Integration of a 1-D river model with object-oriented methodology

This article first details the development of an integrated modelling system (Flow And Solute Transport in Estuaries and Rivers), which is capable of predicting water elevations, velocities and solute and sediment concentration distributions in well-mixed rivers or narrow estuaries. The model comprises hydrodynamic and solute transport solvers, a user-friendly graphical interface—including data management and storage tools—and graphic and tabular reporting facilities. The program, initially written in Fortran, is a numerical modelling program which deploys highly accurate numerical schemes to solve the hydrodynamic and solute transport equations. This model has recently been modified to include a graphical user interface based on an object-oriented methodology, and implemented using the Visual Basic programming language. Details are given herein of the procedures used to combine the Fortran program with a Windows-based programming language, namely Visual Basic. Particular emphasis has been focused on the construction of the interface for unsteady free-surface flow problems. An example application of the model is cited to illustrate the data management capabilities and accuracy of the model when applied to real hydroenvironmental projects.     

Coupled model of surface water flow, sediment transport and morphological evolution

This paper presents a mathematical model coupling water flow and sediment transport dynamics that enables calculating the changing surface morphology through time and space. The model is based on the shallow water equations for flow, conservation of sediment concentration, and empirical functions for bed friction, substrate erosion and deposition. The sediment transport model is a non-capacity formulation whereby erosion and deposition are treated independently and influence the sediment flux by exchanging mass across the bottom boundary of the flow. The resulting hyperbolic system is solved using a finite volume, Godunov-type method with a first-order approximate Riemann solver. The model can be applied both to short time scales, where the flow, sediment transport and morphological evolution are strongly coupled and the rate of bed evolution is comparable to the rate of flow evolution, or to relatively long time scales, where the time scale of bed evolution associated with erosion and/or deposition is slow relative to the response of the flow to the changing surface and, therefore, the classical quasi-steady approximation can be invoked. The model is verified by comparing computed results with documented solutions. The developed model can be used to investigate a variety of problems involving coupled flow and sediment transport including channel initiation and drainage basin evolution associated with overland flow and morphological changes induced by extreme events such as tsunami.     

Modelling the effects of reservoir construction on tidal hydrodynamics and suspended sediment distribution in Danshuei River estuary

A vertical (laterally integrated) two-dimensional numerical model was implemented to study the hydrodynamics, saltwater intrusion, and suspended sediment in the Danshuei River–Tahan Stream due to the Shihmen Reservoir construction in the upriver reaches. The construction of the reservoir and water diversion in the upper reaches of the river system significantly reduces the freshwater inflow and drastically changes the river bathymetry. The model was calibrated and verified with the available hydrographic data measured in 1977, 1978, and 1999 as well as measured salinity and suspended sediment concentration in 1999. The overall performance of the model is in reasonable agreement with the field data. The validated model was then used to investigate the change in hydrodynamics, saltwater intrusion, suspended sediment distribution, and flushing time as a result of reservoir construction in upper river of Tahan Stream. The model simulations indicate that more tidal energy propagates into the estuarine system after reservoir construction because of the substantial increase in river cross-sections. The limits of saltwater intrusion after reservoir construction extended farther inland 2–3 km than those after reservoir construction. The modelling results also reveal that the suspended sediment concentration before reservoir construction was higher than that after reservoir construction along the river mouth to Kuan-Du due to the significant bathymetric change after the reservoir construction. The calculated estuary flushing time was strongly dependent on river flow and reduced 2.3–25 h under different river discharges after reservoir construction due to the change in river bathymetry.     

Sediment transport models in Shallow Water equations and numerical approach by high order finite volume methods

This paper is concerned with the numerical approximation of bedload sediment transport due to water evolution. For the hydrodynamical component we consider Shallow Water equations. The morphodynamical component is defined by a continuity equation, which is defined in function of the solid transport discharge. We present several deterministic models, such as Meyer-Peter & Müller, Van Rijn or Grass model. We also present an unified definition for the solid transport discharge, and we compare with Grass model. Both components define a coupled system of equations that can be rewrite as a non-conservative hyperbolic system. To discretize it, we consider finite volume methods with or without flux limiters and high order state reconstructions. Finally we present several tests, where we observe numerically the order of the numerical schemes. Comparisons with analytical solutions and experimental data are also presented.     

