Browsing by Subject "Numerical"
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Item Fatigue behavior of post-installed shear connectors used to strengthen continuous non-composite steel bridge girders(2016-08) Ghiami Azad, Amir Reza; Engelhardt, Michael D.; Williamson, Eric B., 1968-; Helwig, Todd A; Jirsa, James O; Taleff, Eric MMany older bridges in Texas are constructed with floor systems consisting of a concrete slab over steel girders. A potentially economical means of strengthening these floor systems is to connect the existing concrete slab and steel girders using post-installed shear connectors to change the behavior of the beam from non-composite to partially-composite. Since fatigue is one of the main concerns in designing bridges, investigating the fatigue properties of these post-installed shear connectors becomes crucial. Results from direct-shear testing show that post-installed shear connectors have a better fatigue life compared to conventional welded shear studs. However, based on currently available data from direct-shear tests, fatigue life of post-installed shear connectors is still inadequate for economical retrofit in some cases. Furthermore, it is unclear if direct-shear tests provide an appropriate means of evaluating fatigue performance. The objective of this dissertation is to develop new and more accurate approaches for evaluating the fatigue characteristics of post-installed shear connectors. This objective is addressed through large-scale beam fatigue tests and computational studies. The focus of the work is on evaluating fatigue life of shear connectors based on both slip and stress demands.Item Microscale modeling of layered fibrous networks with applications to biomaterials for tissue engineering(2015-08) Carleton, James Brian; Rodin, G. J. (Gregory J.); Sacks, Michael S.; Gonzalez, Oscar; van de Geijn, Robert; Mear, MarkMany important biomaterials are composed of multiple layers of networked fibers. A prime example is in the field of tissue engineering, in which damaged or diseased native tissues are replaced by artificial tissues that are grown on fibrous polymer networks. For load bearing tissues, it is critical that the mechanical behavior of the engineered tissue be similar to the behavior of the native tissue that it will replace. In the case of soft tissues such as heart valves, the macroscale mechanical behavior is highly anisotropic and nonlinear. This behavior is a result of complex deformations of the collagen and elastin fibers that form the extracellular matrix (ECM). The microstructure of engineered tissues must be properly designed to reproduce this unique macroscopic behavior. While there is a growing interest in modeling and simulation of the mechanical response of this class of biomaterials, a theoretical foundation for such simulations has yet to be firmly established. This work introduces a method for modeling materials that have a layered, fibrous network microstructure. Methods for characterizing the complex network geometry are first established. Then an algorithm is developed for generating realistic network geometry that is a good representation of electrospun tissue scaffolds, which serve as the primary synthetic structure on which engineered tissues are grown. The level of fidelity to the real geometry is a significant improvement on previous representations. This improvement is important, since the scaffold geometry has a strong influence over the macroscopic mechanical behavior of the tissue, cell proliferation and attachment, nutrient and waste flows, and extracellular matrix (ECM) generation. Because of the importance of scaffolds in tissue formation and function, this work focuses on characterizing scaffold network geometry and elucidating the impact of geometry on macroscale mechanics. Simulation plays an important role in developing a detailed understanding of scaffold mechanics. In this work, Cosserat rod theory is used to model individual fibers, which are connected to form a network that is treated as a representative volume element (RVE) of the material. The continuum theory is the basis for a finite element discretization. The nonlinear equations are solved using Newton's method in a parallel implementation that is capable of accurately capturing the large, three-dimensional fiber rotations and large fiber stretches that result from the large macroscopic deformations experienced by these biomaterials in their natural environment. Comparisons of simulation results with existing analytical models of soft tissues show that these models can predict the behavior of scaffold networks with reasonable accuracy, despite the significant differences between soft tissue and scaffold network microstructural geometry. The simulations also reveal how macroscale loading is related to the microscale fiber deformations and the load distribution among the fibers. The effects of different characteristics of the microstructural geometry on macroscopic behavior are explored, and the implications for the design of scaffolds that produce the desired macroscopic behavior are discussed. Overall, the improved modeling of electrospun scaffolds presented in this work is an important step toward designing more functional engineered tissues.Item Numerical examples of output regulation for waves and beams(Texas Tech University, 2005-08) Johnson, Vijay Moses Dev; Gilliam, David S.; Seshaiyer, PadmanabhanThis research work is concerned with the numerical implementation of a geometric design methodology for obtaining feedback control schemes capable of shaping the response of hyperbolic dynamical systems. In this work we are interested in the important design objectives referred to as asymptotic