Controllable Frequency Range Research Articles

Variable Natural Frequency Damper for Minimizing Response of Offshore Wind Turbine: Principle Verification through Analysis of Controllable Natural Frequencies

Resonance causes extreme stress, acceleration of fatigue, and reduction in lifespan of offshore wind structures. The main factors that cause resonance are environmental loads such as wind and waves, and dynamic loads caused by rotor movement. Estimation of the natural frequency at the design stage is highly uncertain, and natural frequency changes occur due to various factors during long-term operation. Therefore, it is important to ensure structural safety from resonance through a vibration-monitoring system or an additional damper. In this study, the effect of seawater existing inside the substructure on the natural frequency of the structure was dealt with. The natural frequency estimation equation for a fixed offshore wind structure was derived with the “inner fluid simplification assumption”. The finite element modal analysis was performed to verify the principle of Variable Natural Frequency Damper (VNFD), a system that controls the natural frequency of offshore wind structures through a pump, and to find the range of natural frequency control. As a result, interior fluid affects the natural frequency of the wind turbine support structure. Specifically, the variable natural frequency range was very low, at about 0.027% for the monopile model at a depth of 10 m, but increased rapidly to about 3.66% at a depth of 70 m. Furthermore, when estimating the natural frequency of a fixed offshore wind turbine in deep water without consideration of interior fluid, the estimates can be higher than with consideration of it.

Study of Parametric Interactions in the Nuclear Reactor Control with Feedback

This article considers the principal theoretical possibility of regulating a nuclear power reactor under changing operating modes conditions when external periodic disturbances take place in conditions of changing the operating mode. By the external periodic perturbation a downward change in the conditions of the heat sink was meant. The magnitude of the changes was preliminarily calculated in such a way that the operating conditions of the power plant did not exceed the boundaries of the safe operation zone of the reactor. In the case of approaching the operation parameters to the critical ones, the heat sink was increased until the working conditions returned to their previous state. In this work the amplitude frequency response of a non-linearly enhanced system in the nuclear power plant operating conditions when non-linearly reacting to external periodic influences has been studied. The external cyclic disturbances effect produced on the reactor that initially existed under stationary operating conditions has been considered. The research was carried out by numerical simulation of the competition between processes occurring in a nuclear power plant and determined by the system’s reaction time and relaxation time while responding to periodic external influences. Calculations of the relaxation time dependence on the fixed frequency-revealing external influence’s temperature are presented. Also, the relaxation time dependence on the frequency of external influence at a fixed temperature for systems with various relaxation periods was calculated. It is determined that when the dependence between system temperature and the external influence time is calculated, there exists a wide range of possible frequency control. To evaluate the behavior of a nuclear power reactor under conditions of operating modes changes, a fundamental physical mathematical model of the reactor’s state under external harmonic influence is presented. It is based on the nonlinear Riccati equation. The external harmonic effect was simulated by changing the heat supply and heat removal conditions near the critical point.

The design concept of high-frequency sound modulators for acoustic tests for the strength and flying life of an aircraft

Modern aircraft are exposed to intense pulsations of sound pressure arising both from engine noise, and from turbulent effects of the environment during flight. The pulsations cause vibrations of the structure leading to fatigue damage of the fuselage skin and primary elements of structure, as well as to the equipment failure. The operating experience shows the necessity of taking into account the acoustic fatigue starting with loads of 130 – 135 dB. At a load value above 160 dB, the acoustic fatigue becomes one of the main factors determining the strength of aircraft and space structures. Despite the development of computational methods for estimating durability under acoustic loads, the most reliable methods are still based on experimental studies. The frequency spectrum is the main characteristic of acoustic loading. Reproducing of acoustic loads in a controlled frequency range 150 – 600 Hz with the intensity of pulsations specified above appeared enough for testing most aircraft structures. However, space apparatus and equipment must be tested for the effect of acoustic noise within the frequency range from 150 to 1200 – 2000 Hz. Domestic low- and medium-frequency generators operating in a frequency range of 20 – 600 Hz are currently used in reverberation chambers in Russia. To generate higher frequencies of acoustic vibrations, we used an ERT-200 electropneumatic converter (LING (USA), the maximum frequency 1000 – 1250 Hz) and a most advanced SEPMOD modulator [SEREME (France), the maximum frequency is 1000 – 2000 Hz]. Information about the design of those sound modulators is not available to consumers. Further development of aerospace technology necessitates developing of domestic high-frequency sound generators for acoustic tests. We propose a method which ensures operation of the sound generator in a controlled frequency range of 150 – 1200 Hz. The essence of the method consists in designing a sound modulator (being part of the generator) which provide that an increase in the electromotive force, driving the movable element of the valve assembly into reciprocating motion, will not entail an increase in heat generation in the electromagnetic propulsion device. For this, we propose to perform the electric propulsion device in the form of synchronously operating two parts located at opposite ends of the movable element of the valve. Supplying each part with the maximum permissible current, we managed to increase the total excitation current by half. The calculations showed that the use of more energy-intensive permanent magnets of neodymium type NdFeB and considered principle of forming a propulsion unit provide a range of sound frequency control of 150 – 1200 Hz at a pulse acoustic load up to 160 dB.

