Resonance Problem Research Articles

Double Resonance of Magnetism-Solid Coupling of in-Plane Moving Thin Plates With Linear Loads and Elastic Supports

For the in-plane moving thin plates with linear loads and elastic supports in magnetic field, the potential energy, the kinetic energy and the electromagnetic force expressions of the system were given. Based on the Hamiltonian variational principle, the magnetism-solid coupling nonlinear vibration equation for the in-plane moving strip plate was deduced. For the clamped-hinged boundary condition, the variable separation method and the Galerkin method were employed to obtain the 2DOF nonlinear vibration differential equations containing the simple harmonic linear load and the electromagnetic damping force terms. The multiscale method was used to analytically solve the principal-internal resonance problem, and the 1st-order state equation and the resonance response characteristic equation for the system under the double joint resonance were obtained. Through numerical examples, the 1st- and 2nd-order resonance amplitude curves of the in-plane moving thin plate were obtained. The effects of different parameters and load positions on vibration characteristics of the system were analyzed. The results show that, for the principal-internal resonance occurring in the system, the multivaluedness and jumping phenomenon of the solution are obvious, and the effects of the elastic support and the linear load position on the resonance are significant. Additionally, the 1st- and 2nd-order resonance multivalued solution areas appear and disappear simultaneously, which reflects obvious internal resonance characteristics.

A priori estimates for the Fractional <i>p</i>-Laplacian with nonlocal Neumann boundary conditions and applications

<p style='text-indent:20px;'>We first prove that solutions of fractional <i>p</i>-Laplacian problems with nonlocal Neumann boundary conditions are bounded and then we apply such a result to study some resonant problems by means of variational tools and Morse theory.</p>

How the “formula” of success has changed: Slovenian bestsellers of the 2010s. “Čefurji raus!” by G. Vojnović and “Belo se pere na devetdeset” by B. Žakelj

In the article, in the context of the studing the problems of Slovenian book market and the sociology of “consumption” of book publications are presented two novels of the 2010s: “Čefurji raus!” (2008) by G. Vojnović and “Belo se pere na devetdeset” (2018) by B. Žakelj. Both have become sales leaders and received the status of national bestsellers. Their curriculum vitae are similar: both were the debut works of authors who were not professional writers, both received the Kresnik national literary prize for the best novel of the year and both caused a heated discussion on social networks. The commercial success of both books was not only related to effective marketing, advertising, place in the rating, taste stereotypes of literary critics and other extra-literary factors, but also to certain artistic references: this is the existential nature of the problematic, autobiographical discourse, the type of narration (“Ich”-form), the specificity of the chronotope. In the focus of Vojnović’s novel is the fate of national minorities in the post-Yugoslav space, told on behalf of a teenager. After the final collapse of Yugoslavia, the inhabitants of the poorest republics and regions of the former Tito empire began to seek refuge in Slovenia, by the mid-2000s there was in the republic an acute problem of interethnic contradictions associated with the younger generation of immigrants. Žakelj’s confession novel focuses on the tragic and dramatic twists and turns of her own life story and the author’s reflection on her experiences. A comparative analysis of the works gives an idea of how the system of values of ordinary Slovenian readers was transformed, how their interest in the resonant problems of modern life in the country was replaced by the need for empathy, the desire to find a psychological refuge in the book.

Analysis of Radial Complex Scaling Methods: Scalar Resonance Problems

We consider radial complex scaling/perfectly matched layer methods for scalar resonance problems in homogeneous exterior domains. We introduce a new abstract framework to analyze the convergence of...

Resonance Suppression Method for Grid-Connected Converter With LCL Filter Under Discontinuous PWM

This paper presents a resonance suppression method that reduces current oscillation incurred by the LCL-filtered grid-connected converter’s discontinuous PWM (DPWM). First, the cause of LCL resonance is analyzed with an aspect of frequency and time domain for DPWM scheme. Then, voltage references are manipulated to decrease the resonance problem. In the proposed method, pole voltage references at the edge of offset voltage are slightly adjusted to reduce the current oscillation. In addition, a perturb and observe (P&O) technique is adopted to search the magnitude of an edge voltage. Through the simulation and experimental tests, the current oscillation is dramatically reduced while keeping the advantages of DPWM scheme. The proposed method can minimize the switching frequency under the grid harmonics regulation.

