Bibliografie tematiche / Gradient de discontinuité

Letteratura scientifica selezionata sul tema "Gradient de discontinuité"

Autore: Grafiati

Pubblicato: 8 giugno 2024

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Articoli di riviste sul tema "Gradient de discontinuité":

Brill, J. P. "Discontinuities in the Orkiszewski Correlation for Predicting Pressure Gradients in Wells". Journal of Energy Resources Technology 111, n. 1 (1 marzo 1989): 34–36. http://dx.doi.org/10.1115/1.3231398.

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The Orkiszewski correlation is used extensively in the petroleum industry for predicting pressure gradients when gas and liquid flow simultaneously in wells. Unfortunately, the correlation contains a parameter called the liquid distribution coefficient, Γ, that can be discontinuous at a superficial mixture velocity of 10 ft/sec. The liquid distribution coefficient is used to predict both the elevation and friction components of the pressure gradient for slug flow. The accepted trial and error method for integrating the pressure gradient to obtain pressure loss in wells can fail to converge when pressure gradients are discontinuous. Examples of discontinuities in Γ for oil as the continuous phase are presented for several liquid viscosities ranging from 0.3 to 200 cp and for pipe diameters of 1.049, 2.441 and 6.049 in. It was found that a constraint recommended for Γ when mixture velocity <10 ft/sec was essentially useless. It was also found that a constraint for velocities >10 ft/sec could actually increase the magnitude of pressure gradient discontinuity. Convergence of pressure loss calculations when the discontinuity was encountered was possible only if the convergence tolerance was temporarily relaxed.

Emmanuel, I., K. D. Adedayo, B. Adeyemi e O. S. Ojo. "Meteorological parameter anomalies and anomalous radio propagation over Nigeria". Nigeria Journal of Pure and Applied Physics 9, n. 1 (21 aprile 2020): 34–50. http://dx.doi.org/10.4314/njpap.v9i1.7.

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Distribution and variation of anomalous radio propagation, temperature and relative humidity anomalies were obtained and analyzed using six years (2010-2015) Era interim data. Seasonal spatial distribution of refractivity gradient and its components were analyzed. The result showed that about 90% of wet component contributed to the variation of refractivity gradient. Highest range of refractivity gradients and its wet components were obtained during the wet season. The result of correlation between ducting occurrence and temperature showed strong negative correlation except in Lagos where positive correlation of 3% was observed. However, positive correlation which ranges between 39% and 70% exist between duct occurrence and relative humidity except in Lagos in Nigeria. Refractivity gradients, relative humidity anomaly and temperature experience a monthly variation. These variations can be attributed to the seasonal movement of inter-tropical discontinuity (ITD) across Nigeria. Keywords: anomalous, anomaly, correlation, ITD

Zakharov, S. V., e A. M. Il'in. "From weak discontinuity to gradient catastrophe". Sbornik: Mathematics 192, n. 10 (31 ottobre 2001): 1417–33. http://dx.doi.org/10.1070/sm2001v192n10abeh000599.

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Carriero, M., A. Leaci e F. Tomarelli. "Free gradient discontinuity and image inpainting". Journal of Mathematical Sciences 181, n. 6 (marzo 2012): 805–19. http://dx.doi.org/10.1007/s10958-012-0716-4.

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Liu, Yahong, Meize Li, Kun Song, Yuhao Jing, Jiale Guo, Qingyu Hai e Xiaopeng Zhao. "Broadband gradient phase discontinuity all-dielectric metasurface". Modern Physics Letters B 34, n. 15 (30 marzo 2020): 2050168. http://dx.doi.org/10.1142/s0217984920501687.

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In recent years, metasurfaces have widely been studied due to their ability to offer a spatially varying phase response, low losses, ultrathin size, and easy fabrication. In this paper, a gradient phase discontinuity all-dielectric metasurface consisting of arrays of silicon cube resonator is designed. By adjusting the dimension of the silicon cube resonator, a [Formula: see text] transmission phase covered from [Formula: see text] to [Formula: see text] with [Formula: see text] phase intervals is realized in a frequency from 9.7 GHz to 11.8 GHz. We demonstrate the all-dielectric metasurface can produce the anomalous refraction, vortex beams, and wave-focusing in the microwave and infrared band, respectively. It can be expected that the proposed metasurfaces can find wide applications in communication, designing integrated optical devices, and focusing lenses.

