The present study considers steady laminar two-dimensional incompressible flow over both in-line and staggered flat tube bundles used in heat exchanger applications. The effects of various independent parameters, such as Reynolds number (Re), Prandtl number (Pr), length ratio (L/Da), and height ratio (H/Da), on the pressure drop and heat transfer were studied. A finite volume based FORTRAN code was developed to solve the governing equations. The scalar and velocity variables were stored at staggered grid locations. Scalar variables (pressure and temperature) and all thermophysical properties were stored at the main grid location and velocities were stored at the control volume faces. The solution to a one-dimensional convection diffusion equation was represented by the power law. The locations of grid points were generated by the algebraic grid generation technique. The curvilinear velocity and pressure fields were linked by the Semi-Implicit Method for Pressure Linked Equations (SIMPLE) algorithm. The line-by-line method, which is a combination of the Tri-Diagonal Matrix Algorithm (TDMA) and the Gauss-Seidel procedure, was used to solve the resulting set of discretization equations. The result of the study established that the flow is observed to attain a periodically fully developed profile downstream of the fourth module. The strength increases and the size of the recirculation gets larger as the Reynolds number increases. As the height ratio increases, the strength and size of the recirculation decreases because the flow has enough space to expand through the tube passages. The increase in length ratio does not significantly impact the strength and size of the recirculation. The non-dimesionalized pressure drop monotonically decreased with an increase in the Reynolds number. In general, the module average Nusselt number increases with an increase in the Reynolds number. The results at Pr = 7.0 indicate a significant increase in the computed module average Nusselt number when compared to those for Pr = 0.7. The overall performance of in-line configuration for lower height ratio (H/Da = 2) and higher length ratio (L/Da = 6) is preferable since it provides higher heat transfer rate for all Reynolds numbers except for the lowest Re value of 25. As expected the staggered configurations perform better than the in-line configuration from the heat transfer point of view.

Orientador: Renato Pavanello / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-10T00:52:29Z (GMT). No. of bitstreams: 1 Moura_MarciodaSilva_M.pdf: 3205928 bytes, checksum: a8344d0c36acf072569df75478f33b23 (MD5) Previous issue date: 2007 / Resumo: o modelo poro elástico é aplicado na representação do comportamento físico de um meio contínuo composto por duas fases distintas, uma sólida e outra fluida. A fase sólida está envolta em um domínio fluídico saturado. A matéria fluida presente no sistema pode ser líquida, gasosa ou uma mistura em função do meio a que se pretende estudar. Estruturas ósseas são um bom exemplo de material poroso, pois são constituídas de uma porção sólida, formada por uma estrutura calcificada e outra fluida, formada pelo sangue, gorduras e fluidos ósseos. Neste trabalho propõem-se elaborar uma ferramenta para simulação computacional da poroelasticidade aplicada em ossos, considerando solicitações estáticas e respostas transientes. Da mesma forma esta ferramenta permite a análise sobre próteses inseridas em ossos e sua interação elástica com uma estrutura poroelástica. O modelo utilizado é baseado no trabalho precursor de Maurice A. Biot, que submeteu uma porção de solo em água saturada a cargas de compressão, analisando suas respostas e o comportamento poroso do sistema. A ferramenta computacional foi desenvolvida em ambiente Fortran90. As análises foram realizadas em termos de tensão, deformação, deslocamentos e pressão e as condições submetidas foram baseadas em situações de solicitação disponíveis na literatura. Os resultados proporcionaram o mapeamento das regiões sujeitas a tensões elevadas avaliando o comportamento da interface osso prótese. Esses estudos possibilitam um melhor entendimento do comportamento dinâmico da fase fluida do osso, permitindo que análises mais precisam próteses implantadas possam ser realizadas / Abstract: The poroelastic model is applied in the representation of the physical behavior of a continuous medium composed by two separate phases: a solid phase and a fiuid one. The solid phase is wrapped in a fiuidic saturated dominium. The fiuid matter in the system may be liquid, gaseous or else a mixture, depending on the medium one intends to study. Bones structures are a good example of a porous material because they comprise a calcified structure and another fiuid structure formed by blood, fat and bones fiuids. In this paper, it propose to develop a tool for computer simulation of poroelasticity applied to bones, considering static loads and transient responses. Likewise, this tool enables analysis of prostheses inserted in bones and their elastic interaction with a poroelastic structure. The model used is based on the early work of Maurice A. Biot, who submitted a portion of sDil in saturated water to compression loads and analyzed its responses and the porous behavior of the system. The computer tool was developed in Fortran90 environment. Analyses were conducted in terms of stress, strain, displacements and pressure. The boundary conditions submitted were based on situations of stress available in the literature. The results enabled to map areas that are subject to high stress 80 the behavior of the bone / prosthesis interface could be assessed. These studies provided a better understanding of the dynamic behavior of the fiuid phase of the bone so more precise analyses of implanted prostheses can be made / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica

