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Bifurcation
Kinds of Bifurcation Terms modified by Bifurcation Selected AbstractsKISSING BALLOON TECHNIQUE IS A USEFUL METHOD FOR ANGIOPLASTY OF THE RADIOCEPHALIC FISTULA BIFURCATION THROUGH A PERCUTANEOUS TRANS-RADIAL ARTERIAL APPROACHNEPHROLOGY, Issue 3 2010JIUNG-HSIUN LIU No abstract is available for this article. [source] Bifurcation modeling in geomaterials: From the second-order work criterion to spectral analysesINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 9 2009F. Prunier Abstract The present paper investigates bifurcation analysis based on the second-order work criterion, in the framework of rate-independent constitutive models and rate-independent boundary-value problems. The approach applies mainly to nonassociated materials such as soils, rocks, and concretes. The bifurcation analysis usually performed at the material point level is extended to quasi-static boundary-value problems, by considering the stiffness matrix arising from finite element discretization. Lyapunov's definition of stability (Annales de la faculté des sciences de Toulouse 1907; 9:203,274), as well as definitions of bifurcation criteria (Rice's localization criterion (Theoretical and Applied Mechanics. Fourteenth IUTAM Congress, Amsterdam, 1976; 207,220) and the plasticity limit criterion are revived in order to clarify the application field of the second-order work criterion and to contrast these criteria. The first part of this paper analyses the second-order work criterion at the material point level. The bifurcation domain is presented in the 3D stress space as well as 3D cones of unstable loading directions for an incrementally nonlinear constitutive model. The relevance of this criterion, when the nonlinear constitutive model is expressed in the classical form (d, = Md,) or in the dual form (d, = Nd,), is discussed. In the second part, the analysis is extended to the boundary-value problems in quasi-static conditions. Nonlinear finite element computations are performed and the global tangent stiffness matrix is analyzed. For several examples, the eigenvector associated with the first vanishing eigenvalue of the symmetrical part of the stiffness matrix gives an accurate estimation of the failure mode in the homogeneous and nonhomogeneous boundary-value problem. Copyright © 2008 John Wiley & Sons, Ltd. [source] Bifurcation and instability modelling by a multimechanism elasto-plastic modelINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 5 2008Kamel Hamadi Abstract The bifurcation and instability conditions in geomechanics are closely related to the elasto-plastic behaviour. In this paper the potential of a multimechanism elasto-plastic model to predict various modes of failure is examined. First, a brief overview for the essential aspects of the constitutive model and the development of the elasto-plastic constitutive matrix for this model are presented. Then, numerical simulations of different drained and undrained paths in the axisymmetric and plane-strain conditions for the Hostun sand are illustrated. These examples confirm the capacity of the model to reproduce instability and strain localization phenomena. The obtained response is in agreement with experimental observations, theoretical developments and numerical analyses existing in the literature. Copyright © 2007 John Wiley & Sons, Ltd. [source] Bifurcation and second-order work in geomaterialsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 8 2007François Nicot Abstract In this paper, the ability of a material rate-independent system to evolve toward another mechanical state from an equilibrium configuration, with no change in the control parameters, is investigated. From a mechanical point of view, this means that the system can spontaneously develop kinetic energy with no external disturbance from an equilibrium state, which corresponds to a particular case of bifurcation. The existence of both conjugate incremental strain and stress such that the second-order work vanishes is established as a necessary and sufficient condition for the appearance of this bifurcation phenomenon. It is proved that this fundamental result is independent of the constitutive relation of the rate-independent material considered. Then the case of homogeneous loading paths is investigated, and, as an illustration, the subsequent results are applied to interpret the well-known liquefaction observed under isochoric triaxial loading conditions with loose granular materials. Copyright © 2006 John Wiley & Sons, Ltd. [source] Bifurcation and stability analysis of laminar flow in curved ductsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2010Werner Machane Abstract The development of viscous flow in a curved duct under variation of the axial pressure gradient q is studied. We confine ourselves to two-dimensional solutions of the Dean problem. Bifurcation diagrams are calculated for rectangular and elliptic cross sections of the duct. We detect a new branch of asymmetric solutions for the case of a rectangular cross section. Furthermore we compute paths of quadratic