Browsing by Author "Akin, John Edward."
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Item A Computational Analysis of Novel Non-circular Nozzles(2014-04-24) Baskici, Gokhan; Akin, John Edward.; Tezduyar, Tayfun E.; Meade, Andrew J., Jr.This thesis presents a computational analysis for determining the flow properties of novel non-circular nozzles. In last few decades, non-circular nozzles have been investigated intensively due to their remarkably superior capabilities in enhancing mass entrainment over circular nozzles. In this thesis, to increase the amount of ambient fluid entrained in the jet flow, three different geometrical modifications are applied to non-circular nozzles. These modifications include changing contraction profiles, the twist angles of transition, and nozzle lengths. The flow properties of air emanating from geometrically modified non-circular nozzles are studied by using computational fluid dynamics (CFD) in the Star CCM+ fluid solver. This computational analysis shows that suitably modified non-circular nozzles are very effective passive flow conditioning devices and can modify the flow field. Particularly, nozzle with a sharp exit and large twist angle entrains the ambient fluid at a higher rate than the circular and other modified non-circular nozzles.Item A computational analysis on an initial application of a Hemiwedge based sub-surface safety valve for use in ultra-deepwater oil wells and extreme high pressure, high temperature environments(2010) Martin, Joel; Akin, John Edward.This study proposes and validates computationally the effectiveness of a novel, hemiwedge model for a sub-surface safety valve (SSSV). With the growing needs in the oil industry and new finds of ultra-deepwater reservoirs in the Gulf of Mexico (GOM), this SSSV will provide a small but necessary advancement to harvest these new oil reserves from extreme high-pressure/high-temperature (XHPHT) environments. Computational fluid dynamics (CFD) in the Ansys RTM CFX flow solver is used to study the flow properties of crude oil through the valve, while both AnsysRTM and SolidWorks RTM Simulation are used to perform stress and fatigue analyses and other solid mechanics studies. Analysis has shown this model to be effective in successfully and safely operating at high pressures (30,000 psi ) and high temperatures (450°F) over the desired life of the SSSV, providing a viable option for helping to recover new oil reserves found in the GOM and other XHPHT environments.Item A finite element model of the tensional state of the human and canine diaphragms(1991) Voigt, Michael Hans Heinrich; Akin, John Edward.The static aspects of the diaphragm under Full Residual Capacity (full lung deflation) were studied. The membrane equations were used to describe the diaphragm. Based on the description, a finite element program was written to determine the position of the diaphragm under various loading conditions. Erect and supine specimens were studied. The results of the finite element model were found to be in agreement with physiological data from X-ray photographs.Item A nonlinear isoparametric contour plotting and filling algorithm(1988) McCleary, Bret Alan; Akin, John Edward.An interactive isoparametric contour plotting and filling program, ISOCON, is developed for use with finite element meshes using common two-dimensional triangular and quadrilateral elements. The program uses the local interpolation functions to compute the contour locations. The predictor-corrector algorithm used to compute the contour locations is derived and discussed. The color filling algorithm is also discussed. The program features are given along with a brief discussion of selected algorithms used in the program. The main feature of ISOCON lies in its portability since most plot drivers are written in FORTRAN 77. Selected contour plots are compared with output from another finite element contour plotting program. The ISOCON-generated plots produce much more realistic looking contours. Partial FORTRAN code along with a flowchart is included.Item A Penalty Method Approach to Experimental Data Coupling in the Sequentially Optimized Meshfree Approximation(2014-04-23) Wood, Jeffre; Meade, Andrew J., Jr.; Akin, John Edward.; Tezduyar, Tayfun E.This thesis presents an overview of recent changes that have been made to the Sequentially Optimized Meshfree Approximation (SOMA) and provides a proof of concept for a penalty method algorithm for coupling experimental data with a computational fluid dynamics (CFD) solver. The penalty method provides a means to apply experimental data to improve SOMA's convergence rate and time to convergence. Using the driven cavity problem as validation, approximations produced using this adaptation are shown. The results successfully reproduces the flow from which the data was taken creating a means of using limited experimental data to generate a complete picture of a simulation domain. Flexibility in data type, location, and