tracking. This type of problem represents one of the central problems in control theory. In this work we want to obtain numerical approximations of control laws capable of controlling a plant, described by hyperbolic partial differential equations, in order to have its output track a reference signal (and/or reject a disturbance) produced by a finite dimensional external generator or exogenous system. For linear distributed parameter systems this represents an extension of the geometric theory of output regulation. We also provide simple criteria for solvability of the regulator equations based on the exosystem. Two different kind of examples of set-point and harmonic tracking are dealt with this work, one for One Dimensional Wave Equation and the other for Hinged Beam Equation. Modified Euler Method is used for solving the two equations numerically. Finally we present several directions of future research in this area.Item Numerical examples of output regulation for waves and beams(2005-08) Johnson, Vijay Moses Dev; Gilliam, David S.; Seshaiyer, PadmanabhanThis research work is concerned with the numerical implementation of a geometric design methodology for obtaining feedback control schemes capable of shaping the response of hyperbolic dynamical systems. In this work we are interested in the important design objectives referred to as asymptotic tracking. This type of problem represents one of the central problems in control theory. In this work we want to obtain numerical approximations of control laws capable of controlling a plant, described by hyperbolic partial differential equations, in order to have its output track a reference signal (and/or reject a disturbance) produced by a finite dimensional external generator or exogenous system. For linear distributed parameter systems this represents an extension of the geometric theory of output regulation. We also provide simple criteria for solvability of the regulator equations based on the exosystem. Two different kind of examples of set-point and harmonic tracking are dealt with this work, one for One Dimensional Wave Equation and the other for Hinged Beam Equation. Modified Euler Method is used for solving the two equations numerically. Finally we present several directions of future research in this area.Item Numerical Investigation of Flow and Heat Transfer Characteristics in Rectangular Channels (AR=4:1) with Circular and Elliptical Pin Fin Arrays(2012-07-16) Velichala, AbhishekThe objective of current study was to numerically investigate the flow and heat transfer characteristics in a stationary one pass rectangular channel (AR=4:1) with circular and elliptical pin fin arrays. Two types of elliptical pin fins (a SEF and an N fin whose minor axis length is equal to the diameter of the circular fin) were used. The analysis was performed with an array of six rows of staggered pin fins in the streamwise direction for Reynolds numbers (Re) of 10,000, 20,000, 30,000, 40,000 and 50,000. 3-D, steady simulations were performed using the low Reynolds number k-omega SST turbulence model in the FLUENT CFD code. The data predicted by the current numerical model showed favorable agreement with the experiments in the validation study. It was observed that SEF array produces minimum pressure loss and the highest thermal performance. It was also observed that N fin array produces minimum hot spots and the highest channel averaged Nusselt number ratio values.Item Numerical simulation of flow and heat transfer of internal cooling passage in gas turbine blade(Texas A&M University, 2007-04-25) Su, GuoguangA computational study of three-dimensional turbulent flow and heat transfer was performed in four types of rotating channels. The first type is a rotating rectangular channel with V-shaped ribs. The channel aspect ratio (AR) is 4:1, the rib height-to-hydraulic diameter ratio (e/Dh) is 0.078 and the rib pitch-to-height ratio (P/e) is 10. The rotation number and inlet coolant-to-wall density ratio were varied from 0.0 to 0.28 and from 0.122 to 0.40, respectively, while the Reynolds number was varied from 10,000 to 500,000. Three channel orientations (90 degrees, -135 degrees, and 135 degrees from the rotation direction) were also investigated. The second type is a rotating rectangular channel with staggered arrays of pinfins. The channel aspect ratio (AR) is 4:1, the pin length-to-diameter ratio is 2.0, and the pin spacing-to-diameter ratio is 2.0 in both the stream-wise and span-wise directions. The rotation number and inlet coolant-to-wall density ratio varied from 0.0 to 0.28 and from 0.122 to 0.20, respectively, while the Reynolds number varied from 10,000 to 100,000. For the rotating cases, the rectangular channel was oriented at 150 degrees with respect to the plane of rotation. In the rotating two-pass rectangular channel with 45-degree rib turbulators, three channels with different aspect ratios (AR=1:1; AR=1:2; AR=1:4) were investigated. Detailed predictions of mean velocity, mean temperature, and Nusselt number for two Reynolds numbers (Re=10,000 and Re=100,000) were carried out. The rib height is fixed as constant and the rib-pitch-to-height ratio (P/e) is 10, but the rib height-to-hydraulic diameter ratios (e/Dh) are 0.125, 0.094, and 0.078, for AR=1:1, AR=1:2, and AR=1:4 channels, respectively. The channel orientations are set as 90 degrees, the rotation number and inlet coolant-to-wall density ratio varied from 0.0 to 0.28 and from 0.13 to 0.40, respectively. The last type is the rotating two-pass smooth channel with three aspect ratios (AR=1:1; AR=1:2; AR=1:4). Detailed predictions of mean velocity, mean temperature and Nusselt number for two Reynolds numbers (Re=10,000 and