Transient Frequency Response Research Articles

Optimum design of phononic crystal perforated plate structures for widest bandgap of fundamental guided wave modes and maximized in-plane stiffness

This paper presents a topology optimization of single material phononic crystal plate (PhP) to be produced by perforation of a uniform background plate. The primary objective of this optimization study is to explore widest exclusive bandgaps of fundamental (first order) symmetric or asymmetric guided wave modes as well as widest complete bandgap of mixed wave modes (symmetric and asymmetric). However, in the case of single material porous phononic crystals the bandgap width essentially depends on the resultant structural integration introduced by achieved unitcell topology. Thinner connections of scattering segments (i.e. lower effective stiffness) generally lead to (i) wider bandgap due to enhanced interfacial reflections, and (ii) lower bandgap frequency range due to lower wave speed. In other words higher relative bandgap width (RBW) is produced by topology with lower effective stiffness. Hence in order to study the bandgap efficiency of PhP unitcell with respect to its structural worthiness, the in-plane stiffness is incorporated in optimization algorithm as an opposing objective to be maximized. Thick and relatively thin Polysilicon PhP unitcells with square symmetry are studied. Non-dominated sorting genetic algorithm NSGA-II is employed for this multi-objective optimization problem and modal band analysis of individual topologies is performed through finite element method. Specialized topology initiation, evaluation and filtering are applied to achieve refined feasible topologies without penalizing the randomness of genetic algorithm (GA) and diversity of search space. Selected Pareto topologies are presented and gradient of RBW and elastic properties in between the two Pareto front extremes are investigated. Chosen intermediate Pareto topology, even not extreme topology with widest bandgap, show superior bandgap efficiency compared with the results reported in other works on widest bandgap topology of asymmetric guided waves, available in the literature. Finally, steady state and transient frequency response of finite thin PhP structures of selected Pareto topologies are studied and validity of obtained bandgaps is confirmed.

Determinación de la Respuesta Dinámica y Estacionaria de la Frecuencia frente a Desbalances de Potencia Producidos por Perturbaciones en la Red

En este trabajo se propone una nueva metodología para determinar la respuesta dinámica y estacionaria de la frecuencia, ante desbalances de generación–carga producidos por perturbaciones en el Sistema Eléctrico de Potencia (SEP). Partiendo del modelo equivalente del sistema de control potencia frecuencia, se derivan expresiones analíticas para calcular la máxima desviación transitoria de la frecuencia, el instante en que se produce, y la cantidad de carga a desconectar por actuación del Esquema de Alivio de Carga (EAC). Con este fi n, se representa al conjunto regulador de velocidad–turbina de cada generador mediante un modelo reducido de 1er orden. En el presente trabajo, el modelo ha sido extendido para representar reguladores de unidades hidráulicas de diferente tecnología. Adicionalmente, la metodología permite determinar el valor estacionario de la frecuencia, luego de la actuación de la Regulación Primaria de Frecuencia (RPF), considerando la carga desconectada por actuación del EAC y/o el déficit de reserva rotante en unidades en RPF. Finalmente, la metodología propuesta es aplicada en dos sistemas de prueba, mostrando una excelente capacidad para estimar, con alta precisión, la respuesta dinámica y estacionaria de la frecuencia ante desbalances de potencia activa.

Determination of draw resonance onsets in tension-controlled viscoelastic spinning process using transient frequency response method

Draw resonance onsets of actual viscoelastic spinning processes with secondary forces operated by constant draw ratio are determined via transient frequency response simulations under a constant tension or force boundary condition, which causes the system to be always stable. Transfer function data between the spinline velocity and the tension at the take-up position in the frequency domain, which are transformed from the transient responses of the take-up velocity with respect to a step change of the take-up force, play a key role in the determination of the onset points for various spinning cases. It is confirmed that the critical draw ratios established in this study are almost the same as those decided by linear stability or direct transient simulation methods for velocity-controlled spinning systems. The transfer function data for the stability analysis can be readily and beneficially applied to an analysis of sensitivity of a spinning process with respect to a sinusoidal disturbance.

