Longitudinal Vibrations of a Single Pile in Saturated Viscoelastic Soil

Based on Biot's theory, the longitudinal vibrations of a single pile in saturated viscoelastic soil are investigated in the frequency domain subject to the harmonic load. By the Novak plane strain model, the control equations for the saturated viscoelastic soil are derived. Regarding the pile as the one-dimensional rod model, the vibration equation of the pile is established. Based on the continuity conditions of the pile and soil, the dynamic stiffness and dynamic damping of the pile top are obtained. It is compared with the solution for Novak, and the influence of different physical parameters of the pile and soil on the longitudinal vibrations of the soil and pile system is examined. It is shown that the dynamic characteristics of the pile in the dry soil as well as the saturated soil have some differences; the resonance effect of dynamic stiffness factor and equivalent damping is obvious weakening with the increase of the ratio of the length to radius of the pile. The resonance effect and natural frequency are increasing when the modulus ratio of the pile to soil increases; the interaction coefficient of the flow-solid and the damping ratio of soil skeleton have few influences on the responses.     

Vibration control of active constrained layer damping structure

A finite element dynamic model for plates with active constrained layer damping (ACLD) treatments is derived based on the constitutive equations of elastic, viscoelastic and piezoelectric materials by application of Hamilton principle. The closed loop control system considering displacement and velocity feedback of self sensing voltage from sensor layer is developed. The dynamic behaviors of active constrained layer damping (ACLD) plates including nature frequencies, loss factors and responses in frequency domain are investigated. The influence of control gains on vibration suppression is discussed. Numerical examples demonstrate the validity of the finite element model and the control strategy approach. The proposed control strategy can be widely used to structure vibration control with ACLD patches due to its simple scheme and easy implementation.     

Analysis on Dynamic Properties of Monolayer Cable Net for Point -supported Glass Facade

Monolayer cable net system for point - supported glass facade is a kind of flexible tension structures with relatively strong nonlinearity. Its stiffness greatly depends on the pretension in cables. Yet there are few literatures at present reported on its dynamic properties. The characteristic of modal analysis for flexible pre - stressed structures such as cable structures is expatiated herein. Corresponding program was developed to analyze two important factors such as pretension and geometric nonlinearity for dynamic behaviors of cable net herein. It is demonstrated that large errors are brought about by omitting nonlinearity. There exists apparent nonlinear relationship between vibration frequency and pretension in cables. The influence of pretension and geometric nonlinearity on the dynamic properties of cable net is in coordination with each other.     

Comparision of Theoritical Solutions and Ultimate Span-Length between FRP Cables and Steel Cables

As the self weight of cable affects mechanical behavior obviously with the inerease of span length.FRP (fiber reinforced polymer) cable that has the lighter weight than the conventional cables has advantage for long span structures.The analysis of single cable is the fundamental theory for the design of cable structures.Based on different considerations of gravity loads.the solutions of the single cable on gravity loads have three sets of solutions: parabola solution.catenary solution and elastic catenary solution.And the equations for the three sets of solutions are derived by taking the end tension force of cable as the control parameter.The comparison between FRP cables and steel cables is conducted by elastic catenary solution.and the results show that the lager span structure can be realized by FRP cables.The precision for the parabola solution and catenary solution is compared for stay cables and horizontal cables.and the proper ranges of both approximate methods are proposed.Based on the above methods.the ultimate span length of FRP cable and steel cable are analyzed.It is concluded that the ultimate span of FRP cable is 4.4 times larger than that of steel cable.     

Axial Response of Viscoelastic Pile-soil Coupling Interaction in Three-dimensional Inhomogeneous Soil

Considering the three-dimensional inhomogeneity of soil surrounding the pile, the response of non-uniform viscoelastic pile under axial dynamic loading is studied. Firstly, combining the boundary condition, the complex stiffness of axial different soil layers are obtained by the complex stiffness transfer model of radial multi-zone plane strain. Then, the analytical solution of dynamic response at pile top in frequency domain is proposed by solving the dynamic equation of non-uniform viscoelastic pile section one by one from the bottom up to the top, and the relevant semi-analytical solution response in time domain is adopted by the convolution theorem and the Inverse Fourier Transform. At last, the effect of parameters of pile and soil are investigated to get the nature of the dynamic response of pile top in frequency domain and time domain.     

Practical considerations for using a TDR cable tester

Time domain reflectometry (TDR) technology can be used to measure soil water content, but due to an incomplete understanding of this technology, some scientists are still reluctant to adopt it. The objectives of this paper are to discuss the basic principles of TDR to measure soil water content, to present the equations to convert TDR screen readings to soil water content values, and to describe a custom built TDR system. Commercial cable testers operate under the assumption the dielectric constant of the medium is known. For soils applications the dielectric constant varies with soil water content and is unknown. The equations which govern the TDR technology presented in logical order allow the user to understand the relationships between wave velocity, dielectric constant, and soil water content. The custom-built TDR system described here uses a commercially available cable tester; a balun transformer; shielded, two-wire transmission cable; and wave guides constructed from stainless steel welding rod. Several of these systems have been successfully used for six years.     

