Modeling and dynamic analysis of a magnetically actuated butterfly valve

In this work, a magnetically actuated butterfly valve is considered and a novel and accurate mathematical model is derived. The equilibrium of the system is investigated and the effects of the inlet velocity and direct current voltage (DC) on the stable rotation angle of the valve are presented. Considering a time periodic perturbation arising from electric circuit, the effects of the operating angle, inlet velocity, and driving parameters on the periodic and chaotic dynamics of the system are investigated. It is observed that, for an opening angle less than the cut-off angle, there exists a unique DC voltage for a stable equilibrium. The stability of this equilibrium depends nonlinearly on the inlet velocity and the seating torque. An expression is derived for the threshold value for the stability of the valve. Under periodic voltage, the inlet velocity and stable angle induce a backward shift on the resonant frequency, and jump phenomena and subharmonics are observed for some values of the driving amplitude. The highest amplitudes of vibration are detected for a fully open valve, for an almost closed valve, and for a valve with large inlet velocity. Using bifurcation diagrams and Lyapunov exponents, it is shown that the system exhibits a route to chaos with windows of period doubling and unbounded motion. Some guidance for design of magnetically actuated butterfly valves is proposed as well as recommendations for future work.     

鲁棒控制在惯性导航系统初始对准中的应用

本文提出并设计了一种新的鲁棒控制方案,并进行了计算机仿真。结果表明,该系统对于不确定性干扰和噪声,具有强鲁棒性,快速性,精度高等特点,是一种应用在实际动态系统中的理想初始对准方案。     

Design of fractional robust adaptive intelligent controller for uncertain fractional-order chaotic systems based on active control technique

In this paper, a robust fractional-order adaptive intelligent controller is proposed for stabilization of uncertain fractional-order chaotic systems. The intelligent neuro-fuzzy network is used to estimate unknown dynamics of system, while the neuro-fuzzy network parameters as well as the upper bounds of the model uncertainties, disturbances and approximation errors are adaptively estimated via separate adaptive rules. An SMC scheme, with a fractional-order sliding surface, is employed, as the controller to improve the velocity and performance of the proposed control system and to eliminate the unknown but bounded uncertainties, external disturbances and approximation errors. The Lyapunov stability theorem has been also employed to show the stability of the closed-loop system, robustness against uncertainties, external disturbances and approximation errors, while the control signal remains bounded. Explanatory examples and simulation results are given to confirm the effectiveness of the proposed procedure, which consent well with the analytical results.     

The design of nonlinear disturbance attenuation controller for TCSC robust model of power system

The control problem of the single machine infinite bus system with TCSC is dealt with. Based on the maximization of the external disturbances on the system model, an adaptive nonlinear controller for large disturbance attenuation and a parameter updating law are designed by using the backstepping method. The parameter uncertainty of the transmission line is considered, as well as the influences of large external disturbances to the system output are mainly discussed. The nonlinear controller does not have the sensitivity to the influences of external disturbances, but also has strong robustness for system parameters variation. The simulation results show that the control effect of the large disturbance attenuation controller more advantages by comparing with the control performance of conventional nonlinear robust controller.     

Compound line-of-sight nonlinear path following control of underactuated marine vehicles exposed to wind,waves, and ocean currents

This paper investigates the problem of nonlinear path following control of underactuated marine vehicles in the horizontal plane. Firstly, appropriate kinematic and dynamic models are established, where the kinematic model is developed in terms of the relative velocity with respect to the ocean current disturbances, and the dynamic model is developed to include the effects of wind and wave disturbances. Based on the time delay control method and the reduced-order linear extended state observer (LESOs) technique, an improved compound line-of-sight (CLOS) guidance law is first proposed which can estimate the unknown sideslip angle and can compensate for the effects of time-varying ocean currents. Secondly, the control law is decomposed into the kinematic and dynamic controllers by the back-stepping technique. The high-order tracking differentiator is applied to construct derivatives of desired yaw angle, which are calculated by the CLOS guidance law. This approach resolves the problem of computational complexity inherent in the traditional back-stepping method and simplifies the overall controller. The lumped disturbances caused by waves and wind are estimated and compensated by the reduced-order LESOs. Finally, stability analysis of the closed-loop system is performed. The simulation results and comparative analysis validate the effectiveness and robustness of the proposed control approach.     

