Limit cycle analysis for electro‐hydraulic systems with friction

Abstract

In this paper, a graphical prediction method is developed to effectively predict the existence of the limit cycles induced by nonlinear friction force in an electro‐hydraulic control system. The friction‐induced nonlinearity is linearized by its corresponding describing function. Then the stability equation method, accompanied by the parameter plane method, provides a useful tool for the establishment of necessary conditions to sustain a limit cycle in the controller coefficient plane. Henceforth, the limit cycles are predicted in a graphical way, and simulations are carried out to verify the accuracy of the prediction method.     

基于系统动力学仿真的医疗资源配置

为了在突发事故发生时在常规病人和突发病人之间进行有效的医疗资源配置,建立了基于系统动力学的仿真模型。模型中考虑了病人病情的实时变化、医务人员的诊断信心和决策以及基于贝叶斯预测分布的评估时间和突发病人到达时间间隔,并基于最小化病人死亡率和系统平均逗留时间建立资源分配方案评价指标。通过仿真实验,比较了3种资源配置规则在不同场景下的性能优劣,证明了基于病人规模的资源分配规则较其他候选规则能够得到更好的应急处置效果,为医院的应急医疗资源配置决策及应急预案制定提供有效的参考。     

On finite plane strain of an isotropic incompressible hyperelastic material

Abstract

The purpose of this paper is to derive a new formulation of the governing equations for the complex variable in the deformed configuration of an isotropic incompressible hyperelastic material, assuming that the material undergoes a constant finite axial stretch and then a finite plane strain.

As an application we consider the circular shear of a tube of such a material and, if we do not take into account torsion, it is proved that the plane deformation is given by an ordinary differential equation of second order, the integration of which requires the determination of the first derivative of the unknown function at the outer wall of the tube and the knowledge of the strain‐energy function. The axial stretch of the tube can be determined through two equations only when the strain‐energy function is specified.     

Evaluation of turbo and hydro‐generator torques due to electromechanical interaction

Abstract

The computer prediction of turbogenerator behaviour following fault or disturbance conditions has become an important feature in the assessment of machine system design, pre‐commissioning test appraisals, system operational procedures, machine monitoring strategy and post‐event damage diagnoses. In this paper computer methods are described to assess the comparative severity of various electrical faults and disturbances, the effect of specific operational practices together with the prediction of peak torsional transient behaviour. This paper is supported by realistic examples simulating the transient behaviour of a number of generational units.     

Epidural Electrotherapy for Epilepsy

Penetrating electronics have been used for treating epilepsy, yet their therapeutic effects are debated largely due to the lack of a large‐scale, real‐time, and safe recording/stimulation. Here, the proposed technology integrates ultrathin epidural electronics into an electrocorticography array, therein simultaneously sampling brain signals in a large area for diagnostic purposes and delivering electrical pulses for treatment. The system is empirically tested to record the ictal‐like activities of the thalamocortical network in vitro and in vivo using the epidural electronics. Also, it is newly demonstrated that the electronics selectively diminish epileptiform activities, but not normal signal transduction, in live animals. It is proposed that this technology heralds a new generation of diagnostic and therapeutic brain–machine interfaces. Such an electronic system can be applicable for several brain diseases such as tinnitus, Parkinson's disease, Huntington's disease, depression, and schizophrenia.     

A transformation of state‐space model to Jordan continued fraction expansion canonical form

Abstract

An algorithm is presented for computing the partial quotients of the Jordan type continued fraction expansion (CFE) of the corresponding transfer function of a linear time‐invariant system from its time‐moments of the impulse response. Explicit formulas for constructing the transformation matrix which transforms a general state‐space model to the Jordan CFE canonical form are derived. The results are given in a recursive form.     

Boundary element‐free method (BEFM) and its application to two‐dimensional elasticity problems

In this study, we first discuss the moving least‐square approximation (MLS) method. In some cases, the MLS may form an ill‐conditioned system of equations so that the solution cannot be correctly obtained. Hence, in this paper, we propose an improved moving least‐square approximation (IMLS) method. In the IMLS method, the orthogonal function system with a weight function is used as the basis function. The IMLS has higher computational efficiency and precision than the MLS, and will not lead to an ill‐conditioned system of equations. Combining the boundary integral equation (BIE) method and the IMLS approximation method, a direct meshless BIE method, the boundary element‐free method (BEFM), for two‐dimensional elasticity is presented. Compared to other meshless BIE methods, BEFM is a direct numerical method in which the basic unknown quantity is the real solution of the nodal variables, and the boundary conditions can be applied easily; hence, it has higher computational precision. For demonstration purpose, selected numerical examples are given. Copyright © 2005 John Wiley & Sons, Ltd.     

