Break Flow Research Articles

Non-hydrostatic depth-integrated models for dam break flows through rigid-emergent vegetation

Dam failures can trigger catastrophic downstream flooding, threatening lives, and infrastructure. Vegetation acts like a natural dam break flow buffer, dissipating energy, reducing wave height and celerity. This highlights importance of vegetation in flood mitigation strategies. Few existing numerical models consider how vegetation affects dam breaks. This is because it is difficult to calculate vegetation drag force in unsteady rapidly varied flows. This study addresses this gap by developing a non-hydrostatic depth-integrated model to simulate the effect of rigid emergent vegetation on dam break flows under various flow conditions. The model was validated with experimental data. Vegetation was simulated with wooden cylinders with different coverage areas and densities within a straight channel. Three dam break scenarios were investigated in the experiment using different Froude numbers to represent diverse flow regimes. The non-hydrostatic depth-integrated model of the General Bottom Velocity method (GBVC4- DWL) was developed to incorporate the vegetation effect through the drag force equation for non-uniform open channel flows. The results show that rigid emergent vegetation significantly reduces wave celerity and height, particularly downstream, demonstrating its importance in flood mitigation. The numerical model accurately predicted wave behaviour outside the vegetation zone but have difficulties within it, highlighting the need for the model to be improved to capture complex vegetation-flow interactions.

Study on the ice-water interaction problem based on MPS-NDEM coupling model

Ice-water coupling is a unique fluid-solid interaction problem characterized by collisions and hydrodynamic interaction between multiple bodies, accompanied by significant changes in the free surface. This paper presents a novel numerical model that achieves two-way coupling between the moving particle semi-implicit (MPS) method and the non-smooth discrete element method (NDEM) to simulate ice-water interactions. The MPS method is employed to model fluid motion, while the NDEM is applied to simulate the motion and collision of ice floes. The improved MPS method presented in this study, based on our previous research, addresses several issues found in the traditional MPS method. To improve the computational efficiency, the domain decomposition method is implemented to parallel the fluid solver and the AMG preconditioned GMRES iterative solver is selected as the optimal solution scheme for the improved MPS method. The accuracy and feasibility of the present coupling model are validated through benchmark cases, such as dam break, wave motion, ice motion in regular waves and debris dam break flow. Furthermore, the simulation of the ship moving in the broken ice field is successfully conducted with the coupling model and the influence of ice-water coupling load on predicting broken ice resistance is also investigated.

Dam break flow through rigid-emergent vegetation

Dam failures pose a significant threat to life and property. This study investigates the potential of rigid emergent vegetation to attenuate dam break waves, reducing their destructive impact. Experiments explored the effect of varying vegetation field lengths on wave propagation. Wooden cylinders with consistent diameter (1.0 cm) and density (0.067) simulated the rigid vegetation in a straight, flat rectangular channel. Four different vegetation lengths and three bore conditions for different reservoir and tailwater depths were examined to analyze their influence on dam break wave behavior. The results demonstrate the effectiveness of vegetation in dissipating wave energy, leading to a rapid decrease in wave height and celerity. Interestingly, increasing vegetation length significantly attenuates the wave height downstream of the vegetation zone, while having no significant impact on the reflection wave height upstream of the vegetation. This finding highlights the targeted effectiveness of strategically placed vegetation in shielding downstream areas. The study also clarifies that celerity can be calculated using shallow water equations for both upstream and downstream regions with wave height and tailwater depth. However, within the vegetation, drag forces significantly reduce celerity. A novel equation, derived from wavefront profiles, was proposed and validated to accurately calculate celerity within the vegetation field. These findings provide valuable data for validating numerical models simulating dam break wave interactions with vegetation.Graphical abstract

Observation of Two-Dimensional Dam Break Flow and a Gaseous Phase of Solitons in a Photon Fluid.

We report the observation of a two-dimensional (2D) dam break flow of a photon fluid in a nonlinear optical crystal. By precisely shaping the amplitude and phase of the input wave, we investigate the transition from one-dimensional (1D) to 2D nonlinear dynamics. We observe wave breaking in both transverse spatial dimensions with characteristic timescales determined by the aspect ratio of the input box-shaped field. The interaction of dispersive shock waves propagating in orthogonal directions gives rise to a 2D ensemble of solitons. Depending on the box size, we report the evidence of a dynamic phase characterized by a constant number of solitons, resembling a 1D soliton gas in integrable systems. We measure the statistical features of this gaslike phase. Our findings pave the way to the investigation of collective solitonic phenomena in two dimensions, demonstrating that the loss of integrability does not disrupt the dominant phenomenology.