A second-order positivity-preserving well-balanced finite volume scheme for Euler equations with gravity for arbitrary hydrostatic equilibria

We present a well-balanced finite volume scheme for the compressible Euler equations with gravity, where the approximate Riemann solver is derived using a Suliciu relaxation approach. Besides the well-balanced property, the scheme is robust with respect to the physical admissible states. General hydrostatic solutions are captured up to machine precision by deriving, for a given initial value problem, suitable time-independent functions and using them in the discretization of the source term. The first-order scheme is extended to a second-order scheme by reconstructing in equilibrium variables while preserving the well-balanced and robustness properties. Numerical examples are performed to demonstrate the accuracy, well-balanced, and robustness properties of the presented scheme for up to three space dimensions.     

Das verhalten von systemen in gleichgewichtslagen innerhalb von gleichgewichtsbereichen

In order to characterize the equilibrium positions of a system inside an equilibrium domain, direction elements are defined. These follow from the response of the autonomous system in such a position to small disturbances by impulses, which effect initial velocities of the system. The direction elements establish for the equilibrium domain a direction field, which gives information about the different behaviour of the system in the equilibrium positions of the domain. Examples are also considered.     

Decentralized adaptive neural network control for mechanical systems with dead-zone input

We propose a decentralized adaptive robust controller for trajectory tracking of mechanical systems with dead-zone input in this paper. The considered mechanical systems are with high-order interconnections and unknown non-symmetric nonlinear input. In each local controller, the neural network control is introduced to estimate the uncertainties and disturbances, meanwhile the siding mode control and adaptive technical are designed to compensate for the approximation errors. A nonlinear function is chosen to deal with the interconnections. Following, the stability and robustness are verified by using Lyapunov stability theorem. Finally, simulations are provided to support the theoretical results     

非线性变形节理中纵波传播特性的理论研究

基于波前动量守恒理论和位移不连续方法所提出的时域分析新方法,引入岩石非线性法向本构关系,对弹性纵波在岩石非线性节理中的传播特性进行了理论分析。采用节理变形的双曲线模型(BB模型),获得纵波P波斜入射非线性节理的传播波动方程,并通过参数研究分析了在岩石节理中节理非线性系数、节理初始刚度、应力波入射角和入射波幅值等因素对纵波传播规律的影响。结果表明:所推导的应力波传播方程在考虑多种非线性问题时,通过迭代计算即可方便求出透射波和反射波的数值解,避免了复杂的数学运算;当波斜入射节理面时,产生了波型转换,节理变形的非线性对透射波和反射波有较大影响,透射系数和反射系数并非随着非线性参数的变化而单调变化。时域内所推导的波传播方程更有益于波斜入射时非线性参数的广泛研究,为开展该方面的理论研究工作提供了借鉴。     

Instabilities of a gas-liquid flow between two inclined plates analyzed using the Navier–Stokes equations

The paper is devoted to a theoretical analysis of a counter-current gas-liquid flow between two inclined plates. We linearized the Navier–Stokes equations and carried out a stability analysis of the basic steady-state solution over a wide variation of the liquid Reynolds number and the gas superficial velocity. As a result, we found two modes of the unstable disturbances and computed the wavelength and phase velocity of their neutral disturbances varying the liquid and gas Reynolds number. The first mode is a “surface mode” that corresponds to the Kapitza's waves at small values of the gas superficial velocity. We found that the dependence of the neutral disturbance wavelength on the liquid Reynolds number strongly depends on the gas superficial velocity, the distance between the plates and the channel inclination angle for this mode. The second mode of the unstable disturbances corresponds to the transition to a turbulent flow in the gas phase and there is a critical value of the gas Reynolds number for this mode. We obtained that this critical Reynolds number weakly depends on both the channel inclination angle, the distance between the plates and the liquid flow parameters for the conditions considered in the paper. Despite a thorough search, we did not find the unstable modes that may correspond to the instability in frame of the viscous (or inviscid) Kelvin–Helmholtz heuristic analysis.     

Wave generation on an interface by vortex disturbances in a shear flow

A linear problem of oscillations of an interface in a two-layer system, in which the upper layer is at rest and the lower layer has a constant velocity shear, is considered. The dynamic perturbations in the lower layer are represented as the sum of vortex and wave disturbances (disturbances with zero vorticity). It is shown that in the shear flow the evolution of the vortex disturbances with a nonsmooth or a singular initial vorticity distribution can result in the resonant excitation of waves on the interface. The occurrence of the resonance corresponds to the coincidence of the oscillation frequencies of the perturbations of both classes. In the absence of hydrodynamic instability of the shear flow, the resonant excitation can be one of the main mechanisms of wave generation in two-layer systems.     

