Power flow analysis for a floating sandwich raft isolation system using a higher-order theory

A higher-order sandwich theory is implemented in conjunction with an equivalent mobility-based power flow progressive method to determine power flow for a sandwich configured floating raft vibration isolation system. The power spectrum changes in whole frequency range effectively when core materials’ properties change. It is also shown that the loss factors of the sandwich configured floating raft influence the power flow transmitted to the foundation effectively in the medium- to high-frequency range and that the resonant peak cannot be avoided by increasing damping only in high-frequency ranges which is not found in floating raft isolation systems with isotropic beams.     

Power flow in the coupled dynamic system of machinery and building floor

I.IntroductinnWithmoreandmoremulthetoreyworkshopsandmultifunctinnaltallbuildingsarebeingconstructednowadays,thereshowsanincreasingtrendformachinesandequlpmentstobemoulltedonupperlloors.Inthesituationofmachinesrunningonupperfloors,thetraditionaltheoryisnotValidbecausetheflooritselfisaflewhlestructure.Therefore,itisinagreatdemandtostudyonthedynaInicillteractionofmachinescoupledwithflekiblefoundationsalldtoproposearesonableandeffectiveapproachtocontrolvibrationandtosuppressnoise.Formachineryonu…     

Direct energy flow measurement in magneto-sensitive vibration isolator systems

The effectiveness of highly nonlinear, frequency, amplitude and magnetic field dependent magneto-sensitive natural rubber components applied in a vibration isolation system is experimentally investigated by measuring the energy flow into the foundation. The energy flow, including both force and velocity of the foundation, is a suitable measure of the effectiveness of a real vibration isolation system where the foundation is not perfectly rigid. The vibration isolation system in this study consists of a solid aluminium mass supported on four magneto-sensitive rubber components and is excited by an electro-dynamic shaker while applying various excitation signals, amplitudes and positions in the frequency range of 20–200 Hz and using magneto-sensitive components at zero-field and at magnetic saturation. The energy flow through the magneto-sensitive rubber isolators is directly measured by inserting a force transducer below each isolator and an accelerometer on the foundation close to each isolator. This investigation provides novel practical insights into the potential of using magneto-sensitive material isolators in noise and vibration control, including their advantages compared to traditional vibration isolators. Finally, nonlinear features of magneto-sensitive components are experimentally verified.     

Power flow and energy distribution in conservatively or non-conservatively coupled oscillators under correlative excitations

As a foundation of SEA for consevatively or non-conservativelycoupled systems under correlative excitations,power flow and energy distribu-tion in two coupled osillators under proportionally correlative excitations arestudied mainly in this paper.Theoretical relationship among power flow andtime averaged vibational energy of the osillators,as well as power balance equa-tions and energy ratio or them,are derived.Further along,power flow,energydistribution and power balance equations of the systems in conservative ornon-conservative coupling and under proportional correlative excitations arediscussed in detail,with comparing with characteristics of those innon-correlative excitations.Numerical resu1ts supporting the basic theory aregiven,too.Results show that the power flow and energy distribution of theosillators under correlative excitations,either conservative or non-conservativecoupling,are much different to those in the condition of non-correlativeexcitations.     

磁绝缘电压叠加器功率流的电路计算方法

以已建成的10级直线变压器驱动源系统为依托,以传输线计算方法为基础,通过引入空间电荷限制流和磁绝缘流阻抗模型,对感应电压叠加(IVA)真空功率流的电路计算方法进行了探索,开发了包含磁绝缘过程的全电路计算程序,提供了一种快速评估该IVA系统真空功率流的方法。计算结果表明:对磁绝缘状态下流阻抗的描述是该方法准确计算的关键;解决好算法的数值稳定性,避免数值振荡的发生,是将这一方法推广应用的重要前提。     

高功率脉冲光隔离器非线性及热效应分析

从理论上分析了脉冲情况下,磁光晶体横向温度梯度引起的光弹效应、消光比以及克尔效应对光隔离器隔离度的影响,并与连续入射情况进行了对比。结果表明:在平均功率相同的情况下,脉冲光束入射比连续光束入射情况隔离度更低;当平均功率较小时,消光比对隔离度的影响较大;当平均功率较大时,消光比对隔离度的影响有限,主要表现出光弹效应对隔离度的影响;当峰值功率密度较大时,克尔效应将显著降低隔离度,并且峰值功率密度越大,对隔离度的降低程度越大。     

全光纤瓦级纳秒脉冲掺Yb放大器

采用单模放大和包层抽运放大的级联方式,在主振荡功率放大系统中,将平均功率0.5 mW、脉宽20 ns以及重复频率为50 kHz的光脉冲安全放大到平均功率0.6 W、峰值功率600 W的脉冲输出.相应增益为30.8 dB.放大输出的脉冲信号信噪比为30 dB,脉冲形状基本没有发生畸变.在前置放大结构中抽运光通过级联熔融拉锥型波分复用器耦合,有效确保了抽运源(976 nm)的正常工作.     

