scholarly journals The Effect of Modifying a CFD-AB Approach on Fish Passage through a Model Hydraulic Dam

Water ◽  
2019 ◽  
Vol 11 (9) ◽  
pp. 1776 ◽  
Author(s):  
Anvar Gilmanov ◽  
Daniel Zielinski ◽  
Vaughan Voller ◽  
Peter Sorensen
Keyword(s):  
Mississippi River ◽  
Computer Modelling ◽  
Fish Passage ◽  
Upstream Migration ◽  
Computational Domain ◽  
Time Step ◽  
Neighboring Node ◽  
Agent Based ◽  
Path Computations ◽  
Swimming Trajectories

The threat of invasive bigheaded carp swimming into the upper reaches of the Mississippi River (USA) demands new and effective approaches to block these species. To explore how navigational Lock and Dams (LDs) on the Mississippi River could be used to deter the upstream migration of invasive fish species, computer modelling that combined computational fluid dynamics (CFD) and agent-based (AB) fish passage model (CFD-AB model) could be used to hypothetically quantify the passage of bigheaded carp (Hypophthalmichthys spp.) through LDs. Agent-based fish (AB-fish) are always located on a node of the CFD mesh and move by selecting the neighboring node that minimizes fatigue. A possible limitation of this approach is that the AB-fish movement exhibits a dependence upon the CFD mesh. The proposed modified approach allows the AB-fish to occupy any point in the computational domain and to continually (within the size of the time step) update their minimum fatigue path. Computations in a simplified channel/dam structure show that the modified CFD-AB results are smoother swimming trajectories and increased estimates of fish passage when compared to the original CFD-AB model.

BIASED RANDOM WALKS, PARTIAL DIFFERENTIAL EQUATIONS AND UPDATE SCHEMES

2013 ◽  
Vol 55 (2) ◽  
pp. 93-108 ◽  
Author(s):  
JACK D. HYWOOD ◽  
KERRY A. LANDMAN
Keyword(s):  
Statistical Physics ◽  
Planck Equation ◽  
Step Length ◽  
Physical Object ◽  
Cell Diameter ◽  
Agent Based Models ◽  
Time Step ◽  
Partial Differential ◽  
Agent Based ◽  
Random Walkers

AbstractThere is much interest within the mathematical biology and statistical physics community in converting stochastic agent-based models for random walkers into a partial differential equation description for the average agent density. Here a collection of noninteracting biased random walkers on a one-dimensional lattice is considered. The usual master equation approach requires that two continuum limits, involving three parameters, namely step length, time step and the random walk bias, approach zero in a specific way. We are interested in the case where the two limits are not consistent. New results are obtained using a Fokker–Planck equation and the results are highly dependent on the simulation update schemes. The theoretical results are confirmed with examples. These findings provide insight into the importance of updating schemes to an accurate macroscopic description of stochastic local movement rules in agent-based models when the lattice spacing represents a physical object such as cell diameter.

scholarly journals Culverts in paved roads as suitable passages for Neotropical fish species

2012 ◽  
Vol 10 (4) ◽  
pp. 763-770 ◽  
Author(s):  
Sergio Makrakis ◽  
Theodore Castro-Santos ◽  
Maristela Cavicchioli Makrakis ◽  
Ricardo Luiz Wagner ◽  
Maurício Spagnolo Adames
Keyword(s):  
Fish Passage ◽  
Fish Movement ◽  
Upstream Migration ◽  
Migratory Species ◽  
Neotropical Fish ◽  
Potential Barriers ◽  
Medium Risk ◽  
Fall Height ◽  
Additional Monitoring ◽  
Spawning Success

Improperly installed or poorly maintained culverts can pose a serious threat to fish by disrupting their habitat and endangering spawning success. Road culverts that are not designed for fish passage frequently can become obstacles. This can be especially problematic for migratory species, but can lead to fragmentation of resident populations as well. This study evaluated 40 culverts of 29 sites within a 25-km radius from Toledo city, Paraná State, southern Brazil, with respect to their likely effects on movement of the local ichthyofauna. We collected data on the shape and length of culverts, culvert material, waterfall height, water column depth, slope, and estimated flow velocity. Culverts were categorized by level of barrier risk for upstream migration: high, medium, low, and impassable, as well as the type of barrier posed (fall height, depth, length and velocity). Most of culverts analyzed were considered potential barriers to fish movement, with 45% classified as impassible, 45% as high risk, 10% as medium risk, and no culverts as low risk. Brazilian culverts as fishways will require additional monitoring and studies to corroborate the premises proposed in the present study. Road culvert projects that are properly built and maintained will be able to simultaneously improve function of roadways and protect fish populations.