Vogt, J., A. Albert e O. Marghitu. "Analysis of three-spacecraft data using planar reciprocal vectors: methodological framework and spatial gradient estimation". Annales Geophysicae 27, n. 8 (19 agosto 2009): 3249–73. http://dx.doi.org/10.5194/angeo-27-3249-2009.

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Abstract. In the context of ESA's Cluster mission, four-point array techniques are widely used to analyze space plasma phenomena such as shocks and discontinuities, waves and turbulence, and spatial gradients. Due to failures of single instruments on the Cluster spacecraft fleet, there is also need for array processing of three-point measurements. In this paper we identify planar reciprocal vectors as a generic tool for this purpose. The class of three-point techniques introduced here includes methods for discontinuity analysis, wave identification, and spatial gradient determination. Parameter vectors can be resolved fully in the spacecraft plane but further assumptions or physical constraints have to be specified to estimate the normal components. We focus on the gradient estimation problem where we check and illustrate our approach using Cluster measurements.

Hanada, Mitsuhiko. "Effects of Peripheral Gradient of Color Saturation on the Feeling of Being Dazzled". Perception 48, n. 5 (13 aprile 2019): 412–27. http://dx.doi.org/10.1177/0301006619842496.

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The feeling of being dazzled that is evoked by images consisting of an achromatic uniform center surrounded by regions with a luminance gradient was investigated. The effects of type of color saturation gradient in the peripheral region on the feeling of being dazzled were examined. Stimulus configuration was also varied. For the stimulus configuration of a disk-annulus, the feeling of being dazzled was lower for an increasing saturation gradient from the center to the periphery than for decreasing and no-saturation gradients when the center and the periphery maximum luminances were the same. This suggests that the presence of a chromaticity difference between the disk and the surrounding annulus strengthens the feeling of being dazzled. Similar results were obtained for the stimulus configuration of a star shape. For the stimulus configuration of a cross shape, quite different results were obtained; the chromaticity discontinuity had little or opposite effect. These results suggest that chromaticity border and stimulus configurations are factors in the feeling of being dazzled that is evoked by images with luminance gradient.

Cortes, P. M. "Cortical Intracellular Electrical Potential in Roots of Unstressed and Stressed Sunflower Seedlings. II. Radial Profiles and Oscillations". Functional Plant Biology 24, n. 5 (1997): 651. http://dx.doi.org/10.1071/pp96037.

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Various models have been proposed to explain how plants can extract water from dry soil against a gradient in water potential. According to one model, it is hypothesised that water uptake from dry soil is associated with a radial gradient in the intracellular electrical potential (Ec) of root cortical cells such that the potential in the outer cells is relatively hyperpolarised. As a partial test of this model, a microelectrode was used to measure radial profiles of Ec in intact roots of sunflower (Helianthus annuus) seedlings. The seedlings were subjected to either a control (unstressed) or one of two stress treatments. Water stress was rapidly imposed and relieved by lowering and raising the level of nutrient solution in a tank which contained all the seedling roots except the lateral root in which Ec was measured. There was a gradient in Ec in roots of unstressed plants with the potential of the outer cortical cells being relatively depolarised. The imposition of stress shifted the gradient in accordance with the hypothesis. Increasing the magnitude of the osmotic potential of the solution perfusing the measured portion of a lateral root of a stressed seedling resulted in a discontinuity in the profile between the second and third cortical layers. The gradients in the profile of Ec indicate there is a limitation in intercellular electrical coupling and the appearance of a discontinuity may indicate a decrease in coupling. Three types of occasional, spontaneous oscillations in Ec are characterised. One type of oscillation may be additional evidence that the electrical coupling between the cortical cell layers is variable and depends on the transport and status of water in the roots.

