Simulation Of Surface Flows Research Articles

Finite Volume method for general compressible naval hydrodynamics

An efficient, pressure-based segregated Finite Volume solution method for two-phase free surface flow simulations including compressibility effects is presented in this paper. Incompressible treatment of the heavier phase enables efficient long evolutions of wave fields without the need for a separate solver. Air is treated as an ideal gas undergoing isentropic compression/expansion, removing the need for an additional energy equation, and related numerical difficulties. The discontinuity in properties at the free surface between the two phases is treated using the Ghost Fluid Method, correctly accounting for the abrupt change in density and compressibility.Detailed verification and validation is conduced on three simple test cases comprising a liquid piston, free fall impact of a horizontal water column and a regular wave propagation to test the stability and accuracy for cases with and without significant compressibility effects. The present approach is compared with the incompressible formulation for industrial-grade simulations, showing that the same level of accuracy can be achieved without significant overhead in computational time. Finally, a compressible wave breaking impact from a large-scale experimental campaign is reproduced, showing that the method is capable of capturing trapped air cushioning effects with good accuracy.

Assessment of CFD turbulence models for free surface flow simulation and 1-D modelling for water level calculations over a broad-crested weir floodway

Floodways, where a road embankment is permitted to be overtopped by flood water, are usually designed as broad-crested weirs. Determination of the water level above the floodway is crucial and related to road safety. Hydraulic performance of floodways can be assessed numerically using 1-D modelling or 3-D simulation using computational fluid dynamics (CFD) packages. Turbulence modelling is one of the key elements in CFD simulations. A wide variety of turbulence models are utilized in CFD packages; in order to identify the most relevant turbulence model for the case in question, 96 3-D CFD simulations were conducted using Flow-3D package, for 24 broad-crested weir configurations selected based on experimental data from a previous study. Four turbulence models (one-equation, k-ε, RNG k-ε, and k-ω) ere examined for each configuration. The volume of fluid (VOF) algorithm was adopted for free water surface determination. In addition, 24 1-D simulations using HEC-RAS-1-D were conducted for comparison with CFD results and experimental data. Validation of the simulated water free surface profiles versus the experimental measurements was carried out by the evaluation of the mean absolute error, the mean relative error percentage, and the root mean square error. It was concluded that the minimum error in simulating the full upstream to downstream free surface profile is achieved by using one-equation turbulence model with mixing length equal to 7% of the smallest domain dimension. Nevertheless, for the broad-crested weir upstream section, no significant difference in accuracy was found between all turbulence models and the one-dimensional analysis results, due to the low turbulence intensity at this part. For engineering design purposes, in which the water level is the main concern at the location of the flood way, the one-dimensional analysis has sufficient accuracy to determine the water level.

Free Surface Flow Simulation by a Viscous Numerical Cylindrical Tank

In order to numerically investigate the free surface flow evolution in a cylindrical tank, a regular structured grid system in the cylindrical coordinates is usually applied to solve control equations based on the incompressible two-phase flow model. Since the grid spacing in the azimuthal direction is proportionate to the radial distance in a regular structured grid system, very small grid spacing would be obtained in the azimuthal direction and it would require a very small computational time step to satisfy the stability restriction. Moreover, serious mass disequilibrium problems may happen through the convection of the free surface with the Volume of Fluid (VOF) method. Therefore in the present paper, the zonal embedded grid technique was implemented to overcome those problems by gradually adjusting the mesh resolution in different grid blocks. Over the embedded grid system, a finite volume algorithm was developed to solve the Navier–Stokes equations in the three-dimensional cylindrical coordinates. A high-resolution scheme was applied to resolve the free surface between the air and water phases based on the VOF method. Computation of liquid convection under a given velocity field shows that the VOF method implemented with a zonal embedded grid is more advanced in keeping mass continuity than that with regular structured grid system. Furthermore, the proposed model was also applied to simulate the sharp transient evolution of circular dam breaking flow. The simulation results were validated against the commercial software Fluent, which shows a good agreement, and the proposed model does not yield any free surface oscillation.

