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Dissertations / Theses on the topic 'Circular Beams'
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1
Babamohammadi, Sajjad. "Mechanical Assessment of Fiber Reinforced Composite Hollow Circular Beams." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
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This thesis presents a study on fiber reinforced hollow beams. The theoretical background is based on published works and some extensions to the present researches.
For some, simple, cases exact solutions are made available, however hollow composite beams have to be studied using 3D modeling in order to capture their actual anisotropic behavior.
At first, we start to investigate if we have enough information to successfully design a structure using FRP materials. Then after studying some published works in this field, we understood that there is a lack of some important details.
We tried to fill this void by first understanding the behavior of FRP beams and prepare a fast and easy way for engineers to use these composite beams and design structures. To do that, we used existing analytical methods. Although analytical, these methods are limited for studying fiber reinforced beams.
Thus, a new approach is here presented based on an equivalent 3D shell model which is used to defined a 3D finite element beam element for frame structural analysis.
This approach is simple and clearly considers the anisotropy inherited in such profiles.
Applications of this procedure are given which show the quality of the present results and the advantages of using composite beams with respect to classical steel beams in civil applications.
2
Lumpp, Dirk Manfred. "An experimental investigation of circular plates, beams and stiffened circular plates subjected to impulsive loading." Master's thesis, University of Cape Town, 1991. http://hdl.handle.net/11427/9658.
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Bibliography: leaves 94-96.This primarily experimental investigation describes a series of experiments on fully-clamped circular plates, rectangular beams and stiffened circular plates. These test specimens were subjected to a uniformly distributed impulse. The impulse was provided by plastic explosive. This was arranged in such a way that a uniformly distributed impulse was imparted to the test specimens. The impulse was measured by means of a ballistic pendulum to which the test specimens were attached. The final mid-point deflections of the plates and beams were measured. The plate and beam results were compared to previous experimental work. A non-dimensional number for plates was modified to include an experimental mass scaling factor due to the ballistic pendulum mass. A non-dimensional number for rectangular beams was developed, including a similar experimental mass scaling factor. Comparing the beam and plate results from this study with those of previous work, using the respective non-dimensional numbers, showed good correlation. The results for the stiffened plates are compared with the plate results.
3
Muluh, Esau Ticha. "Analysis of deformation and tearing of uniformly blast-loaded circular and square plates rectangular beams and T-beams." Master's thesis, University of Cape Town, 2001. http://hdl.handle.net/11427/5500.
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Includes bibliography.This investigation examines the failure of circular and square mild steel plates, aluminium rectangular beams and T-beams subjected to impulsive loads. The objective of this investigation is to numerically determine the dynamic response of circular and square plates, rectangular beams and T-beams clamped and built-in (integral) at the boundary subjected to uniform blast loading; use material properties that include and exclude temperature dependency to model the plates and beams response and failure and finally to compare the numerical results with experimental results.
4
Lawry, James Milson Hassall. "Complex ray theory." Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389022.
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Zhao, H., R. Wang, Dennis Lam, C.-C. Hou, and R. Zhang. "Behaviours of circular CFDST with stainless steel external tube: Slender columns and beams." Elsevier, 2020. http://hdl.handle.net/10454/18141.
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NoIn this work, experimental and numerical investigations were performed on the behaviours of circular concrete filled double steel tubular (CFDST) slender columns and beams, in which the external tube employed stainless steel tube. Eighteen specimens, 12 slender columns and 6 beams, were tested to obtain the failure patterns, load versus deflection relationships and strain developments of stainless steel tube. A finite element (FE) model was developed and verified by experimental results. The validated FE model was then employed to investigate the effects of key parameters, including hollow ratio, eccentric ratio and material strength, on the load-carrying capacity. The load distribution among the components and contact stress between steel tube and sandwiched concrete were also analyzed. Finally, the design methods for CFDST, hollow CFST and solid CFST members with carbon steel external tube respectively suggested by Han et al. (2018), Chinese GB 50936-2014 (2014) and AISC 360-16 (2016) were employed to evaluate their applicability for the circular CFDST slender columns and beams with stainless steel outer tube.
The authors gratefully acknowledge the Shanxi Province Outstanding Youth Fund (No. 201701D211006) and the National Natural Science Foundation (No. 51838008).
The full-text of this article will be released for public view at the end of the publisher embargo on 9th Nov 2021.
6
Too, Gee-Pinn James. "Analytical and numerical approaches for finite amplitude sound beams radiated from a circular baffled piston." Diss., Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/16917.
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Alameer, Maryam. "Polarization Dependent Ablation of Diamond with Gaussian and Orbital Angular Momentum Laser Beams." Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/39850.
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The vectorial nature (polarization) of light plays a significant role in light-matter interaction
that leads to a variety of optical devices. The polarization property of light
has been exploited in imaging, metrology, data storage, optical communication and
also extended to biological studies. Most of the past studies fully explored and dealt
with the conventional polarization state of light that has spatially symmetric electrical
field geometry such as linear and circular polarization. Recently, researchers
have been attracted to light whose electric field vector varies in space, the so-called
optical vector vortex beam (VVB). Such light is expected to further enhance and
improve the efficiency of optical systems. For instance, a radially polarized light
under focusing condition is capable of a tighter focus more than the general optical
beams with a uniform polarization structure, which improves the resolution of the
imaging system [1].
Interaction of ultrafast laser pulses with matter leads to numerous applications
in material processing and biology for imaging and generation of microfluidic systems.
A femtosecond pulse, with very high intensities of (10^{12} - 10^{13} W/cm^2), has
the potential to trigger a phenomenon of optical breakdown at the surface and therefore
induce permanent material modification. With such high intensities and taking
into account the fact that most materials possess large bandgap, the interaction is
completely nonlinear in nature, and the target material can be modified locally upon the surface and even further in bulk. The phenomenon of optical breakdown can be
further investigated by studying the nonlinear absorption. Properties like very short
pulse duration and the high irradiance of ultrashort laser pulse lead to more precise
results during the laser ablation process over the long pulsed laser. The duration of
femtosecond laser pulse provides a high resolution for material processing because
of the significant low heat-affected zone (HAZ) beyond the desired interaction spot
generated upon irradiating the material. Under certain condition, the interaction
of intense ultrashort light pulses with the material gives rise to the generation of
periodic surface structures with a sub-micron periodicity, i.e., much smaller than the
laser wavelength. The self-oriented periodic surface structures generated by irradiating
the material with multiple femtosecond laser pulses results in improving the
functionality of the material's surface such as controlling wettability, improving thin
film adhesion, and minimizing friction losses in automobile engines, consequently,
influences positively on many implementations.
In this work, we introduced a new method to study complex polarization states
of light by imprinting them on a solid surface in the form of periodic nano-structures.
Micro/Nanostructuring of diamond by ultrafast pulses is of extreme importance because
of its potential applications in photonics and other related fields.
We investigated periodic surface structures usually known as laser-induced periodic surface
structures (LIPSS) formed by Gaussian beam as well as with structured light carrying
orbital angular momentum (OAM), generated by a birefringent optical device
called a q-plate (QP). We generated conventional nano-structures on diamond
surface using linearly and circularly polarized Gaussian lights at different number
of pulses and variable pulse energies. In addition, imprinting the complex polarization state of different orders of optical vector vortex beams on a solid surface was fulfilled in the form of periodic structures oriented parallel to the local electric field of optical light. We also produced a variety of unconventional surface structures by superimposing a Gaussian beam with a vector vortex beam or by superposition of different order vector vortex beams.
This thesis is divided into five chapters, giving a brief description about laser-matter
interaction, underlying the unique characterization of femtosecond laser over
the longer pulse laser and mechanisms of material ablation under the irradiation of
fs laser pulse. This chapter also presents some earlier studies reported in formation
of (LIPSS) fabricated on diamond with Gaussian. The second chapter explains the
properties of twisted light possessing orbital angular momentum in its wavefront, a
few techniques used for OAM generation including a full explanation of the q-plate
from the fabrication to the function of the q-plate, and the tool utilized to represent
the polarization state of light (SoP), a Poincar'e sphere. Finally, the experimental details and results are discussed in the third and fourth chapters, respectively,
following with a conclusion chapter that briefly summarizes the thesis and some
potential application of our findings.
8
Fariborz, Jamshid. "Free Vibration of Bi-directional Functionally Graded Material Circular Beams using Shear Deformation Theory employing Logarithmic Function of Radius." Thesis, Virginia Tech, 2018. http://hdl.handle.net/10919/85107.
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Curved beams such as arches find ubiquitous applications in civil, mechanical and aerospace engineering, e.g., stiffened floors, fuselage, railway compartments, and wind turbine blades. The analysis of free vibrations of curved structures plays a critical role in their design to avoid transient loads with dominant frequencies close to their natural frequencies.
One way to increase their areas of applications and possibly make them lighter without sacrificing strength is to make them of Functionally Graded Materials (FGMs) that are composites with continuously varying material properties in one or more directions.
In this thesis, we study free vibrations of FGM circular beams by using a logarithmic shear deformation theory that incorporates through-the-thickness logarithmic variation of the circumferential displacement, and does not require a shear correction factor. The radial displacement of a point is assumed to depend only upon its angular position. Thus the beam theory can be regarded as a generalization of the Timoshenko beam theory. Equations governing transient deformations of the beam are derived by using Hamilton's principle. Assuming a time harmonic variation of the displacements, and by utilizing the generalized differential quadrature method (GDQM) the free vibration problem is reduced to solving an algebraic eigenvalue problem whose solution provides frequencies and the corresponding mode shapes. Results are presented for different spatial variations of the material properties, boundary conditions, and the aspect ratio. It is found that the radial and the circumferential gradation of material properties maintains their natural frequency within that of the homogeneous beam comprised of a constituent of the FGM beam. Furthermore, keeping every other variable fixed, the change in the beam opening angle results in very close frequencies of the first two modes of vibration, a phenomenon usually called mode transition.Master of Science
Curved and straight beams of various cross-sections are one of the simplest and most fundamental structural elements that have been extensively studied because of their ubiquitous applications in civil, mechanical, biomedical and aerospace engineering. Many attempts have been made to enhance their material properties and designs for applications in harsh environments and reduce weight. One way of accomplishing this is to combine layerwise two or more distinct materials and take advantage of their directional properties. It results in a lightweight structure having overall specific strength superior to that of its constituents. Another possibility is to have volume fractions of two or more constituents gradually vary throughout the structure for enhancing its performance under anticipated applications. Functionally graded materials (FGMs) are a class of composites whose properties gradually vary along one or more space directions. In this thesis, we have numerically studied free vibrations of FGM circular beams to enhance their application domain and possibly use them for energy harvesting.
