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  • 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

Formulação do método dos elementos de contorno para análise de chapas com enrijecedores / Formulation of the boundary elements method for analysis of stiffned plates

Wutzow, Wilson Wesley 23 May 2003 (has links)
Neste trabalho, a formulação linear do método dos elementos de contorno - MEC, para elasticidade bidimensional, é empregada para estudo de domínios enrijecidos sendo os enrijecedores abordados de duas formas, a primeira muito conhecida trata-se da técnica de sub-região ou acoplamento MEC/MEC e a segunda também pelo mesmo tipo de acoplamento, mas agora condensando-se as variáveis do contorno para a linha central do enrijecedor. Esta técnica juntamente com a integração completamente analítica dos termos da equação Somigliana proporcionam bons resultados eliminando perturbações em enrijecedores finos. Com o intuito de obter melhores resultados aplica-se ainda a técnica de suavização do contorno por mínimos quadrados. Aspectos gráficos são abordados na criação do pré e pós processador, sendo o pré-processador um interpretador de arquivos de formato dxf e o pós-processador destinado a representação gráfica dos resultados através de mapas e isolinhas de tensão, deformação e deslocamentos. / In this work, the boundary element method - BEM, for two-dimensional elasticity, is used to analyse reinforced domains. The rigidity stiffener contribution are taking into account by two different ways: the first one by the sub-region technique or BEM/BEM coupling, and the second one, also based on BEM/BEM coupling, but now considering the variables defined along the central line of the stiffer. Analytical expressions were found to perform the integrals along boundary and interface elements, providing very good results characterized by the elimination of some perturbations that might occur when using stiffener with small rigidity. In order to obtains better and smooth results the least square method was used. Pre- and post-processors were developed and implemented for visualization of the input data and the final results. The pre-processor was written as a dxf reader program, while the post-processor as a counter map stress, strain and displacement iso-lines.
2

Formulação do método dos elementos de contorno para análise de chapas com enrijecedores / Formulation of the boundary elements method for analysis of stiffned plates

Wilson Wesley Wutzow 23 May 2003 (has links)
Neste trabalho, a formulação linear do método dos elementos de contorno - MEC, para elasticidade bidimensional, é empregada para estudo de domínios enrijecidos sendo os enrijecedores abordados de duas formas, a primeira muito conhecida trata-se da técnica de sub-região ou acoplamento MEC/MEC e a segunda também pelo mesmo tipo de acoplamento, mas agora condensando-se as variáveis do contorno para a linha central do enrijecedor. Esta técnica juntamente com a integração completamente analítica dos termos da equação Somigliana proporcionam bons resultados eliminando perturbações em enrijecedores finos. Com o intuito de obter melhores resultados aplica-se ainda a técnica de suavização do contorno por mínimos quadrados. Aspectos gráficos são abordados na criação do pré e pós processador, sendo o pré-processador um interpretador de arquivos de formato dxf e o pós-processador destinado a representação gráfica dos resultados através de mapas e isolinhas de tensão, deformação e deslocamentos. / In this work, the boundary element method - BEM, for two-dimensional elasticity, is used to analyse reinforced domains. The rigidity stiffener contribution are taking into account by two different ways: the first one by the sub-region technique or BEM/BEM coupling, and the second one, also based on BEM/BEM coupling, but now considering the variables defined along the central line of the stiffer. Analytical expressions were found to perform the integrals along boundary and interface elements, providing very good results characterized by the elimination of some perturbations that might occur when using stiffener with small rigidity. In order to obtains better and smooth results the least square method was used. Pre- and post-processors were developed and implemented for visualization of the input data and the final results. The pre-processor was written as a dxf reader program, while the post-processor as a counter map stress, strain and displacement iso-lines.
3

Post activation potentiation : Modulating factors and mechanisms for muscle performance

