Дисертації з теми "Finite sections"
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1
Boubez, Toufic I. "Three-dimensional finite-element mesh generation using serial sections." Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=63804.
2
Kucukarslan, Sertac. "A Finite Element Study On The Effective Width Of Flanged Sections." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612180/index.pdf.
Анотація:
Most of the reinforced concrete systems are monolithic. During construction,
concrete from the bottom of the deepest beam to the top of slab, is placed at
once. Therefore the slab serves as the top flange of the beams. Such a beam is
referred to as T-beam. In a floor system made of T-beams, the compressive
stress is a maximum over the web, dropping between the webs. The
distribution of compressive stress on the flange depends on the relative
dimensions of the cross section, span length, support and loading conditions.
For simplification, the varying distribution of compressive stress can be
replaced by an equivalent uniform distribution. This gives us an effective
flange width, which is smaller than the real flange width. In various codes
there are recommendations for effective flange width formulas. But these
formulas are expressed only in terms of span length or flange and web
thicknesses and ignore the other important variables. In this thesis, three-dimensional finite element analysis has been carried out on
continuous T-beams under different loading conditions to assess the effective
flange width based on displacement criterion. The formulation is based on a
combination of the elementary bending theory and the finite element method,
accommodating partial interaction in between. The beam spacing, beam span
length, total depth of the beam, the web and the flange thicknesses are
considered as independent variables. Depending on the type of loading, the
numerical value of the moment of inertia of the transformed beam crosssection
and hence the effective flange width are calculated. The input data and
the finite element displacement results are then used in a nonlinear regression
analysis and two explicit design formulas for effective flange width have been
derived. Comparisons are made between the proposed formulas and the ACI,
Eurocode, TS-500 and BS-8110 code recommendations.
3
Goudet, Catherine A. "Finite element analysis of diseased cross-sections of human carotid arteries." Thesis, Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/16816.
4
Roodbaraky, K. "Finite element modelling of tubular cross joints in rectangular hollow sections." Thesis, University of Nottingham, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384702.
5
Nukala, Ramanand. "Efficient finite element modeling of WT sections subjected to uniaxial tension." Morgantown, W. Va. : [West Virginia University Libraries], 2001. http://etd.wvu.edu/templates/showETD.cfm?recnum=2091.
Анотація:
Thesis (M.S.)--West Virginia University, 2001.Title from document title page. Document formatted into pages; contains vii, [90] p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 62-63).
6
Riquelme, Faúndez Edgardo. "Algorithms for l-sections on genus two curves over finite fields and applications." Doctoral thesis, Universitat de Lleida, 2016. http://hdl.handle.net/10803/393881.
Анотація:
We study \ell-section algorithms for Jacobian of genus two over finite fields. We provide trisection (division by
\ell=3) algorithms for Jacobians of genus 2 curves over finite fields \F_q of odd and even characteristic. In odd
characteristic we obtain a symbolic trisection polynomial whose roots correspond (bijectively) to the set of
trisections of the given divisor. We also construct a polynomial whose roots allow us to calculate the 3-torsion
divisors. We show the relation between the rank of the 3-torsion subgroup and the factorization of this 3-torsion
polynomial, and describe the factorization of the trisection polynomials in terms of the galois structure of the 3-
torsion subgroup. We generalize these ideas and we determine the field of definition of an \ell-section with \ell \in {3,
5, 7}. In characteristic two for non-supersingular hyperelliptic curves we characterize the 3-torsion divisors and
provide a polynomial whose roots correspond to the set of trisections of the given divisor. We also present a
generalization of the known algorithms for the computation of the 2-Sylow subgroup to the case of the \ell-Sylow
subgroup in general and we present explicit algorithms for the computation of the 3-Sylow subgroup. Finally we
show some examples where we can obtain the central coefficients of the characteristic polynomial of the Frobenius
endomorphism reduced modulo 3 using the generators obtained with the 3-Sylow algorithm.En esta tesis se estudian algoritmos de \ell-división para Jacobianas de curvas de género 2. Se presentan algoritmos de trisección (división por \ell=3) para Jacobianas de curvas de género 2 definidas sobre cuerpos finitos \F_q de característica par o impar indistintamente. En característica impar se obtiene explícitamente un polinomio de trisección, cuyas raíces se corresponden biyectivamente con el conjunto de trisecciones de un divisor cualquiera de la Jacobiana. Asimismo se proporciona otro polinomio a partir de cuyas raíces se calcula el conjunto de los divisores de orden 3. Se muestra la relación entre el rango del subgrupo de 3-torsión y la factorización del polinomio de la 3- torsión, y se describe la factorización del polinomio de trisección en términos de las órbitas galoisianas de la 3- torsión. Se generalizan estas ideas para otros valores de \ell y se determina el cuerpo de definición de una \ell-sección para \ell=3,5,7. Para curvas no-supersingulares en característica par también se da una caracterización de la 3-torsión y se proporciona un polinomio de trisección para un divisor cualquiera. Se da una generalización, para \ell arbitraria, de los algoritmos conocidos para el cómputo explícito del subgrupo de 2-Sylow, y se detalla explícitamente el algoritmo para el cómputo del subgrupo de 3-Sylow. Finalmente, se dan ejemplos de cómo obtener los valores de la reducción módulo 3 de los coeficientes centrales del polinomio característico del endomorfismo de Frobenius mediante los generadores proporcionados por el algoritmo de cálculo del 3-Sylow.
En aquesta tesi s'estudien algoritmes de \ell-divisió per a grups de punts de Jacobianes de corbes de gènere 2. Es presenten algoritmes de trisecció (divisió per \ell=3) per a Jacobianes de corbes de gènere 2 definides sobre cossos finits \F_q de característica parell o senar indistintament. En característica parell s'obté explícitament un polinomi de trisecció, les arrels del qual estan en bijecció amb el conjunt de triseccions d'un divisor de la Jacobiana qualsevol. De manera semblant, es proporciona un altre polinomi amb les arrels del qual es calcula el conjunt dels divisors d'ordre 3. Es mostra la relació entre el rang del subgrup de 3-torsió i la factorització del polinomi de la 3-torsió, i es descriu la factorització del polinomi de trisecció en termes de les òrbites galoisianes de la 3-torsió. Es generalitzen aquestes idees a altres valors de \ell i es determina el cos de definició d'una \ell-secció per a \ell=3,5,7. Per a corbes nosupersingulars en característica 2 també es proporciona una caracterització de la 3-torsió i un polinomi de trisecció per a un divisor qualsevol. Es dóna una generalització, per a \ell arbitrària, dels algoritmes coneguts per al càlcul explícit del subgrup de 2-Sylow, i es detalla explícitament en el cas del 3-Sylow. Finalment es mostren exemples de com obtenir els valors de la reducció mòdul 3 dels coeficients centrals del polinomi característic de l'endomorfisme de Frobenius fent servir els generadors proporcionats per l'algoritme de càlcul del 3-Sylow.
7
Sousa, Yuri Teixeira e. "Kinematically exact elastoplastic analysis of steelo rods with compact cross sections." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/3/3144/tde-05122017-134523/.
Анотація:
In this work, we present the formulation and implementation of two elastoplastic constitutive equations for kinematically exact thin-walled rod models. The first uses the fact that first order strains due to cross sectional shear stresses and warping are considered to formulate a small strains three-dimensional elastoplastic constitutive model. Given the kinematical hypothesis of non-deformability of the cross section in the projection of its plane, we may also assume that plastic deformations may occur due only to the cross sectional normal stresses, thereby allowing us to formulate a second, simple one-dimensional framework. Our approach adopts a standard additive decomposition of the strains together with a linear elastic relation for the elastic part of the deformation. Both ideal plasticity and plasticity with (linear) isotropic hardening are considered. The models have a computational implementation within a finite element thin-walled rod model and, following the kinematics adopted, we implement this equation on models with consideration of the warping of the cross sections, having 7 degrees of freedom. The formulation and implementation presented is validated by the analysis of problems known in the literature and comparison of the results. We believe that simple elastoplastic models combined with robust thin-walled rod finite element may be a useful tool for the analysis of thin-walled rod structures, such as, e.g., steel structures.Neste trabalho, apresentamos a formulação e implementação de duas equações constitutivas elastoplásticas simples para modelos de barra de parede fina cinematicamente exatos. O primeiro usa o fato de deformações de primeira ordem devido a esforço cortante na seção transversal e empenamento serem considerados para formular um modelo constitutivo elastoplástico tridimensional para pequenas deformações. Dada a hipótese cinemática de não deformabilidade da seção transversal da barra na projeção de seu plano, podemos também assumir que deformações plásticas ocorrem devido apenas às tensões normais à seção transversal, nos permitindo formular um segundo modelo unidimensional simples. Nossa abordagem adota uma decomposição aditiva padrão das deformações com uma relação elástica linear para a parte elástica das deformações. Tanto plasticidade ideal quanto plasticidade com encruamento isótropo (linear) são considerados. Os modelos resultantes têm uma implementação computacional com elementos finitos de barras e, de acordo com a cinemática adotada, implementamos esta equação com consideração do empenamento das seções transversais, possuindo 7 graus de liberdade. A formulação e implementação apresentadas são validadas pela análise de problemas conhecidos na literatura e comparação dos resultados. Acreditamos que modelos elastoplásticos simples combinados com um elemento finito de barras robusto podem ser uma ferramenta útil para a análise de estruturas reticuladas como, por exemplo, estruturas de aço.
8
Cheng, Shanshan. "Fire performance of cold-formed steel sections." Thesis, University of Plymouth, 2015. http://hdl.handle.net/10026.1/3316.
