共查询到20条相似文献，搜索用时 31 毫秒
1.
基于MPA方法的结构滞回耗能计算 总被引：2，自引：0，他引：2
在能量反应分析中,滞回耗能是最具明确工程意义的而又便于工程应用的能量指标,可用以衡量结构的塑性累积损伤。然而,以往研究中,在计算多自由度体系的滞回耗能时,通常采用时程分析法,计算比较烦杂,不利于工程实际的应用。因此,本文提出了一种采用模态pushover分析（MPA）计算多层结构滞回耗能的简便方法,并通过两个高层结构算例,验证了该方法的精度。结果表明：基于模态pushover分析的结构滞回耗能计算方法精度良好,结果可靠;对于框架结构,可以直接采用第一阶模态（倒三角）加载模式对结构进行pushover分析计算,对于高层框架剪力墙结构,必须组合高阶模态的滞回耗能计算结果。 相似文献
2.
ABSTRACT An infiltration model based on the Green-Ampt assumptions is developed for a class of non-uniform soils in which saturated hydraulic conductivity decreases as an exponential function of depth, and the storage-suction factor C = ΔθΔΨ is a constant. An analysis of measured hydraulic conductivity and porosity data suggests that the model may be useful in some soils where the changes of hydraulic characteristics with depth are of this form. A method for using the model with time variable rainfall rates is given. The model is applied to simulate the experimental results of Childs &; Bybordi (1969) who measured infiltration into layered sand profiles. Agreement was satisfactory even for this case. 相似文献
3.
C. R. Mondal 《地球物理与天体物理流体动力学》2013,107(4):295-313
Abstract The problem of unsteady long waves generated by any horizontal and symmetrically distributed, time-periodic surface wind on a rotating ocean is analysed for large times and distances. Uniform asymptotic estimates of the surface displacement in the unsteady state are obtained. The steady-state wave and velocity fields at any distance are also determined. Some characteristics of the unsteady and steady motions are described. Also noted are the features that distinguish the motion from its one-dimensional analogue for which a non-uniform analysis in the unsteady state along with a large-distance form of the surface elevation are already known. 相似文献
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A criterion of stability pertaining to the hybrid frequency-time-domain procedure is derived. It stems from the initial-value theorem on one side and from the condition of convergence which applies to the harmonic counterpart of the procedure on the other side. The criterion depends on the dynamic stiffnesses of both the original non-linear system and the pseudo-linear system evaluated at the Nyquist frequency. Since at this frequency both stiffnesses are usually controlle by the mass, the criterion of stability is satisfied for most structural systems. The procedure must, however, be applie sequentially to individual time segments. The validity of this criterion is confirmed by a numerical investigation performe for a SDOF system. The solution of non-linear dynamic problems requires consideration of implementation issues which are also discusse in the paper. The analysis of a non-linear soil-structure-interaction system in which the soil's stiffness coefficients an directly defined in the frequency domain also demonstrates the accuracy of the hybrid frequency-time-domain procedure. 相似文献
5.
Abstract For the purpose of deriving an analytical parametrization, oceanic mesoscale eddies are represented as a horizontally propagating wave field in a non-uniform environment. The mathematical analysis rests upon the assumption of scale disparity between a short eddy scale and a long mean-flow scale. The novelty resides in the treatment of finite-amplitude eddies, which, moreover, form either a band-like or a cell-like pattern. A barotropic ocean is chosen as a first step to illustrate the mathematical analysis, but dissipation is included. The main result is an analytical derivation of a mesoscale-eddy parametrization: the mean-flow equation contains Reynolds-stress terms which are computed from parameters of the eddy field, which, in turn, are predicted by separate evolution equations. Due to restrictive assumptions (barotropy, orthogonal waves,…), the parametrization established here should be viewed only as a first step toward the design of a more practical parameterization for large-scale modelling. 相似文献
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A direct boundary element procedure is presented to determine the impedance matrix for a three-dimensional foundation supported on an infinitely-long canyon of uniform cross-section cut in a homogeneous half-space. The uniform cross-section of the canyon permits analytical integration along the canyon axis leading to a series of two-dimensional boundary problems involving Fourier transforms of the full-space Green's functions. Solution of these two-dimensional boundary problems leads to a dynamic flexibility influence matrix which is inverted to determine the impedance matrix. The accuracy of the procedure is demonstrated by comparison with previous solutions for a surface-supported, square foundation and results obtained by a three-dimensional boundary element method (BEM) for a foundation of finite-width supported on an infinitely-long canyon. Compared with the three-dimensional BEM, the present method requires less computer storage and is more accurate and efficient. The foundation impedance matrix determined by this procedure can be incorporated in a substructure method for earthquake analysis of arch dams. 相似文献
8.
