Analysis Method for Closed-Loop System

Experimental modal analysis, using an impact hammer and accelerometers, was conducted on a full-scale flap gate with a height of 0.963 m and a span of 14.8 m to determine its in-air natural frequencies, mode shapes and modal damping. Subsequently, the in-water self-excited vibration characteristics of the gate (without any spoilers) were recorded using the same accelerometers. This paper reports the major in-air vibration characteristics (the mode shape, frequency and damping ratio for the damped vibrations), as well as the major in-water self-excited vibration characteristics (the excitation ratio and frequency of the self-excited vibrations in water). In parallel with these experiments, calculations of the inherent in-water vibration frequency of the gate using a potential flow theory, and based on input from the in-air modal testing, are presented. Comparison of the calculated inherent in-water vibration frequency with the measured frequency of the in-water self-excited vibration confirms the validity of the present theoretical analysis.

We investigate the tilting effect of a fast excitation on self-excited vibrations in a delayed van der Pol pendulum. Specifically, we analyze the simultaneous effects of fast excitation and time delay in controlling self-excited oscillations taking into account the influence of the incline angle of the fast excitation. We use an averaging technique to reduce the original oscillator to a slow flow system. Analysis of stationary solutions of this slow flow provides analytical approximations of regions in parameter space where self-excited vibrations can be controlled. We have shown that in the case where the delay and the fast excitation are both imposed in the system, the incline of the fast excitation can be an alternative to control self-excited vibrations.

The self-excited vibration of the static suspension of the hybrid maglev train and the vehicle resonance caused by aerodynamic loads will affect the safety and comfort of vehicle operation. This study investigates the improvement of nonlinear vibration characteristics by analyzing the stable domain of control parameters and bifurcation control. A dual-loop control model for a two-degree-of-freedom hybrid electromagnetic suspension system is derived using the Lagrange equation. The stability domain of the proportional differential control parameters is determined via the Hurwitz algebraic criterion for Hopf bifurcation, revealing that control parameters selected at different positions within the domain influence the system’s vibration characteristics. Additionally, the control parameter conditions for the Hopf bifurcation are given. It is demonstrated that the upper boundary of the stability domain is effectively expanded by increasing the thickness of permanent magnets, thereby enhancing the flexibility in selecting stable control parameters. Although aerodynamic loading broadens the extent of the stability domain, it concurrently induces a downward translation of the entire region and lowers the threshold for self-excited vibrations. The system exhibits good vibration characteristics when control parameters are positioned within the stability domain and distant from its boundaries. Specifically, self-excited vibrations can be suppressed by increasing velocity and current control parameters, while displacement control parameters should avoid approaching the margins of the stability domain. Under aerodynamic forces, the amplitude of unsteady aerodynamic excitation is observed to influence the resonant response amplitude of the suspension system significantly. Velocity and current control parameters are found to strongly reduce the resonance at the natural frequency of the suspension frame. This research provides a theoretical foundation for optimizing control parameters and suppressing nonlinear vibrations in hybrid maglev systems. It holds practical engineering significance for enhancing maglev trains’ operational stability and ride comfort.

We present in this paper gain-scheduling composite nonlinear feedback (CNF) control for a set of second-order linear parameter-varying (LPV) systems that capture commonly used plant models in automatic control. The selected three parameter-varying plant models are double integrator with a gain, a series connection of an integrator and a first order system, and a second-order system without integration. We assume that the parameters of the plant models depend on an exogenous scheduling signal, which is unknown a priori, but it is measurable online and available for feedback control. The resulting model-based parameter-varying CNF controller assigns certain predefined properties for the closed-loop control system, which can be explained using linear time invariant (LTI) control theory. We demonstrate the proposed control structure with a simulation-based design example, in which a plant model is updated through a slowly varying scheduling signal, and, at the same time, the closed-loop system is commanded towards desired reference values. Our simulation results indicate that the closed-loop control system yields satisfactory tracking performance under parameter-varying conditions.

