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1.
A control method is presented for reducing the dynamic response of structures in the inelastic material range using a control force from an active bracing system. Recent full-scale experiments have verified the feasibility of implementing active control systems for control of seismic structures with existing technology. The proposed method of continuous pulse control uses closed-loop feedback control as a combination of two algorithms. The first is the instantaneous optimal algorithm which was derived assuming linear material behaviour, and the second is pulse control which applies a corrective pulse when a prespecified structural displacement, velocity, or acceleration threshold is exceeded. The three criteria of displacement, velocity, and acceleration lead to three pulse control schemes. Each of the three schemes is used in conjunction with the instantaneous optimal control to yield three continuous pulse algorithms, the displacement continuous pulse, velocity continuous pulse and acceleration continuous pulse. Comparisons between the three continuous pulse algorithms and the pulse control for seismic structures in the inelastic range show that the continuous pulse algorithms use less control energy and reduce the response better than pulse control. A comparison between the velocity continuous pulse and the non-linear optimal algorithm shows that the velocity continuous pulse uses a larger control force but is more adaptable than the non-linear optimal algorithm, in the sense that it can reduce the response of a given structure to various probable earthquakes. The non-linear optimal algorithm is more effective than the velocity continuous pulse for a single specific earthquake but is not as effective for other earthquakes which may occur in the life of the structure.  相似文献   

2.
A non-parametric identification technique is presented for chain-like multidegree-of-freedom non-linear dynamic systems. The method uses information about the state variables of non-linear systems to express the system characteristics in terms of two-dimensional orthogonal functions. The technique is applied to a model of a steel frame that has been extensively investigated both analytically and experimentally. The method can be used with deterministic or random excitation to identify dynamic systems with arbitrary non-linearities, including those with hysteretic characteristics. It is also shown that the method is easy to implement and needs much less computer time and storage requirements compared to the Wiener-kernel approach. The method is shown to have low sensitivity to the effects of additive noise in the experimental data.  相似文献   

3.
Modeling of surface water quality based on a deductive approach is highly non-linear, varies with time, is spatially distributed and is difficult to incorporate as part of decision-support systems. A Neural Networks (NNs) procedure provides a reliable analysis in several science and technology fields. NNs are often applied to develop statistical models for intrinsically non-linear systems. In this investigation, NNs are used in the induction of a water quality model from available field measurements for the Bahr Hadus drain in the Eastern Egyptian Delta. Two models, namely, feed-forward back propagation (BP) and cascade correlation (CC), were used. It is concluded that the CCNN model produced slightly more accurate results and learned very quickly compared with the BP procedure. The results indicated that the NNs model could be used as a non-linear dynamic system model to encapsulate site-specific knowledge and emulate the temporal sequence of one-dimensional flow systems. This NNs model undoubtedly will reduce the cost and save time in this class of problems.  相似文献   

4.
The time-integration algorithm is an indispensable element to determine response of the boundary of the numerical as well as physical parts in a hybrid test. Instability of the time-integration algorithm may directly lead to failure of the test, so stability of an integration algorithm is particularly important for hybrid testing. The explicit algorithms are very popular in hybrid testing, because iteration is not needed. Many unconditionally stable explicit-algorithms have been proposed for hybrid testing. However, the stability analysis approaches used in all these methods are valid only for linear systems. In this paper, a uniform formulation for energy-consistent time integrations, which are unconditionally stable, is proposed for nonlinear systems. The solvability and accuracy are analyzed for typical energy-consistent algorithms. Some numerical examples and the results of a hybrid test are provided to validate the effectiveness of energy-consistent algorithms.  相似文献   

5.
IINTRODUCTIONIntherecentdecadesfrequentflooddisasterscausedseriousdamagesandclaimedthousandsoflives,suchasthe1998floodintheYangtzeRiverandthe1996floodintheYellowRiver.The1998floodintheYangtzeandtheSonghuaRiversbroughtdirectlossesofmorethan$30billions.Lowdischargehighstageisthemaincharacterofthefloods.Forexample,thehighestfloodstagein1998wasI.sinhigheranddischargewas14000m3/slowerthanthosein1954atLuoshanStationoftheVangtzeRiver.Anewmodelisrequiredtobedevelopedforaccuratepredictionoffl…  相似文献   

