Effects Of Nonlinear Loads Research Articles

Multiple-Motor-Based Transport

Intra-cellular transport via processive molecular motors plays an important role in maintaining cell structure and function. In many cases, cargoes move distances longer than expected for single motors; there is significant evidence that this increased travel is in part due to multiple motors working together to move cargoes. However, while we understand much about the function of single motors both experimentally and theoretically, our understanding of how multiple motors work together to move cargoes is less developed. We start with a Monte-Carlo model of single motor to theoretically investigate how multiple motors work together. We have investigated the effect of non-linear force-velocity curves and stochastic load sharing on multiple motor transport using stochastic model. We are particularly interested in cargo transport by a few molecular motors which is motivated by in-vivo results that only a few motors are engaged to transport cargo. Predictions for average travel distances and mean velocities obtained from stochastic model are significantly different from those predicted using steady-state model. Our theoretical study of multiple motor transport using stochastic model also shows that single-motor force-velocity curve plays an important role in determining the ensemble function when only a few motors are engaged.

Servomotor velocity tracking using adaptive fuzzy techniques

This paper proposes a stable adaptive fuzzy controller applied to a servomotor for velocity tracking of time-varying references. The control law is composed of two parts. The first part comprises a Proportional controller plus feedforward compensation. An adaptive fuzzy compensator corresponds to the second part and counteracts the effects of nonlinear loads. The only a priori information about the servomotor parameters is a nominal value of the voltage input gain. A depart from current adaptive adaptive controllers is the fact that the proposed control law does not rely on a switching supervisor controller then avoiding chattering. Moreover, the desired time varying reference feeds the membership functions instead of using the measured velocity, which is contaminated by noise. In this way, less measurement noise is injected to the closed loop system. The Lyapunov stability method allows concluding uniform ultimate boundedness of the closed loop system solutions. Experiments performed on a laboratory prototype allow comparing the proposed approach against a Proportional Integral controller endowed with feedforward compensation.

Nonlinear model of a distribution transformer appropriate for evaluating the effects of unbalanced loads

Power packages for calculation of power system transients are often used when studying and designing electromagnetic power systems. An accurate model of a distribution transformer is needed in order to obtain realistic values from these calculations. This transformer model must be derived in such a way that it is applicable when calculating those operating conditions appearing in practice. Operation conditions where transformers are loaded with nonlinear and unbalanced loads are especially challenging. The purpose of this work is to derive a three-phase transformer model that is appropriate for evaluating the effects of nonlinear and unbalanced loads. A lumped parameter model instead of a finite element (FE) model is considered in order to ensure that the model can be used in power packages for the calculation of power system transients. The transformer model is obtained by coupling electric and magnetic equivalent circuits. The magnetic equivalent circuit contains only three nonlinear reluctances, which represent nonlinear behaviour of the transformer. They are calculated by the inverse Jiles–Atherton (J–A) hysteresis model, while parameters of hysteresis are identified using differential evolution (DE). This considerably improves the accuracy of the derived transformer model. Although the obtained transformer model is simple, the simulation results show good agreement between measured and calculated results.

Statistical analysis of wave-induced extreme nonlinear load effects using time-domain simulations

A new hybrid method for the time-domain nonlinear simulation of the hydroelastic load effects and the peak-over-threshold (POT) method for the calculation of the short-term extreme responses are briefly described and applied to a flexible containership of the latest design. Statistical analysis has been carried out to study the sensitivity of the predicted extreme vertical bending moments and vertical shear forces to the changes in the threshold of the POT method, as well as the statistical uncertainty in the prediction due to the limited duration of the nonlinear simulation. It is recommended that 90%–95% quantile should be used as the threshold in the POT method and more than 100 h of time-domain simulation should be carried out in order to obtain satisfactory predictions of the short-term extreme nonlinear load effects.

Two-phase controlled compensator for alternating-current quality improvement of electrified railway systems

The technological development of electrified railway systems during recent decades has demanded higher and higher quality performances of the supply subsystem. For this purpose, the recourse to electronics and to automation techniques can represent the right way to secure a reliable and efficient electric supply to the railway. The paper summarises the general problems of quality in railway electrification and proposes a new configuration of traction substations for single-phase AC-supply railways, based on the use of a two-phase inverter with nonlinear and variable-structure control system. Such an advanced technical solution allows one to obtain full compensation of load unbalances, constant load voltage, satisfactory power factor and a remarkable reduction of both disturbances and nonlinear-load effects. Some numerical applications show the efficacy of the proposed controlled compensator in containing disturbances and power-parameter variations, as well as its high performances in terms of fast response time, accuracy in steady-state conditions and general low sensitivity to disturbances.

