The use of alternating currents for submarine marine cable transmission

This paper contains the results of experiments performed by members of the Signal Corps Research Laboratory, Bureau of Standards, in an attempt to develop a method or methods of signal transmission over submarine cables which would permit of a more effective use of existing cable systems.In the method proposed and developed, signals are transmitted by means of alternating currents simultaneously with the normal battery of direct-current operation of the cable. Currents of several different frequencies may be used, reserving a given frequency for each message, and by tuning or equivalent methods at the receiving end these messages may be separated, so that the simultaneous transmission of a number of messages is redered possible.Accurate determination of the fundamental physical properties of a particular cable for different frequencies has been accompalished, and the results are given herewith. From these physical properties accurate calculations for any length of cable can be made, so that the design of proper apparatus becomes purely a laboratory problem.Actual trial of the proposed alternating-current method was made covering distances up to approximately 700 kilometres, with results which were in all cases completely satisfactory, indicating that the method is an entirely feasible one, and one which will render cables of this length, and undoubtedly of several times this length, much more useful.     

The impulse strength of solid and gas-filled high voltage cables

A method is presented that allows the computation of the impulse strength of insulating oil and of solid and gas-filled cables. The principle of the calculation is that breakdown is initiated by currents due to an electronic emission from the cathode; in gas-filled cables these currents are increased by means of gaseous ionization in the butt spaces. Approximate equations are deduced and numerical impulse strength values for insulating oil and solid cable computed, resulting in fair agreement with experimental observations. Extending the equations to gas-filled cables, numerical impulse data for varying gas pressure and for varying radial butt-space alignment are evaluated.     

复材飞机操纵钢索的设计与应用

文章在现有金属飞机钢索变形理论的基础上,对复材飞机操纵钢索的设计和应用进行了详细的论述。总结性地提出了软式钢索操纵的设计步骤,在已有钢索变形量计算理论的基础上,考虑热、结构、座舱增压等因素的影响,计算钢索变形量并确定了钢索初始张力的予加原则,并给出钢索张力示例曲线,为钢索张力维护和调节提供理论依据。     

Vibration control of a membrane antenna structure using cable actuators

This paper presents a control strategy of using cable actuators to control the vibration of a membrane antenna structure. The tension cables of the membrane antenna structure are used as actuators, the vibration of the structure can be suppressed by controlling the tension force in the cable actuators. First, the antenna structure with cable actuators is discretized by the finite element method (FEM), and governing equation of the whole structure is established. Then, a controller is designed based on the Lyapunov's stability theory, and the mechanism of this controller is studied through a simple single-degree-of-freedom (SDOF) system. The optimal placement of the cable actuators is also studied numerically in this paper. Simulation results indicate that vibration of the membrane antenna structure can be suppressed effectively by the cable actuators, and optimally placed cable actuators can produce better control effect with smaller control input.     

斜拉桥主梁钢锚箱定位测量与精度分析

斜拉桥混凝土主梁庞大的重量都是通过斜拉索与钢锚箱将力传递到索塔上,作为传力载体和对斜拉索线型起控制作用的钢锚箱的定位精度成为直接影响斜拉桥的内力分布、成桥线型的重要因素。如何有效地考虑这些不利的影响因素成为保证斜拉桥梁上钢锚箱定位精度的关键所在。     

电力电缆应用中的问题及防范措施

目前电力电缆已被广泛应用,如何避免电缆在运行中发生问题,确保系统安全可靠运行,是需要探究的问题。本文通过对近年来发生的电力电缆问题进行分析,找出了主要原因,并提出相应的防范对策。     

对解决电缆中间头冷缩工艺遗留问题之浅见

在电力电缆抢修的工作中,高压电缆的中间头制作的优劣与整条电缆线路的运行情况息息相关,日趋成熟的热缩工艺在工作环境要求不允许动火的工作情况中便不能满足需求,冷缩工艺虽然可以克服这种工作环境的要求,却存在一些材料方面的问题,通过一系列的物理措施可使这些缺陷减少到最低。     

