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1.
Two processes using the Newmark implicit integration scheme are presented for the analysis of the earthquake response of a three-dimensional model for arch dam-reservoir systems including the effect of compressibility of the water. The solid structure and fluid regions are modelled separately, and the forcing functions at the interface are due to the hydrodynamic pressures from the reservoir acting on the upstream face of the dam wall, and the accelerations from the dam wall acting in turn on the reservoir. For the purposes of an initial investigation, elastic properties are assumed for the material of the dam, whilst in the reservoir radiation damping at the upstream boundary has been included, but bottom absorption has not. The excitation is provided by means of a combisweep which is fashioned so that its continuously varying frequencies pass through the fundamental frequencies of both the arch dam-reservoir system and the reservoir alone. Consequently the response is highly resonant, thus providing a severe test for the numerical procedures. From the numerical results obtained for an example problem it is concluded that both schemes provide an acceptable solution to the problem posed, and the possibility of enhancement to cater for more complex situations is discussed. 相似文献
2.
The design of seismic resistant concrete gravity dam necessitates accurate determination of hydrodynamic pressure developed in the adjacent reservoir. The hydrodynamic pressure developed on structure is dependent on the physical characteristics of the boundaries surrounding the reservoir including reservoir bottom. The sedimentary material in the reservoir bottom absorbs energy at the bottom, which will affect the hydrodynamic pressure at the upstream face of the dam. The fundamental parameter characterizing the effect of absorption of hydrodynamic pressure waves at the reservoir bottom due to sediment is the reflection coefficient. The wave reflection coefficient is determined from parameters based on sediment layer thickness, its material properties and excitation frequencies. An analytical or a closed-form solution cannot account for the arbitrary geometry of the dam or reservoir bed profile. This problem can be efficiently tackled with finite element technique. The need for an accurate truncation boundary is felt to reduce the computational domain of the unbounded reservoir system. An efficient truncation boundary condition (TBC) which accounts for the reservoir bottom effect is proposed for the finite element analysis of infinite reservoir. The results show the efficiency of the proposed truncation boundary condition. 相似文献
3.
An efficient procedure is developed for the hydrodynamic analysis of dam–reservoir systems. The governing equations of hydrodynamic pressure in the frequency as well as time domain are derived in the framework of the scaled boundary finite element method. The water compressibility and absorption of reservoir sediments can be conveniently taken into consideration. By extending the reservoir to infinity with uniform cross-section, only the dam–reservoir interface needs to be discretized to model the fluid domain, and the hydrodynamic pressure in the stream direction is solved analytically. Several numerical examples including a gravity dam with an inclined upstream face and an arch dam with a reservoir of arbitrary cross-section are provided to demonstrate the computational efficiency and accuracy of the proposed method. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
4.
The linear response of a selected arch dam to harmonic upstream, vertical or cross-stream ground motion is presented for a wide range of the important system parameters characterizing the properties of the dam, foundation rock, impounded water and reservoir boundary materials. Based on these frequency-response functions, the dam-foundation rock interaction effects in the dynamic response of arch dams are investigated. 相似文献
5.
The linear response of a selected arch dam to harmonic upstream, cross-stream or vertical ground motion is presented for a wide range of the important system parameters characterizing the properties of the dam, impounded water, reservoir boundary materials and foundation rock. Based on these frequency response functions, the hydrodynamic and foundation flexibility effects in the dynamic response of arch dams are investigated. 相似文献
6.
Dynamic response of dams is significantly influenced by foundation stiffness and dam-foundation interaction. This in turn,
significantly effects the generation of hydrodynamic pressures on upstream face of a concrete dam due to inertia of reservoir
water. This paper aims at investigating the dynamic response of dams on soil foundation using dynamic centrifuge modelling
technique. From a series of centrifuge tests performed on model dams with varying stiffness and foundation conditions, significant
co-relation was observed between the dynamic response of dams and the hydrodynamic pressures developed on their upstream faces.
The vertical bearing pressures exerted by the concrete dam during shaking were measured using miniature earth pressure cells.