Efficient calculation of wave-induced ship responses considering structural dynamic effects

This paper presents a new method for efficient calculation of wave-induced linear and nonlinear load effects in flexible ships. It is a combination of a modal superposition and the conventional load evaluation approach based on a rigid body model, and implies reduced computation effort in time-domain motion and load simulations. It is applied to a 270 m long containership (SL-7 class) as an example to demonstrate its efficiency. The method can also be used for other long flexible marine structures.

Effects of Imbalances and Nonlinear Loads on the Voltage Balance of a Neutral-Point-Clamped Inverter

The effects of linear imbalances and nonlinear loads on the voltage balance of the neutral-point-clamped converter are described in this paper. The study reveals that a negative sequence of output currents (linear imbalance) may produce additional low-frequency oscillations to the neutral-point voltage. Similar consequences are produced by odd-order current harmonics from a nonlinear load, while even-order harmonics can cause the neutral-point voltage to shift. Furthermore, the second, fourth, and eighth output current harmonics might produce instability to the neutral-point voltage. The second and fourth harmonics are the worst components. The maximum amplitudes of these harmonics superposed to the current fundamentals that the system can tolerate are described. Simulated and experimental examples are presented.

Control for PWM ac chopper feeding nonlinear loads

This paper presents a novel robust control technique for PWM ac choppers with the ability to generate high quality sinusoidal waveforms with adjustable amplitudes over a wide range control. For this purpose a deadbeat-based digital controller has been developed to perform tight closed-loop control of the ac chopper. This controller is based on a generalized predictive control (GPC) approach. A dedicated control algorithm has been developed and implemented. The proposed controller presents the advantages of allowing a very fast transient response and compensating effectively for load disturbance and the effects of nonlinear loads. Computer simulations are performed to investigate the proposed controller performance. The simulation results show that the designed controller has a good dynamic behaviour, a good rejection of impact load disturbance, and is ;very robust. To evaluate the proposed approach an experimental prototype has been constructed. Experimental results under various loading conditions have demonstrated that the system performs well.

Root-mean-square measure of nonlinear effects to the transient response of thin wires

A root-mean-square (rms) measure of effect of nonlinear loading on the transient response of thin wires is proposed. The transient behavior of nonlinearly loaded wires is analyzed directly in the time domain. The problem is formulated via the space-time Hallen integral equation. The equation is solved by the space-time Galerkin Bubnov boundary element procedure. Numerical results for the transient response of a thin wire computed by a time domain code based on this method are compared with results obtained from a frequency domain code. Some illustrative numerical results for the spatial distribution of the rms values of time varying currents are also presented.

Time domain integral equation method for transient scattering from thin wire structures

The transient scattering from various thin wire structures in the presence of a real ground is analyzed directly in the time domain (TD). The mathematical model is based on the corresponding space-time Hallén integral equation. The effect of a two-media configuration is taken into account via the space-time reflection coefficient. The corresponding integral equations are handled by the time domain scheme of the Galerkin–Bubnov boundary integral equation method. The effect of nonlinear loading and the time-domain energy measures associated with the current and charge on thin wires are analyzed by spatially integrating the square of the current and charge along the wire as a function of time. Some illustrative TD computational examples are presented in the paper.

On the role of chiral catalysts in the alkenyl zirconocene/zinc addition to aldehydes: a study of ligand loading and asymmetric amplification.

Unusual nonlinear asymmetric amplification and chiral ligand loading effects were discovered for the use of catalytic quantities of chiral aminoalcohols in the in situ hydrozirconation-transmetalation-aldehyde addition processes. While the stereochemically most efficient aminothiol ligands demonstrated mechanistically conventional reaction parameters in excellent agreement with Kagan's ML(2) system, the asymmetric induction in the presence of a chiral aminoalcohol was found to vary greatly with loading and %ee of the ligand. Aminothiols remain the ligands of choice for the highly enantioselective formation of allylic alcohols and provide experimentally more predictable reaction variables. However, new, optimized conditions lead to a synthetically useful product %ee using the readily available and scalable aminoalcohol 2a.