9
Wellburn, Daniel. "Circular laser beam intensity profile shaping for uniform surface treatments." Thesis, University of Liverpool, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.533912.
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Montanari, Carlo Emilio. "Diffusive approach for non-linear beam dynamics in a circular accelerator." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/19289/.
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Nella fase di design e simulazione di un acceleratore circolare, risulta fondamentale avere una buona comprensione del moto betatronico non-lineare delle singole particelle, e di come questo interferisce con la qualità del fascio.
In questo lavoro vengono studiati sistemi Hamiltoniani sottoposti a perturbazioni stocastiche tramite un framework diffusivo, basato sull'equazione di Fokker-Planck. Tale studio viene poi applicato all'analisi del moto betatronico non-lineare e al problema dell'Apertura Dinamica.
In particolare, vengono impostate le basi per formulare un metodo di interpolazione di processi diffusivi simil-Nekhoroshev e viene proposta una procedura sperimentale per misurare gli effetti di diffusione locale all'interno di un acceleratore.
L'Apertura Dinamica è una quantità chiave per il comportamento a lungo termine di un acceleratore, tuttavia, la misura di questa quantità nelle simulazioni presenta serie difficoltà dal punto di vista computazionale. È dunque nel nostro interesse riuscire a formulare una legge che descriva la dipendenza dal tempo dell'Apertura Dinamica.
11
Alfawakhiri, Farid. "Behavior of high strength concrete filled circular steel tube beam-columns." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/mq26298.pdf.
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Zhu, Lei. "Circular reconstruction and scatter correction in X-ray cone-beam CT /." May be available electronically:, 2007. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
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Warsop, C. M. "Special diagnostic methods and beam loss control on high intensity proton synchrotrons and storage rings." Thesis, University of Sheffield, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251194.
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Penner, Robert Scott. "Focusing, wavelength tuning, beam steering and beam shaping of circular grating surface emitting distributed Bragg reflector lasers." Diss., The University of Arizona, 1999. http://hdl.handle.net/10150/284042.
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Over the past decade, circular grating surface emitting DBR lasers (CGSELs) have progressed from theory to reality. These devices possess several properties that make them attractive options for such applications as optical interconnects and laser arrays. These advantages include low divergence angles, circular beam profiles, and high power output. In this dissertation, the addition of new functionality to these lasers including wavelength tunability, focusing, beam steering and beam shaping is investigated. The theory governing device operation is presented. Pertinent discussions include the coupled mode equations, grating coupling, focusing and changes to the effective index of refraction resulting from current injection through a transparent electrode on the grating. The development and refinement of the device fabrication process is detailed. Key milestones in the grating writing process included achieving first order gratings (Λ = 0.15 μm), creating chirped period gratings for focusing and optimizing the linewidth and uniformity of the grating for high power devices. Of equal importance in obtaining high efficiency devices was the reactive ion etch process. Two different etch recipes were developed: one for mesa-definition and a shallower grating-defining etch. Significant evaluation of the electrical and optical properties of the transparent electrode, Indium Tin Oxide, was performed. Incorporating ITO into the fabrication process required optimization of deposition, patterning, etching and annealing. Device performance, efficiency and functionality improved with each generation. Consequentially, over 225 mW of output power for a injection current of 600 mA, or a slope efficiency of 0.43 mW/mA, was produced by the final generation of high power CGSELs. Focusing was demonstrated by the creation of individual devices with different focal lengths. Coarse mode selection was obtained by removing radial segments of the circular grating thereby eliminating both feedback coupling and surface outcoupling. Dynamic functionality such as beam steering and wavelength tuning was also realized for devices with ITO. Over 1° of beam steering was achieved for an ITO injection current of 35 mA. Similarly, over 1 nm of tuning, or 0.5 nm of continuous tuning, was accomplished. In conclusion, possibilities for improvements in device performance and future work are suggested.
15
Allayioti, Marion. "Beam reconfigurable microstrip antennas based on parasitics with linear and circular polarisation capability." Thesis, University of Surrey, 2018. http://epubs.surrey.ac.uk/847002/.
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Millimetre wave beam and polarization reconfigurable antennas for future wireless communications are investigated in this thesis. The millimetre wave frequency spectrum has recently attracted large attention from researchers and the industry of wireless communications. Millimetre wave frequencies is considered to be the frequency spectrum between 30 GHz and 300 GHz. However, the industry considers the spectrum above 10 GHz as millimetre wave, due to the fact that it shows similar propagation characteristics with the spectrum above 30 GHz. The aforementioned spectrum of frequencies offers a lot of advantages compared to lower frequency spectrum, due to the fact that it offers large and mostly unexploited bandwidths. The need for very high data rates, in future wireless communications, increases the need for bandwidth. Millimetre wave frequencies can be used to fulfill future bandwidth demands. Although millimeter wave frequencies offer several advantages and good potential for future wireless communications, they also impose several challenges. This thesis discusses the need for highly directive and beam reconfigurable antennas for such high frequencies. It also discusses how an antenna design can benefit from being circularly polarised for several wireless communication applications and how antennas for future wireless communications must be able to reconfigure several parameters, without compromising the performance, cost and size, giving the exibility to a wireless terminal to operate in several different modes. This thesis proposes novel reconfigurable antennas for portable devices, which can be used at millimetre wave frequencies, and which offer high gain, wide steering range, low scan loss and multi-parameter reconfigurability; essential characteristics that antennas designed for future wireless communications should offer.
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Bellafont, Peralta Ignasi. "Study of the beam induced vacuum effects in the cryogenic beam vacuum chamber of the Future Circular Hadron Collider." Doctoral thesis, Universitat Politècnica de Catalunya, 2021. http://hdl.handle.net/10803/671476.
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The Future Circular Hadron Collider (FCC-hh) is a proposal for a 100 km long hadron collider conceived as the successor of the Large Hadron Collider (LHC). The FCC-hh is designed to reach 50 TeV of beam energy, greatly surpassing the current energy frontier set by the LHC at 7 TeV. Thus, it is expected to expand the current horizon of understanding of the Standard Model of particle physics. The beam vacuum chamber of the FCC-hh will have to cope with unprecedented levels of synchrotron radiation power for hadron colliders, around 160 times higher than its predecessor, dealing simultaneously with a tighter magnet aperture. Since the higher radiation power will result in a much higher gas load, the difficulty to achieve a good vacuum quality increases considerably compared with the LHC.
This thesis presents a study of the so-called beam induced vacuum effects in the FCC-hh, meaning the different phenomena which, due to the presence of the particle beam, have a detrimental impact on the accelerator’s vacuum level. These studied effects are the photon stimulated desorption (PSD), the electron stimulated desorption (ESD) and ion stimulated desorption (ISD). Each effect has been thoroughly studied, calculating analytically and with a series of Monte Carlo simulations the resulting gas density in the chamber for all the common gas species. Finally, the feasibility of the FCC-hh from the vacuum point of view has been assessed. To mitigate the beam induced effects and to improve the vacuum quality in the FCC-hh (essential for a proper machine operation) it was necessary to propose a new beam screen design. The new beam screen features new solutions to mitigate the e- cloud, to handle the synchrotron radiation and a much higher pumping speed, at the expense of a higher manufacturing complexity. A dedicated experimental setup was used by CERN during the design phase to measure the vacuum performance of the developed beam screen prototypes. Finally, the obtained experimental results were compared with the theoretical results to further enhance their validity.
It is concluded that thanks to the new beam screen design, the vacuum level in the FCC-hh should be adequate. Using nominal beam parameters, the established FCC-hh vacuum specifications could be met within the first months of conditioning, a reasonable amount of time.El Futuro Colisionador Circular de Hadrones (FCC-hh) es un colisionador de hadrones de 100 km de longitud, propuesto como sucesor del Gran Colisionador de Hadrones (LHC). El FCC-hh está diseñado para alcanzar 50 TeV de energía de haz, superando notoriamente la frontera de energía actual establecida por el LHC, 7 TeV. De esta manera, se espera expandir las fronteras de conocimiento actuales del Modelo Estándar de la física de partículas. La cámara de vacío del haz del FCC-hh deberá soportar niveles de potencia de radiación de sincrotrón sin precedente en los colisionadores de partículas, alrededor de 160 veces más altos que su predecesor, debiendo además de adaptarse a una apertura mucho más reducida. Dado que la alta potencia de radiación resulta en una mayor generación de gas en el sistema, la dificultad de alcanzar un buen nivel de vacío se incrementa considerablemente comparado con el LHC. Esta tesis presenta un estudio de los efectos de vacío inducidos por el haz de partículas en el FCC-hh, esto es, los diferentes fenómenos que, debido a la presencia del haz, tienen un impacto perjudicial en el nivel de vacío del acelerador. Los efectos estudiados son la desorción inducida por fotones (PSD), la desorción inducida por electrones (ESD) y la desorción inducida por iones (ISD). Cada efecto ha sido separadamente estudiado, calculando de manera analítica y mediante simulaciones de Monte Carlo la densidad de gas resultante en la cámara para todas las especies de gas habituales. Por último, la viabilidad del FCC-hh desde el punto de vista del vacío ha sido evaluada. Con el fin de mitigar los efectos de vacío inducidos por el haz y mejorar la calidad del vacío del FCC-hh (esencial para una correcta operación de la máquina) ha sido necesario proponer un nuevo diseño de la pantalla del haz. Este nuevo diseño presenta nuevas soluciones para mitigar la nube de electrones en la cámara, lidiar con la radiación de sincrotrón y una velocidad de bombeo mucho más alta, a expensas de una mayor complejidad en su fabricación. Además, un equipo experimental ha sido usado por el CERN durante para medir el rendimiento en vacío de los prototipos de pantalla de haz construidos. Los resultados experimentales obtenidos han sido finalmente comparados con los resultados teóricos para incrementar su fiabilidad. Se concluye que, gracias al nuevo diseño de la pantalla del haz, el nivel de vacío del FCC-hh será adecuado, alcanzando las especificaciones de vacío establecidas con parámetros de haz nominales dentro de los primeros meses de condicionamiento.
Enginyeria mecànica, fluids i aeronàutica
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Lam, Dennis, Jie Yang, Yong Wang, Xianghe Dai, Therese Sheehan, and Kan Zhou. "New composite flooring system for the circular economy." Techno-Press, 2021. http://hdl.handle.net/10454/18598.