The Assessment of Peak Discharge Increment Due to Land Use Change in the Serang Welahan Drainage 1 (SWD 1) River, Central Java Province, Semarang

SWD1 River is located in one of those flood-prone areas in Central Java that generates flood hazards causing high risk to the surrounding rice fields and communities. However, a comprehensive study of flood hazards in SWD1 River has never been conducted. Nowadays, previous comprehensive flood studies in Indonesia only available for several very developed areas, such as the Jakarta Flood [1] – [5], Bandung Flood and Solo Flood , or new iconic area for mangrove conservation such as Langsa City . Most previous studies conclude that flood hazards in Indonesia are commonly generated by rain runoff, tides, and dam break flows, or a combination of these generators . Existing conditions show that SWD 1 is unable to accommodate runoff from the Wulan River, causing flooding. Based on rainfall data from BMKG, the maximum rainfall per month for a year reaches 323 mm. This study is an effort to analyze the impact of land use change.The research method used analysis of the influence of changes in CN (Curve Number) due to changes in land use on flood discharge as shown through changes in the Soil Conservation Service (SCS-CN) hydrograph on discharge and runoff volume. The selection of the SCS-CN method is due to its widespread adoption in various regions, its extensive use in numerous analytical studies, and its suitability for the characteristics of the watershed under review.The analysis results show that there has been a change in flood discharge from 2019 and 2022 with values of 366.920 and 371.154 m3/second. The discharge values did not change significantly because the CN values were as follows, 83.25 and 83.36. Through analysis, it can be seen that an increase in discharge of 1.14% from 2011 to 2022.The several alternatives are needed to reduce flooding, such as watershed conservation upstream, minimizing land use changes and building flood mitigation infrastructure downstream.

Resolving subgrid-scale structures for multiphase flows using a filament moment-of-fluid method

Multiphase flows are present in many industrial and engineering applications as well as in some physical phenomena. Capturing the interface between the phases for complex flows is challenging and requires an accurate method, especially to resolve fine-scale structures. The moment-of-fluid (MOF) method improves drastically the accuracy of interface reconstruction compared to previous geometrical methods. Instead of refining the mesh to capture increased levels of detail, the MOF method, which uses zeroth and first moments as well as a conglomeration algorithm, enables subgrid structures such as filaments to be captured at a small extra cost. Coupled to a finite volume Navier–Stokes solver, the MOF method has been tested on a fixed grid and validated using well-known benchmark problems such as dam break flows, the Rayleigh–Taylor and Kelvin–Helmholtz instability problems, and a rising bubble. The ability of the novel filament MOF method to capture the filamentary structures that eventually form for the Rayleigh–Taylor instability and rising bubble problems is assessed. Good agreement has been found with other numerical results and experimental measurements available in the literature.

A Smoothed Particle Hydrodynamics Approach for One-Dimensional Dam Break Flow Simulation with Boussinesq Equations

A Smoothed Particle Hydrodynamics Approach for One-Dimensional Dam Break Flow Simulation with Boussinesq Equations

The preliminary design of emergency core cooling scheme and loss-of-coolant accident analysis for Tsinghua high flux reactor

This paper proposes the preliminary emergency core cooling scheme for Tsinghua High Flux Reactor. According to the thermohydraulic characteristics of high flux reactors, forced circulation needs to be maintained by emergency pumps in the early stage. When the decay power is low enough, natural circulation between core and the reactor pool is initiated to remove the residual core heat. The sources of safety injection are accumulators and reactor pool. Accumulator injection can ensure core safety in the early stage and reactor pool injection can maintain long time stable forced circulation. To avoid emptying the reactor pool, the waterproof zone needs to be built. The waterproof zone consists of reactor pool and several finite volume dry pools. All pipelines and equipment in the reactor coolant system are placed in the dry pools. Once break accident occurs, the dry pool where the break is located can collect the leaked coolant. With the increase of break back pressure, the break flow is restricted. The current scheme is modeled by Relap5 and different size breaks at four locations (namely core inlet, core outlet, primary heat exchanger inlet and main pump inlet) are assumed. According to the response characteristics of the scheme, the accident process can be divided into five stages: non-shutdown stage, high-injection stage, low-injection stage, stable forced circulation stage and natural circulation stage. Critical heat flux predicted by Sudo CHF correlations is adopted as the primary safety criterion. Through analysis, a success path is found to maintain core safety for a wide range of loss-of-coolant accident scenarios.