quantity are demonstrated as well as the effects of experimental error on the results and a means of negating it.Item A qualitative theory of gas dynamics(1992) Barry, Matthew Robert; Akin, John Edward.Within the realm of research toward the emulation of human intelligence, the problem of how to perform qualitative reasoning with computer programs has received considerable attention. The research field of qualitative physics focuses on the special problems of identifying the basic concepts of nature and the issues related to mechanizing inference about these concepts, so that we might build qualitative models of the physical world. These models are indispensable for providing machines with "common sense" inference capabilities to reason about and describe observations of their environment. This dissertation contributes a qualitative theory of the gas dynamics domain. The theory comprises a qualitative representation of the dynamic behavior of gases, constructed upon a collection of fundamental process elements. These process elements affect the description of a dynamic scenario by manipulating the qualitative values of physical parameters that change in response to certain physical phenomena. The phenomena covered are those occurring in one- and two-dimensional flows of an ideal gas. Deployed in conjunction with an automated inference mechanism, the models built from this theory constrain results to those situations validated by natural physical laws. These models provide qualitative reasoning and simulation capabilities to intelligent computer-aided design systems. The presentation constructs a foundation within the computational framework of Qualitative Process Theory, and shows how an algebra of Qualitative Ratios, introduced herein, provides a convenient representation for describing physical change. The presentation and internal hierarchy of the theory parallels the engineering perspective of this domain, and encourages composition of the fundamental elements into larger, more complex, reasoning components. Several examples demonstrate the utility of the theory during the course of the presentation.Item A three-dimensional finite element method for quantifying stress shielding following total hip replacement(1993) Chen, Weng-Pin; Akin, John Edward.One of the critical problems associated with total hip replacement is the loosening of femoral stem. A major cause of femoral stem loosening is believed to be stress shielding of the proximal femur following implantation. In order to ensure the long-term success of total hip replacement, minimization of stress shielding is desirable. Since currently available femoral prostheses vary markedly in both geometry and material properties, the tendency for a particular prosthesis to result in stress shielding is not immediately obvious. A three-dimensional finite element method for calculating the magnitude of stress shielding in the proximal femur following implantation is described in this study. The computational method for quantifying stress shielding is the first method which allows direct comparison of the stress state produced by different prosthetic designs. By using this method, it may be possible to assess the long term performance of a prosthetic design prior to implantation. This method will also be helpful for performing comparative analysis for different prosthetic designs and for selecting the most suitable prosthesis for the patient undergoing total hip replacement.Item Adaptive refinement and related topics for finite element analysis of linear elliptic problems(1991) Kyriacou, Stelios Kyprou; Akin, John Edward.An overview of the methods for finite element adaptive refinement and error estimation for linear elliptic problems is performed. An error estimator, based on nodal averaging of a gradient measure, suitable for linear, steady state, 2D and 3D stress and thermal analysis, is created and interfaced with the FE program FINITE/GP. An adaptive h-refinement method incorporating the above error estimator is implemented for two sample problems and results are presented which indicate that the method works. Conclusions are drawn concerning the usefulness of the method. A separate chapter gives an overview as well as experience gained with solvers for sparse matrices.Item Adaptive Techniques Applied to the Sequentially Optimized Meshfree Approximation(2014-04-22) Mittelman, Rachel; Akin, John Edward.; Stanciulescu, Ilinca; Meade, Andrew J., Jr.This thesis advances the meshless Sequentially Optimized Meshfree Approximation (SOMA) from a fixed grid to an adaptive one by applying residual-based adaptive techniques. In its fixed grid form, SOMA constructs an approximation of an equation solution using optimized radial basis functions (RBFs), but deletes the RBF parameters once each basis function is appropriately added. The first proposed method saves this information, constructs an approximation of the solution, and intelligently adds points to