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

Dams are considered one of the most important infrastructure facilities of a country, which play a very important role in economic prosperity through storage, regulation of water, and also energy production. Due to the volume of water stored in the reservoir of these dams and sometimes their proximity to residential areas, the failure of dams can lead to a lot of human and financial losses, which can be prevented by having sufficient information and proper forecasts of dam failure. The flow resulting from the dam failure is turbulent, mainly a mixture of fluid and sediment particles. Therefore, after the dam's failure, sediment transport leads to significant morphological changes downstream. Based on this, the analysis and evaluation of the instantaneous failure of the dam have been one of the main challenges of the profession of engineers and activists in this field. By examining the research background, it is clear that the studies focused on fluid flow in non-erodible bed conditions, and a small part of numerical and laboratory research has been focused on the evaluation of changes in the morphology of the bed sediment layer. In addition, one of the effective parameters in the mechanism of sediment transfer and the pattern of morphological changes of the bed is the sediments of the dam reservoir, which has received less attention from researchers. Therefore, in this research, we have evaluated and experimental-numerically modeled the phenomenon of sediment transport due to the sudden failure of the dam, taking into account the sediment layer in the dam reservoir.

In this study, two variables (1- the type of sediment particles (fine sand and coarse sand) and 2- the thickness of the sediment layer in the reservoir and downstream of the dam) have been investigated as the main parameters in the evaluation of the sediment transport mechanism (changes in bed morphology). Based on this, scenarios have been defined for laboratory and numerical modeling. In this research, to evaluate the phenomenon of bed sediment transfer based on the phenomenon of instantaneous dam failure, four tests have been defined and implemented in the hydraulic laboratory flume of Babol University in different conditions. This flume is 10 meters long, 50 cm wide, and 50 cm high and is equipped with an ultrasonic level gauge and a digital pressure gauge. In these experiments, two parameters of the type of bed sediment materials (A, B) and also the thickness of the sediment layer downstream of the dam and the reservoir of the dam have been considered as modeling variables. Type A materials are gravel particles with an average diameter of 20 mm, and type B materials are sand particles with an average diameter of 3 mm.

According to the research variables, four scenarios for laboratory modeling and six scenarios for numerical modeling of the phenomenon of sediment transfer based on instantaneous dam failure have been defined. The results of the numerical modeling showed that the numerical model of the research had acceptable accuracy in simulating the phenomenon of sediment transfer due to dam failure, so the modeling error for two-dimensional numerical models (the first four models based on Table 2) is respectively equal to 2.75%, 4.31%, 2.59%, 5.52% compared to laboratory tests.The results showed that in the models of type B sediment materials, the amount of reduction in the thickness of the sediment layer is greater than in the models with type A sediment materials; in other words, the amount of reduction in the thickness of the sediment layer in type B materials is more than type B. The material was A. Therefore, the decrease in the diameter of the sediment particles has caused an increase in the thickness of the sediment layer (bed morphology) due to the failure of the instantaneous dam. In addition, by examining the results obtained from laboratory and numerical models, it was determined that the reservoir sediment layer of the dam is an effective parameter in the rate of sediment transfer and the occurrence of changes in the morphology of the bed based on the dam failure currents, in such a way that with the increase in the thickness of the sediment layer of the reservoir Compared to the downstream sediment layer of the dam, the changes in the thickness of the bed layer have increased by about 10%, as well as the rate of sediment transfer in these conditions.By evaluating the results of dam failure modeling in three-dimensional space, it is clear that the thickness of the sediment layer in the 3D_DB1_NB1 model with type B materials has decreased more compared to the 3D_DB1_NA1 model with type A materials. In addition, according to the contour of the changes in the thickness of the bed layer, it is clear that the type of material of the sediment particles (diameter of the sediment particles) was an effective factor in evaluating the phenomenon of sediment transport in the 3D modeling space. In both 3D models, the thickness of the sediment layer in the area of the dam valve (failure area) has decreased and increased in the range of 1.8 to 2 meters and decreased from 2.2 to 3 meters.