Application of a discontinuous Galerkin finite element method to special relativistic hydrodynamic models

A Runge–Kutta discontinuous Galerkin (RKDG) finite element method is proposed for solving the special relativistic hydrodynamic (SRHD) equations and as a limiting case the ultra-relativistic hydrodynamic (URHD) equations. The latter model is obtained by ignoring the rest-mass energy when the internal energy of fluid particles is sufficiently large. Several test problems of SRHD and URHD models are carried out. For validation, the results of DG-method are compared with the staggered central scheme. The numerical results verify the accuracy of the proposed method qualitatively and quantitatively.     

Modeling flows and sediment concentrations in a sloping channel with a submerged outlet using a hybrid finite-analytic approach

This paper presents the development of a hybrid finite-analytic (HFA) based model for simulating flows and suspended sediment concentrations along a sloping channel with a submerged outlet. This model solves Reynolds-averaged Navier–Stokes equations and sediment transport equation in a staggered grid system. The spatial discretization of the hybrid finite-analytic expression is formulated using the locally linearized analytical solutions. The performance of HFA scheme in terms of the damping and diffusion effects is examined through the analytical procedure of the von Neumann stability analysis. The model is first tested with several selected cases and the results are shown to compare well with analytical solutions. The model is then extended to simulate the flows in a reservoir with a sloping bottom and a submerged two-dimensional (2-D) orifice downstream. The computed horizontal velocity vectors and the reattachment length show reasonable agreement with Jin’s (1990) [26] experimental measurements. Comparisons of computed sediment concentrations are made with other published numerical results. The model is also applied to study the three-dimensional (3-D) flows in a reservoir with a scouring funnel like bottom topography and a 3-D orifice outlet. The complicated 3-D flow pattern in front of the orifice is presented and discussed.     

Three-dimensional model of radionuclide dispersion in estuaries and shelf seas

The 3-D model THREETOX was developed for the assessment of contamination in coastal seas and inland water bodies. It includes a high resolution numerical hydrodynamic submodel, a dynamic–thermodynamic ice submodel, and submodels for suspended sediment and pollution transport. The results of two case studies are described. The first case concerns a 2-year simulation of the Chernobyl radionuclide contamination of the Dnieper–Bug estuary to validate the model. In the second case study, simulations were performed for the assessment of the consequences of the possible release of radionuclides from scuttled reactors and containers with liquid radioactive wastes in the Novaya Zemlya fjords and the East Novaya Zemlya Trough of the Kara Sea. The simulated results demonstrated the capability of the THREETOX model to describe a wide spatial and temporal range of radionuclide transport processes in the ocean.     

Implementation of a discontinuous Galerkin morphological model on two-dimensional unstructured meshes

The shallow water equations are used to model large-scale surface flow in the ocean, coastal rivers, estuaries, salt marshes, bays, and channels. They can describe tidal flows as well as storm surges associated with extreme storm events, such as hurricanes. The resulting currents can transport bed load and suspended sediment and result in morphological changes to the seabed. Modeling these processes requires tightly coupling a bed morphology equation to the shallow water equations. Discontinuous Galerkin finite element methods are a natural choice for modeling this coupled system, given the need to solve these problems on unstructured computational meshes, as well as the desire to implement hp-adaptivity for capturing the dynamic features of the solution. However, because of the presence of non-conservative products in the momentum equations, the standard DG method cannot be applied in a straightforward manner. To rectify this situation, we summarize and follow an extended approach described by Rhebergen et al., which uses theoretical results due to Dal Maso et al. appearing in earlier work. In this paper, we focus on aspects of the implementation of the morphological model for bed evolution within the Advanced Circulation (ADCIRC) modeling framework, as well as the verification of the RKDG method in both h (mesh spacing) and p (polynomial order). This morphological model is applied to a number of coastal engineering problems, and numerical results are presented, with attention paid to the effects of h- and p-refinement in these applications. In particular, it is observed that for sediment transport, piecewise constant (i.e., finite volume) approximations of the bed are very over-diffusive and lead to poor sediment solutions.     

