Surface Flow Model Research Articles

Characterizing the Climate-Driven Collapses and Expansions of Wetland Habitats with a Fully Integrated Surface–Subsurface Hydrologic Model

Links between climatic forcing and wetland habitats can be conceptualized using a graph-theoretical approach, which treats wetlands as nodes to map habitat connectivity and to define habitat networks for ecological analysis. The first and most crucial step in creating a network model, however, is to characterize the dynamic behaviors of the nodes, i.e., the occurrence of wetlands with ponded water, or water bodies. For the first time, this study applies a 3-D, fully integrated surface and subsurface flow model, HydroGeoSphere (HGS), to simulate the hydrologic dynamics of wetlands in the Prairie Pothole Region (PPR) and to characterize the resulting habitat networks as a function of climate variability. Results show HGS is able to simulate water movement in both surface and subsurface domains and capture “fill-spill” and coalescence/disaggregation behaviors of wetlands as they respond to wet and dry climatic conditions. Our simulations for a small representative subarea of the PPR show wetland networks in the PPR could easily shrink, degrade, or even collapse when the climate becomes drier. This study demonstrates the potential in applying sophisticated hydrologic models to solve critical ecological problems and the practical implications for water-resources management, conservation planning and decision-making in the PPR.

Coupled Two-Dimensional Surface Flow and Three-Dimensional Subsurface Flow Modeling for Drainage of Permeable Road Pavement

AbstractPermeable road pavement has been used widely as a sustainable alternative to the traditional impervious pavement and has become an increasingly important component of the hydrological cycle. The benefits of permeable pavement depend on its hydraulic performance and drainage efficiency, for which there have been very few rigorously tested numerical models. In this paper, a new computational model is presented to simulate fluid motion above and within the porous road pavement. This model solves the coupled equation system for surface and subsurface flows using a finite-volume method. The surface flow and the subsurface flow are modeled by the two-dimensional diffusive wave equation and the three-dimensional Richards equation, respectively. A modified Dirichlet-Neumann partitioning method is used as the coupling algorithm to ensure the continuity of pressure head and the conservation of mass. The diffusive wave model for the surface flow is solved with a flux correction transport (FCT) scheme that co...

Decomposition model for naval hydrodynamic applications, Part I: Computational method

The present paper and its companion present a solution and domain decomposition model for general two-phase, incompressible and turbulent flows encountered in naval hydrodynamics. The mathematical and numerical model are derived within the framework of polyhedral finite volume method. Interface capturing is obtained with implicitly redistanced level set method derived from the phase field equation. This approach removes the need to redistance the level set field, thus saving CPU time and increasing numerical stability. A modified, Spectral Wave Explicit Navier–Stokes Equations method is introduced and used for wave modelling, where the solution is decomposed into incident and perturbation fields. The incident field is readily available from potential flow theories, and only the perturbation component is solved within the non-linear equation set of the free surface flow model. The domain is decomposed with implicit relaxation zones used to prevent wave reflection by forcing the perturbation fields to vanish in the far-field. A second-order, collocated finite volume method is used to discretise the equations. All equations are solved implicitly, which enables the use of higher Courant–Friedrichs–Lewy numbers compared to explicit scheme. The algorithm is implemented in foam-extend-3.1, a community driven fork of the OpenFOAM CFD software. Verification and validation of the model is presented in the accompanying paper.

Simulation of 2D Saint-Venant equations in open channel by using MATLAB

2D surface flow models are useful to understand and predict the flow through breach, over a dyke or over the floodplains. This paper is aimed at the surface flows to study the behavior of flood waves. The open channel water flow in drains and rivers is considered in view of the fact that such flows are the source of flash flood. In order to predict and simulate the flood behavior, a mathematical model with the initial and boundary conditions is established using 2D Saint-Venant partial differential equations. Next, the corresponding model is discretized by using the explicit finite difference method and implemented on MATLAB. For the testing and implementation purpose a simple rectangular flow channel is considered. The output parameters like height or depth of water z (m), the fluid velocity u (m/s) and the volumetric flow rate Q (m3/sec) are simulated numerically and visualized for the different time steps. The initial simulation results are useful to understand and predict the flood behavior at different locations of flow channel at specific time steps and can be helpful in early flood warning systems. It is also suggested that the coupling of the subsurface flow with the surface flow may provide even better approximations for the flood circulation.