Robust predictive scheme for input delay systems subject to nonlinear disturbances

The predictor-based control is known as an effective method to compensate input delays. Yet the traditional predictors, like Smith predictor, have poor robustness with respect to system disturbances. In this paper, with the consideration of future disturbances, a novel robust predictive scheme is developed for input delay systems subject to nonlinear disturbances. The Artstein reduction method is used to provide performance analysis of different predictor-based controllers, which shows that the proposed predictor-based controller can provide better disturbance attenuation than previous approaches in the literature for a wide range of disturbances.     

Shift in Optimal Joint Angle of the Ankle Dorsiflexors Following Eccentric Exercise

Exposure to unaccustomed eccentric exercise causes muscle damage. Popping sarcomere theory [1] has been proposed and assumed that eccentric contraction-induced muscle damage predominantly occurs at muscle length on the descending limb of the force-length relationship. This study investigated changes in the mechanical properties following maximum effort eccentric exercise at systematically different muscle lengths for the human ankle dorsiflexors. The results of this study showed that the eccentric exercise of the ankle dorsiflexors decreased the peak torque, shifted the optimal joint angle towards longer muscle length without changes in the level of muscle activation. However, no difference in the shift of the optimal ankle joint angle was observed between the groups that performed eccentric exercise at long muscle length (ECC_L) and at short muscle length (ECC_S). In conclusion, the muscle length at which the eccentric exercise was performed did not produce differential effects on the neuro-mechanical properties of in-vivo human ankle dorsiflexors, and thus the popping sarcomere theory might not be the sole mechanism to account for the eccentric contraction-induced optimal muscle length change.     

Generation of Transient Waves by Impulsive Disturbances in an Inviscid Fluid with an Ice-Cover

The dynamic responses of an ice-covered fluid to impulsive disturbances are analytically investigated for two- and three-dimensional cases. The initially quiescent fluid of infinite depth is assumed to be inviscid, incompressible and homogenous. The thin ice-cover is modelled as a homogenous elastic plate with negligible inertia. Four types of impulsive concentrated disturbances are considered, namely an instantaneous mass source immersed in the fluid, an instantaneously dynamic load on the plate, an initial impulse on the surface of the fluid, and an initial displacement of the ice plate. The linearized initial-boundary-value problem is formulated within the framework of potential flow. The solutions in integral form for the vertical deflexions at the ice-water interface are obtained by means of a joint Laplace-Fourier transform. The asymptotic representations of the wave motions for large time with a fixed distance-to-time ratio are derived by making use of the method of stationary phase. It is found that there exists a minimal group velocity and the wave system observed depends on the moving speed of the observer. For an observer moving with the speed larger than the minimal group velocity, there exist two trains of waves, namely the long gravity waves and the short flexural waves, the latter riding on the former. Moreover, the deflexions of the ice-plate for an observer moving with a speed near the minimal group velocity are expressed in terms of the Airy functions. The effects of the presence of an ice-cover on the resultant wave amplitudes, the wavelengths and periods are discussed in detail. The explicit expressions for the free-surface gravity waves can readily be recovered by the present results as the thickness of ice-plate tends to zero.     

Input-and-measurement event-triggered control for flexible air-breathing hypersonic vehicles with asymmetric partial-state constraints

In this paper, an input-and-measurement event-triggered control scheme considering asymmetric partial-state constraints is proposed for flexible air-breathing hypersonic vehicles (FAHV) subject to lumped disturbances and limited resources. To realize a precise disturbance rejection with decreased communication burden in sensor-to-control channels, intermittent measurement-based extended state observers using switching threshold samplers are developed in altitude and velocity subsystems, while the quantitative relationship between the upper bounds of observation errors and the design parameters of switching triggering mechanism is derived. Subsequently, to ensure the angle of attack (AoA) well within the allowable operational region and simultaneously achieve a reference tracking with expected characteristic, asymmetric constraints imposed on partial states including AoA, velocity, and altitude are embedded in design process, while a one-to-one nonlinear mapping is designed to avoid the violation of state constraint of AoA without enforcing feasibility conditions on virtual control laws, and a modified prescribed performance control is constructed to govern the output constraints of velocity and altitude, releasing the demand on the precise knowledge of initial states. Next, to maintain the resources occupation (energy and communication in controller-to-actuator channel) at low levels and ensure a desirable tracking precision, robust control laws based on switching event-triggered mechanisms are designed for FAHV to circumvent Zeno phenomena and compensate for the sampling error induced by event-triggered conditions. The simulation results and comparisons validate the effectiveness of the proposed scheme.