Adaptive Roles of Islanded Microgrid Components for Voltage and Frequency Transient Responses Enhancement

This paper introduces a novel framework of coordinated voltage and frequency control strategy for islanded microgrid (MG) operation. The proposed control schemes rely on local measurements as communication-free control approach. Therefore, the distributed controllers of the MG components have been deployed based on their slow, medium, and fast dynamic responses to maintain the voltage and frequency in adherence to IEEE Standards 1547 and 929. The various voltage and frequency control responses associated with reactive power management scheme are efficiently utilized based on well-defined states of operation and transient management scheme. In each state, the roles of each device for voltage and frequency regulations are defined with its regulation capability, and response time based on its local measurements. Consequently, the fast reactive power compensation and rapid frequency regulation are ensured based on the inverter-based devices at challenging operating conditions. As a result, the proposed control strategy improves the voltage and frequency regulation, transient response, and MG stability. A comprehensive simulation study has verified the superior performance of the communication-free approach during steady state and in response to severe disturbances.

Research on Wind Energy Integration in Matsu Islands

The energy costs of island systems are usually higher than those of large grid systems. Therefore, majority of the countries worldwide usually initiate their plans for developing renewable energy on remote islands. The electricity cost of Matsu Islands accounted for roughly 5% of total annual deficit of Taiwan Power Company. Hence, power generation is a critical energy economics issue for the Matsu Islands. This study will examine the possibility of wind power integration into Matsu Islands and investigate the transient frequency response in this system when a fault or disturbance occurs. According to the simulation results, the main target of this study is to improve the system stability on the remote island systems, and achieve the maximum renewable energy penetration.

Optimized suspension kinematic profiles for handling performance using 10-degree-of-freedom vehicle model

In an effort to reduce cost involving repetitive prototype build–test cycles, it is inevitable that simulation on full vehicle will be carried out during the product development stage. Desired suspension kinematic profiles of a given vehicle parameter are often unknown at the initial design stage. This paper demonstrates a simple methodology to obtain optimized kinematic characteristics against quality of handling performance using this model as predictive model in earliest design stage. A full vehicle model that is inclusive of suspension kinematic profiles and nonlinear damper profiles has been derived to enable the engineer to study the characteristics of the nonlinear elements against the vehicle performance when only limited vehicle data are available in the initial stage. Results suggest that the handling characteristics of a vehicle are sensitive to the changes in suspension kinematic profile. Additionally, the proposed vehicle model is able to provide satisfactory handling objective when measured in transient handling and frequency response compared to other vehicle models. A robust prediction model of the vehicle responses in frequency domain is proposed. It is coupled with the vehicle model employed as predictive model to optimize front toe angle profile against vehicle quality of handling performance measured in frequency domain.

Analysis of Dynamic and Transient Response of Frequency Modulated Class E Amplifier

Analysis of Dynamic and Transient Response of Frequency Modulated Class E Amplifier

Transient twenty-first century changes in daily-scale temperature extremes in the United States

A key question for climate mitigation and adaptation decisions is how quickly significant changes in temperature extremes will emerge as greenhouse gas concentrations increase, and whether that emergence will be uniform between hot and cold extremes and across different geographic areas. We use a high-resolution, multi-member ensemble climate model experiment over the United States (U.S.) to investigate the transient response of the annual frequency, duration and magnitude of 8 daily-scale extreme temperature indices during the twenty-first century of the A1B emissions scenario. We evaluate the time of emergence of a permanent exceedance (PE) above the colder part of the historical (1980–2009) extremes distribution, and the time of emergence of a new norm (NN) centered on the historical maxima (for hot extremes) or minima (for cold extremes). We find that during the twenty-first century, hot extremes permanently exceed the historical distribution’s colder half over large areas of the U.S., and that the hot extremes distribution also becomes centered on or above the historical distribution’s maxima. The changes are particularly robust for the exceedance of the annual 95th percentile of daily maximum temperature over the West and the Northeast (with the earliest emergence of a PE by 2030 and of a NN by 2040), for warm days over the Southwest (with the earliest emergence of a PE by 2020 and of a NN by 2030), and tropical nights over the eastern U.S. (with the earliest emergence of a PE by 2020 and of a NN by 2030). Conversely, no widespread emergence of a PE or a NN is found for most cold extremes. Exceptions include frost day frequency (with a widespread emergence of a PE below the historical median frequency by 2030 and of a NN by 2040 over the western U.S.), and cold night frequency (with an emergence of a PE below the historical median frequency by 2040 and of a NN by 2060 in virtually the entire U.S.). Our analysis implies a transition over the next half century to a climate of recently unprecedented heat stress in many parts of the U.S., along with cold extremes that, although less frequent, remain at times as long and as severe as are found in the current climate.