3D CFD validation of invert trap efficiency for sewer solid management using VOF model

Earlier investigators have numerically carried out performance analysis of the invert trap fitted in an open channel using the stochastic discrete phase model (DPM) by assuming the open channel flow to be closed conduit flow under pressure and assuming zero shear stress at the top wall. This is known as the fixed lid model. By assuming the top wall to be a shear free wall, they have been able to show that the velocity distribution looks similar to that of an open channel flow with zero velocity at the bottom and maximum velocity at the top, representing the free water surface, but no information has been provided for the pressure at the free water surface. Because of this assumption, the validation of the model in predicting the trap efficiency has performed significantly poorly. In addition, the free water surface subject to zero gauge pressure cannot be modeled using the fixed lid model because there is no provision of extra space in the form of air space for the fluctuating part of the water surface profile. It can, however, be modeled using the volume of fluid (VOF) model because the VOF model is the appropriate model for open channel or free surface flow. Therefore, in the present study, three-dimensional (3D) computational fluid dynamics (CFD) modeling with the VOF model, which considers open channel flow with a free water surface, along with the stochastic DPM, was used to model the trap efficiency of an invert trap fitted in an open rectangular channel. The governing mathematical flow equations of the VOF model were solved using the ANSYS Fluent 14.0 software, reproducing the experimental conditions exactly. The results show that the 3D CFD predictions using the VOF model closely fit the experimental data for glass bead particles.

An immersed boundary method for unstructured meshes in depth averaged shallow water models

SummaryThe representation of geometries as buildings, flood barriers or dikes in free surface flow models implies tedious and time‐consuming operations in order to define accurately the shape of these objects when using a body fitted numerical mesh. The immersed boundary method is an alternative way to define solid bodies inside the computational domain without the need of fitting the mesh boundaries to the shape of the object. In the direct forcing immersed boundary method, a solid body is represented by a grid of Lagrangian markers, which define its shape and which are independent from the fluid Eulerian mesh. This paper presents a new implementation of the immersed boundary method in an unstructured finite volume solver for the 2D shallow water equations. Moving least‐squares is used to transmit information between the grid of Lagrangian markers and the fluid Eulerian mesh. The performance of the proposed implementation is analysed in three test cases involving different flow conditions: the flow around a spur dike, a dam break flow with an isolated obstacle and the flow around an array of obstacles. A very good agreement between the classic body fitted approach and the immersed boundary method was found. The differences between the results obtained with both methods are less relevant than the errors because of the intrinsic shallow water assumptions. Copyright © 2015 John Wiley & Sons, Ltd.

Numerical Modeling of Free Surface Dynamics of Melt in an Alternate Electromagnetic Field. Part II: Conventional Electromagnetic Levitation

By means of external coupling between electromagnetic (EM) problem in ANSYS and hydrodynamic problem in FLUENT, a numerical model for the liquid metal free surface flow in an alternate EM field has been developed and verified in the first part of the article. Volume of Fluid (VOF) algorithm has been used for tracking of free surface. In this work, improved performance of the model is presented. General validation of the VOF algorithm is performed by comparison of the calculated free oscillations of the liquid column to its analytical solution. The 3D/VOF calculation of coupled EM field and free surface flow with Large Eddy Simulation turbulence description for the first time is applied for modeling of conventional EM levitation. Calculation results are compared with 2D/VOF and 3D/VOF models that use less precise k–e and k–ω SST turbulence formulations. Obtained time-averaged droplet shapes are used for single-phase flow calculations with different turbulence models and free-slip/no-slip velocity conditions at the fixed free surface for validation of the flow. Meanwhile, series of levitation melting experiments are performed for verification of the simulated droplet shapes. In conclusion, parameter impact on the fully developed flow and the levitated droplet shape is discussed.

On magnetic estimation of Earth's core angular momentum variation

AbstractWe study systematically the estimation of Earth's core angular momentum (CAM) variation between 1962.0 and 2008.0 by using core surface flow models derived from the recent geomagnetic field model C3FM2. Various flow models are derived by changing four parameters that control the least squares flow inversion. The parameters include the spherical harmonic (SH) truncation degree of the flow models and two Lagrange multipliers that control the weights of two additional constraints. The first constraint forces the energy spectrum of the flow solution to follow a power law , where l is the SH degree and p is the fourth parameter. The second allows to modulate the solution continuously between the dynamical states of tangential geostrophy (TG) and tangential magnetostrophy (TM). The calculated CAM variations are examined in reference to two features of the observed length‐of‐day (LOD) variation, namely, its secular trend and 6 year oscillation. We find flow models in either TG or TM state for which the estimated CAM trends agree with the LOD trend. It is necessary for TM models to have their flows dominate at planetary scales, whereas TG models should not be of this scale; otherwise, their CAM trends are too steep. These two distinct types of flow model appear to correspond to the separate regimes of previous numerical dynamos that are thought to be applicable to the Earth's core. The phase of the subdecadal CAM variation is coherently determined from flow models obtained with extensively varying inversion settings. Multiple sources of model ambiguity need to be allowed for in discussing whether these phase estimates properly represent that of Earth's CAM as an origin of the observed 6 year LOD oscillation.

