Nonlinear Parameter Variations Research Articles

MEDIUM-TERM OSCILLATIONS OF THE SOLAR ACTIVITY

In addition to the well-known 11-year cycle, longer and shorter characteristic periods can be isolated in variations of the parameters of helio-geophysical activity. Periods of about 36 and 60 years were revealed in variations of the geomagnetic activity and an approximately 60-year periodicity, in the evolution of correlation between the pressure in the lower atmosphere and the solar activity. Similar periods are observed in the cyclonic activity. Such periods in the parameters of the solar activity are difficult to identify because of a limited database available; however, they are clearly visible in variations of the asymmetry of the sunspot activity in the northern and southern solar hemispheres. In geomagnetic variations, one can also isolate oscillations with the characteristic periods of 5-6 years (QSO) and 2-3 years (QBO). We have considered 5-6-year periodicities (about half the main cycle) observed in variations of the sunspot numbers and the intensity of the dipole component of the solar magnetic field. A comparison with different magnetic dynamo models allowed us to determine the possible origin of these oscillations. A similar result can be reproduced in a dynamo model with nonlinear parameter variations. In this case, the activity cycle turns out to be anharmonic and contains other periodicities in addition to the main one. As a result of the study, we conclude that the 5-6-year activity variations are related to the processes of nonlinear saturation of the dynamo in the solar interior. Quasi-biennial oscillations are actually separate pulses related little to each other. Therefore, the methods of the spectral analysis do not reveal them over large time intervals. They are a direct product of local fields, are generated in the near-surface layers, and are reliably recorded only in the epochs of high solar activity.

PIDNN control for Vernier-gimballing magnetically suspended flywheel under nonlinear change of stiffness and disturbance

Vernier-gimballing magnetically suspended flywheel is often used for attitude control and interference suppression of spacecrafts. Due to the special structure of the conical magnetic bearing, the radial component generated by the axial magnetic force and the change of the magnetic air gap will cause the nonlinearity of stiffness and disturbance. That will lead to not only poor stability of the suspension control system but also unsatisfactory tracking accuracy of the rotor position. To solve the nonlinear problem of the system, this article proposes a proportional–integral–derivative neural network control scheme. First, the rotor model considering the nonlinear variation of disturbance and stiffness parameters is established. Then, the weight of neural network is adjusted by the gradient descent method online to ensure the accurate output of magnetic force. Finally, the convergence analysis is carried out based on the Lyapunov stability theory. Compared with the general proportional–integral–derivative control and the radial basis function neural network control, the simulation results demonstrate that the proposed method has the highest tracking accuracy and excellent performance in improving stability. The experimental results prove the correctness of the theoretical analysis and the validity of the proposed method.

Transportation of Marangoni convection and irregular heat source in entropy optimized dissipative flow

This paper is about entropy generation in Marangoni convective flow due to rotating disk with irregular heat source. Nonlinear mixed convection radiative flow is considered here. Exponential base heat source is addressed. Subsequent equations are transformed to the ODE's by using generalized Karman's variables. Results are found by using NDSolve MATHEMATICA. Through graphical illustration velocity, temperature, Bejan number and entropy generation are discussed. Axial velocity enhances via Marangoni number while temperature decays. Velocity is greater via larger nonlinear thermal convection parameter. Entropy rate boosts up for variation of nonlinear convection parameter and Marangoni number. Bejan number decays against Brinkman number and nonlinear convection parameter.

A variety of new traveling and localized solitary wave solutions of a nonlinear model describing the nonlinear low- pass electrical transmission lines

Abstract In this work, we focus on investigating the traveling and other localized solitary wave propagation in nonlinear low-pass electrical transmission lines model practicing the new modified sub-ODE method, the unified Riccati equation expansion method, and the fractional linear transform method. A variety of traveling and solitary wave solutions are emerging comprising of bright, dark, kink, anti-kink, hyperbolic function, and doubly periodic Jacobian elliptic function solutions. The applied three integration schemes are reliable and stalwart for acquiring the new kink, bright, dark, periodic and non-singular soliton solutions of the wave propagation in nonlinear low-pass electrical transmission lines. Also, we give the geometric description of some of the obtained solutions for the considered model by computing the most important geometric quantities viz the Gaussian and the mean curvatures. To display the extant physical significance of the considered model equation, some two, three-dimensional figures and density profiles of the acquired solutions are illustrated for the specific choice of arbitrary parameters. The effects of the variation of nonlinear parameters of the nonlinear low-pass electrical transmission lines model on the evolution of soliton solutions are demonstrated. In addition, all derived solutions were verified by substituting back into the considered equation with the aid of Mathematica software. Furthermore, a comparison of our results for the considered model with the obtained solutions in the literature is also provided.