Unsteady aerodynamics of flexible nonslender delta wings is investigated in an experimental study using various techniques. Dramatic fluid/structure interactions emerge with increasing wing flexibility and result in substantial lift enhancement in the poststall region. This recently discovered phenomenon appears to be a feature of nonslender wings. Self-excited antisymmetric vibrations of the wing promote reattachment of the shear layer, which results in the lift enhancement. These self-excited vibrations are not observed for a half-model. The Strouhal number of the dominant frequency of the structural vibration is on the order of unity for all nonslender wings, which also corresponds to the frequency of the shear-layer instabilities for the rigid wing. Velocity measurements demonstrate the striking difference between the flows over the flexible and rigid wings in the poststall region. The effect of flexibility is to promote the reattachment of the shear layer near or downstream of the apex, depending on the incidence. There are substantial effects on the vortical flow with increasing wing flexibility, which might lead to the axial flow developing within the reattached region. The time-averaged vorticity flux increases due to the oscillating leading edge, which leads to increased circulation.

Based on the investigation of the generation mechanism of the unusual noise generated from a laser-beam printer, it has become clear that self-excited vibration is produced due to the friction between the photosensitive drum and the cleaner blade, and the noise is its vibration noise. The vibration system is that of the tortional vibration of the drum, and the vibration mode is secondary. The self-excited vibration in the secondary vibration mode is caused by the drum structure and the friction force applied to the drum. This drum is made of a thin-walled cylinder having inertia on both ends. The friction force is applied uniformly and axially to the cylinder surface. In this case, the energy can be applied to the tortional vibration of the secondary vibration mode in the drum, and the existence of negative damping friction force results in the generation of the self-excited vibration. Since the vibration frequency is the audio frequency of 10.65kHz, it lies in the audible range. To prevent the vibration and the noise without affecting the function, appropriate and positive damping needs to be applied to the vibration system. Also, the method using friction loss is investigated and verified to evaluate its effect. This method proved to be effective, and it is confirmed that self-excited vibration is discarded, and the generation of unusual noise is completely eliminated. The generation pattern of vibration and noise described in this paper is not limited only to the laser-beam printer. In equipment such as plain paper copiers, liquid crystal printers and so on in which the same mechanical structure is required, the same phenomenon can occur. The cause and the countermeasure described in this paper are expected to be practically useful for development and design.

An algorithm for control of nonlinear discrete-time systems is presented in the paper. Controlled system is linearized by dynamic output feedback so that the linearized closed loop system is equivalent to a predefined discrete-time transfer function representing reference model of the control system. Choice of the reference model provides placement of zeroes and poles of the closed loop system. In the proposed approach at least one of the poles is not fixed and moves during the time of transient process. Evolution of the pole occurs according to certain rules formalized and implemented in the algorithm by means of fuzzy logic. Therefore, the parameters of the transfer function of the linearized closed loop system may be understood as nonlinear functions which depend on the current control error and its derivative. Thus the poles of the closed loop system are placed dynamically according to the predefined rules providing necessary behavior of the control system. Controlled system has to be represented by a nonlinear model with no couplings between different time instances what can be performed by training an Artificial Neural Network of the specific structure. The developed theory and control algorithm are illustrated by means of numerical example.

A flexible shaft with surface-mounted piezoceramic sheets and strain sensors is considered which suffers from resonance and self-excited vibration. Frequency domain models, time domain simulations, and control experiments are used to analyze active modal damping and active modal balancing methods. The generation of electric power from cyclic straining of rotor-fixed piezoelectric material is studied and several self-powering devices for condition monitoring and vibration control are proposed.

