• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 17
  • 4
  • 3
  • 3
  • 3
  • 2
  • 1
  • 1
  • Tagged with
  • 33
  • 33
  • 33
  • 12
  • 9
  • 8
  • 7
  • 7
  • 6
  • 6
  • 6
  • 6
  • 6
  • 6
  • 6
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

CPIM, an Improved Element Free method for Engineering Application

Liu, Chang-jung 13 January 2006 (has links)
Abstract To improve the application of Point Interpolation Method (PIM) in Element Free Galerkin Method (EFG) is the aim of this study. The trait of EFG is using overlap of influence domain between different nodes to construct discretization nodes¡¦ connection. EFG just uses nodal data, but not element. For constructing shape function, EFG has two types of methods, Fitting and Interpolation. Fitting uses Moving Least Square Method (MLS). MLS-EFG has stable effect on numerical analysis; however, users who use it need to choose more numerical parameters and do more computation. Besides, users can not apply boundary conditions directly when using MLS-EFG. Interpolation method applies nodal coordinates to proceed computation, and it called PIM. Boundary conditions could be used directly and less computation is needs while using PIM. However, the coefficient of interpolation function of sample is singular. This study tries to construct Coordination Point Interpolation Method. It owns advantages of both methods that mentioned above, and extra numerical parameters are not needed. It applies the notion of influence domain of MLS-EFG, then search correlative efficient nodes which are contained in near field of sample. The correlative efficient nodes make up matrix that con cause inverse matrix. In addition, via numerical simulations, it shows that CPIM has excellent convergence and accurate solution, and is better that MLS-EFG.
2

Statistical analysis on the effect of splenectomy-induced thrombosis

Hsu, Chung-Hsien 25 July 2000 (has links)
In this work, it is of interest to study the effects of thrombocytosis and microvascular anastomosis to that of vascular thrombosis. Here the splenectomy is used to the experimental subjects to have caused thrombocytosis first and later have the microvascular anastomsis on the divided vessel. Observations on different variables which may be related to vascular thrombosis are obtained during the three stages of the experiments, there are pre-splenectomy, post-splenectomy but before vascular division, and after the vascular anastomsis. These variables include platelet number, RBC count, Nitric oxide(nitrite and nitrate), femoral artery perfusion unit, hematocrit, reticulated-platelet number, and activated-platelets(p-selectin, CD62p). The experimental units are divided into thrombocysis group and control group. Basic statistical analysis are performed first to see the differences between the two groups for the above mentioned variables, and later try to use the profile analysis in multivariate analysis to understand the changes of these variables in different stages as well as their possible relationships with the cause of vascular thrombosis. Finally, classical regression and robust regression analysis for finding outliers are also used to see whether certain characteristics of those outliers have something to do with vascular thrombosis.
3

