جستجوی مقالات مرتبط با کلیدواژه « dam reservoir interaction » در نشریات گروه « عمران »

The present paper investigates and compares the crack propagation in concrete gravity dams using two models of linear fracture mechanics and plasticity damage concrete. The first model is based on linear concrete behavior using the extended finite element method without considering the effect of strain softening on the crack tip while the second model is based on the nonlinear concrete behavior and the strain softening in tension with damage parameter. According to two different algorithms and based on two models, several benchmark examples are reviewed and the results compared with those reported in the literature. Then, path of the crack growth in Koyna gravity dam due to a seismic excitation of Koyna earthquake in 1962 has been performed by considering the dam-reservoir interaction. The results show that due to low compressive stresses during analysis of concrete gravity dams, consideration of compressive nonlinear behavior has no effect on crack initiation and almost is the same for two models. However because of crack opening and closing with tapping the crack faces together in extended finite element model, the compressive stress will be more than the allowable stress of concrete. Crack initiation at downstream and upstream face occurred at angle of 90 and zero degrees respectively, which in both models, the numerical results are in agreement with the experimental model. The crack in the extended finite element model grows faster such that the crest block of dam in this model is separated from the dam body, earlier than the concrete plastic damage model. Also the values of dam crest displacement and hydrodynamic pressure in the reservoir in extended finite element model with linear elastic fracture mechanic are more than the other model, which can be attributed to the linear and nonlinear behavior of concrete in extended finite element and concrete plastic damage model respectively. In the extended finite element model, due to using linear fracture mechanic, the maximum principal stress in the cracked elements reaches the values greater than the maximum tensile strength, but in the concrete plastic damage model as soon as the stress reaches a tension limit value, elements are damaged and the stress is reduced. In both models, the crack located at the slope change area, propagates with the downward slope from downstream dam face and connects to the crack at upstream face which is growth horizontally. Because of laboratory sample dimension and boundary condition of dam-reservoir compared with actual manner, neither of two crack profiles covered the experimental model, accurately. But it is shown that the crack profiles in the extended finite element model are more consistent with experimental results. Finally, the results show that the crack profile are slightly different in the two models because of quasi brittle behavior of the dam concrete, which can be attributed to the small fracture process zone of the crack tip in comparison with the dimension of the concrete gravity dams such that by removing strain softness part, the error in the amount of additional computation can be neglected.

The stability of a gravity dam on a jointed rock foundation might be endangered by weak joints that may be present in the fracture network of the bed rock. A review of the literature shows that there are few studies of the effect of a weak joint in the foundation rock on the stability of dams. This research uses the finite difference numerical modelling software ABAQUS to model a gravity dam, the foundation rock, and the influence of a weak joint (using interfaces), that exist in the bottom of dam with different direction, on the stability of the dam. To do this, a conceptual model has been developed and one representative joint of a discrete fracture network with seven different dip angle was examined. Thses different varying dip angles were studied in order to investigate the critical configuration that has the most significant effect on the dam’s stability.As a case study, Pine Flate dam, is modeled with the ABAQUS software as a two-dimensional and Nonlinear dynamic analysis is done by implicit method with applying vertical and horizontal components of the El-Centro earthquake. The obtained results show that existness of joint in the foundation significantly affected the dynamic responcse of dam.

The present study investigate the effects of mechanical properties of the rock layers in the foundation of concrete gravity dam on the seismic response of gravity dam–reservoir –foundation systems. The mutual effects of different domains are considered in the present research. As a case study the biggest section of Shafarud dam in the north of Iran is modeled two dimensionally using ABAQUS software and its response to the may 1940 El–Centro California earthquake is considered.Four different ratio of elasticity modulus of foundation to the elasticity modulus of concrete of dam body are applied in the analysis obtained results show a significant effect of the foundation material properties on the crest displacement of dam and stress distribution in the dam bodywhich highlight the importance of detailed survey in order to identify the features of the site before construction.

In the present paper a new numerical simulation method based on finite volume is developed for calculating hydrodynamic pressure distribution in the reservoir of dams during earthquake excitation. An explicit finite volume scheme is applied for discretization of dynamic governs equation. In the proposed method the asymmetry effect of reservoir shape on hydrodynamic pressure distribution can be considered. In the simulation quadrilateral elements with center cell algorithm is used. Because of the negligible changing of hydrodynamic pressure in the cross direction with averaging, the average differential partial equation in central vertical plan of reservoir is solved. The absorption effects of bottom sediment and lateral wall are included in the analysis and an exact far end boundary condition is applied in the truncation boundary. Different approaches to the solution of the coupled field problems exist solution of the entire set of equations as one discretized system, referred to as the monolithic approach. This approach is often inefficient due to its attempt to capture with one discretization methodology the completely different spatial and temporal characteristics of fluid and the structure. The second approach often mentioned is the notion of strong coupling, referring to solvers which might use different discretizations for the fluid and the structure but which employ sub-iteration in each time step to enforce coupling between the fluid and the structure. In these methods, the governing equations for fluid and structure are discretized separately in each of the sub-domains and coupled using a synchronization procedure both in time and in space without sub-iteration. Weakly –coupled schemes have been extensively applied to a variety of different fluid-structure interaction problems of engineering interest in past ten years. wo vital issues when coupling two domains are: the method of data transformation between domains and what information must be transferred. The property of fluid adjacent of a structure such as density and viscosity are also key parameters in the efficiency of a numerical scheme.A dense fluid coupled with a structure cause a strong coupling and required some special technique to overcome corresponding difficulties. Key questions with this approach include properly enforcing boundary conditions at the solid-fluid interface, and accurately transmitting tractions between the solid and fluid. The biggest complaint about the explicit staggered partitioned solution procedure is the typical instability associated with the method,that is generally caused by the time lag between the integration of the fluid and structure equations. In the typical partitioned method, the fluid and the structure equations are integrated in time, and the interface conditions are enforced asynchronously. In the solution of coupled problems using partitioned methods, it is necessary to find a cost-minimization (optimization) compromise between a few passes solution with small time steps and a more iterated solution with larger time steps. This compromise may depend, among other things, in the degree of nonlinearity of the structural problem, which may require equilibrium iterations independently of the interaction effects. From the computational point of view, a one–pass solution with no iteration would be optimal, but stability consideration may prove this impractical.

This paper concentrates on the presentation of a closed form solution of dam-reservoir interaction considering reservoir viscosity and bottom absorption under harmonic excitations. For this purpose, the governing equations of dam-reservoir are solved in the frequency domain and using the obtained frequency response function, the effects of different parameters are considered on dam or hydrodynamic pressure response. The results show that consideration of reservoir viscosity creates an imaginary term and the responses depend on values of viscosity, bottom absorption, exited period and dam-reservoir period.