turning points and symmetry breaking bifurcation points under variation of the aspect ratio , (,=0.8,1.5). The computed diagrams extend the results presented by other authors. We succeed in finding two origins of the Hopf bifurcation. Making use of the Cayley transformation, we determine the stability of stationary laminar solutions in the case of a quadratic cross section. All the calculations were performed on a parallel computer with 32×32 processors. Copyright © 2009 John Wiley & Sons, Ltd. [source] Editorial: At the Bifurcation of the Last FrontiersJOURNAL OF INTERVENTIONAL CARDIOLOGY, Issue 4 2010THACH NGUYEN M.D. The concept of coronary angioplasty percutaneous coronary intervention (PCI) was pioneered by Andreas Gruntzig. Since then, several modifications, innovative devices, techniques, and advances have revolutionized the practice of interventional cardiology. Coronary bifurcation and chronic total occlusion are the last two frontiers that continue to challenge the skills of the interventional cardiologists. Proceedings of the second Bifurcation Summit held from November 26 to 28, 2009 in Nanjing, China are published in this symposium. In a general review, the state of the art in management of bifurcation lesion is summarized in the statement of the "Bifurcation Club in KOKURA." A new-presented concept was the "extension distance" between the main vessel and the sidebranch ostia and its association with restenosis. The results of two studies on shear stress (SS) after PCI showed that contradictory lower SS after stenting was associated with lower in-stent restenosis. There was better fractional flow reserve after double kissing crush technique than provisional one-stent technique. There was also lower rate of stent thrombosis after bifurcation stenting with excellent final angiographic results. In a negative note, the SYNTAX score had no predictive values on trifurcated left main stenting. In summary, different aspects of percutaneous management for bifurcated lesion are described seen from different perspectives and evidenced by novel techniques and strategies. (J Interven Cardiol 2010;23:293,294) [source] Police, Probation and the Bifurcation of CommunityTHE HOWARD JOURNAL OF CRIMINAL JUSTICE, Issue 3 2010WENDY FITZGIBBON Abstract: The police and probation services are agencies that have traditionally had close relations with the communities in which they work. Both agencies exhibit tensions in their relations with the community: in policing, in the relation between centralised targets and community needs, and in probation in the role of the community in the process of rehabilitation and desistance. We argue that these tensions mirror deeper contradictions within current urban and social policy concerning the role envisaged for community in the process of urban renewal. [source] Stability, morphology and surface grain size patterns of channel bifurcation in gravel,cobble bedded anabranching riversEARTH SURFACE PROCESSES AND LANDFORMS, Issue 10 2006Leif M. Burge Abstract This study presents the first detailed field-based analysis of the morphology of bifurcations within anabranching cobble,gravel rivers. Bifurcations divide the flow of water and sediment into downstream anabranches, thereby influencing the characteristics of the anabranches and the longevity of river islands. The history, morphology, bed grain size, and flow vectors at five bifurcations on the Renous River, New Brunswick, Canada, were studied in detail. The angles of bifurcations within five anabranching rivers in the Miramichi basin were investigated. The average bifurcation angle was 47°, within the range of values cited for braided river bifurcations. Bifurcation angle decreased when anabranches were of similar length. Shields stresses in channels upstream of bifurcations were lower than reported values for braided rivers. Stable bifurcations displayed lower Shields stresses than unstable bifurcations, contrary to experimental results from braided river bifurcations. Bifurcations in anabranching rivers are stabilized by vegetation that slows channel migration and helps to maintain a uniform upstream flow field. The morphology of stable bifurcations enhances their stability. A large bar, shaped like a shallow ramp that increases in elevation to floodplain level, forms at stable bifurcations. Floodplains at stable bifurcations accrete upstream at rates between 0·9 and 2·5 m a,1. Bars may also form within the entrance of an anabranch downstream of the bifurcation node. These bars are associated with bifurcation instability, forming after a period of stability or an avulsion. Channel abandonment occurs when a bar completely blocks the entrance to one anabranch. The stability of channels upstream of bifurcations and the location of bars at bifurcations influence bifurcation stability and the maintenance of river anabranching in the long term. Copyright © 2006 John Wiley & Sons, Ltd. [source] Bifurcations, instabilities and degradation in geomechanicsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 3 2007I. G. Vardoulakis No abstract is available for this article. [source] Treating