Анотація:
Thin-walled cold-formed steel (CFS) has exhibited inherent structural and architectural advantages over other constructional materials, for example, high strength-to-weight ratio, ease of fabrication, economy in transportation and the flexibility of sectional profiles, which make CFS ideal for modern residential and industrial buildings. They have been increasingly used as purlins as the intermediate members in a roof system, or load-bearing components in low- and mid-rise buildings. However, using CFS members in building structures has been facing challenges due to the lack of knowledge to the fire performance of CFS at elevated temperatures and the lack of fire design guidelines. Among all available design specifications of CFS, EN1993-1-2 is the only one which provided design guidelines for CFS at elevated temperatures, which, however, is based on the same theory and material properties of hot-rolled steel. Since the material properties of CFS are found to be considerably different from those of hot-rolled steel, the applicability of hot-rolled steel design guidelines into CFS needs to be verified. Besides, the effect of non-uniform temperature distribution on the failure of CFS members is not properly addressed in literature and has not been specified in the existing design guidelines. Therefore, a better understanding of fire performance of CFS members is of great significance to further explore the potential application of CFS. Since CFS members are always with thin thickness (normally from 0.9 to 8 mm), open cross-section, and great flexural rigidity about one axis at the expense of low flexural rigidity about a perpendicular axis, the members are usually susceptible to various buckling modes which often govern the ultimate failure of CFS members. When CFS members are exposed to a fire, not only the reduced mechanical properties will influence the buckling capacity of CFS members, but also the thermal strains which can lead additional stresses in loaded members. The buckling behaviour of the member can be analysed based on uniformly reduced material properties when the member is unprotected or uniformly protected surrounded by a fire that the temperature distribution within the member is uniform. However if the temperature distribution in a member is not uniform, which usually happens in walls and/or roof panels when CFS members are protected by plaster boards and exposed to fire on one side, the analysis of the member becomes very complicated since the mechanical properties such as Young’s modulus and yield strength and thermal strains vary within the member. This project has the aim of providing better understanding of the buckling performance of CFS channel members under non-uniform temperatures. The primary objective is to investigate the fire performance of plasterboard protected CFS members exposed to fire on one side, in the aspects of pre-buckling stress distribution, elastic buckling behaviour and nonlinear failure models. Heat transfer analyses of one-side protected CFS members have been conducted firstly to investigate the temperature distributions within the cross-section, which have been applied to the analytical study for the prediction of flexural buckling loads of CFS columns at elevated temperatures. A simplified numerical method based on the second order elastic – plastic analysis has also been proposed for the calculation of the flexural buckling load of CFS columns under non-uniform temperature distributions. The effects of temperature distributions and stress-strain relationships on the flexure buckling of CFS columns are discussed. Afterwards a modified finite strip method combined with the classical Fourier series solutions have been presented to investigate the elastic buckling behaviour of CFS members at elevated temperatures, in which the effects of temperatures on both strain and mechanical properties have been considered. The variations of the elastic buckling loads/moments, buckling modes and slenderness of CFS columns/beams with increasing temperatures have been examined. The finite element method is also used to carry out the failure analysis of one-side protected beams at elevated temperatures. The effects of geometric imperfection, stress-strain relationships and temperature distributions on the ultimate moment capacities of CFS beams under uniform and non-uniform temperature distributions are examined. At the end the direct strength method based design methods have been discussed and corresponding recommendations for the designing of CFS beams at elevated temperatures are presented. This thesis has contributed to improve the knowledge of the buckling and failure behaviour of CFS members at elevated temperatures, and the essential data provided in the numerical studies has laid the foundation for further design-oriented studies.
9
Brackus, Travis R. "Destructive Testing and Finite-Element Modeling of Full-Scale Bridge Sections Containing Precast Deck Panels." DigitalCommons@USU, 2010. https://digitalcommons.usu.edu/etd/861.
Анотація:
Full-depth, precast panel deck systems are becoming more common in bridge installation and repair. The objective of these systems is to achieve the performance of cast-in-place systems while simultaneously saving time and money. The structural behavior of these systems has been the subject of scrutiny in recent research. The Utah Department of Transportation demolished a steel I-girder bridge containing a precast panel deck system and provided two full-scale specimens for this project. Destructive testing was performed at Utah State University on the specimens to investigate three failure modes: flexural, beam shear, and punching shear. Finite-element models were created using ANSYS software to replicate experimental behavior. Overall, it was found that the elastic, post-elastic, and ultimate behavior of the full-scale bridge sections containing precast panel deck systems can be accurately predicted in analytical models.
Another aspect of this project was to investigate changes in dynamic behavior as the system was subjected to flexural yield and failure. Point loads were applied and removed in increments, and dynamic testing was conducted at each load level. It was found that significant damage is somewhat noticeable by monitoring the changes in natural frequencies.
10
Ori, Miklós. "Local Buckling of Doubly-Symmetric I-Sections Subjected to Warping Torsion : The limitations of the Reduced Cross-Section Method under unconventional loading." Thesis, KTH, Bro- och stålbyggnad, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-251031.
Анотація:
In regular design practice, when it comes to conventional loading, such as uniaxial compression and bending, the local buckling of thin plates is taken care of through cross section classification. The effect of warping torsion, which also gives rise to normal stresses in the section, however, is typically not considered in the process. Present work aimed to uncover the influence of warping torsion on the phenomena of local plate buckling and to investigate the limitations of the effective width method when it was applied against its intended use. In the case of varying results, a simple correction to the calculation method was to be developed to improve accuracy. The examined I-sections were tested to failure and results were obtained with two different approaches: with finite element method and a Eurocode-based hand-calculation. The finite element models were refined to closely mimic physical experiments and their results were accepted as the true resistance of the sections, while the calculation method tried to capture the structural response in a practical, easily understandable way. The calculated results showed reasonably good accuracy with that of the finite element analysis. However, what really stood out was how similar the change in resistance was when the section parameters were manipulated. Through a properly chosen function, this allowed for the creation of an exponent that could modify the calculated results to achieve an even greater accuracy. The eccentricity of the applied load on the system was also manipulated to alter the proportion of normal stresses due to the two examined effects. It became clear that the stresses from warping in the applied calculation model were underestimated and the otherwise conservative method of effective width lost much of its safety margin when its application was extended to warping as well. Consequently, the consideration of stresses from warping in the regular design process and stability control of commonly used thin walled open sections seemed to be justified. The effective width method could not reliably cover the issue with retaining its original margin of safety.
11
Hassan, Rusul. "Distortional Lateral Torsional Buckling Analysis for Beams of Wide Flange Cross-sections." Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/24008.
Анотація:
Structural steel design standards recognize lateral torsional buckling as a failure mode governing the capacity of long span unsupported beams with wide flange cross-sections. Standard solutions start with the closed form solution of the Vlasov thin-walled beam theory for the case of a simply supported beam under uniform moments, and modify the solution to accommodate various moment distributions through moment gradient expressions. The Vlasov theory solution is based on the assumption that cross-sectional distortional effects have a negligible effect on the predicted elastic critical moment. The present study systematically examines the validity of the Vlasov assumption related to cross-section distortion through a parametric study.
A series of elastic shell finite element eigen-value buckling analyses is conducted on simply supported beams subject to uniform moments, linear moments and mid span point loads as well as cantilevers subject to top flange loading acting at the tip. Cross-sectional dimensions are selected to represent structural steel cross-section geometries used in practice. Particular attention is paid to model end connection details commonly used in practice involving moment connections with two pairs of stiffeners, simply supported ends with a pair of transverse stiffeners, simply supported ends with cleat angle details, and built in fixation at cantilever roots.
The critical moments obtained from the FEA are compared to those based on conventional critical moment equations in various Standards and published solutions. The effects of web slenderness, flange slenderness, web height to flange width ratio, and span to height ratios on the critical moment ratio are systematically quantified. For some combinations of section geometries and connection details, it is shown that present solutions derived from the Vlasov theory can overestimate the lateral torsional buckling resistance for beams.
12
Wutz, Franziska [Verfasser], and Uwe [Akademischer Betreuer] Jannsen. "Bertini theorems for hypersurface sections containing a subscheme over finite fields / Franziska Wutz. Betreuer: Uwe Jannsen." Regensburg : Universitätsbibliothek Regensburg, 2015. http://d-nb.info/1070996297/34.
13
Lucassen, Mattheüs. "Infuence of the modelling of truss joints made of hollow tube sections in finite element models." Thesis, KTH, Skolan för industriell teknik och management (ITM), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-263912.
