A.Y.T Leung

• City University of Hong Kong

The paper devotes to the synthesis of local and global analysis of a discrete model describing the second-order digital filter with nonlinear signal processors. The discrete model gives rise to a two-dimensional non-invertible map, whose basins of attraction have complicated topological structures due to the intrinsic multi-stability. The influence...

Taking into account the nonlinear demand function, we have developed a multi-agent fishery economic model, where a multitude of agents are bounded by rationality. The fishing decisions of these agents are driven by a profit gradient mechanism. To assess the local stability of the system, stability analysis is performed with the Jury criterion. The...

This paper devotes to a detailed bifurcation analysis of a two-dimensional non-invertible map, obtained using a symmetric coupling between one-dimensional logistic maps. The critical normal form coefficients method is employed to detect bifurcations and to explore further critical conditions without explicit reduction to the center manifold. The re...

Taking the steam turbine cracked rotor system coupling multi-fault as an example, this paper reports systematic numerical experiments exploring two-parameter periodic complexification cascades. Specifically, we report high-resolution phase diagrams predicting and describing how the periodic sequences unfold over a quite extended range of parameter...

A novel class of nanoplate-based mass sensor with corner point supports for detecting attached nanoparticles is proposed. Exact solutions for vibrations of three types of nanoscale mass sensors are obtained by a symplectic superposition method combining with nonlocal elasticity theory. A comparison between theoretical prediction and FEM simulation...

The current century witnessed an overwhelming research interest in phononic crystals (PnCs) and acoustic metamaterials (AMs) research owing to their fantastic properties in manipulating acoustic and elastic waves that are inconceivable from naturally occurring materials. Extensive research literature about the dynamical and mechanical properties of...

The paper proposes a novel calculation method on the sensitivity analysis of bifurcation parameters and states in a single-degree-of-freedom (SDoF) impacting system. It presents the causes to (non-) smooth bifurcations in virtue of parameter sensitivity analysis. The derivation of the system’s Poincaré mappings is used to integrate the Floquet matr...

Composite periodic structures based elastic metamaterials with peculiar effective dynamic material characteristics and fantastic wave manipulation properties to completely impede or amplify the propagation of elastic/acoustic waves have become an active research area since last two decades [1]. The present study deals with the novel idea of dissipa...

In the present article the nonlinear control method is used for dual phase and dual anti-phase synchronizations among fractional order chaotic systems with uncertainties. The control functions are designed to achieve synchronization with the help of nonlinear control technique. The nonlinear control method is found to be very effective and convenie...

In this article, the stability analysis, chaos control and the function projective synchronization between fractional order identical satellite systems have been studied. Based on the stability theory of fractional order systems, the conditions of local stability of nonlinear three-dimensional commensurate and incommensurate fractional order system...

A finite element discretized symplectic method is presented for the determination of modes I and II stress intensity factors (SIFs) for cracked bimaterial plates subjected to bending loads using Kirchhoff’s theory and symplectic approach. The overall plate is meshed by conventional discrete Kirchhoff theory elements and is divided into two regions:...

The paper presents a novel synchronization scheme for uncertain chaotic systems via complete-adaptive-impulsive controls. The controllers are designed in the form of linear-error feedback coupling, but the control gains are completely adaptive. More details on minimizing interaction terms and accelerating synchronization process are revealed. The i...

Stress singularities arising at the multi-material interface in a V-notched plate under bending are studied in the frame work of a Hamiltonian-based method. Exact solutions of V-notched multi-material plates are expressed in an analytical symplectic series. Newly defined generalized stress intensity factor (GSIF) are introduced to evaluate fracture...

A simple coupled method, called “finite element discretized symplectic method” is introduced into the mode III fracture analysis of a V-notched magneto-electro-elastic (MEE) bimaterial. High-accuracy generalized intensity factors and energy release rate are computed to evaluate the singularities of mechanical, electric and magnetic fields. The pres...

In this paper, an analytical approach, namely multi-level residue harmonic balance is introduced and developed for the nonlinear free vibration analysis of axially loaded beams with an internal hinge. The main advantage of this method is that only one set of nonlinear algebraic equations is required to be solved for obtaining the zero level solutio...