Maximum entropy method spectral estimation applied to power cable diagnostics via cepstrum processing

The Cepstrum processing method has been used on power cables (1, 2) for determining regions of damage. The method consists of: (1) observing the spectrum of an original broad band signal source, (2) introducing the signal into the cable, (3) computing the change in the observed spectrum (as a result of echos from regions of cable non-uniformity) when the signal is injected into the cable, and finally (4) computing the power-spectrum of the change in observed spectrum. A limitation of this technique is the use of band-limiting spectrum analyzers. Their limited bandwidth reduces range resolution estimation when used with the Fast Fourier Transform (FFT) technique. The maximum entropy method (MEM) is a more useful spectral estimator for this measurement technique. Examples are presented which show a comparison of the FFT and MEM techniques applied to practical cables.     

预应力索杆结构的施工张力偏差分析

本文基于索长误差的概率分布模型,分析预应力索杆结构施工张拉的初始预应力偏差。首先讨论了索长误差的随机数学模型,建立了一种关于预应力索杆结构索长误差效应的计算方法。其次以实际工程为算例,考察不同的索长误差对结构初始预应力的影响,并比较不同的施工张拉方案对于减小索长误差影响的效果。分析结果表明,合理的张拉方案能有效减小结构的初始张力偏差。     

电力电缆故障测寻定位方法的探

根据高低压电缆检修、运行中处理故障的经验,介绍了目前国内外电缆故障测寻定位的原理、方法、应用及改进意见。     

浅析TAIC、BIPB在橡胶电缆中的应用

文章介绍橡套电缆绝缘胶和护套胶使用三烯丙基异三聚氰酸酯(TAIC)和双叔丁基过氧化二异丙基苯(BIPB)作硫化体系的原因,以及在橡套电缆中的具体应用实例,并阐述在使用过程中应注意的事项。     

Energy conversion in biological systems—part I. chemical reactions and ion transport

Constitutive equations for nonisothermal chemical reactions are derived with attention to temperature dependent parameters. Equations are also developed for the coupling of chemical reactions to ion transport. The equations are shown to be consistent with the laws of thermodynamics.     

Dynamics of the shell class of tensegrity structures

A tensegrity structure is a special truss structure in a stable equilibrium, with selected members designated for only tension loading, and the members in tension form a continuous network of cables separated by a set of compressive members. This paper develops an explicit analytical model of the nonlinear dynamics of a large class of tensegrity structures, constructed of rigid rods connected by a continuous network of elastic cables. The kinematics are described by positions and velocities of the ends of the rigid rods, hence, the use of angular velocities of each rod is avoided. The model yields an analytical expression for accelerations of all rods, making the model efficient for simulation, since the update and inversion of a nonlinear mass matrix is not required. The model is intended for shape control and design of deployable structures. Indeed, the explicit analytical expressions are provided herein for the study of stable equilibria and controllability, but the control issues are not treated in this paper.     

Alternative derivation of equations of motion

Equations of motion in the form of sets of non-linear differential equations are derived for dynamic systems which may exhibit simultaneous changes in their electrical, fluid, mechanical and thermal states. These equations are based on considerations of the physics of components and their eventual topology when forming an assembly. The effect of thermal environment is shown when its capacity is finite and when it is not.     

多功能远程路灯控制装置的设计与实现

路灯是城市建设中重要的公用设施,是城市形象的重要标志。随着社会的不断发展,我国城市路灯照明系统随着城市的发展而不断扩大。由于路灯分布范围广,人工管理落后,造成路灯故障率高,路灯电缆被盗严重等问题日益突出,造成严重社会影响。传统的路灯照明系统的控制方式存在效率低、成本高、无法监控等问题,已经无法满足现代化城市的需要。因此,研制一套功能完备的路灯控制系统具有非常重要意义。文章描述的路灯控制装置能通过GSM通信的方式,远程控制路灯和实时上传电能参数,具有电缆防盗和故障路灯定位等功能。     