Анотація:
Several boom segments form the crane boom. These segments are often truss structures formed out of circular hollow sections, which are welded together forming the truss joints. A adequate modelling of these truss joints is very important for operational strength and life. Due to the large boom sizes, efficient models are used in the finite element method, generally built of beam elements. These models have problems capturing the proper bending moments working in the truss joints. This is caused by a insufficient portrayal of the joint stiffness. In the literature several modelling techniques with beam elements are proposed, which capture the joint stiffness better. These different modelling methods are implemented in a parametric boom section and compared with a shell element FE model. From this comparison the most appropriate modelling method is selected, which improve the portrayal of internal loads and nominal stresses. With these improved nominal stress values, it is investigated to implement a different fatigue assessment. The structural stress can be calculated from the nominal stress in combination with stress concentration factor (SCF) equations. To implement the structural stress method as fatigue assessment, several modelling and extrapolation methods have been compared. Which lead to a method for evaluating the structural stress in a efficient matter. This method is compared with existing SCF K truss joint equations, from which a new set of SCF equations is derived. These equations are constructed from a larger dataset, hold a wider validity range and fit better with the FE models. When applying these SCF equations with the improved beam modelling method in a boom section, the structural stress is not adequately captured. This is caused by unsymmetrical stressed braces in the K truss joints. Both the modelling methods and SCF equations account for uniformly stressed braces forming the truss joints. More research needs to be conducted to this uneven behaviour. If the structural stress method needs to be implemented with efficient FE models, submodels out of shell elements combined with beam elements are recommended. For fatigue evaluation with the nominal stress method, beam models which account for the local joint flexibility give sufficient realistic results.Flera kranarmsegment bildar kranarmen. Dessa segment är ofta fackverk utformade av cirkulära ihåliga profiler, som är sammansvetsade och bildar fackverkslederna. En ordentlig modellering av dessa fackförband är mycket viktig för dess driftsstyrka och livslängd. På grund av storleken används finita elementmetoden, vanligtvis uppbyggt av balkelement. Dessa modeller har problem med att beräkna de korrekta böjmomenten som uppstår i fackverkslederna. Detta orsakas av en otillräcklig beskrivning av ledstyvheten. I litteraturen föreslås flera modelleringstekniker med balkelement som tar hänsyn till ledens styvhet bättre. Dessa olika modelleringsmetoder implementeras i en parametrisk kranarmsektion och jämförs med en FE-modell med skalelement. Med denna jämförelse väljs den mest lämpliga modelleringsmetoden, vilket bör förbättra skildringen av interna belastningar och nominella spänningar. Med dessa förbättrade nominella spänningsvärden, undersöks det att genomföra en annan utmattningsbedömning. Den strukturella spänningen kan beräknas utifrån den nominella spänningen i kombination med spänningskoncentrationsfaktor- (SCF) ekvationerna. För att implementera strukturella spänningsmetoden som utmattningsbedömning, har flera modellerings- och extrapoleringsmetoder jämförts. Detta leder till en metod för att utvärdera den strukturella spänningen effektivt. Denna metod jämförs med befintliga SCF-ekvationer, från vilka en ny uppsättning SCF-ekvationer härleds. Dessa ekvationer är konstruerade från en större datauppsättning, har ett bredare giltighetsområde och passar bättre med FE-modellerna. När man applicerar dessa SCF-ekvationer med den förbättrade balkmodelleringsmetoden i en kranarmsektion, uppsamlas strukturella spänningar inte tillräckligt, detta orsakas av ojämna spänningar i diagonalelementen i fackverkslederna. Både modelleringsmetoderna och SCF-ekvationerna tar hänsyn till jämnt spända diagonalelement som uppstår i fackverkslederna. Mer forskning bör göras över detta ojämna beteende. Om den strukturella spänningsmetoden måste implementeras med effektiva FE-modeller, rekommenderas undermodeller av skalelement kombinerade med balkelement. För utmattningsutvärdering med den nominella spänningsmetoden, ger balkmodeller som tar hänsyn till den lokala ledflexibiliteten tillräckligt realistiska resultat.
14
Green, Vicki L. "Investigation of Structural Responses for Flexible Pavement Sections at the Ohio-SHRP Test Road." Ohio University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1213280487.
15
Lowder, Margaret Loraine. "Distribution of Stress in Three-Dimensional Models of Human Coronary Atherosclerotic Plaque Based on Acrylic Histologic Sections." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16137.
Анотація:
Each year in the United States over a million people experience a myocardial infarction. The majority of these attacks are caused by coronary artery plaque cap rupture with subsequent thrombus formation. Because rupture is a mechanical event and the tendency of a plaque to rupture is due in part to increases in the mechanical stresses in the fibrous cap, mechanical analyses are important to understanding plaque stability.
Histology is the only method capable of identifying plaque features that are associated with vulnerability. Therefore, minimally distorted histologic sections should serve as a basis for constructing the models used in mechanical analyses. Further, because substantial longitudinal variations in geometry and mechanical properties often exist, models should be three-dimensional (3-D). Finally, given the complex geometries of atherosclerotic plaques and the fact that they are composed of different materials, the finite element (FE) method should be used to determine the distribution of stress under physiological loading. Until now, a critical need has existed to determine the distribution of stress in 3-D FE models of human coronary atherosclerotic plaques based on minimally distorted histologic sections.
In this research study, a method to measure and correct for distortions caused by acrylic histologic processing was first created. The devised strain-based method yields a limited set of parameters needed for a first order correction. Thus, corrections can be easily implemented using FE methods. Next, a methodology to create 3-D finite FE models of human coronary atherosclerotic plaques based on stable acrylic histologic sections was developed. Models of plaques, ranging in disease severity, were generated using the developed methodology. Lastly, the distributions of stress in these models were obtained and the effects of some plaque features on stresses were determined.
Results from this study confirm that morphological description of a plaque is not sufficient to predict plaque rupture. The findings suggest that in many cases the 3-D stress field within a plaque must be known in order to assess plaque stability. Finally, the results show that patient specific models must be developed if the 3-D stress field within a plaque is to be determined.
16
Benyamine, Charif Abdallah. "Sections finies d'inégalités multiplicatives de Hilbert et multiplicateurs de l'espace de Dirichlet." Thesis, Bordeaux, 2022. http://www.theses.fr/2022BORD0187.
Анотація:
Nous étudions deux problèmes. Le premier concerne les sections finies de l'inégalité multiplicative de Hilbert. Nous donnons le comportement asymptotique de la meilleure constante $lambda_n$ dans l'inégalité$$Big|sum_{i,j=2}^{n}frac{a_ioverline{a_j}}{ijlog(ij)}Big|leq lambda_n sum_{i=2}^n|a_i|^2.$$Nous donnons aussi le comportement asymptotique de la version $ell^p$ des sections finies de l'inégalité multiplicative de Hilbert.Le deuxième problème concerne l'appartenance des fonctions distance à l'algèbre des multiplicateurs de l'espace de Dirichlet. Les fonctions distance sont les fonctions extérieures dont les valeurs au bord ne dépendent que de la distance par rapport à un ensemble fermé du cercle unité de mesure nulle. Nous donnons une estimation de l'intégrale de Dirichlet d'une fonction distance pour qu'elle appartienne à l'algèbre des multiplicateursWe study two problems. The first one concerns finite sections of the Hilbert multiplicative inequality. We give the asymptotic behaviour of the best constant $lambda_n$ in the inequality$$Big|sum_{i,j=2}^{n}frac{a_ioverline{a_j}}{ijlog(ij)}Big|leq lambda_n sum_{i=2}^n|a_i|^2.$$We also give the asymptotic behaviour of the $ell^p$ version of the finite sections of the Hilbert multiplicative inequality.The second problem concerns the membership of the multiplier algebra of the Dirichlet space of so-called distance functions, namely outer functions whose boundary values depend only on distance to a closed subset of measure zero. We establish an estimate for the Dirichlet integral of such function to belong to the multiplier algebras of the Dirichlet space
17
Calloo, Ansar. "Développement d'une nouvelle modélisation de la loi de choc dans les codes de transport neutronique multigroupes." Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00909705.
Анотація:
Dans le cadre de la conception des réacteurs, les schémas de calculs utilisant des codes de cal- culs neutroniques déterministes sont validés par rapport à un calcul stochastique de référence. Les biais résiduels sont dus aux approximations et modélisations (modèle d'autoprotection, développement en polynômes de Legendre des lois de choc) qui sont mises en oeuvre pour représenter les phénomènes physiques (absorption résonnante, anisotropie de diffusion respec- tivement). Ce document se penche sur la question de la pertinence de la modélisation de la loi de choc sur une base polynômiale tronquée. Les polynômes de Legendre sont utilisés pour représenter la section de transfert multigroupe dans les codes déterministes or ces polynômes modélisent mal la forme très piquée de ces sections, surtout dans le cadre des maillages énergétiques fins et pour les noyaux légers. Par ailleurs, cette représentation introduit aussi des valeurs négatives qui n'ont pas de sens physique. Dans ce travail, après une brève description des lois de chocs, les limites des méthodes actuelles sont démontrées. Une modélisation de la loi de choc par une fonction constante par morceaux qui pallie à ces insuffisances, a été retenue. Cette dernière nécessite une autre mod- élisation de la source de transfert, donc une modification de la méthode actuelle des ordonnées discrètes pour résoudre l'équation du transport. La méthode de volumes finis en angle a donc été développée et implantée dans l'environ- nement du solveur Sn Snatch, la plateforme Paris. Il a été vérifié que ses performances étaient similaires à la méthode collocative habituelle pour des sections représentées par des polynômes de Legendre. Par rapport à cette dernière, elle offre l'avantage de traiter les deux représenta- tions des sections de transferts multigroupes : polynômes de Legendre et fonctions constantes par morceaux. Dans le cadre des calculs des réacteurs, cette méthode mixte a été validée sur différents motifs : des cellules en réseau infini, des motifs hétérogènes et un calcul de réflecteur. Les principaux résultats sont : - un développement polynômial à l'ordre P 3 est suffisant par rapport aux biais résiduels dus aux autres modélisations (autoprotection, méthode de résolution spatiale). Cette modéli- sation est convergée au sens de l'anisotropie du choc sur les cas représentatifs des réacteurs à eau légère. - la correction de transport P 0c n'est pas adaptée, notamment sur les calculs d'absorbant B4 C.
18
Wilkinson, Timothy James. "The Plastic Behaviour of Cold-Formed Rectangular Hollow Sections." University of Sydney. Department of Civil Engineering, 2000. http://hdl.handle.net/2123/843.