A finite element discretized symplectic method is introduced to compute directly the intensity factors of cracked piezoelectric materials. After modelling by the conventional finite elements, the cracked body is divided into two regions: near and far fields. The unknowns in the far field are unchanged while the displacements, electric potentials, s...

Enhancement of fine particle (PM2.5) separation is important for cyclone separators to reduce any extra purification process required at the outlet. Therefore, the present experimental research was performed to explore the performance of cyclone separators modified with down-comer tubes at solid loading rates from 0 to 8.0 g/m3 with a 10 m/s inlet...

Along with the population and building booms of Hong Kong in the 1960s, the problem of building dilapidation was being exacerbated. Buildings in state of dilapidation will not only pose problem in terms of structural failure, hygiene, fire safety but also bring along hazards like object falling from height which would cause injury to innocent passe...

A novel adaptive–impulsive scheme is proposed for synchronizing fractional-order chaotic systems without the necessity of knowing the attractors’ bounds in priori. The nonlinear functions in these systems are supposed to satisfy local Lipschitz conditions but which are estimated with adaptive laws. The novelty is that the combination of adaptive co...

The present paper is based on CFD modelling of gas-solid flow in cyclone separators with different dust outlet geometries (with and without down-comer tubes at the cyclone bottom) to analyse the flow characteristics and the cyclone performance. Numerically obtained cyclone performance parameters, collection efficiency, and pressure drop were compar...

Tower cranes are widely used in construction jobsite for their efficiency. However, tower cranes and construction workers themselves suffer a significant safety hazards from natural sway of payloads. Besides, the external disturbance of wind leads to additional sway and intensifies the oscillation amplitude of crane load on construction site. There...

Based on the stability theory of fractional-order system, a novel unidirectional adaptive full-state linear error feedback coupling scheme is extended to control and synchronize all of fractional-order differential (FOD) chaotic systems with in-commensurate (and commensurate) orders. The feedback strength is adaptive to an updated law rather than p...

A symplectic approach based on the Hamiltonian system is proposed to analyze the electroelastic singularities and intensity factors of an interface crack in piezoelectric–elastic bimaterials. By introducing a total unknown vector consisting of generalized displacements and stresses, the Lagrangian equations are transformed to the Hamiltonian equati...

A finite element discretized symplectic method is proposed to compute the stress intensity factors (SIFs) of interface cracks in multi-material composites subjected to anti-plane loading. The whole body is divided into a near field containing a crack to be solved analytically and a far field to be solved by conventional finite elements. In the near...

A new-finite element discretized symplectic method for solving the steady-state heat conduction problem with singularities in composite structures is presented. The model with a singularity is divided into two regions, near and far fields, and meshed using conventional finite elements. In the near field, the temperature and heat flux densities are...

To deal with the existing building dilapidation problem in Hong Kong, a mandatory building inspection scheme (MBIS) has been introduced. The effectiveness of the scheme is reliant on an adequate supply of registered inspectors (RIs) to inspect and supervise repair works. To ensure that there is an adequate supply and demand of RIs to enable the imp...

An adaptive-feedback control scheme for identical synchronizing two linearly coupled chaotic systems and identifying uncertain parameters is proposed. In comparison with the previous methods it inherited, the present scheme is more flexible and accessible. This is because that the prerequisites on the given chaotic systems are much looser, and the...

This paper studies the ageing effect of mechanical joints reflecting from the tyre/joint impacting noise by measuring the vehicle structure-borne noise change. Field data is collected applying two measurement methods suitable for newly installed and existing old expansion joints. The measurement methodology is improved by designing and applying a t...

This paper addresses the steady-state periodic and quasi-periodic responses of van der Pol–Mathieu system subject to three excitations (i.e., self, parametric and external excitations). Method of multiple scales and double perturbation technique are employed to study the original system. The cases of van der Pol–Mathieu oscillator with and without...

Abstract The performance of collection efficiency of cylindrical inlet-type cyclone separator for relatively low solid loading rate conditions is reported. Cyclone separators usually operate under high solid loading conditions, but the demand of air pollution control at outdoor densely polluting activities as construction sites and application of p...