Coronary Bifurcations: Neither Rhyme nor Reason?JOURNAL OF INTERVENTIONAL CARDIOLOGY, Issue 3 2009FCSANZ, FRACP, SEIF EL-JACK MRCP(U.K.) First page of article [source] Bifurcations on a spring-pendulum oscillatorPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2007A. Gonzalez-Buelga In this paper we study experimentally the dynamics of a non linear system: a spring pendulum coupled to an oscillator. The system was tested using a hybrid technique called Real Time Dynamic Substructuring (RTDS)[1, 2]. RTDS is a testing technique that involves splitting the system under study into two subsystems: one will be physically tested (physical substructure) and the other will be simulated in the computer (numerical model). These substructures interact in real time through a set of transfer systems. RTDS is a very powerful experimental methodology that not only allows full scale and real time testing but also real-time bifurcation tracking in complex engineering systems [3, 4]. In our hybrid experiment the spring pendulum is taken to be the physical substructure while oscillator is the simulated numerical model. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Flow energy and channel adjustments in rills developed in loamy sand and sandy loam soilsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 1 2009Jovan R. Stefanovic Abstract The storms usually associated with rill development in nature are seldom prolonged, so development is often interrupted by interstorm disturbances, e.g. weathering or tillage. In laboratory simulated rainfall experiments, active rill development can be prolonged, and under these conditions typically passes through a period of intense incision, channel extension and bifurcation before reaching quasi-stable conditions in which little form change occurs. This paper presents laboratory experiments with coarse textured soils under simulated rainfall which show how channel adjustment processes contribute to the evolution of quasi-stability. Newly incised rills were stabilized for detailed study of links between rill configuration and flow energy. On a loamy sand, adjustment towards equilibrium occurred due to channel widening and meandering, whereas on a sandy loam, mobile knickpoints and chutes, pulsations in flow width and flow depth and changes in stream power and sediment discharge occurred as the channel adjusted towards equilibrium. The tendency of rill systems towards quasi-stability is shown by changes in stream power values which show short-lived minima. Differences in energy dissipation in stabilized rills indicate that minimization of energy dissipation was reached locally between knickpoints and at the downstream ends of rills. In the absence of energy gradients in knickpoints and chutes, stabilized rill sections tended toward equilibrium by establishing uniform energy expenditure. The study confirmed that energy dissipation increased with flow aspect ratio. In stabilized rills, flow acceleration reduced energy dissipation on the loamy sand but not on the sandy loam. On both soils flow deceleration tended to increase energy dissipation. Understanding how rill systems evolve towards stability is essential in order to predict how interruptions between storms may affect long-term rill dynamics. This is essential if event-based physical models are to become effective in predicting sediment transport on rilled hillslopes under changing weather and climatic conditions. Copyright © 2008 John Wiley and Sons, Ltd. [source] Stability, morphology and surface grain size patterns of channel bifurcation in gravel,cobble bedded anabranching riversEARTH SURFACE PROCESSES AND LANDFORMS, Issue 10 2006Leif M. Burge Abstract This study presents the first detailed field-based analysis of the morphology of bifurcations within anabranching cobble,gravel rivers. Bifurcations divide the flow of water and sediment into downstream anabranches, thereby influencing the characteristics of the anabranches and the longevity of river islands. The history, morphology, bed grain size, and flow vectors at five bifurcations on the Renous River, New Brunswick, Canada, were studied in detail. The angles of bifurcations within five anabranching rivers in the Miramichi basin were investigated. The average bifurcation angle was 47°, within the range of values cited for braided river bifurcations. Bifurcation angle decreased when anabranches were of similar length. Shields stresses in channels upstream of bifurcations were lower than reported values for braided rivers. Stable bifurcations displayed lower Shields stresses than unstable bifurcations, contrary to experimental results from braided river bifurcations. Bifurcations in anabranching rivers are stabilized by vegetation that slows channel migration and helps to maintain a uniform upstream flow field. The morphology of stable bifurcations enhances their stability. A large bar, shaped like a shallow ramp that increases in elevation to floodplain level, forms at stable bifurcations. Floodplains at stable bifurcations accrete upstream at rates between 0·9 and 2·5 m a,1. Bars may also form within the