机非线性干扰对系统辨识产生的作用,进而提出一种借助小波包变换的开环辨识策略,以及一种基于虚拟对象建模的闭环辨识策略,达到提高无刷直流电机模型在非线性干扰环境下的辨识精度,通过仿真与实验验证,所提出的方法在不同工作点、不同干扰位置的情况下,均能大幅提升模型辨识的精准度。展开更多
A CFD-based Numerical Virtual Flight(NVF)simulator is presented,which integrates an unsteady flow solver on moving hybrid grids,a Rigid-Body Dynamics(RBD)solver and a module of the Flight Control System(FCS).A techni...A CFD-based Numerical Virtual Flight(NVF)simulator is presented,which integrates an unsteady flow solver on moving hybrid grids,a Rigid-Body Dynamics(RBD)solver and a module of the Flight Control System(FCS).A technique of dynamic hybrid grids is developed to control the active control surfaces with body morphing,with a technique of parallel unstructured dynamic overlapping grids generating proper moving grids over the deflecting control surfaces(e.g.the afterbody rudders of a missile).For the flow/kinematic coupled problems,the 6 Degree-Of-Freedom(DOF)equations are solved by an explicit or implicit method coupled with the URANS CFD solver.The module of the control law is explicitly coupled into the NVF simulator and then improved by the simulation of the pitching maneuver process of a maneuverable missile model.A nonlinear dynamic inversion method is then implemented to design the control law for the pitching process of the maneuverable missile model.Simulations and analysis of the pitching maneuver process are carried out by the NVF simulator to improve the flight control law.Higher control response performance is obtained by adjusting the gain factors and adding an integrator into the control loop.展开更多
This paper proposes a virtual position-offset injection based permanent magnet temperature estimation approach for permanent magnet synchronous machines(PMSMs). The concept of virtual position-offset injection is math...This paper proposes a virtual position-offset injection based permanent magnet temperature estimation approach for permanent magnet synchronous machines(PMSMs). The concept of virtual position-offset injection is mathematically transforming the machine model to a virtual frame with a position-offset. The virtual frame temperature estimation model is derived to calculate the permanent magnet temperature(PMT) directly from the measurements with computation efficiency. The estimation model involves a combined inductance term, which can simplify the establishment of saturation compensation model with less measurements. Moreover, resistance and inverter distorted terms are cancelled in the estimation model, which can improve the robustness to the winding temperature rise and inverter distortion. The proposed approach can achieve simplified computation in temperature estimation and reduced memory usage in saturation compensation. While existing model-based approaches could be affected by either the need of resistance and inverter information or complex saturation compensation. Experiments are conducted on the test machine to verify the proposed approach under various operating conditions.展开更多
Aiming to the puzzle that the inner load of nonlinear synthesis transmission system is difficult to obtain,a new kind of virtual prototype establishment and simulation method is put forward. The influence on nonlinear...Aiming to the puzzle that the inner load of nonlinear synthesis transmission system is difficult to obtain,a new kind of virtual prototype establishment and simulation method is put forward. The influence on nonlinear vibration with flexible rotor, bearing backlash is analyzed based on a virtual prototype. To validate the virtual prototype of nonlinear gear transmission system, the corresponding test platform is established. The consistency between simulation results and test results proves that the simulation results of the virtual prototype can be used to calculate the fatigue reliability life of key components. A new kind of fatigue reliability life prediction method of gear system considering multi-random parameter distribution is put forward based on the fativipatistic theory. Considering the periodicity of gear meshing, linear interpolation method is adopted to obtain the stress-time course of random load spectrum based on the gear's complicated torque provided by virtual prototype.The gear's P-Sa-Sm-N curved cluster can be simulated based on material's P-S-N curve. The simulation process considers the parameter distributions of stress concentration coefficients, dimension coefficients and surface quality treatment coefficients, and settles the puzzle that traditional test methods cannot acquire the gear's fatigue life of all reliability levels. This method can provide the distribution function and the interval of fatigue reliability life of gear's danger region, and has a guide meaning for the gear maintenance periods determination and reliability evaluation.展开更多
