Made available in DSpace on 2014-10-09T12:51:53Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:43Z (GMT). No. of bitstreams: 0 / Vazamentos em tubos pressurizados geram ondas acústicas que se propagam através das paredes destes tubos, as quais podem ser captadas por acelerômetros ou por sensores de emissão acústica. O conhecimento de como estas paredes podem vibrar, ou de outro modo como as ondas acústicas se propagam neste meio, é fundamental em um processo de detecção e localização da fonte de vazamento. Neste trabalho, foi implementado um modelo analítico, através das equações de movimento da casca cilíndrica, com o objetivo de entender o comportamento da superfície do tubo em função de uma excitação pontual. Como a superfície cilíndrica é um meio fechado na direção circunferencial, ondas que iniciaram sua jornada, a partir de uma fonte pontual sobre a superfície, se encontrarão com outras que já completaram a volta na casca cilíndrica, tanto no sentido horário como no anti-horário, gerando interferências construtivas e destrutivas. Após um tempo suficiente, uma estacionariedade é atingida, criando pontos de picos e vales na superfície da casca, os quais podem ser visualizadas através de uma representação gráfica do modelo analítico criado. Os resultados teóricos foram comprovados através de medidas realizadas em uma bancada de testes composta de um tubo de aço terminado em caixa de areia, simulando a condição de tubo infinito. Para proceder à localização da fonte pontual sobre a superfície, adotou-se o processo de solução inversa, ou seja, conhecidos os sinais dos sensores dispostos na superfície do tubo, determina-se através do modelo teórico onde a fonte que gerou estes sinais pode estar. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

[pt] Este trabalho analisa o efeito das estruturas de suporte do sub-refletor das antenas Cassegrain através da teoria de espalhamento por cilindros. São desenvolvidas expressões das densidades de correntes superficiais sobre cilindros de seção transversal qualquer e obtidas as componentes de campo espalhado. Com esses resultados analisa-se então o efeito que os estais provocam na redução do ganho e no aumento dos lobos secundários. Os resultados finais obtidos são então comparados com outras teorias aproximadas. / [en] This work presents a study on the effect of subreflector support members of Cassegrain antennas using the theory of scattering by cylinders structures. Expressions for the surface current densities on arbitrary cross section cylinders are developed, and the components for the scattered field are obtained. Using these results we analyse the effect of the struts on the gain reduction, and the rise of maximum side-lobe level. The final results aobtained are then compared to other approximate theories.

This work deals with the determination of the heat transfer coefficient in small channels with a rotating wall. The research part of the thesis is focused on specific geometry, namely labyrinth seals used in rotary machines. Existing criteria equations determining heat transfer coefficients and other parameters in these specific geometries are described. The central part describes the built experimental device for the determination of values of heat flows and heat transfer coefficients on both stator and rotor for given airflow and rotor speed. The following section is devoted to presenting the results of the performed experiments with the corresponding criteria equations. The next part describes the basic mathematical models of inverse heat conduction problems. Calculations of heat flux using these inverse methods are performed and compared with reference heat flux sensors.

The aim of this master´s thesis was the design of a small hydraulic press for bio-briquettes according to predetermined parameters. The theoretical part presents the current situation in terms of biomass processing, briquette production and a description of briquetting presses. The practical part deals with solutions and detailed structural design of the selected alternatives. Models and drawings were created in the SolidWorks 2011.

This thesis deals with the velocity distribution in space between the cylinders. All measurement conducted in labs of VUT Brno Faculty of Civil Engineering. Cause of measurement is research, which is being done by Masarykova unverzita within the thesis of one of the students. It is a research of behavior of certain animals in the aquatic enviroment.