Determining resistance coefficient for series 60 vessels using numerical and experimental modelling

In this paper, an experimental and computational approach is presented to determine the residual resistance of a 1.5-m ship-model in the series 60 category. The results are validated with the experimental works which have been confirmed by nine accredited institutes in Japan, including Yokohama and Hiroshima (using a 7-m ship-model established at the 17th International Towing Tank Conference). The 1.5-m model has been designed, manufactured and tested at Isfahan University of Technology (IUT) towing tank. Besides the experimental work, a computational free surface flow modelling is performed by using a finite volume method with the double phase and standard k-ϵ model. Comparison of the results indicates an accurate model design, the establishment of suitable similarity, and accurate computation of the residual resistance coefficients with a maximum deviation of 8%. Furthermore, a comparison of the total resistance coefficient obtained from the numerical analysis and from the experimental results of IUT laboratory, indicates a very low deviation of 1.3%. This verification not only shows the capability of the numerical computation method due to the boundary layer simulation around the body but it also indicates the compatibility of the results obtained in the IUT towing tank.

A surface and subsurface model for the simulation of rainfall infiltration in slopes

Rainfall infiltration is one of the major triggering factors leading to slope failures in geotechnical engineering. Numerical investigation on rainfall infiltration is often based on Richards’ equation, which ignores the surface water effects and simplifies the boundary conditions. In reality, rainfall, infiltration, and surface runoff are interacted simultaneously. In this paper a new conjunctive one-dimensional surface flow and two-dimensional subsurface flow model for geotechnical slope is developed. The interaction between surface and subsurface flow is the interface infiltration rate, which is obtained by iterations. The results of comparisons between coupled and uncoupled models show that the surface water depth rises up as runoff increases and it tends to a dynamic balance state with a steady surface water depth. Interaction between surface and subsurface flow has remarkable effects on infiltration process. According to the results of coupled model, more rainwaters infiltrate into the slope. Therefore, pore water pressure changes faster and the wetting front moves deeper into the soil. Under initial drier condition, the capacity of infiltration is higher and more rainfall can be absorbed into slope, thus the differences of infiltration rate and pore water pressure between the coupled and uncoupled model are more significant.

Fully three-dimensional Reynolds-averaged Navier–Stokes modeling for solving free surface flows around coastal drainage gates

In this study we carry out numerical simulations of free surface flow through the drainage gates of the Saemangeum tidal barrier that is located in the west coast of South Korea and is also known as the world largest man-made tidal barrier. Instead of using depth-averaged numerical models, which have been widely used in hydraulic and coastal engineering, we employ the fully three-dimensional free surface flow model of Kang and Sotiropoulos (2012b) to simulate the flow around the gates. The numerical model is based on the two-phase level set method solving the air and water simultaneously and the curvilinear immersed boundary method that is able to handle arbitrarily complex geometries. In the simulations turbulent flows are also resolved by the shear stress transport k−ω model. The numerical model is applied to simulate fifteen different flow conditions with various gate opening scenarios, and for selected test cases laboratory experiments are also carried out. The computed flowfields at various flow conditions are compared with the laboratory measurements and the field observations and the comparisons showed satisfactory agreements both quantitatively and qualitatively. Using numerical simulation results, we elucidate the structures of turbulent flows associated with a high-speed jet-flow like structure and a hydraulic jump at the far downstream of the gates. The results presented in this paper demonstrate the predictive capabilities of the numerical model and its potential as a powerful engineering tool for estimating the discharge-water level relationship and the three-dimensional flowfield of real-life drainage gates.