Gago, Paulo January 2016 (has links)
Introduction: Acute enhancements of muscle contractile properties and performance subsequent to a maximal or near maximal conditioning contraction are often termed post activation potentiation (PAP). Although still controversial, PAP is commonly linked to enhancements in the myosin regulatory light chain phosphorylation, leading to improvements in the excitation–contraction coupling. The PAP seen after a conditioning task often coexists with fatigue and is known to depend on strength level, muscle fiber type and age. Less is known about how factors such as static and dynamic changes in muscle length affect PAP, and on the relative contribution of contractile and tensile components to PAP. Aim: To enhance our understanding of how, and under what conditions, a single maximal isometric contraction affects plantar flexor muscle contractile performance, and other muscle tendon properties, in power athletes. Methods: Supramaximal twitches were evoked via electrical stimulation of the tibial nerve of athletes before and on several occasions after a 6-second maximal voluntary isometric contraction (6-s MVIC) in both static muscle, and during passive muscle lengthening and shorting at different angular velocities. Several contractile variables were measured from the twitches. The effects of a 6-s MVIC on Achilles tendon stiffness was calculated from torque and ultrasonography based measurements of tendon length at two submaximal contraction intensities. Overall stiffness index was calculated by analyzing the passive lengthening torque/angle curve.Results: A single MVIC enhanced muscle contractile properties and electromechanical delay for up to 5 minutes. Plantar flexor twitch variables such as peak twitch, rate of torque development and rate of torque relaxation were enhanced during shortening compared to lengthening muscle actions, and in an extended as compared to a flexed knee position. Achilles tendon stiffness and overall stiffness index were not significantly modulated by a single 6-s MVIC. Conclusion: The results of this thesis imply that functional enhancements from a 6-s conditioning MVIC would mainly come from improvements in contractile rather than tensile components. Stiffness changes should be monitored in future PAP-related studies since they may still occur after more extensive conditioning protocols than the current one. Improvements in contractile components subserving muscle strength after a conditioning MVIC suggests that enhancements in muscle power after a conditioning task should be greatest in fast concentric muscle actions, though still present in muscle lengthening. Conditioning should be performed in a position where full activation is easy to achieve and tailored to mach an athlete or group of athlete’s current status and characteristics, maximizing performance in a specific sport event. / <p>The project recived financial support from the Swedish National Centre for Research in Sports (CIF). Paulo Gago also wishes to thank the Fundação para a Ciência e Tecnologia (FCT), Portugal for the Ph.D. Grant (SFRH/BD/103572/2014).</p><p>New version 2015-01-25 updates the previous one by correcting the errors described in the correction list file (errata).</p> / Doctoral project: Post activation potentiation - Modulating factors and mechanisms for muscle performance.
4

Rám malosériového sportovního automobilu / Sport car frame

Hubáček, Jan January 2011 (has links)
This master´s thesis deals with the design, calculation and verification of sports car frame. Empahasis was placed on meet standards for homologation. Work on diploma project was produced by the design program INVENTOR 2010 and then calculated in ANSYS 12. The last step was optimization and comparison.
5

Odos ir minkštųjų audinių standumo charakteristikų skaičiavimas baigtinių elementų metodu / Rigidity Characteristic`s Calculation of Skin And Soft Tissue By Finite Element Method

Motiečiūtė, Lina 19 June 2006 (has links)
Stiffnes of leg's receiver and skin and soft tissues at contact place are researched in the master thesis. Using the finite elements method with digital ANSYS programmable packet was made non-linear model of leg's prothesis receiver and stump of soft tissues . Made calculiation have shown that deformation ratio in stump and receiver contact declines when the lood increases. Therefore it is very important to evaluate not only the height of desabled persion but also his weight durind estimation the magnitude of deviations of leg prosthesis manufacturing and assembly.
6