scholarly journals Algorithms for Solving Darcian Flow in Structured Porous Media

10.14311/1829 ◽  
2013 ◽  
Vol 53 (4) ◽  
Author(s):  
Michal Kuráž ◽  
Petr Mayer
Keyword(s):  
Proper Time ◽  
Time Integration ◽  
Mass Term ◽  
Step Length ◽  
Richards Equation ◽  
Parabolic Problems ◽  
Computational Domain ◽  
Wetting Front ◽  
Time Step ◽  
The Matrix

This paper presents several algorithms that were implemented in DRUtES [1], a new open source project. DRUtES is a finite element solver for coupled nonlinear parabolic problems, namely the Richards equation with the dual porosity approach (modeling the flow of liquids in a porous medium). Mass balance consistency is crucial in any hydrological balance and contaminant transportation evaluations. An incorrect approximation of the mass term greatly depreciates the results that are obtained. An algorithm for automatic time step selection is presented, as the proper time step length is crucial for achieving accuracy of the Euler time integration method. Various problems arise with poor conditioning of the Richards equation: the computational domain is clustered into subregions separated by a wetting front, and the nonlinear constitutive functions cover a high range of values, while a very simple diagonal preconditioning method greatly improves the matrix properties. The results are presented here, together with an analysis.

A Meshfree-Based Lattice Boltzmann Approach for Simulation of Fluid Flows Within Complex Geometries

2018 ◽  
pp. 188-222 ◽  
Author(s):  
Sonam Tanwar
Keyword(s):  
Lattice Boltzmann Method ◽  
Lattice Boltzmann ◽  
Moving Boundary ◽  
Fluid Flows ◽  
Computational Domain ◽  
Time Step ◽  
Boundary Problems ◽  
Complex Process ◽  
Element Free ◽  
Boltzmann Method

This chapter develops a meshless formulation of lattice Boltzmann method for simulation of fluid flows within complex and irregular geometries. The meshless feature of proposed technique will improve the accuracy of standard lattice Boltzmann method within complicated fluid domains. Discretization of such domains itself may introduce significant numerical errors into the solution. Specifically, in phase transition or moving boundary problems, discretization of the domain is a time-consuming and complex process. In these problems, at each time step, the computational domain may change its shape and need to be re-meshed accordingly for the purpose of accuracy and stability of the solution. The author proposes to combine lattice Boltzmann method with a Galerkin meshfree technique popularly known as element-free Galerkin method in this chapter to remove the difficulties associated with traditional grid-based methods.

scholarly journals Domain Decomposition Modified with Characteristic Mixed Finite Element and Numerical Analysis for Three-Dimensional Slightly Compressible Oil-Water Seepage Displacement

2017 ◽  
Vol 9 (1) ◽  
pp. 143
Author(s):  
Yirang Yuan ◽  
Luo Chang ◽  
Changfeng Li ◽  
Tongjun Sun
Keyword(s):  
Finite Element ◽  
Domain Decomposition ◽  
Method Of Characteristics ◽  
Mixed Finite Element ◽  
Three Dimensional ◽  
Optimal Error Estimate ◽  
Computational Domain ◽  
Time Step ◽  
Slightly Compressible ◽  
The Method Of Characteristics

A parallel algorithm is presented to solve three-dimensional slightly compressible seepage displacement where domain decomposition and characteristics-mixed finite element are combined. Decomposing the computational domain into several subdomains, we define a special function to approximate the derivative at interior boundary explicitly and obtain numerical solutions of the saturation implicitly on subdomains in parallel. The method of characteristics can confirm strong stability at the fronts, and can avoid numerical dispersion and nonphysical oscillation. It can adopt large-time step but can obtain small time truncation error. So a characteristic domain decomposition finite element scheme is put forward to compute the saturation. The flow equation is computed by the method of mixed finite element and numerical accuracy of Darcy velocity is improved one order. For a model problem we apply some techniques such as variation form, domain decomposition, the method of characteristics, the principle of energy, negative norm estimates, induction hypothesis, and the theory of priori estimates of differential equations to derive optimal error estimate in $l^2$ norm. Numerical example is given to testify theoretical analysis and numerical data show that this method is effective in solving actual applications. Then it can solve the well-known problem.