In this paper, an efficient analytical solution method, namely, multi-level residue harmonic balance, is introduced and developed for the nonlinear vibrations of multi-mode flexible beams on an elastic foundation subject to external harmonic excitation. The main advantage of this solution method is that only one set of nonlinear algebraic equations...

Cyclone separators are extensively used in applications of air pollution control. This paper reported an experimental study based on minimizing solid particles reentrainment from solid collection hopper, with the exit gas flow. The hopper in conventional cyclone separator was modified by implementing a prolonged vertical tube at the bottom. Overall...

A finite element discretized symplectic method is introduced to find the thermal stress intensity factors (TSIFs) under steady-state thermal loading by symplectic expansion. The cracked body is modeled by the conventional finite elements and divided into two regions: near and far fields. In the near field, Hamiltonian systems are established for th...

This study addresses the research on the noise and vibration correlation of a bridge movement joint. The aim of this research is to assess the noise induced by the vibration of a bridge movement joint without lane closure during the operation period. There are two methods of developing the correlation between the tyre/joint noise and vibration: (i)...

This paper presents a simple and rigorous solution procedure of residue harmonic balance for predicting the accurate approximation of certain autonomous ordinary differential systems. In this solution procedure, no small parameter is assumed. The harmonic residue of balance equation is separated in two parts at each step. The first part has the sam...

In this paper, a symplectic method based on the Hamiltonian system is proposed to analyze the interfacial fracture in the piezoelectric bimorph under anti-plane deformation. A set of Hamiltonian governing equations is derived from the Hamiltonian function by introducing dual variables of generalized displacements and stresses which can be expanded...

In this paper, a Duffing-van der Pol oscillator having fractional derivatives and time delays is investigated by the residue harmonic method. The angular frequencies and limit cycles of periodic motions are expanded into a power series of an order-tracking parameter and the unbalanced residues resulting from the truncated Fourier series are conside...

This paper is concerned with the steady state bifurcations of a harmonically excited two-member plane truss system. A two-degree-of-freedom Duffing system having nonlinear fractional derivatives is derived to govern the dynamic behaviors of the truss system. Viscoelastic properties are described by the fractional Kelvin–Voigt model based on the Cap...

The method of symplectic series discretized by finite element is introduced for the stress analysis of structures having cracks at the interface of dissimilar materials. The crack is modeled by the conventional finite elements dividing into two regions: near and far fields. The unknowns in the far field are as usual. In the near field, a Hamiltonia...

When rewriting the governing equations in Hamiltonian form, analytical solutions in the form of symplectic series can be obtained by the method of separation of variable satisfying the crack face conditions. In theory, there exists sufficient number of coefficients of the symplectic series to satisfy any outer boundary conditions. In practice, the...

Active feedback control is commonly used to attenuate undesired vibrations in vibrating machineries and structures, such as bridges, highways and aircrafts. In this paper, we investigate the primary resonance and 1/3 subharmonic resonance of a harmonically forced Duffing oscillator under fractional nonlinear feedback control. By means of the first...

This article deals with the anti-synchronization between two identical chaotic fractional-order Qi system, Genesio–Tesi system, and also between two different fractional-order Genesio–Tesi and Qi systems using active control method. The chaotic attractors of the systems are found for fractional-order time derivatives described in Caputo sense. Nume...

Classical electrical circuits consist of resistors and capacitors and are governed by integer-order model. Circuits may have so-called fractance which represents an electrical element with fractional order impedance. Therefore, fractional order derivative is important to study the dynamical behaviors of circuits. This paper extends the classical co...

With the rapid development of modern technology, high or low temperature environment has become an important factor which can not be ignored. Therefore, the fracture problem caused by loads due to thermal environment has become the key issue in the safety assessment and optimization design of engineering structures. The thermal stress intensity fac...

A generalized Duffing–van der Pol oscillator with nonlinear fractional order damping is introduced and investigated by the residue harmonic homotopy. The cubic displacement involved in fractional operator is used to describe the higher-order viscoelastic behavior of materials and of aerodynamic damping. The residue harmonic balance method is employ...

