A multiscale model is proposed to study the influence of interfacial interactions at the nanoscale in carbon nanotube(CNT)-polymer nanocomposites on the macroscale bulk elastic material properties. The efficiency of CNT reinforcement in terms of interfacial load transferring is assessed for the non-functionalized and functionalized interfaces between the CNTs and polymer matrix using force field based molecular dynamic simulations at the nanoscale. Polyethylene (PE) as a thermoplastic material is adopted and studied first because of its simplicity. Characterization of the nanoscale load transfer has been done through the identification of representative nanoscale interface elements for unfunctionalized CNT-PE interface models which are studied parametrically in terms of the length of the PE chains, the number of the PE chains and the "grip" position. Referring to the non-functionalized interface, CNTs interact with surrounding polymer only through weakly nonbonded van der Waals (vdW) forces in our study. Once appropriate values of these parameters are deemed to yield sufficiently converged results, the representative interface elements are subjected to normal and sliding mode simulations in order to obtain the force-separation responses at 100K and 300K for unfunctionalized CNT-PE interfaces. To study the functionalization effects, atomistic interface representative elements for functionalized CNT-PE interface are built based on non-functionalized interface models by grafting functional groups between the PE matrix and the graphene sheet. This introduces covalent bonding forces in addition to the non-bonded vdW forces. A modified consistent covalent force field (CVFF) and adaptive intermolecular reactive empirical bond order (AIREBO) potentials, both of which account for bond breaking, are applied to investigate the interfacial characteristic of functionalized CNT-PE interface in terms of the force-separation responses at 100K in both normal opening and sliding mode separations. In these studies, the focus has been on the influence of the functionalization density on the load transfer at the nanoscale interface. As an important engineering material, Epon 862/DETDA epoxy polymer,a thermoset plastic, has also been used as the polymer matrix material in order to see the difference in interfacial load transfer between a network structured polymer and the amorphous entangled structure of the PE matrix. As for thermoset epoxy polymer, emphasis has been put on investigating the effects of the crosslink density of the epoxy network on the interfacial load transfer ability for both non-functionalized and functionalized CNT-Epoxy interface at different temperatures(100K and 300K) and on the functionalization effect influenceing the interfacial interactions at the functionalized CNT-Epoxy interface. Cohesive zone traction-displacement laws are developed based on the force-separation responses obtained from the MD simulations for both non-functionalied and functionalized CNT-PE/epoxy interfaces. Using the cohesive zone laws, the influence of the interface on the effective elastic material properties of the nanocomposites are observed and determined in continuum level models using analytic and computational micromechanics approaches, allowing for the assessment of the improvement in reinforcement efficiency of CNTs due to the functionalization. It is found that the inclusion of the nanoscale interface in place of the perfectly bonded interface results in effective elastic properties which are dependent on the applied strain and temperature in accordance with the interface sensitivity to those effects, and which are significantly diminished from those obtained under the perfect interface assumption for non-functionalized nanocomposites. Better reinforcement efficiency of CNTs are also observed for the nanocomposites with the functionalized interface between CNTs and polymer matrix, which results in large increasing for the effective elastic material properties relative to the non-functionalized nanocomposites with pristine CNTs. Such observations indicates that trough controlling the degree of functionalization, i.e. the number and distribution of covalent bonds between the embedded CNTs and the enveloping polymer, one can tailor to some degree the interfacial load transfer and hence, the effective mechanical properties. The multiscale model developed in this study bridges the atomistic modeling and micromechanics approaches with cohesive zone models, which demonstrates to deepen the understanding of the nanoscale load transfer mechanism at the interface and its effects on the effective mechanical properties of the nanocomposites. It is anticipated that the results can offer insights about how to engineer the interface and improve the design of nanocomposites. / Ph. D.

