Dam-reservoir Interaction Research Articles

Failure analysis of concrete gravity dam using coupled acoustic–structural analysis

The failure mechanism of a gravity dam under blast loading is much more complex than failure under other dynamic loads such as earthquakes. It is therefore important to evaluate the safety performance of these structures under blast load. The structural dynamic behaviour of Koyna dam, India, subjected to underwater explosion (UndEx) was investigated. The Johnson–Holmquist 2 model was used to capture the non-linear response of concrete. The dam–reservoir interaction was modelled using the coupled acoustic–structural technique, which employs a total wave formulation to incorporate the propagation of spherical shock waves. Dynamic responses such as displacement, damage profiles and principal stresses under various detonation depths, weights and reservoir levels were examined. The findings indicated that areas facing the explosion experience the most damage, while local damage occurred at the dam’s heel as the explosion depth increased. Additionally, displacement decreased notably as the TNT depth increased for a consistent explosive amount. The damage distribution in the dam was found to depend on both TNT depth and weight. Damage accumulation in the dam was substantially reduced by lowering the reservoir height (five different levels were assessed). The results provide valuable insights into the Koyna gravity dam’s response to UndEx under varying conditions.

Symmetrical fully coupled numerical model for efficient dam–reservoir interaction analysis in time domain

ABSTRACT A numerical model is presented for solving the dam–reservoir interaction (DRI) problem in the time domain. The primary aim of this paper is to introduce a coupling method that could be simply implemented in a monolithic DRI model, yields a symmetrical system of equations, and maintains accuracy comparable to existing studies. The finite element method is employed to solve the equation of motion for the structure, and the finite volume method is for the Navier–Stokes equations in the fluid domain. These two solvers are coupled using an innovative approach to generate a pressure-based symmetric system of equations, which is resolved implicitly. Moreover, unlike most previous DRI studies, free surface waves are considered in the modeling procedure, and their effects are investigated. Comparison of the results with benchmark test cases from the literature demonstrates that the proposed numerical method is both straightforward and precise.

An Efficient Dynamic Coupling Calculation Method for Dam–Reservoir Systems Based on FEM-SBFEM

In the dynamic analysis of dam–reservoir interactions, the computational efficiency of coupling system is relatively low. When numerical methods such as the scaled boundary finite element method (SBFEM) or the finite element method (FEM) are used to deal with hydrodynamic pressure, the additional mass matrix for the hydrodynamic pressure of incompressible reservoir water obtained is the full matrix. In this study, an efficient three dimensional (3D) dynamic fluid–solid coupling analysis method for dam–reservoir systems based on the FEM-SBFEM is proposed and applied to the dynamic calculation and analysis of an arch dam under seismic conditions, which adopts the SBFEM to solve the hydrodynamic pressure of the reservoir and employs the FEM to discretize the dam. In the proposed method, the hydrodynamic pressure additional mass matrix is simplified according to the physical meaning and distribution characteristics of the additional matrix with only a reduction coefficient α (0 < α ≤ 1.0), which is simple and easy to implement. The suggested value of the reduction coefficient α for the added mass matrix of the hydrodynamic pressure is selected to be 0.6 so as to ensure that the error of the maximum value of the dynamic response of the dam is limited within 5%, which is acceptable, and the elapsed time of calculation can be reduced to one twentieth of the accurate solution, which is a great jump in calculation efficiency. The proposed method provides a practical and effective process for the analysis of dam–reservoir dynamic interaction systems with a large computational scale and a fine grid scale.

A Probabilistic Model for Evaluation of the Dynamic Behavior of a Concrete Gravity Dam considering the Fluid-Structure Interaction

Regarding the importance of the interaction effect in the dynamic behavior of a concrete dam and reservoir, the process of hydrodynamic wave propagation in the reservoir and its effects on the response of a concrete gravity dam are examined in this article by presenting a new probabilistic model. For this purpose, a program has been written in an APDL environment of Ansys software capable of dynamic analysis of a system and presenting probabilistic models. The Monte Carlo method with the LHS method has been applied for the probabilistic model, in which the essential parameters in the dam-reservoir interaction problem include excitation frequency, reservoir height, and reservoir length as input variables, and the effect of their changes on the hydrodynamic wave propagation process in the reservoir and the dynamic response of the dam are evaluated. For a better understanding of the dam-reservoir interaction concept and to show the capability of the presented model, two simple and isolated models of the concrete gravity dam and reservoir system have been considered. According to the results, the distribution trend of hydrodynamic pressure along the reservoir can be obviously recognized. Also, the results present the dependence of the responses and the propagation status on the excitation frequency and its relationship with the system frequency and the reservoir natural frequency.