Анотація:
The aim of this thesis is to assess the suitability of cold-formed rectangular hollow sections (RHS) for plastic design. The project involved an extensive range of tests on cold-formed Grade C350 and Grade C450 (DuraGal) RHS beams, joints and frames. A large number of finite element analyses was also carried out on models of RHS beams. The conclusion is that cold- formed RHS can be used in plastic design, but stricter element slenderness (b/t) limits and consideration of the connections, are required. Further research, particularly into the effect of axial compression on element slenderness limits, is required before changes to current design rules can be finalised. Bending tests were performed on cold-formed RHS to examine the web and flange slenderness required to maintain the plastic moment for a large enough rotation suitable for plastic design. The major conclusions of the beam tests were: (i) Some sections which are classified as Compact or Class 1 by current steel design specifications do not maintain plastic rotations considered sufficient for plastic design. (ii) The current design philosophy, in which flange and web slenderness limits are independent, is inappropriate. An interaction formula is required, and simple formulations are proposed for RHS. Connection tests were performed on various types of knee joints in RHS, suitable for the column - rafter connection in a portal frame. The connection types investigated were welded stiffened and unstiffened rigid knee connections, bolted plate knee joints, and welded and bolted internal sleeve knee joints, for use in RHS portal frames. The ability of the connections to act as plastic hinges in a portal frame was investigated. The most important finding of the joint tests was the unexpected fracture of the cold-formed welded connections under opening moment before significant plastic rotations occurred. The use of an internal sleeve moved the plastic hinge in the connection away from the connection centre- line thus eliminating the need for the weld between the RHS, or the RHS and the stiffening plate, to carry the majority of the load. The internal sleeve connections were capable of sustaining the plastic moment for large rotations considered suitable for plastic design. Tests on pinned-base portal frames were also performed. There were three separate tests, with two different ratios of vertical to horizontal point loads, simulating gravity and horizontal wind loads. Two grades of steel were used for comparison. The aims of the tests were to examine if a plastic collapse mechanism could form in a cold-formed RHS frame, and to investigate if plastic design was suitable for such frames. In each frame, two regions of highly concentrated curvature were observed before the onset of local buckling, which indicated the formation of plastic hinges and a plastic collapse mechanism. An advanced plastic zone structural analysis which accounted for second order effects, material non-linearity and member imperfections slightly overestimated the strength of the frames. The analysis slightly underestimated the deflections, and hence the magnitude of the second order effects. A second order plastic zone analysis, which did not account for the effects of structural imperfections, provided the best estimates of the strengths of the frames, but also underestimated the deflections. While cold-formed RHS did not satisfy the material ductility requirements specified for plastic design in some current steel design standards, plastic hinges and plastic collapse mechanisms formed. This suggests that the restriction on plastic design for cold-formed RHS based on insufficient material ductility is unnecessary, provided that the connections are suitable for plastic hinge formation, if required. A large number of finite element analyses were performed to simulate the bending tests summarised above, and to examine various parameters not studied in the experimental investigation. To simulate the experimental rotation capacity of the RHS beams, a sinusoidally varying longitudinal local imperfection was prescribed. The finite element analysis determined similar trends as observed experimentally, namely that the rotation capacity depended on both the web slenderness and flange slenderness, and that for a given section aspect ratio, the relationship between web slenderness and rotation capacity was non-linear. The main finding of the finite element study was that the size of the imperfections had an unexpectedly large influence on the rotation capacity. Larger imperfections were required in the more slender sections to simulate the experimental results. There should be further investigation into the effect of varying material properties on rotation capacity.
19
Remsing, Carmen. "Finite element modelling of a magma chamber surrounded by country-rock, with particular reference to the groundwater flow in sections of different permeability." Thesis, Rhodes University, 2003. http://hdl.handle.net/10962/d1007537.
Анотація:
This thesis presents results of two-dimensional finite element modelling of a magma chamber surrounded by country-rock containing a section of high permeability. The high permeability section in the country-rock simulates structure that is predominant in controlling the groundwater convection pattern and resulting mineral deposits. The models have analogies in nature: for instance the gold mines in the Massif Central of France, the Pogo mine in Alaska and the Pilgrim's Rest gold field in South Africa. This is a complicated coupled system involving fluid flow and heat transfer under extreme conditions. The magma in the chamber convects and as it cools the heat liberated causes convection in the groundwater contained in the surrounding country-rock. This convection in turn affects the rate of liberation of heat from the magma. The software used for the modelling, FLOTRAN, is the computational fluid dynamics component of the commercial ANSYS package. The results obtained describe in detail the flow pattern in the magma chamber, the country-rock and high permeability section thereof. During the cooling of the magma chamber the groundwater convects more vigorously in the high permeability section than elsewhere, and a convection cell is seen forming within this region. This provides a mechanism for hydrothermal formation of valuable mineral deposits in the structure near a magma chamber. It is found that the relationship between the velocity of the flow in the cell and the temperature of the magma chamber is well represented by a first order linear differential equation, providing a simple understanding of this process,KMBT_363
Adobe Acrobat 9.54 Paper Capture Plug-in
20
Chinan, J. A. M. "The use of generalized beam theory, finite elements and experimental testing to investigate the stability of light gauge steel sections subject to axial load." Thesis, University of Salford, 2017. http://usir.salford.ac.uk/43694/.
Анотація:
The aim of the project is to study and investigate the buckling behaviour of unbranched open cold-formed steel sections. First the advantages and disadvantages of cold-formed steel when compared to hot-rolled steel are demonstrated. Thin-wall steel members have lower stiffness which may lead to increased instability and buckling issues for this kind of member. Buckling issues such as Euler buckling, buckling load factors, linear and non-linear analysis, buckling modes (global, distortional and local buckling) and buckling analysis methods (finite element method, finite strip method and generalized beam theory) are addressed. The literature review is concerned with computer software applications, theoretical analyses and experimental tests which can predict buckling loads and related mode shapes for light gauge steel sections. The study focuses on the Generalized Beam Theory (GBT) using the Finite Difference method for solution with a view to developing models using MATLAB to predict buckling loads, buckling mode shapes and non-linear yielding loads of members subjected to axial load for different boundary conditions. Some applications (beam subjected to concentrated load), linear analysis of buckling problems (Eigen value problems) and non-linear analysis (Imperfect Problems) have been addressed. Also, the finite element method (ANSYS) was used to predict the linear eigen-buckling loads and related mode shapes, and the non-linear material and geometric analyses with the post-buckling and initial imperfection effects were addressed. Finally, for validation purposes, a set of 36 cold-formed steel samples (lipped C-section and Zed-section) members with different boundary conditions (pinned and fixed end conditions) were tested in the laboratory to obtain the actual failure loads and failure shape and compare them with the two analytical methods. Good agreement between the analytical methods and the experimental data was evident, and recommendations for development of the GBT analysis are made.
21
Bhat, Akashdeep. "Reexamination of Shear Lag in HSS Tension Members; Side Gusset Plate Connections." University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin154357937610341.
22
Nogueira, Moises da Costa Ferraz 1989. "Avaliação por elementos finitos de tensões ocorridas em diferentes seções transversais do sistema de retenção de overdenture tipo barra-clipe com desajuste vertical : Evaluation by finite element analysis of stress at different cross-sections design of overdenture's bar framework with vertical misfit." [s.n.], 2014. http://repositorio.unicamp.br/jspui/handle/REPOSIP/288565.
Анотація:
Orientadores: Rafael Leonardo Xediek Consani, Mateus Bertolini Fernandes dos SantosDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba
Made available in DSpace on 2018-08-24T21:15:14Z (GMT). No. of bitstreams: 1 Nogueira_MoisesdaCostaFerraz_M.pdf: 1749031 bytes, checksum: 8fa4481a045e127aabb629294129a5b0 (MD5) Previous issue date: 2014
Resumo: O objetivo neste estudo foi avaliar por meio da análise por elemento finito 3-D, as tensões ocorridas em overdentures com sistemas de retenção barra-clipe, quando diferentes formas da seção transversal (circular, ovóide ou Hader) apresentam diferentes níveis de desajuste vertical (50, 100 e 200 µm) e são confeccionadas com diferentes ligas metálicas (Au tipo IV, Ag-Pd, Co-Cr e Ti cp). Modelos tridimensionais foram feitos utilizando software para modelagem 3-D (SolidWorks 2010) e importados para o software de simulação mecânica (ANSYS Workbench 11). Aperto simulado do parafuso foi realizado até obter assentamento adequado entre infraestrutura e plataforma protética. As análises foram realizadas com o objetivo de obter as tensões Máxima Principal e de von Mises (MPa). Os valores da tensão aumentaram com o aumento do desajuste vertical, assim como a barra Hader proporcionou os maiores valores. Barras circulares feitas com Au tipo IV causaram os menores valores na barra e no parafuso protético. Ligas resilientes mostraram melhores resultados que as rígidas, enquanto a maior complexidade da seção transversal da barra e o maior nível de desajuste vertical aumentaram a concentração das tensões na barra, parafuso protético e tecido ósseo cortical. Conclui-se que as tensões induzidas na barra, parafuso protético e tecido ósseo peri-implantar foram influenciadas pelo aumento do desajuste vertical, complexidade da seção transversal e liga da barra
Abstract: The objective of this study was to evaluate by 3-D finite element analysis tensions occurred in overdentures with bar-clip retention systems, when different cross-sectional geometries (circular, oval or Hader) have different levels of vertical misfit (50, 100 and 200 µm) and were maded from different metallic alloys (type IV Au , Ag-Pd , Co-Cr and Ti cp). Three-dimensional models were maded using 3-D modeling software (SolidWorks 2010) and imported into the software of mechanical simulation (ANSYS Workbench 11). A displacement simulating screw tightening was done until proper fitting of the prosthetic platform infrastructure. The analyzes were performed in order to obtain the Maximum Principal Stress and von Mises (MPa). The stress values increased proportionally with the level of vertical misfit and Hader bar showed the highest values. Circular bars made with Au type IV showed the lowest values on the bar and prosthetic screw. Resilient alloys performed better than hard, while the greater complexity of the cross section of the bar and the highest levels of vertical misfit increased stress concentration on the infrastructure of the bar, prosthetic screw and cortical bone tissue. The stress induced on the bar, prosthetic screw and peri-implant bone tissue were influenced by increased vertical misfit, complexity of cross section and different alloys of the bar
Mestrado
Protese Dental
Mestre em Clínica Odontológica
23
Abdullah, S. "Finite element simulation of filling thin section castings." Thesis, Swansea University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.635834.