Determination of global design loads for large high-speed catamarans

Methods for calculation of design loads for high-speed vessels are investigated. The influence of operational restrictions on design loads is emphasized. Relevant operational criteria for high-speed displacement vessels are discussed. Procedures and criteria for numerical calculation of operational limits are incomplete and should be further investigated. Operational limits and design loads for a 60 m catamaran are calculated on the basis of linear strip theory. Non-linear effects on design loads are assessed from calculations in regular waves. Simplified formulae commonly used by classification societies for prediction of operational limits seem to over-predict the reduction of motions and wave loads at reduced speed. When operational limits typically given by the shipmaster or the operator are used, the design loads found by direct calculations are comparable with design loads given by classification societies. For vertical bending moment and torsion, the use of active foils is found to increase the linear loads. Owing to reduced motions, the foils reduce the non-linear loads and hence the total loads. The effect of non-linear horizontal loads is not investigated but can be important for transverse bending moment.

Control strategy of advanced 25 kV-50 Hz electrified railway systems

Technological innovation has been largely involved in the general modernisation of electrified railway systems in the last few decades. Better quality performances of supply and electrification subsystems are thus expected, which have until now made less recourse to electronic and automation techniques than other technological sections of the system. A method is proposed for compensating voltage and current unbalances in single-phase 25 kV-50 Hz railway power supply, based on a new configuration of the traction substation. Two Scott-connected transformers are coupled with an impressed voltage two-phase inverter, to obtain stabilisation of load voltages to rated values. Satisfactory power factor and reduction of network disturbances, as well as nonlinear load effects of the load, can also be reached. The full compensation of load unbalances and a substantial inherent protection against disturbances, even under changing conditions of power parameters, are obtained through a nonlinear control system, based on the variable structure system theory. Numerical simulations confirm the high performance of the compensation method with respect to fast response time, steady-state accuracy, and very low sensitivity to disturbances.

Design considerations for piezoelectric polymer ultrasound transducers

Much work has been published on the design of ultrasound transducers using piezoelectric ceramics, but a great deal of this work does not apply when using the piezoelectric polymers because of their unique electrical and mechanical properties. The purpose of this paper is to review and present new insight into seven important considerations for the design of active piezoelectric polymer ultrasound transducers: piezoelectric polymer materials selection, transducer construction and packaging requirements, materials characterization and modeling, film thickness and active area design, electroding selection, backing material design, and front protection/matching layer design. Besides reviewing these design considerations, this paper also presents new insight into the design of active piezoelectric polymer ultrasonic transducers. The design and fabrication of an immersible ultrasonic transducer, which has no adhesive layer between the active element and backing layer, is included. The transducer features direct deposition of poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer onto an insulated aluminum backing substrate. Pulse-echo tests indicated a minimum insertion loss of 37 dB and -6 dB bandwidth of 9.8 to 22 MHz (71%). The use of polymer wear-protection/quarter-wave matching layers is also discussed. Test results on a P(VDF-TrFE) transducer showed that a Mylar/sup TM/ front layer provided a slight increase in pulse-echo amplitude of 15% (or 1.2 dB) and an increase in -6 dB pulse-echo fractional bandwidth from 86 to 95%. Theoretical derivations are reported for optimizing the active area of the piezoelectric polymer element for maximum power transfer at resonance. These derivations are extended to the special case for a low profile (i.e., thin) shielded transducer. A method for modeling the non-linear loading effects of a commercial pulser-receiver is also included.

Short-pulse transient and characteristics of lossy binomial transmission lines with arbitrary linear and nonlinear termination

Lossy binomial transmission lines with arbitrary linear and nonlinear loads are modeled for use as short-pulse transformers in electrical and optical high-speed interconnects. An efficient method is proposed in this paper to characterize these lines as an equivalent circuit that consist of a cascaded connection of lumped networks and lossy uniform transmission lines in the frequency domain, while nonlinear problems are formulated and solved with time-domain scattering equations via a convolution technique. Results indicate that binomial lines present an advantage over exponential lines or uniform lines for the nonlinear loading effect, and they can be effectively used as a short-pulse transformer in such systems and devices as laser diodes, junction transistors, and metal-oxide-semiconductor field-effect transistors to enhance power coupling efficiency and reshape digital signal waveforms.

