Development of suitable approximation algorithms to be used in the description of heterogeneous reservoirs for secondary recovery studies.

The prediction method makes use of flow capacity distributions in a heterogeneous reservoir.A number of tests using varying degrees of data contamination shows that the model has the potential to reduce bad data effects. It was also shown that the model can be used to easily determine the reservoir floodable volume, the water injection schedule for secondary recovery operations, and an overall waterflooding performance.Our current capability to accurately predict the performance of a reservoir given a detailed description of its heterogeneities, calls for an urgent need for an efficient method of describing these non-conformities at any given locations in a reservoir.In this study, a suitable approximation algorithm was developed for use in the estimation of reservoir performance prior to waterflooding operations. This algorithm, a two dimensional cubic spline, constructs a smooth, and continuous function of the given data values. This smooth function with continuous first and second derivatives, removes the 'wiggly' and undulating characteristics often present in most polynomial approximations

Evaluation of a Semi-Analytical/Numerical Method for Modeling Matrix Diffusion Effects in Groundwater Chemical Transport

Secondary sources of contamination, such as dissolved chemicals in low permeability zones result in plume persistence and limitations for plume remediation as a consequence of the process of matrix diffusion (Mackay and Cherry, 1989; Chapman and Parker, 2005). Existing numerical transport simulators are capable of modeling matrix diffusion; however, they require fine discretization, resulting in large computational effort. An alternative approach was developed combining numerical and analytical modeling to simulate matrix diffusion effects. The semi-analytical/numerical (referred to as semi-analytical for short) approach used here was adapted from geothermal reservoir modeling of transient heat conduction in low permeability cap rocks (Vinsome and Westerveld, 1980). The semi-analytical method discretizes the high permeability parts of the aquifer in the numerical model and the matrix diffusion flux is approximated at the sub-grid scale without modifying the grid. The objective of this research is to test the semi-analytical method for the simulation of matrix diffusion effects in groundwater transport. To achieve this goal the semi-analytical method was used to simulate laboratory-scale studies and the results were compared to experimental data. In addition, various test scenarios representing heterogeneous environments were developed and compared to results from a commercial numerical simulator. Two implementations of the matrix diffusion analysis were tested in this research. Initially, a Visual Basic program in Excel® was compared to experimental results from two published studies from University of Florida and Colorado State University. Results from the Visual Basic code were also compared to fine-grid numerical simulations of two-layer systems. A FORTRAN version of this program, called REMChlor-MD was evaluated by comparing to results from large fine-grid numerical models (approximately 3 million gridblocks) with highly heterogeneous material distributions. The results indicate that the semi-analytical method matches both experimental data and fine grid numerical simulations, even for systems with highly complex heterogeneities. Besides the visual comparison, coefficients of determination were estimated for the cases studied, obtaining values from 0.724 to 0.998, demonstrating good accuracy of the matrix diffusion semi-analytical method for most practical purposes. The semi-analytical model is highly efficient, requiring only a fraction (approximately 1/10000) of the run times of the fine grid numerical simulations used as comparison basis. This evaluation is one of the stages of the project funded by the DoD\u27s Environmental Security Technology Certification Program (ESTCP) and supported in part by the Department of Energy. The project aims to develop and implement a new generation of the screening level transport model REMChlor that considers matrix diffusion in the plume: REMChlor-MD

High order finite volume schemes on unstructured grids using Moving Least Squares reconstruction. Application to shallow water dynamics

Aceptado para su publicación en International journal for numerical methods in engineering, el 08/06/2005[Abstract] This paper introduces the use of Moving Least Squares (MLS) approximations for the development of high-order finite volume discretizations on unstructured grids. The field variables and their succesive derivatives can be accurately reconstructed using this meshfree technique in a general nodal arrangement. The methodology proposed is used in the construction of low-dissipative highorder high-resolution schemes for the shallow water equations. In particular, second and third-orderreconstruction upwind schemes for unstructured grids based on Roe’s flux difference splitting are developed and applied to inviscid and viscous flows. This class of meshfree reconstruction techniques provide a robust and general approximation framework which represents an interesting alternative to the existing procedures, allowing, in addition, an accurate computation of the viscous fluxes.Ministerio de Ciencia y Tecnología; DPI2001-0556Xunta de Galicia; PGDIT01PXI11802PRXunta de Galicia; PGIDIT03PXIC118002P

A Near-Infrared Spectrometer Based on Novel Grating Light Modulators

A near-infrared spectrometer based on novel MOEMS grating light modulators is proposed. The spectrum detection method that combines a grating light modulator array with a single near-infrared detector has been applied. Firstly, optics theory has been used to analyze the essential principles of the proposed spectroscopic sensor. Secondly, the grating light modulators have been designed and fabricated by micro-machining technology. Finally, the principles of this spectroscopic sensor have been validated and its key parameters have been tested by experiments. The result shows that the spectral resolution is better than 10 nm, the wavelength deviation is less than 1 nm, the deviation of the intensity of peak wavelength is no more than 0.5%, the driving voltage of grating light modulators array device is below 25 V and the response frequency of it is about 5 kHz. With low cost, satisfactory precision, portability and other advantages, the spectrometer should find potential applications in food safety and quality monitoring, pharmaceutical identification and agriculture product quality classification

Use of GIS modeling techniques as a planning tool for establishment of wetlands as nitrate and pesticide removal facilities

May 1995.Includes bibliographical references (pages 33-37).Grant no. 14-08-0001-G2008/3, project no. 05

Numerical modelling of jet-forced circulation in reservoirs using boundary-fitted coordinate systems