Precast prestressed concrete piles are widely used in deep foundation construction. Due to unexpected site soil conditions and difficulties associated with transportation and handling long precast piles, splicing is sometimes necessary at the construction site. Available splicing methods utilize steel type connections that are more suitable for reinforced concrete construction and result in limited tensile capacity at the splice. This dissertation describes studies associated with the development of a new post-tensioned splicing system using staggered, embedded anchorages. The new system has the potential to provide the same tensile capacity as a one piece prestressed pile. To develop the post-tensioned splicing system it was necessary to conduct varied numerical analyses to solve immediate technical problems associated with the design, fabrication and testing of a prototype. This included the design of a self-stressing prestressing bed, optimization of the shape of the embedded anchorages and their layout within the piles being spliced. The focus of the dissertation is on non-linear finite element studies conducted to model the flexure behavior of prototype laboratory and full-sized spliced piles in comparison to their identical non-spliced counterpart. Though finite element analysis of prestressed elements is not new, issues relating to modeling post-tensioned, spliced elements with embedded, staggered anchorages have not been the subject of any previous investigation and constitute the principal contribution of this study. Nonlinear finite element analysis was conducted using ANSYS. The William-Warnke failure criterion used to establish concrete failure. A three-dimensional analysis was conducted in which SOLID65 element was used for modeling concrete and LINK8 for the prestressing strands. The post-tensioning ducts were modeled using PIPE20 elements. Perfect bond was assumed between the concrete and the ducts. Embedded anchorages were modeled as fixed locations within the concrete. Epoxy used to join the two splicing surfaces was modeled using contact elements. Since the layout of the post-tensioning ducts was staggered, a full model was required. In contrast, advantage was taken of symmetry for the analysis of the one piece controls. The finite element model was able to accurately capture the flexural behavior of both the control and the spliced piles. The results suggested that tensile separation at the splice interface acted as a pivot about which the section rotated. As a result, the compression failure zone in the spliced pile was confined to a smaller region compared to the control. The stress distribution in the spliced pile indicated that the concrete in the cover above the splice was crushed at the ultimate stage before the steel had yielded. As a result, the ultimate capacity of the spliced pile was controlled by concrete failure. The results also indicated that, among the multiple layers of post-tensioning strands, only one approached yield while others remained in the elastic range. As a result, when the applied load was released, the spliced pile rebounded back to a large degree, which resulted in a much smaller residual permanent deformation. This behavior of a spliced pile can be beneficial for structures in a seismic zone because it will induce smaller secondary moments. This study helped to refine and improve the new post-tensioned splicing system. Its availability makes it possible to extend and further improve the concept without the need for costly prototype fabrication and testing.

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This thesis examines the relationship between gestational age and stillbirths, focusing on the effect of maternal age. Prolonged pregnancies have been associated with an increased risk of stillbirth, prompting the exploration of labor induction as a preventive measure. However, the existing literature suffers from limited sample sizes, leading to uncertainty in the findings.  This study utilizes regional variations in labor induction practices to in- crease the sample size substantially. Moreover, it incorporates the economical aspect by evaluating the cost of induction and how the current policy could be optimized. In Sweden, some regions modified their induction policies in 2019 while others did not, creating a quasi-experimental setting that is exploited in this thesis. The objective is to evaluate the impact of inducing labor before pregnancies are defined as prolonged on stillbirth rates. A panel from 2009 to 2021, comprising over 1.4 million laborers, is analyzed, focusing on approximately 13,500 prolonged pregnancies between 2019 and 2021.  The results suggest that implementing a new induction policy among mothers aged 30 or older would yield annual cost savings of 24.6 MSEK. Specifically, targeting this age group for induction reduces the number of inductions required in week 41 to prevent one stillbirth from 224 to 127, compared to inducing mothers of all ages. These findings contribute to understanding labor induction practices and their impact on stillbirth rates, especially how the current policy could be optimized from a monetary perspective, providing valuable insights to policymakers.