In this research, the main goal is to evaluate the mechanism of sediment transfer due to the sudden failure of the dam, focusing on the effect of the sediment layer in the dam reservoir, which has been implemented in the form of laboratory and numerical modeling. Also, the effect of three parameters, the type of sediment particles and the thickness of the sediment layer in the reservoir and downstream of the dam axis, has been studied.Based on the results of this research and the evaluation and comparisons made between the numerical models and the laboratory model, it is clear that the numerical model created in both two-dimensional and three-dimensional spaces has an acceptable accuracy in simulating the phenomenon of sediment transfer due to dam failure.

Introduction In dam failure studies, prediction of its hydraulic components, including depth and velocity, has always been important for hydraulic engineers due to its impact on the severity of the disaster. There are various hydraulic, hydrological, geotechnical and geometric factors that affect the characteristics of the flow through the failure of the dam. In order to investigate the effect of the factors, research has been carried out especially in the field of laboratory, but little numerical research has been done. Resource surveys show that although the walls of concrete reservoir dams are not perpendicular to the lateral support, but so far, the effect of wall deflection on the hydraulic properties of the flood due to the dam failure has not been considered. Therefore, in this research, the effect of quarries of 2.5 to 10 percent of the wall of the dam was examined from the perpendicular to the base. Since the wall deviation of the dam from the normal state removes physical space from a rectangular state, the use of orthogonal coordinate system is not possible. Therefore, in this study, using the curvilinear coordinate system of the physical non- rectangular space studied, It is very accurately converted to computational space and the governing equations are solved. Materials and Methods In this research, the governing equations for shallow water were discritized in curvilinear coordinates by explicit finite difference method. For more stability Lax and Leap-Frog schemes on staggered mesh are utilized, too. For areas studied, in order to determine the coordinates of points in the physical space, by presenting a computer program, the computational mesh is created in Cartesian coordinates. Then, by converting the coordinates in the Cartesian system (x, y) to the curvilinear coordinates (ξ, η). Results and Discussion In order to validate the present model, its results were compared with experimental investigation by previous researchers. 1- Failure of the dam in the convergent-divergent channel without sloping and sloping: The water level profile of the laboratory model is presented for different times (zero, 4, 20, 60) seconds. The mean error in the results of the present numerical model is 4.02% for the results of the measurements for the non-slope channel and for the channel with a 0.01 slope, 1.65%. 2- Dam Failure in canal with dry bed with trapezoidal reservoir: The results of the model follow a similar trend to the experimental results, and the magnitude of the error in the peak areas that is more important is not significant. 3- The effect of the wall angle of the partial symmetric dam-break in the dry bed: It was observed that with the diversion of the wall angle of the dam from the perpendicular position in the failure site, depth and rate of flow decreased more. A closer examination shows that for diversion of 2.5, 5, 7.5 and 10 percent, peak discharge values were decreased  3.5, 6.1, 9.2, 11 percent, and the maximum water level was 2, 6, 9 and 12 percent.   Conclusions In simulating the ideal failure of the deformed reservoir on a dry bed, the results of this numerical model are adapted with the results obtained from the physical model. In another study, the results of the model were compared in the simulation of the dam failure phenomenon in the convergent-divergent channel without sloping and sloping with the results of the measurements. It was determined that a numerical model with an average error of less than 5% estimated the depth of the flow in the failure location.In order to achieve the main objective of the research, the results of the present numerical model in simulating the partial symmetric dam failure on dry bed have been investigated. It was observed that the diversion of the angle of the dam wall at the failer site affects the depth and discharge peak flow. The variations in “q” from the upstream of the reservoir to the failer site increase sharply and reach the maximum at the fracture site, then slowly decrease to the end of the reservoir wall. Similarly, changes in the water level with the distance from the upstream wall and moving towards the failer site are higher.  Keywords Dam-Break, Leap-frag and Lax schem, Curvilinear grid, Angel of Dam Wall  with Support.