A finite element formulation was presented for the nonlinear free vibration of thin-walled curved beams with non-symmetric open across section. The kinetic and potential energies were derived by the virtual principle....A finite element formulation was presented for the nonlinear free vibration of thin-walled curved beams with non-symmetric open across section. The kinetic and potential energies were derived by the virtual principle. The energy function includes the effect of fiexural-torsional coupling, the torsion warping and the shear centre location. For finite element analysis, cubic polynomials were utilized as the shape functions of the two nodal thin-walled curved elements. Each node possesses seven degrees freedom including the warping degree of freedom. The nonlinear eigenvalue problem was solved by the direct iteration technique. The results are compared with those for straight beams as available in the literature. The results for nonlinear free vibration analysis of curved beams for various radii and subtended angle are presented.展开更多
A lot of work has focused on compensating nonlinear distortions ofthe microspeaker under large excitation, yet it is unclear at which levelthe effect of nonlinear distortion is imperceptible or not annoying. Inthis st...A lot of work has focused on compensating nonlinear distortions ofthe microspeaker under large excitation, yet it is unclear at which levelthe effect of nonlinear distortion is imperceptible or not annoying. Inthis study virtual listening tests were performed to evaluate thedeterioration of sound quality in music signals with different levels ofnonlinear distortion by a microspeaker. Binaural recordings of themusic played by the microspeaker were made at different voltagelevels, adjusted to the same RMS power, and afterwards reproducedby a low distortion reference headphone. The “double-blind triple-stimuluswith hidden reference” method was used in the listening tests. Listenerswere required to not only discern the distortion, but also rank theseverity of the distortion. The effects of several factors includingsubject, program material and distortion level on the perceiveddistortion are discussed.展开更多
Multi-functioning in virtual monitoring and assessment of ultimate dynamics of thin-walled bridges is treated in present paper. The approach enables multiple functions in virtual monitoring of the bridges made of inte...Multi-functioning in virtual monitoring and assessment of ultimate dynamics of thin-walled bridges is treated in present paper. The approach enables multiple functions in virtual monitoring of the bridges made of integrated thin-walled members with their hierarchical configuration. Theoretical, numerical and experimental in situ assessments of the problem are presented. Some results of structural application are submitted.展开更多
基于台架采集数据,采用外部输入非线性自回归(nonlinear autoregressive model with exogenous input,NARX)神经网络建立了具备瞬态特性的柴油机排气温度计算模型作为虚拟传感器,并采用并发式训练方法对模型进行训练。将结果与前馈神经...基于台架采集数据,采用外部输入非线性自回归(nonlinear autoregressive model with exogenous input,NARX)神经网络建立了具备瞬态特性的柴油机排气温度计算模型作为虚拟传感器,并采用并发式训练方法对模型进行训练。将结果与前馈神经网络、长短期记忆网络(long short term memory,LSTM)神经网络及量产发动机的排温传感器采集结果进行对比。经验证,稳态工况下,两种神经网络均能达到较高精度;欧洲瞬态循环(European transient cycle,ETC)工况下,NARX神经网络计算温度的最大偏差为6.6℃,量产发动机排温传感器测得温度最大偏差为45.9℃。NARX神经网络所需的计算时间约为现有电控单元排温模型的2.5倍。展开更多
Dear Editor,This letter addresses the formation control problem for constrained underactuated autonomous underwater vehicles (AUVs). The feasibility condition of the virtual control law is eliminated by introducing a ...Dear Editor,This letter addresses the formation control problem for constrained underactuated autonomous underwater vehicles (AUVs). The feasibility condition of the virtual control law is eliminated by introducing a nonlinear state dependence function (NSDF) that transforms the state of each AUV in the formation.展开更多
基金Supported by National Natural Science Foundation of P.R.China(60572070,60325311,60534010)Natural Science Foundation of Liaoning Province(20022030)
文摘The problem of track control is studied for a class of strict-feedback stochastic nonlinear systems in which unknown virtual control gain function is the main feature.First,the so-called stochastic LaSalle theory is extended to some extent,and accordingly,the results of global ultimate boundedness for stochastic nonlinear systems are developed.Next,a new design scheme of fuzzy adaptive control is proposed.The advantage of it is that it does not require priori knowledge of virtual control gain function sign,which is usually demanded in many designs.At the same time,the track performance of closed-loop systems is improved by adaptive modifying the estimated error upper bound.By theoretical analysis,the signals of closed-loop systems are globally ultimately bounded in probability and the track error converges to a small residual set around the origin in 4th-power expectation.