the problem domain. The second proposed method is a flexible interpolation scheme which does not require this basis saving technique, although the two techniques can be combined. When applied to various equations, these adaptive algorithms demonstrate the convergence required to achieve a satisfactory level of precision, saving time and computational effort for the same mathematical result as a denser grid. Applications of this algorithm include function approximation as well as differential equations which demonstrate its capability and robustness.Item An rp-adaptivity scheme for the finite element analysis of linear elliptic problems(1995) Maddox, James Roger; Akin, John Edward.A finite element analysis methodology employing rp-adaptivity is developed. The p-refinement phase is facilitated through the addition and deletion of general serendipity element edge nodes. The r-refinement phase is based on the reduction of error in the solution using element area as the grid optimization design variable. A series of tiered linked list data structure representations are developed for storing and manipulating the model information. The Zienkiewicz-Zhu error estimator is utilized for determining localized error. A modified superconvergent patch recovery technique is implemented to recover highly accurate nodal gradients utilized in the error estimation phase. Numerical results are presented for an idealized fluid flow problem.Item Automatic mesh generation of two-dimensional objects(1988) Chang, Chih-Han; Akin, John Edward.An approach for the fully automatic generation of two-dimensional finite element meshes is presented. The method follows from the basic concept of the quadtree encoding technique with the specific modifications made to produce valid, user controllable finite element meshes. The use of quadtree method for mesh generation was pioneered by Shephard and Yerry, (6). Our work is similar but more general than theirs. In this thesis after giving an overview of finite element method and mesh requirements, the quadtree and modified quadtree techniques are introduced. Then paper emphasizes on those algorithmic aspects of the mesh generator especially on transferring quadtree code to finite mesh. Finally, examples are included to demonstrate this technique and conclusions are given.Item Axisymmetric fluid jet impingement of a rock half-space(1990) Welsh, Michael Frederick; Akin, John Edward.The effects of an axisymmetric fluid jet impinging on a rock half-space are examined. A recently developed constitutive model for porous elastic materials, which explicitly provides for the compressibilities of the solid grains and fluid that comprise the material, is reconciled to the model developed by M. A. Biot for soils. An increase in pore fluid pressure is shown to reduce the compression in the rock matrix, displacing the Mohr's circle in the direction of the Griffith failure surface. Shear stress due to the subsequent radial flow of fluid, though small and neglected in all previous work, is shown to have significant effect. Shear stress increases the difference between the maximum and minimum effective principal stresses, enlarging the Mohr's circle toward the failure surface. Accurate predictions of threshold pressures to cause failure were achieved when the component compressibilities and shear stress were taken into account.Item Computational Aerodynamics Modeling of Flapping Wings With Video-Tracked Locust-Wing Motion(2013-07-24) Puntel, Anthony; Tezduyar, Tayfun E.; Akin, John Edward.; Meade, Andrew J., Jr.; Takizawa, KenjiThe thesis focuses on special space--time computational techniquesintroduced recently for computational aerodynamics modeling of flapping wings of an actual locust. These techniques complement the Deforming-Spatial-Domain/Stabilized Space--Time (DSD/SST) formulation, which is the core computational technique. The DSD/SST formulation was developed for flows with moving interfaces, and the version used in the computations is "DST/SST-VMST," which is the space--time version of the residual-based variational multiscale (VMS) method. The special space--time techniques are based on using NURBS basis functions for the temporal representation of the motion of the locust wings. The motion data is extracted from the high-speed video recordings of a locust in a wind tunnel. In addition, temporal NURBS basis functions are used in representation of the motion of the volume meshes computed and also in remeshing. These ingredients provide an accurate and e fficient way of dealing with the wind tunnel data and the mesh. The thesis includes a detailed study on how the spatial and temporal resolutions influence the quality of the numerical solution.Item Computer-aided design of femoral stem prostheses(1991) Chang, Chih-Han; Akin, John Edward.In the design of femoral stem prostheses, both biologic factors and prosthetic design features influence the long-term performance of the implant. The analysis of all these