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NoCircular economy is an economic system aimed at minimizing wastes and making the most of the current resources. This regenerative approach contrasts with the traditional linear economy, which has been adopted by the construction industry. Developing new construction technologies for sustainable built environment is a top priority for the construction industry throughout the world. Much of the environmental impact from the construction industry is associated with the consumption of resources and generation of waste. The construction industry in Europe consumes over 70,000 million tonnes of materials each year and generates over 250 million tonnes of waste. Composite flooring formed by connecting the concrete slabs to the supporting steel beams has been widely used for many years and is well established as one of the most efficient floor systems in multi storey steel frame building structures. However, shear connectors are welded through the steel decking to the steel beams and cast into the concrete; this made deconstruction and reuse of these components almost impossible. A new composite flooring system which allows for the reuse of the steel beams and composite floor slabs is developed and tested to assess its potential and suitability for reuse. This paper presents the results of a series of full scale beam tests and demonstrates the reusability of this new form of composite flooring systems. Simplified hand calculations are also provided and compared against beam tests
EPSRC, Structural Metal Deck Ltd.
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Freitas, Pedro César de Barros. "Análise numérica de ligações metálicas viga-coluna com coluna tubular circular." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/18/18134/tde-04082009-144346/.
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As estruturas tubulares, muitas vezes, têm sua aplicação restrita a construções onde a concepção arquitetônica determina o seu uso, no entanto há algumas vantagens do ponto de vista estrutural que podem justificar a sua aplicação. A reduzida área exposta ao fogo e aos ambientes agressivos, boa resistência a compressão axial com baixa tendência ao desenvolvimento de instabilidades localizadas, são algumas das vantagens da utilização destas estruturas. O objetivo principal deste trabalho é analisar numericamente o comportamento da ligação entre viga de seção I com coluna tubular circular, para tanto são consideradas configurações usuais de ligação com anéis externos transversais e chapa de alma. É ainda objetivo trazer um panorama das estruturas tubulares em geral, com o desenvolvimento histórico das pesquisas, e principalmente estabelecer uma compilação dos procedimentos analíticos de cálculo e classificação apresentados pelas normas Eurocode 3 e ANSI/AISC. A análise numérica foi realizada por meio dos pacotes comerciais TRUEGRID® e ANSYS®, os quais aplicam o método dos elementos finitos. Foram empregados modelos que consideram as características mecânicas do aço, como plastificação e encruamento, e ainda as não-linearidades geométricas e de contato. Os resultados numéricos apresentaram coerência razoável com os modelos analíticos normativos. Foi possível o conhecimento do comportamento M-\'fi\' (momento-rotação) das ligações, bem como a determinação dos parâmetros que caracterizam tal relação, como resistência, rigidez inicial e ductilidade. Os estudos comprovaram a eficácia dos anéis externos na distribuição dos esforços oriundos do engastamento parcial da viga, fazendo com que a coluna não seja comprometida.The application of tubular structures is usually restricted to constructions on which the architectural conception demands them. However, there are also several structural advantages which justify their usage, such as a) reduced exposed area concerning fire and agressive environments; b) high axial compression resistance; c) high local buckling resistance. The aim of this work is the numerical analysis on the behavior of the I beam-circular hollow column connection, usually constituted by an external ring with single plate. It is presented a general view about the researchers development over the years on tubular structures focusing the compilation of the analytical design procedures and Eurocode 3 and ANSI/AISC classification as well. Finite element method softwares TRUEGRID and ANSYS are used for the numerical analysis in order to consider steel mechanical properties such as yielding, hardening and also geometric and contact nonlinearities. Numerical results present good agreement to codes\' analytical models. Analysis lead to understanding the connection\'s moment-rotation behavior and some of its parameters such as resistance, initial stiffness and ductility. It is shown external rings significantlly improve the semi-rigid connections stress distribution at the columns face.
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Khador, Majd. "Cyclic behaviour of external diaphragm joint between steel I-section beam and circular hollow section column." Thesis, University of Warwick, 2015. http://wrap.warwick.ac.uk/66903/.
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Tubular columns own many structural and architectural advantages that, in certain cases, make them more favourable than open-section columns in steel moment-resisting frames. These advantages are sometimes underexploited due to the relative lack of design guidance on their moment joints to open-section beams, in particular on semi-rigid joints with special detailing for seismic actions. Different configurations of I-beam to tubular column joints have been investigated in the past, including through, internal and external diaphragm joints. This project investigates experimentally the cyclic behaviour of an external diaphragm joint between a steel I-beam and a circular hollow section column. The proposed joint includes two diaphragm plates (DPs) welded to the outer circumference of the column and bolted to the I-beam flanges with two tapered cover plates (TCPs). A web stub is welded to the column face and bolted to the I-beam web. Full-scale laboratory experiments were conducted to investigate the hysteretic response and energy dissipative performance of the proposed joint under cyclic loading. TCPs were integrated in the joint to act as replaceable sacrificial components that dissipate most of the energy whilst the rest of the joint components remain elastic to minimise the post-seismic repair. The test specimens were identical except their TCPs that had the same geometry but differed in steel grade, size of bolt-holes, use of stiffeners or bolt preloading force. The use of higher grades of steel for the TCPs and stiffening them imposed higher strain demands in the beam and DPs and dissipated less energy than the joints with lower grades and unstiffened TCPs, respectively. The results confirmed that the main energy dissipation fuse in these joints was yielding in the TCPs while the other components remained elastic. Connection slippage created a second fuse for energy dissipation when the bolt preloading force was properly controlled, and the rotation of the plastic hinge region exceeded the minimum threshold of 25mrad for medium ductility class structures.
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Siblini, Ali. "Optimisation des antennes MARPEM (Matrice agile rayonnantes à pixel élaborés en Meta‐matériaux) par l’utilisation de formes d’ondes spécifique." Thesis, Limoges, 2017. http://www.theses.fr/2017LIMO0061/document.
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Cette thèse est basée sur un brevet réalisé chez XLIM Systèmes RF. La thèse précédente se concentre sur la partie théorique MARPEM et une certaine validation en polarisation linéaire. Dans cette thèse, nous avons visé à introduire le système MARPEM aux applications de polarisation circulaire en général et aux applications spatiales en particulier. Dans toute la thèse, MARPEM à polarité circulaire avec une architecture différente est réalisée avec la conception de circuits de polarisation et de diviseurs de puissance. On présente la formation de faisceau du motif Isoflux large avec le taux d'ellipticité, ainsi que des faisceaux de balayage sont réalisés pour grand azimut angles avec un bon taux d'ellipticité. Tous les résultats sont comparés à l'antenne réseau classique AESA. La fabrication de MARPEM à polarité circulaire et les circuits de polarisation et le diviseur de puissance sont effectués et les mesures correspondantes sont présentées. Ensuite, dans les perspectives, on s'attend à des défis différents dans un travail futur pour l'amélioration de système MARPEMThis thesis is based on a patent done at XLIM RF-Systems. Previous thesis focuses on the ARMA theoretical part and some validation in linear polarization. In this thesis we aimed to introduce the system ARMA to the circular polarization applications in general and to space applications especially. In the entire thesis circularly polarized ARMA with different architecture are achieved with the design of polarization circuits and power dividers. Beam forming of the wide Isoflux pattern with the axial ratio are presented, also scanning beams are achieved for far angles with good axial ratio. All the results are compared with the classical array antenna AESA. Manufacturing of circularly polarized ARMA and the polarization circuits and the power divider are done and the corresponding measurements are presented. Then in the perspectives different challenges are expected to be in a future work for enhancement of the whole ARMA system
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Pandit, Malay Kumar. "Circularly-symmetric beam propagation dynamics in linear and quadratic-nonlinear optical devices." Thesis, University of Cambridge, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627540.
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Sikora, Mark. "Recoil polarimetery in meson photoproduction reactions." Thesis, University of Edinburgh, 2011. http://hdl.handle.net/1842/5663.
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A large acceptance polarimeter has been designed to measure recoil polarisation in pseudoscalar (Jπ=0−) meson photoproduction reactions. The device was installed at the MAMI facility at the Institut für Kernphysik in Mainz, Germany. A racetrack microtron provided a longitudinally polarised 1.5 GeV electron beam, which impinged on a 12 μm copper radiator, producing a beam of circularly polarised Bremsstrahlung photons with energies between 400-1400 MeV. The electrons were then momentum analysed in the Glasgow Photon Tagging Spectrometer to tag the photon energy with a resolution of ~4 MeV. The photons were incident on a liquid hydrogen target, and the reaction products were detected using the Crystal Ball and TAPS detectors. The beam-recoil polarisation observable Cx, which describes the fraction of circular polarisation transferred from the photon beam to the recoiling nucleon, was measured in the reactions γp→pπ0 and γp→pη from data taken in September-October 2008. The results for π0 production give a significant expansion of the world data set and are shown to be consistent with the few previous measurements taken at Jefferson Lab, USA, while the results for the η channel are a world first. The observed values for Cx are compared to the current solutions from the two leading partial wave analyses, SAID and MAID, with wide angular coverage up to a photon beam energy of 1400 MeV. Significant discrepancies in the prediction of Cx can be resolved by the new data.
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Drebot, Illya. "Electron beam dynamics with and without Compton back scattering." Phd thesis, Université Paris Sud - Paris XI, 2013. http://tel.archives-ouvertes.fr/tel-00920424.
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This thesis introduce my work on transverse and longitudinal non linear dynamics of an electron beam in ThomX, a novel X-ray source based on Compton backscattering. In this work I implemented in simulation code theoretical models to calculate transverse and longitudinal non linear dynamics under Compton back scattering. The processes studied include collective effect such as longitudinal space charge, resistive wall and coherent synchrotron radiation, intra beam scattering. I also implemented a longitudinal feedback algorithm and studied the effect of the feedback's delay in the simulation to explore its effects on beam dynamics. This code allows to perform a full 6D simulation of the beam dynamics in a ring under Compton back scattering taking into account the feedback stabilisation for the 400 000 turns (~ 20 ms) of one injection cycle. One important feature is that this simulation code can be run on a computer farm. Using this code I investigated the electrons dynamics in ThomX and the flux of scattered Compton photons. I analysed the relative contribution of each physical phenomena to the overall beam dynamics and how to mitigate their disruptive effect. As part of my work on longitudinal phase feedback I also measured and analysed properties of the ELETTRA RF cavity to be used on ThomX.
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Di, Palma Luca. "Antennes réseaux transmetteur reconfigurables aux fréquences millimétriques." Thesis, Rennes 1, 2015. http://www.theses.fr/2015REN1S092/document.