The Vehicle Routing Problem with Time Windows (VRPTW) is an important and computationally hard optimization problem frequently encountered in Scheduling and logistics. The Vehicle Routing Problem (VRP) can be described as the problem of designing the most efficient and economical routes from one depot to a set of customers using a limited number of vehicles. This research addresses the VRPTW under the following additional complicating features that are often encountered in practical problems: 1. Customers have strict time windows for receiving a vehicle, i.e., vehicles are not allowed to arrive at the customer’s location earlier than the lower limit of the specified time window, which is relaxed in previous research work. 2. There is a limited number of loading/unloading docks for dispatching/receiving the vehicles at the depot The main goal of this research is to propose a framework for solving the VRPTW with the constraints stated above by generating near-optimal routes for the vehicles so as to minimize the total traveling distance. First, the proposed framework clusters customers into groups based on their proximity to each other. Second, a Probabilistic Route Generation (PRG) algorithm is applied to each cluster to find the best route for visiting customers by each vehicle; multiple routes per vehicle are generated and each route is associated with a set of feasible dispatching times from the depot. Third, an assignment problem formulation determines the best dispatching time and route for each vehicle that minimizes the total traveling distance. iii The proposed algorithm is tested on a set of benchmark problems that were originally developed by Marius M. Solomon and the results indicate that the algorithm works well with about 1.14% average deviation from the best-known solutions. The benchmark problems are then modified by adjusting some of the customer time window limits, and adding the staggered vehicle dispatching constraint. For demonstration purposes, the proposed clustering and PRG algorithms are then applied to the modified benchmark problems.

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No description available.

No description available.

Mathematical modeling of ocean waves is based on the formulation and solution of the appropriate equations of continuity, momentum and the choice of proper initial and boundary conditions. Under the influence of gravity, many free surface water waves can be modeled by the shallow water equations (SWE) with the assumption that the horizontal length scale of the wave is much greater than the depth scale and the wave height is much less than the fluid's mean depth. Furthermore, to describe three dimensional flows in the hydrostatic and Boussinesq limits, the multilayer SWE model is used, where the fluid is discretized horizontally into a set of vertical layers, each having its own height, density, horizontal velocity and geopotential. In this study, we used an explicit staggered finite volume method to solve single and multilayer SWE, with and without density stratification and bathymetry, to understand the dynamic of surface waves and internal waves. We implemented a two-dimensional version of the incompressible DYNAMICO method and compare it with a one-dimensional SWE. For multilayer SWE, we considered both two layer and a linear stratification of density, with very small density gradient, consistent with Boussinesq approximation. We used Lagrangian vertical coordinate which doesn't allow mass to flow across vertical layers. Numerical examples are presented to verify multilayer SWE model against single layer SWE, in terms of the phase speed and the steepness criteria of wave profile. In addition, the phase speed of the barotropic and baroclinic mode of two-layer SWE also verified our multilayer SWE model. We found that, for multilayer SWE, waves move slower than single layer SWE and get steeper than normal when they flow across bathymetry. A series of numerical experiment were carried out to compare 1-D shallow water solutions to 2-D solutions with and without density as well as to explain the dynamics of surface wave and internal wave. We found that, a positive fluctuations on free surface causes water to rise above surface level, gravity pulls it back and the forces that acquired during the falling movement causes the water to penetrate beneath it's equilibrium level, influences the generation of internal waves. Internal waves travel considerably more slowly than surface waves. On the other hand, a bumpy or a slicky formation of surface waves is associated with the propagation of internal waves. The interaction between these two waves is therefore demonstrated and discussed. / Thesis / Master of Science (MSc) / In the modelling of ocean wave, the formulation and solution of appropriate equations and proper initial and boundary conditions are required. The shallow water equations (SWE) are derived from the conservation of mass and momentum equations, in the case where the horizontal length scale of the wave is much greater than the depth scale and the wave height is much less than the fluid's mean depth. In multilayer SWE, the fluid is discretized horizontally into a set of vertical layers, each having its own height, density, horizontal velocity and geopotential. In this study, we used an explicit staggered finite volume method to solve single and multilayer SWE, with and without density stratification and bathymetry, to understand the dynamic of surface waves and internal waves. A series of numerical experiments were carried out to validate our multilayer model. It is found that, in the presence of density differences, surface waves for the multilayer SWE move slowly and get more steep than normal when they flow across bathymetry. Also, a positive fluctuations on free surface generates internal waves at the interior of ocean which propagate along the line of density gradient.