influences is difficult, if not impossible, at the present time. This research presents a computational approach, using automatic contour detection, octree automesh and a special finite element program, that allows the stress analysis of different prostheses to be performed with minimal human interaction. Using computed tomography scans of a femur, the stress pattern in the femur when subjected to physiologic loading with or without a implanted prosthesis can be generated. A variety of prosthetic designs can be evaluated and the most suitable design can be selected for a particular patient prior to the operation. With an accurate inner contour generated by the computer algorithm developed in this study, a femoral prosthesis can be designed which most closely reproduces the stress pattern in the intact femur. Based on this study, different design parameters can be evaluated and the optimal prosthetic design can then be carried out with more advanced computer hardware.Item Conformal mapping and grid generation for general two-dimensional profiles(1988) Kwas, Robert; Akin, John Edward.A conformal grid generation scheme has been developed and is automated in a general purpose code which can be used for the generation of computational grids for complex geometries. The code uses the repetitive application of a general analytical mapping function known as the Karman-Trefftz equation. This program can generate highly orthogonal grids having virtually any internal structure desired by the user. The only input attributes required by the program are the body coordinates of the shape, the orthogonality requirement of the grid, and information concerning the physical structure of the grid. Computational grids generated by this program are especially well suited for the numerical computation of supersonic flow fields.Item Developing Innovative Designs with Manufacturing Capability Using the Level Set Method(2012-09-05) Baradaran Nakhjavani, Omid; Meade, Andrew J., Jr.; Akin, John Edward.; Padgett, Jamie E.; Dick, Andrew J.This thesis discusses how to use topology and shape optimization, specifically the level set method, for innovative design. The level set method is a numerical algorithm that simulates the expansion of dynamic implicit surfaces. In this research, the equations for manufacturability are generated and solved through use of the level set method joined with the COMSOL multi-physics package. Specific constraints are added to make the optimization practical for engineering design. The resulting method was applied to design the best underlying support structure, conforming to both curvature and manufacturability constraints, for the longerons used with the International Space Station solar panels.Item Development of an elastic solution for predicting the dynamic response of beams subjected to a moving mass(1989) Mofid, Massood; Akin, John Edward.In this investigation, the problem of the response of beams subjected to a moving mass has been studied. The main objective in this thesis is to provide easy and acceptable solutions for this problem. Three different methods of solution are presented. (I) The first method demonstrates the transformation of a familiar governing differential equation into a new solvable series of ordinary differential equations. (II) The second method discusses the solution of the same problem based on a new discrete element model for beams. (III) The third method is based on a finite element technique. The computer program used in this investigation is called PAFEC. The validity of the solutions is ascertained by comparison. Furthermore, the study shows that the response of beams due to a moving mass, which has often been neglected in the past, must be properly taken into account because it often differs significantly from the moving load model. Based on the cost of computations and desirable accuracy, a designer can choose the appropriate method.Item Differential roles of adhesion receptors during neutrophil adhesion to endothelial cells under flow conditions(1998) Gopalan, Priya Kadambi; Akin, John Edward.; McIntire, Larry V.Neutrophil emigration from the vasculature is an essential part of the primary immune response to infections. It is a multi-step process of cell interaction with the endothelium (capture, rolling, arrest and transmigration) that involves several classes of receptors. Neutrophils are captured (tethered) and then roll on the endothelial surface. This initial interaction is thought to involve the selectin family of cell adhesion molecules. Cell arrest (firm adhesion) follows neutrophil activation. Activated CD18 integrins and ICAM-1, a member of the immunoglobulin gene superfamily, mediate arrest. Finally, the neutrophils transmigrate beneath the endothelial cells, a process also thought to be dependent on the CD18 integrins and ICAM-1. We used a parallel plate flow chamber to simulate laminar flow along vessel walls in the vasculature. We demonstrate that L-selectin can activate the adhesive function the CD18 integrins. In this work, we show for the first time that L-selectin can activate LFA-1. We also show that two of the members of the CD18 integrin family, LFA-1 and Mac-1, are both sufficient to mediate neutrophil arrest and transmigration across endothelial cells stimulated for 4 hr with IL-$1\beta .