The evaluation of the dynamic response of non-classically damped linear structures requires the solution of an eigenproblem with complex eigenvalues and modal shapes. Since in practice only a small number of complex modes are needed, the complex eigenvalue problem is solved in the modal subspace in which the generalized damping matrix is not uncoupled by classical real modes. It follows that the evaluation of the structural response requires in both cases the determination of complex modes by numerical techniques, which are not as robust as techniques currently used for the solution of the real eigenvalue problem, and the use of complex algebra. In the present paper an unconditionally stable step-by-step procedure is presented for the response of non-classically damped structures in the modal subspace without using complex quantities. The method is based on the evaluation of the fundamental operator in approximated form of the numerical procedure. In addition, the method can be easily modified to incorporate the modal superposition pseudo-static correction terms. 相似文献
9.
基于多自由度空间结构体系地震响应分析的基本理论,利用ANSYS建立空间有限元模型,采用动力时程分析法分析某大跨度连续钢桁架柔性拱桥在一致和非一致激励作用不同地震工况下的空间地震响应。研究结果表明:非一致激励作用下,拱肋轴力、主桁弯矩峰值出现在拱脚和边墩附近;地震波组合输入较其单向输入拱脚轴力和面内弯矩最大分别可达1.28和8.32倍;非一致输入较一致激励作用拱脚轴力和面内弯矩分别可达2.5和8.4倍;地震波横向输入较纵向输入横向位移峰值比可达2.4倍,纵向输入较横向输入纵向位移峰值比可达2.6倍;结构的支座形式对结构构件地震响应结果也有一定影响;建议大跨度钢桁拱桥抗震设计应充分考虑地震波的空间和时间效应。 相似文献
10.
W. Dalmau 《Surveys in Geophysics》1997,18(2-3):213-223
The use of some Arabic medieval solar and lunar eclipse records for the determination of secular changes in the Earth's rotation is critically reviewed. The published results derived from these data suggest a non-uniform decrease in the Earth's rotation rate over the last 27 cy. There is, however, up to this day no sound physical explanation for the deduced non-tidal oscillations, with an apparent period of about 1500 yr and a semi-amplitude of some 4 ms in the l.o.d., which overlayed to a constant secular tidal change in the Earth's rotation rate produce a net non-uniform deceleration of the Earth's rotation. In this paper we discuss a set of observations, which were executed by professional Arabic astronomers. We show by our analysis the way in which the non-uniform deceleration of the Earth's rotation was constructed. A correct reading of the Arabic medieval observations shows that they do not contradict a secular constant decrease in the Earth's rotation rate of nearly -4.6 10-22 rad s-2. This value is in accordance with other similar ones derived from ancient eclipse records and from satellite tracking data. 相似文献
11.
Leiv-J. Gelius 《Geophysical Prospecting》1995,43(1):3-29
A generalized diffraction tomography algorithm is developed, which in principle can handle irregularly spaced data, curved acquisition lines and non-uniform background models. By direct comparison with medical diffraction tomography, it is shown that the generalized method involves the same two processing steps: data filtering and back-propagation. The filter handles the irregular sampling of the model space and the uneven energy coverage, while the back-propagation operator removes the wave propagation effects. Paraxial ray-tracing techniques are employed to compute both these quantities. In medical diffraction tomography, the resolution vector (i.e. the Fourier vector of the model space) is defined by the incident and scattered plane-wave directions. It is shown here that a similar relationship exists for a non-uniform background, where the resolution vector at a particular image point is defined by the incident and scattered ray directions. Consequently, the impulse response of the generalized algorithm becomes space variant. Finally, a general processing procedure for transmission mode seismic data, based on this generalized algorithm, is proposed. The potential of the method is demonstrated using synthetic cross-hole data. 相似文献
12.
H. Sandstrom 《地球物理与天体物理流体动力学》2013,107(1):231-270
Abstract For a two-dimensional geometry the internal wave eigenfunctions are constructed as combinations of non-uniform wave trains to satisfy variable boundary conditions. All the notable features of the wave-topography interaction problem can be derived from the form of in homogeneous phase function; hence its construction is the central theme of this paper. It is shown that the general solution can be expanded in many (perhaps an infinite number) complete sets of eigenfunctions, but that the application of physical constraints (if available) narrows the choice to at most two sets, in terms of which the general topographic generation and coupling problem can be solved. The general method is illustrated by several special cases, which indicate that coupling is relatively weak for sub-critical slopes but strong for critical and also for supercritical slopes. 相似文献
13.
Abstract The stability of a plane parallel shear flow with the profile U(z) = tanh z is considered in a rotating system with the axis of rotation in the z-direction. The establishment of the basic flow requires a baroclinic state, but baroclinic effects are suppressed in the stability analysis by assuming a limit of high thermal conductivity. It is shown that the strongest growing disturbance changes from a purely transverse form in the limit of vanishing rotation rate to a nearly longitudinal form as the angular velocity of rotation increases. An analytical solution of the stability equation is obtained for vanishing growth rates of the transverse form of the instability. But, in general, the solution of the problem requires numerical integrations which demonstrate that the preferred direction of the wave vector of the instability is towards the left of the direction of the mean flow. 相似文献
14.