Characterization of the acoustic properties of cementitious materials

Sun, Ruting (Michelle) January 2017 (has links)
The primary aim of this research was to investigate the fundamental acoustic properties of several cementitious materials, the influence of mix design parameters/constituents, and finally the effect of the physical and mechanical properties of cementitious material concrete/mortar on the acoustic properties of the material. The main objectives were: To understand the mechanism of sound production in musical instruments and the effects of the material(s) employed on the sound generated; To build upon previous research regarding selection of the tested physical/mechanical properties and acoustic properties of cementitious materials; To draw conclusions regarding the effect of different constituents, mix designs and material properties upon the acoustic properties of the material; To build a model of the relationship between the acoustic properties of a cementitious material and its mix design via its physical/mechanical properties. In order to meet the aim, this research was conducted by employing the semi-experimental (half analytical) method: two experimental programmes were performed (I and II); a mathematical optimization technique (least square method) was then implemented in order to construct an optimized mathematical model to match with the experimental data. In Experimental Programme I, six constituents/factors were investigated regarding the effect on the physical/mechanical and acoustic properties: cementitious material additives (fly ash, silica fume, and GGBS), superplasticizer, and basic mix design parameters (w/c ratio, and sand grading). 11 properties (eight physical/mechanical properties: compressive strength, density, hardness, flexural strength, flexural modulus, elastic modulus, dynamic modulus and slump test; and three acoustic properties: resonant frequency, speed of sound and quality factor (internal damping)) were tested for each constituents/factors related mortar type. For each type of mortar, there were three cubes, three prisms and three cylinders produced. In Experimental Programme I, 20 mix designs were investigated, 180 specimens produced, and 660 test results recorded. After analysing the results of Experimental Programme I, fly ash (FA), w/b ratio and b/s ratio were selected as the cementitious material/factors which had the greatest influence on the acoustic properties of the material; these were subsequently investigated in detail in Experimental Programme II. In Experimental Programme II, various combinations of FA replacement level, w/b ratios and b/s ratios (three factors) resulted in 1122 test results. The relationship between these three factors on the selected 11 properties was then determined. Through using regression analysis and optimization technique (least square method), the relationship between the physical/mechanical properties and acoustic properties was then determined. Through both experimental programmes, 54 mix designs were investigated in total, with 486 specimens produced and tested, and 1782 test results recorded. Finally, based upon well-known existing relationships (including, model of compressive strength and elastic modulus, and the model of elastic modulus and dynamic modulus), and new regressioned models of FA-mortar (the relationship of compressive strength and constituents, which is unique for different mixes), the optimized object function of acoustic properties (speed of sound and damping ratio) and mix design (proportions of constituents) were constructed via the physical/mechanical properties.
4

Experimental verification of an instrument to test flooring materials.

Philip, Rony January 2017 (has links)
The focus of the project is to validate the fluid model with different flooring materials and the measurements of an instrument to test flooring materials and its force attenuating capabilities using mathematical models to describe the signature and coefficients of the floor.As a part of improving the knowledge about the linear dynamics of vibrations involved during the sudden impact caused on hip bones of elderly people during fall. The project initiated in January 2017 and end date was set to May 2017.The main contribution of the present work focuses on the development of a mathematical fluid model for floors. The aim of the thesis was to analyze, compare different floor materials and to study the linear dynamics of falling impacts on floors. The impact of the hammer during a fall is captured by an accelerometer and response is collected using a picoscope. The collected data was analyzed using matlab least square method which is coded as per the fluid model.The finding from this thesis showed that the fluid model works with a more elastic model but it doesn't work for rigid materials like wood. The importance of parameters like velocity, mass, energy loss and other coefficients of a floor which influences the model during the impact of falling on floors were identified and a standardized testing method was set.
5

Influência das irregularidades da forma em peças de madeira na determinação do módulo de elasticidade longitudinal / Influence of timber pieces shape irregularities in longitudinal modulus of elasticity determination

Christoforo, André Luis 06 December 2007 (has links)
Atualmente, os documentos normativos que tratam da determinação das propriedades de rigidez e resistência para elementos roliços estruturais de madeira não levam em consideração em seus modelos matemáticos a influência das irregularidades existentes na geometria dessas peças. O presente trabalho tem como objetivo determinar o valor ótimo do módulo de elasticidade longitudinal para peças roliças estruturais de madeira por intermédio de uma técnica de otimização aliada ao método da análise inversa, ao método dos elementos finitos e ao método dos mínimos quadrados. / Currently, the normative documents that deal with the determination of the properties of rigidity and resistance for round structural timber elements round timber do not take in consideration in both calculations and mathematical models the influence of the existing of irregularities in the geometry of these elements. An objective of this work is to determine the optimum value of the modulus of elasticity for round structural timber elements by an optimization technique associated to the inverse analysis method, to the finite element method and the least squares method.
6

Modelagem e investigação numérica de escoamentos de fluidos estruturados tixotrópicos