Re=100,000) were carried out. The rotation number and inlet coolant-to-wall density ratio varied from 0.0 to 0.28 and from 0.13 to 0.40, respectively. A multi-block Reynolds-averaged Navier-Stokes (RANS) method was employed in conjunction with a near-wall second-moment turbulence closure.Item Numerical simulation of inviscid wave-current interaction with an FPSO(2009-05-15) Bae, Sang-YunThis study investigated Floating Production Storage and Offloading (FPSO) responses under wave and current interactions. A higher order boundary element method (HOBEM) was adopted to probe the behavior of an FPSO. Forces and moment of an FPSO were studied under wave and current interactions. The simulations of diffracted and radiated waves were performed in a time domain. Time marching schemes were used for this time domain calculation. The predictor-corrector(P-C) method was used. Boundary integral equations were used to solve each problem with Rankine sources and distributed over the entire calculation domain. For the far-field boundary condition, Orlanski?s truncated open boundary condition was used for an open truncated boundary condition to prevent reflected waves. The current effect was considered an explicit term due to being a moving coordinate. Various current heading angles were also studied. Truncated open boundary, maximum likelihood method, proper element size and shape, modulation function, and Chebyshev filtering were studied to avoid diverged solutions. From our findings, higher order elements fitted a complicated model such as an FPSO. We found that this method required considerably fewer elements than the constant panel method in order to obtain reasonable outcomes. Using our developed numerical method, we calculated wave forces and moment, mean drift forces, added mass, and damping coefficients. Conclusively, HOBEM was found to be more effective and more reliable in calculating and predicting wave and current influence on an FPSO. Future studies are needed to develop finer simulation tools for FPSO?s large horizontal behavior.Item Numerical Study of Abutment Scour in Cohesive Soils(2010-01-16) Chen, XingnianThis research is part of the extension of the SRICOS-EFA method for predicting the maximum scour depth history around the bridge abutment. The basic objective is to establish the equation for predicting the maximum bed shear stress around the abutment at the initial condition of scouring. CHEN3D (Computerized Hydraulic ENgineering program for 3D flow) program is utilized to perform numerical simulations and predict bed shear stress before scouring. The Chimera technique incorporated in CHEN3D makes the program capable of simulating all kinds of complex geometry and moving boundary. CHEN3D program has been proven to be an accurate method to predict flow field and boundary shear stress in many fields and used in bridge scour study in cohesive soils for more than ten years. The maximum bed shear stress around abutment in open rectangular channel is studied numerically and the equation is proposed. Reynolds number is the dominant parameter, and the parametric studies have been performed based on the dimensional analysis. The influence of channel contraction ratio, abutment aspect ratio, water depth, abutment shape, and skew angle has been investigated, and the corresponding correction This research is part of the extension of the SRICOS-EFA method for predicting the maximum scour depth history around the bridge abutment. The basic objective is to establish the equation for predicting the maximum bed shear stress around the abutment at the initial condition of scouring. CHEN3D (Computerized Hydraulic ENgineering program for 3D flow) program is utilized to perform numerical simulations and predict bed shear stress before scouring. The Chimera technique incorporated in CHEN3D makes the program capable of simulating all kinds of complex geometry and moving boundary. CHEN3D program has been proven to be an accurate method to predict flow field and boundary shear stress in many fields and used in bridge scour study in cohesive soils for more than ten years. The maximum bed shear stress around abutment in open rectangular channel is studied numerically and the equation is proposed. Reynolds number is the dominant parameter, and the parametric studies have been performed based on the dimensional analysis. The influence of channel contraction ratio, abutment aspect ratio, water depth, abutment shape, and skew angle has been investigated, and the corresponding correction factors have been proposed. The study of the compound channel configuration is conducted further to extend the application of the proposed equation. Numerical simulations of overtopping flow in straight rectangular channel, straight compound channel and channel bend have been conducted. The bridge deck is found to be able to change the flow distribution and the bed shear stress will increase significantly once overtopping. The influence of the channel bend curvature, abutment location in the channel bend, and the abutment shape is also investigated. The corresponding variation of the bed shear stress has been concluded. The scour models, including the erosion rate function, roughness effect, and the turbulence kinetic energy, have been proposed and incorporated into the CHEN3D program. One flume test case in NCHRP 24-15(2) has been simulated to determine the parameters for the roughness and the turbulence kinetic energy. The prediction of the maximum scour depth history with the proposed model is in good agreement with the measurement for most cases. The influence of overtopping flow on the abutment scour development is also studied and the corresponding correction factor is proposed.