In this paper, we investigate the damping characteristics of two Duffing–van der Pol oscillators having damping terms described by fractional derivative and time delay respectively. The residue harmonic balance method is presented to find periodic solutions. No small parameter is assumed. Highly accurate limited cycle frequency and amplitude are ca...

In this article, the active control method is used to investigate the hybrid phase synchronization between two identical Rikitake and Windmi systems, and also between two nonidentical systems taking Rikitake as the driving system and Windmi system as the response system. Based on the Lyapunov stability theory, the sufficient conditions for achievin...

The stress intensity factor (SIF) of a multi-material magnetoelectroelastic wedge in anti-plane deformation is analytically determined by the symplectic method. The Lagrangian equations in configuration variables alone are transformed to Hamiltonian equations in dual variables (configuration and momentum) which allow the use of the method of separa...

The nonlinear single-mode dynamic behaviour of the viscoelastic arch whose damping is governed by fractional derivatives is considered. A set of ordinary differential equations is derived for the primary resonance and is solved by the residue harmonic homotopy to obtain all the steady state solutions. A parametric study is carried out to determine...

Symmetry breaking is a ubiquitous and important phenomenon arising in a wide range of physical systems. We propose the use of the harmonic balance in combination with homotopy continuation to investigate symmetry breaking occurrence in the periodically excited systems involving time delay. Two numerical examples are given to show the details. When...

An analytical method is presented for finding the complex stress intensity factors (SIFs) and T-stress at an edge bi-material interface crack. A Hamiltonian system is first established by introducing dual (conjugate) variables of displacements and stresses whose solutions are expanded in terms of the symplectic series. With the aid of the adjoint s...

This paper investigates the steady state bifurcation of a periodically excited system subject to time-delayed feedback controls by the combined method of residue harmonic balance and polynomial homotopy continuation. Three kinds of delayed feedback controls are considered to examine the effects of different delayed feedback controls and delay time...

For the coupled static and dynamic buckling of thin walled beam subjected to various forces, such as axial force, uniform bending moment, and bending moment due to concentrated and distributed lateral forces, the spline finite element method is employed to obtain the dynamic stiffness matrix. Second order effects of the axial force and moment are c...

We introduce the residue harmonic balance method to generate periodic solutions for nonlinear evolution equations. A PDE is firstly transformed into an associated ODE by a wave transformation. The higher-order approximations to the angular frequency and periodic solution of the ODE are obtained analytically. To improve the accuracy of approximate s...

A general version of the fractional Mathieu equation and the corresponding fractional Mathieu–Duffing equation are established for the first time and investigated via the harmonic balance method. The approximate expressions for the transition curves separating the regions of stability are derived. It is shown that a change in the fractional derivat...

In this paper, we predict the accurate bifurcating periodic solution for a general class of first-order nonlinear delay differential equation with reflectional symmetry by constructing an approximate technique, named residue harmonic balance. This technique combines the features of the homotopy concept with harmonic balance which leads to easy comp...

The residue harmonic balance is developed for coupled systems exemplified by the damped Duffing resonator driven by a van der Pol oscillator. This technique combines the features of harmonic balance and parameter bookkeeping to obtain approximate solutions to any desired accuracy. For the two degrees of freedom system, the zeroth-order approximatio...

Both the primary and superharmonic resonance responses of a rigid rotor supported by active magnetic bearings are investigated by means of the total harmonic balance method that does not linearize the nonlinear terms so that all solution branches can be studied. Two sets of second order ordinary differential equations governing the modulation of th...

The two main objectives of this article are (1) to determine the bifurcating periodic responses accurately and to study the effects of time delay and feedback gain on the steady state response in autonomous oscillators by means of the residue harmonic balance method; and (2) to study the dynamics of both the autonomous and non-autonomous Duffing-va...

An analytical quadrilateral p element is developed for solving the free vibrations of piezoelectric-laminated plates. The formulations of the displacement and strain fields are based on first-order shear deformation plate theory. The coupling effect between the electrical and stress fields is also considered. The Legendre orthogonal polynomials are...

We use the residue harmonic balance scheme to study the periodic motions of a class of second-order delay-differential equations with cubic nonlinearities near and after Hopf bifurcation. The multiple solutions are found by homotopy continuation. Then, the approximation to any desired accuracy for a specific solution is captured by solving linear e...