Gobbino, Massimo, e Maria Giovanna Mora. "Finite-difference approximation of free-discontinuity problems". Proceedings of the Royal Society of Edinburgh: Section A Mathematics 131, n. 3 (giugno 2001): 567–95. http://dx.doi.org/10.1017/s0308210500001001.

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We approximate functionals depending on the gradient of u and on the behaviour of u near the discontinuity points by families of non-local functionals where the gradient is replaced by finite differences. We prove pointwise convergence, Γ-convergence and a compactness result, which implies, in particular, the convergence of minima and minimizers.

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Più fonti

Tesi sul tema "Gradient de discontinuité":

Khazraj, Kaoutar. "Paramétrisation hybride champ/objet et inversion full-wave hybride de données sismiques de puits dans un contexte subsalt". Electronic Thesis or Diss., CY Cergy Paris Université, 2024. http://www.theses.fr/2024CYUN1267.

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Les techniques d'imagerie sismique jouent un rôle crucial dans l'exploration et la compréhension des structures sous la surface de la terre. Dans le domaine de l'exploration pétrolière les zones sous les corps de sel (dites subsalt) représentent un défi pour les techniques d'imagerie conventionnelles. L'application de la full-wave inversion (FWI) aux données sismiques de puits devrait permettre de résoudre au moins partiellement ces difficultés. Dans ce contexte subsalt, l'objectif principal est d'imager et aussi de caractériser les réservoirs d'hydrocarbures pouvant se trouver aux flancs et sous les corps de sel. Néanmoins, le contexte particulier de la sismique de puits, combiné aux défis liés à l'imagerie sous et autour des corps de sel nécessitent l'introduction de contraintes fortes dans le problème inverse géophysique en raison d'une sous-détermination du problème. La présente thèse propose une approche en trois étapes pour aborder ces défis. Tout d'abord, elle suggère d'incorporer de l'information géologique extit{a priori} dans le processus d'inversion en définissant des objets géologiques délimités par des discontinuités permettant aussi une introduction plus fine de l'information ext{a priori} sur les paramètres physiques par objet. Ensuite, elle vise à formaliser et à calculer le gradient par rapport aux paramètres géométriques du modèle qui définissent ces discontinuités. Enfin, elle propose de mettre en place un algorithme d'inversion full-wave hybride qui combine les approches de type champ et de type objet. Cette FWI hybride utilise à la fois le gradient des champs physiques et le gradient relatif aux paramètres géométriques. Le contenu de la thèse est réparti en quatre chapitres. Le premier chapitre présente les concepts fondamentaux utilisés dans l'algorithme FWI hybride. Il met l'accent sur des approches de représentation duale des interfaces (explicite/implicite) par l'utilisation de maillages non-structurés déformables pour la discrétisation des discontinuités et de la méthode level set pour la représentation implicite des objets géologiques dans le problème inverse. Le chapitre 2 décrit les étapes du développement d'une plateforme logicielle permettant l'implémentation numérique de ces approches et la réalisation de tests FWI hybride. Cette plateforme logicielle comprend un code de modélisation de la propagation des ondes par la méthode des éléments spectraux et un code d'inversion basé sur le calcul des gradients simples ou conjugués, avec une approche probabiliste du problème inverse. Le troisième chapitre détaille les différentes étapes de l'algorithme FWI géométrique et sa mise en application à des données de sismique de puits pour estimer la position des interfaces sel/sédiment pour un milieu 2D. Enfin, le quatrième chapitre présente l'algorithme d'inversion hybride et sa mise en oeuvre avec des données de sismique de puits dans le but d'estimer les vitesses des ondes de compression et de cisaillement, ainsi que la position de la frontière des corps de sel pour un milieu 2D. Les résultats des tests numériques présentés sont prometteurs, ce qui permet de valider notre approche d'inversion hybride
Seismic imaging techniques play a crucial role in the exploration and understanding of subsurface structures. In the field of petroleum exploration, subsalt zones present a challenge for conventional imaging techniques and full-wave inversion (FWI). The application of FWI to seismic well data is expected to overcome these challenges. The primary goal is to characterize hydrocarbon reservoirs that may be located beneath and alongside salt bodies. However, the context of well seismic imaging, combined with the challenges of imaging beneath and around salt bodies, requires the introduction of strong constraints into the geophysical inverse problem due to its underdetermined nature.This thesis presents a three-step approach to tackle these challenges. Firstly, it suggests incorporating extit{a priori} geological information into the inversion process by defining geological objects bounded by discontinuities. Secondly, it aims to formalize and compute the gradient with respect to the geometric parameters that define these discontinuities. Thirdly, it proposes the implementation of a hybrid full-wave inversion algorithm that combines field and object-based approaches. This hybrid FWI utilizes both the gradient of physical fields and the gradient relative to geometric parameters.The thesis content is divided into four distinct chapters. The first chapter introduces the fundamental concepts used in the hybrid FWI algorithm. It highlights the approach based on a dual representation of interfaces (explicit/implicit) using deformable unstructured meshes for the explicit discretization of discontinuities and the level-set method for the implicit representation of the geological objects in the inverse problem. Chapter 2 describes the development steps of a software platform for the numerical implementation of these approaches and the execution of hybrid FWI tests. This software platform includes a wave propagation modeling code based on the spectral elements method and an inversion code based on the gradient computation using the Green's function method, with a probabilistic approach to the inverse problem. The third chapter outlines the various stages of the geometric FWI algorithm and its application to well seismic data to estimate the position of salt/sediment interfaces in 2D environments. Finally, the fourth chapter presents the hybrid inversion algorithm and its implementation with well seismic data to estimate the velocities of compression and shear waves, as well as the position of salt body boundaries in 2D environments. The results of the presented numerical tests are promising, validating our hybrid inversion approach

