共振式混凝土路面破碎车的自适应反推滑模控制

基于共振式混凝土路面破碎车共振机构的结构,给出了其共振频率和振幅的模型.建立了基于比例泵控马达的频率调节的非线性不确定性控制模型,设计了自适应反推滑模的控制算法,针对系统模型中的不确定性项,给出了各参数项的自适应律,基于Lyapunov函数,证明了频率输出跟踪的渐近收敛.仿真和车载测试结果表明,该方法具有较好的频率跟踪性能,能满足共振式路面破碎车的施工控制要求.     

面向铁氧体裂纹检测的感应加热电源研制

针对常规感应加热电源对铁氧体加热时存在加热均匀性差和负载回路谐振频率漂移的问题,提出了一种全桥逆变拓扑结构的串联谐振式数字感应加热电源.基于负载串联谐振回路换流时电压和电流的相位差特性,通过PSPICE软件分析了阻性、感性和容性三种换流状态,仿真结果表明,串联谐振回路工作于弱感性状态,可以保证电路安全可靠运行;基于电磁耦合原理,对比分析了原边补偿和副边补偿两类负载匹配变压器,通过匹配负载等效电阻实现电源系统最大能效输出;采用Fuzzy-PI频率跟踪技术实现负载谐振频率实时跟踪.最后,将研制的数字感应加热电源成功地应用于铁氧体裂纹检测实验.     

基于改进的强跟踪滤波GPS校频系统误差处理方法

GPS信号校准晶振信号频率源系统可输出高准确度时频信号,但GPS信号在传输和接收过程中会产生随机抖动或野值,给系统频率校准带来误差。为减小GPS信号随机抖动和野值所带来的影响,根据GPS信号与晶振信号准确度互补的特点,建立GPS信号校准晶振信号频差模型,利用强跟踪滤波算法对频差信号误差进行修正。针对GPS信号中存在的野值问题,对强跟踪滤波算法进行改进,根据残差变化率的大小判别野值,利用替代法对野值加以修正,提高滤波准确度。将该方法应用于某GPS信号校准晶振信号频率源系统,可使系统输出频率准确度达到10-11量级。     

基于任意波形发生器的高压短路试验测量系统校准方法和装置的研究

提出了一种将标准短路试验波形注入多通道任意波形发生器,来产生模拟实际的校准波形,进而对测量系统进行校准的方法。校准装置使用现场可编程门阵列(FPGA)、直接数字频率合成器(DDS)等器件。对装置的检定结果表明:在10 Hz^200 kHz频率范围内,输出频率、输出电压最大误差分别为2.1×10^-6、3×10^-3。重复输出10次,输出幅值的最大相对标准偏差为5.7×10^-4,1年内幅值变化的最大相对标准偏差为1.9×10^-4。通过将该装置用于实际高压短路试验测试系统的校准,验证了试验波形的噪声、零漂及带宽均会对测量系统的准确度产生显著影响。     

基于锁相环的谐振筒式液体密度传感器检测系统

为实现液体密度的在线测量,设计了一种基于谐振原理的液体密度传感器检测系统,并进行了检测实验.液体密度传感器由薄壁短管式谐振筒和检测系统构成,所设计的检测系统以锁相环为核心,可实现无相差的频率跟踪,并由单片机对频率进行测量、控制和输出显示.实验测试结果表明:在1~5 k Hz频率范围内,检测系统能够实时跟踪谐振频率的变化,频率跟踪不确定度为0.01 Hz;20℃下的传感器系数K0、K1、K2分别为153.867 0 kg/m3、-3.321 4×106kg/(m3·s)、1.766 7×1010kg/(m3·s2).在密度为700~1 200 kg/m3的测量范围内,传感器综合测量精度为0.076%.     