Concrete Deterioration Effects on Dynamic Behavior of Gravity Dam–Reservoir Interaction Problems

Concrete Deterioration Effects on Dynamic Behavior of Gravity Dam–Reservoir Interaction Problems

Comparison of the Seismic Responses of an Arch Dam under Excitation from the Design Response Spectrum in the New and Old Chinese National Standards

The new Chinese national standard, Standard for the seismic design of hydraulic structures (GB51247-2018), has been published. Compared with the Specifications for the seismic design of hydraulic structures (SL203-1997), the standard design response spectrum curve was revised in the new national standard. In order to compare the seismic responses of an arch dam under excitation from the design response spectrum in the new and old standards, the dynamic calculation of a 240 m high arch dam is carried out by a three-dimensional finite element method. In the dynamic calculation, the B-differentiable equation is used to simulate the tension motion of arch dam contraction joints, and the multi-transmitting boundary method and the Westergaard added mass method are used to simulate the dam–infinite foundation and dam–reservoir interactions, respectively. The results show that the dynamic stress responses of the arch dam under excitation from the design response spectrum in the new standard are increased compared with those of the old standard. The seismic safety of an arch dam may decrease under excitation from the design response spectrum in the new standard. Thus, the seismic validation on built arch dams should be carried out by using the new standard when it is possible.

Earthquake damage estimation of the Koyna concrete gravity dam using explicit GFVM model considering fluid–structure interaction

In this paper, an Explicit Galerkin Finite Volume Method (E-GFVM) is employed to estimate damage paths in concrete structures through the definition of nonlinear behavior of concrete. Furthermore, to verify the accuracy and efficiency of the present method, the E-GFVM outcomes are compared with the Explicit Finite Element Method (E-FEM) which is a well-known numerical method for investigating numerous solid mechanics problems. Due to the essence of explicit methods, the method in question uses a few matrix operations in nonlinear analysis, so it diminishes computation workloads for time-dependent cases with small time-step. The reason for using E-GFVM was its simplicity and high accuracy in estimating stresses and displacements for the analysis of Computational Solid Mechanics (CSM) problems. Furthermore, one important feature of FVM is its local conservation properties which guarantee the global conservation of variables that provides more stability, particularly in dealing with complex problems. To model the nonlinear behavior of concrete, the two equivalent uniaxial stress–strain relations, taking into consideration the softening and hardening behavior in both compression and tension, are implemented in the proposed numerical method. In other words, the bi-axial concrete behavior is defined by applying the idea of current strength in principal stress space. Therefore, this study aims to introduce a new numerical method that in addition to reducing time consumption, can maintain the accuracy of the results. For reaching this purpose, first, the nonlinear behavior of concrete is modeled and two different specimens are placed under pure pressure and tension loads. The results calculated by the E-GFVM are compared with other literature. After verification of the nonlinear behavior of concrete using E-GFVM, the ability of the proposed method for analysis of a real-world case under time-dependent conditions, namely Koyna concrete gravity dam which experienced a destructive earthquake in 1967, is tested, considering the impacts of dam–reservoir interaction. Then, this problem with the same conditions is modeled and analyzed using the E-FEM. The results show that, in spite of good harmony between two utilized methods for estimating the damage on the body of Koyna dam, the CPU time of the E-GFVM became about 3 times less than the E-FEM.

An efficient finite element model for dynamic analysis of gravity dam-reservoir-foundation interaction problems

In this paper, a finite element (FE)-based model that efficiently evaluates the dynamic behavior of dam-reservoir-foundation interaction (DRFI) problem was proposed including the radiation of waves to the unbounded rock and reservoir domains. Lagrangian fluid elements were used to discretize the near-field reservoir domain, while the presented infinite fluid elements were used to discretize the far-field reservoir domain. The fully coupled equation of motion for DRFI problem was solved by direct method. A two-dimensional (2D) plane-strain FE formulation of the problem is written in FORTRAN 90 programming language. Investigations were conducted on the effect of near-field domain size (length and depth) on the dynamic behavior of DRFI, dam-foundation interaction (DFI), and dam-reservoir interaction (DRI) problems. The results of this study demonstrate that the proposed model outperforms many other models that have been evolved in the literature in terms of accuracy and speed. The reflected hydrodynamic pressures at the far-field reservoir domain were efficiently absorbed by the suggested infinite fluid elements. The near-field domains size has a noticeable impact on the dynamic behavior of the dam. Making an exact choice about the size is more challenging. However, it was observed that the size of 1.5H is the physically appropriate response.