Анотація:
The finite element simulation of filling thin section cavities has been studied in the present research, with an emphasis on the casting application. This thesis describes the development of appropriate governing equations for filling thin section cavities and finite element analysing software used to simulate some selected filling examples as case studies. As the transverse velocity profile across a thin section can be approximated between the parabolic and plain distributions, the flow throughout the cavity can be represented by in-plane velocity components and simulated using a quasi three-dimensional formulation. By applying an appropriate velocity profile and accounting for any thickness variation, the governing filling formulation was derived using the conservation laws of mass, momentum and free surface, which produced the thickness-integrated continuity, Navier-Stokes and pseudo-concentration equations, respectively. Appropriate transformations were incorporated into the thickness-integrated Navier-Stokes equations to accommodate the three-dimensional form of the cavity. Since surface tension also affects the flow in thinner sections, a study on the inclusion of this topic was also included. The finite element flow formulation was constructed by discretising the governing equations spatially and temporally using the conventional Galerkin method and the implicit backward difference method, respectively, and was solved via a mixed formulation. This was found to be the best approach for the cavity having thickness changes. For free surface tracking, the explicit Taylor-Galerkin method was used to discretise the pseudo-concentration equation since it gave more accurate results. This filling simulation model was applied to three case studies, where the numerical results were compared with the experimental data for the benchmark gravity sand casting as gathered by other researchers, a cylindrical shaped cavity in the laboratory and a high pressure die casting in the foundry. Good agreement was obtained in each case.
24
Espinós, Capilla Ana. "Numerical analysis of the fire resistance of circular and elliptical slender concrete filled tubular columns." Doctoral thesis, Editorial Universitat Politècnica de València, 2012. http://hdl.handle.net/10251/17579.
Анотація:
El empleo de pilares tubulares de acero rellenos de honnigón (CFT) ha crecido en las
últimas décadas, debido a su excelente comportamiento estructural, que aprovecha el efecto
combinado del acero y honnigón trabajando juntos. Esta asociación ofrece una serie de
ventajas que hacen de las columnas CFT una solución interesante: su alta capacidad portante
o su eficiente tecnología constructiva pueden citarse entre sus beneficios ampliamente
conocidos, que se completan con una elevada resistencia al fuego sin necesidad de protección
externa.
Tradicionalmente, se han venido utilizando secciones huecas circulares, cuadradas y
rectangulares para formar estas columnas compuestas. Adicionalmente, la sección elíptica ha
sido recientemente introducida dentro de la gama de secciones de acero huecas disponib les
comercialmente. Su atractivo estético y su reducida intrusión visual, junto con sus ventajas
estructurales asociadas a secciones con diferentes propiedades en sus ejes fuerte y débil,
hacen a las secciones elípticas de gran interés para los diseñadores. En esta tesis se estudian
pi lares CFT de sección tanto circular como elíptica.
Pese a que el comportamiento de los pilares CFT a temperatura ambiente ha quedado
bien establecido en los últimos años, en situación de incendio la degradación de las
propiedades del material da lugar a un comportamiento extremadamente no lineal de estas
columnas compuestas, lo que hace dificil predecir su fallo. El estado del arte en el campo del
comportamiento frente al fuego de columnas CFT se revisa en esta tesis, mostrando que es
necesario profundizar en su investigación para una comprensión completa del funcionamiento
de tales columnas en situación de incendio. En el caso de las secciones elípticas, este trabajo
constituye una investigación novedosa.
El comportamiento frente al fuego de los pilares CFT se estudia en esta tesis por
medio de un modelo realista tridimensional de elementos finitos. Los valores adoptados de los
parámetros delEspinós Capilla, A. (2012). Numerical analysis of the fire resistance of circular and elliptical slender concrete filled tubular columns [Tesis doctoral]. Editorial Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/17579
Palancia
25
Pacheco, Joe 1978. "Finite difference techniques for body of revolution radar cross section." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/8121.
Анотація:
Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2000.Includes bibliographical references (p. 267-272).
Although a number of radar cross section prediction techniques have been developed which exploit body of revolution symmetry, the use of finite-difference techniques with these geometries has not been throughly explored. This thesis investigates several finite-difference approaches which vary both in the approximations they introduce as well as the computational resources they require. These techniques include body of revolution finite-difference time-domain methods with both staircase and conformal grids, a hybrid FD-TD/geometrical optics method, and a body of revolution parabolic wave equation method. In addition, the use of the monostatic-bistatic equivalence principle is explored in approximating monostatic RCS at multiple angles from a single FD-TD simulation. Both canonical and more realistic BOR targets are modeled. The results from these techniques are compared, with each other and with method of moment predictions, physical theory of diffraction predictions, and analytic results. From these comparisons the tradeoffs possible between accuracy and computation with this collection of finite-difference tools is determined.
by Joe Pacheco, Jr.
M.Eng.
26
Gao, Sasa. "Development of a new 3D beam finite element with deformable section." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEI026/document.
Анотація:
Le nouvel élément de poutre est une évolution d'un élément de Timoshenko poutre avec un nœud supplémentaire situé à mi-longueur. Ce nœud supplémentaire permet l'introduction de trois composantes supplémentaires de contrainte afin que la loi constitutionnelle 3D complète puisse être utilisée directement. L'élément proposé a été introduit dans un code d'éléments finis dans Matlab et une série d'exemples de linéaires/petites contraintes ont été réalisées et les résultats sont systématiquement comparés avec les valeurs correspondantes des simulations ABAQUS/Standard 3D. Ensuite, la deuxième étape consiste à introduire le comportement orthotrope et à effectuer la validation de déplacements larges / petites contraintes basés sur la formulation Lagrangienne mise à jour. Une série d'analyses numériques est réalisée qui montre que l'élément 3D amélioré fournit une excellente performance numérique. En effet, l'objectif final est d'utiliser les nouveaux éléments de poutre 3D pour modéliser des fils dans une préforme composite textile. A cet effet, la troisième étape consiste à introduire un comportement de contact et à effectuer la validation pour un nouveau contact entre 3D poutres à section rectangulaire. La formulation de contact est dérivée sur la base de formulation de pénalité et de formulation Lagrangian mise à jour utilisant des fonctions de forme physique avec l'effet de cisaillement inclus. Un algorithme de recherche de contact efficace, qui est nécessaire pour déterminer un ensemble actif pour le traitement de contribution de contact, est élaboré. Et une linéarisation constante de la contribution de contact est dérivée et exprimée sous forme de matrice appropriée, qui est facile à utiliser dans l'approximation FEM. Enfin, on présente quelques exemples numériques qui ne sont que des analyses qualitatives du contact et de la vérification de l'exactitude et de l'efficacité de l'élément de 3D poutre proposéThe new beam element is an evolution of a two nodes Timoshenko beam element with an extra node located at mid-length. That extra node allows the introduction of three extra strain components so that full 3D stress/strain constitutive relations can be used directly. The second step is to introduce the orthotropic behavior and carry out validation for large displacements/small strains based on Updated Lagrangian Formulation. A series of numerical analyses are carried out which shows that the enhanced 3D element provides an excellent numerical performance. Indeed, the final goal is to use the new 3D beam elements to model yarns in a textile composite preform. For this purpose, the third step is introducing contact behavior and carrying out validation for new 3D beam to beam contact with rectangular cross section. The contact formulation is derived on the basis of Penalty Formulation and Updated Lagrangian formulation using physical shape functions with shear effect included. An effective contact search algorithm is elaborated. And a consistent linearization of contact contribution is derived and expressed in suitable matrix form, which is easy to use in FEM approximation. Finally, some numerical examples are presented which are only qualitative analysis of contact and checking the correctness and the effectiveness of the proposed 3D beam element
27
Lentz, W. Karl. "Optimum coupling in thin-walled, closed section composite beams." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/12018.
28
Rabe, Hermann. "The finite section method for infinite Vandermonde matrices and applications / H. Rabe." Thesis, North-West University, 2007. http://hdl.handle.net/10394/2034.
29
Chakravarty, Uttam Kumar. "Section builder: a finite element tool for analysis and design of composite." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22640.
Анотація:
Thesis (Ph. D.)--Aerospace Engineering, Georgia Institute of Technology, 2008.Committee Chair: Bauchau, Olivier; Committee Member: Craig, James; Committee Member: Hodges, Dewey; Committee Member: Mahfuz, Hassan; Committee Member: Volovoi, Vitali.
30
Assenso, Antwi Akwasi. "LOCATION AND CONFIGURATION OF REDUCED BEAM SECTION CONNECTION EFFECTS ON STRENGTH, STIFFNESS AND DUCTILITY OF MOMENT STEEL FRAMES." OpenSIUC, 2018. https://opensiuc.lib.siu.edu/dissertations/1532.
Анотація:
Moment resistant frames are mainly used in resisting lateral loads in buildings. During the 1994 Northridge Earthquake, some of these moment steel frame connections could not undergo inelastic deformation which led to many structural damages. New connection systems were proposed and tested which performed better than the pre-Northridge moment frame connections. Reduced beam section (RBS) connection is one of the most widely used connections after the Northridge Earthquake. Instead of increasing the steel at beam-column, the RBS connection rather removed steel from the flange of the beam. This connection thus gives the designer the option of deciding where the yield will occur in the frame. This research studies the three different parameters used in describing the location and configuration of the radius cut reduced beam section by employing finite element modeling. Variations in ductility, strength and elastic displacement were observed as these parameters were changed. Reducing the flange thus helped with ductility but affected the lateral load carrying capacity and stiffness of the frame.
31
Kadets, Borys. "Arboreal representations, sectional monodromy groups, and abelian varieties over finite fields." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/126927.
Анотація:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mathematics, May, 2020Cataloged from the official PDF of thesis.
Includes bibliographical references (pages 93-97).
This thesis consists of three independent parts. The first part studies arboreal representations of Galois groups - an arithmetic dynamics analogue of Tate modules - and proves some large image results, in particular confirming a conjecture of Odoni. Given a field K, a separable polynomial [mathematical expression], and an element [mathematical expression], the full backward orbit [mathematical expression] has a natural action of the Galois group [mathematical expression]. For a fixed [mathematical expression] with [mathematical expression] and for most choices of t, the orbit [mathematical expression] has the structure of complete rooted [mathematical expression]. The Galois action on [mathematical expression] thus defines a homomorphism [mathematical expression]. The map [mathematical expression] is the arboreal representation attached to f and t.
