scholarly journals Numerical Simulation of the Coagulation Dynamics of Blood

2008 ◽  
Vol 9 (2) ◽  
pp. 83-104 ◽  
Author(s):  
T. Bodnár ◽  
A. Sequeira
Keyword(s):  
Blood Coagulation ◽  
Computational Study ◽  
Time Integration ◽  
Three Dimensional ◽  
Circular Cross Section ◽  
Clot Formation ◽  
Diffusion Reaction ◽  
Numerical Code ◽  
Injured Region ◽  
Reaction Equations

The process of platelet activation and blood coagulation is quite complex and not yet completely understood. Recently, a phenomenological meaningful model of blood coagulation and clot formation in flowing blood that extends existing models to integrate biochemical, physiological and rheological factors, has been developed. The aim of this paper is to present results from a computational study of a simplified version of this coupled fluid-biochemistry model. A generalized Newtonian model with shear-thinning viscosity has been adopted to describe the flow of blood. To simulate the biochemical changes and transport of various enzymes, proteins and platelets involved in the coagulation process, a set of coupled advection–diffusion–reaction equations is used. Three-dimensional numerical simulations are carried out for the whole model in a straight vessel with circular cross-section, using a finite volume semi-discretization in space, on structured grids, and a multistage scheme for time integration. Clot formation and growth are investigated in the vicinity of an injured region of the vessel wall. These are preliminary results aimed at showing the validation of the model and of the numerical code.

scholarly journals Computational Study of Zigzag Spacer Design with Elliptical Cross-Section Filaments

2020 ◽  
Vol 307 ◽  
pp. 01047
Author(s):  
Gohar Shoukat ◽  
Farhan Ellahi ◽  
Muhammad Sajid ◽  
Emad Uddin
Keyword(s):  
Mass Transfer ◽  
Cross Section ◽  
Cross Sections ◽  
Computational Study ◽  
Flow Direction ◽  
Three Dimensional ◽  
Circular Cross Section ◽  
Two Dimensional ◽  
Permeate Flux ◽  
Elliptical Cross

The large energy consumption of membrane desalination process has encouraged researchers to explore different spacer designs using Computational Fluid Dynamics (CFD) for maximizing permeate per unit of energy consumed. In previous studies of zigzag spacer designs, the filaments are modeled as circular cross sections in a two-dimensional geometry under the assumption that the flow is oriented normal to the filaments. In this work, we consider the 45° orientation of the flow towards the three-dimensional zigzag spacer unit, which projects the circular cross section of the filament as elliptical in a simplified two-dimensional domain. OpenFOAM was used to simulate the mass transfer enhancement in a reverse-osmosis desalination unit employing spiral wound membranes lined with zigzag spacer filaments. Properties that impact the concentration polarization and hence permeate flux were analyzed in the domain with elliptical filaments as well as a domain with circular filaments to draw suitable comparisons. The range of variation in characteristic parameters across the domain between the two different configurations is determined. It was concluded that ignoring the elliptical projection of circular filaments to the flow direction, can introduce significant margin of error in the estimation of mass transfer coefficient.

scholarly journals A Finite Volume-Complete Flux Scheme for a Polluted Groundwater Site

2016 ◽  
Vol 2016 ◽  
pp. 1-12
Author(s):  
M. F. P. ten Eikelder ◽  
J. H. M. ten Thije Boonkkamp ◽  
M. P. T. Moonen ◽  
B. V. Rathish Kumar
Keyword(s):  
Time Integration ◽  
Stability Result ◽  
Coupled System ◽  
Diffusion Reaction ◽  
Advection Diffusion ◽  
Guarani Aquifer ◽  
Space Discretization ◽  
Reaction Equations ◽  
Advection Diffusion Reaction Equations ◽  
Good Agreement

We present a model of a polluted groundwater site. The model consists of a coupled system of advection-diffusion-reaction equations for the groundwater level and the concentration of the pollutant. We use the complete flux scheme for the space discretization in combination with the ϑ-method for time integration and we prove a new stability result for the scheme. Numerical results are computed for the Guarani Aquifer in South America and they show good agreement with results in literature.

Random walk on rectangles and parallelepipeds algorithm for solving transient anisotropic drift-diffusion-reaction problems

2019 ◽  
Vol 25 (2) ◽  
pp. 131-146 ◽  
Author(s):  
Karl K. Sabelfeld
Keyword(s):  
Random Walk ◽  
First Passage Time ◽  
Three Dimensional ◽  
Passage Time ◽  
Diffusion Reaction ◽  
Exit Point ◽  
Drift Diffusion ◽  
Continuity Equations ◽  
Reaction Equations ◽  
Reaction Problem

Abstract In this paper a random walk on arbitrary rectangles (2D) and parallelepipeds (3D) algorithm is developed for solving transient anisotropic drift-diffusion-reaction equations. The method is meshless, both in space and time. The approach is based on a rigorous representation of the first passage time and exit point distributions for arbitrary rectangles and parallelepipeds. The probabilistic representation is then transformed to a form convenient for stochastic simulation. The method can be used to calculate fluxes to any desired part of the boundary, from arbitrary sources. A global version of the method we call here as a stochastic expansion from cell to cell (SECC) algorithm for calculating the whole solution field is suggested. Application of this method to solve a system of transport equations for electrons and holes in a semicoductor is discussed. This system consists of the continuity equations for particle densities and a Poisson equation for electrostatic potential. To validate the method we have derived a series of exact solutions of the drift-diffusion-reaction problem in a three-dimensional layer presented in the last section in details.