entrance of an anabranch downstream of the bifurcation node. These bars are associated with bifurcation instability, forming after a period of stability or an avulsion. Channel abandonment occurs when a bar completely blocks the entrance to one anabranch. The stability of channels upstream of bifurcations and the location of bars at bifurcations influence bifurcation stability and the maintenance of river anabranching in the long term. Copyright © 2006 John Wiley & Sons, Ltd. [source] Three-dimensional flow modelling and sediment transport in the River KlarälvenEARTH SURFACE PROCESSES AND LANDFORMS, Issue 7 2004Bijan Dargahi Abstract A three-dimensional ,ow model that uses the RNG k - , turbulence model and a non-equilibrium wall function was applied to the River Klarälven in the southwest part of Sweden. The objectives were to study the nature of the ,ow in the river bifurcation and to investigate the short-term sediment transport patterns in the river. The effectiveness of three-dimensional ,ow models depends upon: (1) how well the river geometry and it surface roughness are modelled; and (2) the choice of the closure model. Improvements were obtained by modelling the river in two parts: the entire river reach, and a selected part. Composite Manning coef,cients were used to account for roughness properties. The method requires a calibration process that ensures the water surface pro,les match the ,eld data. The k - , model under-predicted both the extent of ,ow separation zones and the number of secondary ,ow regions having a spiral motion, in comparison with the RNG k - , model. The 3-D model could predict with good accuracy both the general and secondary ,ow ,elds in the river. The results agreed well with the 3-D velocity measurements using an acoustic Doppler current pro,ler. A conceptual model was developed that accounts for the development of secondary ,ows in a river bifurcation having two bends. The main ,ow feature in the river cross-sections was the existence of multiple counter-rotating spiral motions. The number of spiral motions increased as the river bends were approached. The river bends also caused vorticity intensi,cation and increased the vertical velocities. The application of the 3-D ,ow model was extended by solving the sediment continuity equation. The sediment transport patterns were related to the secondary ,ow ,elds in the river. The sediment transport patterns at the river bifurcations are characterized by the growth of a sandbank. Copyright © 2004 John Wiley & Sons, Ltd. [source] The genome of Syntrophomonas wolfei: new insights into syntrophic metabolism and biohydrogen productionENVIRONMENTAL MICROBIOLOGY, Issue 8 2010Jessica R. Sieber Summary Syntrophomonas wolfei is a specialist, evolutionarily adapted for syntrophic growth with methanogens and other hydrogen- and/or formate-using microorganisms. This slow-growing anaerobe has three putative ribosome RNA operons, each of which has 16S rRNA and 23S rRNA genes of different length and multiple 5S rRNA genes. The genome also contains 10 RNA-directed, DNA polymerase genes. Genomic analysis shows that S. wolfei relies solely on the reduction of protons, bicarbonate or unsaturated fatty acids to re-oxidize reduced cofactors. Syntrophomonas wolfei lacks the genes needed for aerobic or anaerobic respiration and has an exceptionally limited ability to create ion gradients. An ATP synthase and a pyrophosphatase were the only systems detected capable of creating an ion gradient. Multiple homologues for ,-oxidation genes were present even though S. wolfei uses a limited range of fatty acids from four to eight carbons in length.Syntrophomonas wolfei, other syntrophic metabolizers with completed genomic sequences, and thermophilic anaerobes known to produce high molar ratios of hydrogen from glucose have genes to produce H2 from NADH by an electron bifurcation mechanism. Comparative genomic analysis also suggests that formate production from NADH may involve electron bifurcation. A membrane-bound, iron,sulfur oxidoreductase found in S. wolfei and Syntrophus aciditrophicus may be uniquely involved in reverse electron transport during syntrophic fatty acid metabolism. The genome sequence of S. wolfei reveals several core reactions that may be characteristic of syntrophic fatty acid metabolism and illustrates how biological systems produce hydrogen from thermodynamically difficult reactions. [source] Pathology of lethal peripartum broad ligament haematoma in 31 Thoroughbred maresEQUINE VETERINARY JOURNAL, Issue 6 2010T. UENO Summary Reasons for performing study: Broad ligament haemorrhage in peripartum mares is a life-threatening disease and there are few reports on the aetiology and pathogenesis of broad ligament haematoma. Objectives: To obtain information regarding the sites for the early diagnosis and pathogenesis of broad ligament haematoma of mares. Methods: Thirty-one mares that died of broad ligament haematoma peripartum were examined pathologically for bleeding sites. The arterial distribution of 5 young mares with several parities served as negative controls. Results: Age and/or