Design and experimental validation of a robust input shaper for eliminating vibration in dielectric elastomer actuators under varying applied voltage

Dielectric elastomer actuators (DEAs) are an emerging type of soft actuator. When electrostatically actuated the DEA with a step signal, the inherent vibrations may limit their motion accuracy in practical applications. Moreover, increasing the applied voltage reduces the natural frequency of the dielectric elastomer structure, as the electrostatic stress decreases the tension in the DE device. This paper proposes a robust input shaper for a DEA system to eliminate vibration under various applied voltage. To extend the frequency control range of the shaper, an improved zero distribution method is proposed. The zeros are symmetrically distributed in the radial direction of the designed zero of a distributed zero-vibration (DZV) shaper. Simulations and experiments are performed to explain the robust control effects of the proposed design method. The step responses of the DEA are conducted at 2, 3 and 4 kV, the vibration attenuations of 27.66, 4.867 and 9.803 dB are achieved, respectively. Meanwhile, the overshoots are eliminated from the step responses. The designed method can pave the way to improve the control accuracy of soft material devices under varying operating conditions.

Dynamic analysis of a simply supported beam with LaSMP patches

Light-activated shape memory polymer (LaSMP) is a novel smart material, whose stiffness can be tuned by irradiating with UV light. By changing the Young’s modulus of LaSMP patches, the natural frequency of a simply supported beam laminated with LaSMP patches can be actively affected and the dynamic response of the beam can be influenced. Based on the stepped beam theory, dynamic equations were established for a simply supported beam laminated with LaSMP patches. The effect of LaSMP patch properties on the frequency variation of the first three modes was analyzed. It was found that the frequency variation range increases with increasing length. The strategy of locating the LaSMP patch pair on a single location was discussed first, and it was observed that when the LaSMP patch pair was located at antinodes of each mode, the widest frequency control range can be obtained. When multiple LaSMP patch pairs were considered, analytical results showed that the natural frequency ranges were 24.97% and 52.47% higher than by concentrating the patches on a single location for the second and third mode, respectively. When the controllable natural frequency range increases, the control capability of the LaSMP patch on the dynamic response of the beam structure increases as well. As a result, multiple LaSMP patches would have better potential for vibration control than single patches.

Microstrip Multifunctional Reconfigurable Wideband Filtering Power Divider with Tunable Center Frequency, Bandwidth, and Power Division

In this paper, a microstrip reconfigurable wideband filtering power divider (FPD) with tunable center frequency (CF), bandwidth (BW), and power division is presented. The proposed structure consists of two trimode stub-loaded resonators, a three-line coupled structure loaded two varactor diodes, and two output parallel-coupled lines loaded a lumped capacitor. The CF and BW of wideband filtering response can be tuned by controlling the varactor diodes loaded onto the open end of trimode resonators. Meanwhile, the power division ratio (PDR) is controlled by tuning the coupling strength between the center line and sidelines of three-line coupled structure. Compared with the conventional wideband FPDs, the capacitor loaded onto the parallel-coupled line of two output ports is to enlarge the coupling, which can increase the return loss (RL), and thus relieve the limitation of the line space between two coupled lines. A complete design procedure with analytical design equations for driving parameters of the structure is described. The measured results show that the CF can be tuned from 0.86 to 1.32 GHz with RL better than 16 dB, while the 1-dB BW can be tuned from 180 to 710 MHz. The measured isolation is better than 21 dB from dc to 2.5 GHz. Then, the achieved PDR can be tuned from 1:1 to 3:1. The proposed circuit can be also utilized as a switchless bandstop filter, where the isolation is better than 20 dB from dc to 19 GHz. The proposed tunable wideband FPD exhibits good RL, wide range of frequency and BW control, wide harmonic suppression, high isolation, and multifunctional application.