Fuzzy stochastic elements method. Spectral approach

We study a complex dynamic problem, which concerns a structure with uncertain parameters subjected to a stochastic excitation. Formulation of such a problem introduces fuzzy random variables for parameters of the structure and fuzzy stochastic processes for the load process. The uncertainty has two sources, namely the randomness of structural parameters such as geometry characteristics, material and damping properties, load process and imprecision of the theoretical model and incomplete information or uncertain data. All of these have a great influence on the response of the structure. By analyzing such problems we describe the random variability using the probability theory and the imprecision by use of fuzzy sets. Due to the fact that it is difficult to find an analytic expression for the inversion of the stochastic operator in the stochastic differential equation, a number of approximate methods have been proposed in the literature which can be connected to the finite element method. To evaluate the effects of excitation in the frequency domain we use the spectral density function. The spectral analysis is widely used in stochastic dynamics field of linear systems for stationary random excitation. The concept of the evolutionary spectral density is used in the case of non-stationary random excitation.We solve the considered problem using fuzzy stochastic finite element method. The solution is based on the idea of a fuzzy random frequency response vector for stationary input excitation and a transient fuzzy random frequency response vector for the fuzzy non-stationary one. We use the fuzzy random frequency response vector and the transient fuzzy random frequency response vector in the context of spectral analysis in order to determine the influence of structural uncertainty on the fuzzy random response of the structure.We study a linear system with random parameters subjected to two particular cases of stochastic excitation in a frequency domain. The first one when the excitation is a weakly stationary stochastic process with a given spectral density function and the second one which is constituted by a non stationary process with evolutionary spectral density function. We derive the formulas for both cases. The presented computational algorithm has a quite general scope and may be used in the vibration analysis of different kinds of structures.

Scanning tunneling microscope-quartz crystal microbalance study of temperature gradients at an asperity contact

Investigations of atomic-scale friction frequently involve setups where a tip and substrate are initially at different temperatures. The temperature of the sliding interface upon contact has thus become a topic of interest. A method for detecting initial tip-sample temperature differences at an asperity contact is described, which consists of a scanning tunneling microscope (STM) tip in contact with the surface electrode of a quartz crystal microbalance (QCM). The technique makes use of the fact that a QCM is extremely sensitive to abrupt changes in temperature. In order to demonstrate the technique's capabilities, QCM frequency shifts were recorded for varying initial tip-substrate temperature differences as an STM tip was brought into and out of contact. The results are interpreted within the context of a recent model for thermal heat conduction at an asperity contact, and it is concluded that the transient frequency response is attributable to small changes in temperature close to the region of contact rather than a change in the overall temperature of the QCM itself. For the assumed model parameters, the results moreover reveal substantial temperature discontinuities at the boundary between the tip and the sample, for example, on the order of 10-15 °C for initial temperature differences of 20 °C.