Synthesis and mechanical properties of iron-filled carbon nanotubes

Weißker, Uhland 05 March 2014 (has links) (PDF)
Carbon forms the basis of a variety of compounds. The allotropic forms of carbon include graphene, fullerenes, graphite, carbon nanotubes and diamond. All these structures possess unique physical and chemical properties. This work focusses on the usage of carbon nanotubes (CNT), especially iron-filled CNT. An industrial application of CNT requires the understanding of the growth mechanism and the control of the synthesis process parameters. Regarding iron-filled CNT the shell formation as well as the filling process has to be understood in order to control the CNT morphology and distribution and dimension of the iron filling. The thesis involves two topics - synthesis of CNT and characterization of their mechanical properties. Chapter 2 of the present work deals with the synthesis of iron-filled CNT. In this thesis all experiments and the discussion about the growth process were conducted with respect to the demands of magnetic force microscopy probes. The experimental work was focused on the temperature profile of the furnace, the aluminum layer of the substrate, the precursor mass flow and their impact on the morphology of in-situ iron-filled CNT. By selecting appropriate process parameters for the temperature, sample position, gas flow and by controlling the precursor mass flow, CNT with a continuous filling of several microns in length were created. Existing growth models have been analyzed and controversially discussed in order to explain the formation of typical morphologies of in-situ filled CNT. In this work a modified growth model for the formation of in-situ filled CNT has been suggested. The combined-growth-mode model is capable to explain the experimental results. Experiments which were conducted with respect to the assumptions of this model, especially the role of the precursor mass flow, resulted in the formation of long and continuous iron nanowires encapsulated inside multi-walled CNT. The modified growth model and the synthesis results showed, that besides the complexity of the parameter interaction, a control of the morphology of in-situ iron-filled CNT is possible. In chapter 3 the measurements of mechanical properties of in-situ iron-filled CNT are presented. Two different experimental methods and setups were established, whereby one enabled a static bending measurement inside a TEM and another a dynamical excitation of flexural vibration of CNT inside SEM. For the first time mechanical properties and in particular the effective elastic modulus Eb of in-situ iron-filled CNT were determined based on the Euler-Bernoulli beam model (EBM). This continuum mechanic model can be applied to describe the mechanical properties of CNT and especially MWCNT in consideration of the restriction that CNT represent a macro molecular structure built of nested rolled-up graphene layers. For evaluation and determination of the elastic modulus the envelope of the resonant vibrating state was evaluated by fitting the EBM to the experimental data. The experiments also showed, that at the nanoscale the properties of sample attachment have to be taken into account. Thus, instead of a rigid boundary condition a torsion spring like behavior possessing a finite stiffness was used to model an one side clamped CNT. The extended data evaluation considering the elastic boundary conditions resulted in an average elastic modulus of Eb = 0.41 ± 0.11 TPa. The low standard deviation gives evidence for the homogeneity of the grown material. To some extend a correlation between the formation process, the morphology and the mechanical properties has been discussed. The obtained results prove the usability of this material as free standing tips for raster scanning microscopy and especially magnetic force microscopy. The developed methods provide the basis for further investigations of the CNT and the understanding of mechanical behavior in greater detail.
7