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De nombreuses applications civiles et militaires (faisceaux hertziens, futurs réseaux mobiles, communications par satellite, radars automobiles, systèmes d’imagerie haute résolution) nécessitent des antennes à faisceau reconfigurable (dépointage de faisceau, faisceaux multiples, faisceaux formés). Les antennes à réseaux transmetteurs apparaissent comme une alternative aux réseaux phasés classiques ou aux réseaux réflecteurs pour ces applications. L’objectif principal de cette thèse est de démontrer la faisabilité de réseaux reconfigurables fabriqués avec des technologies standards en bande Ka (20-30 GHz). Divers cellules élémentaires utilisant des diodes p-i-n et fonctionnant en polarisation linéaire ou circulaire ont été conçues, optimisées et caractérisées. Les mesures en guide d’onde montrent des pertes minimales de 1,09 dB à 29,0 GHz et une bande passante à 3 dB de 14,7%. Une méthode de simulation hybride a été développée afin d’analyser efficacement des réseaux de grandes dimensions utilisant des rotations séquentielles d’éléments pour optimiser la qualité de polarisation et les diagrammes de rayonnement. Un réseau de 400 cellules élémentaires fonctionnant en polarisation circulaire a été réalisé et testé en chambre anéchoïque. Un dépointage électronique de ±60° et la possibilité de commuter entre les deux polarisations circulaires (droite/gauche) ont été démontrésSeveral civil and military applications (hertzian beams, satellite communications, automotive radars, high resolution imaging systems) require antennas with reconfigurable beam capabilities (beam-scanning, beamshaping, multiple beam generation). Transmitarray antennas are good candidates and represent an alternative to classical phased arrays or reflect-arrays for these applications. The main objective of this thesis is to demonstrate the feasibility of reconfigurable transmitarrays fabricated with standard technologies in Ka-band (20-30 GHz). Different unit-cell designs based on p-i-n diodes have been developed to work in linear and circular polarization. Their optimization and experimental characterization have been performed. Waveguide measurements show insertion losses of 1.09 dB at 29.0 GHz with a 3-dB bandwidth of 14.7%. A hybrid simulation technique has been developed in order to analyze efficiently large transmitarrays in which the sequential rotation technique has been applied to optimize the polarization quality and the radiation patterns. A 400-elements transmitarray operating in circular polarization has been realized and tested in anechoic chamber. A beam-scanning angular coverage of ±60° and circular polarization selection (left/right) have been demonstrated
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Alcântara, Segundinho Pedro Gutemberg de [UNESP]. "Análise teórico-experimental de um tabuleiro misto madeira-concreto composto por vigas circulares." Universidade Estadual Paulista (UNESP), 2005. http://hdl.handle.net/11449/91482.
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alcantarasegundinho_pg_me_ilha.pdf: 4485630 bytes, checksum: 0e58733013f71fa0d93bb68c2fdabebb (MD5)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
O estudo em estruturas mistas é dedicado ao emprego do material madeira-concreto em estruturas de pontes, mais precisamente no seu tabuleiro. No entanto, a aplicação desse material no Brasil não está regulamentada por normas que permitam ao engenheiro civil fazer sua aplicação nas estruturas correntes. Com a proposta de viabilizar o uso desse material madeira-concreto esse estudo vem contribuir com um melhor entendimento do comportamento físico da ligação entre os materiais madeira e concreto. O estudo dessa ligação foi realizado quantificando o módulo de deslizamento em corpos-de-prova do tipo push-out, vigas T e tabuleiro de madeira-concreto. Os resultados experimentais do módulo de deslizamento obtidos por esses três tipos de ensaios foram comparados com os resultados obtidos teoricamente pelo Eurocode 5 (1993). Também, no seguinte estudo foi feito uma simulação numérica do tabuleiro de madeira-concreto usando um programa para análise estrutural baseado no Método dos Elementos Finitos (MEF). Na conclusão dessa pesquisa verificou-se que o comportamento estrutural desse material misto pode-ser calculado usando o Eurocode 5 (1993) e o Método dos Elementos Finitos (MEF).
The study of mixed structures is dedicated to the use of timber-concrete material in bridges' structures, more precisely in its tray. However, the application of this material in Brazil is not regulated by standards that allow the civil engineer to make its application in the current structures. With the proposal to make possible the use of this timber-concrete material this study contributes to understand better the physical behavior of the linking between wood and concrete. The study of this connection was carried through quantifying the slip's module in specimens of push-out type, T beams and timber-concrete's tray. The experimental results of the slip's module from these three kinds of tests had been compared with the results obtained theoretically for Eurocode 5 (1993). Also, in the following study it was made a mathematical simulation of the wood-concrete's tray using a numerical analysis' program based on the Finite Elements' Method (MEF). In the conclusion of this research it was verified that the structural behavior of this mixed material can to be calculated using Eurocode 5 (1993) and the Method of the Finite Elements (MEF).
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Masioli, Calil Zumerle. "Análise teórica e experimental de ligações em aço entre pilar tubular de seção circular e viga de seção I." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/18/18134/tde-10062011-153037/.
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O atrativo estético proporcionado pela forma arredondada é o fator que na maioria das vezes determina a utilização de estruturas tubulares circulares. É crescente a concepção de pórticos formados por colunas tubulares e as tradicionais vigas de seção I. Esse tipo de ligação ainda é pouco estudado no Brasil, e esse trabalho busca avançar no entendimento do comportamento estrutural dessas ligações. Foram realizados estudos analíticos, numéricos e experimentais em quatro configurações de ligação, com diafragmas externos transversais, chapa de alma, soldas, parafusos e enrijecedor. Avaliou-se a relação M-\'fi\' (momento-rotação) das ligações estudadas e os parâmetros envolvidos como resistência, rigidez e ductilidade, evidenciando-se o modo de colapso das ligações. O estudo analítico foi desenvolvido baseado nas recomendações do Eurocode 3 (2005), com a utilização do Método das Componentes. A análise numérica, através do Método dos Elementos Finitos, foi realizada por meio dos programas computacionais TRUEGRID® e ANSYS®. Os modelos numéricos consideram as características mecânicas do aço, como plastificação, encruamento e não-linearidades geométricas e de contato. As formulações do Eurocode 3 (2005), adaptadas para a determinação da resistência das ligações viga-coluna, apresentaram resultados coerentes e a análise numérica foi representativa frente aos resultados experimentais. A utilização de diafragmas externos conectados à viga apresentou boa funcionalidade, ajudando na distribuição das tensões na região da ligação, melhorando o comportamento da coluna.The aesthetic appeal provided by the round shape is the factor that mostly determines the use of circular tubular structures. There is an increasing conception of structures formed by hollow columns and traditional beams of section I. This type of connection hasn\' t been sufficiently studied in Brazil, and this paper tries to advance the comprehension of the structural behavior of these connections. Analytical, numerical, and experimental study were performed in four connections configurations, with transverse external diaphragms, web plate, welds, bolts and stiffener. The relation M-\'fi\' (moment-rotation) of the studied connections and the parameters involved such as strength, stiffness and ductility were evaluated, evidencing the failure mode of connections. The analytical study was developed based on recommendations of Eurocode 3 (2005) using the Method of Components. The numerical analysis using the Finite Element Method was performed with the computer programs TRUEGRID® and ANSYS®. The numerical models consider the mechanical characteristics of steel, such as yielding and hardening, and also the geometric and contact nonlinearity. The formulations of Eurocode 3 (2005), adapted for determining the strength of beam-column connections, showed coherent results and the numerical analysis was representative compared to experimental results. The use of external diaphragm connected to the beam showed good functionality, helping in the distribution of stress in the region of connection, improving the behavior of the column.
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Pereira, Daniel Henrique Fidelis. "Análise do comportamento estrutural de ligações em aço entre viga de seção I e pilar de seção tubular circular." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/18/18134/tde-11122013-101943/.
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Esta pesquisa consiste de uma investigação acerca do comportamento estrutural de ligações entre viga de seção I e pilar de seção tubular circular em situações de pilar de canto e de pilar solicitado por quatro vigas simultaneamente (pilar central). A associação entre a viga de seção I e o pilar de seção tubular circular remete à análise de ligações com comportamento complexo. A partir da análise numérica, via Método dos Elementos Finitos com os softwares ANSYS® e TrueGrid® foi avaliado o comportamento momento-rotação e parâmetros como resistência, rigidez inicial e ductilidade das ligações. Foram analisadas as tipologias de ligação soldada e ligação com a presença do diafragma externo como mecanismo de enrijecimento. Avaliou-se a influência de 6 variáveis, sendo o comprimento da viga, a espessura do pilar, a força aplicada nas vigas dispostas ortogonalmente, a compressão axial do pilar, a espessura do diafragma e o diâmetro dos parafusos do diafragma totalizando 20 modelos numéricos. O aumento da espessura da seção do pilar e a força aplicada simultaneamente nas 4 vigas representou uma melhoria na resistência e rigidez inicial das ligações soldadas. A redução do diâmetro dos parafusos do diafragma foi a principal variável capaz de influenciar negativamente as propriedades de rigidez inicial e resistência das ligações com o diafragma. Todos os modelos analisados apresentaram comportamento semi-rígido segundo o Eurocode 3 (2005). O dimensionamento analítico pelo Eurocode 3 (2005) e por Winkel (1998) apresentou boa aproximação com os resultados da análise numérica. A obtenção da resistência das ligações com diafragma pelo método das componentes apresentou resultados, em média, 20% inferiores ao verificado na modelagem numérica. A utilização do diafragma como mecanismo de enrijecimento das ligações mostrou-se eficiente. As ligações soldadas apresentaram maior ductilidade comparada às com diafragma. O aumento da espessura do pilar nas ligações soldadas demonstrou-se uma alternativa eficaz no enrijecimento das ligações.This research consists of an investigation above the structural behavior of connections between I-beam and circular hollow section (CHS) columns in situation of corner columns and column loaded by 4 beams simultaneously (inside columns). The association between the I-beam and the CHS column presupposes the analysis of connections with a complex structural behavior. Based on a numerical analysis, using the Finite Element Method with ANSYS® and TrueGrid® softwares, the connection parameters like strength, stiffness and ductility was evaluated. The typologies of welded connections and connections with an external diaphragm was analyzed. An amount of 6 variables (beam length, column thickness, force applied on the beams, compression of the column, diaphragm thickness and bolt diameter) was analyzed in a total of 20 numerical specimens. The increase of the column thickness and the force applied simultaneously on the 4 beam ends culminated on a substantial improvement on strength and stiffness of the welded connections. The reduction of the diaphragm bolts diameter was the main reason for the negatively influence on strength and stiffness properties of the diaphragm connections. All specimens presented a semirigid behavior according to the Eurocode 3 (2005). The analytical design, based on the Eurocode 3 (2005) and Winkel (1998), obtained good results in terms of connections strength compared with the numerical analysis. The obtainment of the connections strength with the component method demonstrated results 20% less than numerical analysis. The external diaphragm as a stiffening mechanism showed effective. The welded connections presented more ductility than the diaphragm ones. The increase on the column thickness demonstrated an effective alternative for the connection stiffening.