scholarly journals Parallel graph-grammar-based algorithm for the longest-edge refinement of triangular meshes and the pollution simulations in Lesser Poland area

2021 ◽  
Author(s):  
Krzysztof Podsiadło ◽  
Albert Oliver Serra ◽  
Anna Paszyńska ◽  
Rafael Montenegro ◽  
Ian Henriksen ◽  
...  
Keyword(s):  
Time Integration ◽  
Three Dimensional ◽  
Reaction Model ◽  
Graph Grammar ◽  
Diffusion Reaction ◽  
Integration Scheme ◽  
Triangular Meshes ◽  
Time Integration Scheme ◽  
Parallel Graph ◽  
Refinement Algorithm

AbstractIn this paper, we propose parallel graph-grammar-based algorithm for the longest-edge refinements and the pollution simulations in Lesser Poland area. We introduce graph-grammar productions for Rivara’s longest-edged algorithm for the local refinement of unstructured triangular meshes. We utilize the hyper-graph to represent the computational mesh and the graph-grammar productions to express the longest-edge mesh refinement algorithm. The parallelism in the original Rivara’s longest edge refinement algorithm is obtained by processing different longest edge refinement paths in different three ads. Our graph-grammar-based algorithm allows for additional parallelization within a single longest-edge refinement path. The graph-grammar-based algorithm automatically guarantees the validity and conformity of the generated mesh; it prevents the generation of duplicated nodes and edges, elongated elements with Jacobians converging to zero, and removes all the hanging nodes automatically from the mesh. We test the algorithm on generating a surface mesh based on a topographic data of Lesser Poland area. The graph-grammar productions also generate the layers of prismatic three-dimensional elements on top of the triangular mesh, and they break each prismatic element into three tetrahedral elements. Next, we propose graph-grammar productions generating element matrices and right-hand-side vectors for each tetrahedral element. We utilize the Streamline Upwind Petrov–Galerkin (SUPG) stabilization for the pollution propagation simulations in Lesser Poland area. We use the advection–diffusion-reaction model, the Crank–Nicolson time integration scheme, and the graph-grammar-based interface to the GMRES solver.

A computer investigation of chemically mediated detachment in bacterial biofilms

Microbiology ◽  
2003 ◽  
Vol 149 (5) ◽  
pp. 1155-1163 ◽  
Author(s):  
Stephen M. Hunt ◽  
Martin A. Hamilton ◽  
John T. Sears ◽  
Gary Harkin ◽  
Jason Reno
Keyword(s):  
Life Cycle ◽  
Cellular Automata ◽  
Three Dimensional ◽  
Bacterial Biofilm ◽  
Diffusion Reaction ◽  
Bacterial Biofilms ◽  
Biofilm Development ◽  
Reaction Equations ◽  
Growth Movement ◽  
Cellular Automata Algorithm

A three-dimensional computer model was used to evaluate the effect of chemically mediated detachment on biofilm development in a negligible-shear environment. The model, BacLAB, combines conventional diffusion-reaction equations for chemicals with a cellular automata algorithm to simulate bacterial growth, movement and detachment. BacLAB simulates the life cycle of a bacterial biofilm from its initial colonization of a surface to the development of a mature biofilm with cell areal densities comparable to those in the laboratory. A base model founded on well established transport equations that are easily adaptable to investigate conjectures at the biological level has been created. In this study, the conjecture of a detachment mechanism involving a bacterially produced chemical detachment factor in which high local concentrations of this detachment factor cause the bacteria to detach from the biofilm was examined. The results show that the often observed ‘mushroom’-shaped structure can occur if detachment events create voids so that the remaining attached cells look like mushrooms.

Investigation of the Flow Around Two Circular Cylinders Employing the Spectral Element Method With Modal Decomposition

2004 ◽  
Author(s):  
Bruno Souza Carmo ◽  
Julio Romano Meneghini ◽  
Paulo Jose Saiz Jabardo ◽  
Fa´bio Saltara
Keyword(s):  
Computational Study ◽  
Vortex Formation ◽  
Three Dimensional ◽  
Circular Cross Section ◽  
Spectral Element ◽  
Circular Cylinders ◽  
Offshore Platforms ◽  
Modal Decomposition ◽  
Vortex Induced Vibration ◽  
Element Method

Flow induced vibrations play an important role in the process of fatigue in cylindrical elements of offshore platforms. One of the main sources of vibration is due to vortex shedding. Such vortices are originated from the separation of the boundary layer and the low-pressure regions cause the hydrodynamic forces to oscillate. This kind of vibration is known in literature as vortex-induced vibration (VIV), and it has some points that are not well understood yet. When a circular cross section is considered, the point of separation changes with the Reynolds number, increasing the complexity of the phenomena. Additionally, when two bluff bodies are disposed near each other, the vortices shed by one of them can reach the other, interfering with the vortex formation close to the later, and constituting another source of vibration. This work is an effort to provide a better comprehension of the vortex-induced vibration phenomena in a flow around groups of cylinders. In this paper, a detailed computational study of the flow around two rigid cylinders in a tandem arrangement is carried out. The spectral/hp element method is used in the simulations, with a modal decomposition in the span direction. The three-dimensional structures in the wake are analysed, and the level of synchronization of the flow along the span is verified for a gap of five diameters between the cylinders.

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