小垂度单根悬索方程的改进

推导了小垂度单根悬索在纵向均布荷载和横向线性分布荷载作用下的悬索公式，获得了一个解析的更为精确的单索方程．并通过实例计算与传统方程进行了对比，指出了这一改进方程在理论上和实践上的双重意义。     

收缩徐变对砼斜拉桥索力和主梁标高的影响

收缩徐变是混凝土材料固有的时变特性,会导致混凝土结构受力与变形随着时间的变化而变化。斜拉桥属于高次超静定结构,其受力和变形受收缩徐变的影响更加明显,本文为了研究收缩徐变对这种复杂超静定结构受力和变形的影响,以某双塔单索面混凝土斜拉桥的某一施工阶段为例,通过理论计算和实际监测,研究分析了在某一挂篮移动阶段,混泥土收缩徐变在短时间范围内对拉索索力及主梁标高的影响。研究结果表明,收缩徐变的影响不可忽略。     

Nonlinear dynamic modeling and responses of a cable dragged flexible spacecraft

The space debris removal system (SDRS) of tethered space tug is modelled as a cable dragged flexible spacecraft. The main goal of this paper is to develop a dynamic modeling approach for mode characteristics analysis and forced vibration analysis of the planar motion of a cable dragged flexible spacecraft. Solar arrays of the spacecraft are modelled as multi-beams connected by joints with additional rotating spring where the nonlinear stiffness, damping and friction are considered. Using the Global mode method (GMM), a novel analytical and low-dimensional nonlinear dynamic model is developed for vibration analysis of SDRS to enhance the design capacity for better fulfillment of space tasks. The linear and nonlinear partial differential equations that governing transverse vibration of solar arrays, transverse and longitudinal vibrations of cable are derived, along with the matching and boundary conditions. The natural frequencies and analytical global mode shapes of SDRS are determined, and orthogonality relations of the global mode shapes are established. Dynamical equations of the system are truncated to a set of ordinary differential equations with multiple-DOF. The validity of the method is verified by comparing the natural frequencies obtained from the characteristic equation with those obtained from FEM. Interesting mode localization and mode shift phenomena are observed in mode analysis. Dynamic responses of the system excitated by fluctuation of attitude control torque and short-time attitude control torque are worked out, respectively. Nonlinear behaviors are observed such as hardening, jump and super-harmonic resonances. Residual vibration of the overall system with considering the varous values of nonlinear stiffness, damping coefficient and friction coefficient has shown that the nonlinearity of joints has a great influence on the vibration of the overall system.     

国际金属价格指数、广义需求与中国稀土产品价格

本文采用月度数据考察国际金属价格是否影响我国稀土产品价格及其程度、机制问题,采用VEC模型得出10种稀土产品价格与国际金属价格具有整合关系。在存在整合关系下,从需求角度出发,引入了多需求变量指标,在控制了其他影响因素的情况下证实国际金属价格指数对国内某些稀土产品价格经济意义具有显著性,且这些稀土产品价格对国际金属价格指数表现出了富有弹性的特征。文章进一步研究22种中国轻、重稀土产品价格影响因素及作用机制,结论表明,我国目前仅对稀土初级产品具有有限价格控制能力,而应用于高科技、战略军事领域的稀土产品价格更多地受控于国际市场需求影响;同时定量研究还发现,我国稀土产品价格波动与投机、投资需求密不可分。该结论为进一步的稀土产业布局指明了方向、为加速稀土期货市场的建立提供了理论依据。     

Circular Plate on Multipoint Supports

Formulae are derived for the deflection surface of a symmetrically loaded circular plate having several points supports which are situated at equal distances apart on a single concentric circle. There is no restriction on the diameter of the support circle, which may be as large as the diameter of the plate itself. The results of this paper compare favorably with published experimental results. Numerical deflection coefficients for a uniformly loaded plate are provided, and these could be utilized for optimizing the positions and the number of concentrated supports.