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Alcântara, Segundinho Pedro Gutemberg de. "Análise teórico-experimental de um tabuleiro misto madeira-concreto composto por vigas circulares /." Ilha Solteira : [s.n.], 2005. http://hdl.handle.net/11449/91482.
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Orientador: José Antônio MatthiesenBanca: Renato Bertolino Junior
Banca: Antonio Alves Dias
Resumo: O estudo em estruturas mistas é dedicado ao emprego do material madeira-concreto em estruturas de pontes, mais precisamente no seu tabuleiro. No entanto, a aplicação desse material no Brasil não está regulamentada por normas que permitam ao engenheiro civil fazer sua aplicação nas estruturas correntes. Com a proposta de viabilizar o uso desse material madeira-concreto esse estudo vem contribuir com um melhor entendimento do comportamento físico da ligação entre os materiais madeira e concreto. O estudo dessa ligação foi realizado quantificando o módulo de deslizamento em corpos-de-prova do tipo "push-out", vigas T e tabuleiro de madeira-concreto. Os resultados experimentais do módulo de deslizamento obtidos por esses três tipos de ensaios foram comparados com os resultados obtidos teoricamente pelo Eurocode 5 (1993). Também, no seguinte estudo foi feito uma simulação numérica do tabuleiro de madeira-concreto usando um programa para análise estrutural baseado no Método dos Elementos Finitos (MEF). Na conclusão dessa pesquisa verificou-se que o comportamento estrutural desse material misto pode-ser calculado usando o Eurocode 5 (1993) e o Método dos Elementos Finitos (MEF).
Abstract: The study of mixed structures is dedicated to the use of timber-concrete material in bridges' structures, more precisely in its tray. However, the application of this material in Brazil is not regulated by standards that allow the civil engineer to make its application in the current structures. With the proposal to make possible the use of this timber-concrete material this study contributes to understand better the physical behavior of the linking between wood and concrete. The study of this connection was carried through quantifying the slip's module in specimens of "push-out" type, T beams and timber-concrete's tray. The experimental results of the slip's module from these three kinds of tests had been compared with the results obtained theoretically for Eurocode 5 (1993). Also, in the following study it was made a mathematical simulation of the wood-concrete's tray using a numerical analysis' program based on the Finite Elements' Method (MEF). In the conclusion of this research it was verified that the structural behavior of this mixed material can to be calculated using Eurocode 5 (1993) and the Method of the Finite Elements (MEF).
Mestre
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Ibáñez, Usach Carmen. "FIRE RESPONSE ANALYSIS OF CIRCULAR CONCRETE FILLED TUBULAR COLUMNS AND THE EFFECTS OF AXIAL AND ROTATIONAL RESTRAINTS." Doctoral thesis, Universitat Politècnica de València, 2016. http://hdl.handle.net/10251/60150.
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[EN] The combination of different materials to form a single structural member to take profit of their individual good characteristics is a successfully established practice in building industry. In concrete filled tubular columns (CFT) the combined action of steel and concrete results in many positive attributes at ambient temperature: high load-bearing capacity with smaller cross-section size, aesthetics, high stiffness and ductility and reduced construction cost.
In the last decades, the use of CFT columns in building industry, especially in high-rise buildings, has increased not only because of their positive characteristics at room temperature, but also for their inherent high fire resistance. Besides, CFT sections are greatly versatile given that they admit different types of concrete infill such as plain concrete, bar-reinforced concrete or fiber reinforced concrete; and also a wide variety of shapes. Although the more commonly used shapes are circular, and rectangular, new configurations and shapes are continuously appearing together with innovative materials.
The ambient temperature behavior of CFT columns has been deeply studied and, in turn, the investigations dealing with their fire behavior have increased. For its structural analysis, the column can be considered as an isolated member or as a column integrated in a structure interacting with other structural members. The review of the state of the art in the area of CFT columns in fire carried out in the framework of this thesis has pointed out that most works cover the fire response of isolated members and that the existing studies on columns within frames differ in their proposals and conclusions.
In this thesis, the fire response of CFT columns is analyzed by means of a fiber beam element model. First, a realistic cross-sectional thermal model is implemented to be integrated in the thermo-mechanical model developed whose accuracy is validated against experimental results after its calibration. Parametric studies are carried out with the aim of investigating the main factors affecting the problem and developing a simple calculation method based on Eurocode 4 and using the concept of equivalent concrete core cross-section. Finally, given the reduced computational cost of the fiber model, the effects of axial and rotational restraint in the fire response of CFT columns are investigated by integrating the heated CFT column within a frame. A parametric analysis is performed in order to draw conclusions about this interaction and contrast the current code provisions.
The scope of this thesis is limited to circular CFT columns subjected to concentric axial loads.[ES] Combinar diferentes materiales en un único elemento estructural para aprovechar las fortalezas individuales de cada uno es una práctica consolidada con éxito en el sector de la construcción. En los pilares tubulares de acero rellenos de hormigón (CFT) la acción conjunta del acero y el hormigón presenta muy buenas cualidades a temperatura ambiente: alta capacidad de carga con secciones pequeñas, buena apariencia, alta rigidez y ductilidad y bajo coste de puesta en obra. En las últimas décadas, el uso de pilares CFT en el sector de la construcción, especialmente en edificios de gran altura, ha aumentado no solo debido a sus buenas características a temperatura ambiente sino también por su inherente alta resistencia al fuego. Además, las secciones de pilares CFT son muy versátiles ya que admiten diferentes tipos de relleno, como hormigón en masa, con armaduras o reforzado con fibras; y también una amplia variedad de formas. Aunque los perfiles tubulares más usados son los circulares y rectangulares, nuevas configuraciones están continuamente en desarrollo junto con nuevos materiales. El comportamiento de los pilares CFT a temperatura ambiente ha sido ampliamente estudiado y, a su vez, las investigaciones sobre su comportamiento a fuego han aumentado. Para su análisis estructural, el pilar puede ser considerado como un elemento aislado o como un elemento integrado en una estructura que interactúa con otros elementos estructurales. La revisión del estado del arte en el área de los pilares CFT sometidos a fuego llevado a cabo en el marco de esta tesis ha puesto de manifiesto que la mayoría de los trabajos cubren la respuesta a fuego de elementos aislados y que los estudios existentes sobre pilares en estructuras difieren en sus propuestas y conclusiones. En esta tesis, la respuesta a fuego de pilares CFT se analiza por medio de un modelo de elementos viga con integración por fibras. En primer lugar, se implementa un modelo térmico realista para ser integrado en el modelo termo-mecánico desarrollado cuya precisión se valida con resultados experimentales después de ser calibrado. Un estudio paramétrico se lleva a cabo con el objeto de estudiar los principales factores que afectan al problema y desarrollar un modelo simplificado de cálculo basado en el Eurocódigo 4 Parte 1-1 y que emplea el concepto de sección equivalente del núcleo de hormigón. Finalmente, dado el reducido coste computacional del modelo de fibras, se investigan los efectos de la restricción axial y rotacional en la respuesta frente al fuego de los pilares CFT integrando la columna expuesta a fuego dentro de una subestructura. Se ejecuta un estudio paramétrico para extraer conclusiones sobre esta interacción y contrastar las prescripciones de la normativa actual. El alcance de esta tesis queda limitado a pilares CFT sin protección externa, de sección circular y sometidos a carga axial centrada.
[CAT] Combinar distints materials en un únic membre estructural per a aprofitar les fortaleses individuals de cada u és una pràctica consolidada amb èxit en el sector de la construcció. En els pilars tubulars d'acer omplerts de formigó (CFT) l'acció conjunta de l'acer i el formigó presenta molt bones qualitats a temperatura ambient: alta capacitat de càrrega amb seccions xicotetes, bona aparença, alta rigidesa i ductilitat i baix cost de posada en obra. En les últimes dècades, l'ús de pilars CFT en el sector de la construcció, especialment en edificis de gran altura, ha augmentat no sols degut a les seues bones característiques a temperatura ambient, sinó també per la seua inherent alta resistència al foc. A més, les seccions de pilars CFT són molt versàtils, doncs admeten distints tipus de farcit, com formigó en massa, amb armadures o reforçat amb fibres; i també una àmplia varietat de formes. Encara que els perfils tubulars més usats són els circulars i rectangulars, noves configuracions estan contínuament en desenvolupament junt amb nous materials. El comportament dels pilars CFT a temperatura ambient ha sigut àmpliament estudiat i, al mateix temps, les investigacions sobre el seu comportament a foc han augmentat. Per a la seua anàlisi estructural, el pilar pot ser considerat com un element aïllat o com un element integrat en una estructura que interactua amb altres elements estructurals. La revisió de l'estat de l'art en l'àrea dels pilars CFT sotmesos a foc, duta a terme en el marc d'aquesta tesi, ha posat de manifest que la majoria dels treballs cobreixen la resposta a foc d'elements aïllats, i que els estudis existents sobre pilars en estructures difereixen en les seues propostes i conclusions. En aquesta tesi, la resposta a foc de pilars CFT s'analitza mitjançant un model d'elements biga amb integració per fibres. En primer lloc, s'implementa un model tèrmic realista per a ser integrat en el model termo-mecànic desenvolupat, i la seua precisió es valida amb resultats experimentals desprès de ser calibrat. Un estudi paramètric es du a terme amb l'objectiu d'estudiar els principals factors que afecten al problema i desenvolupar un model simplificat de càlcul basat en l'Eurocodi 4, Part 1-1 i que empra el concepte de secció equivalent del nucli de formigó. Finalment, tenint en compte el reduït cost computacional del model de fibres, s'investiguen els efectes de les restriccions axial i rotacional en la resposta a foc dels pilars CFT integrant la columna exposada a foc dins d'una subestructura. Un estudi paramètric s'executa per a obtenir conclusions sobre aquesta interacció i contrastar les prescripcions de la normativa actual. L'abast d'aquesta tesi queda limitat a pilars CFT sense protecció externa, de secció circular i sotmesos a càrrega axial centrada.