Fonseca, Cleiton Elsner da January 2013 (has links)
Fluidos Não-newtonianos estão presentes em grande quantidade na natureza e em muitas aplicações industriais. Tais fluidos apresentam uma variedade de comportamentos específicos. Dentre eles podemos citar: elasticidade, plasticidade, viscosidade variando com a taxa de deformação, tixotropia. Esta tese de doutorado apresenta um recente modelo para Fluidos Estruturados Tixotrópicos (de Souza Mendes, 2009), no qual baseasse nas tradicionais equações de balanço de momentum e massa, em uma equação constitutiva de Maxwell-b modificada e uma equação de evolução para o nível de estrutura do material. Na equação constitutiva de Maxwell-b modificada, tempo de relaxação e viscosidade estrutural são funções da estrutura do material. A equação evolutiva para o parâmetro de estruturação prevê efeitos de tixotropia, dependentes do tempo de equilíbrio do material. As equações que constituem o modelo mecânico para Fluidos Estruturados Tixotrópicos são aproximadas numericamente através do Método de Elementos Finitos de Galerkin Mínimos-quadrados (GLS). Tal método adicionou termos dependentes de malha ao método clássico de Galerkin, de forma a aumentar a estabilidade da formulação original, proporcionando compatibilizar os sub-espaços de velocidade e pressão. São investigados escoamentos creeping flow de Fluidos Estruturados Tixotrópicos em dois problemas clássicos de engenharia: em torno de um cilindro confinado entre duas placas e em uma expansão planar abrupta. Parâmetros relevantes ao modelo são variados em faixas pertinentes ao problema físico simulado e os resultados demonstraram uma boa capacidade de previsão. / Non-Newtonian fluids are present in large quantities in nature and in many industrial applications. Such fluids exhibit a variety of specific behaviors. Among them we can mention: elasticity, plasticity, viscosity varying with the strain rate, thixotropy, etc. This thesis presents a new model for thixotropic Structured Fluids (de Souza Mendes, 2009), in which were a basis in traditional balance equations of mass and momentum, the constitutive equation of Maxwell-type and an evolution equation for the level structure of the material. In the modified constitutive equation of Maxwell-b, relaxation time and structural viscosity are functions of material structure. The structure parameter evolutive equation provides effects of thixotropy, dependent on the equilibration time of the material. The equations which constitute the mechanical model for Structured Thixotropic fluids are approximated numerically using the Galerkin Least-squares Finite Element Method (GLS). Such a method added mesh dependent terms to the classical method of Galerkin in order to increase the stability of the original formulation, providing compatibility between sub-spaces of velocity and pressure. Are investigated Structured Thixotropic Fluids creeping flow in two classical problems in engineering: around a cylinder confined between two plates and in a planar abrupt expansion. Relevant parameters to the model are varied in pertinent ranges to physical problem simulated and the results demonstrated a good predictive capability.
7

Localização de faltas de alta impedância : formulação baseada na impedância aparente e no método de mínimos quadrados

Ferraz, Renato Gonçalves January 2014 (has links)
As linhas de transmissão são usadas para transmitir energia elétrica por longas distâncias e estão naturalmente expostas a condições climáticas severas e à ocorrência de faltas, especialmente as linhas aéreas. Estatísticas mostram que entre 70% - 90% das faltas em linhas de transmissão aéreas são momentâneas (ou transitórias) e apresentam formação de arco elétrico. O arco elétrico é a principal característica de uma falta de alta impedância e resulta do pobre contato entre um condutor energizado e a superfície envolvida. Esta tese aborda o problema de localização de faltas de alta impedância em linhas de transmissão curtas. Propõese uma nova técnica de localização de faltas de alta impedância baseada na impedância aparente, desenvolvida no domínio da frequência e que utiliza componentes de fase. A estimativa da distância da falta é obtida a partir da solução de um sistema sobredeterminado de equações lineares, obtida pela aplicação do método de mínimos quadrados. A abordagem proposta permite estimar a distância de faltas de alta impedância momentâneas e permanentes, em linhas de transmissão curtas simples e paralelas, transpostas ou não. O desempenho da técnica de localização de faltas proposta é avaliado mediante estudos de casos simulados no Alternative Transients Program (ATP) considerando análises de sensibilidade e comparativa, bem como casos reais de faltas. Os resultados obtidos, considerando faltas de alta impedância simuladas e reais, indicam claramente que a abordagem proposta possui validade como técnica de localização de faltas em linhas de transmissão curtas em decorrência do desempenho demonstrado e, também, por características tais como: formulação simplificada no domínio da frequência, simplicidade e facilidade de implementação em dispositivos reais e aplicabilidade a casos reais. / Transmission lines are used to transmit electric power over long distances and are naturally exposed to severe weather conditions, especially overhead lines. Such conditions are highly favorable to the occurrence of faults. Statistics show that between 70% - 90% of faults on overhead lines are nonpermanent (or transient), and present arcing. Arcing is the main characteristic of a nonlinear high impedance fault and is the result of poor contact between an energized conductor and the ground or a grounded object. This thesis approaches the high impedance fault location on short transmission lines problem. It is proposed an impedancebased nonlinear high impedance fault location formulation developed in frequency domain and phase components. The formulation uses the least square method and synchronized phasors, measured by, for example, digital fault recorders installed at both line terminals. The proposed approach allows to estimate the distance of high impedance momentary and permanent faults on short transposed or untransposed transmission lines. The performance of the proposed fault location approach is evaluated through analysis of simulated cases in the Alternative Transients Program (ATP) considering sensitivity and comparative analyzes, and actual cases of high impedance faults. The results, considering simulations of high impedance faults and actual cases, indicate clearly that the proposed approach is valid as fault location technique in short transmission lines due to the demonstrated performance.
8