SUMMARYA simple structure under earthquake excitation is modeled as a single‐degree‐of‐freedom system with nonlinear stiffness subject to modulated Kanai–Tajimi excitation. The nonstationary responses including the nonstationary probability densities of the system responses and the statistical moments are obtained in semi‐analytical form. By applyi...

Due to the high complexity and difficulty involved, the behavior of plastic hinge of reinforced concrete members has been previously investigated experimentally. This work investigates the plastic hinge analytically, using the finite element method. Lengths in the plastic hinge region involving rebar yielding zone, concrete crushing zone and curvat...

For reinforced concrete (RC) flexural members, the plastic deformation is localized in a small zone namely the plastic hinge zone after the yielding of the member. The performance of the plastic hinge zone is critical for flexural members as it governs the load carrying and deformation capacities of the member. Therefore, plastic hinge has been of...

In this article, the fractal two-level finite element method, which has mainly been used for static crack problems, is applied to mode III elastodynamic plane crack problems. Using the transformation process in the proposed method, the infinite dimension of the finite element matrices that are assembled for a singular region is made finite in terms...

A residue harmonic balance method is extended to determine the approximations and bifurcations for a coupled airfoil system with cubic structural nonlinearity analytically. The approximate solutions to any desired accuracy can be obtained easily by solving a set of linear algebraic equations in each step. The strongly cubic nonlinear pitching and p...

The problems of acoustic waves scattered by scatterer immersed in unbounded domain is an essential ingredient in the study of acoustic-structure interaction. In this paper the problems of acoustic scattering in an infinite exterior region are investigated by using a fractal two-level finite element mesh with self-similar layers in the media which e...

Stress intensity factors are analytically derived for an edge-cracked circular disk subjected to transient thermal stresses using symplectic technique. The transient temperature function for the time independent boundary conditions is obtained by a generalized symplectic approach and the method of separation of variables. From the obtained temperat...

In this paper, a powerfully analytical technique is proposed for predicting and generating the steady state solution of the fractional differential system based on the method of harmonic balance. The zeroth-order approximation using just one Fourier term is applied to predict the parametric function for the boundary between oscillatory and non-osci...

A residue harmonic balance is established for accurately determining limit cycles to parity- and time-reversal invariant general non-linear jerk equations with cubic non-linearities. The new technique incorporates the salient features of both methods of harmonic balance and parameter bookkeeping to minimize the total residue. The residue is separat...

Theoretical analysis of the nonlinear vibration effects on the sound absorption of a panel absorber and sound transmission loss of a panel backed by a rectangular cavity is herein presented. The harmonic balance method is employed to derive a structural acoustic formulation from two-coupled partial differential equations representing the nonlinear...

The harmonic balance method truncates the Fourier series in a finite number of terms. In this paper we show that the truncated residues may be important to determine the stability of the approximated solution and that the truncated residues in the stability analysis can fully be considered without increasing the number of equations in the original...

Fracture mechanism is pertinent to minimize the catastrophic failures and optimize the structural design. An exact treatment on the electromagnetic permeable crack problems in a magnetoelectroelastic medium is presented by establishing a Hamiltonian system in terms of the symplectic eigenfunctions. The coefficients of the series are determined from...

A new approach that the iterative homotopy harmonic balancing is presented for charactering and predicting analytical approximations of conservative oscillator with strong odd-nonlinearity in the paper. The new technique does not depend upon small parameter assumption and incorporates the salient features of both methods of the parameter-expansion...

Both the autonomous and non-autonomous systems with fractional derivative damping are investigated by the harmonic balance method in which the residue resulting from the truncated Fourier series is reduced iteratively. The first approximation using a few Fourier terms is obtained by solving a set of nonlinear algebraic equations. The unbalanced res...

This paper reports a systematic computational study of wind-induced natural ventilation and pollutant transport of re-entrant bays on a total of 30 generic building models of different building heights and with bays of different dimensions. Mean wind flow around each building model and wind-induced flow inside re-entrant bays are computed. To deter...