Ibáñez Usach, C. (2016). FIRE RESPONSE ANALYSIS OF CIRCULAR CONCRETE FILLED TUBULAR COLUMNS AND THE EFFECTS OF AXIAL AND ROTATIONAL RESTRAINTS [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/60150
TESIS
Premiado
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Portolés, Flaj José Manuel. "Estudio experimental y numérico de soportes tubulares circulares de acero esbeltos rellenos de hormigón de alta resistencia." Doctoral thesis, Universitat Jaume I, 2010. http://hdl.handle.net/10803/669145.
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En los últimos años la utilización de perfiles tubulares de acero rellenos de hormigón (CFT) se ha incrementado debido a su excelente comportamiento frente al sismo, alta resistencia, alta ductilidad y la gran capacidad de absorción de energía. Aunque España y en particular la Comunidad Valenciana no son zonas de riesgo sísmico elevado, el uso de este tipo de pilares ofrece también otras ventajas, como por ejemplo el incremento en la velocidad del proceso de construcción, la posibilidad de estandarización de las uniones y lo que es muy importante, una mayor resistencia al fuego.
Por otra parte, el uso del hormigón de alta resistencia (HSC) en la construcción de estructuras de hormigón se está generalizando gracias al abaratamiento de su tecnología. La utilización de este material presenta enormes ventajas, sobre todo en elementos sometidos a axiles de compresión importantes, como ocurre en el caso de soportes de edificación o de pilas de puente. Sin embargo, el Eurocódigo 4, con el que de diseñan estas estructuras mixtas, queda limitado a hormigones de hasta 60 MPa.
Dada la mayor resistencia seccional de las columnas CFT rellenas de HSC, es posible reducir su sección, para un mismo nivel de carga. De esta forma la esbeltez y los efectos de segundo orden cobran más importancia.
En esta tesis doctoral se estudia el comportamiento de las columnas de acero, esbeltas, de sección circular, rellenas de hormigón de alta resistencia. Para ello se ha desarrollado una campaña experimental que ha sido ampliada con modelos numéricos. Se ha comprobado la validez del Eurocódigo 4 y se ha realizado un estudio paramétrico de las variables que influyen en la respuesta de estas columnas.
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Yang, Zhenchao. "High-Efficiency Passive and Active Phased Arrays and Array Feeds for Satellite Communications." BYU ScholarsArchive, 2015. https://scholarsarchive.byu.edu/etd/5741.
Full textAbstract:
Satellite communication (Satcom) services are used worldwide for voice, data, and video links due to various appealing features. Parabolic reflector antennas are typically used to serve a cost effective scheme for commercial applications. However, mount degradation, roof sag, and orbital decay motivate the need for beam steering. Limited scan range beam steering opens a third option for electronic beam steering with lower cost than full aperture phased arrays and higher tracking speed and accuracy than mechanical-only steering.Multiple high efficiency passive patch array feeds were designed, fabricated, and measured, including a 2x2 MSA array, a stacked shorted annular patch antenna, and an SIW-fed hexagonal array feed based on PTFE material, achieving performance comparable to a horn feed. For multiband dual polarization applications, passive MSA feed solutions are also provided. Multiple MSA array feeds with high isolation were designed for dual band dual polarization applications. More functionality can be realized with multi-layer PCB techniques for complex communication scenarios.Limited scan range electronic beam-steering with a parabolic reflector fed by an active array feed which only needs gain control was demonstrated experimentally, leading to a low cost and effective solution for active beam scanning. A cost-effective flat-panel phased array with limited scan range electronic beam-steering was proposed by tiling high efficiency 4x4 passive subarrays and performing beam scanning at the tile level. The sidelobe issue was also investigated to comply with the pattern mask requirement set by FCC.To enable better use of circularly polarized (CP) MSAs for electronically beam-formed antenna systems, the impact of mutual coupling on the performance of high-sensitivity dual-polarized receivers for satellite communications applications was analyzed. A new analysis method for intrinsically dual-CP MSAs based on an equivalent circuit model and Jones matrices was proposed and validated to overcome the port isolation challenge. The model provides accurate estimates of impedances and S-parameters, as well as field parameters such as axial ratio. The feasible region for XPI and impedance mismatch factor is found for dual CP antennas. The circuit model enables multiple useful applications. Effective decoupling and matching schemes was proposed and demonstrated, leading to a high isolation, good match, and wide AR bandwidth dual CP MSA for satellite communications.
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Martin, Roman. "Interaction Region Design for a 100 TeV Proton-Proton Collider." Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/19416.
Full textAbstract:
Mit der Entdeckung des Higgs-Bosons hat ein Messprogramm begonnen, bei dem die Eigenschaften dieses neuen Teilchens mit der höchstmöglichen Präzision untersucht werden soll um die Gültigkeit des Standardmodells der Teilchenphysik zu prüfen und nach neuer Physik jenseits des Standardmodells zu suchen. Für dieses Ziel wird der Large Hadron Collider (LHC) und sein Upgrade, der High Luminosity-LHC bis etwa zum Jahr 2035 laufen und Daten produzieren.
Um an der Spitze der Teilchenphysik zu bleiben, hat die “European Strategy Group for Particle Physics” empfohlen, ambitionierte Nachfolgeprojekte für die Zeit nach dem LHC zu entwickeln. Entsprechend dieser Empfehlung hat das CERN die “Future Circular Collider” (FCC) -Studie gestartet, die die Machbarkeit neuer Speicherringe für Teilchenkollisionen (Collider) untersucht. In dieser Arbeit wird die Entwicklung der Wechselwirkungszonen für FCC-hh, einem Proton-Proton-Speicherring mit einer Schwerpunktsenergie von 100 TeV und einem Umfang von 100 km, beschrieben.
Die Wechselwirkungszone ist das Herzstück eines Colliders, da sie die erreichbare Luminosität bestimmt. Es ist daher entscheidend, schon früh im Entwicklungsprozess eine möglichst hohe Kollisionsrate anzustreben. Ausgehend von der optische Struktur der Wechselwirkungszonen des LHC und dem geplanten High Luminosity-LHC (HL-LHC) werden Strategien zur Skalierung hergeleitet um der höheren Strahlenergie gerecht zu werden. Bereits früh im Entwicklungsprozess wird die Strahlungsbelastung durch Teilchentrümmer vom Wechselwirkungspunkt als entscheidender Faktor für das Layout der Wechselwirkungszone identifiziert und eine allgemeine Design-Strategie, die den Schutz der supraleitenden Endfokussierungsmagnete mit einer hohen Luminosität verbindet, wird formuliert und implementiert. Aufgrund des deutlichen Spielraums in Bezug auf beta* wurde die resultierende Magnetstruktur zum Referenzdesign für das FCC-hh-Projekt.The discovery of the Higgs boson is the start of a measurement program that aims to study the properties of this new particle with the highest possible precision in order to test the validity or the Standard Model of particle physics and to search for new physics beyond the Standard Model. For that purpose, the Large Hadron Collider (LHC) and its upgrade, the High Luminosity-LHC, will operate and produce data until 2035. Following the recommendations of the European Strategy Group for Particle Physics, CERN launched the Future Circular Collider (FCC) study to design large scale particle colliders for high energy physics research in the post-LHC era. This thesis presents the development of the interaction region for FCC-hh, a proton-proton collider operating at 100 TeV center-of-mass energy. The interaction region is the centerpiece of a collider as it determines the achievable luminosity. It is therefore crucial to aim for maximum production rates from the beginning of the design process. Starting from the lattices of LHC and its proposed upgrade, the High Luminosity LHC (HL-LHC), scaling strategies are derived to account for the increased beam rigidity. After identifying energy deposition from debris of the collision events as a driving factor for the layout, a general design strategy is drafted and implemented, unifying protection of the superconducting final focus magnets from radiation with a high luminosity performance. The resulting FCC-hh lattice has significant margins to the performance goals in terms of beta*. Protecting the final focus magnets from radiation with thick shielding limits the minimum beta* and therefore the luminosity. An alternative strategy to increase the magnet lifetime by distributing the radiation load more evenly is developed. A proof of principle of this method, the so-called Q1 split, is provided. In order to demonstrate the feasibility of the derived interaction region lattices, first dynamic aperture studies are conducted.
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Khalil, Khaled. "Investigation, design and implementation of circular-polarised antennas for satellite mobile handset and wireless communications : simulation and measurement of microstrip patch and wire antennas for handheld satellite mobile handsets and investigations of polarization polarity, specific absorption rate, and antenna design optimization using genetic algorithms." Thesis, University of Bradford, 2009. http://hdl.handle.net/10454/4319.
Full textAbstract:
The objectives of this research work are to investigate, design and implement circularly-polarized antennas to be used for handheld satellite mobile communication and wireless sensor networks. Several antennas such as Quadrifilar Spiral Antennas (QSAs), two arm Square Spiral and stripline or coaxially-fed microstrip patch antennas are developed and tested. These antennas are investigated and discussed to operate at L band (1.61-1.6214GHz) and ISM band (2.4835-2.5GHz) A substantial size reduction was achieved compared to conventional designs by introducing special modifications to the antenna geometries. Most of the antennas are designed to produce circularly-polarized broadside-beam except for wireless sensor network application a circularly-polarized conical-beam is considered. The polarization purity and Specific Absorption Rate (SAR) of two dual-band antennas for satellite-mobile handsets next to the human head are investigated and discussed, using a hybrid computational method. A small distance between the head and the handset is chosen to highlight the effects of the relatively high-radiated power proposed from this particular antenna. A Genetic Algorithm in cooperation with an electromagnetic simulator has been introduced to provide fast, accurate and reliable solutions for antenna design structures. Circularly-polarized quadrifilar helical antenna handset and two air-dielectric microstrip antennas were studied. The capabilities of GA are shown as an efficient optimisation tool for selecting globally optimal parameters to be used in simulations with an electromagnetic antenna design code, seeking convergence to designated specifications. The results in terms of the antenna size and radiation performance are addressed, and compared to measurements and previously published data.
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Morin, Matthew Robertson. "Design and Analysis of Receiver Systems in Satellite Communications and UAV Navigation Radar." BYU ScholarsArchive, 2014. https://scholarsarchive.byu.edu/etd/4210.