Modelagem e investigação numérica de escoamentos de fluidos estruturados tixotrópicos

Fonseca, Cleiton Elsner da January 2013 (has links)
Fluidos Não-newtonianos estão presentes em grande quantidade na natureza e em muitas aplicações industriais. Tais fluidos apresentam uma variedade de comportamentos específicos. Dentre eles podemos citar: elasticidade, plasticidade, viscosidade variando com a taxa de deformação, tixotropia. Esta tese de doutorado apresenta um recente modelo para Fluidos Estruturados Tixotrópicos (de Souza Mendes, 2009), no qual baseasse nas tradicionais equações de balanço de momentum e massa, em uma equação constitutiva de Maxwell-b modificada e uma equação de evolução para o nível de estrutura do material. Na equação constitutiva de Maxwell-b modificada, tempo de relaxação e viscosidade estrutural são funções da estrutura do material. A equação evolutiva para o parâmetro de estruturação prevê efeitos de tixotropia, dependentes do tempo de equilíbrio do material. As equações que constituem o modelo mecânico para Fluidos Estruturados Tixotrópicos são aproximadas numericamente através do Método de Elementos Finitos de Galerkin Mínimos-quadrados (GLS). Tal método adicionou termos dependentes de malha ao método clássico de Galerkin, de forma a aumentar a estabilidade da formulação original, proporcionando compatibilizar os sub-espaços de velocidade e pressão. São investigados escoamentos creeping flow de Fluidos Estruturados Tixotrópicos em dois problemas clássicos de engenharia: em torno de um cilindro confinado entre duas placas e em uma expansão planar abrupta. Parâmetros relevantes ao modelo são variados em faixas pertinentes ao problema físico simulado e os resultados demonstraram uma boa capacidade de previsão. / Non-Newtonian fluids are present in large quantities in nature and in many industrial applications. Such fluids exhibit a variety of specific behaviors. Among them we can mention: elasticity, plasticity, viscosity varying with the strain rate, thixotropy, etc. This thesis presents a new model for thixotropic Structured Fluids (de Souza Mendes, 2009), in which were a basis in traditional balance equations of mass and momentum, the constitutive equation of Maxwell-type and an evolution equation for the level structure of the material. In the modified constitutive equation of Maxwell-b, relaxation time and structural viscosity are functions of material structure. The structure parameter evolutive equation provides effects of thixotropy, dependent on the equilibration time of the material. The equations which constitute the mechanical model for Structured Thixotropic fluids are approximated numerically using the Galerkin Least-squares Finite Element Method (GLS). Such a method added mesh dependent terms to the classical method of Galerkin in order to increase the stability of the original formulation, providing compatibility between sub-spaces of velocity and pressure. Are investigated Structured Thixotropic Fluids creeping flow in two classical problems in engineering: around a cylinder confined between two plates and in a planar abrupt expansion. Relevant parameters to the model are varied in pertinent ranges to physical problem simulated and the results demonstrated a good predictive capability.
9