Time-Domain Hydroelasticity Theory of Ships Responding to Waves

A time-domain linear theory of fluid-structure interaction between floating structures and the incident waves is presented. The structure is assumed to be elastic and represented by general separation of variables, whereas the fluid is described as an initial boundary value problem of potential free surface flow. The general interface boundary condition is used in the mathematical formulation of the fluid motion around the flexible structure. The general time-domain theory is simplified to a slender-body theory for the analysis of wave-induced global responses of monohull ships. The structure is represented by a nonuniform beam, while the generalized hydrodynamic coefficients can be obtained from two-dimensional potential flow theory. The linear slender body theory is generalized to treat the nonlinear loading effects of rigid motion and structural response of ships traveling in rough seas. The nonlinear hydrostatic restoring force and hydrodynamic momentum action are considered. A numerical solution is presented for the slender body theory. Numerical examples are given for two ship cases with different geometry features, a warship hull and the S175 containership with two different bow flare forms. The predicted results include linear and nonlinear rigid motions and structural responses of ships advancing in regular and irregular waves. The results clearly demonstrate the importance and the magnitude of nonlinear effects in ship motions and internal forces. Numerical calculations are compared with experimental results of rigid and elastic material ship model tests. Good agreement is obtained.

Postbifurcation Equilibrium Paths Modified by Nonlinear Configuration-Dependent Conservative Loading Using Nonsmooth Analysis*

ABSTRACT This paper discusses the effect of deformation-sensitive loading devices because the nature of loading is generally not perfectly dead, being independent of the deflections that occur. This paper presents the effect of nonlinear variable load. Postbifurcation equilibrium paths and structural tangent stiffness are modified on the basis of a polygonal approximation and nonsmooth analysis. The effects of dead and variable loads are compared. Configuration-dependent loading devices can be characterized by some load-deflection functions, much like the nature of material behavior can be characterized by stress-strain functions. The effect of a deformation-sensitive load is similar to that of the material. Consequently, in the stability analysis of structures, a configuration-dependent loading program can be handled like material behavior. Thus, in the tangent stiffness of the structure, much like the tangent modulus of the material, the tangent modulus of the load appears. Previous research has shown that nonlinear material behavior can be handled using nonsmooth analysis—approximating nonlinear material functions by polygonals. In this paper, this method and its results are extended to the case of nonlinear loading programs. The present analysis is based on earlier work in which a complete stability analysis was introduced for dead-loaded structures that have polygonal constitutive law, namely nonsmooth material functions and non-smooth internal potential. The aim of this paper is to extend these results to cases involving nonlinear configuration-dependent conservative loading by introducing nonsmooth loading functions.

Origin, development, and design of K-factor transformers

Large rectifier transformers, because of the harmonics, always had to be specially designed to cope with the additional heating. But at that time there was no market or demand for 480 Delta-208Y1120 volt transformers to cope with the harmonic problem. Many people were aware of the problems with overheating but did not know the cause. In addition, average reading ammeters read too low when harmonic currents flowed in the neutral, and it rook true RMS meters to give accurate results. The problem was how to quantify the heating effect of harmonics. ANSI/IEEE C57.110, a guide for determining the heating effects of nonlinear loads, developed an equation for calculating the heating effects. By squaring the frequency and the per-unit current and multiplying them together, the guide arrived at a number without any designation. This was going to be called C for "constant", but was decided against because of possible confusion with "centigrade". The letter K for "Konstant" seemed reasonable to use, and Underwriters Laboratory accepted this designation in the original submission of a low voltage dry type transformer. K since became the standard measure of the ability of a transformer to withstand nonlinear loads. The features of the K-transformer are briefly discussed.

Static and dynamic nonlinear loads and structural stability in power systems

In this paper, the authors review the basic concepts of structural stability theory and show its application to multimachine power systems. Specifically they establish a connection between structural stability and bifurcation theory. They examine the effect of nonlinear loads as well as different sizes of induction motor loads on the structural stability limits. Detailed generator models are used in the study throughout. They conclude that in studying power system structural stability, load modeling is a crucial factor and needs more research.

Transient responses of an exponential transmission line and its applications to high-speed backdriving in in-circuit test

Step responses of an exponential line terminated with resistive loads are evaluated by means of time-domain scattering parameters. The results are used to illustrate the interaction between a nonuniform line and a nonlinear load. We find that an exponential line could be used to compensate the nonlinear load effects in high-speed backdriving. >