Full textAbstract:
The design of a low cost electronically steered array feed (ESAF) is implemented and tested. The ESAF demonstrated satellite tracking capabilities over four degrees. The system was compared to a commercial low-noise block downconverter (LNBF) and was able to receive the signal over a wider angle than the commercial system. Its signal-to-noise ratio (SNR) performance was poor, but a proof of concept for a low cost ESAF used for tracking is demonstrated. Two compact low profile dual circularly polarized (CP) reflector feed antenna designs are also analyzed. One of the designs is a passive antenna dipole array over an electromagnetic band gap (EBG) surface. It demonstrated high isolation between ports for orthogonal polarizations while also achieving quality dual CP performance. Simulations and measurements are shown for this antenna. The other antenna was a microstrip cross antenna. This antenna demonstrated high gain and quality CP but had a large side lobe and low isolation between ports. A global positioning system (GPS) denied multiple input multiple output (MIMO) radar for unmanned aerial vehicles (UAVs) is simulated and tested in a physical optics scattering model. This model is developed and tested by comparing simulated and analytical results. The radar uses channel matrices generated from the MIMO antenna system. The channel matrices are then used to generate correlation matrices. A matrix distance between actively received correlation matrices to stored correlation matrices is used to estimate the position of the UAV. Simulations demonstrate the ability of the radar algorithm to determine its position when flying along a previously mapped path.
35
Sicha, Jakub. "Statické řešení zastřešení nádrže." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2020. http://www.nusl.cz/ntk/nusl-409778.
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Grobelný, Petr. "Mikrofonová pole pro prostorovou separaci akustických signálů." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2011. http://www.nusl.cz/ntk/nusl-218906.
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The goal of this master’s thesis is to explore the possibilities of multichannel localization of acoustic signal sources and their following application on a real signal localization and separation, using Beamforming methods. During this thesis two beamforming methods were selected, namely Delay and Sum a Constant Directivity Beamforming - Circular Arrays, and were applicated on real environment signals using two microphone arrays’ geometries ULA (Uniform linear array) and UCA (Uniform Circular array).
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Warmowska, Dominika. "Terahertzová anténní pole pro komunikaci." Doctoral thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2020. http://www.nusl.cz/ntk/nusl-432466.
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The thesis is focused on the research of THz antenna arrays to be used for communications. Attention is turned to modeling metallic surfaces at THz frequencies, a proper characterization of gold conductivity, its relation to Drude model and corresponding measurements. Moreover, the best methods for modeling thin metallic layers (depending on the skin depth related to the metal thickness) are presented. An optimized element of a THz 2×2 antenna array designed for the application of communications is developed in a way that enables an expansion to a larger array. The expansion ability is demonstrated on a 4×4 antenna array which is presented in the thesis too. The designed antennas achieve parameters better than the state-of-art antennas. The presented antennas radiate circularly polarized wave at THz frequencies, operate in a wide bandwidth, have a high gain and are of a compact size. In the thesis, an 8×8 antenna array with a beam steering capability is presented. The main beam of the antenna array can be controlled in two dimensions. A high gain of the radiated circularly-polarized wave can be achieved that way. Different approaches to modeling antennas with thin metallic layers are compared and the best methods are recommended from the viewpoint of different requirements. The designed 2×2 and 4×4 antenna arrays are manufactured using a microfabrication technology. Each step of the fabrication is described in detail and discussed. The reflection coefficient at the input of antennas is measured and compared with simulations. Discrepancies in results are associated with surface roughness which is analyzed by a scanning probe microscope and a scanning electron microscope. By down-scaling the developed THz antenna, a low-profile high-gain antenna for Ka-band space applications is designed. The presented antenna achieves better results than state-of-art CubeSat antennas. The antenna performance is verified by a prototype to be operated at 9 GHz, and the radiation characteristics are experimentally confirmed.
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Eck, James Arthur. "Compact Antennas and Arrays for Unmanned Air Systems." BYU ScholarsArchive, 2014. https://scholarsarchive.byu.edu/etd/4297.
Full textAbstract:
A simple and novel dual-CP printed antenna is modelled and measured. The patch antennais small and achieves a low axial ratio without quadrature feeding. The measured pattern showsaxial ratio pattern squinting over frequency. Possible methods of improving the individual element are discussed, as well as an array technique for improving the axial ratio bandwidth. Three endfire printed antenna structures are designed, analyzed, and compared. The comparison includes an analysis of costs of production for the antenna structures in addition to their performance parameters. This analysis concludes that cost of materials primarily reduces the size of antennas for a given gain and bandwidth. An antenna stucture with an annular beam pattern for down-looking navigational radar is proposed. The antenna uses sub-wavelength grating techniques from optics to achieve a highly directive planar reflector which is used as a ground plane for a monopole. A fan-beam array element is fabricated for use in a digitally steered receive array for obstacle avoidance radar. The steered beam pattern is observed. The element-dependent phase shifts for a homodyned signal in particular are explored as to their impact on beam steering.
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Mainos, Constantinos. "Etude des transitions mutiphotoniques dans des molécules diatomiques." Paris 13, 1986. http://www.theses.fr/1986PA132001.
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Etude des transitions rovibroniques multiphotoniques de type dipolaire électrique pour des états moleculaires présentant un couplage de hund (a),(b) ou un couplage intermediaire entre (a) et (b), à l'approximation adiabatique pour décrire la vibration et la rotation. Expressions de l'intensité des raies rotationnelles dans le cas d'une polarisation linéaire ou circulaire et pour des photons identiques. Régles de sélection pour la rotation et le couplage ou se trouvent les états moléculaires (initial et final) pour le cas général d'une transition à "n" photons et d'une multiplicité quelconque. Rapport d'intensités polarisationlinéaire / polarisation circulaire. Expérience à 2 photons pour la bande gamma (o,o) de no et comparaison aux valeurs théoriques calculées
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Metral, Elias. "Coupled Landau damping of transverse coherent instabilities in particle accelerators." Université Joseph Fourier (Grenoble), 1999. http://www.theses.fr/1999GRE10048.
Full textAbstract:
L'effet du couplage lineaire entre les plans transversaux d'un accelerateur circulaire sur l'amortissement de landau des instabilites coherentes est etudie en considerant deux distributions caracteristiques de frequences (lorentzienne et elliptique). Celles-ci correspondent a des cas limites modelisant des spectres avec et sans longues queues. Un critere general de stabilite, ou interviennent la force du couplage (du aux quadrupoles tournes) et la distance des nombres d'ondes betatroniques aux resonances de couplage, est obtenu dans les deux cas. Ce dernier revele la possibilite de partager les dispersions de frequences stabilisatrices entre les deux plans, ce qui peut considerablement ameliorer la stabilite coherente du faisceau, en particulier dans les cas ou la situation est plus critique dans un plan. Une seconde observation importante est que l'effet d'une grande partie imaginaire de l'impedance de couplage, qui normalement requiert une dispersion de frequences equivalente pour l'amortissement de landau, peut etre compense (du moins dans un plan) par un choix judicieux du couplage. Les resultats d'experiences effectuees au synchrotron a protons (ps) du cern confirment le comportement general predit par la theorie. Le mecanisme de l'amortissement de landau couple pourrait donc expliquer pourquoi une machine comme le ps peut etre stabilisee en rapprochant le point de fonctionnement pres d'une resonance de couplage. Il peut par consequent etre utilise pour determiner des valeurs optimales du point de fonctionnement et de la force du couplage lineaire.
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Chao, Jeng-Chung, and 趙介中. "Vibration Analysis of Nonuniform Circular Beams." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/71485324819278918253.
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博士國立成功大學
機械工程學系
88
ABSTRACT The governing differential equations for the out-of-plane and in-plane vibrations of curved nonuniform beams of constant radius are derived. Eight physical parameters are introduced to simplify the analysis and the explicit relations between the torsional displacement and the flexural displacement for out-of plane direction, the axial displacement and the flexural displacement for in-plane direction are derived. With these explicit relations, the four coupled governing characteristic differential equations can be decoupled and reduced to four sixth-order ordinary differential equations with variable coefficients in the out-of-plane flexural displacement, the in-plane flexural displacement, the torsional displacement and the axial displacement, respectively. It is shown that if the material and geometric properties of the beam are in arbitrary polynomial forms, then the exact solutions for the out-of-plane and in-plane vibrations of the beam can be obtained. The derived explicit relations can also be used to reduce the difficulty in experimental measurement. Finally, eight limiting cases are considered and the influence of taper ratio, center angle and arc length on the first two natural frequencies of the beams are illustrated.
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Shih-Ho, Jaw, and 趙世鶴. "DYNAMIC ANALYSIS OF MULTISPAN HORIZONTALLY CIRCULAR CURVED BEAMS." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/84545867346540851768.
Full textAbstract:
碩士國立中興大學
土木工程研究所
83
The thesis is devoted to the dynamic analysis of horizontally circular curved beams. The direct stiffness method is used to derived the dynamic stiffness matrix for finding the natural frequ- encies and joint moments of curved beams having different rectangular cross-sections. Several examples are presented to illustrate the appli- cation of the proposed method and to show the effects of rotatory inertia, shear deformation, torsional inertia, warping and opening angle of the arc on the beam. The first examples are for the free vibration of the beam. In these exampl- es, beams with different thickness are used for finding effects of warping. In each example, there are three cases; case(a) consider rotatory inertia, shear deformation, torsional inertia and warping effects; case(b) consider rotatory inertia, shear deformation and torsional inertia effects; case( c) consider rotatory inertia, shear deformation and warping effects. The last example is for the forced vibration of the beam subjected to a uniformly distributed load. The results of the last examples show the effects of case(a),(b) and (c) on the joint moment of the beam. We also let the forced frequency to be zero for finding the static special moment.
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Hsiao, Jui Yang, and 蕭瑞陽. "In-plane Vibrations of Non-uniform Circular Beams." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/45598354027332869596.
Full textAbstract:
博士國立成功大學
機械工程學系
89
By introducing two physical parameters, the analysis is simplified and the explicit relations between the in-plane flexural displacement and the longitudinal displacement are derived. With these explicit relations, the two-coupled governing differential equations are reduced to a complete sixth-order ordinary differential equation with variable coefficients in the longitudinal displacement or in the flexural displacement, and the limiting study from the curved beam theory to the straight beam theory is successfully revealed. Semi-exact solutions for the free in-plane vibrations of curved non-uniform beams with constant radius are developed. The influence of center angle, taper ratio and arc length on the first two natural frequencies of the beams is studied. In forced in-plane vibrations of curved non-uniform beams, the method of variation of parameters is applied to solve the problem. When the frequencies approach the natural frequencies, the deflection approaches to infinity. As to the in-plane vibrations of non-uniform curved beams of constant radius with time dependent boundary conditions, by introducing shifting functions and new dependent variables, the boundary conditions become homogeneous for the new dependent variables, and the physical meanings of the shifting functions are revealed. The coupled differential equations are uncoupled successfully by introducing two physical parameters. The solution is obtained by Laplace transform and Green’s function methods.