The thesis has been done in collaboration with Kalmar Solutions AB and is a conceptual study that aims to design a hydraulic steering arrangement for the reachstacker DRG 450 where each wheel is steered independently of each other. This is done in order to reduce tire wear by achieving an Ackermann steering geometry; lesser tire wear reduces costs for customers. When steered independently of each other the same steering arrangement could be used on multiple different wheelbases while still achieving an Ackermann steering geometry. During the thesis, calculations for required steering angles and their required piston strokes has been done by creating a geometrical model of the steering arrangement. CAD-modeling and kinematic simulations of concepts has been conducted with CATIA R2024x where the concepts movement when turning could be simulated. Three main concepts of the steering arrangement were studied and developed during the thesis. Kinematic simulations concluded that by changing to two independent cylinders, along the same axis, and redesigning the steering knuckles could allow for the same steering arrangement to achieve an Ackermann steering geometry for multiple different wheelbases. This reduces tire wear and turning radius when compared to the current steering axle. Having the cylinders along the same axis proved to be best because less redesigns were needed and mainly no major redimensioning of the steering arrangement or chassis were needed.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第25248号 / 工博第5207号 / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 八木 知己, 教授 杉浦 邦征, 教授 高橋 良和 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Splitter plates are passive flow control devices for reducing drag and suppressing vortex shedding from bluff bodies. Most studies of splitter plates involve the flow around an “infinite” circular cylinder, however, in the present study the flow around a surface-mounted finite-height circular cylinder, with a wake-mounted splitter plate, was studied experimentally in a low-speed wind tunnel using a force balance and single-component hot-wire anemometry. Four circular cylinders of aspect ratios AR = 9, 7, 5 and 3 were tested for a Reynolds number range of Re = 1.9×10^4 to 8.2×10^4. The splitter plates had lengths, relative to the cylinder diameter, of L/D = 1, 1.5, 2, 3, 5 and 7, thicknesses ranging from T/D = 0.10 and 0.15, and were the same height as the cylinder being tested. The cylinders were partially immersed in a flat-plate turbulent boundary layer, where the range of boundary layer thickness relative to the cylinder diameter was δ/D = 1.4 to 1.5. Measurements were made of the mean drag force coefficient, the Strouhal number at the mid-height position, and the Strouhal number and power spectra along the cylinder height. For all four finite circular cylinders, the splitter plates were effective at reducing the magnitude of the Strouhal number, and weakening or even suppressing vortex shedding, depending on the specific combination of AR and L/D. Compared to the case of an infinite circular cylinder, the splitter plate is less effective at reducing the mean drag force coefficient of a finite circular cylinder. The largest drag reduction was obtained for the cylinder of AR = 9 and splitter plates of L/D = 1 to 3, while negligible drag reduction occurred for the shorter cylinders.

Controlling the temperature of the exhaust valves is paramount for proper functioning of engines and for the long lifespan of valve train components. The majority of the heat outflow from the valve takes place along the valve-seat-cylinder head-coolant thermal path which is significantly influenced by the thermal contact resistance (TCR) present at the valve/seat and seat/head interfaces. A test rig facility and experimental procedure were successfully developed to assess the effect of the valve/seat and seat/head interfaces on heat outflow from the valve, in particular the effects of the valve/seat interface geometry, seat insert assembly method, i.e. press or shrink fit, and seat insert metallic coating on the operating temperature of the valve. The results of tests have shown that the degree of the valve-seat geometric conformity is more significant than the thermal conductivity of the insert: for low conforming assemblies, the mean valve head temperature recorded during tests on copper-infiltrated insert seats was higher than that recorded during tests on noninfiltrated seats of higher conformance. The effect of the insert-cylinder head assembly method, i.e. shrink-fitted versus press-fitted inserts, has proved negligible: results have shown insignificant valve head temperature variations, for both tin-coated and uncoated inserts. On the other hand, coating the seat inserts with a layer of tin (20-22μm) reduced the mean valve head temperature by approximately 15°C as measured during tests on uncoated seats. The analysis of the valve/seat and seat/head interfaces has indicated that the surface asperities of the softer metal in contact would undergo plastic deformation. Suitable thermal contact conductance (TCC) models, available in the public domain, were used to evaluate the conductance for the valve/seat and seat/cylinder head interfaces. Finally, a FE thermal model of the test rig has been developed with a view to assess the quality of the calculated TCC values for the valve/seat and seat/head interfaces. The results of the thermal analysis have shown that predicted temperatures at chosen control points agree with those measured during tests on thermometric seats with an acceptable level of accuracy, proving the effectiveness of the used TCC models.