A High-Gain ${X}$ -Band Overmoded Relativistic Klystron

A high-gain ${X}$ -band overmoded relativistic klystron is presented in this paper. The device mainly consists of an input cavity, two buncher cavities, and an output cavity. Moreover, two reflectors are added before and after the input cavity, therefore a standing wave is formed between the two reflectors, improving the initial modulation of the electron beam. With two sectional RF lossy materials inserted, the input cavity and the two buncher cavities are effectively isolated with each other. An additional reflector located just before the output cavity further reflects the backward-flowing power. Particle-in-cell simulations show that for a 10-kW injected microwave with a frequency of 9.37 GHz, the generated microwave power is 1.2 GW, corresponding to a beam-wave interaction efficiency of 30% and a gain of 50.8 dB. As the injected power increases from 10 to 100 kW, the frequency control range extends from 30 to 130 MHz.

A Clock and Data Recovery Circuit with Adaptive Loop Bandwidth Calibration and Idle Power Saved Frequency Acquisition

This paper presents a clock and data recovery circuit with an adaptive loop bandwidth calibration scheme and the idle power saved frequency acquisition. The loop bandwidth calibration adaptively controls injection currents of the main loop with a trimmable bandgap reference circuit and trains the VCO to operate in the linear frequency control range. For stand-by power reduction of the phase detector, a clock gating circuit blocks 8-phase clock signals from the VCO and cuts off the current paths of current mode D-flip flops and latches during the frequency acquisition. 77.96% reduction has been accomplished in idle power consumption of the phase detector. In the jitter experiment, the proposed scheme reduces the jitter tolerance variation from 0.45-UI to 0.2-UI at 1-MHz as compared with the conventional circuit.

Design and evaluation of an intelligent artificial anal sphincter system powered by an adaptive transcutaneous energy transfer system.

The aim of this study was to optimize an intelligent artificial anal sphincter system (AASS) II for patients with severe fecal incontinence. Redesigning and integrating a pressure sensor into the sphincter prosthesis allows us to reduce the sensor volume and makes it suitable for a chronic, ambulatory application. Furthermore, a close-loop frequency control method was designed for the transcutaneous energy transfer system. Finally, a longer working time of the implanted device was obtained by the low-power design of the hardware and software. The new model was implanted in 2 dogs and studied for periods of up to 5 weeks. The output voltage induced on the load of 30 Ω, for a variation range in k of 0.12 ~ 0.42, was maintained at approximately 6.8 V with a frequency control range of the 270 ~ 320 kHz. The minimum and maximum output voltages of the pressure sensor were found to be 1.7 V and 2.34 V, respectively, which corresponded to a pressure range of 90 ~ 120 kPa with maximum change rate of approximately 3.7% caused by the temperature variations. Moreover, compared with AASS I, the low-power design resulting in 94% reduction in power consumption. The efficacy of the device in achieving continence and sensing the need to defecate was assessed in an animal model. The technical concept and the design of the AASS II turned out to be capable of fulfilling the medical requirements.

SDR 기반 Polar 송신 변환부의 DDS 주파수 특성 분석

본 논문에서는 차세대 디지털 무선통신시스템에 적용하기 위하여 소프트웨어를 기반으로 한 Polar 송신기를 설계하고 분석하였다. 구현한 Polar 송신기는 CORDIC 알고리즘을 적용하여 I/Q데이터를 입력받아서 진폭과 위상정보를 독립적으로 처리하는 Polar 변환을 하도록 하였으며, 소프트웨어를 이용하여 DDS의 출력신호의 주파수를 Sweep시킬 수 있도록 구성하였다. 구현한 Polar 송신기는 소프트웨어 제어를 통해 DDS의 주파수 제어범위 내에서 1.16 GHz까지 주파수를 제어할 수 있음을 보였다. 향후 이득, 위상, 출력 등 제어 가능한 블록요소들을 제어할 수 있음을 보였으며, 소프트웨어를 이용하여 SDR기반 디지털 무선통신시스템에 적용이 가능함을 보였다. In this paper, we implemented polar transmitt converter based on software for next generation digital wireless communication system. The implemented converter converted from rectangular to polar by CORDIC algorithm, and be made up of sweep for DDS output frequency using software control. The implemented converter shows can frequency control up to 1.16GHz within DDS frequency control range by software control. it means that transmitter can be control of varied blocks such as gain, phase, output and etc.. The implemented converter can be applied digital wireless communication system based on SDR.