Flooding caused by dam failure is been one of the most awful events in the past two centuries. In this type of flooding, a considerable amount of water releases in the river downstream in a short time and causes huge waves in the coastal. Due to the nature of wave, the use of mathematical models is common for simulating advancing and spreading of flood caused by it. In this case study, the subsequences of the flood volume released by the failure of Mirza Shirazi storage dam that is under construction (in Fars province) and estimating of damage with respect to two probable dam break scenarios: 1) immediate failure due to overtopping; and 2) gradual failure due to overtopping, is been investigated. In immediate failure scenario, calculated peak of flood discharge at the point of failure was 118,000 m3/s and in gradual failure was 80,000 m3/s. The average velocity of water in the river bed in immediate failure scenario is 10.2 m/s and in gradual failure scenario is 5.06 m/s. The result estimated damage cost of flood caused by dam break, in scenario of gradual failure is 5578 billion Rials and in immediate scenario is 9136 billion Rials.

In this paper, the dam break phenomena has been simulated in curved rivers using 3D numerical model, Flow-3D. It utilizes the finite volume scheme for structured meshes was used for solving the unsteady Reynolds-averaged Navier-Stokes equations in conjunction with the RNG k-ε closure model. In the utilized software, the Fractional Area/Volume Obstacle Representation (FAVOR) method is used to inspect the geometry in the finite volume mesh. FAVOR appoints the obstacles in a calculation cell with a factional value between 0 to 1 as obstacle fills in the cell. Fluid surface shape is illustrated by volume-of-fluid (VOF) function F(x,y,z,t). With the VOF method, grid cells are classified as empty, full, or partially filled with fluid. Cells are allocated in the fluid fraction varying from zero to one, depending on fluid quantity. The pressure and velocity are coupled implicitly by using the time-advanced pressures and time-advanced velocities in the momentum and continuity equations, respectively. FLOW3D solves these semi-implicit equations iteratively using relaxation techniques. In this paper the GMRES technique has been used as pressure implicit solver. A flux surface is a diagnostic feature in FLOW-3D for computing fluid flow rates. It can be used to obtain time-dependent information about the flow in different parts of the domain. A typical flux surface is a 100% porous baffle with no flow losses, so it does not affect the flow in any way. This feature gives the opportunity to determine the flood hydrograph at various stations downstream of the dam. Effects of curve angle and radious of curvature on the flood wave propagation and unsteady flow features along the curved reach, downstream of the dam has been investigated. Results showed that at the initial instants of the dam break in the straight channel, due to the effects of the dynamic wave, flood hydrographs at the dam location and at a distance downstream of the dam have local peak values, while in the curved chnnel cases, the flood wave becomes unstable immediately after the dam break and the local peak occures just at the dam section. The curved reach decelerate the flood wave propagation compared to the straight channel. Effect of channel curvature on the movement of the flood wave along the inner bank is higher than the outer bank and also the centerline of the curved channel. By decreasing the central radious of the bend, slope of the rising limb of the hydrograph and also the peak discharge, attenuates. Furthermore, the peak discharge time reduces. Unlike to effects of the curvature of the bend, increasing the bend angle does not affect the peak discharge. Changing the bend curvature and curve angle has no effect on the falling limb of the flood hydrograph at various stations downstream of the dam.