6.
A finite element procedure to model the non-linear earthquake response of concrete gravity dam systems is presented. A two-dimensional idealization is adopted for the dam and water in order to simplify the analysis and reduce the computational effort. The foundation of the dam is modelled as a rigid rectangular massless plate attached to a three-dimensional viscoelastic half-space. The non-linear behaviour is represented by smearing techniques and includes tensile cracking with subsequent opening, closing and sliding, as well as water cavitation in the reservoir. Special treatments are applied to suppress spurious oscillations in the water response associated with cavitation and to prevent cracks in the dam from spreading into wide zones. Experience from non-linear analyses is cited as it affects the design of the algorithm.  相似文献   

7.
A modal procedure for non-linear analysis of multistorey structures with high-damping base-isolation systems was proposed. Two different isolation devices were considered in the analysis: an high-damping laminated rubber bearing and a lead-rubber bearing. Starting from deformational properties verified by tests, the isolation systems were characterized using three different analytical models (an Elastic Viscous, a Bilinear Hysteretic and a Wen's Model) with parameters depending from maximum lateral strain. After non-linear modelling of isolation and lateral-force-resisting systems, the effects of material non-linearities were considered as pseudo-forces applied to the equivalent linear system (Pseudo-Force Method) and the formally linearized equations of motion were uncoupled by the transformation defined by the complex mode shapes. The modal responses were finally obtained with an extension of Nigam–Jennings technique to non-linear and non-classically damped systems, in conjunction with an iterative technique searching for non-linear contributions satisfying equations of motion and constitutive laws. Since the properties of the isolated structure usually change with maximun lateral strain of isolation bearings, the integration of a new set of governing equations was required for each design-displacement value. The procedure proposed was described in detail and then applied for the determination of modal and total seismic responses in some real cases. At first, a very good agreement between non-linear responses obtained with the proposed mode superposition and with a direct integration method was observed. Then a comparison of results obtained with the three different analytical models of the isolation bearings was carried out. At last, the exact modal response obtained with analytical models depending from the design displacement of the isolation bearings was compared with two different approximated solutions, evaluated using mode shapes and isolation properties, respectively, calculated under simplified hypothesis.© 1998 John Wiley & Sons, Ltd.  相似文献   

8.
The dynamic analysis of complex non-linear structural systems by the finite element approach requires the use of time-step algorithms for solving the equations of motion in the time domain. Both an implicit and an explicit version of such a time-step algorithm, called the ρ-method, the parameter ρ being used for controlling numerical damping in the higher modes, are presented in this paper. For the implicit family of algorithms unconditional stability, consistency, convergence, accuracy and overshoot properties are first discussed and proved. On the basis of the algorithmic damping ratio (dissipation) and period elongation (dispersion) the ρ-method is then compared with the well-known implicit algorithms of Hilber, Newmark, Wilson, Park and Houbolt. An explicit version of the algorithm is also derived and briefly discussed. This shows numerical properties similar to the central difference method. Both versions of the algorithm have been implemented in a general purpose computer program which has been often used for both numerical tests and practical applications.  相似文献   

9.
An approximate procedure is introduced to analyse non-linear multistorey structures within the framework of the conventional response spectrum method. Its derivation is based on the use of non-linear response spectra and an approximate decomposition of the equation of motion for multi-degree-of-freedom non-linear systems. The decomposition is attained by considering the non-linear terms in this equation of motion as additional external forces and, thus, by interpreting it as the equation of motion of linear systems with the initial properties of the non-linear ones when subjected to a modified set of inertia forces. For simplicity, the procedure is herein limited to elastoplastic systems of the shear-beam type. Its accuracy is evaluated by comparing the approximate and step-by-step integration solutions of systems with three and ten degrees of freedom when subjected to three different earthquake ground motions.  相似文献   

10.
A new family of generalized‐α (G‐α) algorithm without overshoot is presented by introducing seven free parameters into the single‐step three‐stage formulation for solution of structural dynamic problems. It is proved through finite difference analysis that these algorithms are unconditionally stable, second‐order accurate and numerical dissipation controllable. The comparison of the new G‐α algorithms with the commonly used G‐α algorithms shows that the newly developed algorithms have the advantage of eliminating the overshooting characteristics exhibited by the commonly used algorithms while their excellent property of dissipation is preserved. The numerical simulation results obtained using a single‐degree‐of‐freedom system and a two‐degree‐of‐freedom system to represent the character of typical large systems coincide well with the results of theoretical analyses. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