Comparative Evaluation of the HVDC and HVAC Links Integrated in a Large Offshore Wind Farm—An Actual Case Study in Taiwan

This paper mainly focuses on the transient voltage and frequency responses of a large offshore wind farm integrated system in Taiwan. It adopts a simulation study by using different submarine cable technologies and wind turbine types, including high-voltage direct current (HVDC) link based on line-commutated converter (LCC), high-voltage alternating current (HVAC) link, and three types of wind turbines. In addition, it utilizes an actual system that connects the Taiwan grid and a 200-MW offshore wind farm in the Penghu area via two submarine cables. The aim of this paper is to analyze the transient characteristics of both the HVDC and the HVAC connected wind power systems. According to the simulation results, it shows that the HVDC link can provide better voltage and frequency responses, which are independent on the types of wind turbines. Moreover, the HVDC link can alleviate the effect of grid faults on the wind farm and provide the wind farm better voltage and frequency stability.

Research on the Influence of Unsprung Mass on Vehicle Handling Stability

A dynamical model of engine vehicle was built by using ADAMS/Car. Based on that, another dynamical model of four-independent-wheel-drive electric vehicle was built too. Two simulation experiments of steering wheel angle step input and steering wheel angle impulse input were done. Considering the vehicle mathematical model with two linear degrees of freedom, the transient response and frequency response characteristics were evaluated. Simulation results indicated that time-domain and frequency-domain characteristics of four-independent-wheel-drive electric vehicle were influenced because of its heavy unsprung mass, and that leaded to the deteriorative handling stability.

A Generalized Multiconductor Transmission Line Model and Optimized Method for the Solution of the MTL Equations

A generalized multiconductor transmission line (MTL) model is developed for modeling of wide frequency transient response on busbars, cables and core-type transformer windings. Different from the traditional MTL model, the equations of the generalized MTL model are built in the cylindrical coordinate system beside rectangular coordinate system. Based on further discussion, it is found that generalized MTL model could be changed to MTL model where all lines have the same length as to the core-type transformer windings. Then, the optimized solution based on Time domain finite element method (TDFEM) is developed for the above MTL equations. It avoids numerical oscillation of the finite difference time domain (FDTD) method. The numerical results are in agreement with ones calculated by Bergeron's method and FDTD method.

System Response Function–Based Leak Detection in Viscoelastic Pipelines

The possibility of leak detection in a viscoelastic pipe system is studied. The frequency response function method (FRFM) is used for leak detection, and the analytical expression for the FRFM originally developed for an elastic pipeline is extended to the viscoelastic situation in this study. The extended FRFM is validated from numerical experiments with one-dimensional viscoelastic transient models. The analysis shows that the pipe-wall viscoelasticity effect has significant impact on the amplitude damping and phase shift of the pressure wave, but little influence on the leak-induced patterns of pressure head peaks in transient system frequency responses. The results indicate that the extended FRFM is applicable to the viscoelastic situation. The impact of viscoelastic parameters and incident wave bandwidth on the applicability of the extended FRFM i also investigated in this paper, and the results imply that transient input signals with rapid changes in time are preferable for leak location in viscoelastic pipelines.

Transient Response of Supported Beams to Moving Forces with Sinusoidal Time Variation

Moving forces are a common loading pattern for flexible beams, found in many applications in both civil and mechanical engineering. These forces give rise to a transient response, the nature of which depends on the time variation of the amplitude of the force and its position along the beam. In addition to the possibility of numerical evaluation, closed form solutions of the beam response are beneficial for their simplicity of use, and because they allow an understanding of the system behavior. On the other hand, these prove to be rather complicated in most cases, and only a limited number of cases are available in the literature. This paper studies the simple but common case of a supported beam loaded by a force with sinusoidal time variation moving at a constant speed. Simple equations are presented for the approximated responses at and away from resonance, and their accuracy is discussed. Transient frequency response functions are also shown. Finally, as an example, the results are applied to an evaluation of the response of a beam footbridge to the action of a walker, and compared to code specifications.