Souchotte, Pascal. "Pressions pariétales induites par des discontinuités de surface soumises à un gradient de pression externe : applications à l'automobile". Ecully, Ecole centrale de Lyon, 1999. http://www.theses.fr/1999ECDL0027.

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La présente étude vise à caractériser expérimentalement le champ de pression pariétal généré au voisinage de discontinuités de surface soumises à un gradient de pression externe. Pour recréer un écoulement soumis à un gradient de pression représentatif de celui existant autour d'un sous-ensemble automobile, une veine d'essais spécifique (le guide d'écoulement) a été conçue. Dans un premier temps, le cas de la marche tournée vers l'aval a étudié en détails. Les résultats obtenus ont ainsi permis de dégager les paramètres fondamentaux et les grandeurs sans dimensions liés à l'excitation pariétale d'une telle configuration. Dans une seconde étape, des discontinuités de surface, telles le joint de pare-brise ou l'antenne de toit, ont été placées dans un écoulement moyen représentatif de celui qui se développe autour du sous-ensemble capot / pare brise / pavillon. Une base importante de données a ainsi été constituée afin, d'une part, de fournir des données d'entrée à des codes de calculs vibro-acoustiques industriels, et d'autre part, de poser les bases d'une modélisation du champ excitateur au voisinage d'une zone de recirculation
Wall pressure fluctuations inducted by a surface roughness in adverse pressure gradient: Automobile applications Wall pressure fluctuations near isolated singularities under an adverse mean pressure gradient are experimentally investigated. A new concept of anechoic wind tunnel is designed in order to obtain a channel flow which is representative of the flow around a given region of a real car. The experiment is carried out in two phases: first, the flow around a singularity is examined under an unperturbed mean flow, the singularities being a backward facing step; second, singularities like windshield joints or roof antennas are placed into the adverse pressure gradient flow which mimics the around the upper side of the car. An extensive data base is provided both as validation tool for computer programs and as input for vibro-acoustic models. Furthermore results give a new insight into the physics of flow reattachment

Kawagoe, Daisuke. "Regularity of solutions to the stationary transport equation with the incoming boundary data". Kyoto University, 2018. http://hdl.handle.net/2433/232413.

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Wilke, Daniel Nicolas. "Approaches to accommodate remeshing in shape optimization". Thesis, University of Pretoria, 2010. http://hdl.handle.net/2263/24270.