RETRACTED: Harmonics mitigation in hybrid shunt active power filter connected renewable energy source using an intelligent controller

This paper proposes an intelligent technique-based optimal controller for harmonics mitigation to maintain the power quality in renewable energy source (RES)-based distribution systems. The proposed intelligent technique is the joint execution of both the fractional-order proportional integral controller and moth-flame optimization with random decision forest. In the proposed approach, moth-flame optimization optimizes the dataset of fundamental and harmonic loop parameters such as terminal voltage and direct current voltage present in the hybrid shunt active power filter. The dataset is generated based on the linear and nonlinear load variation and parameter variation of the renewable energy sources, subject to the minimum error objective function. Based on the accomplished dataset, random decision forest accurately predicts the parameters and produces optimized control signals. The proposed technique guarantees the system with less complexity for the harmonics mitigation of the power quality event and hence the accuracy of the system is raised. Then, the proposed model is executed in the Matrix Laboratory/Simulink working platform and the execution is assessed with the existing techniques. The simulation analysis of the proposed approach is tested using the six test cases with various combinations of nonlinear loads. In all the test cases, the performance of various system parameters, such as source current with and without filter, source voltage, hybrid shunt active power filter current, load current and voltage, is analysed. Furthermore, the total harmonic distortion at different load ratings is also examined.

Experimental and theoretical investigation of localized CO2 laser interaction with fused silica during the process of surface damage mitigation

Localized CO2 laser repairing of surface damage on fused silica optics has been successfully applied in high-power laser system in the field of controllable nuclear fusion. In order to accurately predict the surface topography evolution and to reveal the intrinsic physical mechanism during the process of laser mitigation, experiments of localized CO2 laser mitigation were firstly carried out to analyze the features of mitigated craters under different laser powers. Then a multi-physics coupled mathematical model was developed based on the fluid control equation, heat and mass transfer equation and material phase transition kinetics to investigate the thermodynamic and kinetic behaviors of laser interaction with silica. The model considered the effects of Marangoni convection, gravity, capillary force and vaporization recoil pressure, as well as the nonlinear variation of physical parameters of silica material with respect to temperature. The results showed that with the increase of laser power, the material ablation and the appearance of raised rim occurred simultaneously. The depth of the mitigated crater increased sharply when the threshold for material ablation was attained, while the lateral dimension increased linearly. The vaporization recoil pressure was found to be the dominant factor for the formation of Gaussian crater with the raised rim feature. The capillary force caused the material at the edge of the molten pool to have a tendency to reflow after laser shutting down, but it was too small to change the surface topography. This work could significantly contribute to the understanding of laser mitigation process, which laid the foundation for the accurate prediction and evaluation of surface quality of CO2 laser repaired fused silica surface.

Investigation of Transport and Kinetic Nonideality in Solid Li-Ion Electrodes through Deconvolution of Electrochemical Impedance Spectra

The development of Li-ion battery management systems (BMSs) is highly dependent on high fidelity computer simulations. In traditional physics-based models (PBMs), Fick’s law coupled with the Butler–Volmer equation has been employed to describe both Li-ion diffusion and solid/liquid interfacial Li-ion intercalation/deintercalation, but this methodology makes the primary assumption that there is no nonideality caused by Li–Li interactions. Such nonideality phenomena are usually described by the activity coefficient (γ) of Li-ions in a solid solution. With the nonideality, the activity of Li-ion species is not equivalent to the concentration of Li-ions. This research has demonstrated, through the deconvolution of electrochemical impedance spectra, that significant nonideality exists in the solid active materials during charge/discharge cycles, and it leads to nonlinear variation of both transport and kinetic parameters of the electrodes. We also show that PBMs with new pre-factors derived from nonequilibrium thermodynamics of concentrated solution theory can make battery-level predictions that are consistent with EIS data. The pre-factors developed in this paper are functions of the activity coefficient of the solid phase. They show a three order-of-magnitude variation for diffusivity in the solid active material and a one-to-two order of magnitude change in the reaction rate constant at the solid/liquid interface. The results presented here could provide baseline parameters for PBMs and improve their accuracy for high-fidelity BMSs.