Development of a Three-Dimensional Iterative Methodology Using a Commercial CFD Code for Flow Scouring Around Bridge Piers

2012 ◽  
Author(s):  
Phani Ganesh Elapolu ◽  
Pradip Majumdar ◽  
Steven A. Lottes ◽  
Milivoje Kostic
Keyword(s):  
Shear Stress ◽  
Three Dimensional ◽  
Critical Shear Stress ◽  
Shear Stresses ◽  
Computational Domain ◽  
Time Step ◽  
Mesh Morphing ◽  
River Bed ◽  
Scour Hole ◽  
The Stability

One of the major concerns affecting the safety of bridges with foundation supports in river-beds is the scouring of river-bed material from bridge supports during floods. Scour is the engineering term for the erosion caused by water around bridge elements such as piers, monopiles, or abutments. Scour holes around a monopile can jeopardize the stability of the whole structure and will require deeper piling or local armoring of the river-bed. About 500,000 bridges in the National Bridge Registry are over waterways. Many of these are considered as vulnerable to scour, about five percent are classified as scour critical, and over the last 30 years bridge failures caused by foundation scour have averaged about one every two weeks. Therefore it is of great importance to predict the correct scour development for a given bridge and flood conditions. Apart from saving time and money, integrity of bridges are important in ensuring public safety. Recent advances in computing boundary motion in combination with mesh morphing to maintain mesh quality in computational fluid dynamic analysis can be applied to predict the scour hole development, analyze the local scour phenomenon, and predict the scour hole shape and size around a pier. The main objective of the present study was to develop and implement a three dimensional iterative procedure to predict the scour hole formation around a cylindrical pier using the mesh morphing capabilities in the STARCCM+ commercial CFD code. A computational methodology has been developed using Python and Java Macros and implemented using a Bash script on a LINUX high performance computer cluster. An implicit unsteady approach was used to obtain the bed shear stresses. The mesh was iteratively deformed towards the equilibrium scour position based on the excess shear stress above the critical shear stress (supercritical shear stress). The model solves the flow field using Reynolds Averaged Navier-Stokes (RANS) equations, and the standard k–ε turbulence model. The iterative process involves stretching (morphing) a meshed domain after every time step, away from the bottom where scouring flow parameters are supercritical, and remeshing the relevant computational domain after a certain number of time steps when the morphed mesh compromises the stability of further simulation. The simulation model was validated by comparing results with limited experimental data available in the literature.

COMPUTER MODELLING OF THE OXFORDIAN DEPOSITIONAL SYSTEMS IN THE KENDREW TROUGH, DAMPIER SUB-BASIN

2001 ◽  
Vol 41 (1) ◽  
pp. 463 ◽  
Author(s):  
K. Liu ◽  
C.M. Griffiths ◽  
C.P. Dyt
Keyword(s):  
Computer Modelling ◽  
Temporal Distribution ◽  
Sedimentary Facies ◽  
Sediment Supply ◽  
Three Dimensions ◽  
Spatial And Temporal Distribution ◽  
Time Step ◽  
Sea Level Fluctuations ◽  
Basin Scale ◽  
Depositional Systems

A 3D depositional modelling program, SEDSIM, was used to model the various depositional systems operating in the Kendrew Trough, Dampier Sub-basin during a two million year period of the Oxfordian. The simulation covers an area of 40 km by 100 km, from the Goodwyn Field in the southwest to the Lambert Field in the northeast, covering the Rankin Trend, Kendrew Trough, Madeleine Trend and part of the Lewis Trough. The simulation started from the Jurassic main unconformity (156.7 Ma) forward to 154.7 Ma using a spatial resolution of 1 km and a time step of 5 ka.The 3D model from the simulation quantitatively mimics the interaction of the palaeogeographic setting, sediment supply, sea level fluctuations, tectonic movement and palaeo-oceanographic setting in three dimensions, to simulate the spatial and temporal distribution of sedimentary facies. The model identified five Oxfordian leads within the Kendrew Trough, including two major slope and basin-floor fan systems, a shelfal-shoreface system, a deltaic system, and a submarine channel system.The study has shown that 3D depositional models produced by SEDSIM are not only able to depict the spatial and temporal distribution of depositional systems on a basin scale, but are also capable of making useful contributions to the understanding of play fairway and lead development.