Resonance Suppression Strategy for Humanoid Robot Arm

To address the problem of resonance in the control of a robot arm, a resonance suppression strategy is proposed for a single-joint humanoid robot arm based on the proportional-resonant(PR) controller. First, an arm joint model of the humanoid robot is established. Then the influence of resonance frequency on the performance of the control system with the robot arm is analyzed. The voltage fluctuation of the drive motor caused by the changes in arm motion is recognized as the disturbance of the current loop. The PR controller has the characteristic of disturbance rejection at a specific frequency. The output fluctuation of the driving system caused by the change of arm motion state at the resonance frequency is suppressed. Therefore the output current of the inverter will not be affected by the vibration of the arm at the resonance frequency. Finally, the control system is verified by MATLAB/Simulink simulation. The simulation results demonstrate that the control strategy for the humanoid robot arm based on the PR controller can suppress the resonance of the arm effectively, improving the dynamic performance and system stability.

EMI Noise Reduction for the Single-Phase Grid-Connected Inverter With A Modified Harmonic Filter Design

Harmonics and conducted electromagnetic interference (EMI) are two main issues in grid-connected inverter system. In this article, a modified LCL-LC harmonic filter is structured to strengthen its EMI suppression ability. Considering the common mode and differential mode EMI propagation paths, the traditional LCL-LC filter is split into a symmetrical topology, and with the midpoint of the split filtering capacitors connected to the midpoint of the dc-link capacitor. Compared to the traditional LCL-LC filter, the modified one can maintain the satisfied harmonic attenuation ability and strengthen the EMI suppression. Also, a double closed-loop control strategy is employed to solve the severe resonance problem caused by the harmonic filter. Moreover, a system calibration method is proposed and introduced to design the controller parameters to improve the high-order grid-connected system's stability. A comprehensive analysis and discussions concerning the traditional and modified LCL-LC filters are conducted in simulation and experiment on a 2 kW/220 V/50 Hz single-phase grid-connected inverter. The results have verified the feasibility of the proposed design method, and shown the superiority of the modified LCL-LC filter and active damping strategy in EMI mitigation. Besides, the weight and volume of the harmonic filter can be significantly reduced through this strategy.

Finite-Control-Set Model Predictive Control for Three-Level NPC Inverter-Fed PMSM Drives With $LC$ Filter

The installment of LC filter between the voltage source inverter and motor terminal can reduce the value of dv/dt considerably, and further mitigate the surge voltage stress on the motor windings during the long-distance transmission. However, the sophisticated controller needs to be designed to solve the additional resonance problems caused by the filter. Conventional active damping (AD) scheme mainly introduce the multiloop feedback based on the analysis in s-domain or z-domain, which is realized with limited bandwidth and high tuning complexity. In this article, the finite-control-set model predictive control (FCS-MPC) is adopted to realize the q-axis current reference tracking for motor and suppress the filter resonance simultaneously. Different from the transfer-function-based AD scheme, the mechanism of resonance generation is revealed in the time-domain, where the cost function of FCS-MPC is designed to directly regulate the multivariable trajectory of the system. Therefore, the proposed FCS-MPC controller expresses the intuitive design principle, a simple structure, and fewer tuning parameters, which could be an alternative to the existing AD scheme. To reduce the number of sensors, the Kalman-filter based state estimation is used by considering the one-step delay of the control input. The cost function is further optimized to a simplified form that suits the implementation of the digital platform, and the lower computational burden is obtained. The experimental results prove that the proposed FCS-MPC scheme can ensure the motor-friendly waveform and overcome the resonance problem effectively. The robustness of the controller to parameter variations of the filter is also verified.