Gaussian smoothed particle hydrodynamics: A high-order meshfree particle method

Smoothed particle hydrodynamics (SPH) has attracted significant attention in recent decades, and exhibits special advantages in modeling complex flows with multiphysics processes and complex phenomena. Its accuracy depends heavily on the distribution of particles, and will generally be lower if the particles are distributed non-uniformly. A high-order SPH scheme is proposed in the present work for simulating both compressible and incompressible flows. It uses a Gaussian quadrature rule to perform the particle approximation of SPH by introducing Gaussian nodes. Unfortunately, the Gaussian nodes hardly overlap with SPH particles due to the Lagrangian feature, and thus we use a high-order interpolation method to obtain the corresponding physical quantities at the Gaussian nodes. The accuracy and robustness of the proposed Gaussian SPH are demonstrated by several numerical tests, including the Sod problem, Poiseuille flow, Couette flow, cavity flow, Taylor–Green vortex and dam break flow, and a convergence analysis is also conducted to evaluate the effects of particle resolution and distribution for reconstructing a given function. The simulation results for each test case are in good agreements with the available analytical, experimental or numerical results, showing that the proposed Gaussian SPH method is accurate and reliable but expensive for simulating compressible and incompressible flow problems.

Spatio-temporal water height prediction for dam break flows using deep learning

Spatio-temporal prediction of the water height for dam break flow is of great significance in flood control projects. In this article, we propose a novel deep learning model named AE-LSTM-ATT that combines AutoEncoder (AE) and Long Short-Term Memory with Attention (LSTM-ATT) to predict the dynamic behavior of the dam-break water height field in spatial and temporal dimensions. The prediction performance of the AE-LSTM-ATT model was demonstrated using dam-break flow cases with different initial heights of the water column. The AE first compresses high-dimensional inputs into low-dimensional latent space using its encoder to enable a fast computation process. Then, the latent space is adopted as an input for the LSTM-ATT to predict low-dimensional representations at future time instances that can be restored to the water height field by the decoder of the AE. The major findings of this article include three parts: (1) AE-LSTM-ATT model can successfully achieve the spatio-temporal prediction of the water height for dam break flows with high precision; (2) The proposed AE presents much better performance than those of the widely used Principal Component Analysis (PCA) and Kernel Principal Component Analysis (KPCA) in the dimension reduction; (3) The developed LSTM-ATT performs far better than the commonly used Recurrent Neural Network (RNN) and Long Short-Term Memory (LSTM) in the time-series prediction. These promising results suggest that the proposed AE-LSTM-ATT model can play an essential role in capturing and advancing the spatio-temporal features of dam-break water height, which can be applied in the field of real-time decision making for dam-break floods.

A new 2D ESPH bedload sediment transport model for rapidly varied flows over mobile beds

A 2D Eulerian meshless bedload sediment transport model is developed using smoothed particle hydrodynamics (SPH) to simulate rapidly varied flows over mobile beds. In the developed model, we adopt a weakly coupled numerical approach to explicitly solve the governing equations, including 2D shallow water equations for fluid flow motion and the Exner equation for bed sediment movement at the same time step. A defined virtual bedload velocity in a weakly coupled approach is involved in the calculation of time step sizes. However, nonphysical virtual bedload velocities, which often occur in cases with nearly flat beds, require extremely small time step sizes. A formulation of the lower and upper bounds of information propagation speeds for an HLLC approximate Riemann solver is thus proposed to remedy the problem. Four case studies involving dam break flows in prismatic and erodible channels, knickpoint migration, dam erosion due to overtopping flow and dam-break flow in an erodible channel with an abrupt expansion are adopted to validate the developed model. In addition, to compare the performances of different particle interaction configurations under Cartesian uniform particle arrangements, four and eight interacting particles are obtained by changing the smoothing length. Against the measured results, the case of eight interacting particles shows more accurate predictions of erosion peaks along the measured cross-sections because the lateral flows are significant. The good agreement between the simulated and measured results shows that the developed 2D Eulerian SPH bedload sediment transport model with eight interacting particles is well suited for simulating complicated flow-induced bed erosion.