Reference Modulation for Performance Enhancement of Motion Control Systems With Nonlinear Parameter Variations

In general, it is not intuitive to quantify the performance of nonlinear systems; thus, designing controllers and/or estimators is not easy. Moreover, there are situations in which a system designed with a fixed feedback controller is not customizable, and yet its closed-loop performance (e.g., disturbance attenuation) is not satisfactory. In this study, we first present an equivalent linear model for motion control systems with nonlinear parameter variations. The linear model facilitates the quantitative analysis of the motion control system. Furthermore, we introduce a reference modulation technique that enhances the performance by boosting loop-gain over a desired range of frequencies. The proposed approach, by introducing an additional modulated function and a direct feedforward channel, facilitates the separation of the closed-loop sensitivity function from other issues of the closed-loop system design so that both disturbance attenuation and tracking performance can be improved. We also provide robust stability analysis of the motion control systems by reference modulation. The simulations and experiments are performed on a permanent magnet synchronous motor system with a predesigned feedback controller. The simulation and experimental results show that both the tracking and disturbance attenuation performance of the closed-loop system are enhanced via reference modulation.

H∞ Control Using Linear Parameter Varying Approach for Motion Control Systems Under Communication Delays: Application to PMSM

Over the past decades, various control methodologies have been studied to improve the performance of motion control systems. However, such methods have no general guidelines for controller gain tuning or performance optimization in the presence of nonlinearities and/or uncertainties. Linear parameter-varying (LPV) control methods have recently been studied to improve the performance of motion control systems by treating the nonlinearities as parameter variations. By contrast, with motion control systems, the plant, microprocessors, controllers, actuators, and sensors are interconnected using a communication network, where the network inherently induces communication delays while sending and receiving information. Hence, when designing an LPV control system, it is necessary to consider both communication delays and nonlinearities. In this study, we address an LPV-approach based H∞ control problem for motion control systems under communication delays between the actuator and plant, and between the sensor and plant. We obtained a linear matrix inequality (LMI) condition under which a closed-loop system using the proposed controller satisfies the H∞ control performance and stability when subjected to a communication delay. The main technique applied to obtain the corresponding LMI condition for an LPV system is interpolating the scheduling variables of the nonlinear parameter variations at each vertex. Finally, we applied the proposed control method to the driver set of a permanent magnet synchronous motor and verified the H∞ control performance under a communication delay.

Research on the relationship between early surface deformation and microstructure evolution of Ni-based single crystal alloy

During the early service phase of Ni-based single crystal alloy (NSCA), the degree of its surface deformation is closely related to the service life. It is important to quantitatively characterize the surface deformation of NSCA from the microscopic scale. However, the studies on the quantitative relationship between the degree of surface deformation and the microstructure evolution of NSCA have not been found yet. Thus, we establish the theoretical relationship between the microstructure evolution of NSCA and its early surface deformation through nonlinear expression methods. The MD method is used to calculate the dislocation density change of NSCA in different crystal orientations, by which the variation of the characteristic parameter and the damage degree of NSCA are predicted. Moreover, the results of the MD simulation are consistent with the variation of nonlinear characteristic parameter obtained in the experiment, which further confirms the correctness of the theoretical relationship. This research will offer a theoretical basis for the predictive maintenance of aero-engine turbine blades.

Application of nonlinear ultrasonic technique to characterize the microresidual strain in metal

Abstract

Stability and Asymtotic Behavior of the Causal Operator Dynamical Systems Using Nonlinear Variation of Parameters.

Stability and Asymtotic Behavior of the Causal Operator Dynamical Systems Using Nonlinear Variation of Parameters.