We investigate the fractal properties on the distribution of natural frequencies of elastic structures. We use the multi-level-multi-scale dynamic substructure method so that we need only to eliminate a few nodes in advancing a fractal level. We shall give four numerical examples including the von Koch curves and the L-system. The natural frequenci...

The present paper deals with the natural vibration of thin circular and annular plates using Hamiltonian approach. It is based on the conservation principle of mixed energy and is constructed in a new symplectic space. A set of Hamiltonian dual equations with derivatives with respect to the radial coordinate on one side of the equations and to the...

Free vibration and buckling of pre-twisted beams exhibit interesting coupling phenomena between compression, shears, moments and torque and have been the subject of extensive research due to their importance as models of wind turbines and helicopter rotor blades. The paper investigates the influence of axial compression and torque on the natural vi...

An analytical method using symplectic expansion is introduced to find the solutions of edge-cracked circular magneto-electro-elastic media to handle general boundary conditions. A symplectic system is established so that these unknowns are expanded in terms of the symplectic eigenfunctions. The coefficients of the eigenfunctions series are determin...

Since 1996, the provision of a refuge floor has been a mandatory feature for all new tall buildings in Hong Kong. These floors are designed to provide for the building occupants a fire safe environment that is also free from smoke. However, the desired cross ventilation on these floors to achieve the removal of smoke, assumed by the Building Codes...

We solve the nonlinear ordinary differential equations which describe the motion of oscillators with discontinuous and/or fractional power restoring force by reducing the residue of harmonic balance sequentially. The new technique incorporates the salient features of both methods of harmonic balance and parameter bookkeeping. The residue is separat...

A recent experiment of layered stainless steel with nanostructured interface has suggested that a brittle interface can lead to an overall structure with high ductility. Here a cohesive finite element method is employed to investigate the paradox of a brittle nanostructured interface (nanograined interface layer) and a ductile layered stainless ste...

We use the Hamiltonian formalism in elasticity to analyze edge-cracked cylinder under various three-dimensional loading conditions. The Hamiltonian form enables the successful separation of the independent variables in polar coordinates so that symplectic eigenfunctions can be analytically determined. The displacements and stresses are proved to be...

The response of energy envelop in complex nonlinear oscillator networks to stochastic excitations is studied. First, by using the stochastic averaging method for quasi-nonintegrable-Hamiltonian systems, the averaged Fokker–Planck–Kolmogorov equation governing the probability density of the Hamiltonian is established. Then, the stationary probabilit...

One of recent experimental progresses in strengthening and toughening metals simultaneously is to adopt techniques of surface mechanical attrition treatment (SMAT) and warm co‐rolling to 304 stainless steel (SS). To capture deformation behavior and associated damage initiation∕evolution process in the co‐rolled SMATed 304SS, cohesive finite element...

In this study, the fractal two‐level finite element method, which has mainly been used for static cracked plane problems, is applied to the cracked plane problem. Using the transformation process in the proposed method, the infinite dimension of the finite element matrices that are assembled for a singular region is made finite in terms of the dyna...

As a technique of grain refinement process by plastic deformation, surface mechanical attrition treatment (SMAT) has been developed to be one of the most effective ways to optimize the mechanical properties of various materials including pure metals and alloys. SMAT can significantly reduce grain size into nanometer regime in the surface layer of...

This paper presents the application of a novel Artificial Neural Network (ANN) model for the diagnosis of structural damage. The ANN model, denoted as the GRNNFA, is a hybrid model combining the General Regression Neural Network Model (GRNN) and the Fuzzy ART (FA) model. It not only retains the important features of the GRNN and FA models (i.e. fas...

In this paper, the second‐order two‐scale analysis method for bending behaviors of the plate made from composites with 3‐D periodic configuration is presented by means of construction way. It can capture the microscopic 3‐D mechanics behaviors caused from 3‐D micro‐structures. First, directly starting from the 3‐D elastic plate model of composite m...

To address the issues in the area of design customization, this paper expressed the specification and application of the constrained surface deformation, and reported the experimental performance comparison of three prevail effective similarity assessment algorithms on constrained surface deformation domain. Constrained surface deformation becomes...