Numerical investigation of dam break flow over erodible beds with diverse substrate level variations

Abstract This study aimed to comprehensively investigate the influence of substrate level difference and material composition on dam break wave evolution over two different erodible beds. Utilizing the Volume of Fluid (VOF) method, we tracked free surface advection and reproduced wave evolution using experimental data from the literature. For model validation, a comprehensive sensitivity analysis encompassed mesh resolution, turbulence simulation methods, and bed load transport equations. The implementation of Large Eddy Simulation (LES), non-equilibrium sediment flux, and van Rijn’s (1984) bed load formula yielded higher accuracy compared to alternative approaches. The findings emphasize the significant effect of substrate level difference and material composition on dam break morphodynamic characteristics. Decreasing substrate level disparity led to reduced flow velocity, wavefront progression, free surface height, substrate erosion, and other pertinent parameters. Initial air entrapment proved substantial at the wavefront, illustrating pronounced air-water interaction along the bottom interface. The Shields parameter experienced a one-third reduction as substrate level difference quadrupled, with the highest near-bed concentration observed at the wavefront. This research provides fresh insights into the complex interplay of factors governing dam break wave propagation and morphological changes, advancing our comprehension of this intricate phenomenon.

Quantitative comparison of dam break and bubble flows based on CF-VOF and IR-VOF schemes

In this study, an incompressible and immiscible two-phase flow solver was employed to assess the accuracy of phase-interface capturing methods in simulating two-phase flows. Three benchmark investigations were conducted involving two dam break flows with deformable free surfaces and the upward motion of a gas bubble through a liquid column. Four phase-interface capturing schemes, namely, MULES, HRIC and CICSAM from the Color Function Volume of Fluid (CF-VoF), and Interface Reconstruction Volume of Fluid (IR-VoF), were utilized. Comparative analysis of the phase interfaces indicated that CICSAM and IsoAdvector consistently provided sharp interfaces across all cases when compared to MULES and HRIC. The mass conservation performance of all schemes excelled in the dam-break case with relatively simple free-surface development and the rising bubble case. An examination of the local pressure distribution over time revealed that methods yielding diffusive interfaces produced inaccurate results. Thus, the importance of employing denser grids or schemes that yield sharper interfaces, such as CICSAM and IsoAdvector, to enhance simulation accuracy was underscored. Overall, the results of this analysis confirm that the IsoAdvector scheme, which provides sharp interfaces, is a reliable option for simulating incompressible immiscible two-phase flows.

A numerical model for simulation of two-phase flows interaction with flexible slender bodies

This paper introduces a fluid–structure interaction (FSI) model for simulation of the coupled dynamics between two-phase flows and elastic slender structures. This model is extended from the early FSI model for single-phase flows by Wang et al. [“A coupled flow and beam model for fluid–slender body interaction,” J. Fluids Struct. 115, 103781 (2022)] to two-phase flows with interfaces of two liquids or free surfaces between gas and liquid. To better capture the interface movement of the two-phase flows and the interaction with the deformable structure, a consistent mass and momentum flux scheme is developed to reduce the spurious oscillation of fluid velocities near the interface, especially in the lower density (e.g., air) region. The proposed model is validated by a series of two-dimensional laboratory experiments of flow impact on a deformable plate, demonstrating that the model has good capabilities of conserving mass and momentum during the process of plate deformation by impulsive flow forces. The model is also applied to the investigation of three-dimensional dam break flow impact on a column of elastic plates. The complex interaction between the plates and the flow is discussed based on the simulation results.

Two-Dimensional Simulation of Dam Break with Partial Damage Condition using Ansys Software

The issue of dam failure has been a key contributor to massive catastrophes, as well as economic and physical destruction. Nevertheless, the effectiveness and accuracy of the simulation of a dam break model are still under debate. In this study, a simulation of a 2D model of the dam breaking half-filled water tank was carried out using Ansys software to evaluate the deformation and water pressure of dam break flow. Four sensors were installed to examine the changes in pressure of the water deformation. Deformation of water at a certain time of the dam break simulation and the pressure of water inside were analyzed and compared with the experimental result, which has been reported by Lobovský. Validation and verification of hydrostatic tests have been found to be in agreement with the current model simulation. An extensive set of data for the simulation is given access as supplementary materials for the direct result of the recent initiative. The results show that by excluding minor differences in wave shape and duration of water movement, the deformation of water exemplifies the same behavior as the experimental results. For experimental data, the non-dimensional time of the dam break event is ranged within 0 to 7.14828 ms while the pressure of water flow is within 0 to 3.0441 Pa. As for simulation results, the non-dimensional time of the dam break event is ranged within 0 to 202 ms whereas the pressure of water flow is within 0 to 0.54124 Pa. Thus, to strengthen the quality numerical model, future work should emphasize the initiative to incorporate the Smooth Particle Hydrodynamics (SPH) method with the goal of improving computational validity and efficiency.