Modelling the role of self-weight consolidation on the morphodynamics of accretional mudflats

We develop a consolidation module and merge it into a morphodynamic model to assess the role of consolidation on estuarine morphodynamics. We test the model using two settings: point models without hydrodynamic forcing to validate against two benchmark experimental datasets; and a profile model to simulate a mudflat restoration. The modelled self-weight consolidation influences the simulations by gradually reducing the bed level and decreasing the bed erodibility (i.e., increasing the critical bed shear stress). Both effects modify sediment transport processes on mudflats, leading to long-term morphodynamic effects. Depending on the initial bathymetry, the hydrodynamic forcing and the soil properties, the simulated morphological change of the restored mudflat may differ considerably with and without considering consolidation. The consolidation model developed can be utilised to assess the medium to long term effects related to estuarine development (e.g., wetland restoration) and aims to be a publicly available tool.     

Modeling sediment resuspension and transport induced by storm wind in Apalachicola Bay, USA

Sediment is an important environmental factor for aquatic ecosystem and oyster productivities of Apalachicola Bay located in Florida, USA. Based on the data analysis in this study, surface wind speed is highly correlated to the turbidity of water column, which results from sediment resuspension and transport in the Apalachicola Bay. In this paper, an application of a 3D sediment transport model to predict the wind-induced sediment transport in Apalachicola Bay is described. The sediment model is coupled with a 3D hydrodynamic module in the Environmental Fluid Dynamics Code (EFDC) model that provides information on estuarine circulation and salinity transport under normal temperature conditions. The hydrodynamic model was calibrated with field observations of water levels and salinity. The sediment transport model solves the transport equation with sources and sinks terms to describe sediment deposition and resuspension. The coupled hydrodynamic and sediment transport models were used to investigate wind-induced total suspended sediments (TSS) resuspension and transport in the bay. For the period June 1–July 30, 2005 two storm events with strong winds gave model results of TSS concentrations that compared well with the field observations. Model simulations reasonably reproduce the sudden increase of sediment concentrations during the storm events. Maximum sediment concentrations in the bay during the two storm events were 10 times or more than those in the pre-storm conditions. Spatial sediment transport from model simulations indicate active sediment resuspension and transport near areas of highly productive oyster beds. The model predictions of TSS and salinity can be used as inputs to an oyster dynamic model (Wang, H., Huang, W., Harwell, M., Edmiston, L., Johnson, E., Hsieh, P., Milla, K., Christensen, J., Stewart, J., Liu, X., 2008. Modeling eastern oyster population dynamics in response to changing environment in Apalachicola Bay, Florida. Journal of Ecological Modeling 211, 77–89) to support the ecological study of oyster growth and mortality in the aquatic ecosystem of Apalachicola Bay.     

Applicability of a coastal morphodynamic model for fluvial environments

The dominant processes of sediment transport and morphological changes are different between rivers and coastal areas. In many situations rivers, estuaries and coasts need to be modelled together in an integrated way. This paper investigates the capability of a freely available, open source, coastal morphodynamic software (XBeach) to estimate sediment transport and morphological changes in fluvial environments. Four benchmark tests were designed to test code performance and included simple unidirectional flow cases, complex topography, fluvial flood flows (hydrographs) and dam break scenarios (fast transient, supercritical flow fields). The results were compared to laboratory experimental results or simulations results from industry standard software. Analysis suggested that the coastal morphodynamic code is able to simulate sediment transport and morphological changes in a fluvial environment, but there are limitations to what can be modelled and the accuracy to which they are modelled. General morphological trends are replicated reasonably well by the code however specific bed forms and rapid erosive responses are less well modelled. Suggestions are made for applicability of the code, code improvement and future work.     