Baigiamajame magistro darbe nagrinėjama iešmo elektros pavara su tiesiaeigiu asinchroniniu cilindriniu varikliu. Programiniu paketu ,,Matlab“ yra sudaryti pavaros matematiniai modeliai α, β koordinačių sistemoje. Uždaviniai – tiesiaeigės iešmo elektros pavaros kompiuterinio modelio sudarymas, tyrimas ir dinaminių charakteristikų imitavimas. Literatūros analizės dalyje išnagrinėtos tiesiaeigės elektros pavaros, jų taikymo sritys bei valdymo būdai. Magistro darbo teorinėje dalyje pateikiamos tiesiaeigių elektros pavarų skaičiavimo ir valdymo metodikų analizės. Tiriamoji dalis apima iešmo elektros pavaros su tiesiaeigiu cilindriniu asinchroniniu varikliu matematinių modelių sudarymą ir dinaminių charakteristikų tyrimą programiniu paketu ,,Matlab“. Matematiniai modeliai yra sudaromi pavarai veikiant skirtingais darbo režimais (pavara perjungiama neapkrauta, pavara perjungiama apkrovus nominalia apkrova ir iešmą perjungiant pabaigoje ir pradžioje trukdant papildomai pasipriešinimo jėgai) ir tyrimo rezultatai pateikiami grafiškai. Gauti rezultatai yra palyginami ir apibendrinami. Išnagrinėjus teorinius tiesiaeigės iešmo elektros pavaros su asinchroniniu cilindriniu varikliu darbo režimų aspektus, pateikiamos išvados ir pasiūlymai. Tyrimo rezultatai gali būti panaudoti iešmo elektros pavaros su tiesiaeigiu asinchroniniu varikliu racionaliam ir optimaliam realizavimui geležinkelio transporto automatinio valdymo sistemose. Darbą sudaro 9 dalys: santrumpos ir simboliai, įvadas... [toliau žr. visą tekstą] / The final Bachelor thesis analyses point electric drive with cylinder-type linear asynchronous motor. Software package ,,Matlab“ was used to prepare mathematical models of the drive in α, β coordinate system. Objectives: preparing and analyzing a computer model of linear point electric drive, simulation of dynamic characteristics. The analysis of literary sources deals with linear electric drives, their application areas and methods of control. Theoretical part of the Master thesis presents analyses of calculation and control methods of linear electric drives. The analytical part of the thesis includes mathematical models of point electric drive with cylinder-type linear asynchronous motor and the analysis of dynamic characteristics using software package ,,Matlab“. Mathematical models were prepared when the drive operated in different modes (the drive switched without load, the drive switched with nominal load, the switch connected at the end or beginning, thereby blocking additional resistance force). Research results were presented in a graphical form. Obtained results were compared and summarized. Following the analysis of the theoretical aspects of operating modes of linear point electric drive with cylinder-type asynchronous motor, conclusions and recommendations were presented. Research results can be used for rational and optimal realization of point electric drive with linear asynchronous motor in automatic railway control systems. The thesis consists of nine parts:... [to full text]

Within this body of work several series of experiments will investigate the nature of complex combustion in an experimental single-cylinder engine emulating a modern passenger car size compression-ignition (CI) engine. Regimes of single, piloted single and piloted split-main injections will be tested and compared in terms of combustion characteristics, specific emission output and cyclic behaviour to determine how increased injection complexity affects the emissions and output of the modern CI engine. Through these tests, the effect of fuel-line stationary waves will be demonstrated and investigated, showing conclusively that optimised engine calibration is essential to account for injector-generated waves in any multiple injection scenario. This data will then be confirmed with a dedicated analysis using an injector rate measuring tube. The tests will then be expanded to include examination into the behaviour of injector needle-lift standard deviation over its operating cycle, in-cylinder pressure standard deviation behaviour and trends over the combustion cycle as well as IMEP variability. Through these tests a novel method to detect start of combustion will be proposed and compared to conventional methods. Low temperature combustion (LTC) will be tested under incremental injection complexity. Tests will be optimised for combustion phasing and injection pressure, with a view to analysis of emissions, output and cyclic behaviour to establish whether the knowledge gained about conventional combustion holds true under LTC. Optimization of engine parameters will be shown to result in easier to implement LTC regimes with superior emissions characteristics. Finally, LTC tests will be expanded to include 30% and 50% by volume gas-to-liquid fuel (GTL) blends in order to determine whether fuel characteristics further influence emissions, output and cyclic behaviour in LTC through complex injection regimes. How GTL-blend ratio affects trends in emissions and cyclic behaviour will also be examined and compared to conventional diesel fuel.