These reveal the dynamic changes of earth pressures and changes in rocking behaviour of the concrete dam as the earthquake
loading progresses. Pore water pressures were measured below the dam and in the free-field below the reservoir. Analysis of
this data provides insights into the cyclic shear stresses and strains generated below concrete dams during earthquakes. In
addition, the sliding and rocking movement of the dam and its settlement into the soil below are discussed. 相似文献
7.
Hydrodynamic-stiffness matrix based on boundary elements for time-domain dam-reservoir-soil analysis
For a reservoir with an arbitrary shape of the upstream dam face and of the bottom including an adjacent regular part of constant depth extending to infinity, the hydrodynamic-stiffness matrix in the frequency domain for a displacement formulation is derived using the boundary-element method. The fundamental solution takes the boundary condition at the free surface into account. The analytical solution of the semi-infinite reservoir is used to improve the accuracy. To be able to transform the hydrodynamic-stiffness matrix from the frequency to the time domain, the singular part consisting of its asymptotic value of ω ∞ is split off. It consists of an imaginary linear term in ω which can be interpreted as a damper with a coefficient per unit area equal to the product of the mass density and the wave velocity. This also applies for a reservoir bottom of arbitrary shape. The remaining regular part of the stiffness matrix is transformed numerically. The corresponding interaction force-displacement relationship involves convolution integrals. This boundary-element solution agrees well with analytical results and with those of other numerical procedures based on a time-stepping method. The method is also applied to an actual earthquake acting on a reservoir with an irregular part with an inclined bottom and a regular part extending to infinity. The results of the analysis in the time domain coincide with those determined in the frequency domain. 相似文献
8.
An analysis procedure in the frequency domain is developed for determining the earthquake response of two-dimensional concrete gravity and embankment dams including hydrodynamic effects; responses of the elastic dams and compressible water are assumed linear. The dam and fluid domain are treated as substructures and modelled with finite elements. The only geometric restriction is that an infinite fluid domain must maintain a constant depth beyond some point in the upstream direction. For such an infinite uniform region, a finite element discretization over the depth is combined with a continuum representation in the upstream direction. The fluid domain model approximately accounts for interaction between the fluid and underlying foundation medium through a damping boundary condition applied along the reservoir bottom, while the dam foundation is assumed rigid. Several examples are presented to demonstrate the accuracy of the fluid domain model and to illustrate dam responses obtained from the analysis procedure. 相似文献
9.
The transient analysis of dam–reservoir systems by employing perfectly matched layers has been investigated. In previous studies, boundary conditions of the PML region in the reservoir have been neglected. In this paper, they are incorporated completely in the formulation. Moreover, a technique is introduced to involve the effect of incident waves caused by vertical ground motions at the reservoir bottom in the analysis. Performing several numerical experiments indicates that applying boundary conditions of the PML domain and utilizing the proposed method for vertical excitation cases reduce the computational cost significantly and make the PML method a very efficient approach for the transient analysis of dam–reservoir systems. 相似文献
10.
Ali Seiphoori S. Mohsen Haeri Masoud Karimi 《Soil Dynamics and Earthquake Engineering》2011,31(5-6):792-804
In this study, the nonlinear seismic analysis of a typical three-dimensional concrete faced rockfill dam is reported. Three components of the Loma Prieta (Gilroy 1 station) earthquake acceleration time history are used as input excitation. The dam under study is considered as if it were located in a prismatic canyon with a trapezoidal cross-section. A nonlinear model for the rockfill material is used, and contact elements with Coulomb friction law are utilized at the slab–rockfill interface. Vertical joints in the face slab are also considered in the finite element model. A substructure method, in which the unbounded soil is modelled by the scaled boundary finite element method (SBFEM), is used to obtain the scattered motion and interaction forces along the canyon. The dam is subjected to spatially variable P, SV, and SH waves, and the effect of dam–foundation interaction and the reservoir water effects are considered. The results are compared with the non-scattered input motion analysis. Results of the analyses indicate that due to applying the scattered motion to the canyon the response of the dam and concrete face slab significantly increases. The reservoir water pressure affects the tensile stresses induced in the face slab by reducing the uplift movement of the concrete panels.Large horizontal axial forces are induced in the face slab due to out-of-phase and out-of-plane motions of the abutments. Although the normal movements of vertical joints are reduced due to the reservoir water confinement, the opening movements are still significant, and the local failure of construction joints is inevitable. 相似文献
11.