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Hung, Chien-Hsing, and 洪建興. "Strengthening of R.C. Beams and Circular Compressive Structures Using Prestressed Glass Fiber Reinforced Polymer." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/57859936589162735008.
Full textAbstract:
博士國立中興大學
土木工程學系
93
ABSTRACT The main topic of this dissertation is to use prestressed glass fiber reinforced polymers (PGFRP) to strengthen beams and hollow circular specimens. In these years, carbon fiber- reinforced polymer (CFRP) material has been popular used to repair or rehabilitate in deteriorated reinforced concrete ( ) structures. However, the stiffness variation between CFRP and concrete material lowers the effort in transferring the prestress from CFRP sheets to member. The reason for why this study chose glass fiber- reinforced polymers (GFRP) material was the Young’s modulus of GFRP material being quite close to concrete material. This dissertation was divided into two parts, Part I to study the strengthening of reinforced concrete ( ) beams using prestessed glass fiber-reinforced polymer (PGFRP) and Part Ⅱ to study the strengthening of hollow circular specimens using PGFRP. The main subject of part Ⅰ of this dissertation is to compare the test and theoretical analysis strengthening results in using GFRP and PGFRP sheets for the load-carrying capacities (ultimate loads) and deflections of beams. Two beams shapes, T and -shaped, were used as the under-strengthened and over-strengthened beams. The GFRP sheets were prestressed to one-half their tensile capacities before bonded to the T and -shaped R. C. beams. The prestressed tensions in the PGFRP sheets caused cambers in R.C. beams without cracking on the tensile faces. The PGFRP sheets also enhanced the load-carrying capacities. The test results indicate that T-shaped beams with GFRP sheets exhibit an increase of load-carrying capacity by 55% while the same beams with PGFRP sheets can increase 100%. The -shaped beams with GFRP sheets can increase the load-carrying capacity by 97% while the same beams with PGFRP sheets increase the capacity by 117%. Under the same external loads, beams with GFRP sheets produce larger deflections than beams with PGFRP sheets. In the theoretical part, the equations obtained by theory match the test results quite well. It is suggested that this analytical method can be widely used for analyzing and designing beams strengthened using GFRP or PGFRP sheets. The main subject of part Ⅱ of this dissertation is to study the strengthening of hollow and solid circular specimens using PGFRP. The purpose of this study is to strengthen the damaged solid and hollow circular specimens which were used to simulate the structures of large hollow circular pipes. The test results show that GFRP can increase a great deal of strength for specimens, even for the broken specimens. For instance, the solid specimens wrapped by GFRP can increase the strength around 200% and the hollow specimens wrapped by GFRP can even increase 400%. The results also show that PGFRP can’t increase more strength than GFRP. But PGFRP can increase the lateral stiffness of the specimens. In the theoretical part, the equations obtained by theory match the test results very well. In this study, all the test results are greater than the theoretical results within a range of 10%.
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Wu, Cheng-Shen, and 吳建昇. "On the out-of-plane Vibrations of Nonuniform Circular Beams with Time Dependent Boundary Conditions." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/75362051246778768297.
Full textAbstract:
碩士國立成功大學
機械工程學系
86
In the present study，the analysis of dynamic response for beam structures is presented. The governing equations and the associated boundary conditions for an out-of-plane non-uniform circular beams , time dependent boundary conditions and general elastic end restraints , are derived via the Hamilton`s principle. The explicit relations between the flexural displacement and the torsional displacement for the out-of-plane vibrations of the beam are established. The two coupled governing differential equations for the out-of-plane vibration are uncoupled and reduced to two complete sixth-order ordinary differential equations with variable coefficients in the out-of- plane flexural displacement. The solution for these differential equations can be solved by using the method of Mindlin-Goodman. In the Mindlin - Goodman method , the non-homogeneous boundary conditions are transformed into homogeneous ones by a procedure of change of variable and the solution of dynamic response of the beam is obtained by using the method of mode superposition. A general form of change of dependent variable with shifting functions is introduced and the physical meanings of these shifting functions are explored. The orthogonality condition for the eigenfunctions of a non-uniform circular beams with elastic boundary conditions is also derived. Finally , several limiting cases are examined and the limiting procedures are revealed.
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Chung, Wei-Hung, and 鍾威宏. "Acoustic Reflection and Transmission of Gaussian Beams from Fluid Coupled Laminates and Circular Cylindrical Shells." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/27267289614945793271.
Full textAbstract:
碩士國立交通大學
機械工程系
89
This thesis presents an analysis of acoustic wave propagation across layered cylindrical structures that are immersed in fluids and obliquely insonified by acoustic Gaussian beams from the concave side. The acoustic nonspecular reflection is due to the interference of geometric reflection and leaky guided waves. Contrast to the ealier studies assuming that incident rays are all parallel to the central beam axis. The acoustic Gaussian beam is modeled by the complex source point (CSP) method and angular spectrum. In the present method the beam is not limited with well collimation. Spectral integral representation of the reflected and transmitted acoustic fields are replaced by a Fourier series due to circumferential period in polar coordinates. The exact forms of reflection and transmission coefficients of a layered cylindrical structure are derived using Thomson-Haskell method. The cylindrical structure made of chopped-fiber glass/epoxy is assumed to be isotropic. Two acoustic impedance matching layers added on both sides of the structure to construct a laminated acoustic window is also studied. Influences of various design parameters on nonspecular reflected and transmitted acoustic fields are well-disscussed.
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Lam, Dennis, Xianghe Dai, Ashraf F. Ashour, and Naveed Rehman. "Recent research on composite beams with demountable shear connectors." 2017. http://hdl.handle.net/10454/12114.
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YesThis paper presents experimental and numerical investigation on an innovative composite floor system with deconstructability. In this system, a composite slab formed with metal profiled decking is connected to a steel beam using demountable shear connectors. A series of push tests was conducted to investigate the behaviour of this form of shear connectors. In addition to the push tests, a full-scale composite beam was tested to failure in the laboratory under a number of cycles of monotonic loading. For direct comparison, a similar composite beam test was conducted using same section size, concrete strength, but using the conventional welded headed stud connectors. Test results showed that the behaviour of the composite beam with demountable shear connectors is comparable with the specimen with welded shear connectors. After the test was terminated, the demountable shear connectors were unfastened and the composite floor can be easily lifted off from the steel beam. Test result showed that these demountable shear connectors possess high ductility in comparison with the equivalent welded shear connectors. Simple design rules currently use in Eurocode 4 for the welded shear connections and Eurocode 3 for bolts are proposed to predict the shear resistance of this form of demountable shear connectors.
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Chen, Jian-Hao, and 陳健皓. "Formulation of geometric stiffness matrix for circular beams based on the rigid body rule and force equilibrium conditions." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/30614446294703230150.
Full textAbstract:
碩士國立臺灣海洋大學
河海工程學系
101
Conventionally, researchers or scientists usually need to select a set of suitable shape functions in formulating structural matrices of curved beam elements. In addition, the geometric stiffness matrix derived for the curved beam element has to satisfy the rigid body test due to equilibrium considerations. These two procedures are not easy to attain because of locking problems. Thus most researchers adopted straight beam elements to simulate curved beam structures for nonlinear structural analyses in existing literature. This paper intends to develop an alternative approach that can satisfy both conditions of the rigid body test and incremental force equilibrium through the transfer matrices and state equations of a curved beam. The entire project is divided into four parts. The first part is aimed at establishing the relationship of curved beam structural stiffness matrix, the beam element transfer matrix, and state transfer matrix of curved beam. Based on the state transfer matrix method developed in the first part, the second research work is focused on the theoretical development of transformation relation among the three structural matrices that can satisfy both conditions of the rigid body test and incremental force equilibrium. In this stage, the transformation matrix has taken into account the second order effect induced by external forces due to buckling. In the third part, the structural matrices including beam transfer matrix, elastic and geometric stiffness matrices of a spatially curved-beam element are derived through the curved-beam state matrix that has been obtained from the second part. The fourth part is the use of the three parts, establish procedures to derive stiffness matrix is considered nonlinear effects, and the complete stiffness matrices of spatial straight beams or curved beams can be deduced. This paper approach has two features: concise physical meanings and simple matrix manipulation in deriving structural stiffness matrices of a spatially curved bar, from which laborious mathematical derivation in dealing with nonlinear strains, potential energy and suitable selection of shape functions can be avoided. Besides, both the qualification of rigid body test and the conditions of force equilibrium are always satisfied in the process of theoretical development. It is emphasized that the locking problem of curved beam elements using conventional variational principle based on displacement shape selections will not occur using the present curved-beam element. For this, a number of examples of buckling and large deformations of curved beam structures will be demonstrated in this study.
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Polocoser, Tiberiu. "Evaluation of remediation techniques for circular holes in the webs of wood I-joists." Thesis, 2012. http://hdl.handle.net/1957/30477.
Full textAbstract:
The objective of this project was to evaluate methods to remediate a wood I-joist with a single, circular hole in the web while leaving utilities in place. The methods were experimentally evaluated with a full-scale bending test using four equally spaced point loads. There were three depths of joists with varying flange widths and two span lengths (4.88 m & 2.44 m). Failure modes for the long span joists without holes were in the flanges in either tension, compression or lateral buckling; but once a hole was introduced the majority were classified as shear failures. Effectiveness of the remediation was evaluated based on three criteria: strength, stiffness, and ease of installation/cost. The OSB collar patch was effective for 8 out of the 12 series tested. A maximum reduction of load from a joist with no hole to one with a hole was 49% for the long span and 58% for the short span. The OSB collar was not as effective in returning stiffness to the joists, but was easier to install and less expensive than the LSL patch.Graduation date: 2013
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Hsu, Bao-Chia, and 許保嘉. "Beam Shaping with Circular Cone." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/72450947684705856450.
Full textAbstract:
碩士國立交通大學
顯示科技研究所
96
The purpose of this research is to apply the optical design to the laser applications by analyzing the circular refractive-reflective cone lens thoroughly. As considering the incident ray via a system called refractive-reflective circular cone lens system, a kind of circular cone lens application, the incident ray of the system propagation via a circular cone which refract the incident the ray first and then reflect the ray by the cine surface. Finally, the ray is guided out of the cone. It’s shown that the cone parameter restriction of refractive-reflective cone lens system, and the field distribution algorithm and its expression , then we also find the restriction of all kind of field distribution and its property. Finally, we check the correctness of field distribution algorithm by experiment and take it into practice in laser cutting.