In analogy with Serre's open image theorem, one expects [mathematical expression] to hold for most f, t, but until very recently for most degrees d not a single example of a degree d polynomial [mathematical expression] with surjective [mathematical expression],t was known. Among other results, we construct such examples in all sufficiently large even degrees. The second part concerns monodromy of hyperplane section of curves. Given a geometrically integral proper curve [mathematical expression], consider the generic hyperplane [mathematical expression]. The intersection [mathematical expression] is the spectrum of a finite separable field extension [mathematical expression] of degree [mathematical expression]. The Galois group [mathematical expression] is known as the sectional monodromy group of X. When char K = 0, the group [mathematical expression] equals [mathematical expression] for all curves X.
This result has numerous applications in algebraic geometry, in particular to the degree-genus problem. However, when char K > 0, the sectional monodromy groups can be smaller. We classify all nonstrange nondegenerate curves [mathematical expression], for [mathematical expression] such that [mathematical expression]. Using similar methods we also completely classify Galois group of generic trinomials, a problem studied previously by Abhyankar, Cohen, Smith, and Uchida. In part three of the thesis we derive bounds for the number of [mathematical expression]-points on simple abelian varieties over finite fields; these improve upon the Weil bounds. For example, when q = 3, 4 the Weil bound gives [ .. ] for all abelian varieties A. We prove that [mathematical expression], [mathematical expression] hold for all but finitely many simple abelian varieties A (with an explicit list of exceptions).
by Borys Kadets.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Mathematics
32
Jeong, Woo Yong. "Structural analysis and optimized design of general nonprismatic I-section members." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53020.
Анотація:
Tapered I-section members have been employed widely for the design of long-span structures such as large clear-span buildings, stadiums, and bridges because of their structural efficiency. For optimized member design providing maximum strength and stiffness at minimum cost, general non-prismatic (tapered and/or stepped cross-sections) as well as singly-symmetric cross-sections have been commonly employed. Fabricators equipped to produce web-tapered members can create a wide range of optimized members from a minimal stock of different plates and coil. Linearly tapered web plates can be nested to minimize scrap. In many cases, the savings in material and manufacturing efficiencies lead to significant cost savings relative to the use of comparable rolled shapes. To employ Design Guide 25 (DG25) which provides guidance for the application of the provisions of the AISC Specification to the design of frames composed of general non-prismatic members, designers need a robust and general capability for determining the elastic buckling loads. Furthermore, robust tools are needed to facilitate the selection of optimum non-prismatic member designs based on minimum cost.
This research addresses the calculation of the elastic buckling loads for general non-prismatic members subjected to general loadings and bracing conditions (typically involving multiple brace points along a given member). This research develops an elastic buckling analysis tool (SABRE2) that can be used to define general geometries, loadings and bracing conditions and obtain a rigorous calculation of the elastic buckling load levels. The three-dimensional finite element equations using open section thin-walled beam theory are derived and formulated using a co-rotational approach including load height effects of transverse loads, stepped flange dimensions, and bracing and support height effects. In addition, this research addresses an algorithmic means to obtain automatic optimized member and frame designs using the above types of members based on Genetic Algorithms (GA). These capabilities are implemented in the tool SABRE2D, which provides a graphical user interface for optimized member and frame design based on updated DG25 provisions and the elastic buckling load calculations from SABRE2.
33
Ba-abbad, Mazen. "Reliability-based Design Optimization of a Nonlinear Elastic Plastic Thin-Walled T-Section Beam." Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/27895.
Анотація:
A two part study is performed to investigate the application of reliability-based design
optimization (RBDO) approach to design elastic-plastic stiffener beams with Tsection.
The objectives of this study are to evaluate the benefits of reliability-based
optimization over deterministic optimization, and to illustrate through a practical
design example some of the difficulties that a design engineer may encounter while
performing reliability-based optimization. Other objectives are to search for a
computationally economic RBDO method and to utilize that method to perform
RBDO to design an elastic-plastic T-stiffener under combined loads and with
flexural-torsional buckling and local buckling failure modes. First, a nonlinear
elastic-plastic T-beam was modeled using a simple 6 degree-of-freedom non-linear
beam element. To address the problems of RBDO, such as the high non-linearity and
derivative discontinuity of the reliability function, and to illustrate a situation where
RBDO fails to produce a significant improvement over the deterministic
optimization, a graphical method was developed. The method started by obtaining a
deterministic optimum design that has the lowest possible weight for a prescribed
safety factor (SF), and based on that design, the method obtains an improved
optimum design that has either a higher reliability or a lower weight or cost for the
same level of reliability as the deterministic design. Three failure modes were
considered for an elastic-plastic beam of T cross-section under combined axial and
bending loads. The failure modes are based on the total plastic failure in a beam
section, buckling, and maximum allowable deflection. The results of the first part
show that it is possible to get improved optimum designs (more reliable or lighter
weight) using reliability-based optimization as compared to the design given by
deterministic optimization. Also, the results show that the reliability function can be
highly non-linear with respect to the design variables and with discontinuous
derivatives. Subsequently, a more elaborate 14-degrees-of-freedom beam element
was developed and used to model the global failure modes, which include the
flexural-torsional and the out-of-plane buckling modes, in addition to local buckling
modes. For this subsequent study, four failure modes were specified for an elasticplastic
beam of T-cross-section under combined axial, bending, torsional and shear
loads. These failure modes were based on the maximum allowable in-plane, out-ofplane
and axial rotational deflections, in addition, to the web-tripping local buckling.
Finally, the beam was optimized using the sequential optimization with reliabilitybased
factors of safety (SORFS) RBDO technique, which was computationally very
economic as compared to the widely used nested optimization loop techniques. At
the same time, the SOPSF was successful in obtaining superior designs than the
deterministic optimum designs (either up to12% weight savings for the same level of
safety, or up to six digits improvement in the reliability for the same weight for a
design with Safety Factor 2.50).Ph. D.
34
Akman, Mehmet Nazim. "Analysis Of Thin Walled Open Section Tapered Beams Using Hybrid Stress Finite Element Method." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/2/12609246/index.pdf.
Анотація:
In this thesis, hybrid stress finite element is formulated for the analysis of the isotropic, thin walled, open section beams with variable cross sections. The beam element has two nodes each having seven degrees of freedom. Assumption of stress field is sufficient to determine the element stiffness matrix. Axial, flexural and torsional effects are taken into account in the analysis. The methodology can be applied both to the tapered and the uniform beams. Throughout this study, firstly element cross-sectional properties are computed using the flow analogy of the inter-connected elements which may have different thicknesses. Then another computer program calculates the displacements and stresses at the nodes along the beam. The results obtained are compared to the results taken from literature and commercial FEM program Nastran.
35
Guler, Togan Kemal. "Thermo-mechanical Finite Element Analysis And Design Of Tail Section For A Ballistic Missle." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12615165/index.pdf.
Анотація:
During the flight of missiles, depending on the flight conditions, rotation of missiles around its centerline can cause instabilities. To override this issue, missile generally is designed in 2 sections. In the missile, the rear tail section and the front section are to rotate freely by means of bearings. Tail section on which bearings are mounted is designed according to thermal loads due to flow of hot gasses through the nozzle and mechanical loads due to inertial load, interference fit and thread preload which appear during flight of missile.
The purpose of this thesis is to determine the most suitable structural parameters according to the flight conditions of missile.
The geometrical and load parameters which have effect on the results were determined. Finite element model is formed by using FEA software. After that, transient nonlinear thermo-mechanical analyses are performed and the most effective parameter on VM (Von-Mises) stress and force is determined.
DOE (Design of Experiments) method was used to determine the most suitable values for the structural parameters. Totally 27 different configurations are studied to achieve to the most suitable values for variable set.
It is observed that VM stress and force results for all configurations are within the ±%5 ranges. So this means parameters don&rsquo
t affect the systems response very much. By taking manufacturing processes into consideration, configuration with the highest bearing inner/outer ring interference is taken. From the comparison of the results, the most suitable configuration is obtained after checking forces and VM stress on the bearings.
36
Tao, Jiwen. "Finite element simulation for superplastic forming using a non-Newtonian viscous thick section element." Thesis, University of the West of England, Bristol, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340817.
37
Rouhani, Siamak. "Temperature analyses of Concrete Frame Bridges with Finite Elements." Thesis, KTH, Bro- och stålbyggnad, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-145904.
Анотація:
FE-modeling is a rapidly spreading method to analyze structures nowadays. With this theunderstanding of the outcome is of very high importance and potential inaccuracies areimportant to find so that faulty and over dimensioning of the structure does not occur whichleads to unnecessary costs. One of these inaccuracies is the unrealistic sectional forces that occurdue to thermal effects in the transversal direction for concrete frame bridges which leads to anexcessive amount much reinforcement in the structure than actually needed. This has beenstudied with several cases by using two approaches on how to apply the temperature in the framebridge, only in the superstructure and in the whole structure, but also by analyzing severalboundary conditions. By examining the results for the sectional forces and stresses one of thetemperature approaches could be disregarded because of the extreme values in the transitionbetween superstructure and support. But the other approach was much more useful because ofits better compliance with reality. With these results and by calculating the reinforcement neededfor the worst case, one model has been found to be the most favorable and can be used whenmodeling concrete frame bridges with acceptable outcome. The study resulted in a model whereone applies a varying temperature on the whole structure, with spring boundary conditions over asurface that represents the bottom slab.
38
Gorak, Mark S. Libby Jeffrey A. "Finite element modeling of the RAH-66 Comanche Helicopter Tailcone section using PATRAN and DYTRAN /." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2001. http://handle.dtic.mil/100.2/ADA392096.
39
Libby, Jeffrey A. "Finite element modeling of the RAH-66 Comanche Helicopter Tailcone section using PATRAN and DYTRAN." Thesis, Monterey, California. Naval Postgraduate School, 2001. http://hdl.handle.net/10945/2595.