A Parameter Study of the Burton–Miller Formulation in the BEM Analysis of Acoustic Resonances in Exterior Configurations

The application of a boundary element technique in combination with a contour integral approach to the numerical analysis of acoustic resonances in exterior configurations is investigated in this paper. Similar to the boundary element analysis of exterior acoustic radiation or scattering problems, spurious eigenfrequencies also turn up in the boundary element solution to exterior acoustic resonance problems. To filter out the spurious eigenfrequencies, the Burton–Miller-type combined formulation is employed to shift them from the real axis to the complex domain. The shifting effect brought by the combined formulation with different types of coupling parameters is investigated. Unlike in acoustic radiation and scattering analyses for which [Formula: see text] is suggested as the coupling parameter, it will be shown that the coupling parameter specified as [Formula: see text] with [Formula: see text] (the time-dependent term herein is [Formula: see text]) is more desirable in distinguishing the spurious eigenfrequencies in the boundary element analysis of exterior acoustic resonances.

A New Technique for Controlling Hybrid Stepper Motor Through Modified Pid Controller (Dept.E)

Due to the development of digital control systems, hybrid stepper motors became more attractive to be used in robotics and computer numerical control machines where they have to perform high precision positioning operations without any feedback sensor. However, at open loop control (especially at higher stepping rate), the speed response of the stepper motor suffer from large overshoot, oscillatory response and long settling time. Therefore, a closed loop control system essentially required for a good precise operation performance. However, due to the non-linear characteristics and the resonance problem of the hybrid stepper motor, it is difficult to settle the classical control systems with this type of motor. Moreover, the use of discrete pulses to drive the hybrid stepper motor in half stepping mode leads to jerky and noisy movements at high and low stepping rate respectively. The objective of the present paper is to use the PID control system to enhance the performance of the open loop control system to control the speed of the hybrid stepper motor for a given reference input. Also, a microstepping technique, which consists of sine and cosine waveforms, is also used to drive the hybrid stepper motor instead of discrete pulses. Therefore, a simulation program is constructed using MATLAB software version 7.7 to simulate the hybrid stepper motor performance in open loop, classical PID and modified PID control systems. Results show that the open loop control system suffers from oscillatory response at half stepping mode and form from large overshoot and long settling time at microstepping mode. Also, the classical PID control system didn't give consistent results. And, the proposed control algorithm gives a better performance than that of the open loop even when the system is subjected to a sudden load disturbance up to 41% and working at high motor speed.

Perfectly-matched-layer method for optical modes in dielectric cavities

The optical resonance problem is similar to but different from time-steady Schr\"{o}dinger equation. One big challenge is that the eigenfunctions in resonance problem is exponentially growing. We give physical explanation to this boundary condition and introduce perfectly matched layer (PML) method to transform eigenfunctions from exponential-growth to exponential-decay. Based on the complex stretching technique, we construct a non-Hermitian Hamiltonian for the optical resonance problem. We successfully validate the effectiveness of the Hamiltonian by calculate its eigenvalues in the circular cavity and compare with the analytical results. We also use the proposed Hamiltonian to investigate the mode evolution around exceptional points in the quad-cosine cavity.

Stability and control of maglev vehicle–girder coupled system considering torsional vibration of the girder

The EMS (Electro-Magnetic Suspension) maglev vehicle uses controlled electromagnetic forces to achieve stable levitation; however, the interactions between the vehicle and the flexible girder may induce strong coupled resonances. Recently, a new type of girder resonance has been encountered, and field measurements indicate that this resonance is caused by torsional vibration of the girder. However, up to now, the principle of the girder torsional resonance has not been studied, and related control strategies have not been developed either. In this paper, a typical maglev girder with a steel track is investigated through finite element analysis, and a searching algorithm is proposed to obtain a best fit of the girder transfer function. Then, a maglev vehicle with twenty levitation control units is considered, and together with the girder model, the vehicle–girder coupled system is established. Factors that affect the coupled resonances are analyzed, and it is found that the velocity feedback of the electromagnet, which is effective to suppress the bending resonance of the girder, may lead to torsional resonance of the girder. This conclusion is validated by experiments in a real maglev system. To solve this problem, a distributed virtual tuned mass damper scheme is discussed, and suggestions to avoid the torsional resonances are also presented. This work not only interprets the principle underlying the vehicle–girder coupled torsional resonance, but also presents a methodology for dealing with the maglev vehicle–girder coupled resonance problems.