Climate Change Predictions of Increased Watershed Flow in Atlantic Canada: Implications for Surface Water Vulnerability and Ameliorative Land Use Planning and Management

Essential for comprehensive and sustainable watershed management is the need to understand interactions between climate change predictions and landuse modifications in concert on ecohydrology. The Atlantic Canada region is expected to experience elevated rainfall due to climate change over the next century. We undertook a predictive modeling study of a watershed in rural Nova Scotia, Thomas Brook, to investigate the potential of riparian reforestation to mitigate the deleterious environmental effects projected to occur from future climate change. A Watershed Analysis Risk Management Framework (WARMF) model was used to predict increased watershed flows using data from projections of the Canadian Regional Climate Change Model. The cold climate-validated WARMF model, which has been used previously to simulate surface flow hydrology in many agricultural and mixed-use landscapes, was found to predict increases of 9% to 25% in flow for the Thomas Brook watershed throughout the rest of the century. A spatial, exposure-based model, used previously in several studies, was adopted for assessing changes in surface water vulnerability based on GIS land-use and landscape topography estimates of nutrient loading, sedimentation, runoff, wetland loss, and stream geomorphology. This model indicated that increases in drainage intensity and drainage sensitivity expected through the climate change WARMF model resulted in greater proportions (from 5% to 27%) of the Thomas Brook watershed area being classified as “High vulnerability” for impacting surface water quality. In terms of land use planning, implementation of runoff and nutrient entrapment techniques through low impact development may need to become increasingly required in order to maintain aquatic health. In terms of land-use management, empirically increasing the width of riparian forest buffers was projected to reduce the predicted areal extent of “High vulnerability”. However, widths of 90 m would be required in order to achieve the same degree of protection that presently exists. Our conclusions are that climate-proofing this watershed through riparian reforestation would come at a cost in terms of the extent of land needed to be set aside by being taken out of agricultural production or commercial forestry.

Integrated Hydrological Modeling of Climate Change Impacts in a Snow-Influenced Catchment.

The potential impact of climate change on water resources has been intensively studied for different regions and climates across the world. In regions where winter processes such as snowfall and melting play a significant role, anticipated changes in temperature might significantly affect hydrological systems. To address this impact, modifications have been made to the fully integrated surface-subsurface flow model HydroGeoSphere (HGS) to allow the simulation of snow accumulation and melting. The modified HGS model was used to assess the potential impact of climate change on surface and subsurface flow in the Saint-Charles River catchment, Quebec (Canada) for the period 2070 to 2100. The model was first developed and calibrated to reproduce observed streamflow and hydraulic heads for current climate conditions. The calibrated model was then used with three different climate scenarios to simulate surface flow and groundwater dynamics for the 2070 to 2100 period. Winter stream discharges are predicted to increase by about 80, 120, and 150% for the three scenarios due to warmer winters, leading to more liquid precipitation and more snowmelt. Conversely, the summer stream discharges are predicted to fall by about 10, 15, and 20% due to an increase in evapotranspiration. However, the annual mean stream discharge should remain stable (±0.1m3 /s). The predicted increase in hydraulic heads in winter may reach 15 m and the maximum decrease in summer may reach 3m. Simulations show that winter processes play a key role in the seasonal modifications anticipated for surface and subsurface flow dynamics.

Two methods of surface tension treatment in free surface flow simulations

We describe our approach to treatment of surface tension in free surface flow simulations on adaptive octree-type grids. The approach is based on the semi-Lagrangian method for the transport and momentum equations and the pressure projection method to enforce the incompressibility constrain. The surface tension contributes to the Dirichlet boundary condition for the pressure equation at the projection step. The treatment of surface tension is based either on accurate finite difference calculation of the mean curvature or on a curvature estimation by the implicit solution of conservative mean curvature flow problem. The first method provides almost the second order accuracy in space for surface tension forces. The second method is characterized by greater stability and essentially larger time steps. Numerical experiments illustrate the main features of the methods.

Simulating surface flow and baseflow in Poko catchment, Kon Tum province, Vietnam

Abstract Estimating the volume of water resources has important significance in assessing water availability in a basin, particularly in mountainous areas. The Poko catchment, a sub-basin of Se San river basin, is located in the Central Highland of Vietnam with an area of about 3,210 km2. This study focused on evaluating the performance of SWAT model and baseflow filtering algorithm in simulating surface flow and baseflow in Poko catchment. The model was calibrated and validated for the period 1996–2004 and 2005–2013, respectively, using the observed water discharge data at Dak Mot stream gauge. Statistical measures including R2 (coefficient of determination), NSI (Nash–Sutcliffe index), and PBIAS (percent bias) indicated good performance of the model in simulating water discharge on monthly time step during the calibration and validation period. Using baseflow filtering algorithm with filter parameter (0.925), surface flow and baseflow were separated from water discharge. The results demonstrated good performance in capturing the patterns of surface flow and baseflow, which confirmed the appropriateness of the model for future scenario simulation. These findings provide useful information for water resources planning in Poko catchment, in particular, and other basins, which have a hydro-meteorological response similar to this catchment, in general.

