悬索非线性动力学中的直接法与离散法

以悬索为例对结构非线性动力学中直接法与离散法的应用进行了研究. 针对悬索面内运动的第$n$阶模态的主共振，分别利用这两种方法对悬索的非线性响应进行求解，得到悬索非线性响应的二次近似解以及相应的幅频响应曲线，并比较和讨论了这两种方法得到的结果及其差异. 通过分析得知：离散法在用于非对称结构非线性动力学的求解时可能导致错误的结果.     

悬索在外激励作用下的1∶3内共振分析Ⅰ∶离散法

研究了悬索在受到外激励作用和考虑1∶3内共振情况下的两模态非线性响应。对于一定范围内的悬索弹性-几何参数而言,悬索第三阶面内对称模态的固有频率接近于第一阶面内对称模态的固有频率的3倍,从而导致1∶3内共振的存在。首先利用Galerkin方法把悬索的面内运动方程进行离散,然后利用多尺度法对离散的运动方程进行摄动,可得到两组不同主共振情况下的平均方程。     

Experimental Investigation of the Nonlinear Response of a Hanging Cable. Part I: Local Analysis

An experimental model of an elastic cable carrying eight concentrated masses and hanging at in-phase or out-of-phase vertically moving supports is considered. The system parameters are adjusted to approximately realize multiple 1:1 and 2:1 internal resonance conditions involving planar and nonplanar, symmetric and antisymmetric modes. Response measurements are made in various frequency ranges including meaningful external resonance conditions. A local analysis of the system response is made on the basis of numerous amplitude-frequency and amplitude-forcing plots obtained in different ranges of the control parameter space. Attention is mainly devoted to the detection of the main features of the regular motions exhibited by the system, and to the analysis of the relevant phenomena of nonlinear modal interaction, competition, and local bifurcation between planar and nonplanar regular responses. The resulting picture appears very rich and varied.     

Non-linear modal properties of non-shallow cables

A non-linear mechanical model of non-shallow linearly elastic suspended cables is employed to investigate the non-linear modal characteristics of the free planar motions. An asymptotic analysis of the equations of motion is carried out directly on the partial-differential equations overcoming the drawbacks of a discretization process. The direct asymptotic treatment delivers the approximation of the individual non-linear normal modes. General properties about the non-linearity of the in-plane modes of different type—geometric, elasto-static and elasto-dynamic—are unfolded. The spatial corrections to the considered linear mode shape caused by the quadratic geometric forces are investigated for modes belonging to the three mentioned classes. Moreover, the convergence of Galerkin reduced-order models is discussed and the influence of passive modes is highlighted.     

Verfahren und Meßanordnung zur kontinuierlichen,berührungslosen und zerstörungsfreien Durchmesserkontrolle strangförmiger Gebilde

Ein neuartiges Verfahren und eine Meβanordnung zu kontinuierlichen, berūhrungslosen und zerstörungsfreien Durchmesser-kontrolle werden beschrieben. Als Meβgut kommen strangförmige Gebilde, wie Kabel, Drāhte oder Rohre, in Betracht. Strahlenquelle und Detektor sind so angeordnet, daβwert ein Maβ für die Querschnittsflāche des Prüflings senkrecht zur Abzugsrichtung ist. Dadurch kann z. B. bei der Kabelfertigung der Ummantelungsprozeβ nicht nur fūr Leiter mit kreisförmigem Querschnitt, sondern auch für solche mit elliptischem oder kreissektorförmigen Querschnitt ūberwacht werden. Positions-änderungen des Meβgutes relativ zur Meβstrecke haben keinen Einfluβ auf den Meβwert. Mit dem beschriebenen Funktionsmuster können Durchmesseründerungen von 0,02 mm für Material mit kreisförmigem Querschnitt im Durchmesserberich 3 bis 20 mm nachgewiesen werden.     

An exact, closed-form solution for equilibrium of trveling, sagged, elastic cables under uniformly distributed loading

IntroctionThquilibrium of sagged, elastic cable s under its own weight loading is needed in tiledesign of cable structures. In 1851 RO'htsLll first investigated a uniform, inextensible suspendedchain hanging freely under its own weight. Ro.th[Zj considered a model of a heterogeneouschain hanging in the form of a cycloid, and application of this model to the uniform chainreduced to the Rohrs model when the sag ratio is small. However, the chain was modeled asinextensible. Pugsley['] develope…     

Dispersive Blow-Up Ⅱ.Schrdinger-Type Equations,Optical and Oceanic Rogue Waves

Addressed here is the occurrence of point singularities which owe to the focusing of short or long waves, a phenomenon labeled dispersive blow-up. The context of this investigation is linear and nonlinear, strongly dispersive equations or systems of equations. The present essay deals with linear and nonlinear Schrdinger equations, a class of fractional order Schrdinger equations and the linearized water wave equations, with and without surface tension. Commentary about how the results may bear upon the formation of rogue waves in fluid and optical environments is also included.     

高温超导强电应用研究进展与展望

评述了目前高温超导材料强电应用研究的进展,着重介绍了故障电流限制器(FCL)、输电电缆、变压器等热点项目,以及美国在军事方面的应用动向,对高温超导强电应用前景进行了展望。     

Electrical and magnetic characterization of hot-extruded BSCCO tape samples

Summary Ag/BSCCO-2223 phase tapes were prepared with a new plastic deformation cycle. Starting from the hot extrusion of composite billets, hundreds of metres of tape 0.15×3 mm were obtained by drawing and rolling the extruded bars. The cross-section, monofilamentary with a central Ag insert, is quite regular along all the length. Samples from 30 cm to 100 cm in length were heat-treated at different temperatures between 830°C and 480°C in Ar+10% O₂ atmosphere. Electrical-transport properties were tested at 77K.J _c of 3000 A/cm² were usually achieved after first heat treatment. The superconducting properties were also tested by magnetic measurements using a vibrating sample magnetometer. Paper presented at the ?VII Congresso SATT?, Torino, 4–7 October 1994.     

Transport properties of long monofilamentary Bi(2223) tapes

Summary Monofilamentary Bi(2223) tapes withJ _c(77 K, 0 tesla) up to 30 000 A/cm² have been prepared by cold rolling using the powder-in-tube method. An optimization of the precursor powders has led to a higher phase purity after the reaction heat treatment. The deformation process has been optimized in order to increase the oxide density and to reduce sausaging effects on the oxide thickness. The transport properties of these tapes have been studied in a wide range of temperature (4.2K-T _c) and magnetic fields (up to 28 tesla). The critical-current values at 77 K fields of 0.5 T and 1 T parallel to the tape surface are 10 000 A/cm² and 5400 A/cm², respectively. At 4.2 K theJ _c value decreases from 1.6·10⁵ A/cm² at 0 T to 6·10⁴ A/cm² at 15 T. At fields higher than 15 tesla a very low field dependence ofJ _c has been found, regardless of the tape orientation. Transport properties have also been studied by cutting small sections of the tape in order to investigate the local critical-current distribution. It has been found that, even in rolled tapes of good quality (J _c (77 K, 0 T)>20000 A/cm²), theJ _c distribution is homogeneous: the critical current density increases gradually from the centre of the tape to the sides, the latter exhibiting much higherJ _c (46000 A/cm²) than in the centre (18000 A/cm²). Paper presented at the ?VII Congresso SATT?, Torino, 4–7 October 1994.