In this paper,the heat transfer enhancement(HTE)of supercritical nitrogen flowing downward in a vertical small tube(diameter 2 mm)is studied using the commercial software CFX of Ansys16.1,to provide theoretical guidan...In this paper,the heat transfer enhancement(HTE)of supercritical nitrogen flowing downward in a vertical small tube(diameter 2 mm)is studied using the commercial software CFX of Ansys16.1,to provide theoretical guidance on the design of high-performance heat transfer systems.An effective numerical simulation method,which employs the SSG Reynolds stress model with enhanced wall treatment,is applied to study the heat transfer of supercritical nitrogen under typical working conditions.The objective is to evaluate the effect of the main parameters taking into account the buoyancy and flow acceleration effects.Simulation results are compared with results calculated from three well-known empirical correlations and the applicability of empirical correlation is discussed in detail.It is discovered that the Watts and Chou correlation accurately fits the simulation results of supercritical nitrogen and the Dittus-Boelter and Jackson correlations can only be used for high-pressure conditions.The HTE of supercritical nitrogen is closely related to the laminar sub-layer and buffer layer of a boundary layer.The buoyancy effect on the HTE should be considered at low mass flux conditions,and thermal acceleration can be completely ignored for the cases studied.The special HTE featured by the increment in heat transfer coefficient with increasing heat flux is discovered at low pressure,and simulation results proved that this HTE is caused by the combined actions of buoyancy as well as significant variations in specific heat and viscosity.展开更多
To achieve fast, smooth and accurate set point tracking in servo positioning systems, a parameterized design of nonlinear feedback controllers is presented, based on a so-called composite nonlinear feedback (CNF) cont...To achieve fast, smooth and accurate set point tracking in servo positioning systems, a parameterized design of nonlinear feedback controllers is presented, based on a so-called composite nonlinear feedback (CNF) control technique. The controller designed here consists of a linear feedback part and a nonlinear part. The linear part is responsible for stability and fast response of the closed-loop system. The nonlinear part serves to increase the damping ratio of closed-loop poles as the controlled output approaches the target reference. The CNF control brings together the good points of both the small and the large damping ratio cases, by continuously scheduling the damping ratio of the dominant closed-loop poles and thus has the capability for superior transient performance, i.e. a fast output response with low overshoot. In the presence of constant disturbances, an integral action is included so as to remove the static bias. An explicitly parameterized controller is derived for servo positioning systems characterized by second-order model. Practical application in a micro hard disk drive servo system is then presented, together with some discussion of the rationale and characteristics of such design. Simulation and experimental results demonstrate the effectiveness of this control design methodology.展开更多
The post-Newtonian scheme in multiple systems with post-Newtonian parameters presented by Klioner and Soffel is extended to the post-post-Newtonian (PPN) order for light propagation problem in the solar system.Under c...The post-Newtonian scheme in multiple systems with post-Newtonian parameters presented by Klioner and Soffel is extended to the post-post-Newtonian (PPN) order for light propagation problem in the solar system.Under considering the solar system experiment requirement,a new parameter ε is introduced.This extension does not change the virtue of the scheme on the linear partial differential equations of the potential and vector potential mentioned in previous work.Furthermore,this extension is based on the former work done by Richter and Matzner in one global system theory.As an application,we also consider the deflection of light ray in the global coordinates.And the deflection angle of light ray is obtained with post-Newtonian parameters.展开更多
An observer-based adaptive iterative learning control (AILC) scheme is developed for a class of nonlinear systems with unknown time-varying parameters and unknown time-varying delays.The linear matrix inequality (LMI)...An observer-based adaptive iterative learning control (AILC) scheme is developed for a class of nonlinear systems with unknown time-varying parameters and unknown time-varying delays.The linear matrix inequality (LMI) method is employed to design the nonlinear observer.The designed controller contains a proportional-integral-derivative (PID) feedback term in time domain.The learning law of unknown constant parameter is differential-difference-type,and the learning law of unknown time-varying parameter is difference-type.It is assumed that the unknown delay-dependent uncertainty is nonlinearly parameterized.By constructing a Lyapunov-Krasovskii-like composite energy function (CEF),we prove the boundedness of all closed-loop signals and the convergence of tracking error.A simulation example is provided to illustrate the effectiveness of the control algorithm proposed in this paper.展开更多