In this work, a ghost-cell immersed boundary method is proposed for the hydrodynamic response of earthquake excited dam-reservoirs. The numerical method employs a second order accurate two-step projection algorithm including compressibility effects in pressure field due to earthquake. The effects of reservoir bottom absorption are treated by introducing damping terms into the momentum equations. Hydrodynamic response of earthquake excited dam with a sloping face is simulated to demonstrate the accuracy of the present numerical method. Numerical results compared with previous numerical and analytical solutions show that the present immersed boundary method can accurately compute the hydrodynamic forces on inclined and curved dam faces including the effects of water compressibility and reservoir bottom absorption for the possibility of resonance. The proposed numerical method was shown to have significant advantages in computational time and memory usage for the hydrodynamic simulation of large dam-reservoirs with arbitrary geometries. Hydrodynamic forces on a double curvature arch dam subjected to real earthquake induced ground motion are also simulated to demonstrate the capability of the method. 相似文献
12.
The previously developed two-dimensional boundary element procedure for analysing the propagation of a single discrete crack is extended to simultaneous multiple cracking in concrete gravity dams. A brief discussion of the generalized methodology is presented and the validity of the extended procedure is verified by performing a fracture analysis of the Fongman dam and comparing the predicted rupture process with the available experimental results. The fracture response of the Koyna dam is then studied extensively under the Koyna earthquake. Both single and multiple cracking models are employed to investigate the fracture process as well as final rupture in the dam. Similar final damage involving complete separation of the crest block of the dam is predicted, irrespective of whether single or multiple crack propagation models are employed. In relation to the phenomenon of hydrodynamic uplift pressure within propagating cracks, openings of the crack on the upstream face of the dam are examined in particular. The results indicate that this phenomenon is not expected to be significant during the crack development phase, and hence unlikely to affect the final rupture characteristics of dams undergoing strong earthquake excitation. 相似文献
13.
The boundary element method has been successfully applied in the past to the analysis of hydrodynamic forces in two-dimensional infinite as well as two- and three-dimensional finite reservoirs subjected to seismic ground motions. This paper presents the results of more recent research on the application of the constant boundary element method to the 3D analysis of reservoir vibration. Special boundary conditions, previously used in the 2D case, to treat infinite radiation damping and damping from foundation soil and banks have been incorporated in this formulation. Numerical results for vibration of a 3D infinite rectangular reservoir as well as of a 3D infinite reservoir impounded by an arch dam are presented and compared with some existing results obtained by other researchers. 相似文献
14.
The seismic response of a dam is strongly influenced by its interaction with the water reservoir and the foundation. The hydrodynamic forces in the reservoir are in turn affected by radiation of waves towards infinity, wave absorption at the reservoir bottom, and cross-coupling between the foundation below the dam and the reservoir bottom. The fluid–foundation interaction effect, i.e. the wave absorption along the reservoir bottom, can be accounted for by using either an approximate one-dimensional (1D) wave propagation model or a rigorous analysis of interaction between the flexible soil along the base and the water. The rigorous approach requires enormous computational effort because of (a) cross-coupling between the foundation of the dam and the soil below the reservoir and (b) frequency dependence of the boundary condition along the fluid-foundation interface. The analysis can be simplified by ignoring the cross-coupling and by using the approximate 1D wave propagation model. The effects of each of these two simplifications on the accuracy and computational efficiency of the procedure used for the seismic response analysis of a dam are examined. Analytical results are presented for the complex frequency-response functions as well as the time histories of the response of Pine Flat dam to Taft and E1 Centro ground motions. 相似文献
15.
ＰＲＥＤＩＣＴＩＮＧＲＥＳＥＲＶＯＩＲＳＥＤＩＭＥＮＴＡＴＩＯＮＷＩＴＨ２ＤＭＯＤＥＬＦＬＯＯＤＳＩＭＷ．ＢＥＣＨＴＥＬＥＲ１ａｎｄＭ．ＮＵＪＩＣ２ＡＢＳＴＲＡＣＴＰｒｅｄｉｃｔｉｏｎｏｆｓｅｄｉｍｅｎｔａｔｉｏｎｉｓｖｅｒｙｉｍｐｏｒｔａｎｔｂｅｆ... 相似文献
16.