Photon Migration in a Two-layer Turbid Medium a Diffusion Analysis

Abstract

We analyse the diffusion of photons in a two-layer turbid medium, paying specific attention to parameters suggested by the use of lasers for diagnostic purposes in a medical setting. The data produced by such experiments consists of an intensity profile measured on the surface of the medium, which is measured either as a function of time at a fixed distance from the input laser beam, or else as a function of distance keeping the measurement time fixed. In both cases we demonstrate that the presence of a second layer can be detected provided that physical properties of the two layers differ by a sufficient amount, and also show up in calculated values of such parameters as the mean travel time of a photon to the surface of the medium, and the distribution of the maximum depth reached by an arbitrary photon.     

Experimental investigation of the stability of a clearance‐excited rotor system with optimal parameters

Abstract

The instability caused by aerodynamic forces from blade‐tip clearance is one of the most troublesome problems found in high performance tur‐bomachinery. An optimization technique has been proposed in previous work to improve the stability of a rotor‐bearing system. In this work, the validity and the practical procedure of the optimization technique are experimentally verified and demonstrated using a rotor‐bearing system. The experimental results verify the important theoretical conclusion that the threshold of stability of a rotor‐bearing system can be significantly increased by slight modification of the rotor diameters. Two examples are given to show the detailed procedure when the proposed optimization technique is used to increase the threshold of stability of an existing rotor‐bearing system.     

State‐space characterization of all solutions to a positive real control problem

Abstract

The purpose of this paper is to give a state‐space characterization of all internally stabilizing finite‐dimensional linear time‐invariant output feedback controllers for a given finite‐dimensional linear time‐invariant plant which ensure that the resulting closed‐loop transfer function is extended strictly positive real(ESPR). All such controllers are parameterized by a fixed linear fractional transformation with an ESPR, stable free parameter. The parameterized controllers have a state dimension not less than that of the open‐loop plant. The development uses only elementarily algebraic ideas beginning with a change of variables, an extended version of Kalman‐Yacubovich‐Popov positive real lemma, and Youla parameterization, thus the proofs given are simple and clear.     

A new boundary element method for resonance of an acoustic enclosure

Abstract

This paper presents a new boundary element formulation in which the eigenvalue appears outside the integral operator, which distinguishes it from the Helmholtz integral equation. Thus, the formation of global matrices need only be assembled once. Since the kernel of the operator used in the new formulation is real‐valued, all calculations can be carried out in a much simpler way in the real domain. The complex acoustic pressure amplitude is considered herein to deivate by a certain amount from a harmonic function. It is an important contribution that an exact relation between the deviator and the complex acoustic pressure amplitude is constructed locally and thus no more approximations are introduced except conventional boundary discretizations. Several examples are given to illustrate the feasibility of an accurate, effective prediction of resonance.     

Tracking problem of discrete control‐delayed systems

Abstract

The tracking problem of the discrete‐time control‐delayed system has been studied. A state feedback control law has been derived to make the output of the system to track a command input, a polynomial function of time index k, in finite steps. A numerical example is given in the last section to illustrate the results obtained in this paper.     

Generating experimental designs involving control and noise variables using genetic algorithms

Efficient estimation of response variables in a process is an important problem that requires experimental designs appropriated for each specific situation. When we have a system involving control and noise variables, we are often interested in the simultaneous optimization of the prediction variance of the mean (PVM) and the prediction variance of the slope (PVS). The goal of this simultaneous optimization is to construct designs that will result in the efficient estimation of important parameters. We construct new computer‐generated designs using a desirability function by transforming PVM and PVS into one desirability value that can be optimized using a genetic algorithm. Fraction of design space (FDS) plots are used to evaluate the new designs and six cases are discussed to illustrate the procedure. Copyright © 2009 John Wiley & Sons, Ltd.     

Optimization‐based stability analysis of structures under unilateral constraints

This paper discusses an optimization‐based technique for determining the stability of a given equilibrium point of the unilaterally constrained structural system, which is subjected to the static load. We deal with the three problems in mechanics sharing the common mathematical properties: (i) structures containing no‐compression cables; (ii) frictionless contacts; and (iii) elastic–plastic trusses with non‐negative hardening. It is shown that the stability of a given equilibrium point of these structures can be determined by solving a maximization problem of a convex function over a convex set. On the basis of the difference of convex functions optimization, we propose an algorithm to solve the stability determination problem, at each iteration of which a second‐order cone programming problem is to be solved. The problems presented are solved for various structures to determine the stability of given equilibrium points. Copyright © 2008 John Wiley & Sons, Ltd.     