Анотація:
The United States Army contracted Boeing-Sikorsky to develop the RAH-66 Comanche, a new, armed reconnaissance helicopter that features stealth technology designed to improve survivability when operating in hostile environments. Ballistic testing is required on any new technology, including the Comanche, prior to fielding. This thesis uses computer programs called PATRAN and DYTRAN from MSC Software Corporation to build a model and simulate the effects of an explosive round detonating in the Comanche tailcone section. This thesis describes in great detail the process of creating and modifying the model in PATRAN to most accurately depict the Comanche tailcone section, and of creating the input decks for DYTRAN to run the analysis. A test case involving an explosion with a high amount of explosive energy, or specific internal energy (SIE) was simulated. From this test, several results are shown to display the capabilities of DYTRAN. These results, when compared with live fire data, can be used to validate the computer-based simulation in order to reduce the requirements of expensive live fire testing.US Army (USA) author
40
Penekli, Ufuk. "Finite Element Analysis Of Bending Operation Of Aluminum Profiles." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609463/index.pdf.
Анотація:
Bending process is an important forming process in most industrial fields. Springback and cross-section distortion are commonly faced problems in bending process. Springback behavior of closed and open section beams changes with different parameters such as cross-section type, cross-section dimensions, bend radius and bend angle. For closed sections like tube, the dominating problem is cross-section distortion. The thickness of the tube at intrados (inner surface of tube being in contact with die) increases, whereas the thickness of the tube at extrados (outer surface of tube) decreases. Furthermore, another cross-section distortion type for tubes is flattening at extrados which is undesirable in some manufacturing operations.
The present research, using finite element method, focuses on investigating the springback behavior of commonly used aluminum beams which are T-Shaped, U-Shaped and tubular for different cases. A series of analyses is performed for a beam and the changing parameters in the analyses are bend radius and thickness.
Furthermore, for tubes, the effects of axial force on springback behavior are investigated. It is seen that the axial force causes stretching and the springback angles are decreased.
Moreover, in order to overcome cross-section distortion in flattening for tubes, different internal pressures are used and the effects of internal pressure are investigated. By applying appropriate internal pressure, the flattening distortion is mostly eliminated.
Conclusions are drawn revealing springback behaviors and cross-section distortions with respect to bend radius, bend angle, thickness, axial pull and internal pressures. They are in good agreement with other published researches and experimental results. Therefore, the models can be used to evaluate tooling and process design in bending operations.
41
Persson, Daniel. "Efficient Calculations of Two-Dimensional Radar Cross-Section Using DGFEM." Thesis, Uppsala universitet, Avdelningen för beräkningsvetenskap, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-424009.
Анотація:
A two-dimensional discontinuous Galerkin finite element method algorithm in the time domain was developed for calculation of the radar cross-section of an arbitrary object. The algorithm was formed using local nodal basis functions in each element and coupling them via numerical upwind flux. Both transverse electric and transverse magnetic polarization, as well as three different dispersive material models, were handled. The computational domain was effectively truncated with low reflections using the uniaxial perfectly matched layer method. Two different time stepping methods were used, low-storage explicit Runge-Kutta and Leap-Frog, to allow for flexibility in the time step and application of a stabilization method. The algorithm was verified with geometries, which have analytical expressions, and an existing validated code. The algorithm was also compared to an existing algorithm, which utilized the continuous finite element method with implicit time stepping, and showed outstanding performance regarding computation time and memory allocation. Since the developed algorithm had explicit time stepping could no general conclusions favoring any of the methods beyond these specific algorithms be made. The results still encouraged continued development of the DGFEM algorithm, where the expansion into three dimensions and optimizations could be explored further.
42
Nanayakkara, Masarachige A. "Finite element analysis for the elastic stability of thin walled open section columns under generalized loading." Thesis, Loughborough University, 1986. https://dspace.lboro.ac.uk/2134/7501.
Анотація:
The current interest in collapse characteristics brought about by crashworthiness requirements ýas shown the need for a better understanding and predictive capability for the thin walled open section structures. In general three possible modes exist in which a loaded thin walled open section column can buckle: 1) they can bend in the plane of one of the principal axes; 2) they can twist about the shear. centre; 3) or they can bend and twist simultaneously. The following study was undertaken to investigate the general failure of thin walled open section structures. A literature survey was conducted and it prevailed that a basic fundamental theoretical study was vital in describing the behaviour of thin walled structural members. The following stages of theoretical study have been completed: 1) Formulation of the stiffness matrix to predict the generalised force-displacement relationships assuming the small displacement theory in the linear elastic range. 2) Formulation of the geometric stiffness matrix to predict the buckling criteria under generalised loading and end constraints in the linear elastic range. 3) Formulation of the compound coordinate transformation matrix to relate local and global displacements or forces. 4) Preparation of the associated finite element computer program to solve general thin walled open sections structural problems.
43
Jimmy, Adamo, and Abdi Hamse. "Behavior of polygonal semi-closed thin-walled cross-section : A study based on finite strip analysis." Thesis, Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-62257.
Анотація:
The acceptance and the use of cold-formed steel sections has significantly increased in recent years due to advantages such as consistency and accuracy of profile, ease of fabrication, high strength and stiffness to the lightness in the weight. For thin-walled columns, made by folding a plane plate into a section, it is possible that when they are subjected to compression loads they may buckle either locally, if the member is very short, or globally if the member is very long. In addition to local and global buckling, a thin-walled member of an open cross section may also show buckling involving a “distortion” of the cross section. Compared to local and global buckling, distortional buckling is not very familiar and has been discovered only in thin-walled members of open cross sections such as cold-formed steel section columns. The objective of this study is to investigate the behavior of polygonal semi-closed cross-section with pure compression. The study comprise to only elastic buckling and the methodology is consisted by using CUFSM analysis. In order to execute CUFSM of polygonal profiles, the scripts have created which match the Matlab script files (m-files) downloaded from CUFSM 4 open source. The distortional buckling mode is governing as a buckling failure, which occur and dominate in the cases where spring values are 100 kN or higher. However, the contrary result reveals by a decreasing of the spring values. The behavior of the cross-section is dependent on how the interaction of different buckling modes prevails at the corresponding critical half-wavelength. Considering the predomination of distortional buckling mode indicates that the most of polygonal cross-section do not behave as rigid, i.e. as whole cross-section. A reducing of distortional mode and increasing of local mode as well as global mode gives indication that the behavior of the cross-section has changed and turned significantly into more rigid and thus is expected to behave more as whole cross-section. The more spring values decrease, the higher global mode arises and dominates for the lower slenderness range. The critical half-wavelength for each profile illustrates the needed density between bolts on the longitudinal part of the member. In the interest of eliminating distortional buckling failure, due the fact that distortional buckling is unpredictable, the bolt-density should be lower than the corresponding half-wavelength for the profile where the distortional mode is predominating.
44
Hart, Daniel Constantine. "Development of a Progressive Failure Finite Element Analysis For a Braided Composite Fuselage Frame." Thesis, Virginia Tech, 2002. http://hdl.handle.net/10919/34026.
Анотація:
Short, J-section columns fabricated from a textile composite are tested in axial compression to study the modes of failure with and without local buckling occuring.The textile preform architecture is a 2x2, 2-D triaxial braid with a yarn layup of [0 deg 18k/+-64 deg 6k] 39.7% axial. The preform was resin transfer molded with 3M PR500 epoxy resin. Finite element analyses (FEA) of the test specimens are conducted to assess intra- and inter- laminar progressive failure models. These progressive failure models are then implemented in a FEA of a circular fuselage frame of the same cross section and material for which test data was available. This circular frame test article had a nominal radius of 120 inches, a forty-eight degree included angle, and was subjected to a quasi-static, radially inward load, which represented a crash type loading of the frame. The short column test specimens were cut from some of the fuselage frames. The branched shell finite element model of the frame included geometric nonlinearity and contact of the load platen of the testing machine with the frame. Intralaminar progressive failure is based on a maximum in-plane stress failure criterion followed by a moduli degradation scheme. Interlaminar progressive failure was implemented using an interface finite element to model delamination initiation and the progression of delamination cracks. Inclusion of both the intra- and inter- laminar progressive failure models in the FEA of the frame correlated reasonably well with the load-displacement response from the test through several major failure events.Master of Science
45
Dere, Fatih. "Experimental And Finite Element Analysis Of Rotary Draw Tube Bending Process." Master's thesis, METU, 2013. http://etd.lib.metu.edu.tr/upload/12615433/index.pdf.
Анотація:
Rotary draw bending, which has very good flexibility and easy tooling, is one of the most preferred bending types for tubular profiles. Cross-section distortion and the spring-back phenomena are commonly faced problems in bending processes. Spring-back is the inevitable problem that is to be solved by manufacturer, generally by overbending. For hollow tubes cross-section distortion is another difficulty since using hollow tubes results in higher strain rates and distortions. During the process the thickness of the hollow tube at the inner surface, which is contacting with the die, increases and the thickness of the tube at the outer surface decreases. Wrinkling is another important defect that occurs at the inner surface of the tube in large diameter thin walled tube bendings.
This research compares the experimental results with the finite element analysis of the rotary draw bending process. The aim is to obtain bending characteristics of the two material types, SS304 and St37 and so, to reduce the number of the bending in manufacturing. The main parameters in rotary draw bending process are the bending angle, bend radius, material properties and the geometry of the tube that is to be bent. In this study, to deal with the process, two different materials, three different bending angles and three different tube geometries are used in experiments as well as in finite element analysis. In finite element analysis explicit method is used. It is seen that the experimental results are in good agreement with the numerical results.
46
Wilson, Kevin E. "A Finite Element Investigation of Non-Orthogonal Moment Connections in Steel Construction." University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1445609099.
47
Carlson, Ryne. "Flexural Strength of Steel Beams with Holes in the Tension Flange." University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1563527519192391.
48
Martin, Maverick. "Structures spatiales déployables constituées de mètres rubans : analyse et implémentation de modèles de poutre à section flexible." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0571/document.
