Nonlinear Parameter Variations Research Articles

Influence of gas generation in electro‐osmosis consolidation

SummaryThis paper presents a numerical model for the elasto‐plastic electro‐osmosis consolidation of unsaturated clays experiencing large strains, by considering electro‐osmosis and hydro‐mechanical flows in a deformable multiphase porous medium. The coupled governing equations involving the pore water flow, pore gas flow, electric flow and mechanical deformation in unsaturated clays are derived within the framework of averaging theory and solved numerically using finite elements. The displacements of the solid phase, the pressure of the water phase, the pressure of the gas phase and the electric potential are taken as the primary unknowns in the proposed model. The nonlinear variation of transport parameters during electro‐osmosis consolidation are incorporated into the model using empirical expressions that strongly depend on the degree of water saturation, whereas the Barcelona Basic Model is employed to simulate the elasto‐plastic mechanical behaviour of unsaturated clays. The accuracy of the proposed model is evaluated by validating it against two well‐known numerical examples, involving electro‐osmosis and unsaturated soil behaviour respectively. Two further examples are then investigated to study the capability of the computational algorithm in modelling multiphase flow in electro‐osmosis consolidation. Finally, the effects of gas generation at the anode, the deformation characteristics, the degree of saturation and the time dependent evolution of the excess pore pressure are discussed. Copyright © 2016 John Wiley & Sons, Ltd.

Experimental and numerical studies of nonlinear ultrasonic responses on plastic deformation in weld joints**Project supported by the National Natural Science Foundation of China (Grant Nos. 51325504, 11474093, and 11474361) and the Shanghai Rising-Star Program, China (Grant No. 14QA1401200).

The experimental measurements and numerical simulations are performed to study ultrasonic nonlinear responses from the plastic deformation in weld joints. The ultrasonic nonlinear signals are measured in the plastic deformed 30Cr2Ni4MoV specimens, and the results show that the nonlinear parameter monotonically increases with the plastic strain, and that the variation of nonlinear parameter in the weld region is maximal compared with those in the heat-affected zone and base regions. Microscopic images relating to the microstructure evolution of the weld region are studied to reveal that the change of nonlinear parameter is mainly attributed to dislocation evolutions in the process of plastic deformation loading. Meanwhile, the finite element model is developed to investigate nonlinear behaviors of ultrasonic waves propagating in a plastic deformed material based on the nonlinear stress–strain constitutive relationship in a medium. Moreover, a pinned string model is adopted to simulate dislocation evolution during plastic damages. The simulation and experimental results show that they are in good consistency with each other, and reveal a rising acoustic nonlinearity due to the variations of dislocation length and density and the resulting stress concentration.

Complex Evolution of Built-in Potential in Compositionally-Graded PbZr(1-x)Ti(x)O3 Thin Films.

Epitaxial strain has been widely used to tune crystal and domain structures in ferroelectric thin films. New avenues of strain engineering based on varying the composition at the nanometer scale have been shown to generate symmetry breaking and large strain gradients culminating in large built-in potentials. In this work, we develop routes to deterministically control these built-in potentials by exploiting the interplay between strain gradients, strain accommodation, and domain formation in compositionally graded PbZr1-xTixO3 heterostructures. We demonstrate that variations in the nature of the compositional gradient and heterostructure thickness can be used to control both the crystal and domain structures and give rise to nonintuitive evolution of the built-in potential, which does not scale directly with the magnitude of the strain gradient as would be expected. Instead, large built-in potentials are observed in compositionally-graded heterostructures that contain (1) compositional gradients that traverse chemistries associated with structural phase boundaries (such as the morphotropic phase boundary) and (2) ferroelastic domain structures. In turn, the built-in potential is observed to be dependent on a combination of flexoelectric effects (i.e., polarization-strain gradient coupling), chemical-gradient effects (i.e., polarization-chemical potential gradient coupling), and local inhomogeneities (in structure or chemistry) that enhance strain (and/or chemical potential) gradients such as areas with nonlinear lattice parameter variation with chemistry or near ferroelastic domain boundaries. Regardless of origin, large built-in potentials act to suppress the dielectric permittivity, while having minimal impact on the magnitude of the polarization, which is important for the optimization of these materials for a range of nanoapplications from vibrational energy harvesting to thermal energy conversion and beyond.