$ We provide evidence for the existence of a pathway independent of the CD18 integrins that can mediate arrest and transmigration. Neutrophils utilizing this pathway are able to transmigrate with a rate comparable to CD18-dependent transmigration. We provide some preliminary data that demonstrates that PECAM-1 ligation does not activate neutrophil CD18 integrin-mediated arrest, in contrast to published reports. Finally, we report the results of some initial experiments that suggest that L-selectin and PSGL-1 mediate the capture of neutrophils by endothelial monolayers stimulated for 4 hr with IL-$1\beta ,$ while E-selectin and sialic acids are involved in rolling, but not in capture. Our results give insight into the interplay between laminar shear flow and adhesion receptor function which enable neutrophil emigration during inflammatory conditions.Item Finite element approaches to phase change problems with application to casting processes(1993) Teng, Yang-Ming; Akin, John Edward.An overview of two categories of numerical approaches to phase change problems, front tracking and fixed domain methods, is given. A further comparison of several fixed domain methods is made with some benchmark test problems. The approximation of the latent heat for isothermal phase change is a key point for these numerical approaches. Generally the space-average approach is better than the others. The Euler backward, Crank-Nicolson, and Dupont schemes are the best for thermal analysis involving phase changes. The new effective and apparent capacity methods can eliminate the need of an artificially assumed temperature range for isothermal transformation and obtain accurate results. They are also computationally efficient compared with other methods. The new apparent capacity technique is invoked to model the isothermal part of phase change for several solidification models. The same approach is applied to the thermal analyses of the casting processes and the results are in good agreement with experiment data. A convective type interface element formulation is derived for the heat transfer at the interface of the cast and the mold, which can simplify the element matrix calculation. A thermal elasto-plastic stress model is derived and the public domain software NIKE2D is used for the stress analyses of the casting processes. The initial stage of ingot cooling in the mold and the continuous casting process are simulated. The latent heat released during solidification can affect the temperature field and the phase transformation in the solid state has an essential effect on the stress generation. The cast size, material hardening effect, and cast speed are all important factors for the temperature and stress distributions.Item Finite Element Nonlocal Technique Based on Superconvergent Patch Second Derivative Recovery(2012) Gan, Xiaoge; Akin, John Edward.This dissertation proposes a finite element procedure for evaluating the high order strain derivatives in nonlocal computational mechanics. The superconvergent second derivative recovery methods used are proven to be effective in evaluating the Laplacian of the equivalent strain based on low order (linear) elements. Current nonlocal finite element techniques with linear elements are limited to structured meshes, while the new technique can deal with unstructured meshes with various element types. Other superconvergent patch recovery (SCP) based nonlocal approaches, such as the patch projection techniques only utilize nodal based patches to evaluate the first derivatives of the strain. The SCP technique has not yet been used for recovery of higher order strain derivatives. The proposed technique is capable of evaluating the Laplacian of the equivalent strain and has the potential for even higher order derivative recovery. The same patches can be easily utilized for error estimation and adaptive meshing for nonlocal problems. We employ two super-convergent patch options: the element based patch with all neighbors or only facing neighbors. The nonlocal strain derivatives can be recovered through either a mesh nodal averaging process or directly at the patch element quadrature points after the patch least square fitting problems are solved. Numerical examples for both strain gradient damage mechanics and strain gradient plasticity problems are given. In summary, the new finite element nonlocal computational technique based on the superconvergent second derivative recovery methods is proven to be robust in evaluating the high order strain derivatives with low order element unstructured meshes.
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