One of the first attempts to derive energy-to-peak performance criteria and state-feedback controller design problem for linear parameter-varying discrete time systems with time delay is provided. Firstly, we present ...One of the first attempts to derive energy-to-peak performance criteria and state-feedback controller design problem for linear parameter-varying discrete time systems with time delay is provided. Firstly, we present a parameter-dependent l 2-l ∞ performance criterion using a parameter-dependent Lyapunov function. Upon the conditions addressed, an improved parameter-dependent l 2-l ∞ performance criterion is established by the introduction of a slack variable, which exhibits a kind of decoupling between Lyapunov functions and system matrices. This kind of decoupling enables us to obtain more easily tractable conditions for analysis and synthesis problems. Then, the corresponding parameter-dependent state-feedback controller design is investigated upon these performance criteria, with sufficient conditions obtained for the existence of admissible controllers in terms of parameterized linear matrix inequalities. Finally, a numerical example is provided to illustrate the feasibility and advantage of the proposed controller design procedure.展开更多
A computer aided design system of welding fixture(called WFCAD system)is introduced in this paper.Themicrocomputer graphics software AutoCAD has been used as the supporting software of WFCAD system.By means ofprogramm...A computer aided design system of welding fixture(called WFCAD system)is introduced in this paper.Themicrocomputer graphics software AutoCAD has been used as the supporting software of WFCAD system.By means ofprogramming,2-D and 3-D parameterized graphic libraries of components of welding fixtrue are established. With the aid of AutoCAD’s advanced development system(ADS),menus and dialogs are constructed for convenient use ofgraphic library,and it also makes the system has a good man-machine interface.展开更多
Radio Frequency(RF) fingerprinting is one physical-layer authentication method for wireless communication, which uses the unique hardware characteristic of the transmitter to identify its true identity.To improve the ...Radio Frequency(RF) fingerprinting is one physical-layer authentication method for wireless communication, which uses the unique hardware characteristic of the transmitter to identify its true identity.To improve the performance of RF Fingerprint(RFF)based on preamble with fixed duration, a nonlinear RF fingerprinting method based on payload symbols is proposed for the wireless OFDM communication with the bit mapping scheme of QPSK. The wireless communication system is modeled as a Hammerstein system containing the nonlinear transmitter and multipath fading channel. A parameter separation technique based on orthogonal polynomial is presented for the estimation of the parameters of the Hammerstein system. The Hammerstein system parameter separation technique is firstly used to estimate the linear parameter with the training signal, which is used to compensate the adverse effect of the linear channel for the demodulation of the successive payload symbols. The demodulated payload symbols are further used to estimate the nonlinear coefficients of the transmitter with the Hammerstein system parameter separation technique again, which is used as the novel RFF for the authentication of the QPSK-OFDM device. Numerical simulations have verified the proposed method, which can also be extended to the OFDM signals with other bit mapping schemes.展开更多
This article aims to discuss the design process of the CAD system dedicated for sport bike frame structure, introducing in detail its design concept and the scheme of implementation. Based on the different usages of s...This article aims to discuss the design process of the CAD system dedicated for sport bike frame structure, introducing in detail its design concept and the scheme of implementation. Based on the different usages of sport bikes and the requirements on the system made out by Beijing Hanglun Sport Apparatus Company Limited. Structural analysis on two types of bikes frames is carried out. The system defines the basic design parameters and analyses the constraint conditions.Then calculating formulas with constraint conditions are derived. The system solves equations with Visual C++ program, realizes input of the original data and output of the results through interactive system. With AutoCAD14.0 as the platform, the system uses VC++ and ObjectARX to realize auto output of bike frame graphics. The system has been put into use. Practice has affirmed that the system抯 convenience, applicability and reliability all have reached the expected goal.展开更多
This paper investigates a parameterization method of adaptive H∞ controllers for dissipative Hamiltonian systems with disturbances and unknown parameters.The family of adaptive H∞ controllers with full information i...This paper investigates a parameterization method of adaptive H∞ controllers for dissipative Hamiltonian systems with disturbances and unknown parameters.The family of adaptive H∞ controllers with full information is obtained by interconnecting an adaptive H∞ controller with a generalized zero-energy-gradient (ZEG) detectable,free generalized Hamiltonian system.The present parameterization method avoids solving Hamilton-Jacobi-Issacs equations and thus the controllers obtained are easier in operation as compared to some existing ones.Simulations show the effectiveness and feasibility of the adaptive control strategy proposed in this paper.展开更多