Analysis and Experimental Validation of Dynamic Performance for Slotted Limited-Angle Torque Motor

Field-circuit coupling method is increasingly drawing attention from researchers who engage in electric machine design. It is worth mentioning that no related field-circuit coupling methods have been presented to investigate the dynamic performance for slotted limited-angle torque motor (LATM). Hence, this paper presents a simplified field-circuit coupling method to evaluate the dynamic performance including position tracking ability and operating temperature for slotted LATM during its design optimization process. All magnetic saturation problems including nonlinear torque characteristic and inductance parameter variation with rotor position can be taken into account, which is completely consistent with the actual operation condition. The simplified field-circuit coupling method contains a thermal resistance network (TRN) module which can be applied to estimate the slotted LATM operating temperature in accordance with the accurate winding current and copper loss information. Therefore, whether the slotted LATMs meet design requirements should be evaluated before manufacturing prototypes. Related experiments for the slotted LATM are carried out to validate the field-circuit coupling method cooperating with TRN module.

Numerical simulation of electro-osmotic consolidation coupling non-linear variation of soil parameters

Electro-osmotic consolidation is an effective method for soft ground improvement. A main limitation of previous numerical models on this technique is the ignorance of the non-linear variation of soil parameters. In the present study, a multi-field numerical model is developed with the consideration of the non-linear variation of soil parameters during electro-osmotic consolidation process. The numerical simulations on an axisymmetric model indicated that the non-linear variation of soil parameters showed remarkable impact on the development of the excess pore water pressure and degree of consolidation. A field experiment with complex geometry, boundary conditions, electrode configuration and voltage application was further simulated with the developed numerical model. The comparison between field and numerical data indicated that the numerical model coupling of the non-linear variation of soil parameters gave more reasonable results. The developed numerical model is capable to analyze engineering cases with complex operating conditions.

Tuning of Photoluminescence and Local Structures of Substituted Cations in xSr2Ca(PO4)2–(1 – x)Ca10Li(PO4)7:Eu2+ Phosphors

Local structure modification in solid solution is an essential part of photoluminescence tuning of rare earth doped solid state phosphors. Herein we report a new solid solution phosphor of Eu2+-doped xSr2Ca(PO4)2–(1 – x)Ca10Li(PO4)7 (0 ≤ x ≤ 1), which share the same β-Ca3(PO4)2 type structure in the full composition range. Depending on the x parameter variation in xSr2Ca(PO4)2–(1 – x)Ca10Li(PO4)7:Eu2+, the vacancies generated in the M(4) site enable the nonlinear variation of cell parameters and volume, and this increases the magnitude of M(4)O6 polyhedra distortion. The local structure modulation around the Eu2+ ions causes different luminescent behaviors of the two-peak emission and induces the photoluminescence tuning. The shift of the emission peaks in the solid solution phosphors with different compositions has been discussed. It remains invariable at x ≤ 0.5, but the red-shift is observed at x > 0.5 which is attributed to combined effect of the crystal field splitting, Stokes shift, and energy trans...

Variation of Parameters for Causal Operator Differential Equations

The operator T from a domain D into the space of measurable functions is called a nonanticipating (causal) operator if the past information is independent from the future outputs. We will study the solution x(t) of a nonlinear operator differential equation where its changes depends on the causal operator T, and semigroup of operator A(t), and all initial parameters (t0, x0) . The initial information is described x(t)=φ(t) for almost all t ≤t0 and φ(t0) =φ0. We will study the nonlinear variation of parameters (NVP) for this type of nonanticipating operator differential equations and develop Alekseev type of NVP.

Variation of Linear and Nonlinear Parameters in the Swim Strokes According to the Level of Expertise

The aim was to examine the variation of linear and nonlinear proprieties of the behavior in participants with different levels of swimming expertise among the four swim strokes. Seventy-five swimmers were split into three groups (highly qualified experts, experts and nonexperts) and performed a maximal 25m trial for each of the four competitive swim strokes. A speed-meter cable was attached to the swimmer's hip to measure hip speed; from which speed fluctuation (dv), approximate entropy (ApEn) and fractal dimension (D) variables were derived. Although simple main effects of expertise and swim stroke were obtained for dv and D, no significant interaction of expertise and stroke were found except in ApEn. The ApEn and D were prone to decrease with increasing expertise. As a conclusion, swimming does exhibit nonlinear properties but its magnitude differs according to the swim stroke and level of expertise of the performer.