全光纤瓦级纳秒脉冲掺Yb放大器

采用单模放大和包层抽运放大的级联方式,在主振荡功率放大系统中,将平均功率0.5 mW、脉宽20 ns以及重复频率为50 kHz的光脉冲安全放大到平均功率0.6 W、峰值功率600 W的脉冲输出.相应增益为30.8 dB.放大输出的脉冲信号信噪比为30 dB,脉冲形状基本没有发生畸变.在前置放大结构中抽运光通过级联熔融拉锥型波分复用器耦合,有效确保了抽运源(976 nm)的正常工作.     

高功率隔离器热致退偏分析与补偿设计

针对磁光晶体在大功率光隔离器中的应用,结合实际光学元件参数,利用琼斯矩阵分析了隔离度与入射光功率间的关系。提出基于外置材料,对磁光晶体热致退偏效应的补偿方案:针对两种不同的常见补偿材料,给出了它们的设计参数,并对两种材料的补偿效果进行对比。结果表明,在50 W的光功率下,利用CaF2晶体和SiO2,可分别提高隔离度约15dB和4dB。     

A study of power transmissibility for the vibration isolation of coherent vibratory machines on the floor of a building

Vibration isolation is commonly adopted by engineers to reduce the vibratory effect caused by building services equipment. However, the relationship between the amount of sound power transmitted to the floor and the interaction between the mounting points of several machines is uncertain, as it is common to install several coherent machines on the same floor, for example, two water pumps of the same type in a plant room. We conduct an analytical study of the effects of the interaction between two coherent vibratory sources on the power transmitted to the floor. The study is based on two simple vibratory sources with a single contact point, two rectangular machine models of even-mass distribution with four symmetrical supports and the calculated mobilities of a simply supported concrete floor. We find that the total power obtained from coherent sources (point sources or machine models) differs considerably from that obtained from independent sources at some frequencies in a vibration isolation region. To predict the performance of isolators more accurately, the power transmissibility method proposed previously by Mak and Su should consider not only the effect of effective floor mobility and the interactions of the mounting points of the same sources, but also the interactions of the mounting points of different sources on the floor.     

Analysis of cascading failure in electric grid based on power flow entropy

Large-scale blackouts are an intrinsic drawback of electric power transmission grids. Here we propose a concept of power flow entropy to quantify the overall heterogeneity of load distribution and then investigate the relationship between the power flow entropy and cascading failure. Simulation results, from the small-world 300-node test system and the IEEE 300-bus system, show that the power flow entropy has close relations with the cascading failure in terms of both the dynamic propagation course and the static blackout size. Particularly, at the early stage of failure spreading the potential large blackout can be identified according to the power flow entropy. The power flow entropy can serve as an index not only for long-term planning, but also for short-term operational defense to large-scale blackouts.     

紧凑型矩形波导内功率合成器设计

介绍了一种基于常规速调管功率合成和脉冲压缩的微波源系统,为实现多路高峰值功率速调管的功率合成,设计了一种紧凑型、近平面结构的微波功率合成器。在2.856 GHz频点处,合成器各端口反射损耗和相对端口隔离度均大于45 dB。当两路峰值功率为50 MW的微波功率合成时,合成器内的最大场强约为9.6 MV/m,合成效率大于99%。在四端口功率合成器的基础上,通过两级合成可实现一种八端口微波功率合成器,当四路峰值功率50 MW的微波功率合成时,合成器内最大场强约为13.5 MV/m。     

Free vibrations of an infinite plate of parabolically varying thickness on elastic foundation

A simple model is presented for use by research workers in seismology, soil mechanics and earthquake vibrations in problems where the resistance offered by the soil foundation is very close to that of Winkler's assumption. In earth vibrations one earth layer can be treated as an infinite plate of variable thickness while layers below it may approximately serve as an elastic foundation. Here, the transverse displacement of a plate of parabolically varying thickness on an elastic foundation is expressed as a power series and the frequencies, deflections and moments corresponding to the first two modes of vibration are computed for various values of foundation modulus and taper constant, and for two combinations of boundary conditions. A problem discussed in previous work [1] can be considered as a particular case of the present problem if the foundation modulus is taken to be zero.     