Flooding induced by large dam breaks causes severe and heavy damages to human lives and civil facilities. Knowing the volume and direction of the ood spreading, due to the breaking of a certain dam, in advance, may allow us to specify the areas prone to ood damage and help the institutions in charge to be on full alert before catastrophe occurs. The main aim of this research is to study the in uence of the shape factor of a dam reservoir on a ood hydrograph, induced due to a dam break, by means of a physical model in the laboratory. Thus, the sudden dam break phenomenon has been modeled in the hydraulic laboratory of Amirkabir University of Technology. Dierent tests have been planned and carried out in the laboratory for shape factors ranging from 0.040 to 0.557. Hence, 7 series of reservoir with dierent dimensions and geometry have been built and tested. To measure the ow velocity and also the variations of water level at dierent points of the channel, the ADV speed meter and Ultrasonic and Micro sonic sensors were used, respectively. Having the variations of velocity and water level, the ow rate, due to dam break, is calculated and the corresponding hydrograph for each reservoir shape factor is obtained. Finally, the obtained hydrographs are evaluated and compared, and a correlation between the reservoirs shape factor and the Froude Number is developed. The experimental data were compared with those obtained from dierent actual dam break case histories. Although good agreement between the trends was found, large deviations from actual cases were observed. This may be due to several simpli ed procedures applied to the physical model developed in the laboratory to study the phenomenon. Thus, more sophisticated models with larger capabilities are needed to reach more accurate and reliable results in future research.

Smoothed Particle Hydrodynamic method is a Lagrangian numerical particle method, best fitted for free surface hydrodynamics. SPHysics is one of the most well-known computer models based on SPH. However, this open source code is limited to one-phase Newtonian fluid problems. In this research, after developing the standard serial SPH code to a two-phase non-Newtonian model, the movable bed dam break problem has been modeled. An added pressure term is used in the pressure equation of state. Afterward, the model has been used for various problems and the validity of results was evaluated by related numerical models and experiments. Finally, the model has been challenged with modeling of dam break movable bed material by non-Newtonian Bingham model and compared with MPS method and experimental results.

Mesh-free particle (Lagrangian) methods، such as moving-particle semi-implicit (MPS) and smoothed particle hydrodynamics (SPH)، are the newest methods in computational fluid dynamics، which have been applied in flow problems with large deformations and inconsistency. The aim of ths research was to develop and improve the simulation of free surface flows، using the new method of weakly compressible MPS (WC-MPS). In the MPS method، pressure is determined by solving Poisson equation. This equation is solved implicitly، which needs too much computer time. In the present research، the WC-MPS method is used to calculate pressure. In this method، as in SPH method، the state equation is used. This equation is solved explicitly، which does not occupy too much computer time. To evaluate the proposed method، the famous applied flow problem of dam break is analyzed. The program is written in C language and validations are performed for this code. To compare the Lagrangian approach with Eulerian approach، dam break is modeled by using FLOW-3D software too. The results of modeling approaches and physical models showed that both approaches have acceptable accuracy in modeling the free surface flow، but the accuracy of Lagrangian approach، especially the WC-MPS، is more than Eulerian approach. The proposed methos had some pressure oscillations، which were analyzed thereafter. Simulation of free surface flows using Weakly compressible moving-particle semi-implicit methodMesh-free particle (Lagrangian) methods، such as moving-particle semi-implicit (MPS) and smoothed particle hydrodynamics (SPH)، are the newest methods in computational fluid dynamics، which have been applied in flow problems with large deformations and inconsistency. The aim of ths research was to develop and improve the simulation of free surface flows، using the new method of weakly compressible MPS (WC-MPS). In the MPS method، pressure is determined by solving Poisson equation. This equation is solved implicitly، which needs too much computer time. In the present research، the WC-MPS method is used to calculate pressure. In this method، as in SPH method، the state equation is used. This equation is solved explicitly، which does not occupy too much computer time. To evaluate the proposed method، the famous applied flow problem of dam break is analyzed. The program is written in C language and validations are performed for this code. To compare the Lagrangian approach with Eulerian approach، dam break is modeled by using FLOW-3D software too. The results of modeling approaches and physical models showed that both approaches have acceptable accuracy in modeling the free surface flow، but the accuracy of Lagrangian approach، especially the WC-MPS، is more than Eulerian approach. The proposed methos had some pressure oscillations، which were analyzed thereafter. Simulation of free surface flows using Weakly compressible moving-particle semi-implicit method