A Novel Passivity-Based Resonant Instability Suppression Method for Grid-Connected VSC

The interaction between the three-phase voltage source converters (VSCs) and the power grid may cause high-frequency resonant instable problems. Studies have indicated that the non-passivity of VSCs is the main reason that leads to the resonances. The above-mentioned passive means that the equivalent output admittance of the VSC has a positive real part. In this paper, a novel damped Smith predictor is proposed to suppress the resonant instability problem that caused by time delay. The research proved that the proposed Smith predictor can significantly improve the passivity of the VSC by reducing the width of the negative real part at the high-frequencies. Simulation and experimental results demonstrate that the proposed Smith predictor can distinctly improve the robustness of the VSC.

Three Numerical Eigensolvers for 3-D Cavity Resonators Filled With Anisotropic and Nonconductive Media

This paper mainly investigates the classic resonant cavity problem with anisotropic and nonconductive media, which is a linear vector Maxwell's eigenvalue problem. The finite element method based on edge element of the lowest-order and standard linear element is used to solve this type of 3-D closed cavity problem. In order to eliminate spurious zero modes in the numerical simulation, the divergence-free condition supported by Gauss' law is enforced in a weak sense. After the finite element discretization, the generalized eigenvalue problem with a linear constraint condition needs to be solved. Penalty method, augmented method and projection method are applied to solve this difficult problem in numerical linear algebra. The advantages and disadvantages of these three computational methods are also given in this paper. Furthermore, we prove that the augmented method is free of spurious modes as long as the anisotropic material is not magnetic lossy. The projection method based on singular value decomposition technique can be used to solve the resonant cavity problem. Moreover, the projection method {cannot} introduce any spurious modes. At last, several numerical experiments are carried out to verify our theoretical results.

Clinical interventions and speech outcomes for individuals with submucous cleft palate.

BackgroundThis study aimed to identify the initial diagnostic characteristics and treatment status of children with submucous cleft palate (SMCP) and to examine the relationship between the timing of surgical correction and the degree of articulation and resonance improvement.MethodsThis retrospective study included 72 children diagnosed with SMCP between 2008 and 2016. The evaluation criteria were the age of the initial visit, total number of visits, age at the end of treatment, speech problems, resonance problems, and speech therapy.ResultsChildren with SMCP first visited the hospital at an average age of 34.32 months, and speech problems were identified at an average age of 48.53 months. Out of 72 children, 46 underwent surgery at an average age of 49.74 months. Four of these children required secondary surgery at an average age of 83.5 months. Among the children who underwent surgery before 3 years of age, 70% exhibited articulation improvements, with mild-to-moderate hypernasality. Articulation improvements showed no statistically significant differences according to age at the time of surgery. However, children who underwent surgery before 4 years had a better hypernasality rating than those who underwent surgery after 4 years of age.ConclusionsChildren with SMCP tend to undergo delayed treatment because the anatomical symptoms in some children with SMCP are unclear, and surgical interventions are considered only after speech problems are clarified. Starting interventions as early as possible reduces the likelihood of receiving secondary surgery and speech therapy, while increasing expectations for positive speech function at the end.

A new implicit high-order six-step singularly P-stable method for the numerical solution of Schrödinger equation

In this paper, we present a new implicit six-step singularly P-stable method with vanished phase-lag and its derivatives up to fifth order for the numerical integration of the one-dimensional radial time independent Schrodinger equation. The periodicity region of the method is plotted and the numerical stability and phase properties of the new methods are analyzed. The advantage of the new method in comparison with similar methods—in terms of efficiency, accuracy and stability—have been shown by implementing them in the radial time-independent Schrodinger equation during the resonance problems with the use of the Woods–Saxon potential.