O desenvolvimento da indústria offshore fez com que a demanda por unidades flutuantes para operações em águas ultraprofundas aumentasse e, com isso, surgiu um maior interesse nos fenômenos decorrentes de vibrações induzidas pelo escoamento em plataformas do tipo spar, TLP e semissubmersível, além de torres para produção de energia eólica (instaladas no mar). Para ampliar o conhecimento nesta área, experimentos foram realizados com cilindros flutuantes com baixa razão de aspecto (L/D = 2) e com diferentes geometrias na extremidade livre . Experimentos com a vibração induzida pelo escoamento em cilindros de seção quadrada e cilindros de seção quadrada e arestas arredondadas com baixa razão de aspecto foram realizados em um tanque de reboque. Estas diferentes geometrias de cilindros foram testadas e suportadas elasticamente por um conjunto de molas lineares. Dois ângulos de incidência diferentes foram testados: 0 e 45 graus. Os resultados de amplitude na direção transversal para modelos submetidos à incidência de 0 graus mostraram ser maiores. Além disso, as oscilações em yaw se mostraram importantes em todos os caso analisados. O efeito das arestas se mostrou importante, particularmente na incidência de 45 graus, para velocidades reduzidas maiores que 8. / The development of the offshore industry has meant that the demand for ultradeep water floating units has increased, and with this, a greater interest in the phenomena arising from FIV in spar, TLP and semi-submersible platforms has arisen. In order to increase the area knowledge, experiments were performed with floating cylinders with different geometries, with low aspect ratio (L/D = 2). Experiments of flow-induced vibration in cylinders with sharp aokokoknd rounded square section with low aspect ratio were performed in a towing tank. These geometries have been tested and elastically supported by a set of linear springs to provide low structural damping to the system. Two different incidence angles were tested: 0 and 45 degrees. The transverse response amplitudes for the 0-degree flow incidence were found to be larger. Moreover, yaw oscillations are important for all the cases analyzed. The rounded effect on the cylinders of square section were important, particularly for the the 45-degree incidence at reduced velocities higher than 8.