共振式水泥混凝土路面破碎车共振频率和振幅的控制研究

基于共振式水泥混凝土路面破碎车共振机构的载荷分析,给出了其共振频率和振幅的模型。针对共振机构电液比例控制系统的非线性和不确定性问题,建立了基于比例泵控马达的频率控制数学模型,设计了自适应反推滑模的频率控制算法,针对系统模型中的不确定项,给出了各参数项的自适应律,基于Lyapunov函数,证明了频率输出跟踪的渐近收敛。仿真和车载实验结果表明,该方法具有较好地频率跟踪性能,能满足共振式水泥混凝土路面破碎车的施工作业要求。     

基于STM32的频率和功率可调非接触供电超声电源设计

为解决接触式供电中漏电、磨损、电能传输不良以及超声电源在加工中谐振频率漂移、跟踪速度慢、输出功率不稳定等问题,文章以STM32单片机作为主控系统,设计了一种频率和功率可调的非接触供电超声电源。根据采样反馈电路采集的电压电流相位差和有效值信号,采用锁相环和模糊比例积分(Proportional Integral, PI)控制相结合的方法对频率进行跟踪,并用传统 PI 控制法控制输出功率。在 Matlab 软件中搭建电源仿真模型,利用附加电阻、附加电感和附加电容模拟加工过程中负载参数的突变,对有频率调节和功率控制子系统以及没有子系统的电源模型分别进行仿真。仿真结果表明,电源输出功率稳定在 248 W。当负载参数发生改变时,电源的谐振频率发生漂移,经过频率自动跟踪子系统的调节后,电源在 0.01 s 后重新回到谐振状态。此控制算法实现了频率快速跟踪和功率控制。     

乘性三值噪声作用下微分电路中的随机共振现象研究

基于线性系统理论,利用三值噪声的统计性质,推导出了系统输出幅度增益的解析表达式。研究表明,随着输入信号频率、三值噪声的定态概率、噪声状态间的跃迁速率、参数k(电容C的倒数)的增大,输出幅度增益出现一个最大值。当信号频率较低时,输出幅度增益随着k的增大而单调下降;当信号频率较高时,输出幅度增益随着k的增大而单调增大。当信号频率较低时,输出幅度增益随着定态概率的增大而单调增大;当信号频率较高时,输出幅度增益随着定态概率的增大而单调下降。随着G0(电阻的倒数)的增大,输出幅度增益单调减小。     

B-71和B-81骨导耳机的性能比较

为探索新型骨导耳机在临床听力测试中的优势和潜在应用价值,设计了一套骨导耳机声学参数测量系统,选取5个测听频率,比较了 B-71和B-81两种常用骨导耳机的最大输出强度和谐波失真指标.在最大输出强度相同时,250～2000 Hz的4个频率点上B-81耳机谐波失真明显小于B-71;在4000 Hz,B-71和B-81耳机谐...     

基于啮合频率和频谱校正的风电齿轮箱振动信号阶比跟踪分析

克服风电齿轮箱输入转频能量低、输出转频混叠,难以直接提取转速信号的难点,提出了一种基于啮合频率和频谱校正的风电齿轮箱振动信号阶次跟踪方法。该方法利用能量重心法精确估计瞬时啮合频率,间接获得转速信号,进行阶次跟踪,提取风电齿轮箱的运行状态特征。仿真和工程应用结果验证了该方法的有效性和实用性。应用所提方法获得了正常风电齿轮箱振动信号的边频带特性:1)行星轮系的啮合频率同时被太阳轮和行星架的转频调制;2)定轴轮系啮合频率被输出轴的二倍频调制,双弹性支撑导致正常风电齿轮箱输出轴天然地存在轴不对中现象。     

A Wide Range Voltage-Controlled Oscillator

An understanding of the fundamental constraints which limit the performance of controlled oscillators has permitted the development of a VCO having exceptional performance. The output frequency is relatively independent of power supply and temperature and is proportional to the controlling voltage for at least four decades. The switching circuitry is operated in a nonsaturating mode which allows frequency operation to 5 MHz. The entire circuit is compatible with monolithic IC technology.     