Numerical Study on Acoustic Resonance Excitation in Closed Side Branch Pipeline Conveying Natural Gas

Flow-induced acoustic resonance in the closed side branch of a natural gas pipeline can cause intensive vibration which threatens the safe operation of the pipeline. Accurately modeling this excitation process is necessary for a workable understanding of the genetic mechanism to resolve this problem. A realizable k-ε Delayed Detached Eddy Simulation (DDES) model was conducted in this study to numerically simulate the acoustic resonance problem. The model is shown to accurately capture the acoustic resonance phenomenon and self-excited vibration characteristics with low calculation cost. The pressure pulsation component of the acoustic resonance frequency is gradually amplified and transformed into a narrowband dominant frequency in the process of acoustic resonance excitation, forming a so-called “frequency lock-in phenomenon.” The gas is pressed into and out of the branch in sinusoidal mode during excitation. The first-order frequency, single vortex moves at the branch inlet following the same pattern. A quarter wavelength steady standing wave forms in the branch. The mechanism and characteristics presented in this paper may provide guidelines for developing new excitation suppression methods.

Intrinsic molecular vibration and rigorous vibrational assignment of benzene by first-principles molecular dynamics

Vibrational assignment, which establishes the correspondence between vibrational modes and spectral frequencies, is a key step in any spectroscopic study. Due to the lack of experimental technique to directly observe the thermal vibration of atoms, the assignment is usually done by empirical trial-and-error method with considerable uncertainty. Here we demonstrate a successful study of intrinsic molecular vibration property based on first-principles molecular dynamics trajectory. A unified approach for calculating and assigning vibrational frequencies is developed and applied to solve some historical issues of benzene vibration. As a major achievement, the experimental frequencies of benzene a2g and b2u vibrations are reassigned, which breaks a deadlock in contemporary spectroscopic science and removes a cloud over the application of density-functional theory in organic chemistry. This work paves the way for the comprehensive realization of the first-principles spectroscopic research, and provides crucial clues to solve the century-old problems of Kekule resonance, π-deformation, and aromaticity.

NARMA-L2 controller for stepper motor used in single link manipulator with low-speed-resonance damping

Stepper motors are used in robotic applications, industrial machines, and many different application areas. Mechanical resonance problems occur in the control of stepper motors at low speeds. In the control of robotic systems with nonlinear characteristics, conventional control methods are inadequate. Single link manipulators are the most basic structure used in the identification and control of the nonlinear load in robotic systems. In this study, the control of single link manipulator was performed using the stepper motor. As in a real system, the single link manipulator is modelled by connecting to the stepper motor via the gearbox. An Artificial Neural Network (ANN)-based NARMA-L2 controller was preferred for the control of the stepper motor. The NARMA-L2 controller offers superior performance especially in the control of nonlinear loads. Firstly, simulation of the single link manipulator and the stepper motor, which also included resonance moments, was carried out in the MATLAB/Simulink environment. Then the training data of the NARMA-L2 controller was created and the training process was realized. Position control of the stepper motor was performed in MATLAB/Simulink environment using conventional control method and NARMA-L2 controller. The simulation results were obtained at three different speeds and for different angle values. By comparing the conventional control method with the proposed control method, the superior performance of the NARMA-L2 controller in the speed and position control of the motor was demonstrated.

Experimental and numerical study of free-surface wave resonance in the gap between two elongated parallel boxes with square corners

Experiments with wave groups are carried out to investigate 3D wave resonance in the gap between two fixed parallel elongated boxes with square corners. The gap responses are re-created in a numerical wave tank using computational fluid dynamics (CFD) with reasonable accuracy. Based on the CFD results with high temporal and spatial resolution, the free-surface behaviour, internal flow velocity and vortex structures near the gap are interrogated in detail to gain insights into the behaviour. It is found that the damping which affects the oscillatory motion in the gap appears to be linear (or at least dominated by linear damping) except for the largest excitation, though substantial flow separation is present. A phase-based harmonic separation method is used to extract the harmonics of the wave field, which is found useful in understanding the dynamics of wave-structure interactions for gap resonance problems.