O escoamento em torno de corpos tem sido objeto de estudo de muitos pesquisadores e é muito explorado experimental e computacionalmente, devido a sua grande aplicabilidade na engenharia. No entanto, simular computacionalmente este tipo de escoamento requer uma atenção especial ao escolher o tipo malha a ser utilizado. Em muitos casos faz-se necessário o uso de uma malha que se adapte ao contorno do obstáculo, o que pode ocasionar um aumento no esforço computacional. Um maneira de contornar este problema é a utilização do Método das Fronteiras Imersas, que possibilita o uso de malha cartesiana na simulação computacional do escoamento em torno de obstáculos. Isso é possível através da adição de um termo forçante nas equações que modelam o escoamento, e assim as forças que agem sobre o contorno do corpo são transferidas diretamente para a malha. O objetivo deste trabalho de mestrado foi implementar o método das Fronteiras Imersas e simular o escoamento em torno de um cilindro circular em repouso, movimentando-se na mesma direção do escoamento, na direção perpendicular ao escoamento, ou rotacionando em torno do próprio eixo. As simulações computacionais possibilitaram a captura do fenômeno de Atrelagem Síncrona, caracterizado pela sincronia entre a frequência de desprendimento natural de vórtices e a frequência de oscilação do mesmo. O Método das Fronteiras Imersas mostrou um ótimo desempenho quando comparado a resultados experimentais e numéricos encontrados na literatura / The flow around bodies have been studied by many researchers. Both experimental and computational approaches have been extensively explored in researches on flow around bodies and have been applied in many engeneering problems. However, to choose an appropriate type of mesh to perform computational simulations of this type of problem requires special attention. In many cases, it is necessary to use a mesh that is able to conform to the boundary if a given obstacle. The need to perform this adaptation may increase the computational effort. The Immersed Boundary Method enables the use of cartesian meshes to perform computational simulations of flows around obstacles. The idea of this method is to add a forcing term in the equations that model the flow. Thus, the forces applied on the body boundaries are directly transfered to the mesh. The aim of this work was to perform a computational implementation of the Immersed Boundary Method to simulate the flow over a oscilating circular cylinder. This oscilation may be inline with the flow, cross-flow, or rotating. The computational simulations enabled the capture of the lock-in phenomena, which consists of the syncronization between the vortex shedding frequency and the cylinder oscilation frequency. The results obtained from the computational simulations using the Immersed Boundary Method were in good agreement with the numerical and experimental results found in the literature

O problema de empacotamento de cilindros em níveis é comumente encontrado nas indústrias de cerâmica. Solucionar este problema significa encontrar o posicionamento ideal dos itens cerâmicos cilíndricos dentro do forno de modo que o menor número de fornos seja utilizado e os itens não se sobreponham e obedeçam aos limites do recipiente. Também é considerado o uso de prateleiras para que haja uma melhor ocupação do espaço do forno. Propomos uma formulação matemática não-linear inteira mista e métodos de resolução heurísticos e exato para o problema. Os métodos heurísticos consistem em escolher uma estratégia de ordenação, posicionar os itens em cada nível por meio da heurística Bottom-Left e posicionar os níveis no recipiente utilizando as estratégias Best-Fit, First-Fit ou Worst-Fit. Ao total, propomos seis variações heurísticas para resolução do problema. O método exato consiste em estimar o número de níveis e recipientes necessários e resolver o problema por meio de um solver de otimização global. Os experimentos computacionais foram realizados para um conjunto de instâncias que criamos. Os resultados mostraram que o método exato é capaz de encontrar a solução ótima em um curto período de tempo para instâncias de pequeno porte e que as heurísticas são capazes de resolver o problema em um tempo computacional baixo, para instâncias de pequeno, médio e grande porte, sendo que algumas heurísticas apresentam melhor desempenho que outras. / The cylinder packing problem in levels is commonly found in ceramic industries. Solving this problem consists in finding the ideal position of items inside furnaces so that the minimum number of furnaces is used and the items do not overlap and obeying furnaces size. In this case, it is possible to add levels to the furnace. We proposed a non-linear integer mixed mathematical model for the problem and heuristic and exact resolution methods. Heuristic methods consist of choosing a sorting strategy, packing the items at each level by a Bottom-Left heuristic, and positioning the levels in the furnace using Best-Fit, First- Fit or Worst-Fit strategy. In total, it is proposed six heuristic variations to solve the problem. The exact method consists in solving the problem by a global optimization solver. The computational experiments were run over a set of new proposed instances. The results have shown that the exact method is able to find an optimal solution in a short period of time for small instances and that the proposed heuristics are capable of solving the problem in a low computational time for small, medium and large instances. Furthermore, some of them have performed better than others.