Modelling sewer discharge via displacement of manhole covers during flood events using 1D/2D SIPSON/P-DWave dual drainage simulations

In urban areas, overloaded sewers may result in surcharge that causes surface flooding. The overflow from sewer systems mainly starts at the inlets until the pressure head in the manhole is high enough to lift up its cover, at which stage the surcharged flow may be discharged via the gap between the bottom of the manhole cover and the ground surface. In this paper, we propose a new approach to simulate such a dynamic between the sewer and the surface flow in coupled surface and sewer flow modelling. Two case studies are employed to demonstrate the differences between the new linking model and the traditional model that simplifies the process. The results show that the new approach is capable of describing the physical phenomena when manhole covers restrict the drainage flow from the surface to the sewer network and reduce the surcharge flow and vice versa.

Derivation and use of core surface flows for forecasting secular variation

AbstractImproving forecasts of the temporal and spatial changes of the Earth's main magnetic field over periods of less than 5 years has important scientific and economic benefits. Various methods for forecasting the rate of change, or secular variation, have been tried over the past few decades, ranging from the extrapolation of trends in ground observatory measurements to computational geodynamo modeling with data assimilation from historical magnetic field models. We examine the utility of an intermediate approach, using temporally varying core surface flow models derived from relatively short periods of magnetic field data to produce, by advection, secular variation estimates valid for the Earth's surface. We describe a new method to compute a core flow changing linearly with time from magnetic secular variation and acceleration data. We invert a combination of data from the CHAMP satellite mission and ground observatories over the period 2001.0 to 2010.0 for a series of such models. We assess their ability to forecast magnetic field changes by comparing them to CHAOS‐4, a state‐of‐the‐art model using data from 1997 to 2014.5. We show that the magnetic field predictions tend to have a lower root‐mean‐square difference from CHAOS‐4 than the International Geomagnetic Reference Field or World Magnetic Map series of secular variation models.

Water management plan for olive orchards in a semi-mountainous area of Crete, Greece

<div> <p>In the present work the physically based distributed rainfall–runoff modeling system, MIKE SHE, is used to simulate the surface runoff at a semi-mountainous impermeable area of Tavronitis River basin in Crete-Greece.  The objective of this surface flow model is to develop an appropriate irrigation plan for olive trees. For the model calibration, a simulation time of one year (01/09/2000 - 31/08/2001) was considered, while for the model verification a two-year period (01/09/2001 - 31/08/2003). During these periods river flow measurements were obtained at two specified locations. These measurements were employed as targets for calibration and verification of the surface flow model. After the successful calibration and validation processes, the 2D maps of the overland flow were produced. Using these maps, the locations of significant surface water accumulation in the study region and for a specific time period were identified. Next, these locations were proposed for the construction of potential small hydraulic structures (dam or/and reservoir), for covering the irrigation needs of olive trees in the study area. </p> </div> <p> </p>

Research on Construction of Major Drainage System for urban area of Shijiazhuang

In recent years, many cities of China suffered from urban waterlogging, therefore, prevention of urban waterlogging became one of the main targets of urban drainage. Based on the comprehensive plan of drainage and waterlogging Prevention of Shijiazhuang, this study introduced the relationship between major and minor drainage systems, as well as the significance of major drainage system construction. According to the current problems of urban drainage systems of Shijiazhuang, two-dimensional surface flow modelling tools was applied, with the consideration of urban master planning, major drainage system was established. Which contains eight conveyances for exceedance flow based on urban rivers and fifteen major detention & retention facilities based on urban green space. Thereby, effective alleviation of urban waterlogging was achieved.

A Topology Based Discretization of PDAEs Describing Water Transportation Networks

AbstractWe consider partial differential algebraic systems (PDAEs) describing water transportation networks. Similar to the approach in [6], we follow the method of lines for the discretization. However, we do not consider free surface flow models but pressure flow models covering hydraulic shocks. Moreover, we include switching models reflecting the on/off state of pumpes and valves. Aiming at a stable numerical simulation of the PDAEs we present a topology based spatial discretization that results in a differential algebraic system (DAE) of index 1. Furthermore we show that the DAE index can be higher than 1 if the spatial discretization is not adapted to the position of reservoirs and demand nodes within the network. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

3D LBM NUMERICAL SIMULATION OF MIXED SAND SORTING UNDER OSCILLATORY FLOWS AND PROGRESSIVE WAVES

A 3D numerical model based on Lattice Boltzmann Method (LBM) has been developed to investigate the particle behavior of mixed-grain-size sediments under oscillatory flows and progressive waves. The model considers both particle-particle interaction and particle-fluid interaction with free surface flow and SGS turbulence model. By applying the present model, simulations of mixed-grain-size sediments with different influence factors (i.e., Shields parameters, periods, bottom layer thicknesses) under symmetric oscillatory flows as well as under progressive cnoidal wave are performed to understand the vertical sorting process of graded sands. The results of mixed sands under symmetric oscillatory flows show that the water particle semi-excursion is a key influence factor on the armoring effect. For the cnoidal wave, the vertical sorting proceeds until the wave crest passes by and it fully develops in a complete period. The concentration centroid of large particles becomes higher landward within 2 periods.