Throughout the past decade, interest has grown in the use of boundary-fitted coordinate systems in many areas of computational fluid dynamics. The boundary-fitted technique provides an exact method of implementing finite-difference numerical schemes in curved flow geometries and offers an alternative solution procedure to the finite-element method. The unavoidable large bandwidth of the global stiffness matrix, employed in finite-element algorithms, means that they are computationally less efficient than corresponding finite-difference schemes. As a consequence, the boundary-fitted method offers a more efficient process for solving partial differential flow equations in awkwardly shaped regions. This thesis describes a versatile finite-difference numerical scheme for the solution of the shallow water equations on arbitrary boundary-fitted non-orthogonal curvilinear grids. The model is capable of simulating flows in irregular geometries typically encountered in river basin management. Validation tests have been conducted against the severe condition of jet-forced flow in a circular reservoir with vertical side walls, where initial reflections of free surface waves pose major problems in achieving a stable solution. Furthermore, the validation exercises have been designed to test the computer model for artificial diffusion which may be a consequence of the numerical scheme adopted to stabilise the shallow water equations. The thesis also describes two subsidiary numerical studies of jet-forced recirculating flow in circular cylinders. The first of these implements a Biot-Savart discrete vortex method for simulating the vorticity in the shear layers of the inflow jet, whereas the second employs a stream function/vorticity-transport finite-difference procedure for solving the two-dimensional Navier-Stokes equations on a distorted orthogonal polar mesh. Although the predictions from the stream function/vorticity-transport model are confined to low Reynolds number flows, they provide a valuable set of benchmark velocity fields which are used to confirm the validity of the boundary-fitted shallow water equation solver

Numerical simulation of fracture pattern development and implications for fuid flow

Simulations are instrumental to understanding flow through discrete fracture geometric representations that capture the large-scale permeability structure of fractured porous media. The contribution of this thesis is threefold: an efficient finite-element finite-volume discretisation of the advection/diffusion flow equations, a geomechanical fracture propagation algorithm to create fractured rock analogues, and a study of the effect of growth on hydraulic conductivity. We describe an iterative geomechanics-based finite-element model to simulate quasi-static crack propagation in a linear elastic matrix from an initial set of random flaws. The cornerstones are a failure and propagation criterion as well as a geometric kernel for dynamic shape housekeeping and automatic remeshing. Two-dimensional patterns exhibit connectivity, spacing, and density distributions reproducing en echelon crack linkage, tip hooking, and polygonal shrinkage forms. Differential stresses at the boundaries yield fracture curving. A stress field study shows that curvature can be suppressed by layer interaction effects. Our method is appropriate to model layered media where interaction with neighbouring layers does not dominate deformation. Geomechanically generated fracture patterns are the input to single-phase flow simulations through fractures and matrix. Thus, results are applicable to fractured porous media in addition to crystalline rocks. Stress state and deformation history control emergent local fracture apertures. Results depend on the number of initial flaws, their initial random distribution, and the permeability of the matrix. Straightpath fracture pattern simplifications yield a lower effective permeability in comparison to their curved counterparts. Fixed apertures overestimate the conductivity of the rock by up to six orders of magnitude. Local sample percolation effects are representative of the entire model flow behaviour for geomechanical apertures. Effective permeability in fracture dataset subregions are higher than the overall conductivity of the system. The presented methodology captures emerging patterns due to evolving geometric and flow properties essential to the realistic simulation of subsurface processes

VALIDATION OF COMPUTATIONAL FLUID DYNAMIC SIMULATIONS OF MEMBRANE ARTIFICIAL LUNGS WITH X-RAY IMAGING

The functional performance of membrane oxygenators is directly related to the perfusion dynamics of blood flow through the fiber bundle. Non-uniform flow and design characteristics can limit gas exchange efficiency and influence susceptibility of thrombus development in the fiber membrane. Computational fluid dynamics (CFD) is a powerful tool for predicting properties of the flow field based on prescribed geometrical domains and boundary conditions. Validation of numerical results in membrane oxygenators has been predominantly based on experimental pressure measurements with little emphasis placed on confirmation of the velocity fields due to opacity of the fiber membrane and limitations of optical velocimetric methods. A novel approach was developed using biplane X-ray digital subtraction angiography to visualize flow through a commercial membrane artificial lung at 1–4.5 L/min. Permeability based on the coefficients of the Ergun equation, α and β, were experimentally determined to be 180 and 2.4, respectively, and the equivalent spherical diameter was shown to be approximately equal to the outer fiber diameter. For all flow rates tested, biplane image projections revealed non-uniform radial perfusion through the annular fiber bundle, yet without flow bias due to the axisymmetric position of the outlet. At 1 L/min, approximately 78.2% of the outward velocity component was in the radial (horizontal) plane verses 92.0% at 4.5 L/min. The CFD studies were unable to predict the non-radial component of the outward perfusion. Two-dimensional velocity fields were generated from the radiographs using a cross-correlation tracking algorithm and compared with analogous image planes from the CFD simulations. Velocities in the non-porous regions differed by an average of 11% versus the experimental values, but simulated velocities in the fiber bundle were on average 44% lower than experimental. A corrective factor reduced the average error differences in the porous medium to 6%. Finally, biplane image pairs were reconstructed to show 3-D transient perfusion through the device. The methods developed from this research provide tools for more accurate assessments of fluid flow through membrane oxygenators. By identifying non-invasive techniques to allow direct analysis of numerical and experimental velocity fields, researchers can better evaluate device performance of new prototype designs