Rapid evaluation of fatigue limit in AZ31B magnesium alloy using acoustic emission

Acoustic emission (AE) was used in a fatigue experiment to characterise AE signals and to rapidly determine the fatigue limit of AZ31B magnesium (Mg) alloy. The AE signals during fatigue were characterised according to waveforms and frequency. Meanwhile, the energy dissipation in the process of fatigue, which was represented by the accumulative AE energy, can be used to determine the fatigue limit. Based on the AE parameters, the fatigue limit was 97?MPa, with an 8% error value when compared with the results obtained by the conventional S–N curve method. This model only requires the accumulated energy of the signals during strain hardening. Therefore, the fatigue limit can be determined rapidly.     

Cesium microwave emission without population inversion

The use of coherent population trapping (CPT) for the realization of a Cs coherent microwave emitter without population inversion is described. Preliminary experimental results are reported regarding the radio frequency spectrum of the emitted microwave radiation, the emission profile width, and the transient behavior of the output power. This new approach, based on the coherence properties of the laser radiation, allows the implementation of a microwave frequency standard where the linear light shift is absent and the thermal noise limit for the frequency instability is below 10(-12) for an integration time of 1 s.     

A fiber optic phase modulator with an optical frequency shift of up to 20 GHz

A fiber optic phase modulator is described in which the phase of a light wave traveling in an optical fiber is modulated by a composite electromechanical resonator with Q≌1000. The instantaneous frequency of the wave at the modulator output varies according to a harmonic law. The interval of tuning of the instantaneous light wave frequency achieved in the experiment is 20 GHz, which corresponds to a modulation index of ≌10⁶. It is demonstrated that a maximum value of the frequency tuning range is determined by the elastic limit of the resonator material.     

Convergence of a three-dimensional quantum lattice Boltzmann scheme towards solutions of the Dirac equation

We investigate the convergence properties of a three-dimensional quantum lattice Boltzmann scheme for the Dirac equation. These schemes were constructed as discretizations of the Dirac equation based on operator splitting to separate the streaming along the three coordinate axes, but their output has previously only been compared against solutions of the Schr?dinger equation. The Schr?dinger equation arises as the non-relativistic limit of the Dirac equation, describing solutions that vary slowly compared with the Compton frequency. We demonstrate first-order convergence towards solutions of the Dirac equation obtained by an independent numerical method based on fast Fourier transforms and matrix exponentiation.     

The adiabatic anti-jitter circuit

The anti-jitter circuit (AJC) is able to reduce phase noise and spurious content of any frequency source at sideband frequencies above a defined cut-off frequency. By contrast, a phase-locked loop (PLL) can only reduce the intrinsic phase noise of its output oscillator closer to carrier lower than a defined cut-off frequency. The AJC has no output oscillator, but its phase noise performance can be assessed as if it had. This paper reports the invention of the adiabatic AJC (AAJC), giving the AJC improved power consumption, frequency range, and maximum frequency of operation. The term “adiabatic” is adopted to indicate that the core part of the new circuit does not require a power supply. It takes power from the input source directly to create the sawtooth waveform that has considerably reduced time jitter on the longer of its two ramp waveforms. Discrete models of the AJC are now operational at 30 MHz, which is twice the 15-MHz operation previously reported. The cut-off frequency of suppression has been maintained at a few kiloHertz. Noise analysis now shows performance comparable with an LC oscillator is possible. SPICE simulations show potential operation up to 5 GHz. The AAJC is also cascadable up to the intrinsic (shot) noise limit. Shot noise can be reduced by feedback     

Transverse Acoustic Response Measured by AC-cut Quartz Transducer in Superfluid Helium-3

No Heading The transverse acoustic response in the B phase of superfluid ³He has been measured using an AC-cut quartz transducer at a pressure of 17.0 bar. The measurements were performed by a CW bridge method at a frequency of 9.3 MHz utilizing a quadrature hybrid and a high-frequency lock-in amplifier. By sweeping frequency around the resonance frequency of the transducer, in-phase and quadrature responses of the resonance were obtained from the output of the lock-in amplifier. We successfully separated the quality factor and the resonance frequency. Quality factor of the transducer had a small dip just below T_c and increased as _n by cooling, while its resonance frequency decreased sharply at T_c and gradually recovered to the normal state value in the low temperature limit.PACS numbers: 67.57.Jj, 43.58.+z.     