A static equilibrium method for tension identification of in-service cable

To identify the tension of in-service cable expediently and accurately, a cable tension identification method based on static testing measures is proposed by taking cable stress stiffening effect and principle of static equilibrium into account. According to the analysis on the process of cable tension identification and the key technique, a new compound clamp type with the soft metal lining is proposed. The rule of the contact distortion evolvement between the clamp and the cable is analyzed by dynamic nonlinear explicit analysis method, and the law of the friction change following the clamping force is studied. Thus, the reasonability and feasibility of this method is theoretically illuminated. The identified tension only depends on the displacement of load application point and the load force. The proposed method avoids the drawback of normal cable measuring methods where the measuring accuracy is greatly affected by cable boundary conditions and values of material parameters. The tension measured in the method is only related to the displacement of force point and the value of force. Therefore, it provides a new idea for cable tension identification of flexible cable.     

上覆分数阶粘弹性饱和场地土位移地震放大系数

考虑土体液相和固相的耦合作用,将基岩上覆场地土视为两相饱和多孔介质。为了考虑饱和场地土的粘弹性特性,其固相土骨架的应力应变关系利用分数阶Kelvin粘弹性模型来描述,建立了上覆分数阶粘弹性饱和场地土在简谐地震波作用下的运动控制方程。运用分数导数的性质并考虑上覆场地土的边界条件和透水性条件求解了上覆分数阶粘弹性场地土在简谐地震波作用下的振动问题,得到了饱和场地土的位移地震放大系数。采用数值算例分析讨论了分数导数的阶数、液固耦合系数、土体模型参数、基岩土体剪切模量比等参数对位移地震放大系数的影响。研究结果表明,分数导数的阶数、液固耦合系数、土体模型参数、基岩土体剪切模量比对饱和场地土的地震响应有较大的影响,通过压实场地土,可以达到增大液固耦合系数减小地震响应的作用,通过增大饱和场地土的粘性和剪切模量也可以减小地震反应。     

模式识别的斜拉桥损伤诊断动力指纹与识别算法

为有效并准确诊断出斜拉桥损伤,对基于模式识别的斜拉桥损伤诊断方法进行了研究。选取易于测试出的低阶模态频率和部分关键点竖向振型数据为动力指纹,无需模态扩展或模型缩聚。研究并采用全因子设计进行动力指纹库的创建,可精确评估设定的损伤因子及其交互作用对损伤识别结果的影响。设计并增加了带随机误差的动力指纹库样本集。编制了基于Matlab的模式识别的多种算法,重点研究了精确度高的多层感知器识别算法及其提高该算法预测准确率的装袋集成算法。最后给出一座单塔双跨双索面斜拉桥的多种识别算法的损伤诊断过程和结果,得到一种可包容测试随机误差的高精确度斜拉桥损伤诊断评估模型。     

The Non-Linear Finite Element Analysis of Cable Structures Based on Four-Node Isoparametric Curved Element

In this paper,based on the geometric nonlinear behavior of cable structures,a finite element method with four-node isoparametric element was presented,the third order polynomial was used as displacement functions and initial curve of the element.By means of the principle of virtual work and the updated Lagrangian method,the authors derived the finite element equations,and solved them by Newton-Raphson method.The proposed model leads to high precision and can meet the engineering requirements.The model presented in this paper can be applied in the analysis of long-span tension structures,such as cable structures,cable domes and so forth.     

The Analysis of Abnormal State for Power Distribution Network Based on MATLAB

Along with the extensive use of power cable lines in power distribution system, the probability of fundamental frequency resonance has greatly increased. It may endanger the security operation and power supply reliability of the power system. On the basis of theoretical analysis and numerical calculations using MATLAB language combined with a real instance, it is indicated that the improper electrical parameter coordination caused by the abundance of power cable lines result in fundamental frequency current resonance, in addition, the countermeasures based on SVC to solve the problem are put forward. Further more, digital simulations have been carried out in detail based on the dynamic simulation model developed by the application of MATLAB/Simulink and its power system simulation software. Simulation results proves the effectiveness and practicability of the scheme presented.     