Synthesis and mechanical properties of iron-filled carbon nanotubes

Weißker, Uhland 16 October 2013 (has links)
Carbon forms the basis of a variety of compounds. The allotropic forms of carbon include graphene, fullerenes, graphite, carbon nanotubes and diamond. All these structures possess unique physical and chemical properties. This work focusses on the usage of carbon nanotubes (CNT), especially iron-filled CNT. An industrial application of CNT requires the understanding of the growth mechanism and the control of the synthesis process parameters. Regarding iron-filled CNT the shell formation as well as the filling process has to be understood in order to control the CNT morphology and distribution and dimension of the iron filling. The thesis involves two topics - synthesis of CNT and characterization of their mechanical properties. Chapter 2 of the present work deals with the synthesis of iron-filled CNT. In this thesis all experiments and the discussion about the growth process were conducted with respect to the demands of magnetic force microscopy probes. The experimental work was focused on the temperature profile of the furnace, the aluminum layer of the substrate, the precursor mass flow and their impact on the morphology of in-situ iron-filled CNT. By selecting appropriate process parameters for the temperature, sample position, gas flow and by controlling the precursor mass flow, CNT with a continuous filling of several microns in length were created. Existing growth models have been analyzed and controversially discussed in order to explain the formation of typical morphologies of in-situ filled CNT. In this work a modified growth model for the formation of in-situ filled CNT has been suggested. The combined-growth-mode model is capable to explain the experimental results. Experiments which were conducted with respect to the assumptions of this model, especially the role of the precursor mass flow, resulted in the formation of long and continuous iron nanowires encapsulated inside multi-walled CNT. The modified growth model and the synthesis results showed, that besides the complexity of the parameter interaction, a control of the morphology of in-situ iron-filled CNT is possible. In chapter 3 the measurements of mechanical properties of in-situ iron-filled CNT are presented. Two different experimental methods and setups were established, whereby one enabled a static bending measurement inside a TEM and another a dynamical excitation of flexural vibration of CNT inside SEM. For the first time mechanical properties and in particular the effective elastic modulus Eb of in-situ iron-filled CNT were determined based on the Euler-Bernoulli beam model (EBM). This continuum mechanic model can be applied to describe the mechanical properties of CNT and especially MWCNT in consideration of the restriction that CNT represent a macro molecular structure built of nested rolled-up graphene layers. For evaluation and determination of the elastic modulus the envelope of the resonant vibrating state was evaluated by fitting the EBM to the experimental data. The experiments also showed, that at the nanoscale the properties of sample attachment have to be taken into account. Thus, instead of a rigid boundary condition a torsion spring like behavior possessing a finite stiffness was used to model an one side clamped CNT. The extended data evaluation considering the elastic boundary conditions resulted in an average elastic modulus of Eb = 0.41 ± 0.11 TPa. The low standard deviation gives evidence for the homogeneity of the grown material. To some extend a correlation between the formation process, the morphology and the mechanical properties has been discussed. The obtained results prove the usability of this material as free standing tips for raster scanning microscopy and especially magnetic force microscopy. The developed methods provide the basis for further investigations of the CNT and the understanding of mechanical behavior in greater detail.
8

Asfaltové směsi s vyšší životností za použití R-materiálu / Bituminous mixtures with a higher lifetime using recycled asphalt

Stromecký, Roman January 2019 (has links)
This diploma thesis deals with a project of asphalt mixtures with high stiffness modulus using R-material. The theoretical part describes the characteristics of these mixtures in the Czech Republic and in Switzerland. Further this part deals with the use of R-material in the Czech Republic and chosen other countries of the world, it also deals with the ways of recycling roads. The theoretical part also deals with the testing methods used. In the practical part two new asphalt mixtures of the high stiffness modulus type with the addition of 25 % R-material are suggested. As a base for these two mixtures a mixture of the high stiffness modulus type, which was taken from an asphalt mixing plant, was used. Tests were run on the binders and several functional tests (stiffness modulus, fatigue resistance, low temperature qualities) wer done on the suggested asphalt mixtures and also the mixture taken from the mixing plant. Consequently, the results were compared. The conclusion of the thesis is devoted to modelling a construction of a road using the program LayEps, which verified if the suggested mixtures could reduce the thickness of roads.
9

Měření parametrů pneumatik / Tyre Parameters Measurement

Pokorný, Pavel January 2012 (has links)
It is the tyre that ensures the interaction between a wheel and road surface and it is the the tyre which also acts as a primary cushioning. Its construction, features and condition highly influence driving properties of a car and thus passenger safety as well. In motorsports the tyre is a key part of the vehicle and therefore it is necessary to make use of its complete potential for reaching the best results. The aim of this thesis is a device construction suitable for tyre parameter and their characteristics measurement. The next task is to design a measuring system for tyre pressure and temperature monitoring. With using of these devices a few real-tyre measurements and subsequent result evaluation will be done. The output of the thesis is an overview of construction details, overview of selected tyre parameters, design and drawing documentation of multipurpose measuring device and the results of my measurements.

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