Fast transient control of power systems using a partial energy function

Abstract

The partial energy function is applied to assess the transient stability for a power system subjected to a large disturbance. Following this assessment, an energy‐based analytical sensitivity method for fast transient control to prevent loss of synchronism of generators is presented. The sensitivity of the partial energy margin at any instant to the change of generation level has been analytically derived in a closed form. The proposed sensitivity technique offers a systematic calculation for quantitative estimation of generation that must be adjusted to maintain system stability. Furthermore, this paper proposes two local control strategies using the energy‐based sensitivity method with the superconducting magnetic energy storage (SMES) unit as an adaptive transient controller to enhance the power system transient performance. The accuracy test of the partial energy function and the effectiveness of both control schemes are illustrated with the Taipower system. The results are found to be encouraging.     

A simple practical analytic design method for multiloop‐controlled PWM switching regulators

Abstract

In this paper, a simple practical analytic method is proposed for designing multiloop‐controlled pulse width modulation (PWM) switching regulators. First, an equivalent single loop gain is presented and an approximate optimal set of closed‐loop poles is suggested according to the given specification such that the familiar design concept of a single‐loop second order system can be applied directly. In particular, closed form expressions of the feedback gains and the unknown parameters of the standard implemented circuit are derived. This renders the implementation problem surprisingly simple. Finally, some experimental results are also presented to demonstrate the effectiveness of the proposed method.     

Prediction intervals for load-sharing systems in accelerated life testing

Based on accelerated lifetime experiments, we consider the problem of constructing prediction intervals for the time point at which a given number of components of a load-sharing system fails. Our research is motivated by lab experiments with prestressed concrete beams where the tension wires fail successively. Due to an audible noise when breaking, the time points of failure could be determined exactly by acoustic measurements. Under the assumption of equal load sharing between the tension wires, we present a model for the failure times based on a birth process. We provide a model check based on a Q-Q plot including a simulated simultaneous confidence band and four simulation-free prediction methods. Three of the prediction methods are given by confidence sets where two of them are based on classical tests and the third is based on a new outlier-robust test using sign depth. The fourth method uses the implicit function theorem and the δ-method to get prediction intervals without confidence sets for the unknown parameter. We compare these methods by a leave-one-out analysis of the data on prestressed concrete beams. Moreover, a simulation study is performed to discuss advantages and drawbacks of the individual methods.     

Feature Selection Method Based on Class Discriminative Degree for Intelligent Medical Diagnosis

By using efficient and timely medical diagnostic decision making, clinicians can positively impact the quality and cost of medical care. However, the high similarity of clinical manifestations between diseases and the limitation of clinicians’ knowledge both bring much difficulty to decision making in diagnosis. Therefore, building a decision support system that can assist medical staff in diagnosing and treating diseases has lately received growing attentions in the medical domain. In this paper, we employ a multi-label classification framework to classify the Chinese electronic medical records to establish corresponding relation between the medical records and disease categories, and compare this method with the traditional medical expert system to verify the performance. To select the best subset of patient features, we propose a feature selection method based on the composition and distribution of symptoms in electronic medical records and compare it with the traditional feature selection methods such as chi-square test. We evaluate the feature selection methods and diagnostic models from two aspects, false negative rate (FNR) and accuracy. Extensive experiments have conducted on a real-world Chinese electronic medical record database. The evaluation results demonstrate that our proposed feature selection method can improve the accuracy and reduce the FNR compare to the traditional feature selection methods, and the multi-label classification framework have better accuracy and lower FNR than the traditional expert system.     

Solutions of population balance equations by double Legendre polynomial transformation

Abstract

First‐order partial differential equations of population balance are solved by employing the Legendre polynomials. The key of the method is that the dependent variable of the population density function is assumed to be expressed by a double series of Legendre polynomials with respect to time and space variables. The approach algorithm is that a series of ordinary differential equations are obtained by making the Legendre transformation with respect to the space coordinate. The series of time‐function ordinary differential equations are further transformed into algebraic equations of expansion coefficients with respect to time. The expansion coefficients of the Legendre polynomials are obtained by solving matrix equations which represent the series of algebraic equations. Illustrative examples are given, and the computational results are compared with those of other numerical values given in the literature. Satisfactory agreements are obtained.     

A design of fast‐locking without overshoot frequency‐locked servo system by fuzzy control technique

Abstract

In this paper, a Fuzzy Pulse Pump Controller (FPPC) is proposed to realize a Fuzzy‐Controlled Frequency‐Locked Servo system (FC‐FLS) for getting a fast locking response without overshoot. A prototype FC‐FLS is designed and built to assess the system performance. In comparison with the Frequency Pump Controller‐based FLS (FPC‐FLS) and Variable Slope Pulse Pump Controller‐based FLS (VSPPC‐FLS), the acquisition times of the FC‐FLS are improved over 40%. In particular, there is no overshoot in the FC‐FLS for any servo distance. This means that a fast‐locking FLS, without overshoot, has been successfully implemented as theoretical prediction.