     

Dynamic consistent correlation-variational approach for robust optical flow estimation

We present in this paper a novel combined scheme dedicated to the measurement of velocity in fluid experimental flows through image sequences. The proposed technique satisfies the Navier–Stokes equations and combines the robustness of correlation techniques with the high density of global variational methods. It can be considered either as a reenforcement of fluid dedicated optical-flow methods towards robustness, or as an enhancement of correlation approaches towards dense information. This results in a physics-based technique that is robust under noise and outliers, while providing a dense motion field. The method was applied on synthetic images and on real experiments in turbulent flows carried out to allow a thorough comparison with a state of the art variational and correlation methods.     

模拟不同节理粗糙度对单裂隙渗流的影响

在研究岩体裂隙间的渗流特性时,节理粗糙度会影响裂隙水流的渗流特性和路径,因此需要对粗糙表面进行恰当的描述。本文选取伸长率、最大起伏高度、最大起伏角和分维数4个参数刻画粗糙度。结合分维数的计算方法,选择当最大起伏高度为2.5mm、节理宽度为5mm时,随机生成4组直线和曲线节理边界。建立二维模型模拟发现,最大起伏角、伸长率和分维数是影响水流流速分布的敏感因素。在节理最高起伏处的下边界,流速值最大。此外,粗糙度的方向性对渗流影响较大。同等节理条件下,可发现沿水流方向,最大起伏高度的位置越靠后,越能抑制最大流速值,从而减小渗流破坏。最后,根据规则锯齿状的节理试验分析表明,在外力条件下,渗流量一定时,节理通道一旦发生改变,内部形成的漩涡便与水流的有效路径呈现负相关关系。     

一种改进的粒子滤波算法在SINS初始对准中的应用

在实际工程环境中,针对捷联惯导系统(SINS)大失准角初始对准中噪声统计特性未知的问题,设计了一种基于H?滤波算法的鲁棒无迹粒子滤波算法(RUPF)。通过将无迹卡尔曼滤波算法(UKF)和鲁棒环节引入到粒子滤波(PF)的重要性密度函数中,得到了RUPF算法,提高了算法的鲁棒性。通过半物理实验,将RUPF算法与无迹粒子滤波算法(UPF)在SINS静基座大失准角对准中的性能进行了比较,在不同实验条件下,航向失准角精度至少提高了40%,对准精度优于0.05°,对准时间减少了约50 s。实验结果表明,RUPF算法可以以较高的精度和较快的速度完成大失准角初始对准,且对准精度和对准速度均优于UPF算法。     

Three-dimensional dynamics of supported pipes conveying fluid

This paper deals with the three-dimensional dynamics and postbuckling behavior of flexible supported pipes conveying fluid, considering flow velocities lower and higher than the critical value at which the buckling instability occurs. In the case of low flow velocity, the pipe is stable with a straight equilibrium position and the dynamics of the system can be examined using linear theory. When the flow velocity is beyond the critical value, any motions of the pipe could be around the postbuckling configuration (non-zero equilibrium position) rather than the straight equilibrium position, so nonlinear theory is required. The nonlinear equations of perturbed motions around the postbuckling configuration are derived and solved with the aid of Galerkin discretization. It is found, for a given flow velocity, that the first-mode frequency for in-plane motions is quite different from that for out-of-plane motions. However, the second- or third-mode frequencies for in-plane motions are approximately equal to their counterparts for out-of-plane motions, keeping almost constant values with increasing flow velocity. Moreover, the orientation angle of the postbuckling configuration plane for a buckled pipe can be significantly affected by initial conditions, displaying new features which have not been observed in the same pipe system factitiously supposed to deform in a single plane.     

Unsteady waves in a viscous fluid of finite depth

Here we study the plane and three-dimensional problems of unsteady waves which arise on the surface of a viscous fluid of finite depth under the influence of a velocity pulse applied on the bottom of the basin.The problem is considered as the simplest scheme for studying, with account for the effect of viscosity, the propagation of waves of the tsunami type which result from an underwater shock.Similar problems on the propagation of waves which arise from initial surface disturbances are considered in [1–9].