Localização de faltas de alta impedância : formulação baseada na impedância aparente e no método de mínimos quadrados

Ferraz, Renato Gonçalves January 2014 (has links)
As linhas de transmissão são usadas para transmitir energia elétrica por longas distâncias e estão naturalmente expostas a condições climáticas severas e à ocorrência de faltas, especialmente as linhas aéreas. Estatísticas mostram que entre 70% - 90% das faltas em linhas de transmissão aéreas são momentâneas (ou transitórias) e apresentam formação de arco elétrico. O arco elétrico é a principal característica de uma falta de alta impedância e resulta do pobre contato entre um condutor energizado e a superfície envolvida. Esta tese aborda o problema de localização de faltas de alta impedância em linhas de transmissão curtas. Propõese uma nova técnica de localização de faltas de alta impedância baseada na impedância aparente, desenvolvida no domínio da frequência e que utiliza componentes de fase. A estimativa da distância da falta é obtida a partir da solução de um sistema sobredeterminado de equações lineares, obtida pela aplicação do método de mínimos quadrados. A abordagem proposta permite estimar a distância de faltas de alta impedância momentâneas e permanentes, em linhas de transmissão curtas simples e paralelas, transpostas ou não. O desempenho da técnica de localização de faltas proposta é avaliado mediante estudos de casos simulados no Alternative Transients Program (ATP) considerando análises de sensibilidade e comparativa, bem como casos reais de faltas. Os resultados obtidos, considerando faltas de alta impedância simuladas e reais, indicam claramente que a abordagem proposta possui validade como técnica de localização de faltas em linhas de transmissão curtas em decorrência do desempenho demonstrado e, também, por características tais como: formulação simplificada no domínio da frequência, simplicidade e facilidade de implementação em dispositivos reais e aplicabilidade a casos reais. / Transmission lines are used to transmit electric power over long distances and are naturally exposed to severe weather conditions, especially overhead lines. Such conditions are highly favorable to the occurrence of faults. Statistics show that between 70% - 90% of faults on overhead lines are nonpermanent (or transient), and present arcing. Arcing is the main characteristic of a nonlinear high impedance fault and is the result of poor contact between an energized conductor and the ground or a grounded object. This thesis approaches the high impedance fault location on short transmission lines problem. It is proposed an impedancebased nonlinear high impedance fault location formulation developed in frequency domain and phase components. The formulation uses the least square method and synchronized phasors, measured by, for example, digital fault recorders installed at both line terminals. The proposed approach allows to estimate the distance of high impedance momentary and permanent faults on short transposed or untransposed transmission lines. The performance of the proposed fault location approach is evaluated through analysis of simulated cases in the Alternative Transients Program (ATP) considering sensitivity and comparative analyzes, and actual cases of high impedance faults. The results, considering simulations of high impedance faults and actual cases, indicate clearly that the proposed approach is valid as fault location technique in short transmission lines due to the demonstrated performance.
10

Influência das irregularidades da forma em peças de madeira na determinação do módulo de elasticidade longitudinal / Influence of timber pieces shape irregularities in longitudinal modulus of elasticity determination

André Luis Christoforo 06 December 2007 (has links)
Atualmente, os documentos normativos que tratam da determinação das propriedades de rigidez e resistência para elementos roliços estruturais de madeira não levam em consideração em seus modelos matemáticos a influência das irregularidades existentes na geometria dessas peças. O presente trabalho tem como objetivo determinar o valor ótimo do módulo de elasticidade longitudinal para peças roliças estruturais de madeira por intermédio de uma técnica de otimização aliada ao método da análise inversa, ao método dos elementos finitos e ao método dos mínimos quadrados. / Currently, the normative documents that deal with the determination of the properties of rigidity and resistance for round structural timber elements round timber do not take in consideration in both calculations and mathematical models the influence of the existing of irregularities in the geometry of these elements. An objective of this work is to determine the optimum value of the modulus of elasticity for round structural timber elements by an optimization technique associated to the inverse analysis method, to the finite element method and the least squares method.

Page generated in 0.1025 seconds