PSO-scaled fuzzy logic to load frequency control in hydrothermal power system

This paper, presents the particle swarm optimization-based fuzzy logic controller (PSO FLC) design for load frequency control in a two-area interconnected hydrothermal power system. Flexible alternating current transmission system devices and energy storage devices are being installed to improve the reliability and stability of the system under dynamic conditions. One such devices namely thyristor-controlled phase shifter (TCPS) is connected in series with the tie-line to damp out the power swings and frequency oscillations. Similarly at the terminal of one control area, a fast acting energy storage device of superconducting magnetic energy storage (SMES) is connected to meet the sudden changes in demand. The existing conventional controllers are unable to provide the satisfactory performance over a wide range of operating conditions due to system nonlinearity and plant parameter variations. To improve the dynamic performance of the system, this work proposes an intelligent tuning approach using a combination of particle swarm optimization (PSO) and fuzzy logic technique. In this work, PSO algorithm is employed for the optimal selection of membership function parameters of the proposed fuzzy PI, TCPS and SMES controllers by minimizing the time domain objective function. The simulation study is performed by the proposed PSO FLC in a two-area interconnected power system. To show the effective performance of the proposed controller, a comparative study has been made with the conventional, genetic algorithm and fuzzy logic-based optimized controller under varying load conditions.

Position Control of Hydraulic Actuators Using Fuzzy Pulse Width Modulation (PWM)

Hydraulic actuators are widely employed for industrial automation for its high power over weight ratio, functionality in tough operating conditions and low cost. However, the dynamics of hydraulic systems are non-linear and the system subjected to non-smooth and discontinuous non-linearities due to directional change of valve opening, friction, valve overlap and changes of hydraulic pressure acted on valve spool. Taking into account the effect of nonlinear parameter variations such as bulk modulus, compressibility of oil or viscosity of oil, fuzzy logic approach is chosen. Fuzzy control can adapt the inconstant working condition and non-linear system alongside of its robustness. For PWM controlled hydraulic component such as solenoid valve, effective approximation of the flow properties in a solenoid valve is essential. In this paper, the effect of fuzzy logic approach incorporated on pulse width modulation (PWM) controlled hydraulic system is to be investigated and experimentally verified.

Reliable Solution in Dynamic River Flow System Computations

Reliable Solution in Dynamic River Flow System Computations Application and limitation of various computational methods handling hydrologic runoff and varied unsteady river flow equations was studied here. Investigations were focused on many numerical aspects linear, non-linear solution of continuity and dynamic equations. A river catchment was examined, hydrometric stations, water control measures at upstream and hydrodynamic systems of river- reservoir at downstream were modeled provided evaluation and performance of water conveyance systems proposed for water resources planning and management. Application of modeling flow discharge in rivers was reviewed through a number of flow routing techniques. These classical computational methods have been widely used in water resources engineering and are subject of front line research by hydrologic and hydraulic modelers. Application of conventional and practical methods such as Muskingum-Cunge which are classified under hydrologic and hydraulic routing categories was examined for nonlinear variation of hydrodynamic parameters. Several methods including various numerical schemes were used and compared for modeling accurate unsteady flows computations. Analysis were ranked based on four criterions (consistency, stability, convergence and accuracy) examined with field observations and recorded data. Result of analysis verified that with careful description of constant and variable parameters involved in the Muskingum-Cunge model, the nonlinear terms and physical behavior of the problem was best fitted as compared by developed numerical solutions. The kinematic wave model and Hydrologic Engineering Centre (HEC) and Danish Hydraulic Institute (DHI) Mike series software were employed to verify developed fully dynamic wave model. A 42 kilometer reach length (a location between two hydrometric stations) was modeled with hydrologic and hydro-informatics parameters in Kor River were used. Comparing performances of two constant and variable Muskingum-Cunge methods, nonlinear model with variable parameters had highest reliability and accurately was used for dynamic water wave routing in water conveyance systems (especially for rivers without measuring gage stations).

A Proposed GA Based PID Controller for Three Phase Brushless DC Motor

Brushless DC motors are widely used for many industrial applications because of their high efficiency, high torque, higher speed ranges, noiseless operation and low volume. More advanced controllers are used to manage acceleration, control speed and fine-tune efficiency of BLDC motor. A proportional–integral–derivative controller is a generic control loop feedback mechanism widely used in industrial control systems because of its simple structure and easy implementation. The conventionally tuned PID controller is not providing optimum performance under nonlinear conditions and parameter variations. The aim of this research is to develop a complete model of the BLDC motor and to design an optimal controller for its control. The Genetic Algorithm is proposed as a global optimizer to find the optimized PID gains for control of BLDC motor.