Multifractal characterisation of a simulated surface flow: A case study with Multi-Hydro in Jouy-en-Josas, France

In this paper we suggest to innovatively use scaling laws and more specifically Universal Multifractals (UM) to analyse simulated surface runoff and compare the retrieved scaling features with the rainfall ones. The methodology is tested on a 3 km2 semi-urbanised with a steep slope study area located in the Paris area along the Bièvre River. First Multi-Hydro, a fully distributed model is validated on this catchment for four rainfall events measured with the help of a C-band radar. The uncertainty associated with small scale unmeasured rainfall, i.e. occurring below the 1 km × 1 km × 5 min observation scale, is quantified with the help of stochastic downscaled rainfall fields. It is rather significant for simulated flow and more limited on overland water depth for these rainfall events. Overland depth is found to exhibit a scaling behaviour over small scales (10 m–80 m) which can be related to fractal features of the sewer network. No direct and obvious dependency between the overland depth multifractal features (quality of the scaling and UM parameters) and the rainfall ones was found.

Application of lattice Boltzmann method in free surface flow simulation of micro injection molding

The filling flow in micro injection molding was simulated by using the lattice Boltzmann method (LBM). A tracking algorithm for free surface to handle the complex interaction between gas and liquid phases in LBM was used for the free surface advancement. The temperature field in the filling flow is also analyzed by combining the thermal lattice Boltzmann model and the free surface method. To simulate the fluid flow of polymer melt with a high Prandtl number and high viscosity, a modified lattice Boltzmann scheme was adopted by introducing a free parameter in the thermal diffusion equation to overcome the restriction of the thermal relaxation time. The filling flow simulation of micro injection molding was successfully performed in the study.

Novel techniques in wind engineering

While the Alan Davenport Wind Engineering Chain is still valid today, the wind engineering techniques and methodologies have evolved. These changes relate to methods of collecting full scale data, physical and numerical modeling techniques, analysis techniques and wind-structure interaction approaches. These methodologies allow us to look at a more diverse spectrum of wind events including non-stationary, non-synoptic winds and their impact on buildings and structures. Spatially distributed full scale data combined with mesoscale and microscale simulations are more fitted today to characterize the local climatic scales associated to these complex wind events. These wind fields are three-dimensional, non-stationary and sometimes non-Gaussian in nature. However, our well-established Boundary Layer Wind Tunnels produce straight and steady wind and are limited in Reynolds number.The development of larger, multi-fan and sometimes three-dimensional wind facilities has now enabled more realistic laboratory simulations of surface flows for these events. Also, it invites new insight in data analysis and the way we treat the wind-structure interaction problems in a non-stationary context.In view of all this, we provide a review of new emerging technologies and examples of their applicability in the context of new experiments conducted at the WindEEE Research Institute at Western.

Constrained Interpolation Profile Conservative Semi-Lagrangian Scheme Based on Third-Order Polynomial Functions and Essentially Non-Oscillatory (CIP-CSL3ENO) Scheme

AbstractWe propose a fully conservative and less oscillatory multi-moment scheme for the approximation of hyperbolic conservation laws. The proposed scheme (CIP-CSL3ENO) is based on two CIP-CSL3 schemes and the essentially non-oscillatory (ENO) scheme. In this paper, we also propose an ENO indicator for the multimoment framework, which intentionally selects non-smooth stencil but can efficiently minimize numerical oscillations. The proposed scheme is validated through various benchmark problems and a comparison with an experiment of two droplets collision/separation. The CIP-CSL3ENO scheme shows approximately fourth-order accuracy for smooth solution, and captures discontinuities and smooth solutions simultaneously without numerical oscillations for solutions which include discontinuities. The numerical results of two droplets collision/separation (3D free surface flow simulation) show that the CIP-CSL3ENO scheme can be applied to various types of fluid problems not only compressible flow problems but also incompressible and 3D free surface flow problems.