Анотація:
Les mètres rubans sont utilisés comme dispositif de déploiement car ils sont légers, compacts, se déploient de manière autonome et ont une capacité d'auto-blocage en position déployée. Ces structures élancées de forme cylindrique présentent un comportement complexe avec formation de plis localisés. Leur modélisation est donc difficile : bien que des modèles de poutre à section flexible (RFleXS) aient été développés. Les travaux réalisés consistent à développer des outils numériques d'aide au dimensionnement de structures déployées par des rubans. Un modèle RFleXS adimensionné dédié aux rubans peu profonds est introduit et analysé, mettant en évidence des liens avec le modèle de barre d'Ericksen régularisé. Ces liens expliquent la formation de plis et caractérisent les trois zones constitutives d'un pli. On détermine de façon analytique le nombre et la position des points de bifurcation des branches de solution obtenues pour un essai de flexion pure d'un ruban. Un enrichissement de la cinématique de section est intégré dans les modèles RFleXS. Les simulations de flexion de ruban montrent alors une bonne corrélation avec les modèles de coque. Une nouvelle formulation des modèles RFleXS est implémentée et conduisant au développement de deux outils numériques : un code de calcul par éléments finis complet et un élément à deux noeuds intégré dans un code commercial. Des essais de flexion réalisés sur des rubans composites viennent compléter ces travaux afin de confronter les simulations numériques à des essais réels. Bien que des écarts soient observés, le comportement global du ruban est bien retranscrit par les modèles de poutre à section flexibleDue to their lightness, compactness, their autonomous deployment and their ability to self-locking while deployed, tape-springs are considered to deploy structures. These slender and cylindrical structures highlight a complex behaviour because of the formation of localised folds. Tape-springs are then difficult to model but a rod model with flexible cross-section (RFleXS) has been developed in order to characterise the tape-spring behaviour.The purpose of this PhD was to develop numerical tools dedicated to design structures deployed by tape-spings. A dimensionless form of the RFleXS model dedicated to shallow tape spring has been developed and links with a regularised Ericksen's bar have been made. These links help to explain folds creation and to determine characteristics of the three constitutive areas of a fold. Analysis of the dimensionless model leads to determine the finite number and the position of bifurcation points for the pure bending of a tape-spring. The cross-section kinematic is enriched; simulations of bending tests then show a good correlation with shell models. A new implementation of RFleXS models is introduced, leading to the creation of two numerical tools: a full finite element software and a one-dimensional element with two nodes incorporated in Abaqus. Some bending experiments have been performed in order to compare simulations with measured data. Even if discrepancies are observed, these comparisons show that the tape-spring overall behaviour is well predicted by rod models with flexible cross-section
49
Kreutz, Johannes [Verfasser]. "Augmented Beam Elements Using Unit Deflection Shapes Together with a Finite Element Discretisation of the Cross Section / Johannes Kreutz." Aachen : Shaker, 2013. http://d-nb.info/1050342348/34.
50
Blanco, Oscar. "Dynamique des faisceaux dans la section finale de focalisation du futur collisionneur linéaire." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112108/document.
Анотація:
L’exploration d’une nouvelle physique à l’échelle d’énergie des « Tera electron Volt » (TeV) nécessite de collisionner des leptons dans de grands accélérateurs linéaires à grande luminosité. Ces collisionneurs linéaires requiert une taille de faisceau à l’echelle nanométrique au Point d’Interaction (IP).Parmi les multiples effets participant à la degradation de la luminosité, la correction de la chromaticité, l’effet du rayonnement synchrotronique et la correction des erreurs dans la ligne sont parmi les trois effets à maîtriser afin de réduire la taille du faisceau dans la Section Finale de Focalisation (FFS).Cette these propose un nouveau schéma de correction de la chromaticitè que l’on appelera “non-entrelacé”, appliqué ici au projet CLIC. Lors de l’implementation de cette nouvelle methode, il a été mis en evidence que le probléme principal est la dispersion de deuxième ordre au Doublet Final (FD), qui traverse un sextupole utilisé pour annuler les composantes géometriques restantes.L’effet du rayonnement peut être evalué par méthode de tracking des particules ou par des approximations analytiques. Afin d’inclure ces effets du rayonnement et les paramétres optiques de la ligne pendant la conception et le processus d’optimisation, l’effet Oide et le rayonnement dû aux aimants dipolaires ont été etudiés.Le résultat analytique du rayonnement synchrotronique dans les aimants dipolaires fut generalisé dans les cas avec alpha et dispersion non-nulles à l’IP. Cette généralisation est utilisée pour améliorer le code de simulation PLACET.Le rayonnement dans les aimants quadripolaires finaux imposent une limite à la taille verticale minimale du faiceau, connu comme l’effet Oide. Celui-ci est uniquement important à 3 TeV, donc deux possibilités sont explorées pour atténuer sa contribution dans la taille du faisceau : doubler la longueur et réduire le gradient du dernièr quadripole (QD0), ou integrer une paire d’aimants octupolaires, un en amont et un en aval du QD0.Une partie des exigences du FFS pour les nouveaux collisionneurs linéaire à leptons est testée expérimentalement dans l’« Accelerator Test Facility » (ATF). La réduction de la taille du faisceau d’électrons en utilisant le schéma local de correction de la chromaticité est explorée dans une extension de la ligne originale, appellé ATF2, oú deux buts furent fixés : atteindre 37 nm de taille verticale du faisceau à l’IP, et stabiliser de l’ordre du nanomètre la position verticale du faisceau à l’IP. Depuis 2014, une taille de 44 nm avec un nombre de particules d’environ 0.1 × 10^10 par paquet est atteint de manière regulière.Des cavités radio-frequence seront utilisées pour la stabilisation du faisceau, et également pour détecter le déplacement/les fluctuations du faisceau au dehors la marge tolerable pour le systéme de mesure, ainsi que des erreurs non detectées dans l’optique.Un set de trois cavités furent installées et sont utilisées pour mesurer la trajectoire du faiceau dans la région de l’IP, fournissant ainsi des informations pour reconstruire la position et l’angle à l’IP. Les specifications pour l’optique nominale d’ATF2, i.e. 1 nm de résolution sur 10 μm de gamme dynamique à un nombre de particules de 1.0 × 10^10 par paquet, n’ont pas encore été atteint.La meilleur résolution atteinte jusqu’ici correspond à 50 nm pour 0.4 × 10^10 particules par paquet, où le bruit de l’éléctronique impose une limite de 10 nm par cavité sur la résolution. La gamme dynamique est de 10 μm à 0.4 × 10^10 particules par paquet et 10 dB d’attenuation du signal des cavités, nécéssitant de mettre l’électronique à niveau. Le test du système d’asservissement pour stabiliser le faisceau a atteint une réduction de la fluctuation jusqu’a 67 nm, compatible avec la résolution des cavitésThe exploration of new physics in the “Tera electron-Volt” (TeV) scale with precision measurements requires lepton colliders providing high luminosities to obtain enough statistics for the particle interaction analysis. In order to achieve design luminosity values, linear colliders feature nanometer beam spot sizes at the Interaction Point (IP).Three main issues to achieve the beam size demagnification in the Final Focus Section (FFS) of the accelerator are the chromaticity correction, the synchrotron radiation effects and the correction of the lattice errors.This thesis considers two aspects for linear colliders: push the limits of linear colliders design, in particular the chromaticity correction and the radiation effects at 3 TeV, and the instrumentation and experimental work on beam stabilization in a test facility.A new chromaticity correction scheme, called non-interleaved, is proposed to the local and non-local chromaticity corrections for CLIC. This lattice is designed and diagnosed, where the main issue in the current state of lattice design is the non-zero second order dispersion in the Final Doublet (FD) region where a strong sextupole is used to correct the remaining geometrical components.The radiation effect can be evaluated by tracking particles through the lattice or by analytical approximations during the design stage of the lattices. In order to include both, radiation and optic parameters, during the design optimization process, two particular radiation phenomena are reviewed: the Oide effect and the radiation caused by bending magnets .The analytical result of the radiation in bending magnets in was generalized to the case with non-zero alpha and non-zero dispersion at the IP, required during the design and luminosity optimization process. The closed solution for one dipole and one dipole with a drift is compared with the tracking code PLACET, resulting in the improvement of the tracking code results.The Oide effect sets a limit on the vertical beamsize due to the radiation in the final quadrupole. Only for CLIC 3 TeV this limit is significant, therefore two possibilities are explored to mitigate its contribution to beam size: double the length and reduce the QD0 gradient, or the integration of a pair of octupoles before and after QD0.Part of the requirements of the FFS for new linear accelerators are tested in The Accelerator Test Facility (ATF). The beam size reduction using the local chromaticity correction is explored by an extension of the original design, called ATF2 with two goals: achieve 37 nm of vertical beam size at the IP, and the stabilization of the IP beam position at the level of few nanometres. Since 2014 beam size of 44 nm are achieved as a regular basis at charges of about 0.1 × 10^10 particules per bunch.A set of three cavities (IPA, IPB and IPC), two upstream and one downstream of the nominal IP and on top of separate blocks of piezo-electric movers, were installed and are used to measure the beam trajectory in the IP region, thus providing enough information to reconstruct the bunch position and angle at the IP. These will be used to for beam stabilization and could detect beam drift/jitter beyond the tolerable margin and undetected optics mismatch affecting the beam size measurements. The specifications required of 1 nm resolution over 10 μm dynamic range at 1.0 × 10 10 particules per bunch with the ATF2 nominal optics have not been yet achieved.The minimum resolution achieved is just below 50 nm at 0.4 × 10^10 particules per bunch with a set of electronics impossing a noise limit on resolution of 10 nm per cavity. The dynamic range is 10 μm at 10 dB attenuation and 0.4 × 10^10 particules per bunch, indicating the need to upgrade theelectronics. The integration to the ATF tuning instruments is ongoing. Nonetheless, feedback has been tested resulting in reduction of beam jitterdown to 67 nm, compatible with resolution