Study on parameter optimization in a passively mode-locked Erbium-doped fiber laser

Optical soliton communication is the frontier research topic of optical fiber communication. In this paper, we study optical solitons generated by passively mode-locked Erbium-doped (Er-doped) fiber (EDF) laser. We analyze the variation of nonlinear equilibrium point parameter N of the passively mode-locked EDF laser in the role of group-velocity dispersion (GVD) and small-signal gain, and adjusting system parameter N is as close as to possible to 1. The ground state first-order optical soliton which generated through system parameter optimization of the passively mode-locked EDF laser will improve the efficiency and stability of optical soliton communication system. The research of this paper will have provided the theoretical foundation of parameter optimization in a passively mode-locked EDF laser. And it will be possible for the passively mode-locked fiber laser in optical fiber communication system to be applied from the laboratory stage to the practical application.

Spatiotemporal dynamics of a digital phase-locked loop based coupled map lattice system

We explore the spatiotemporal dynamics of a coupled map lattice (CML) system, which is realized with a one dimensional array of locally coupled digital phase-locked loops (DPLLs). DPLL is a nonlinear feedback-controlled system widely used as an important building block of electronic communication systems. We derive the phase-error equation of the spatially extended system of coupled DPLLs, which resembles a form of the equation of a CML system. We carry out stability analysis for the synchronized homogeneous solutions using the circulant matrix formalism. It is shown through extensive numerical simulations that with the variation of nonlinearity parameter and coupling strength the system shows transitions among several generic features of spatiotemporal dynamics, viz., synchronized fixed point solution, frozen random pattern, pattern selection, spatiotemporal intermittency, and fully developed spatiotemporal chaos. We quantify the spatiotemporal dynamics using quantitative measures like average quadratic deviation and spatial correlation function. We emphasize that instead of using an idealized model of CML, which is usually employed to observe the spatiotemporal behaviors, we consider a real world physical system and establish the existence of spatiotemporal chaos and other patterns in this system. We also discuss the importance of the present study in engineering application like removal of clock-skew in parallel processors.

Capture in Nonlinear Differential Games of Pursuit

We look at a brief historical survey of controllability problems of time optimal control theory. We next look at nonlinear variation of parameters to investigate controllability of basically nonlinear systems whereby we establish nonlinear differential games of pursuit results.

Robust adaptive controller for continuous bioreactors

Bioreactor control has become very important in recent years due to the difficulty in controlling highly non-linear behavior, model mismatch and parameter variation. Adaptive back-stepping control is a recursive design method that employs the Lyapunov stability theory in its design procedures. Adaptive back-stepping control is applied to the problem, which drives a continuous bioreactor to its optimal productivity point. However the designed control law may not work at the optimal productivity point, since controlling the optimal productivity point frequently causes the control system to fall into a singular point. Thus in this study, we apply the back-stepping design to a bioreactor system by introducing a simple parameter into the design techniques to prevent the control system from operating at a singular point. The parameter introduced in the control law can be understood intuitively and the proposed control scheme is endowed with strong robustness properties. The resulting controllers are compared to the feedback linearization based proportional-integral controller and internal model control, as well as nonlinear model predictive control and observer-based linearizing control by theoretical simulations. It is shown that the proposed control strategy is versatile and effective in implementing robust control for regulating productivity in the presence of model mismatch, model uncertainty and parameter variation. The proposed control scheme successfully drives the productivity of the controlled continuous bioreactor to its optimal point.

Nonlinear parameters of heart rate variability during mental stress

IntroductionThis study investigates the variations of nonlinear parameters of heart rate variability (HRV) due to an arithmetic stress test.Material and methodsWe tested 83 healthy students with a mean age of 21.12±0.21 years. The students were examining in the following sequence: recording of HRV at rest and during mental arithmetic. HRV was assessed by applying Poincare plot analysis (SD1, SD2, SD2/SD1, SS) to the R‐R interval series on a 10‐min ECG. The traditional (GI) and redefined Guzik's index (GIp) (Karmakar, 2010) was calculated for each subjects in each phase of the experiments.Results and discussionSD1 during mental arithmetic was significantly smaller (24.51±1.77) than that at rest (34.57±2.05; p<0.0001). SD1/SD2 ratio during mental stress was significantly lower than that at rest (0.331±0.013 vs 0.469±0.017; p<0.00001). SS was significantly lower during the test than that at rest (2756.13±313.97 vs 3822.66±370.57; p=0.008). There was no significant difference in the GI during mental stress (0.495±0.008) than that at rest (0.485±0.005; p>0.05). But after redefinition, we have found pronounced changes in this parameter with a maximum at rest day and minimum during arithmetic test (0.446±0.024 vs 0.398±0.018; p<0.05).This findings suggest that nonlinear HRV analysis could be effective in automatically detecting functional status during mental stress.