Numerical investigation on crack propagation process of concrete gravity dams under static and dynamic loads with in-crack reservoir pressure

Proper consideration of external and internal loads acting on concrete gravity dams is of vital importance in concrete dam engineering, since it plays a significant role in the stability assessment of cracked dams under static/dynamic conditions. Several factors which may affect the mechanical response of concrete gravity dams, however, have not been comprehensively accounted for in most previous crack propagation analyses. To adequately evaluate the crack propagation response of concrete gravity dams, a finite element-based numerical analysis is carried out to estimate the crack propagation in a concrete gravity dam under static and seismic loads. In this work, the effects of the water pressure inside the stress-free crack and the fracture process zone (FPZ), the cohesive force within the FPZ, the hydrostatic water pressure, and the dam-reservoir interaction are incorporated via a series of reasonable assumptions. On the basis of a stress intensity factor (SIF)-based mixed mode I-II crack propagation criterion, a generic numerical algorithm is proposed to estimate the crack growth process of concrete gravity dams under static and seismic loads. Application of this algorithm to two case studies of concrete gravity dams under different loading conditions demonstrates the validity of the algorithm in estimating the static and seismic crack propagation response. It is found that when a concrete gravity dam is subjected to static loading, crack initiation does not occur before the reservoir water level exceeds the dam height, and that the water pressure inside stress-free cracks has a slight negative effect on the structural resistance against cracking while the water pressure within the FPZ has no effect on the dam capacity. The seismic crack growth analysis indicates that the water pressure inside cracks causes the crack to propagate at a larger downward angle towards the downstream face with a larger crack growth length.

Structural Behavior of a Coupled Concrete Dam-Reservoir system under Effect of Earthquake loads Using Concrete Damaged Plasticity Model

In this study the effect of dam-reservoir interaction on the dynamic response of gravity dam by assuming the mass concrete is able to be cracked and crushed in tension and compression, respectively is considered. Where the effect of reservoir fluctuation on the dynamic response of concrete dam is investigated. In this study, to simulate the nonlinear behavior of concrete and specifying the position and direction of cracks which is occurred in gravity dam, the concrete damaged plasticity model is used. The results of this study indicate that, the maximum relative displacement in the downstream direction of a dam subjected to an earthquake is occurred when the height of water in the reservoir is at the middle of the dam. In addition, in the case of water level in the reservoir is at the base of dam, the maximum relative displacement of the dam is at the upstream.

Decoupled scaled boundary finite element method for analysing dam–reservoir dynamic interaction

In this study, an efficient method is developed for solving systems of partial differential equations governing seismic analysis of 2D dam reservoir interaction, in the frequency domain. Using Chebyshev higher-order polynomials as mapping function, special shape function, integration method of Clenshaw–Curtis and the integral form used to weighted residual method, coefficient matrices of the system of governing equations become diagonal. This means that the governing partial differential equation for each degree of freedom becomes independent from others. This feature and discretizing only boundaries of domain significantly reduce computational costs in comparison with other methods. In this regard, various problems such as dynamic analysis of empty gravity dam, calculating the hydrodynamic pressure on rigid dam, and dam–reservoir interaction analysis due to the horizontal motion of foundation are examined. Comparing the results of this method with other analytical/numerical methods shows high capability and accuracy of the proposed method.

Seismic performance and failure modes of the Jin'anqiao concrete gravity dam based on incremental dynamic analysis

To investigate the potential failure modes of concrete gravity dams under seismic loads, a typical non-overflow dam section of the Jin'anqiao roller compacted concrete (RCC) gravity dam is taken as a case study. A compressive and integral analysis model of the dam body–foundation–reservoir water interaction system is established, in which the viscous–spring boundary and its corresponding free field input mechanism is employed to account for the dam–foundation interaction and fluid–solid coupling method is used to account for the dam–reservoir interaction. Based on the incremental dynamic analysis (IDA) method, IDA curves are generated with the relative displacement angle on the x-axis (damage measure, DM) and peak ground acceleration (PGA) on the y-axis (intensity measure, IM). The damage processes and potential failure modes for the Jin'anqiao gravity dam under different peak accelerations are investigated. It is concluded that under ground motion loadings of the Jin'anqiao dam, the locations at which functional failure may occur are mostly found in the stress concentration of the dam slope, the boundary of the rolling section, the junction between the dam and dam foundation, and the top of the corridor. Therefore, strengthening the seismic protection in these areas is conducive to improving the overall aseismic level of the dam.