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This study proposes novel optimization methodologies for the optimization of problems that reveal non-physical step discontinuities. More specifically, it is proposed to use gradient-only techniques that do not use any zeroth order information at all for step discontinuous problems. A step discontinuous problem of note is the shape optimization problem in the presence of remeshing strategies, since changes in mesh topologies may - and normally do - introduce non-physical step discontinuities. These discontinuities may in turn manifest themselves as non-physical local minima in which optimization algorithms may become trapped. Conventional optimization approaches for step discontinuous problems include evolutionary strategies, and design of experiment (DoE) techniques. These conventional approaches typically rely on the exclusive use of zeroth order information to overcome the discontinuities, but are characterized by two important shortcomings: Firstly, the computational demands of zero order methods may be very high, since many function values are in general required. Secondly, the use of zero order information only does not necessarily guarantee that the algorithms will not terminate in highly unfit local minima. In contrast, the methodologies proposed herein use only first order information, rather than only zeroth order information. The motivation for this approach is that associated gradient information in the presence of remeshing remains accurately and uniquely computable, notwithstanding the presence of discontinuities. From a computational effort point of view, a gradient-only approach is of course comparable to conventional gradient based techniques. In addition, the step discontinuities do not manifest themselves as local minima.
Thesis (PhD)--University of Pretoria, 2011.
Mechanical and Aeronautical Engineering
unrestricted

Shunde, Yin. "Geomechanics-Reservoir Modeling by Displacement Discontinuity-Finite Element Method". Thesis, 2008. http://hdl.handle.net/10012/3826.

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There are two big challenges which restrict the extensive application of fully coupled geomechanics-reservoir modeling. The first challenge is computational effort. Consider a 3-D simulation combining pressure and heat diffusion, elastoplastic mechanical response, and saturation changes; each node has at least 5 degrees of freedom, each leading to a separate equation. Furthermore, regions of large p, T and σ′ gradients require small-scale discretization for accurate solutions, greatly increasing the number of equations. When the rock mass surrounding the reservoir region is included, it is represented by many elements or nodes. These factors mean that accurate analysis of realistic 3-D problems is challenging, and will so remain as we seek to solve larger and larger coupled problems involving nonlinear responses. To overcome the first challenge, the displacement discontinuity method is introduced wherein a large-scale 3-D case is divided into a reservoir region where Δp, ΔT and non-linear effects are critical and analyzed using FEM, and an outside region in which the reservoir is encased where Δp and ΔT effects are inconsequential and the rock may be treated as elastic, analyzed with a 3D displacement discontinuity formulation. This scheme leads to a tremendous reduction in the degrees of freedom, yet allows for reasonably rigorous incorporation of the reactions of the surrounding rock. The second challenge arises from some forms of numerical instability. There are actually two types of sharp gradients implied in the transient advection-diffusion problem: one is caused by the high Peclet numbers, the other by the sharp gradient which appears during the small time steps due to the transient solution. The way to eliminate the spurious oscillations is different when the sharp gradients are induced by the transient evolution than when they are produced by the advective terms, and existing literature focuses mainly on eliminating the spurious spatial temperature oscillations caused by advection-dominated flow. To overcome the second challenge, numerical instability sources are addressed by introducing a new stabilized finite element method, the subgrid scale/gradient subgrid scale (SGS/GSGS) method.

Libri sul tema "Gradient de discontinuité":

Geological Survey (U.S.), a cura di. Combining edge-gradient information to improve adaptive discontinuity-preserving smoothing of multispectral images. Reston, VA (521 National Center, Reston 22092): U.S. Geological Survey, 1994.

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Combining edge-gradient information to improve adaptive discontinuity-preserving smoothing of multispectral images. Reston, VA (521 National Center, Reston 22092): U.S. Geological Survey, 1994.

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Combining edge-gradient information to improve adaptive discontinuity-preserving smoothing of multispectral images. Reston, VA (521 National Center, Reston 22092): U.S. Geological Survey, 1994.