11.
Sequences of magnetostatic equilibria can often be used to model the quasi-static pre-eruptive energy storage phase of eruptive phenomena in e.g. Earth's magnetosphere or the solar corona. During these phases the systems evolve only due to slow changes in their environment, being practically in equilibrium on large scales. The eruption onset would then be identified with a bifurcation or catastrophe point in the solution diagram. Different energy storage mechanisms can be studied by different parameterizations of e.g. the boundary conditions. Also from the more fundamental point-of-view of the theory of dynamical systems, studying the possible stationary states and the bifurcation properties of plasma systems should be the first step towards a more thorough understanding of their full dynamical behaviour. In any case one will have to solve highly non-linear partial differential equations with the possibility of the existence of multiple solutions (or of none at all) for a given set of boundary conditions. Such problems can, in general, only be solved numerically. The most appropriate class of numerical algorithms for this type of problem are continuation methods which can calculate complete solution branches and detect bifurcation points. In this work a numerical bifurcation code based on a continuation method is presented. In addition to solving the non-linear magnetohydrostatic equations, the code can check a sufficient linear stability criterion for each solution. Some preliminary results for simple magnetohydrostatic equilibria are presented and potential future applications are discussed.  相似文献   

12.
Viscoelastic (VE) dampers and active control (AC) systems are studied together as a hybrid system for their effectiveness in reducing the response of seismic structures. VE dampers have properties which are both frequency and temperature-dependent. On the other hand, AC systems for seismic structures require rather large control forces in order to be effective. The possibility of combining VE dampers and AC systems to improve the performance of both systems is examined. It is found that for the same response reduction, the addition of VE dampers to an AC system reduces the required control forces considerably, which reduces the cost of the AC system. The addition of the AC system helps improve the velocity performance of VE dampers and considerably reduces the possibility of shear failure of the viscoelastic material. Two procedures for evaluating the damping effect of the VE dampers are suggested which can be applied to either shear-type or framed structures. Two control algorithms based on drift and velocity/acceleration feedback are compared to existing algorithms. A method of determining the weighting matrices of an AC system is presented which reduces the required control forces for certain control algorithms.  相似文献   

13.
随着并行计算技术的发展,非线性反演计算效率在不断提高,但对于基于单点搜索的非线性反演方法,其并行算法的实现则是一个难题。本文将群体搜索的思想引入到基于单点搜索的非线性反演方法,构建了并行算法,以量子蒙特卡罗方法为例进行了二维地震波速度反演及实际资料波阻抗反演,并测试了使用不同节点数进行计算的效率。计算结果表明:该并行算法在理论和实际资料反演中是可行的和有效的,具有很好的通用性;算法计算效率随着使用节点数的增加而提高,但算法计算效率的提高幅度随着使用节点数的增加逐渐减小。  相似文献   

14.
A method for variance component estimation (VCE) in errors-in-variables (EIV) models is proposed, which leads to a novel rigorous total least-squares (TLS) approach. To achieve a realistic estimation of parameters, knowledge about the stochastic model, in addition to the functional model, is required. For an EIV model, the existing TLS techniques either do not consider the stochastic model at all or assume approximate models such as those with only one variance component. In contrast to such TLS techniques, the proposed method considers an unknown structure for the stochastic model in the adjustment of an EIV model. It simultaneously predicts the stochastic model and estimates the unknown parameters of the functional model. Moreover the method shows how an EIV model can support the Gauss-Helmert model in some cases. To make the VCE theory into EIV model more applicable, two simplified algorithms are also proposed. The proposed methods can be applied to linear regression and datum transformation. We apply these methods to these examples. In particular a 3-D non-linear close to identical similarity transformation is performed. Two simulation studies besides an experimental example give insight into the efficiency of the algorithms.  相似文献   

15.
Hilbert-Huang变换与ELF信号处理   总被引：4，自引：2，他引：2       下载免费PDF全文
Hilbert-Huang变换(HHT)是近年出现的一种自适应的非平稳、非线性信号处理方法,该方法迄今已在许多非线性、非平稳信号处理的研究领域得到了很好的应用.本文简要介绍了Hilbert-Huang变换的基本实现原理与算法基础,通过仿真信号验证了该方法的有效性,并以实际数据为例,探讨了它在极低频(ELF)信号处理及噪声压制方面的应用.利用Hilbert-Huang变换对ELF信号进行频率域滤波,可以对噪声进行有效压制,从而提取已知频率的电磁信号,极大地提高信号质量.  相似文献   