Viscous Damping and Contraction Joint Friction in Underwater Explosion Resistant Design of Arch Dams

The aim of this study is to clarify the parameter-determination issue with regard to the viscous damping and contraction joint friction in the underwater explosion (UNDEX) resistant design of arch dams. A 141-m-high double-curvature arch dam is chosen as the study subject, and the finite-element program ABAQUS/Explicit is employed. Both the dam-reservoir interaction and the contraction-joint nonlinearity are considered. The calculation results suggest that in a routine range of values for the viscous damping ratio (less than 0.05), the damping effect on the UNDEX-induced displacement and damage responses of the arch dam seem limited. To be conservative in the design, the viscous damping ratio could be assigned a zero value (neglecting the damping effect). The calculation results have highlighted the importance of the monolith-to-monolith friction to the tensile damage to the dam base. We believe that a value of 0.65 assigned to the friction coefficient should be appropriate for the UNDEX resistant design of an arch dam in case the shear keys’ shear-transferring roles are not considered.

SA2USING GENETIC INSTRUMENTS TO ASSESS CAUSAL PATHWAYS TO EDUCATIONAL ATTAINMENT IN ADHD AND AUTISM: EVIDENCE FROM A TWO SAMPLE MENDELIAN RANDOMISATION STUDY

Fluid–structure interaction formulated in the Lagrangian–Eulerian approach with pressure-based fluid elements, which inherently results in non-symmetric matrices, is commonly treated by either direct un-symmetric solvers or staggered solution methods. Developing an in-house finite element code called SNACS, we implement the pressure-based Eulerian formulation so that a usual symmetric solver can be employed for dam–reservoir interaction analyses. The equilibrium equations of motion for such a coupled system are directly integrated herein by the HHT time marching algorithm in an incremental–iterative solution procedure to tackle a highly nonlinear dynamic analysis of jointed arch dams. The HHT time integration scheme is able to damp out high-frequency noises resulting from sudden changes in the stiffness due to opening/closing of pre-existing joints during an earthquake. First, a Pseudo-Symmetric technique is proposed to store the total matrices and solve the coupled non-symmetric equations in a symmetric manner. Then, the interface element formulation and stress update procedures of two discrete crack constitutive models suitable for contraction and peripheral joints of arch dams are detailed. Afterwards, results of the analysis on a typical arch dam are compared with the case in which the interaction is approximately represented by added masses as a widely-used method in dam engineering practice to illustrate the effects of water compressibility and reservoir bottom absorption. Besides, the straightforward implementation of pressure-based fluid–structure interaction utilizing a symmetric solution strategy is validated herein to be efficient for a 3-D large scale practical usage in other finite element codes even the commercial ones to avoid using un-symmetric solvers. Employing this symmetric implementation for the dam–water interaction drastically reduces the computational effort, particularly when an iterative scheme is required to solve such a highly nonlinear system.

A Ritz Procedure for Transient Analysis of Dam–Reservoir Interaction

A simple and accurate variational formulation is proposed to study the transient dynamic responses of two-dimensional dam–reservoir system. The proposed methodology uses a simple weak formulation with Ritz procedure to reduce the governing partial differential equations of the fluid and structure to a set of ordinary differential equations. An analog procedure is then presented to exactly implement the natural boundary condition of the problem at fluid–structure interface. The Newmark time integration scheme is used to solve the resulting system of ordinary differential equations. To demonstrate the accuracy and efficiency of the proposed formulation, the problem is also solved using the finite element method (FEM). It is found that the proposed method can produce better accuracy than the FEM using less computational time. The technique presented in this investigation is general and can be used to solve various fluid–structure interaction problems.

Seismic Improvement of Gravity Dams Using Isolation Layer in Contact Area of Dam–Reservoir in Smeared Crack Approach

This study has been conducted to evaluate the effect of the isolation layer on the seismic improvement of concrete gravity dams considering dam–reservoir interaction. Koyna dam in India, due to both horizontal and vertical components of Koyna earthquake, is modeled as a case study to show the effect of the upstream isolation layer on the seismic response of concrete gravity dams, and also the interaction effect is considered in models. The water is taken as a compressible, inviscid fluid and the foundation as rigid. Gravity dams are considered as 2D structures due to long dimension in cross-stream direction and plane strain assumptions. ANSYS software was used for analysis so that the fixed smeared crack model is used to consider the nonlinear behavior of mass concrete. A flexible layer which is attached to the upstream face of the dam under different thickness and material properties is considered. The response of unisolated and isolated dams is compared under various conditions. Finally, the effect of unisolated and isolated layers in the reduction of the seismic response of the concrete is evaluated under various thicknesses comparatively. Considering obtained results revealed that the layer can have the reducing effect on responses and crack propagation process of dam model because of damping the induced hydrodynamic pressure due to the earthquake.