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Capitoli di libri sul tema "Gradient de discontinuité":

Carriero, Michele, Antonio Leaci e Franco Tomarelli. "Local Minimizers for a Free Gradient Discontinuity Problem in Image Segmentation". In Variational Methods for Discontinuous Structures, 67–80. Basel: Birkhäuser Basel, 2002. http://dx.doi.org/10.1007/978-3-0348-8193-7_5.

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Vatulyan, Alexander O., Sergey A. Nesterov, Victor O. Yurov e Oksana V. Yavruyan. "On the Structure of Solutions in the Vicinity of Discontinuity of Boundary Conditions for Gradient Models". In Advanced Structured Materials, 687–98. Cham: Springer International Publishing, 2023. http://dx.doi.org/10.1007/978-3-031-26186-2_42.

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Imre, E., J. Szendefy, J. Lőrincz, P. Q. Trang e Vijay P. Singh. "On the Effect of Soil Modification with Lime Using Grading Entropy". In Discrete Element Modelling of Particulate Media, 271–79. The Royal Society of Chemistry, 2012. http://dx.doi.org/10.1039/bk9781849733601-00271.

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Agglomeration may take place in the presence of a cementing agent like lime. If the failure of an agglomerated body is caused by the failure of bonds then the processes are symmetric. This study shows that the effect of lime modification on the grading curve evolution in the non-normalised grading entropy diagram is basically opposite to the effect of the usual particle breakage. Both can be related to the “entropy principle” through the grading entropy concept. In the normalised grading entropy diagram the grading curve evolution path is the same except that discontinuity occurs upon the change in the fraction number. The entropy coordinate A can be used as a stability measure (i.e. in the sense that the stability increasing with A). The discontinuous change in A results in a more stable structure for breakage and less stable structure if lime is added to a small plasticity soils. In case of very high clay content the discontinuity at lime modification was stabilized.

Atti di convegni sul tema "Gradient de discontinuité":

Vallecchi, A., S. Hubert, A. Schuchinsky e C. Craeye. "Phase gradient discontinuity metasurface with intertwined spiral arrays". In 2016 10th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics (METAMATERIALS). IEEE, 2016. http://dx.doi.org/10.1109/metamaterials.2016.7746407.

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Cosimo, Alejandro, V´ıctor Fachinotti e Alberto Cardona. "TEMPERATURE GRADIENT DISCONTINUITY AWARE NUMERICAL SCHEME FOR SOLIDIFICATION PROBLEMS". In 10th World Congress on Computational Mechanics. São Paulo: Editora Edgard Blücher, 2014. http://dx.doi.org/10.5151/meceng-wccm2012-18375.

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Li, Yuebing, Jianwei Zhu, Shiyi Bao e Zengliang Gao. "Analysis on Ultimate Load Capacity of Cylinder With Local Discontinuity Under High Temperature Gradient". In ASME 2014 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/pvp2014-29051.

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A severe accident management concept, known as ‘in-vessel retention (IVR)’, is widely used in advanced pressurized water reactor, such as AP600, AP1000, and so on. The severe accident management strategy is to flood the reactor cavity, submerging the reactor pressure vessel (RPV). In such condition, the temperature on the inside of RPV may exceed the melting point (about 1327 °C) of RPV material, and results in the localized wall thinning. On the outside, the temperature is remained at about 127 °C, by assuming the flow regime is kept to be nucleate boiling. So it will form a high temperature gradient on the wall, and caused high thermal stress. It will bring about the local discontinuity on the PRV wall because of the wall molten under the elevated temperature. A cylinder model is established to simulate the local discontinuity. The model is composed of the cylinder with the same external radius, but different wall thickness in the local discontinuity zone. Two elastic perfectly plastic models are used to analyze the stress and strain distributions on the wall and ultimate load capacity, based on the hot tensile curves and isochronous stress-strain curves at 100 hour with the change of temperature. The effect of local discontinuity is discussed, under the case of high temperature gradient and internal pressure. The results show that the Mises stress on the whole wall-thickness in the region of local discontinuity will achieve yield stress, under the high thermal stress. Appling internal pressure, the stress decreases in the zone of local discontinuity. The weakest link takes place in the thin segment of the cylinder model, and the ultimate pressure is obtained.