A Numerical Simulation Model for Conjunctive Water Use in Basin Irrigated Canal Command Areas

Basin irrigation is a common practice for growing water intensive crops like paddy. Irrigation water, when supplied through a network of canal, is often found to be inadequate to meet the crop water requirement uniformly throughout the irrigated command area. The most deprived are the cultivators of the lower end of the command, who resort to supplementing the crop water requirement by extractions from the ground. This practice is noticeable in irrigation system without a proper canal water distribution schedule and often result in water logging in the upper command regions contrasted with excessively depleted groundwater table in the lower commands. The present contribution attempts to model the conjunctive water use of such a canal irrigated command using physically based numerical sub-models for simulating surface flow, groundwater flow and the interlinking process of moisture movement through the unsaturated zone for a given quantum of supplied water and crop water demand. Individual models are validated to demonstrate their applicability in an integrated framework. Various plausible conjunctive water use scenarios are tested on a hypothetical command area practising basin irrigation to identify the best possible water distribution strategy under given constraints.

Implementation of the Ghost Fluid Method for free surface flows in polyhedral Finite Volume framework

This paper presents an extension of the Ghost Fluid Method to arbitrary polyhedral Finite Volume framework for free surface flow simulations, primarily intended for marine hydrodynamics applications. Two immiscible, incompressible fluids are implicitly coupled via interface jump conditions, allowing the formulation of a single set of equations for both fluids. The jump conditions at the free surface are discretised with one sided extrapolates, using a compact computational stencil in second-order accurate, collocated polyhedral Finite Volume Method. The free surface is captured using the Volume-of-Fluid method with an additional compressive term. Even though the Volume-of-Fluid method is used, density and dynamic pressure exhibit sharp distribution at the interface due to jump conditions. The paper also demonstrates how the conditionally averaged equations with segregated solution algorithms cause spurious velocities at the free surface, which are resolved by the present approach since the Ghost Fluid Method relocates the pressure–density coupling inside the pressure equation. The method is implemented in OpenFOAM Computational Continuum Mechanics software, and the verification and validation is performed on two sets of test cases: free surface flow over a ramp and a steady resistance simulation of a container ship free to sink and trim.

A new coupled level set and volume-of-fluid method to capture free surface on an overset grid system

We present a new coupled level set and volume-of-fluid (CLSVOF) method for free surface flow simulations on an overset grid system. The coupled method takes advantages of the strengths of the level set (LS) method and the volume-of-fluid (VOF) method, and is superior to either single method. The novelty of the present method lies in that we develop the methodology for an overset grid system of embedding, overlapping and moving structured grids. The new methodology accurately captures interface and greatly preserves mass on an overset grid system by demonstrating the 3D sphere advection test. The method is coupled to a well validated Reynolds-Averaged Navier–Stokes incompressible flow solver. The method is validated with the dam-breaking flow interacting with a 3D obstacle (square structure/circular cylinder) by comparing the numerical results with available experimental and numerical studies. The water impact of a sphere case is further performed to demonstrate the capabilities of the new method on a complicated moving overset grid system.

A HIGH-PERFORMANCE METHOD FOR SIMULATING SURFACE RAINFALL-RUNOFF DYNAMICS USING PARTICLE SYSTEM

The simulation of rainfall-runoff process is essential for disaster emergency and sustainable development. One common disadvantage of the existing conceptual hydrological models is that they are highly dependent upon specific spatial-temporal contexts. Meanwhile, due to the inter-dependence of adjacent flow paths, it is still difficult for the RS or GIS supported distributed hydrological models to achieve high-performance application in real world applications. As an attempt to improve the performance efficiencies of those models, this study presents a high-performance rainfall-runoff simulating framework based on the flow path network and a separate particle system. The vector-based flow path lines are topologically linked to constrain the movements of independent rain drop particles. A separate particle system, representing surface runoff, is involved to model the precipitation process and simulate surface flow dynamics. The trajectory of each particle is constrained by the flow path network and can be tracked by concurrent processors in a parallel cluster system. The result of speedup experiment shows that the proposed framework can significantly improve the simulating performance just by adding independent processors. By separating the catchment elements and the accumulated water, this study provides an extensible solution for improving the existing distributed hydrological models. Further, a parallel modeling and simulating platform needs to be developed and validate to be applied in monitoring real world hydrologic processes.