Simultaneous identification of the pollutant release history and the source location in groundwater by means of a geostatistical approach 总被引：4，自引：1，他引：3
Ilaria Butera Maria Giovanna Tanda Andrea Zanini 《Stochastic Environmental Research and Risk Assessment (SERRA)》2013,27(5):1269-1280
This paper describes an innovative procedure that is able to simultaneously identify the release history and the source location of a pollutant injection in a groundwater aquifer (simultaneous release function and source location identification, SRSI). The methodology follows a geostatistical approach: it develops starting from a data set and a reliable numerical flow and transport model of the aquifer. Observations can be concentration data detected at a given time in multiple locations or a time series of concentration measurements collected at multiple locations. The methodology requires a preliminary delineation of a probably source area and results in the identification of both the sub-area where the pollutant injection has most likely originated, and in the contaminant release history. Some weak hypotheses have to be defined about the statistical structure of the unknown release function such as the probability density function and correlation structure. Three case studies are discussed concerning two-dimensional, confined aquifers with strongly non-uniform flow fields. A transfer function approach has been adopted for the numerical definition of the sensitivity matrix and the recent step input function procedure has been successfully applied. 相似文献
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In this study,a comprehensive parametric analysis was performed on non-uniform excitation of V-shaped topography using the boundary element method in time domain.For this purpose,wave scattering analysis was carried out on a topography subjected to the SV-wave for different predominant frequencies and shape ratios.Based on the numerical results,new coherence and time delay functions are proposed to generate non-uniform ground motion for topographic irregularities.The efficiency and accuracy of the proposed functions for real engineering problems are indicated by comparison with observations reported in previous literature. 相似文献
17.
A step‐by‐step approximate procedure taking into consideration high‐frequency modes, usually neglected in the modal analysis of both classically and non‐classically damped structures, is presented. This procedure can be considered as an extension of traditional modal correction methods, like the mode‐acceleration method and the dynamic correction method, which are very effective for structural systems subjected to forcing functions described by analytical laws. The proposed procedure, herein called improved dynamic correction method, requires two steps. In the first step, the number of differential equations of motion are reduced and consequently solved by using the first few undamped mode‐shapes. In the second step, the errors due to modal truncation are reduced by correcting the dynamic response and solving a new set of differential equations, formally similar to the original differential equations of motion. The difference between the two groups of differential equations lies in the forcing vector, which is evaluated in such a way as to correct the effects of modal truncation on applied loads. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
18.
S. Ghoshal 《Pure and Applied Geophysics》1970,80(1):335-345
Summary In this article, we have solved the problem of natural convection along a vertical plate with variable temperature and a transverse non-uniform magnetic field. It also represents a unified analysis of the works of other including the present author, on natural convection with or without transverse magnetic field, and with uniform or non-uniform plate temperature.The author is indebted to Prof.K. B. Ranger, Department of Mathematics, for his continuous and active interest in my research work. I am also grateful to him for offering me a fellowship from his N.R.C. (Canada) research fund. 相似文献
19.
A procedure for deriving the Lanczos vectors is explained and their use in structural dynamics analysis as an alternative to modal co-ordinates is discussed. The vectors are obtained by an inverse iteration procedure in which orthogonality is imposed between the vectors resulting from successive iteration cycles. Using these Lanczos vectors the equations of motion are transformed to tridiagonal form, which provides for a very efficient time-stepping solution. The effectiveness of the method is demonstrated by a numerical example. 相似文献
20.
A series of shaking table tests were conducted on scaled utility tunnel models with and without construction joints under non-uniform input earthquake wave excitation. Details of experimental setup are first presented with particular focuses on: design and fabrication of double-axis laminar shear box with a rectangular hole opened on its side walls; design of two devices for measuring the slippage between the interface of test soil and the structure, and the relative deformation and rotation between joints of the structure model; and procedure for construction of input earthquake wave. The experiments were conducted in three phases. Phase 1 is free-field test. A 2-norm index is suggested to quantify the boundary effect and it is found that the designed laminar box does not impose significant boundary effect. Phases 2 and 3 are model tests in longitudinal and transversal directions, respectively. Test results are discussed in items of shear force–slip relationship at the soil–model structure interaction surface, movement and rotation of the construction joint, and effect of non-uniform earthquake input. The comparison shows that structural response under non-uniform earthquake excitation is larger than that under uniform excitation. The effect of spatial distribution of earthquake excitation should be considered in the seismic design of utility tunnel. 相似文献