A new invention has been developed by CorPower Ocean; a mechanical rack and pinion solution called a cascade gearbox. The primary function of the gearbox is transforming a linear motion into a rotational motion. The novelty is its unique properties; it is capable of combining heavy loads and high velocities, and at a high efficiency. CorPower Ocean is aiming at finding applications where the gearbox’s unique properties can be of use. If the gearbox is combined with a motor it forms an electromechanical actuator. Therefore, an investigation of applications using actuators has been targeted. More specifically, the master thesis assignment was to examine in which applications the transition of a cascade electromechanical actuator was technically viable. Research questions that derived was to answer if an implementation of an cascade electromechanical cylinder is technically feasible and if it implicates improved results regarding environmental related goals. The methodology executed to finalize the project included several stages. The first stage was the background study which consisted of reviewing trends and gathering technical data for case studies of targeted applications. The targeted applications were heavy lifting equipment and injection molding machines. With the help of CorPower software, gearbox dimensioning examples were drafted and could be evaluated from a size and weight perspective. To further evaluate potential applications, interviews were conducted with targeted equipment manufacturers. The selection of applications was completed by evaluating the interview responses and the drafted gearbox examples. Chosen applications were ultimately a nine tonnes forklift and an empty container handler, mainly due to good customer response, integration ability and potential of performance enhancement. An optimisation was performed to achieve a concept solution that satisfied customer needs such as low cost and a slim design. In order review the business cases in each application, energy savings and performance cases were conducted, benchmarking against the hydraulic solution. In the ECH case, the energy saved was 54% and the productivity increased with 9.6%. In the forklift case, the energy saved was 52% and the productivity increased with 1%. Both of applications have great potential of a transition from hydraulic cylinders to electromechanical cylinders in terms of implementation and technical feasibility. The final concept solutions exceeded the hydraulics in performance, retaining a slim and acceptable size and design. Furthermore, this sector of heavy lifting equipment had high potential for electrification which can contribute to reduced emissions and fuel savings. Keywords: electromechanical cylinders, concept development, cascade gearbox / En ny innovation har utvecklats av CorPower Ocean; en mekanisk rack och pinjonglösning kallad kaskadväxel. Dess primära funktion är att transformera en linjär rörelse till en roterande rörelse och vice versa. Nyhetsvärdet är växellådans unika prestanda; den kan hantera kombinationen av höga laster och höga hastigheter till en hög verkningsgrad. Nu önskar CorPower Ocean att hitta applikationer där kaskadväxelns unika prestanda kommer till användning. Om kaskadväxeln kombineras med en motor bildas en elektromekanisk aktuator, och därför har en utredning av applikationer som använder aktuatorer utsetts som en marknad att undersöka närmare. Mer specifikt var examensuppdraget att undersöka i vilka applikationer en sådan övergång skulle vara genomförbar ur ett tekniskt perspektiv. Forskningsfrågor som önskades besvaras var huruvida en sådan övergång är genomförbar ur ett tekniskt perspektiv och om en sådan implementation innebär förbättringar vad gäller miljörelaterade mål. Metodologin som användes för att slutföra projektet utgjordes av flera steg. Första steget var att genomföra en bakgrundsstudie om elektrifiering och produkttrender samt samla teknisk data på utsedda applikationer. De utsedda övergångsområdena var maskiner för tunga lyft samt plastformssprutningsmaskiner. Med CorPowers mjukvara kunde dimensioneringsexempel göras för kaskadväxellådor och utvärderas utifrån sin storlek och vikt. För en fortsatt utvärdering av applikationer genomfördes intervjuer med tillverkare av de utsedda applikationerna. Val av applikationer slutfördes genom att utvärdera svar från målkunder samt dimensioneringsexempel av växellådorna. De valda applikationerna blev slutligen en nio tons gaffeltruck och en tomcontainertruck. Valet baserades huvudsakligen på bra respons från kunder, bra integrationsmöjligheter samt potentiella prestandaförbättringar. Fokus låg på att byta ut lyftcylindrarna och bortse från övriga mindre cylindrar. Lösningarna optimerades för att matcha kundkrav så som kostnad och passform. Ett energibesparingscase utfördes för att jämföra kaskadlösningen med nuvarande hydrauliska lösning. I tomcontainertruckens fall sänktes energiförbrukningen med 54 % och produktiviteten ökade med 9.6%. I gaffeltruckens fall sjönk energiförbrukningen med 52 % och produktiviteten ökade med 1 %. Båda applikationerna uppvisade stor potential för ett byte från hydraulcylindrar till elektromekaniska cylindrar. De slutgiltiga koncepten överträffade hydraulikens prestanda medan de bibehöll en acceptabel storlek. Vidare fanns det en stor potential inom lyftindustrin att genom elektrifiering kunna minska utsläpp och bränsleförbrukning. Nyckelord: elektromekanisk cylinder, konceptutveckling, kaskadväxel