자기동조 퍼지 제어기를 이용한 스위치드 릴럭턴스 모터의 전류제어

본 논문은 가격이 저렴하고 친환경적이면서도 고성능, 고내구성, 구조적 단순함의 장점을 갖고 있어 최근에 폭넓은 관심을 받고 있는 스위치드 릴럭턴스 모터(SRM: Switched Reluctance Motor)의 보다 정확하고 안정적인 전류제어 방법에 대해 설명한다. 대부분의 전동기의 전류제어 방법에는 알고리즘과 제어 이득의 선정이 다른 제어기에 비해 상대적으로 간편한 PI 제어기를 이용한 방법이 주로 사용되어 왔다. 그러나 일반적인 PI 제어기는 SRM과 같이 고정자 권선의 전류 및 회전자의 위치마다 비선형적으로 파라미터가 급변하는 시스템의 경우 변하는 동작 지점마다 제어 이득을 조정해 주어야 하는 어려움이 발생한다. 본 논문에서는 비선형적으로 특성이 변하는 SRM 드라이브 시스템에 제어 성능이 우수한 자기동조 퍼지 제어기를 이용한 제어기법을 적용하여 비선형적인 파라미터의 변화에도 보다 안정적인 전류제어가 가능한 것을 보였다. 또한 Matlab/Simulink 시뮬레이션을 이용하여, SRM 드라이브의 전류제어에 PI 전류 제어기(PICC: PI Current Controller)와 자기동조 퍼지 전류 제어기(STFCC: Self-tuning Fuzzy Current Controller)를 각각 적용한 후 그 결과를 비교하였으며 제안한 자기동조 퍼지 제어기의 제어성능이 우수함을 확인하였다. This paper describes an accurate and stable current control method of switched reluctance motors(SRMs), which have recently attracted considerable wide attention owing to their favorable features, such as high performance, high durability, structural simplicity, low cost, etc. In most cases, the PI controllers(PICC) have been used mostly for the current control of electric motors because their algorithm and selection of controller gain are relatively simpler compared to other controllers. On the other hand, the PI controller requires an adjustment of the controller gains for each operating point when nonlinear system parameters change rapidly. This paper presents a stable current control method of an SRM using self-tuning fuzzy current controller(STFCC) under nonlinear parameter variation. The performance of the considered method is validated via a dynamic simulation of the current controlled SRM drive using Matlab/Simulink program.

Experimental study of nonlinear ultrasonic behavior of soil materials during the compaction

In this paper, the nonlinear ultrasonic behavior of unconsolidated granular medium – soil during the compaction is experimentally studied. The second harmonic generation technique is adopted to investigate the change of microstructural void in materials during the compaction process of loose soils. The nonlinear parameter is measured with the change of two important environmental factors i.e. moisture content and impact energy of compaction. It is found the nonlinear parameter of soil material presents a similar variation pattern with the void ratio of soil samples, corresponding to the increased moisture content and impact energy. A same optimum moisture content is found by observing the variation of nonlinear parameter and void ratio with respect to moisture content. The results indicate that the unconsolidated soil is manipulated by a strong material nonlinearity during the compaction procedure. The developed experimental technique based on the second harmonic generation could be a fast and convenient testing method for the determination of optimum moisture content of soil materials, which is very useful for the better compaction effect of filled embankment for civil infrastructures in-situ.

Nonlinear behaviour of glass fibre reinforced composites with delamination

Abstract The aim is to assess the nonlinear behaviour of glass fibre composite having controlled delaminations. The experimental analysis focused on the variation of nonlinear parameters as function of delamination size. Through a set of increasing resonance amplitudes applied on a delaminated glass fibre reinforced composite, the frequency shift and the specific damping coefficient shift were evaluated as a function of strain amplitude. The nonlinear elastic and dissipative parameters related respectively to the frequency and damping, were determined for different bending modes and different delamination lengths. These parameters were compared with the linear vibration parameter. The results show that nonlinear parameters are more sensitive to the presence of delamination in composite.