Three-Phase (LC)(L)-Type Series-Resonant Converter With Capacitive Output Filter

This paper presents a three-phase (LC)(L)-type dc-dc series-resonant converter with capacitive output filter. Operation of the converter has been presented using the operating waveforms and equivalent-circuit diagrams during different intervals. An approximate analysis is used, and design procedure is presented with a design example. Intusoft simulation results for the designed converter are given for input voltage and load variations. Experimental results obtained with a 300-W converter are presented. Major advantages of this converter are the leakage and magnetizing inductances of the high-frequency transformer that are used as a part of resonant circuit, and the output-rectifier voltage is clamped to the output voltage. Also, the converter operates in soft switching for the inverter switches with a narrow frequency control range and the tank current decreases with the load current.

Prosodic control in severe dysarthria: preserved ability to mark the question-statement contrast.

Speakers with severe dysarthria are known to have reduced range in prosody. Consistent control within that range, however, has largely been ignored. In earlier investigations speakers with severe dysarthria were able to control pitch and duration for sustained vowel production despite reduced flexibility of control (Patel, 1998). The present experiment examined whether 8 speakers with severe dysarthria due to cerebral palsy used prosodic parameters of pitch contour and syllable duration for phrase-level productions. Speakers with dysarthria (N = 8) produced 3-syllable phrases as questions and statements. Naïve listeners (N = 48) classifed dysarthric productions as either questions or statements. Listeners were able to distinguish questions from statements with accuracy levels ranging from 81% to 98%. We were also interested in studying how dysorthric speakers marked the question-statement contrast. Prosodic features of pitch contour and syllable duration were systematically removed from the original recorded vocalizations to examine the salience of these features on listener classification. Removal of pitch contour cues dramatically reduced listener accuracy scores to almost chance performance. Listeners found pitch contour cues to be information-bearing cues in dysarthric vocalizations even though the range of frequency control in these speakers may be reduced. That speakers with dysarthria were able to exert sufficient control to signal the question-statement contrast has implications for diagnostic and intervention practices aimed to optimally exploit prosodic control for enhancing communication efficiency.

Vibration Control of a Smart Structure Using Fixed Order Dynamic Compensation

The use of direct contact type sensors and actuators for structural vibration control offers the advantage of adding less mass to the structure and permits a wide fre quency range of control, facilitating a means of tunability for structural systems that age or change. The design of a controller using output feedback for such systems is considered in this paper. A recently developed loop transfer recovery procedure for designing fixed- order dynamic compensators that improve both performance and robustness has been applied in the controller design for active vibration control of a cantilever beam with bonded piezoceramic sensors and actuators. For a given order of the compensator, the trade-off between performance and robustness is investigated.

A 250-MHz monolithic voltage-controlled oscillator with low temperature coefficient

A monolithic voltage-controlled oscillator (VCO) with dual-loop feedback, designed and fabricated in a 2- mu m oxide-isolated bipolar technology, is discussed. The VCO, consuming 220 mW from a single 5-V supply and occupying 2200 mil/sup 2/, achieves a -65 p.p.m./ degrees C temperature coefficient of frequency. It has a 5:1 frequency control range, and the maximum oscillation frequency is 250 MHz with better than a 2% voltage-to-frequency linearity. The modulation bandwidth of the VCO is greater than 12 MHz, and the power supply rejection ratio is 0.4%/V.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Sinusoidal oscillator with voltage controlled frequency and amplitude

A sinusoidal oscillator is considered of which both the frequency and amplitude are electronically controlled. The control of frequency is obtained with two multipliers used as controlled amplifiers. The circuit for amplitude control also uses multipliers; the output voltages of the oscillator are squared and summed and the resulting DC voltage is compared with the reference. This approach provides fast frequency and amplitude control. The practical range of frequency control depends on the distortion level requirements. A detailed consideration of non-linear distortion is given. The main sources of the distortion are the non-linearity and mismatch of the multipliers and the offset of operational amplifiers in the oscillation loop. The frequency can be controlled in the range 16 Hz–16 kHz (in three overlapping bands) with a level of distortion that varies between − 40 dB and − 55 dB.