The demand for using shell theories comes from its efficiency in computational and analytical cost. On another side, new materials that are orthotropic and/or anisotropic in nature are discovered and broadly used in many fields. Many advanced shell theories are developed for these new materials, particularly in the recent decades. A study about the accuracy of these shell theories is very meaningful to build confidence in them for further applications. This study requires a precise benchmark against which shell theories can be tested. This is the main research subjective in this dissertation: to build a set of solutions using the three dimensional (3D) theory of elasticity against which shell theories can be tested for accuracy. The contents of this dissertation to support this research include a comprehensive literature review for the shell theories and recent usage and to find the gaps which need to be filled. These gaps include, among others, the lack of studies on the accuracy of the theories used and the absence of results using the 3D theory, particularly for orthotropic materials. Some of these studies are conducted here. The deficiency of some commercial finite element packages is discussed here. The reasons for the absence of accurate results are investigated. The 3D theory and analyses of isotropic and orthotropic materials of hollow cylinders is investigated here for reliable results.

Boundary conditions for the cable equation - such as voltage-clamped or sealed cable ends, branchpoints, somatic shunts, and current clamps - result in multi-exponential series representations of the voltage or current. Each term in the series expansion is characterized by a decay rate (eigenvalue) and an initial amplitude (Fourier coefficient). The eigenvalues are determined numerically and the Fourier coefficients are subsequently given by the residues at the eigenvalues of the Laplace transform of the solution. In this paper, we introduce an alternative method for estimating the Fourier coefficients which works for all types of boundary conditions and is practical even when analytic expressions for the Fourier coefficients become intractable. It is shown that terms in the analytic expressions for the Fourier coefficients result from derivatives of the equation for the eigenvalues, and that simple numerical estimates for the amplitude coefficients are easily derived by replacing analytical derivatives by numerical eigenslope. The physical quantity represented by the slope is identified as effective neuron capacitance.

Thesis: Sc. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 1980 / Includes bibliographical references. / by Afarin Ordubadi. / Sc. D. / Sc. D. Massachusetts Institute of Technology, Department of Mechanical Engineering

The response of elliptical composite cylindrical shells under torsion is studied. The torsional condition is developed by rotating one end of the cylinder relative to the other. Prebuckling, buckling, and postbuckling responses are examined, and material failure is considered. Four elliptical cross sections, defined by their aspect ratio, the ratio of minor to major radii, are considered: 1.00 (circular), 0.85, 0.70, and 0.55. Two overall cylinder sizes are studied; a small size with a radius and length for the circular cylinder of 4.28 in. and 12.85 in., respectively, and a large size with radii and lengths five times larger, and thicknesses two times larger than the small cylinders. The radii of the elliptical cylinders are determined so the circumference is the same for all cylinders of a given size. For each elliptical cylinder, two lengths are considered. One length is equal to the length of the circular cylinder, and the other length has a sensitivity of the buckling twist to changes in the length-to-radius ratio the same as the circular cylinder. A quasi-isotropic lamination sequence of a medium-modulus graphite-epoxy composite material is assumed. The STAGS finite element code is used to obtain numerical results. The geometrically-nonlinear static and transient, eigenvalue, and progressive failure analysis options in the code are employed. Generally, the buckling twist and resulting torque decrease with decreasing aspect ratio. Due to material anisotropy, the buckling values are generally smaller for a negative twist than a positive twist. Relative to the buckling torque, cylinders with aspect ratios of 1.00 and 0.85 show little or no increase in capacity in the postbuckling range, while cylinders with aspect ratios of 0.70 and 0.55 show an increase. Postbuckling shapes are characterized by wave-like deformations, with ridges and valleys forming a helical pattern due to the nature of loading. The amplitudes of the deformations are dependent on cross-sectional geometry. Some elliptical cylinders develop wave-like deformations prior to buckling. Instabilities in the postbuckling range result in shape changes and loss of torque capacity. Material failure occurs on ridges and in valleys. Cylinder size and cross-sectional geometry influence the initiation and progression of failure. / Ph. D.