Robust Assist for Conveyance of Flexible Structures Taking Account of Structured Uncertainties and Vibration Influence to Operators

Power assist systems have been introduced to reduce workers' load in industrial production. The authors have studied on control systems for power assisted conveyance of flexible structures. Generally, the systems include influences of various kinds of uncertainties. One of them is vibration influence of controlled objects to operators. Another one is structured uncertainties such as nonlinear friction or parameter variations. This paper shows a robust assist system design by taking these uncertainties into account. It consists of an impedance controller, a disturbance accommodating optimal controller, a disturbance observer and a reaction force controller. The first and second elements have already been applied to the authors' previous paper. In addition, the disturbance observer is needed for eliminating the influence of the structured uncertainties. Moreover, taking the characteristic of the controlled object model into account, the simple reaction force controller is applied in order to eliminate the influence of the reaction force from the vibration reduction actuator. As a controlled object example, this paper adopts a power assist cart with a vibration system. The effectiveness of the proposed control system is verified by experiments and their corresponding simulations.

Application of Frequency-Shaped Disturbance Accommodating Optimal Control to Robust Assist for Conveyance of Flexible Structures

Power assist systems have been introduced to reduce workers' load in industrial production. The author has studied on control systems for power assisted conveyance of flexible structures. Generally, the systems include influences of various kinds of uncertainties. One of them is vibration influence of controlled objects to operators. Another one is structured uncertainty such as nonlinear friction or parameter variations. The author's previous paper proposed a robust assist system design by taking these uncertainties into account. It consisted of an impedance controller, a disturbance accommodating optimal controller, a disturbance observer and a reaction force controller. However, the nonlinear friction such as Coulomb friction often induces chattering motion. Such a motion may cause a controlled object spill-over instability because the previous control system design does not take influences of unstructured uncertainties into account. Therefore, this note provides a modified version of the previous design by using the frequency-shaped disturbance accommodating optimal control. This note adopts the same controlled object as the author's previous paper. The effectiveness of the modification is verified by simulations.

Fundamental and second-harmonic ultrasound field computation of inhomogeneous nonlinear medium with a generalized angular spectrum method

The simulation of nonlinear propagation of ultrasound waves is typically based on the Kuznetsov-Zabolotskaya- Khokhlov equation. A set of simulators has been proposed in the literature but none of them takes into account a possible spatial 3-D variation of the nonlinear parameter in the investigated medium. This paper proposes a generalization of the angular spectrum method (GASM) including the spatial variation of the nonlinear parameter. The proposed method computes the evolution of the fundamental and second-harmonic waves in four dimensions (spatial 3-D and time). For validation purposes, the one-way fields produced by the GASM are first compared with those produced by established reference simulators and with experimental one-way fields in media with a homogeneous nonlinear parameter. The same simulations are repeated for media having an axial variation of the nonlinear parameter. The mean errors estimated in the focal region are less than 4.0% for the fundamental and 5.4% for the second harmonic in all cases. Finally, the fundamental and second-harmonic fields simulated for media having nonlinear parameter variations in the axial, lateral, and elevation directions, which cannot be simulated with other currently available methods, are presented. The new approach is also shown to yield a reduction in computation time by a factor of 13 with respect to the standard nonlinear simulator.

Self organizing fuzzy sliding mode controller for the position control of a permanent magnet synchronous motor drive

In this paper, a self organizing fuzzy sliding mode controller (SOFSMC) which emulates the fuzzy controller with gain auto-tuning is proposed for a permanent magnet synchronous motor (PMSM) drive. The proposed controller is used for the position control of the PMSM drive. The performance and robustness of the control system is tested for nonlinear motor load torque disturbance and parameter variations. It has a novel gain self organizing strategy in response to the transient or tracking responses requirement. To illustrate the performance of the proposed controller, the simulation studies are presented separately for the SOFSMC and the fuzzy controller with gain auto-tuning. The results are compared with each other and discussed in detail. Simulation results showing the effectiveness of the proposed control system are confirmed under the different position changes.