Control system networks are increasingly being connected to enterprise level networks. These connections leave critical industrial controls systems vulnerable to cyber-attacks. Most of the effort in protecting these cyber-physical systems (CPS) from attacks has been in securing the networks using information security techniques. Effort has also been applied to increasing the protection and reliability of the control system against random hardware and software failures. However, the inability of information security techniques to protect against all intrusions means that the control system must be resilient to various signal attacks for which new analysis methods need to be developed. In this paper, sensor signal attacks are analyzed for observer-based controlled systems. The threat surface for sensor signal attacks is subdivided into denial of service, finite energy, and bounded attacks. In particular, the error signals between states of attack free systems and systems subject to these attacks are quantified. Optimal sensor and actuator signal attacks for the finite and infinite horizon linear quadratic (LQ) control in terms of maximizing the corresponding cost functions are computed. The closed-loop systems under optimal signal attacks are provided. Finally, an illustrative numerical example using a power generation network is provided together with distributed LQ controllers.

In this paper, finite element simulations are used to estimate the fatigue life of big turbo-generator shaft in uncontrolled and controlled system. The torque generated by the synchronous generator under loaded condition is analyzed for various types of electrical faults. The dq0 approach is used to model synchronous generator connected to an infinite bus. The torque outcome of loaded synchronous generator under various electrical faults is numerically simulated using MATLAB. The turbo-generator shaft is modeled using finite element formulation using different elements, i.e., solid cylindrical element, hollow cylindrical element and tapered element. The coupled dynamic MDOF equations are solved numerically to estimate the torque variation in shaft. The numbers of stress cycles are calculated using Rain Flow Counting method using stress at critical nodes of turbo-generator shaft. Further using piezoelectric sensor and actuator an active control system is achieved to reduce the vibrations produced in the shaft due to various faults. A closed-loop system is analyzed numerically using proportional and velocity feedback. The results of uncontrolled and controlled system are compared and vibrations in the controlled system found are to be reduced significantly using PD control law. Comparison of fatigue life generated shown that critical stress of the shaft can be reduced effectively in controlled system.

This work details research on the formation mechanism of wheel polygonalization in high-speed trains and its effect factors by numerical modeling in order to prevent the increasingly prevalent problem of wheel polygonal wear. The lateral self-excited vibration model of a wheel was developed using the LuGre friction model and self-excited vibration theory. The properties of wheel self-excited vibration and the crucial condition of Hopf bifurcation were investigated; the process of wheel polygonal wear was simulated and the results were validated using field tracking data. The results demonstrated that periodic self-excited vibration generated by Hopf bifurcation is a required condition for polygonal wheel attrition at a given speed. The wheel’s polygonal wear has the following characteristics: “Constant speed—Self-excited—Fixed frequency—Divisible.” The order of the polygon is determined by the ratio of the wheel lateral self-excited vibration frequency to its rotational frequency. Wheel polygonal wear was caused by the vertical dynamic force of the wheel rail. The findings of the study can serve as a theoretical foundation for the prediction and reduction of wheel polygonal wear.

Managed software development organizations are de facto closed loop systems, in which management actions influence future behavior based on observations of previous behavior thus forming a closed feedback loop. It is well known from control theory that a closed loop system might exhibit dynamics very different from the dynamics of its open loop components. Therefore, it is the goal of this work to study the importance of closed loop effects in the context of software process dynamics. To this end, an exemplary model is presented with a work-test-rework cycle as operational part and a productivity estimation and personnel allocation model as management component. The behavior of this closed loop system is probed with respect to typical disturbances and nonlinearities of software processes. The results underscore the importance of such a closed loop analysis.

Optimal Protection from Impact, Shock, and Vibration

"The human-in-the-control-loop" is just as a closed-loop system, and is a controlled system with human operation. To analyze the human operation, the closed-loop identification is required because the person's operation can be regarded as a controller. The tracking operation of the operator is considered in this paper. The subspace identification method is utilized for the identification process. The experimental results are presented

This paper presents an interactive design for fractional order PI (FOPI) controller based on inverse Fourier transform method (IFTM) in accordance with stability region of a closed-loop control system in LabVIEW, which is a powerful graphical program. Stability boundary locus (SBL) method is used to obtain the stability region including all stabilising FOPI controller parameters in (Kp, Ki) plane. The time response of the closed-loop control system with FOPI controller is then obtained by IFTM using the stabilising controller parameters selected from stability region. Changing the selected fractional order controller parameters in stability region, users can observe the step response of the system interactively.