A high resolution finite volume method for solving the shallow water equations with voronoi mesh is developed applying MATLAB software in this paper. The scheme is formally uniformly second order accurate and satisfies maximum principles. The model is verified by comparing the model output with condition of anti-symmetric and circular dam break with documented results. For more investigation we utilized SPSS statistical software. Very good agreement has been achieved in the verification phase. It can be considered as an efficient implement for the computation of shallow water problems, especially concerning those having discontinuities. A simple example of the collapse of water supply reservoir in a valley is used to demonstrate the capability of the model. The presented model is able to resolving shocks, handling, complex geometry, including the influence of steep bed slopes.

Preparing for the consequences of dam failure is very important and should be considered. The failure of a dam can have major effects, such as injury and loss of life, economic, property and environmental damage. More than a century, scientists have seriously studied the dam failure. Flooding caused by a dam failure can occur in a relatively short period. Downstream communities located close to the dam typically have short warning times. Numerical modeling of dam-break flood analysis due to the shallow water equations are often developed as the next one. Initial studies in this area were done by Ritter [1] Dressler [2] and Stoker [3]. In the last decade, remarkable progress has been made in the field of numerical modeling of dam failure. Bellos et al. [4] applied a two-dimensional numerical model to simulate flood waves resulting from the instantaneous break of dams. The McCormack two step predictorcorrector scheme was used for the solution of the transformed system of equations. Comparisons between computed and experimental data showed a satisfactory agreement. The rapidly varied unsteady flow caused by the failure of a dam in a rectangular dry bed horizontal channel has been studied by Hassanzadeh [5]. In the literatures, many researchers have investigated various aspects of dam failure. In this paper, dam break and its flood wave propagation was simulated using finite volume method in twodimensional vertical condition. Numerical results are compared with experimental results for the evaluation ofnumerical model. In this paper, dam break wave propagation in two-dimensional vertical state is simulated by FLUENT model. FLUENT provides comprehensive modeling capabilities for a wide range of incompressible and compressible, laminar and turbulent fluid flow problems. To permit modeling of fluid flow and related transport phenomena inindustrial equipment and processes, various useful features are provided. A very useful group of models in FLUENT is the set of free surface and multiphase flow models. For these types of problems, FLUENT provides the volumeof- fluid (VOF) model. Robust and accurate turbulence models are a vital component of the FLUENT suite of models. The turbulence models provided have a broad range of applicability, and they include the effects of other physical phenomena, such as buoyancy and compressibility. Particular care has been devoted to addressing issues of near-wall accuracy via the use of extended wall functions and zonal model [6]. In this paper, numerical model was tested by three different turbulence models, k-ε, k-ω, and RSM. By use of statistical analysis method, NRMSE, the best turbulence model for 2D dam break, was obtained the k-ε standard(Table 1). Dam break have always been regarded as an extremely risky event and hence the research programs, government planning and investment in coastal dams are of the utmost importance. In this paper, dam break induced wave propagation was simulated using FLUENT model in two-dimensional vertical state, and numerical results were compared with experimental data for the evaluation and verification of numerical model. Dam break was simulated in both dry and wet bed performance for different sizes of the grid mesh, different discretization schemes (such as First Order Upwind, Second Order Upwind, Quick and Power Law) and different turbulence models (k-ε standard,k-ε RNG, k-ε Realizable, RSM and k-ω). Results show that the turbulence k-ε standard model and the First Order Upwind scheme are more accurate than others. After testing the sensitivity and accuracy of the model, simulation is done for basin slopes of 0, 1% and 2% and the roughness of the substrate with coefficients 0.009, 0.015, 0.0185, and0.0198 performance and results were analyzed. The results showed that the numerical model can be used to simulate a dam break in both dry and wet beds and provides acceptable results.