A new analytical development of the seismic hydrodynamic pressure inside pre-existing cracks on the upstream face of concrete dams is presented. The finite control volume approach is utilized to derive an expression for the seismic hydrodynamic pressure using the continuity principle and the linear momentum theorem for the fluid inside the crack. The derived pressure expression is a function of the relative crack-opening acceleration and velocity. The acceleration and velocity terms are then recast in the form of added mass and damping matrices which can then be included at the nodes inside the discrete crack of a finite element model. This procedure linearizes the solution of the problem. A dam, 55 m high and having an initial crack opening of 2 mm at the base or near the crest and subjected to two different accelerograms, is analysed. For high-frequency ground motion, the seismic hydrodynamic pressure inside the crack, at the base of the dam, appears to be 50 per cent higher than the corresponding hydrostatic pressure. 相似文献
17.
深厚库底回填料是影响面板堆石坝动力响应的重要因素之一。为深入研究深厚库底回填料对面板堆石坝动力响应的影响,基于某拟建抽水蓄能电站,采用三维动力有限元分析系统研究其上库面板坝的地震反应,主要包括坝体加速度、面板动力响应、接缝变位情况以及库底防渗土工膜的动应变等。计算结果表明:由于库底回填料的存在,坝体加速度放大效应被明显削弱;面板周边以受拉为主,中部大部分区域受压;垂直缝呈现出周边张开、中间闭合的趋势;土工膜的顺河向和坝轴向的动拉应变皆小于屈服应变,最大应变出现在库底材料分界处,为提高坝体渗透安全性,建议对主堆石区与连接板相接处的回填料进行适当范围换填的处理措施。研究成果可以为类似工程提供参考。 相似文献
18.
K.G.RANGARAJU U.C.KOTHYARI 《国际泥沙研究》2005,20(1):52-61
Withdrawal of water from a river into a canal involves the construction of a barrage or a dam across the river depending on whether the river is perennial or not. The design of the reservoir upstream of the dam and of the canal requires consideration of the sediment load carried by the river in case the river is sediment-laden. The basic equations concerning morphological changes in such rivers are discussed with particular reference to computation of reservoir sedimentation. The hydraulics of lined canals carrying wash load is examined from the point of view of limiting transport capacity and changes in frictional resistance. Lastly, the methods of design of sediment extraction devices like settling basins and vortex chambers are presented. 相似文献
19.
A three-dimensional dam-reservoir system under seismic load is analysed. The dam is assumed to be rigid. The reservoir is an infinite channel with semi-circular cross-section. The exact analytical solution, based on the assumption of potential fluid motion is presented, as well as numerical results for selected parameters.The most significant parameters are: the direction and frequency content of the seismic input; the radiation damping at the reservoir bottom; and the compressibility of the fluid. The response of the system depends strongly on the direction of the input ground motion. This is shown by the transfer functions as well as by the pressure time histories due to two earthquakes with different frequency content. The energy absorption at the reservoir bottom is important. A simple plane-wave model shows, that even for a rock foundation, the amount of transmitted energy can reach up to 80%. For comparison the case without bottom absorption is also shown. Compressbility has to be included to capture the resonance effects. The exact analytical solution is also used to verify numerical results obtained by a new method that combines a finite element model with a rigorous radiation boundary for the infinite channel in the time domain. 相似文献
20.
Using reciprocal theorems for dynamic and static boundary value problems, boundary integral equations are presented for wave propagation in elastic, isotropic media and compressible, inviscid fluids in the time domain as well as in the frequency domain. For the analysis of fluid–soil and fluid–structure systems, suitable coupling conditions are prescribed along the interfaces. The numerical treatment of the boundary integral equations consists of a point collocation and of a discretization of the boundary, in which constant and linear approximation functions are assumed. Step-by-step integration is applied to the time-dependent equations, where again the states are taken to be linear and constant over each time interval. These boundary element procedures are used to analyse the response of dams due to horizontal and vertical ground motions considering dam–water interaction and absorption of hydrodynamic pressure waves at the reservoir bottom or at the far end into the soil medium. Both the frequency response and the impulse generated transient response are investigated. 相似文献