Reinforced cylindrical shells are used in numerous industries; common examples include undersea vehicles and industrial piping. Current models typically incorporate approximate theories to determine shell behavior, which have limitations in terms of both thickness and frequency. In addition, many applications feature coatings on the shell surface that normally have thicknesses which must also be considered. To increase the fidelity of such systems, this work develops an analytical model of an elastic cylindrical shell featuring periodically spaced ring stiffeners with an acoustic coating applied to the outer surface. There is an external fluid environment. Beginning with the equations of elasticity for a solid, spatial-domain displacement field solutions are produced incorporating unknown wave propagation coefficients. These fields are used to determine stresses at the boundaries of the shell and coating, which are then coupled with stresses from the stiffeners and fluid. The stress boundary conditions contain double-index infinite summations, which are decoupled, truncated, and recombined into a global matrix equation. The solution to this global equation results in the displacement responses of the system as well as the scattered pressure field. Two distinct loadings are considered: a ring loading and an incident acoustic wave. Thin-shell reference models are used for validation, and the acoustic response of the system is examined. It is shown that the reinforcing ribs and acoustic coating have a considerable effect on system behavior. / Master of Science

A finite element model of a fracture test specimen is developed using the STAGS computer code (STructural Analysis of General Shells). The test specimen was an internally pressurized, aluminum cylindrical shell reinforced with two externally bonded aluminum tear straps around its circumference. The shell contained an initial, axial through-crack centered between the straps. The crack propagated slowly in the axial direction as the pressure increased above a certain value until a maximum pressure was attained, and then the crack propagated dynamically. The tear straps sufficiently toughened the shell such that the dynamic crack path bifurcated near the edges of the straps. The bifurcated crack branches ran circumferentially, parallel to the straps causing the shell wall to flap open. The STAGS analysis for the static equilibrium configurations of the fractured shell include geometric nonlinearity and elastic-plastic material behavior. The crack tip opening angle (CTOA) is used in the criterion for ductile crack growth, and the critical value of the CTOA is determined by correlating the STAGS predictions of the stable portion of the crack growth curve (internal pressure versus half crack length) to the test. With the employment of a new STAGS algorithm, the complete axial crack growth curve, including both the stable and unstable portions, through the tear strap is obtained. The complete axial crack growth curve indicates that crack growth through the strap is unlikely. STAGS models with long cracks which bifurcate at various half crack lengths are developed to assess the location of crack bifurcation. Three different stress based crack turning criteria are investigated from the axial crack growth results as a second method for assessing a location of bifurcation. The bifurcation analyses and stress based turning criteria corroborate the experimentally measured bifurcation point. A parametric study is then conducted to determine the influence of tear strap thickness and width on the location of crack bifurcation. / Master of Science

Future launch vehicle payload fairings will be manufactured from advanced lightweight composite materials. The loss of distributed mass causes a significant increase in the internal acoustic environment, causing a severe threat to the payload. Using piezoelectric actuators to control the fairing vibration and the internal acoustic environment has been proposed. The control authority of these actuators for this problem has not yet been determined. To help determine the acoustic control authority of piezoelectric actuators mounted on a rocket fairing, the internal acoustic response created by the actuators needs to be determined. In this work the internal acoustic response of a closed simply-supported (SS) cylinder actuated by piezoelectric (PZT) actuators is presented. A research-grade SS cylinder is created and the modal properties are analyzed experimentally. The experimental modal properties are compared to finite element analysis (FEA) and to results predicted by Love shell theory. The experimental results indicate that the created cylinder has dynamic properties that are similar to the analytical and FEA results. The formulation for the structural response uses an impedance model to predict transverse vibration of the cylinder excited by PZT actuators. The model is also shown to be valid. To obtain the internal acoustic response of the cylinder a boundary element analysis using the Kirchoff-Helmholtz integral is used. The motion of the structure is assumed to be uncoupled with the internal acoustics, and so the structural-acoustic interaction is not considered in this analysis. An analytical solution to the internal acoustic response within the cylinder is derived for a single mode structural vibration. The numerical and analytical models are shown to be in agreement. The numerical model is also verified experimentally by measuring the acoustic field within the cylinder. The experimental results and the results predicted by the acoustic model are in agreement. A measure of the acoustic loss factor for the aluminum cylinder is also determined experimentally. The validated model is used to extrapolate results for a SS cylinder that emulates a Minotaur payload fairing. The internal cylinder acoustic levels are investigated for PZT actuation between 35 and 400 Hz. It is found that changes in cylinder parameters (stiffness and material density) do not have a large effect on the magnitude of the structural response. Likewise the interior acoustic response is not greatly affected by changes to the cylinder parameters. As the applied voltage increases linearly, the internal sound pressure level (SPL) varies logarithmically. This behavior is a limiting factor in using a PZT actuator to generate high internal SPLs. Significant reductions in the structural response due to increased damping do not equate to similar reductions in the acoustic SPLs for the cylinder. The sound levels at the acoustic resonant frequencies are essentially unaffected by the significant increase in structural damping while the acoustic levels at the structural resonant frequencies are mildly reduced. The interior acoustic response of the cylinder is dominated by the acoustic modes and therefore significant reductions in the overall interior acoustic levels will not be achieved if only the structural resonances are controlled. The model indicates that the maximum acoustic levels generated by the baseline PZT actuator are sufficient at the higher frequency range but are not commensurate with the levels found in a typical fairing in the lower frequency range (below ~200 Hz). Since the baseline actuator's applied voltage can not be increased, additional actuators are required in order to increase the response of the cylinder at some of the lower frequencies. The baseline actuator is clearly better at generating sound within the cylinder as the frequency increases. This implies that more actuators will be required to control the lower frequency modes than the higher frequency modes. As the actuation frequency is reduced, the number of actuators required to generate acoustic levels commensurate to that found in the fairing increases to impractical values. Below approximately 100 Hz, the current demands reach levels that are extremely difficult to achieve with a practical system. The results of this work imply that PZT actuators do not have the authority to control the payload fairing internal acoustics below ~100 Hz. / Ph. D.