The Effects of Nonlinear Maxwell Source on the Magnetic Solutions in Einstein-Gauss-Bonnet Gravity

Considering both the power Maxwell invariant source and the Einstein--Gauss--Bonnet gravity, we present a new class of static solutions yields a spacetime with a longitudinal nonlinear magnetic field. These horizonless solutions have no curvature singularity, but have a conic geometry with a deficit angle $\delta \phi$. In order to have vanishing electromagnetic field at spatial infinity, we restrict the nonlinearity parameter to $s>1/2$. Investigation of the energy conditions show that these solutions satisfy the null, weak and strong energy conditions simultaneously, for $s>1/2$, and the dominant energy condition is satisfied when $s \in ({1/2,1}]$. In addition, we look for about the effect of nonlinearity parameter on the energy density and also deficit angle, and find that these quantities are sensitive with respect to variation of nonlinearity parameter. We find that for special values of nonlinearity parameter, two important subclass of solutions, so-called conformally invariant Maxwell and BTZ-like solutions, with interesting properties, emerge. Then, we generalize the static solutions to the case of spinning magnetic solutions and find that, when one or more rotation parameters are nonzero, the brane has a net electric charge which is proportional to the magnitude of the rotation parameters. We also use the counterterm method to compute the conserved quantities of these spacetimes such as mass, angular momentum, and find that these conserved quantities do not depend on the nonlinearity parameter.

Torque Feedforward Control Technique for Permanent-Magnet Synchronous Motors

This paper proposes a torque control method for interior permanent-magnet (IPM) motors operating in a wide speed range requiring high torque/power accuracy and a fast dynamic response. Using the fact that the motor parameters are nonlinear and significantly vary with direct and quadrature current operating points, a new optimal operating plane is generated. This operating plane combines the maximum torque per ampere (MTPA) curve, current limit circle, and maximum torque per volt (MTPV) curve, voltage limitations, and torque calculation under the nonlinear parameter variations. As a result, new feedforward tables are generated, which make full use of measured motor parameters. The new torque and flux regulators built around the feedforward tables provide a fast dynamic response and accurate steady-state torque/power production. The proposed controller was implemented and successfully tested on a 105-kW IPM motor electric drive used in a fuel-cell vehicle program.

High performance speed tracking of induction motor drives using an adaptive fuzzy-neural network control

This paper relates an adaptive speed control of hybrid fuzzy-neural network for high-performance induction motor drives. The speed control performance of induction motors is affected by parameter variations and non-linearities in the induction motor. The aim of the proposed control scheme is to improve the performance and robustness of the induction motor drives under non-linear loads and parameter variations. Both the design of the fuzzy controller and its integration with neural networks in a global control system are discussed. The simulation results showed excellent tracking performance of the proposed control system, and have convincingly demonstrated the usefulness of the hybrid fuzzy-neural controller in high-performance drives with uncertainty.

Nonlinearity in bent optical fibers

An interferometric method to study the induced variations of nonlinear parameters in bent optical fiber such as third-order susceptibility chi((3)) and second-order refractive index n(2) is presented. Due to the expected nonlinear response of the Young's modulus of fiber material, the profiles of asymmetric variations of the two parameters with curvature are observed and calculated, revealing the high spatial and index resolution of the method. The investigation is done in single-mode optical fibers at the standard operating wavelengths of 1300 and 1550 nm and at radii of curvature from 5 to 11 mm. At the minimum radius of curvature R=5 mm, the cladding chi((3))=4.131x10(-15) esu on the tensile side, whereas on the compressed side it is 4.601x10(-15) esu for lambda=1300 nm. On the tensile side n(2)=1.09x10(-13) esu, whereas on the compressed side it is 1.216x10(-13) esu. For lambda=1550 nm, the cladding chi((3)) and n(2) on the tensile side are 3.96x10(-15) esu and 1.055x10(-13) esu, whereas in the compressed cladding side they are 4.435x10(-15) esu and 1.174x10(-13) esu, respectively. At lambda=1300 nm and R=5 mm, the core chi((3)) is given by 4.631x10(-15) esu on the tensile side and 4.649x10(-15) esu on the compressed side. The asymmetry in n(2) is given by 1.223x10(-13) esu on the tensile side and by 1.227x10(-13) esu on the compressed side. With lambda=1550 nm, the core chi((3)) asymmetry is given by 4.46x10(-15) esu on the tensile side and by 4.477x10(-15) esu on the compressed side. For n(2) its asymmetry is provided by 1.181x10(-13) esu on the tensile side and by 1.185x10(-13) esu on the compressed side.