Fairness in Agent Based Simulation Frameworks

2008 ◽  
Author(s):  
Lawrence Welch ◽  
Stephen Ekwaro-Osire
Keyword(s):  
Initial Conditions ◽  
Scheduling Algorithm ◽  
Random Order ◽  
Multiple Agents ◽  
Agent Based Simulation ◽  
Time Step ◽  
Thread Scheduling ◽  
Agent Based ◽  
Simulation Engine ◽  
Over Time

An agent based simulation engine should provide a fair playing field for all of its agents. A fundamental design axiom of agent based simulation frameworks is that the simulation engine should not arbitrarily bias its execution towards one agent or another. This fairness is basic to giving the agent modeler confidence that differences in behavior and performance between agents derive legitimately from the simulation modeling, initial conditions or specific agent characteristics, rather than the capriciousness of the underlying framework. One aspect of fairness in a simulation is the relative order of execution of agents over time. This order of execution is affected by techniques employed by frameworks to simulate the concurrent activities of multiple agents. One such technique is multi-threading. Multi-threaded operating systems, or programming languages and environments, such as Java, allow multiple agents, represented by software threads, to share the computer’s execution time by taking turns, thus appearing to act simultaneously. The precise order of execution of peer threads in multi-threaded applications is often out of the hands of the programmer, and may be determined exclusively by the operating system or program execution environment. However, if overlooked by the framework developer, the idiosyncrasies of a particular thread ordering mechanism can pass on to the modeler inherent random behavior that is neither intuitive, nor in line with the modeler’s expectations. To be considered fair, the engine should aim to provide all agents with equal probability of executing first within a time step, or last, or in any position in between. This paper analyzes the sequencing of agent thread execution within a Java framework that implements a multi-threaded, time-stepping, agent based simulation engine. The natural ordering of Java thread execution is demonstrated to be unfair (that is, not uniform) in its treatment of agents. This research shows that the standard mechanism of Java thread scheduling, while appropriate for most applications, is inappropriate on its own for the agent based framework. It is demonstrated that with Java’s standard thread scheduling algorithm, over time certain agents tend to execute ahead of others within each time step, while others tend to execute in the middle or at the back of the pack. This paper then introduces and demonstrates the “Uniform Specific Notification” pattern, a technique that produces a fairer, uniformly distributed random order for the initial execution of Java agent threads at each simulation time step.

Numerical Simulation of Nonlinear Water Wave Propagation Over Rippled Bed

2007 ◽  
Author(s):  
Gerasimos A. Kolokythas ◽  
Athanassios A. Dimas
Keyword(s):  
Free Surface ◽  
Boundary Conditions ◽  
Water Waves ◽  
Stokes Equations ◽  
Surface Flow ◽  
Surface Boundary ◽  
Computational Domain ◽  
Time Step ◽  
Outflow Boundary ◽  
Rippled Bed

In the present study, numerical simulations of the free-surface flow, developing by the propagation of nonlinear water waves over a rippled bottom, are performed assuming that the corresponding flow is two-dimensional, incompressible and viscous. The simulations are based on the numerical solution of the Navier-Stokes equations subject to the fully-nonlinear free-surface boundary conditions and the suitable bottom, inflow and outflow boundary conditions. The equations are properly transformed so that the computational domain becomes time-independent. For the spatial discretization, a hybrid scheme with finite-differences and Chebyshev polynomials is applied, while a fractional time-step scheme is used for the temporal discretization. A wave absorption zone is placed at the outflow region in order to efficiently minimize reflection of waves by the outflow boundary. The numerical model is validated by comparison to the analytical solution for the laminar, oscillatory, current flow which develops a uniform boundary layer over a horizontal bottom. For the propagation of finite-amplitude waves over a rigid rippled bed, the case with wavelength to water depth ratio λ/d0 = 6 and wave height to wavelength ratio H0/λ = 0.05 is considered. The ripples have parabolic shape, while their dimensions — length and height — are chosen accordingly to fit laboratory and field data. Results indicate that the wall shear stress over the ripples and the form drag forces on the ripples increase with increasing ripple height, while the corresponding friction force is insensitive to this increase. Therefore, the percentage of friction in the total drag force decreases with increasing ripple height.

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