基金financially sponsored by the National Natural Science Foundation of China(No.51876024 and No.51976204)Science and Technology on Reactor System Design Technology Laboratory。
文摘In this paper,the heat transfer enhancement(HTE)of supercritical nitrogen flowing downward in a vertical small tube(diameter 2 mm)is studied using the commercial software CFX of Ansys16.1,to provide theoretical guidance on the design of high-performance heat transfer systems.An effective numerical simulation method,which employs the SSG Reynolds stress model with enhanced wall treatment,is applied to study the heat transfer of supercritical nitrogen under typical working conditions.The objective is to evaluate the effect of the main parameters taking into account the buoyancy and flow acceleration effects.Simulation results are compared with results calculated from three well-known empirical correlations and the applicability of empirical correlation is discussed in detail.It is discovered that the Watts and Chou correlation accurately fits the simulation results of supercritical nitrogen and the Dittus-Boelter and Jackson correlations can only be used for high-pressure conditions.The HTE of supercritical nitrogen is closely related to the laminar sub-layer and buffer layer of a boundary layer.The buoyancy effect on the HTE should be considered at low mass flux conditions,and thermal acceleration can be completely ignored for the cases studied.The special HTE featured by the increment in heat transfer coefficient with increasing heat flux is discovered at low pressure,and simulation results proved that this HTE is caused by the combined actions of buoyancy as well as significant variations in specific heat and viscosity.
文摘To achieve fast, smooth and accurate set point tracking in servo positioning systems, a parameterized design of nonlinear feedback controllers is presented, based on a so-called composite nonlinear feedback (CNF) control technique. The controller designed here consists of a linear feedback part and a nonlinear part. The linear part is responsible for stability and fast response of the closed-loop system. The nonlinear part serves to increase the damping ratio of closed-loop poles as the controlled output approaches the target reference. The CNF control brings together the good points of both the small and the large damping ratio cases, by continuously scheduling the damping ratio of the dominant closed-loop poles and thus has the capability for superior transient performance, i.e. a fast output response with low overshoot. In the presence of constant disturbances, an integral action is included so as to remove the static bias. An explicitly parameterized controller is derived for servo positioning systems characterized by second-order model. Practical application in a micro hard disk drive servo system is then presented, together with some discussion of the rationale and characteristics of such design. Simulation and experimental results demonstrate the effectiveness of this control design methodology.
基金supported by the National Natural Science Foundation of China (Grant No. 10674099)the National Science Foundation for Young Scientists of China (Grant No. 10925313)the Shandong Provincial Natural Science Foundation,China (GrantNo. ZR2010AQ023)
文摘The post-Newtonian scheme in multiple systems with post-Newtonian parameters presented by Klioner and Soffel is extended to the post-post-Newtonian (PPN) order for light propagation problem in the solar system.Under considering the solar system experiment requirement,a new parameter ε is introduced.This extension does not change the virtue of the scheme on the linear partial differential equations of the potential and vector potential mentioned in previous work.Furthermore,this extension is based on the former work done by Richter and Matzner in one global system theory.As an application,we also consider the deflection of light ray in the global coordinates.And the deflection angle of light ray is obtained with post-Newtonian parameters.
基金Sponsored by the National Natural Science Foundation of China under Grang No.10735030the National Basic Research Programs of China(973 Programs 2007CB814800 and 2005CB422301)K.C.Wong Magna Fund in Ningbo University
基金supported by National Natural Science Foundation of China(No.60804021,No.60702063)
文摘An observer-based adaptive iterative learning control (AILC) scheme is developed for a class of nonlinear systems with unknown time-varying parameters and unknown time-varying delays.The linear matrix inequality (LMI) method is employed to design the nonlinear observer.The designed controller contains a proportional-integral-derivative (PID) feedback term in time domain.The learning law of unknown constant parameter is differential-difference-type,and the learning law of unknown time-varying parameter is difference-type.It is assumed that the unknown delay-dependent uncertainty is nonlinearly parameterized.By constructing a Lyapunov-Krasovskii-like composite energy function (CEF),we prove the boundedness of all closed-loop signals and the convergence of tracking error.A simulation example is provided to illustrate the effectiveness of the control algorithm proposed in this paper.