Analytical modeling of the root cause of cylinder-to-cylinder variation and the impact on CO2 emission caused by the reduction in engine efficiency <br>

<p>Combustion supervision by evaluating flywheel speed variations is a common approach in the automotive industry. This often involves preliminary measurements. An adequate model for simulating flywheel speed can assist to avoid some of these preliminary measurements. </p><p>A physical nonlinear model for simulating flywheel speed based on cylinder pressure information is investigated in this work. Measurements were conducted at Scania in a test bed and on a chassis dynamometer. The model was implemented in MATLAB/Simulink and simulations are compared to measured data. The first model can not explain all dynamics for the measurements in the test bed so extended models are examined. A model using a dynamically equivalent model of the crank-slider mechanism shows no difference from the simple model, whereas a model including a driveline can explain more from the test-bed measurements. When simulating the setups used at the chassis dynamometer, the simplest model works best. Yet, it is not very accurate and it is proposed that optimization of parameter values might improve the model further. A sensitivity analysis shows that the model is fairly robust to parameter changes.</p><p>A continuation of this work might include optimization to estimate parameter values in the model. Investigating methods for combustion supervision may also be a future issue.</p>

Combustion supervision by evaluating flywheel speed variations is a common approach in the automotive industry. This often involves preliminary measurements. An adequate model for simulating flywheel speed can assist to avoid some of these preliminary measurements. A physical nonlinear model for simulating flywheel speed based on cylinder pressure information is investigated in this work. Measurements were conducted at Scania in a test bed and on a chassis dynamometer. The model was implemented in MATLAB/Simulink and simulations are compared to measured data. The first model can not explain all dynamics for the measurements in the test bed so extended models are examined. A model using a dynamically equivalent model of the crank-slider mechanism shows no difference from the simple model, whereas a model including a driveline can explain more from the test-bed measurements. When simulating the setups used at the chassis dynamometer, the simplest model works best. Yet, it is not very accurate and it is proposed that optimization of parameter values might improve the model further. A sensitivity analysis shows that the model is fairly robust to parameter changes. A continuation of this work might include optimization to estimate parameter values in the model. Investigating methods for combustion supervision may also be a future issue.

<p>The demands on tomorrows diesel engines regarding fuel consumption and emission levels keep getting more difficult to fulfill. Due to this fact, the control demand is getting bigger and bigger. To be able to comply with the Euro 6 standards, it is believed that engine control need to be conducted individually from cylinder to cylinder if the need for after-treatment systems should be minimized.</p><p>Scania’s approach to handle emission levels so far has been to use exhaust gas recirculation (EGR). To be able to optimize the use of EGR it is necessary to know how the inert gases, water and carbon dioxide, are distributed between the cylinders. The distribution variation become even more difficult to predict since the EGR is cooled, sometimes leading to condensation of some of the water content. The condensation of water and its behavior in the inlet manifold is studied in this thesis.</p><p>Different ways of measuring non-uniformity in the gas composition between cylinders with respect to EGR in general and water content in particular are evaluated. Using these results, measurements have been conducted on an engine and conclusions are drawn from them.</p><p>The conclusions are that uneven distribution of above all liquid water, due to puddle formation, have an impact on emission formation that should be accounted for in some of the examined operating conditions.</p>