A nonlinear analysis of dynamic interactions of CFRD–compressible reservoir system based on FEM–SBFEM

Reservoir water compressibility is a major factor affecting dynamic dam–reservoir interactions, and most studies focus on the analysis of concrete dams. However, few studies have been conducted with respect to the effects of reservoir water compressibility on the dynamic response of CFRDs (concrete-faced rockfill dams). Furthermore, new researches show the hydrodynamic pressure is significant for evaluating the seismic performance of high CFRD. In this paper, a method to calculate the nonlinear dynamic interactions of CFRD–compressible reservoir water system in the time-domain is established based on a FEM–SBFEM approach. The CFRD is discretized using the finite element method (FEM), and the hydrodynamic pressure of the semi-infinite water on the upstream face of the dam is calculated using the efficient scaled boundary finite element method (SBFEM), in which the degrees of freedom of the hydrodynamic pressure to be solved for are relatively few. The objective of this work is to investigate the effects of reservoir water compressibility and the sediment absorption layer at the reservoir bottom and bank slopes on the dynamic response of a high CFRD–reservoir-coupled system under seismic action in various directions. When the reservoir water is considered compressible, partial absorption of the hydrodynamic pressure wave by the sediments can be considered. The results show that water compressibility can significantly affect the stress in the face slabs.

The Effects of Dam–Reservoir Interaction on the Nonlinear Seismic Response of Earth Dams

ABSTRACTThe objective of this study is to investigate the effects of dam–reservoir interaction (DRI) on the nonlinear seismic response of earth dams. Although DRI effects have for long been considered as insignificant for earth dams, that conclusion was mainly based on linear elastic investigations which focused only on the acceleration response of the crest without examining the seismic shear stresses and strains within the dam body. The present study explores further the impact of DRI focusing on the nonlinear behavior of earth dams. The effects of reservoir hydrodynamic pressures are investigated in terms of both seismic dam accelerations and nonlinear dynamic soil behavior (seismic shear stresses and strains). It is shown that although dam crest accelerations are indeed insensitive to DRI, the stress and strain development within the dam body can be significantly underestimated if DRI is ignored.

Dynamic failure analysis of concrete dams under air blast using coupled Euler-Lagrange finite element method

In this study, the air blast response of the concrete dams including dam-reservoir interaction and acoustic cavitation in the reservoir is investigated. The finite element (FE) developed code are used to build three-dimensional (3D) finite element models of concrete dams. A fully coupled Euler-Lagrange formulation has been adopted herein. A previous developed model including the strain rate effects is employed to model the concrete material behavior subjected to blast loading. In addition, a one-fluid cavitating model is employed for the simulation of acoustic cavitation in the fluid domain. A parametric study is conducted to evaluate the effects of the air blast loading on the response of concrete dam systems. Hence, the analyses are performed for different heights of dam and different values of the charge distance from the charge center. Numerical results revealed that 1) concrete arch dams are more vulnerable to air blast loading than concrete gravity dams; 2) reservoir has mitigation effect on the response of concrete dams; 3) acoustic cavitation intensify crest displacement of concrete dams.

Numerical simulation of nonlinear structural responses of an arch dam to an underwater explosion

Abstract This paper is a preliminary attempt to examine nonlinear structural responses of an arch dam to an underwater explosion (UNDEX) shock loading based on numerical simulation. The numerical simulation is based upon the explicit dynamics finite element program ABAQUS/Explicit. Both the dam-reservoir interaction and the contraction-joint non-linearity are considered. Our research has underlined the importance of the shear keys to the integrity of the arch dam. Failures of the shear keys make each monolith more independent and thus the dam structure as a whole more flexible. Two major failure modes of the arch dam have been identified: (a) a break-off failure of the monolith closest to the explosive source, and (b) tensile cracking of the dam base concrete. The presented simulation procedure based upon ABAQUS/Explicit is time-efficient and relatively undemanding owing to its cut-off computational strategy. We believe that it is more suitable for a large-scale three-dimensional UNDEX simulation involving an arch dam than the full-process simulation procedure.