Investigation of density flow in dam reservoirs using a three-dimensional mathematical model including Coriolis effect

This paper aims to simulate and discuss the propagation of density current and divergence flow in a dam reservoir. The density plunging flow is modeled in three-dimensions through a dam reservoir with diverging and sloping bottom channels, and the plunging phenomenon has been reproduced in the present model. Nonlinear and unsteady continuity, momentum, energy and turbulence model equations are formulated in the Cartesian coordinates both in a sloping and in a diverging channel. For the turbulence viscosity, a k-ε turbulence model including buoyancy effects is used to reproduce the main flow characteristics. To investigate the Coriolis force effect on the density flow in a dam reservoir, Coriolis force parameter is also included in the governing equations. The equations of the model are solved based on the initial and boundary conditions of the dam reservoir flow for a range of bottom slopes and divergence angles. In this paper the main interest is the formation of separated flows, such as wall-jet and free-jet flows. The model successfully simulates the formation of attached flow, wall jets, and free jets in a negatively buoyant environment. The simulation results obtained from this study are compared with previous experimental work, and the mathematical model studies data on density current generated by the plunging of cold water in ambient warm water in a diverging channel, and is found to be of the same magnitude as the experimental measurements and followed the expected basic trend.     

Simplification of physical system theory in the modelling of manufacturing,organizational and other socio-economic systems

The number of variables and equations associated with the system model of any large scale system are sufficiently large. In the case of models developed using physical system theory (PST), the number of variables and equations are twice the number of edges in the system graph. The system graph represents the interactions of discrete components united at a finite number of interfaces. The PST model of any real life manufacturing, organizational or socio-economic system has a large number of edges and equations. If, somehow, the number of variables can be reduced, the PST model can be simplified, thus increasing its practicability. An approach is presented to simplify the PST models of manufacturing, organizational and other socio-economic systems that exhibit some peculiar features. For the special case of forward flow systems (which are quite common in real life) the solution procedure is simplified considerably. The proposed methodology of simplification is illustrated with the example of a multi-stage manufacturing sytem.     

Computer Simulation of Compositional Flow Using Unstructured Control Volume Finite Element Methods

In this paper, we study the computer simulation of gas cycling in a rich retrograde condensate reservoir. Two prediction cases are studied. The first case is gas cycling with constant sales gas removal, and the second case is cycling with some gas sales deferral to enhance pressure maintenance in the early life of this reservoir. In this problem the great majority of cycling takes place at pressure below the dew point pressure, indicating the need for modeling the compositional three-phase, multicomponent flow in the reservoir. This compositional model consists of Darcy's law for volumetric flow velocities, mass conservation for hydrocarbon components, thermodynamic equilibrium for mass interchange between phases, and an equation of state for saturations. The control volume finite element (CVFE) method on unstructured grids is used to discretize the model governing equations for the first time. Numerical experiments are reported for the benchmark problem of the third comparative solution project (CSP) organized by the society of petroleum engineers (SPE). The PVT (pressure-volume-temperature) data are based on a real fluid analysis.     

Particle method for phase separation on membranes

The phenomenon of phase separation has been observed in lipid membranes. This process is remarkable, since both in-membrane and solvent-mediated hydrodynamic effects affect separation dynamics. The Cahn–Hilliard model for phase separation is here considered, coupled with the overdamped (Stokes) fluid equations. The convection term of the Cahn–Hilliard equations, which is due to hydrodynamic effects, is here treated by a Lagrangian method, in which fluid particles move along the velocity field carrying the concentration field. The method is combined with a projection onto a fixed regular mesh, where the rest of the equations are solved in Fourier space. In this space, spatial derivatives are evaluated quite easily. Moreover, the effect of the underlying fluid is straightforward in Fourier space, through the modification of the Oseen tensor. This hybrid treatment is the main contribution of this work. Results are in good agreement with experimental findings. Some agreement is found with previous simulations, but some striking differences are present.     

