Le but final de cette thèse est la proposition dune technique de résolution du problème du sixième degré de liberté des méthodes de bandes finies et déléments finis de plaque et de coque surbaissée déformable en cisaillement (le problème de rotation dans le plan) et de lappliquer dans la formulation des bandes finies et des éléments finis afin danalyser le comportement des structures à parois minces. Tout dabord, le présent travail introduit les caractéristiques des profils à parois minces tels que formes de la section, nuances dacier et imperfections initiales de type géométrique (défaut de rectitude, de planéité), structural (contraintes résiduelles) ou matériel (écrouissage). Ceux-ci sont nécessaires aux analyses ultérieures. Ensuite, une étude bibliographique aborde les méthodes de calcul des barres à parois minces tant analytiques que semi-empiriques ou numériques. Les méthodes analytiques ont été basées sur les théories de VLASOV et de BENSCOTER et une méthode intitulée Generalized Beam Theory développée par SCHARDT avec ses collègues depuis le début des années 1970 en Allemagne. Les méthodes semi-empiriques tiennent compte de linfluence du voilement sur le comportement global par le concept de largeur et de section effectives. Les méthodes numériques sont la méthode des éléments finis de type plaque, de type coque et la méthode des bandes finies. Puis, une technique originale est proposée avec succès pour introduire dans les relations standard déformation-déplacement des théories des plaques et des coques surbaissées, la rotation dans le plan pour assurer la conformité des variables nodales rotatives aux jonctions spatiales. Lapplication de cette technique sert à mettre au point les bandes finies et les éléments finis de type plaque et coque surbaissée. Il est proposé un programme déléments finis, nommé FENALYSE, qui est capable danalyser la linéarité, la non-linéarité et le flambement des structures à parois minces qui sont composées ou peuvent être modélisées par plaques planes et coques surbaissées. Tandis que les bandes finies ne sont développées que pour calculer le flambement des profils à parois minces qui sont simplement appuyés et un programme intitulé FLAMBANDE est proposé. Les verrouillages de cisaillement et de membrane sont éliminés par la technique dintégration réduite. La description lagrangienne actualisée est utilisée dans lanalyse non-linéaire. Les éléments finis de type plaque et de type coque surbaissée permettent de considérer, entre autre, les phénomènes inhérents aux profils à parois minces tels que la torsion non uniforme avec gauchissement, la distorsion de la section, les phénomènes dinstabilité couplées, la plasticité, les contraintes résiduelles, les imperfections locales et globales, le changement de la limite délasticité sur la section. Plusieurs exemples numériques tant académiques que pratiques sont réalisés afin de montrer la fiabilité de ces éléments finis.

The considerable progress in the research and development of thin-walled beam structures responds to their growing use in engineering construction and to their increased need for efficiency in strength and cost. The result is a structure that exhibits large shear strains and important non uniform warping under different loadings, such as non uniform torsion, shear bending and distortion.<p><p>A unified approach is formulated in this thesis for 3D thin walled beam structures with arbitrary profile geometries, loading cases and boundary conditions. A single warping function, defined by a linear combination of longitudinal displacements at cross sectional nodes (derived from Prokic work), is enhanced and adapted in order to qualitatively and quantitatively reflect and capture the nature of a widest possible range of behaviors. Constraints are prescribed at the kinematics level in order to enable the study of arbitrary cross sections for general loading. This approach, differing from most published theories, has the advantage of enabling the study of arbitrary cross sections (closed/opened or mixed) without any restrictions or distinctions related to the geometry of the profile. It generates automatic data and characteristic computations from a kinematical discretization prescribed by the profile geometry. The amount of shear bending, torsional and distortional warping and the magnitude of the shear correction factor is computed for arbitrary profile geometries with this single formulation.<p><p>The proposed formulation is compared to existing theories with respect to the main assumptions and restrictions. The variation of the location of the torsional center, distortional centers and distortional rotational ratio of a profile is discussed in terms of their dependency on the loading cases and on the boundary conditions.<p><p>A 3D beam finite element model is developed and validated with several numerical applications. The displacements, rotations, amount of warping, normal and shear stresses are compared with reference solutions for general loading cases involving stretching, bending, torsion and/or distortion. Some examples concern the case of beam assemblies with different shaped profiles where the connection type determines the nature of the warping transmission. Other analyses –for which the straightness assumption of Timoshenko theory is relaxed– investigate shear deformation effects on the deflection of short and thin beams by varying the aspect ratio of the beam. Further applications identify the cross sectional distortion and highlight the importance of the distortion on the stresses when compared to bending and torsion even in simple loading cases. <p><p>Finally, a non linear finite element based on the updated lagrangian formulation is developed by including torsional warping degrees of freedom. An incremental iterative method using the arc length and the Newton-Raphson methods is used to solve the non linear problem. Examples are given to study the flexural, torsional, flexural torsional and lateral torsional buckling problems for which a coupling between the variables describing the flexural and the torsional degrees of freedom occurs. The finite element results are compared to analytical solutions based on different warping functions and commonly used in linear stability for elastic structures having insufficient lateral or torsional stiffnesses that cause an out of plane buckling. <p> / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished

Indiana University-Purdue University Indianapolis (IUPUI) / Crashworthiness design is gaining more importance in the automotive industry due to high competition and tight safety norms. Further there is a need for light weight structures in the automotive design. Structural optimization in last two decades have been widely explored to improve existing designs or conceive new designs with better crashworthiness and reduced mass. Although many gradient based and heuristic methods for topology and topometry based crashworthiness design are available these days, most of them result in stiff structures that are suitable only for a set of vehicle components in which maximizing the energy absorption or minimizing the intrusion is the main concern. However, there are some other components in a vehicle structure that should have characteristics of both stiffness and flexibility. Moreover, the load paths within the structure and potential buckle modes also play an important role in efficient functioning of such components. For example, the front bumper, side frame rails, steering column, and occupant protection devices like the knee bolster should all exhibit controlled deformation and collapse behavior. This investigation introduces a methodology to design dynamically crushed thin-walled tubular structures for crashworthiness applications. Due to their low cost, high energy absorption efficiency, and capacity to withstand long strokes, thin-walled tubular structures are extensively used in the automotive industry. Tubular structures subjected to impact loading may undergo three modes of deformation: progressive crushing/buckling, dynamic plastic buckling, and global bending or Euler-type buckling. Of these, progressive buckling is the most desirable mode of collapse because it leads to a desirable deformation characteristic, low peak reaction force, and higher energy absorption efficiency. Progressive buckling is generally observed under pure axial loading; however, during an actual crash event, tubular structures are often subjected to oblique impact loads in which Euler-type buckling is the dominating mode of deformation. This undesired behavior severely reduces the energy absorption capability of the tubular structure. The design methodology presented in this paper relies on the ability of a compliant mechanism to transfer displacement and/or force from an input to desired output port locations. The suitable output port locations are utilized to enforce desired buckle zones, mitigating the natural Euler-type buckling effect. The problem addressed in this investigation is to find the thickness distribution of a thin-walled structure and the output port locations that maximizes the energy absorption while maintaining the peak reaction force at a prescribed limit. The underlying design for thickness distribution follows a uniform mutual potential energy density under a dynamic impact event. Nonlinear explicit finite element code LS-DYNA is used to simulate tubular structures under crash loading. Biologically inspired hybrid cellular automaton (HCA) method is used to drive the design process. Results are demonstrated on long straight and S-rail tubes subject to oblique loading, achieving progressive crushing in most cases.

Работа посвящена разработке нового технического решения узла крепления подкрановых балок к ригелю покрытия рамы здания из ЛСТК (легких стальных тонкостенных конструкций), а также изучению его работы под нагрузкой. В результате исследования разработаны рабочие чертежи узла крепления и инженерный метод расчета данного узла, что позволяет расширить область применения каркасов из ЛСТК для строительства однопролетных зданий с подвесными кранами грузоподъемностью до 2-3 тс. В рамках настоящего исследования разработана расчетная пространственная модель здания в ПК ЛИРА-САПР 2016, произведен статический расчет по расчетным сочетаниям усилий. На основании результатов расчета методом конечных элементов определены максимальные действующие усилия, возникающие в несущих конструкциях. / Present work is devoted to the development of a new technical solution for the attachment joint of crane beams to the girder of the building frame covering made of LSTWS (Light steel thin-walled structures), as well as the study of its operation under load. As a result of the study, working drawings of the attachment joint and an engineering method for calculating this unit were developed, which makes it possible to expand the scope of application of frames from LSTWS for the construction of single-span buildings with overhead cranes with a lifting capacity of up to 2-3 t. Within the framework of this study, a computational spatial model of the building was developed in the FEA software LIRA-SAPR 2016. Static calculation was performed based on the design combinations of efforts. Based on the results of the calculation by the finite element method (FEM), the maximum acting forces arising in the supporting structures are determined.

This master’s thesis is dealing with analysis of fluid flow pulse in a flexible tube representing e.g. an artery in a human body. In ANSYS program, 3D simulations were performed, and these are so-called interrelated FSI analysis. In Maple software, 1D simulations of fluid flow in the tube were performed for various thin-walled and thick-walled variants. The aim is using these programs to determine the flow rates and pressures in the tube, its wall deformation and stress. Therefore, the theoretical part deals mainly with basic equations of flow dynamics, linear and nonlinear models and rotationally symmetric vessels. In the computational part are described individual procedures in the mentioned programs.