Shaikh, J. A., K. Murata, H. Kuramata e H. K. Mogensen. "Impact of a Vertical Temperature Gradient on H2S Gradient in Sour, Near-Critical Reservoir Fluids". In SPE Conference at Oman Petroleum & Energy Show. SPE, 2024. http://dx.doi.org/10.2118/218801-ms.

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Abstract An equation of state model is presented, developed for an H2S-rich field, where the fluid type changes smoothly from gas to oil through a zone with a critical fluid and not through a classical gas-oil contact with a discontinuity in fluid properties. For use in connection with compositional reservoir simulation studies, a depth gradient model has been developed that provides a good representation of the compositional variation with depth, including the depth where the fluid type changes from gas to oil. The depth gradient model considers the influence of both gravity and the vertical temperature gradient on the distribution of the individual components in the fluid column. A depth gradient model that only considers gravity and ignores the temperature gradient will simulate an increasing H2S concentration with depth, while the fluid samples show that the H2S concentration decreases with increasing depth. When the effect of the temperature gradient is included, a good match is obtained of the development of fluid composition, saturation point and GOR with depth.

Asadkarami, Ali, e Wolf Reinhardt. "Shakedown at Thermal Discontinuities Involving Thermal Membrane and Thermal Bending Stress". In ASME 2012 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/pvp2012-78660.

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The current ASME Code Section III NB-3200 rules on thermal stress ratchet require that the thermal stress must be less than the ratchet condition that Bree established for a cyclic pure thermal bending stress as a function of the level of primary membrane stress. It has been shown that this method can predict shakedown when elastic-perfectly plastic analysis shows ratcheting. However, there is also conservatism in the Code rules because the highest stresses that dominate the evaluation of a component are typically found at discontinuities, where there is a stress gradient at least in the axial direction. The stress limits, on the other hand, are based on stress distributions that are constant in the axial (and circumferential) direction. This paper investigates the effect of thermal discontinuities on the shakedown limit in the presence of a thermal through-wall gradient and a pressure-induced primary stress. The investigation is based on the simple model of a cylinder with an isolated thermal discontinuity. The effect of proximity to another discontinuity is explored, to obtain the minimum distance between two discontinuities that would allow them to be considered separately. Simple rules are developed and proposed to take potentially advantage of higher stress limits at an isolated discontinuity.

Bayoumy, Ahmed H., Ayman A. Nada e Said M. Megahed. "Modeling Slope Discontinuity of Large Size Wind-Turbine Blade Using Absolute Nodal Coordinate Formulation". In ASME 2012 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/detc2012-70467.

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This paper describes the use of the Absolute Nodal Coordinate Formulation (ANCF) in modeling large-size wind turbine blades. An efficient procedure is developed for mapping NACA airfoil wind-turbine blades into ANCF thin plate models. The procedure concerns the wind turbine blade with non-uniform, twisted nature. As a result, the slope discontinuity problem arises and presents numerical errors in the dynamic simulation. This investigation illustrates a method for modeling slope discontinuity resulting from the variations of the cross sectional layouts across the blade. A method is developed and applied for the gradient-deficient thin plate element in order to account for structural discontinuity. The numerical results show a numerical convergence and satisfy the principle of work and energy in dynamics. The simulation results are compared with those obtained using ANSYS code with a good agreement.

Steinbrink, Scott E. "On a Proposed New Kinematic Assumption for Analysis of Laminated, Fiber-Reinforced Composite Shells: Part 1". In ASME 2003 Pressure Vessels and Piping Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/pvp2003-1914.

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A proposal is made for a new form of kinematic assumption for inclusion into a theory of laminated shells. The proposed form is a variant of the first-order transverse shear deformation theory, incorporating a stiffness-based discontinuity term at lamina interfaces, in order to provide complete, a priori satisfaction of interlaminar continuity of transverse shear and transverse normal stresses, and correspondent intelaminar discontinuity of thickness-direction gradients of displacement. Continuity of displacement is maintained, as is the possibility of interlaminar discontinuity of in-plane stresses. It is hoped that this kinematic form will enhance the utility of shell theories for analysis of laminated structures. The paper deals only with the development of the kinematic assumption, and not its implementation into analysis code.