Physics-based flow estimation of fluids

We present a physics-based method to compute the optical flow of a fluid. In most situations, gray level changes in an image do not provide sufficient information to completely ascertain optical flow, necessitating the use of a supplementary constraint. For this, the smoothness constraint is often employed. This constraint is, however, general and does not express well a priori knowledge of a specific object. We therefore propose a method in which physical equations describing the object are used as supplementary constraints. In this way, more accurate flow estimation can be achieved. The physical model employed is a combination of the continuity equation and Navier-Stokes’ equations. After describing how we integrate these equations into fluid flow estimation, we demonstrate the effectiveness of the proposed method by presenting experimental results of its application to simulated and real Karman flows.     

Electrokinetic transport and separation of droplets in a microchannel

This work presents theoretical, numerical and experimental investigations of electrokinetic transport and separation of droplets in a microchannel. A theoretical model is used to predict that, in case of micron-sized droplets transported by electro-osmotic flow, the drag force is dominant as compared to the dielectrophoretic force. Numerical simulations were performed to capture the transient electrokinetic motion of the droplets using a two-dimensional multi-physics model. The numerical model employs Navier–Stokes equations for the fluid flow and Laplace equation for the electric potential in an Arbitrary Lagrangian–Eulerian framework. A microfluidic chip was fabricated using micromilling followed by solvent-assisted bonding. Experiments were performed with oil-in-water droplets produced using a cross-junction structure and applying electric fields using two cylindrical electrodes located at both ends of a straight microchannel. Droplets of different sizes were produced by controlling the relative flow rates of the discrete and continuous phases and separated along the channel due to the competition between the hydrodynamic and electrical forces. The numerical predictions of the particle transport are in quantitative agreement with the experimental results. The work reported here can be useful for separation and probing of individual biological cells for lab-on-chip applications.     

Single-Velocity Model of Two-Phase Liquids for Calculating Flows According to the First Principles’ Approach

A single velocity model of one-component media for calculating two-phase flows is presented. The model is based on conservation laws with minimal additional assumptions. The model and numerical method are intended for the direct numerical simulation (DNS) of complex two-phase flows with high-performance computing systems (exascale computing). The closed set of governing equations is written for nonaveraged parameters (so-called microparameters) and for a medium with a complex equation of state. It is assumed that each point of the flow is completely characterized by a single density, single velocity, and single internal energy. The diffused interface model is used for describing an interphase boundary. A method for generating the relationship between thermodynamic functions and all possible values of density and internal energy is presented. The real functions for the pure phases are used. The hydrodynamic basis of the model consists of Navier-Stokes equations or Euler equations that take heat conductivity processes into consideration. The reliability of the model is tested on a 1D problem for real water, in particular, on the Stefan problem and on the problem on the formation and coalescence of bubbles.     

基于NoC的SoC中实时跟踪数据的传输

片上网络(NoC)技术使片上系统(SoC)的通信机制发生了根本改变,直接影响了SoC中处理器内核的实时跟踪技术。该文以ARM Coresight构架的实时跟踪机制为参考,分析了在NoC环境中实现实时跟踪数据传输的难点,提出相应的解决方案。通过对实验系统的仿真,验证了其中的关键技术。     

Experimental validation of a model of an uncontrolled bicycle

In this paper, an experimental validation of some modelling aspects of an uncontrolled bicycle is presented. In numerical models, many physical aspects of the real bicycle are considered negligible, such as the flexibility of the frame and wheels, play in the bearings, and precise tire characteristics. The admissibility of these assumptions has been checked by comparing experimental results with numerical simulation results. The numerical simulations were performed on a three-degree-of-freedom benchmarked bicycle model. For the validation we considered the linearized equations of motion for small perturbations of the upright steady forward motion. The most dubious assumption that was validated in this model was the replacement of the tires by knife-edge wheels rolling without slipping (non-holonomic constraints). The experimental system consisted of an instrumented bicycle without rider. Sensors were present for measuring the roll rate, yaw rate, steering angle, and rear wheel rotation. Measurements were recorded for the case in which the bicycle coasted freely on a level surface. From these measured data, eigenvalues were extracted by means of curve fitting. These eigenvalues were then compared with the results from the linearized equations of motion of the model. As a result, the model appeared to be fairly accurate for the low-speed low-frequency behaviour.