A HIGH-PERFORMANCE METHOD FOR SIMULATING SURFACE RAINFALL-RUNOFF DYNAMICS USING PARTICLE SYSTEM

Abstract. The simulation of rainfall-runoff process is essential for disaster emergency and sustainable development. One common disadvantage of the existing conceptual hydrological models is that they are highly dependent upon specific spatial-temporal contexts. Meanwhile, due to the inter-dependence of adjacent flow paths, it is still difficult for the RS or GIS supported distributed hydrological models to achieve high-performance application in real world applications. As an attempt to improve the performance efficiencies of those models, this study presents a high-performance rainfall-runoff simulating framework based on the flow path network and a separate particle system. The vector-based flow path lines are topologically linked to constrain the movements of independent rain drop particles. A separate particle system, representing surface runoff, is involved to model the precipitation process and simulate surface flow dynamics. The trajectory of each particle is constrained by the flow path network and can be tracked by concurrent processors in a parallel cluster system. The result of speedup experiment shows that the proposed framework can significantly improve the simulating performance just by adding independent processors. By separating the catchment elements and the accumulated water, this study provides an extensible solution for improving the existing distributed hydrological models. Further, a parallel modeling and simulating platform needs to be developed and validate to be applied in monitoring real world hydrologic processes.

SWAT 모형의 지표유출해석 알고리즘 개선

ABSTRACTSWAT model usually underestimates daily peak discharges. To resolve this problem, in this study, the algorithm related with the surface flow simulation was modified by pa rtitioning excessive infiltration based on the relative length between overland flow time of concentration and percolation travel time in soil water zone and by computing time of concentration varying with the amount of surface flow. The modified SWAT was applied to the Chungju dam watershed to assess the increasing effects of daily peak discharges. The daily peaks simulated by the modified SWAT were on average 10% higher than those by original SWAT for the peaks above 5,000 m 3 /s. The modified SWAT was found to be able to more accurately reproduce daily peaks, particularly showing increase rates of 9.9%, 1 8.6% and 12.6%, respectively, for top three peaks that occurred in the years of 1990, 2002, and 2006.Key words : SWAT, Daily peak discharge, Excessive infiltration, Time of concentration초 록본 연구에서는 SWAT 모형으로 일 유출량을 모의할 경우에 수문곡선의 첨두부가 과소하게 산정되는 문제를 개선하기 위해서 지표유출의 집중시간과 토양수의 연직 유하시간의 상대적 길이를 고려하여 초과침투량의 일부를 지표유출량에 추가로 할당하고 지표유출량의 크기에 따라 집중시간이 가변적으로 계산되도록 지표유출해석 알고리즘을 수정하였다 . 개선된 SWAT 모형을 충주댐 상류유역에 적용한 결과 첨두유량이 5,000 m

A self-tuning ANN model for simulation and forecasting of surface flows

Artificial neural networks (ANN) are applicable for and forecasting without the need to calculate complex nonlinear functions. This paper evaluates the effectiveness of temperature, evapotranspiration, precipitation and inflow factors, and the lag time of those factors, as variables for simulating and forecasting of runoff. The genetic algorithm (GA) is coupled with ANN to determine the optimal set of variables for streamflow forecasting. The minimization of the total mean square error (MSE) is considered as the objective function of the ANN-GA method in this paper. Our results show the effectiveness of the ANN-GA for simulating and forecasting runoff with consistent accuracy compared with using pure ANN for runoff simulation and forecasting.

Fully Hydrodynamic Coupled Simulation of Surface Flows in Irrigation Furrow Networks

AbstractSaint-Venant equations are accurately solved by a fully implicit solution, and a numerical model for furrow water flow is proposed with unconditional stability. Furthermore, this numerical ...

GPUを用いた格子ボルツマン法による船舶周りの自由表面流解析の高速化

船舶の推進性能や安定性解析など気液界面を含む問題において，気液界面の変形・分離を捉えた高性能な非定常大規模解析の必要が高まっている．本研究では，格子ボルツマン法を，気相・液相の両相の時間発展を行う二流体モデルへと拡張し，それぞれの相に対してLESの乱流モデルを適用することで，気液二相流解析を行った．検証問題として，気液密度比が約800の条件において，物体を含むダム崩壊計算を行い実験結果と比較を行った結果，気液界面の高さおよび圧力分布が定性的に良くあっていることが確認された．また，TSUBAME2.5を用いた弱スケーリングの実効性能測定においては，8台から125台の並列数において良いスケーリングが得られることが確認された．