Dam Break Flow: A Comparative Model Study Using OpenFOAM and BASEMENT

Dam Break Flow: A Comparative Model Study Using OpenFOAM and BASEMENT

Effects of mechanical recycling on the properties of glass fiber–reinforced polyamide 66 composites in automotive components

Abstract In this study, we aimed to reveal the effective reusability of waste generated during the injection molding process of polyamide 66 (PA66) reinforced with 30 wt% of short glass fiber (PA66-GF30) widely used in the automotive industry. PA66-GF30 was subjected to the three mechanical recycling cycles, including regranulation and reinjection molding steps, and the recycled materials obtained in each of these cycles were included at the ratios of 15, 20, 25, and 30 wt% to the virgin composite. Thermogravimetric analysis and differential scanning calorimeter analyses showed that the number of recycling cycles and recycled material content in the composite had no significant change in the thermal stability and crystallinity degree of the PA66-GF30. The average fiber length determined by optical microscope analysis shifted to lower values from 300–350 to 150–250 μm by increasing the number of recycling cycles and the recycled material content. The fact that the recycled material content in the composite exceeds 25 wt% and the recycling cycle is applied three times played a key role in changing the mechanical and melt flow behaviors of the composite. Tensile strength, elastic modulus, and impact energy slightly decreased while the elongation at break and melt flow index increased.

Numerical three-dimensional modeling of earthen dam piping failure

A physically-based numerical three-dimensional earthen dam piping failure model is developed for homogeneous and zoned soil dams. This model is an erosion model, coupled with force/moment equilibrium analyses. Orifice flow and two-dimensional (2D) shallow water equations (SWE) are solved to simulate dam break flows at different breaching stages. Erosion rates of different soils with different construction compaction efforts are calculated using corresponding erosion formulae. The dam's real shape, soil properties, and surrounding area are programmed. Large outer 2D-SWE grids are used to control upstream and downstream hydraulic conditions and control the boundary conditions of orifice flow, and inner 2D-SWE flow is used to scour soil and perform force/moment equilibrium analyses. This model is validated using the European Commission IMPACT (Investigation of Extreme Flood Processes and Uncertainty) Test #5 in Norway, Teton Dam failure in Idaho, USA, and Quail Creek Dike failure in Utah, USA. All calculated peak outflows are within 10% errors of observed values. Simulation results show that, for a V-shaped dam like Teton Dam, a piping breach location at the abutment tends to result in a smaller peak breach outflow than the piping breach location at the dam's center; and if Teton Dam had broken from its center for internal erosion, a peak outflow of 117 851 m3/s, which is 81% larger than the peak outflow of 65 120 m3/s released from its right abutment, would have been released from Teton Dam. A lower piping inlet elevation tends to cause a faster/earlier piping breach than a higher piping inlet elevation.

Numerical study of the dam-break flood over natural rivers with macroscopic rocks on movable beds

This paper presents a three-dimensional model of dam break flows over fixed and movable beds. As the consequences of a dam break, the model considers the transport of solid particles and deposition due to the momentum of the flow. The movement of the free surface of water and mud is performed by Newtonian and non-Newtonian fluid models, and the solid macroscopic particles movement is carried out by the discrete phase model (DPM) and macroscopic particle model (MPM) models. It has been detected that the model was reliable and well balanced, and could accurately capture the dam break flow movement in complex terrain. Moreover, using the proposed model, a partial dam break of the Mynzhylky Dam was simulated. Even more in the calculation, the presence of mud sediment and solid particles were taken into account, which is very close to the real dam break problem.

A 2D Hydraulic Simulation Model Including Dynamic Piping and Overtopping Dambreach

Numerical simulation of unsteady free surface flows using depth averaged equations that consider the presence of initial discontinuities has been often reported for situations dealing with dam break flow. The usual approach is to assume a sudden removal of the gate at the dam location. Additionally, in order to prevent any kind of dam risk in earthen dams, it is very interesting to include the possibility of a progressive dam breach leading to dam overtopping or dam piping so that predictive hydraulic models benefit the global analysis of the water flow. On the other hand, when considering a realistic large domain with complex topography, a fine spatial discretization is mandatory. Hence, the number of grid cells is usually very large and, therefore, it is necessary to use parallelization techniques for the calculation, with the use of Graphic Processing Units (GPU) being one of the most efficient, due to the leveraging of thousands of processors within a single device. The aim of the present work is to describe an efficient GPU-based 2D shallow water flow solver (RiverFlow2D-GPU) supplied with the formulation of internal boundary conditions to represent dynamic dam failure processes. The results obtained indicate that it is able to develop a transient flow analysis taking into account several scenarios. The efficiency of the model is proven in two complex domains, leading to >76× faster simulations compared with the traditional CPU computation.