multiparity were the predisposing factors for the disease. Arterial injuries were most commonly observed in the uterine artery (24 of 31 mares). Among these, the proximal uterine artery that lies within 15 cm of the bifurcation of the iliac artery was the most frequent site for rupture (18 mares). The lesions occurred preferentially at the bifurcations, lateral part of curvatures and abrupt flexures of the artery. The morphology of the injuries was classified into 3 types: ruptures with and without longitudinal fissures, and transections. Histologically, the arterial wall adjacent to the rupture showed atrophy of smooth muscle cells with fibrosis of the tunica media and disruption and/or calcification of the internal elastic lamina. Conclusions: Arterial injuries that led to broad ligament haematoma in peripartum mares occurred most frequently in the proximal uterine artery, and atrophy of smooth muscle cells with fibrosis of the arterial wall was as one of the predisposing factors in aged and multiparous mares. Potential relevance: Monitoring small aneurysms, mural tearing, medial fibrosis at the proximal uterine artery by transrectal echography could provide useful information for the early diagnosis and possible prevention of broad ligament haematoma of peripartum mares. [source] Distinct contributions of different CD40 TRAF binding sites to CD154-induced dendritic cell maturation and IL-12 secretionEUROPEAN JOURNAL OF IMMUNOLOGY, Issue 3 2003Matthew Abstract The mechanisms by which CD40 controls the maturation and antigen presentation functions of dendritic cells (DC) remains largely undefined in this critical cell type. To examine this question, we have employed retroviral transduction of primary bone marrow-derived mouse DC. Mutation of the distinct binding sites for TNF receptor-associated factor 6 (TRAF6) and for TRAF 2, 3, and 5 in the CD40 cytoplasmic domain revealed their independent contributions to DC maturation and activation of NF-,B. In contrast, disruption of the TRAF6 but not the TRAF 2,3,5 binding site markedly decreased IL-12 p40 secretion along with p38 and JNK activation in response to CD154 stimulation. These data document a clear bifurcation of the CD40 signaling cascade in primary DC at the level of thereceptor's two distinct and autonomous TRAF binding sites, and reveal the predominant role of the TRAF6 binding site in CD40-induced pro-inflammatory cytokine production by these cells. [source] Cover Picture: Anisotropy and Dynamic Ranges in Effective Properties of Sheared Nematic Polymer Nanocomposites (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 12 2005Mater. Abstract Forest and co-workers report on p.,2029 that nematic polymer nanocomposite (NPNC) films can be processed in steady shear flows, which generate complex orientational distributions of the nanorod inclusions. Distribution functions for a benchmark NPNC (11,vol.-% of 1,nm,×,200,nm rods) are computed for a range of shear rates, yielding a bifurcation diagram with steady states at very low (logrolling) and high (flow-aligning) shear rates, and limit cycles (tumbling, wagging, kayaking) at intermediate shear rates. The orientational distributions dictate the effective conductivity tensor of the NPNC film, which is computed for all distribution functions, and extract the maximum principal conductivity enhancement (Emax, averaged in time for periodic distributions) relative to the matrix. The result is a "property bifurcation diagram" for NPNC films, which predicts an optimal shear rate that maximizes Emax. Nematic, or liquid-crystalline, polymer nanocomposites (NPNCs) are composed of large aspect ratio, rod-like or platelet, rigid macromolecules in a matrix or solvent, which itself may be aqueous or polymeric. NPNCs are engineered for high-performance material applications, ranging across mechanical, electrical, piezoelectric, thermal, and barrier properties. The rods or platelets possess enormous property contrasts relative to the solvent, yet the composite properties are strongly affected by the orientational distribution of the nanophase. Nematic polymer film processing flows are shear-dominated, for which orientational distributions are well known to be highly sensitive to shear rate and volume fraction of the nematogens, with unsteady response being the most expected outcome at typical low shear rates and volume fractions. The focus of this article is a determination of the ranges of anisotropy and dynamic fluctuations in effective properties arising from orientational probability distribution functions generated by steady shear of NPNC monodomains. We combine numerical databases for sheared monodomain distributions[1,2] of thin rod or platelet dispersions together with homogenization theory for low-volume-fraction spheroidal inclusions[3] to calculate effective conductivity tensors of steady and oscillatory sheared mesophases. We then extract maximum scalar conductivity enhancement and anisotropy for each type of sheared monodomain (flow-aligned, tumbling, kayaking, and chaotic). [source] The influence of elevation error on the morphometrics of channel networks