Adaptive Filtering Algorithm to GPS/INS Integrated System

GPS/INS integrated systems are applied in the self-positioning of the high dynamic targets. This paper forms state equations and observation equations by the integrated system and GPS observation respectively. An adaptive filtering algorithm is introduced which estimates observation noise covariance with observation data, and estimates dynamic noise covariance by use of Sage-Husa filtering algorithm which has faster convergent speed and better stability than the conventional Kalman filtering algorithm. At last, simulations are given to verify the effectiveness of the algorithm.     

Mode-Superposition Method for Passive Energy Dissipation Structures

The methods of equivalent linearization of different energy dissipation devices are different in analyzing passive energy dissipation structure including different type of energy dissipation device by using of mode-superposition response spectrum method based on equivalent linearization, which results in the differences in computing accuracy and cost in dynamic analysis. For structures separately installed different energy dissipation devices, authors utilize relatively uncoupled mode-superposition method and complex mode-superposition method for contrast analysis, and probe into the suitability of the two methods in the dynamic analysis of passive energy dissipation structure. Numerical results show that complex mode-superposition method could be better for structure with viscous dampers in order to guarantee accuracy, and relatively uncoupled mode-superposition method is recommended for structure with viscoelastic, metallic or frictional ones.     

THE MATRIX METHOD FOR ESTABLISHING DISCRETE SYSTEM DYNAMIC EQUATIONS

In this paper a matrix method for establishing discrete system dynamic equations is presented. Using this method to establish discrete system dynamic equations, netting but the derivative of function, and matrix multiplication are required. This method suits to the holonomic system as well as the linear nonholomic system.     

Finite element model of coupled systems for vibration reduction plates with smart constrained layer damping

Considering the relationships of coupling movement and compatible displacement among bonding layer, piezoelectric layer, damping layer, and base structure, a finite element dynamic model of coupled systems for vibration reduction plates is established. The model combined with piezoelectric theory, finite element theory and ADF model of viscoelastic damping material can be suitable for vibration model of complex SCLD structure. The dynamics parameters for clamped-clamped steel plate with partially treated smart constrained layer damping are obtained by theoretical calculation, ANSYS modal analysis and modal experiment. The results show that theoretical values are closer to the test results and ANSYS analysis, and the methods proposed is more accurate and effective.     

ORTHOGONAL COLLOCATION METHOD AND IT APPLICAIONS IN THE CALCULATION OF DYNAMIC CHARACTERISTICS OF HEAT EXCHANGER

Being a kind of MWR, the orthogonal colloacation method can be conveniently used to reduce the initial-boundary value problems of the partial differential equations to initial value problems of ordinary differential equations. In this paper, the orthogonal collocation method is introduced in detail and by using it the dynamic characteristics of a steam-water heater are investigated.     

A POWER FLOW IN INFINITE VISCOELASTIC CYLINDRICAL SHELLS

In this paper, a solution of propagation wave in an. unconstrained damping viscoelastic cylindrical shells of infinte length under forced vibration is derived by Fourier integral transform techniques. The power flow transmitted along it is analysed. The power flow in an elastic cylindrical shell and that in a viscoelastic shell are compared. The effects of vibration reduction in two viscoelastic shells with different thickness are compared. The results provide a reference for designer in structural vibration reduction.     

Symplectic Methods of the Dynamic Equations of Constrained Multibody Systems

The differential-algebraic equation of the dynamic equations of constrained multibody system is a system of index three.It is a very difficult problem for solving. At present,there are no satisfactory numerical methods yet,we construct the symplectic composition Runger-Kutta methods for the differential-algebraic equations,and use mainly it for simulation in the canonical form of the equations.The results arebetter than Baumgarte's methods.     

Dynamic Analysis of Steel Plate Truss Composite Girder on Long Span Two layer Cable stayed Bridge

Based on the refined three dimensional modeling method, a coupled vibration FEA(finite element analysis) model was established for light railway train and long span two layer cable stayed bridge with the consideration of the material and geometry nonlinearity and over 2.2 million of element and nodes.To overcome the computing difficulty for large number of element, the solution was carried out with the Dawning 4000A supercomputer in Shanghai Supercomputer Center based on Contact Balance Bisection Algorithm for parallel computing.Through the simulation of one way and two way conditions, the key component's stress of cable stayed bridge girders and dynamic response of middle span section was respectively analyzed.     

A New Method to Measure Cable Force and Its Application in Cable Structures

In cable structures cables are very important components. The magnitude of cable pretensioning is a vital parameter in the design of cable structures and a crucial component in controlling the construction of such structures. Developing a new sensor type is an innovative theme in the monitoring and control of cable structures construction. Based on the elastic magnetic characteristics of ferromagnetic material, we introduce a theory of an elastic magnetic method to measure cable force and developed a new flux sensor. Applying this method in the model test of an hyperbolic cable net demonstrates that it can acquire the accurate cable force value conveniently. This study can provide scientific references for structural engineering.