16.
A general theory of mode combination is developed for structural systems subjected to stationary stochastic excitation. The analysis begins with a brief review of a mode combination expression for first-order systems. Then, new fundamental properties of this result are developed. These properties are used to establish common analytical foundations and make new extensions of previously developed mode combination results for under-critically damped, classically damped, cascaded and non-linear structures. In the second part of the paper, an efficient and general mode combination method is developed for cascaded structures. It is shown how the unified mathematical framework established herein can be applied to cascaded structures composed of different types of substructures without the need to derive separate mode combination expressions.  相似文献   

17.
Gravity and magnetic data have been inverted to obtain the continuous lower surface of a 2.5 dimensional sedimentary basin. The non-linear problem is linearized and a solution is calculated through a recursive process until the predicted data matches the observed data. An average model is then calculated and a resolution analysis shows which features are uniquely determined. The results of individual inversion indicate that a final solution is initial model dependent but the average models are independent of the initial model except at the margins. The average model for the magnetic solutions have uniformly smaller spreads than the gravity solutions. The algorithms were applied to data from the Sanford Basin in North Carolina. The results indicate that the basin is asymmetrical in shape with a maximum depth of 3.2 km. Comparing these results with those obtained from a generalized linear inverse (GLI) algorithm indicate that the higher-frequency features determined from the GLI algorithm are not resolved.  相似文献   

18.
The problem of free vibration of non-linear structures is considered initially. It is shown that this problem can be represented as a non-linear eigenvalue problem. Variational principles for non-linear eigenvalue problems are defined. These variational principles are implemented with finite element models to define numerical approximations for the free vibration problem. The solution of these approximate equations provides a set of non-linear modal vectors and natural frequencies which vary with the amplitude of the solution. The non-linear eigenvalue parameters can be used in modal expansion approximations for the non-linear transient or steady state response of structural systems. To demonstrate the proposed techniques the free vibration and steady state vibration characteristics of a geometrically non-linear circular plate are determined.  相似文献   

19.
In this paper, different methods for generating synthetic earthquakes are compared in terms of related non-linear seismic response of ductile structures. The objective of the investigation is to formulate recommendations for the use of synthetic earthquakes for reliable seismic analysis. The comparison is focused on the accuracy of the reproduction of the characteristics of the structural non-linear response due to recorded earthquakes. First the investigations are carried out for non-linear single-degree-of-freedom systems. Later, the results are validated for a set of realistic buildings modelled as multi-degree-of-freedom systems. Various options of the classical stationary simulation procedure of SIMQKE and a non-stationary simulation procedure proposed by Sabetta and Pugliese are examined and compared. The adopted methodology uses a set of recorded earthquakes as a reference. Hundred synthetic accelerograms are generated for each examined simulation option with the condition that the related elastic responses are similar to those of the reference set. The non-linear single-degree-of-freedom systems are defined using six recognized hysteretic models and four levels of increasing non-linearity. The non-linear responses computed for the reference set and the studied simulation options are then statistically compared in terms of displacement ductility and energy. The results show that the implementation of the classical stationary procedure always leads to a significant underestimation of the ductility demand and a significant overestimation of the energy demand. By contrast, non-stationary time histories produce much better results. The results with the multi-degree-of-freedom systems are shown to confirm these conclusions.  相似文献   

20.
The response spectrum method has been widely used in earthquake engineering design, but cannot be directly applied to non-linear systems such as the lead-filled rubber bearing used in base isolation systems. An appraoch to determine the equivalent linearized stiffness and damping coefficient of the lead-filled rubber bearing by use of the results of shaking table tests is developed. Comparisons of time histories for the equivalent linear systems and the actual model show the method gives accurate maxima for displacement and acceleration and at the appropriate times. It is found that the identified parameters vary with the maximum deformation and the simplified formulae that can optimally describe the variations are derived. Using these formulae, an iterative algorithm using the response spectrum method to calculate the dynamic response of buildings isolated by lead-filled rubber bearings is also presented.  相似文献   

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