The demands on tomorrows diesel engines regarding fuel consumption and emission levels keep getting more difficult to fulfill. Due to this fact, the control demand is getting bigger and bigger. To be able to comply with the Euro 6 standards, it is believed that engine control need to be conducted individually from cylinder to cylinder if the need for after-treatment systems should be minimized. Scania’s approach to handle emission levels so far has been to use exhaust gas recirculation (EGR). To be able to optimize the use of EGR it is necessary to know how the inert gases, water and carbon dioxide, are distributed between the cylinders. The distribution variation become even more difficult to predict since the EGR is cooled, sometimes leading to condensation of some of the water content. The condensation of water and its behavior in the inlet manifold is studied in this thesis. Different ways of measuring non-uniformity in the gas composition between cylinders with respect to EGR in general and water content in particular are evaluated. Using these results, measurements have been conducted on an engine and conclusions are drawn from them. The conclusions are that uneven distribution of above all liquid water, due to puddle formation, have an impact on emission formation that should be accounted for in some of the examined operating conditions.

Orientador: João Carlos de Menezes / Dissertação (mestrado profissional) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica, Faculdade de Engenharia Eletrica e de Computação e Instituto de Química / Made available in DSpace on 2018-08-16T19:47:41Z (GMT). No. of bitstreams: 1 Nahas_LeandroLafiandre_M.pdf: 2528374 bytes, checksum: 557f889189fdbae7ea36996fe0893714 (MD5) Previous issue date: 2010 / Resumo: Este projeto originou-se quando a família de motores objeto deste estudo foi introduzida no mercado e já os primeiros lotes de motores produzidos apresentaram esta falha, vulgarmente conhecida como degola da camisa. Esta falha compreende a trinca e propagação por todo o perímetro da camisa de cilindro e consequentemente a descida da camisa para a parte inferior do bloco do motor. Durante a descida, a camisa choca-se com elementos girantes do motor e vem por sua vez colapsar por completo. Este trabalho tem como base a extrapolação dos limites especificados em projeto da camisa de cilindro do tipo seca. Veremos que mínimas variações dimensionais no projeto da camisa de cilindro podem ter consequências gravíssimas para o conjunto. Analisaremos um caso real onde a mínima variação no projeto foi fatal para o componente e suas conseqüências, catastróficas para o motor. Para a determinação da causa raiz e consequentemente a solução do problema, foi utilizada a metodologia ¿Six Sigma¿. / Abstract: This project has been started as a consequence of repeated failures reported by users of a family of diesel engines introduced in the Brazilian market. The reported imperfections were investigated and in all cases a failure of the engine sleeve could be observed as the main cause of the engines breakdown. Cracks propagations have been in the region of the flange of cylinder sleeves. As the cracks propagate at the inner region of the flanged of the sleeve, where high stresses can be anticipated, a rupture of the flange, separating this part from the sleeve, used to occur. This occurrence is vulgarly named as the "decapitation of the sleeve". As a consequence of this phenomenon, the sleeve descends to the lower part of the engine block crashing against the moving parts of the engine, causing a complete collapse of the internal parts of the engine. The present work reports all phases of the investigation which revealed the main cause of the failures. In order to accomplish this research, the "Six Sigma" method has been employed as a supporting methodology. / Mestrado / Dinâmica / Mestre em Engenharia Automobilistica

The topic area of this bachelor’s thesis is mechatronics. The thesis explores how grip strength can be increased through the use of an exoskeleton. This was done by making an exoskeleton that was powered by pneumatics. This thesis features the design and construction process of making a pneumatic exoskeleton. This includes research, methods and results of the project. The requirements for the exoskeleton was to increase grip strength and make the device safe to use. Both of these requirements were achieved. After completing the project it was also apparent that geometry and the layout of exoskeletons are important as this directly impacts the transfer of forces. It was also found that having a weight distribution that takes advantage of stronger body parts is important to make the use of the exoskeleton comfortable. However this prototype was also limited in the range of motion and was somewhat unreliable. / Ämnesområdet för denna kandidatuppsats är mekatronik. Avhandlingen undersöker hur greppstyrkan kan ökas genom användning av ett exoskelett. Detta gjordes genom att tillverka ett exoskelett som drevs av pneumatik. Denna avhandling beskriver design- och konstruktionsprocessen för att tillverka ett pneumatiskt exoskelett. Detta inkluderar forskning, metoder och resultat av projektet. Kraven på exoskelettet var att öka grepp styrkanoch göra exoskelettet säker att använda. Båda dessa krav uppfylldes. Efter att ha avslutat projektet var det uppenbart att geometrin och utformningen av exoskelett är en viktig del eftersom detta direkt påverkar kraftöverföring. Man fann också att det är viktigt att ha en viktfördelning som drar fördel av starkare kroppsdelar för att göra användningen av exoskelettet bekväm. Men denna prototyp var också begränsad i rörelseomfånget och varopålitlig.