文摘The stiffness reduction is studied in detail of compact W-Shapes （wide-flange steel shapes） that results from yielding of the cross-section due to uniaxial bending and axial compression. Three-dimensional m-p-τ surface plots developed from detailed fiber element models of a W8x31 are used to develop a generalized material model for direct implementation in the virtual work method. A portal steel frame is used to illustrate the virtual work method with the nonlinear material model in a first-order, inelastic analysis implementation and in a second-order, inelastic analysis condition. The nonlinear modeling capabilities of MASTAN2 are used to verify the accuracy of the virtual work results and are found to be in very close agreement.
基金supported by the National Natural Science Foundation of China (Grant Nos.12375005,12022513,and12235007)the National Safety Academic Fund(Grant No.U2330401)。
文摘We uncover the virtual monopoles underlying the nontrivial phases of the one-dimensional nonlinear excitations of rogue waves by extending the Dirac magnetic monopole theory to a complex plane. We find that the density zeros of the nonlinear waves on the extended complex plane constitute the virtual monopole fields with a quantized flux of elementary π. We then explain the exotic properties of rogue waves by means of a virtual monopole collision mechanism and find that the maximum amplitude amplification ratio and multiple phase steps of the high-order rogue waves are closely related to the number of their contained monopoles. These results open a new avenue for studying topological properties of nonlinear waves and provide an alternative way to understand their dynamics.
文摘无刷直流电机(Brushless DC Motor,简称BLDCM)凭借高功率密度、高效能以及低维护费用等优势,在工业自动化、航空航天、电力巡检等多个领域被广泛采用[1]。不过,受其自身独特结构的制约,电机在运转过程中会产生以齿槽转矩为主导的非线性干扰,这极大地阻碍了系统模型的精准辨识,进而对高性能控制算法的研发与应用造成限制。通过深入剖析了无刷直流电机非线性干扰对系统辨识产生的作用,进而提出一种借助小波包变换的开环辨识策略,以及一种基于虚拟对象建模的闭环辨识策略,达到提高无刷直流电机模型在非线性干扰环境下的辨识精度,通过仿真与实验验证,所提出的方法在不同工作点、不同干扰位置的情况下,均能大幅提升模型辨识的精准度。
基金supported partially by National Key Research and Development Program (No. 2016YFB0200701)National Natural Science Foundation of China (Nos. 11532016 and 11672324)
文摘A CFD-based Numerical Virtual Flight(NVF)simulator is presented,which integrates an unsteady flow solver on moving hybrid grids,a Rigid-Body Dynamics(RBD)solver and a module of the Flight Control System(FCS).A technique of dynamic hybrid grids is developed to control the active control surfaces with body morphing,with a technique of parallel unstructured dynamic overlapping grids generating proper moving grids over the deflecting control surfaces(e.g.the afterbody rudders of a missile).For the flow/kinematic coupled problems,the 6 Degree-Of-Freedom(DOF)equations are solved by an explicit or implicit method coupled with the URANS CFD solver.The module of the control law is explicitly coupled into the NVF simulator and then improved by the simulation of the pitching maneuver process of a maneuverable missile model.A nonlinear dynamic inversion method is then implemented to design the control law for the pitching process of the maneuverable missile model.Simulations and analysis of the pitching maneuver process are carried out by the NVF simulator to improve the flight control law.Higher control response performance is obtained by adjusting the gain factors and adding an integrator into the control loop.
基金supported in part by the National Natural Science Foundation of China under Grant 52105079 and 62103455。
文摘This paper proposes a virtual position-offset injection based permanent magnet temperature estimation approach for permanent magnet synchronous machines(PMSMs). The concept of virtual position-offset injection is mathematically transforming the machine model to a virtual frame with a position-offset. The virtual frame temperature estimation model is derived to calculate the permanent magnet temperature(PMT) directly from the measurements with computation efficiency. The estimation model involves a combined inductance term, which can simplify the establishment of saturation compensation model with less measurements. Moreover, resistance and inverter distorted terms are cancelled in the estimation model, which can improve the robustness to the winding temperature rise and inverter distortion. The proposed approach can achieve simplified computation in temperature estimation and reduced memory usage in saturation compensation. While existing model-based approaches could be affected by either the need of resistance and inverter information or complex saturation compensation. Experiments are conducted on the test machine to verify the proposed approach under various operating conditions.