Mohammadi-Araz, Pishdad. "Finite Element Analysis and Stress Intensification Factor Determination for Core to Jacket Joints". In ASME 2009 Pressure Vessels and Piping Conference. ASMEDC, 2009. http://dx.doi.org/10.1115/pvp2009-78007.

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In this study Stress Intensification Factor (“SIF”) and stress analysis for core to jacket joints are investigated. The three-dimensional finite element shell model consists of two shells: the jacket and the core. The effect of the welded joint discontinuity is taken into account by applying a stress concentration factor. It is presumed that the core and shell are ASTM A-106 GR B [1]. The joint is modeled for different pipe-outside diameters and wall-thicknesses and SIF is calculated for different Head shapes, which are discussed further in this paper. The model is examined with different mesh types and the results are discussed. Temperature gradient in pipe wall-thickness causes thermal stress. The thermal stress, combined with operating, sustained and differential expansion stress are considered in the stress analysis of core and jacket shell. The results for different temperature gradients are compared. The imposed displacement loads caused by global temperature difference between core and the jacket are taken from a beam model run of a typical discontinuous steam jacketed piping system.

Ahmed, Moinuddin, e Roger E. Khayat. "Flow of a Thin Viscoelastic Jet". In ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting collocated with 8th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2010. http://dx.doi.org/10.1115/fedsm-icnmm2010-30505.

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The influence of elasticity and inertia for steady flow of a thin viscoelastic fluid jet is examined theoretically. The fluid is assumed to emerge from a vertical channel and driven by a pressure gradient and/or gravity. The boundary-layer equations are generalized for a viscoelastic thin film obeying the Oldroyd-b constitutive model. Special emphasis is placed on the initial stages of jet development. The formulation and simulation are carried out for two-dimensional jet flow in order to better understand the intricate wave and flow structures for a viscoelastic jet. In contrast to the commonly used depth-averaging solution method, the strong nonlinearities are preserved in the present formulation as the viscoelastic boundary-layer equations are solved by expanding the flow field in terms of orthonormal shape functions. It is found that for a steady viscoelastic jet, a reduction in inertia or a rise in elasticity leads to the emergence of surface waviness and excessive normal stress, which leads to the formation of sharp gradients in the velocity and shear stress. These gradients can be sufficiently substantial to cause a discontinuity or shock in the flow. During transition, the surface profiles adhere earlier to the shape of the final steady state instead of a traveling wave, the transition between the two states takes the form of a standing wave, which grows essentially in amplitude only.

Enakoutsa, Koffi, Fazle R. Ahad, Kiran N. Solanki, Yustianto Tjiptowidjojo e Douglas J. Bammann. "Localization Effects in Bammann-Chiesa-Johnson Metals With Damage Delocalization". In ASME 2011 International Mechanical Engineering Congress and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/imece2011-65935.

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The presence of softening in the Bammann-Chiesa-Johnson (BCJ) material model presents a major physical drawback: the unlimited localization of strain which results in spurious zero dissipated energy at failure. This difficulty resolves when the BCJ model is modified to incorporate a nonlocal evolution equation for the damage, as proposed by Pijaudier-Cabot and Bazant (1987). The objective of this work is to theoretically assess the ability of such a modified BCJ model to prevent unlimited localization of the strain. To that end, we investigate two localization problems in nonlocal BCJ metals: appearance of a spatial discontinuity of the velocity gradient in a finite, inhomogeneous body, and localization into finite bands. We show that in spite of the softening arising from the damage, no spatial discontinuity occurs in the velocity gradient. Also, we find that the dissipation energy is continuously distributed in nonlocal BCJ metals and therefore can not localize into zones of vanishing volume. As a result, the appearance of any vanishing width adiabatic shear band is impossible in a nonlocal BCJ metal. Finally, we study the finite element (FE) solution of shear banding in a rectangular mesh, deformed in plane strain tension and containing an imperfection, thereby illustrating the effects of imperfections on the localization of the strain.