Effect of frequency and environment on fatigue behavior of a CVI SiC/SiC ceramic matrix composite at 1200 °C

The fatigue behavior of a SiC/SiC CMC (ceramic matrix composite) was investigated at 1200 °C in laboratory air and in steam environment. The composite consists of a SiC matrix reinforced with laminated woven Hi-Nicalon™ fibers. Fiber preforms had boron nitride fiber coating applied and were then densified with CVI SiC. Tensile stress-strain behavior and tensile properties were evaluated at 1200 °C. Tension-tension fatigue tests were conducted at frequencies of 0.1, 1.0, and 10 Hz for fatigue stresses ranging from 80 to 120 MPa in air and from 60 to 110 MPa in steam. Fatigue run-out was defined as 10⁵ cycles at the frequency of 0.1 Hz and as 2 × 10⁵ cycles at the frequencies of 1.0 and 10 Hz. Presence of steam significantly degraded the fatigue performance. In both test environments the fatigue limit and fatigue lifetime decreased with increasing frequency. Specimens that achieved run-out were subjected to tensile tests to failure to characterize the retained tensile properties. The material retained 100% of its tensile strength, yet modulus loss up to 22% was observed. Composite microstructure, as well as damage and failure mechanisms were investigated.     

Monitoring the Condition of Non‐linear Packaging Materials Subject to Varying Excitation Levels Using a Reverse Multiple Input/Single Output Based Approach

During transportation, protective packaging is subjected to random dynamic compressive loads that arise from random vibrations generated by the vehicle. The ability of the protective packaging to withstand these dynamic compressive loads depends on the environmental vibration levels, the nominal stresses and the material's characteristics. Previous research has shown that cumulative damage, in the packaging system under random dynamic compression, will result in a change in the overall stiffness of the system. This change is manifested as a shift in the system's fundamental resonant frequency. Natural frequency estimates are often extracted using a least squares regression curve fit applied to an estimate of the system's frequency response function. Frequency response function estimates are generally obtained using the Fourier transform with a single input/single output (SISO). This approach is suitable for many applications; however, it is not well suited to non‐linear systems subjected to non‐stationary excitation where the vibration level (overall root‐mean‐square value) can vary. This paper investigates the use of an optimised reverse multiple input/single output algorithm for reliably tracking variations in the condition of packaging elements subjected to excitation with varying magnitude (root‐mean‐square). Results are presented from the analysis of physical experiments performed on expanded polystyrene cushions as well as empty corrugated paperboard containers. The experiments performed using the polystyrene samples were designed to limit natural variation in the system's natural frequency; whereas the paperboard samples were allowed to naturally damage under dynamic loading. Copyright © 2015 John Wiley & Sons, Ltd.     

Diameter-controlling growth of solid-cored carbon nanofibers on a pulse plated iron nanocrystalline substrate in flames

A novel process was introduced in this paper for the diameter-controlling synthesis of carbon nanofibers (CNFs) in the ethanol flames. The carbon nanofibers were grown on a nanocrystalline Fe layer, which was electro-deposited on a substrate using periodic reverse (P.R.) pulse plating. It was found that the quality of the plating nanocrystalline and the corresponding carbon nanofibers was related with two plating parameters: output pulse frequency (f) and duty cycle (r). In addition to that the straight and helical carbon nanofibers were selectively synthesized by addition of different additives in plating bath. In this paper, the base-growth mechanism of carbon nanofibers was clearly discussed.