A higher-efficient three-dimensional numerical model for small amplitude free surface flows

A higher-efficient three-dimensional non-hydrostatic model is developed to simulate small amplitude free surface flows based on a staggered unstructured grid. In this model, a fractional step algorithm is adopted to solve the Navier-Stokes equations in two major steps. A top-layer pressure method is proposed to minimize the number of vertical layers and subsequently the computational cost. Three classical examples of small amplitude free surface flows are used to demonstrate the capability and efficiency of the model. The satisfactory results demonstrated the capability and efficiency of modelling a range of small amplitude free surface flows with only a small number of vertical layers.

분지형 도시유역에서의 노면류를 고려한 침수모의

도시홍수에 대한 관심과 함께 도시유출모형은 지속적으로 발전해왔다. 최근에는 1차원 우수관망 해석 모형과 2차원 지표면 흐름 모형을 연계하는 방법으로 지하 우수관으로부터의 월류량으로 인한 지표면 침수를 정량적으로 해석할 수 있는 모형이 개발되기도 하였다. 그러나 현재까지 개발된 도시유출모형은 지하 우수관으로부터의 월류량으로 인한 침수만 해석할 수 있으며, 지하 우수관로 시스템으로 유입되지 못한 노면류에 의한 침수는 해석할 수 없는 한계가 있다. 본 연구에서는 이러한 한계를 극복하기 위하여 도시유출모형 구성 시 지하 우수관로 시스템으로의 유입효율을 고려할 수 있는 가상의 1차원 우수관망 레이어를 추가하는 유역중첩법을 고안하였다. 도시유출모형으로는 XP-SWMM 2011 모형을 이용하였으며, 2011년 7월 27일에 급경사 분지지형인 서울시 사당천 유역에서 발생한 홍수사상을 분석 대상으로 하였다. 모의결과 유역중첩법으로 모의한 경우가 일반적인 방법으로 모의한 경우에 비해 측정된 침수현상을 유사하게 구현하였다. 노면 유출수로 인한 침수를 저감하기 위해 배수시설 개선이 필요함을 밝혔으며, 분지형 도시유역의 치수계획규모 설정 시 고려사항으로 활용될 수 있을 것이라 판단된다. Urban runoff models have been continuously developing with concerns for urban flood. Recently, models that be able to quantitatively analyze surface inundation caused by overflowed water from storm sewer were also developed by coupling 1-dimensional sewer model and 2-dimensional surface flow model. However, only overflowed water from storm sewer can be analyzed by the models have been developed until now. They are limited to be not able to analyze surface inundation caused by surface runoff that could not flow into the storm sewer. In order to overcome the limitation, basin-overlap method was devised adding a dummy 1-dimensional sewer layer to the model, so it can consider the efficiency of inflow to the storm sewer system. XP-SWMM 2011 is applied for urban runoff model and the flood event occurred on July 27, 2011 in basin-shaped Sadangcheon watershed is chosen for study inundation event. According to simulation results basin-overlap method reappear the observed inundation event more precisely than traditional method. This results suggest that drainage system has to be improved for reducing inundation caused by surface runoff and would be used as considerations for planning an urban basin design magnitude.

Accuracy and efficiency of time integration methods for 1D diffusive wave equation

The diffusive wave approximation of the Saint-Venant equations is commonly used in hydrological models to describe surface flow processes. Numerous numerical approaches can be used to solve this highly nonlinear equation. Nonlinear time integration schemes—also called methods of lines (MOL)—were proven very efficient to solve other nonlinear problems in geosciences but were never considered to deal with surface flow modeling with the diffusive wave equation. In this paper, we study the relative performance of different time and space integration schemes by comparing the results obtained with classical approaches and with nonlinear time integration approaches. The results show that (i) the integration method with a higher order in space shows high accuracy regarding an integrated indicator such as the global mass balance error but is less accurate regarding local indicators, and (ii) nonlinear time integration techniques perform better than classical ones. Overall, it seems that integration techniques combining nonlinear time integration and a low spatial order need to be considered when developing hydrological modeling tools owing to their simplicity of implementation and very good performance.