文摘One of the first attempts to derive energy-to-peak performance criteria and state-feedback controller design problem for linear parameter-varying discrete time systems with time delay is provided. Firstly, we present a parameter-dependent l 2-l ∞ performance criterion using a parameter-dependent Lyapunov function. Upon the conditions addressed, an improved parameter-dependent l 2-l ∞ performance criterion is established by the introduction of a slack variable, which exhibits a kind of decoupling between Lyapunov functions and system matrices. This kind of decoupling enables us to obtain more easily tractable conditions for analysis and synthesis problems. Then, the corresponding parameter-dependent state-feedback controller design is investigated upon these performance criteria, with sufficient conditions obtained for the existence of admissible controllers in terms of parameterized linear matrix inequalities. Finally, a numerical example is provided to illustrate the feasibility and advantage of the proposed controller design procedure.
文摘A computer aided design system of welding fixture(called WFCAD system)is introduced in this paper.Themicrocomputer graphics software AutoCAD has been used as the supporting software of WFCAD system.By means ofprogramming,2-D and 3-D parameterized graphic libraries of components of welding fixtrue are established. With the aid of AutoCAD’s advanced development system(ADS),menus and dialogs are constructed for convenient use ofgraphic library,and it also makes the system has a good man-machine interface.
文摘Radio Frequency(RF) fingerprinting is one physical-layer authentication method for wireless communication, which uses the unique hardware characteristic of the transmitter to identify its true identity.To improve the performance of RF Fingerprint(RFF)based on preamble with fixed duration, a nonlinear RF fingerprinting method based on payload symbols is proposed for the wireless OFDM communication with the bit mapping scheme of QPSK. The wireless communication system is modeled as a Hammerstein system containing the nonlinear transmitter and multipath fading channel. A parameter separation technique based on orthogonal polynomial is presented for the estimation of the parameters of the Hammerstein system. The Hammerstein system parameter separation technique is firstly used to estimate the linear parameter with the training signal, which is used to compensate the adverse effect of the linear channel for the demodulation of the successive payload symbols. The demodulated payload symbols are further used to estimate the nonlinear coefficients of the transmitter with the Hammerstein system parameter separation technique again, which is used as the novel RFF for the authentication of the QPSK-OFDM device. Numerical simulations have verified the proposed method, which can also be extended to the OFDM signals with other bit mapping schemes.
文摘This article aims to discuss the design process of the CAD system dedicated for sport bike frame structure, introducing in detail its design concept and the scheme of implementation. Based on the different usages of sport bikes and the requirements on the system made out by Beijing Hanglun Sport Apparatus Company Limited. Structural analysis on two types of bikes frames is carried out. The system defines the basic design parameters and analyses the constraint conditions.Then calculating formulas with constraint conditions are derived. The system solves equations with Visual C++ program, realizes input of the original data and output of the results through interactive system. With AutoCAD14.0 as the platform, the system uses VC++ and ObjectARX to realize auto output of bike frame graphics. The system has been put into use. Practice has affirmed that the system抯 convenience, applicability and reliability all have reached the expected goal.
基金supported by National Natural Science Foundation of China (No. 61074189)
文摘This paper investigates a parameterization method of adaptive H∞ controllers for dissipative Hamiltonian systems with disturbances and unknown parameters.The family of adaptive H∞ controllers with full information is obtained by interconnecting an adaptive H∞ controller with a generalized zero-energy-gradient (ZEG) detectable,free generalized Hamiltonian system.The present parameterization method avoids solving Hamilton-Jacobi-Issacs equations and thus the controllers obtained are easier in operation as compared to some existing ones.Simulations show the effectiveness and feasibility of the adaptive control strategy proposed in this paper.
文摘为实现中速磁浮列车悬浮系统的数据驱动异常检测,首先,引入基于参数化残差的异常检测方法;然后,针对当前悬浮系统的异常先验信息非常缺乏的问题,建立悬浮系统健康数据置信集和异常数据置信集,确定悬浮系统的异常检测评估函数与阈值;接着,异常误报率固定时以最小化异常漏检率为设计目标,从数理角度设计满足该目标的最优参数向量,并以此构建基于最低漏检率的悬浮系统异常检测算法;最后,以长沙磁浮快线的悬浮系统运行数据为例,对悬浮系统的间隙突变异常、砸轨异常和加速度传感器异常进行分析和检测.结果表明,在异常误报率为5%时,所提出的方法能够实现3种典型异常的全部检测,不存在对3种异常的漏检和对正常数据段的误检,最大异常检测滞后0.2 s.