Experimental Identification Method for Small-Signal Analysis of Smart Power ICs

Smart power integrated circuits (ICs), as the combination of control and power functions on a single chip, enable the production of more miniaturized systems. This paper presents an experimental method for the small-signal frequency-response analysis of smart power ICs in switch-mode power supplies. In this method, the switching-duty-cycle output of a power IC is converted into a digital signal by using two high-speed counters during each switching period, and the power IC's control input signal is simultaneously converted into a digital signal by an analog-to-digital converter. After processing the data of the duty-cycle output and the control input, not only the transient response but also the frequency response of the power IC can be obtained. Using least square identification, the smart power IC's transfer function is finally synthesized from the measurement data. This analysis method, referred to as sampling the transient responses and frequency responses of power ICs, can efficiently provide reliable and accurate transfer functions whether the switching frequency of a power IC is jittered or frequency modulated. The experiments using different power ICs were presented herein to validate the analysis method. The results were discussed, and the effectiveness and practicality of the method were verified.

Transient Behavior and Frequency Response of Constant Frequency One Cycle Charge Control Modulator (O3C)

This paper presents a new pulse width modulator capable of adjusting the conversion duty ratio so that the necessary output filter charge will reach its steady-state value in only one switching period, when any disturbance of the input voltage, output current or output voltage occurs. The proposed modulator is based on the calculation of the variation of the electric charge required to restore the steady-state operation in only one switching period, and therefore is designated by <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">one</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cycle</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">charge</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">control</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(O3C)</i> . The synthesis of the proposed modulator is presented in detail. It will be also shown, theoretically, by simulation and experimentally, that the use of this modulator in a buck converter presents as a major advantage, the fact that the output voltage gain is not limited by the cutoff frequency of the output filter. As a consequence, very low output ripple can be achieved without compromising the dynamic response of the converter. Comparative simulation results considering the presented modulator and the conventional one cycle control, both applied to a buck converter in the same conditions, are also presented.

Effects of an absorber on impact characteristics in machine cushion design with area ratio modified guiding structure

A machine cushion with guiding structure can transfer impact and vibration waves into branches of balanced forces along pre-designed paths, to reduce the effects of those waves between the machine and the ground. To improve impact load absorption and vibration wave suppression, we designed a machine cushion with an attached absorber and “area ratio modified” (ARM) guiding structure. We compared variations in vibration using impulse responses of machine cushions as a performance index, of four alternative machine cushion designs: One was an ARM with absorber design; the second was the same machine cushion but without an absorber; the third and fourth were simple passive machine cushions with and without an absorber. The related dynamic equations for these structures were derived and the related transient responses and frequency responses were evaluated. The main objectives of the study were to demonstrate the capacity of our ARM with absorber structure to absorb impact forces and vibration waves, and to measure the effect of parameter variation on the absorption of impact forces and vibration waves. As expected, simulation results showed that under test conditions, the proposed ARM with absorber machine cushion had the best impact and vibration suppression capability.

Spectral stochastic analysis of structures with uncertain parameters

We present a probabilistic analysis of a structure with uncertain parameters subject to arbitrary stochastic excitations in a frequency domain. The problem of stochastic dynamic analysis of a linear system in a frequency domain is formulated by taking into consideration the uncertainty of structural parameters. The solution is based on the idea of a random frequency response vector for stationary input excitation and a transient random frequency response vector for nonstationary one which are used in the context of spectral analysis in order to determine the influence of structural uncertainty on the random response of structure. The numerical spectral analysis of the building structure under wind and earthquake excitation is provided to demonstrate the described algorithms in the context of computer implementation.

Research of BJMOSFET frequency characteristics

The parasitic capacitance effect and its influence to the performance have been investigated in Bipolar Junction Metal-Oxide-Semiconductor Field-Effect Transistor (BJMOSFET). The frequency characteristic equivalent circuit and high frequency response model of BJMOSFET have been presented. The frequency characteristic of BJMOSFET is simulated using the multi-transient analytical method and PSPICE9 simulator. The conclusions that BJMOSFET owns less total capacitance, wider frequency band, better transient characteristic and better frequency responses are reached by comparing with the traditional MOSFET at the same structure parameters and bias conditions. BJMOSFET, as a novel promising high frequency device, would be desired to find application in future integrated circuit.