文摘Aiming to the puzzle that the inner load of nonlinear synthesis transmission system is difficult to obtain,a new kind of virtual prototype establishment and simulation method is put forward. The influence on nonlinear vibration with flexible rotor, bearing backlash is analyzed based on a virtual prototype. To validate the virtual prototype of nonlinear gear transmission system, the corresponding test platform is established. The consistency between simulation results and test results proves that the simulation results of the virtual prototype can be used to calculate the fatigue reliability life of key components. A new kind of fatigue reliability life prediction method of gear system considering multi-random parameter distribution is put forward based on the fativipatistic theory. Considering the periodicity of gear meshing, linear interpolation method is adopted to obtain the stress-time course of random load spectrum based on the gear's complicated torque provided by virtual prototype.The gear's P-Sa-Sm-N curved cluster can be simulated based on material's P-S-N curve. The simulation process considers the parameter distributions of stress concentration coefficients, dimension coefficients and surface quality treatment coefficients, and settles the puzzle that traditional test methods cannot acquire the gear's fatigue life of all reliability levels. This method can provide the distribution function and the interval of fatigue reliability life of gear's danger region, and has a guide meaning for the gear maintenance periods determination and reliability evaluation.
文摘A finite element formulation was presented for the nonlinear free vibration of thin-walled curved beams with non-symmetric open across section. The kinetic and potential energies were derived by the virtual principle. The energy function includes the effect of fiexural-torsional coupling, the torsion warping and the shear centre location. For finite element analysis, cubic polynomials were utilized as the shape functions of the two nodal thin-walled curved elements. Each node possesses seven degrees freedom including the warping degree of freedom. The nonlinear eigenvalue problem was solved by the direct iteration technique. The results are compared with those for straight beams as available in the literature. The results for nonlinear free vibration analysis of curved beams for various radii and subtended angle are presented.
文摘A lot of work has focused on compensating nonlinear distortions ofthe microspeaker under large excitation, yet it is unclear at which levelthe effect of nonlinear distortion is imperceptible or not annoying. Inthis study virtual listening tests were performed to evaluate thedeterioration of sound quality in music signals with different levels ofnonlinear distortion by a microspeaker. Binaural recordings of themusic played by the microspeaker were made at different voltagelevels, adjusted to the same RMS power, and afterwards reproducedby a low distortion reference headphone. The “double-blind triple-stimuluswith hidden reference” method was used in the listening tests. Listenerswere required to not only discern the distortion, but also rank theseverity of the distortion. The effects of several factors includingsubject, program material and distortion level on the perceiveddistortion are discussed.
文摘Multi-functioning in virtual monitoring and assessment of ultimate dynamics of thin-walled bridges is treated in present paper. The approach enables multiple functions in virtual monitoring of the bridges made of integrated thin-walled members with their hierarchical configuration. Theoretical, numerical and experimental in situ assessments of the problem are presented. Some results of structural application are submitted.
文摘基于台架采集数据,采用外部输入非线性自回归(nonlinear autoregressive model with exogenous input,NARX)神经网络建立了具备瞬态特性的柴油机排气温度计算模型作为虚拟传感器,并采用并发式训练方法对模型进行训练。将结果与前馈神经网络、长短期记忆网络(long short term memory,LSTM)神经网络及量产发动机的排温传感器采集结果进行对比。经验证,稳态工况下,两种神经网络均能达到较高精度;欧洲瞬态循环(European transient cycle,ETC)工况下,NARX神经网络计算温度的最大偏差为6.6℃,量产发动机排温传感器测得温度最大偏差为45.9℃。NARX神经网络所需的计算时间约为现有电控单元排温模型的2.5倍。
基金supported by the National Natural Science Foundation of China(62073094)the Fundamental Research Funds for the Central Universities(3072024GH0404)
文摘Dear Editor,This letter addresses the formation control problem for constrained underactuated autonomous underwater vehicles (AUVs). The feasibility condition of the virtual control law is eliminated by introducing a nonlinear state dependence function (NSDF) that transforms the state of each AUV in the formation.