The inertial dynamics of thin film flow of non-Newtonian fluids

Consider the flow of a thin layer of non-Newtonian fluid over a solid surface. I model the case where the viscosity depends nonlinearly on the shear-rate; power law fluids are an important example, but the analysis here is for general nonlinear dependence. The modelling allows for large changes in film thickness provided the changes occur over a relatively large enough lateral length scale. Modifying the surface boundary condition for tangential stress forms an accessible foundation for the analysis where flow with constant shear is a neutral critical mode, in addition to a mode representing conservation of fluid. Perturbatively removing the modification then constructs a model for the coupled dynamics of the fluid depth and the lateral momentum. For example, the results model the dynamics of gravity currents of non-Newtonian fluids when the flow is not creeping.     

热耦合型二级高频脉冲管制冷机实验研究

降低制冷温度至4 K温区是高频脉冲管制冷机的最新发展要求。本文介绍了一套热耦合型二级高频脉冲管制冷机的性能特性,它可以达到低于15 K以下的最低温度,是目前报道的高频二级脉冲管制冷机能获得的最低温度．通过对制冷机一级预冷、二级输入功率、二级冷量、室温条件等影响的分析,从实验角度揭示了该二级制冷系统的复杂影响,为进一步的深入分析和改进提供了基础。     

Research on performance indices of vibration isolation system

Power flow transmissibility is proposed as a performance index to evaluate the performance of isolation system. It is defined as the ratio of the power flow input into the equipment and the power flow transmitted into the receiver. Based on a simple vibration isolation system, its relationship with other performance indices is given by theoretical and numerical analysis. The results show that power flow transmissibility can reflect the response characteristics of the whole isolation system effectively. In addition, power flow transmissibility can be estimated easily according to vibration acceleration level difference and does not involve the measurement of power flow. Furthermore, the influences of several parameters such as the damping, loss factor and stiffness of isolator on power flow transmissibility are analyzed.     

Design of a Broadband E-Plane Power Combiner Based on Quarter-Arc Bent Rectangular Waveguides for Sub-THz and THz Wave

A method of designing an E-plane power combiner composed of two quarter-arc bent rectangular waveguides is proposed for sub-THz and THz waves.The quarter-arc bent-waveguide power combiner has a simple geometry which is easy to design and fabricate.By HFSS codes,the physical mechanism and performance of the power combiner are analyzed,and the relationship between the output characteristics and the structure/operating parameters is given.Simulation results show that our power combiner is suitable for the combining of two equalpower and reversed-phase signals,the bandwidth of the combiner is wide and can be adjusted by the radius of the quarter-arc,and the isolation performance of the combiner can be improved by adding thin film resistive septa at the junction of two quarter-arc bent waveguides.Meanwhile,an approximate method based on the analytic geometrical analysis is given to design this power combiner for different frequency bands.     

Shock isolation using an isolator with switchable stiffness

A semi-active control strategy is presented for the shock isolation of resiliently mounted equipment where the isolator has light damping. This is achieved by switching the stiffness of the isolator between a high-state and a low-state. The control strategy involves two stages: the first stage involves the displacement control of the equipment during the shock, and the second stage involves suppression of the subsequent residual vibrations. The performance of the switchable isolation system is illustrated using a base-excited single degree-of-freedom system. It is characterized in terms of the maximum absolute acceleration and displacement of the isolated mass, the relative displacement between the base and the mass, and the effective damping ratio of the system. Provided that the damping in the isolator is light, it is found that the semi-active system can outperform a linear passive system during both stages of control.     

Fiber Bragg grating-based self-referencing technique for wavelength-multiplexed intensity sensors

An amplitude-phase-conversion self-referencing technique for intensity-modulated photonic sensors that uses two different-wavelength fiber Bragg gratings is presented. With this technique, the system response has been demonstrated to be almost unafffected by network power variations as high as 90% of the total power launched by the source. We prove the multiplexing capability of this type of self-referenced fiber sensor by wavelength-division multiplexing two of them in a star network. A tunable fused biconical wavelength-division multiplexer is used for sensor addressing at the detection block, providing both good isolation and low cross-talk values.     

高功率光隔离器永磁系统的理论研究与优化

基于Halbach阵列永磁体的特点以及光隔离器对磁场的需求,设计了两种适用于高功率隔离器的永磁系统,分析了其磁场分布、磁场非均匀性对隔离度的影响,研究了磁体装配误差对磁场的影响。研究结果表明:通过引入斜向磁化永磁体,选择合适的磁化角度和磁体长度,可以提高永磁体的磁场强度,大幅度减小旋转器所需磁光晶体长度;受磁场非均匀性影响的隔离度与磁光晶体的孔径、长度以及入射激光的光斑半径有关,当晶体长度一定时,减小晶体半径和入射光的半径可以显著提高隔离度。在入射光半径为1.5mm、磁光晶体半径5mm时,对应的隔离度分别为105.8dB和45.4dB。