extracted from DEMs and the implications for hydrological modellingHYDROLOGICAL PROCESSES, Issue 11 2008John B. Lindsay Abstract Stream network morphometrics have been used frequently in environmental applications and are embedded in several hydrological models. This is because channel network geometry partly controls the runoff response of a basin. Network indices are often measured from channels that are mapped from digital elevation models (DEMs) using automated procedures. Simulations were used in this paper to study the influence of elevation error on the reliability of estimates of several common morphometrics, including stream order, the bifurcation, length, area and slope ratios, stream magnitude, network diameter, the flood magnitude and timing parameters of the geomorphological instantaneous unit hydrograph (GIUH) and the network width function. DEMs of three UK basins, ranging from high to low relief, were used for the analyses. The findings showed that moderate elevation error (RMSE of 1·8 m) can result in significant uncertainty in DEM-mapped network morphometrics and that this uncertainty can be expressed in complex ways. For example, estimates of the bifurcation, length and area ratios and the flood magnitude and timing parameters of the GIUH each displayed multimodal frequency distributions, i.e. two or more estimated values were highly likely. Furthermore, these preferential estimates were wide ranging relative to the ranges typically observed for these indices. The wide-ranging estimates of the two GIUH parameters represented significant uncertainty in the shape of the unit hydrograph. Stream magnitude, network diameter and the network width function were found to be highly sensitive to elevation error because of the difficulty in mapping low-magnitude links. Uncertainties in the width function were found to increase with distance from outlet, implying that hydrological models that use network width contain greater uncertainty in the shape of the falling limb of the hydrograph. In light of these findings, care should be exercised when interpreting the results of analyses based on DEM-mapped stream networks. Copyright © 2007 John Wiley & Sons, Ltd. [source] Bifurcation and second-order work in geomaterialsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 8 2007François Nicot Abstract In this paper, the ability of a material rate-independent system to evolve toward another mechanical state from an equilibrium configuration, with no change in the control parameters, is investigated. From a mechanical point of view, this means that the system can spontaneously develop kinetic energy with no external disturbance from an equilibrium state, which corresponds to a particular case of bifurcation. The existence of both conjugate incremental strain and stress such that the second-order work vanishes is established as a necessary and sufficient condition for the appearance of this bifurcation phenomenon. It is proved that this fundamental result is independent of the constitutive relation of the rate-independent material considered. Then the case of homogeneous loading paths is investigated, and, as an illustration, the subsequent results are applied to interpret the well-known liquefaction observed under isochoric triaxial loading conditions with loose granular materials. Copyright © 2006 John Wiley & Sons, Ltd. [source] Kinematic modelling of shear band localization using discrete finite elementsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 4 2003X. Wang Abstract Modelling shear band is an important problem in analysing failure of earth structures in soil mechanics. Shear banding is the result of localization of deformation in soil masses. Most finite element schemes are unable to model discrete shear band formation and propagation due to the difficulties in modelling strain and displacement discontinuities. In this paper, a framework to generate shear band elements automatically and continuously is developed. The propagating shear band is modelled using discrete shear band elements by splitting the original finite element mesh. The location or orientation of the shear band is not predetermined in the original finite element mesh. Based on the elasto-perfect plasticity with an associated flow rule, empirical bifurcation and location criteria are proposed which make band propagation as realistic as possible. Using the Mohr,Coulomb material model, various results from numerical simulations of biaxial tests and passive earth pressure problems have shown that the proposed framework is able to display actual patterns of shear banding in geomaterials. In the numerical examples, the occurrence of multiple shear bands in biaxial test and in the passive earth pressure problem is confirmed by field and laboratory observations. The effects of mesh density and mesh alignment on the shear band patterns and limit loads are also investigated. Copyright © 2003 John Wiley & Sons, Ltd. [source] Simulation of fluid,structure interaction with the interface artificial compressibility methodINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 3-4 2010Joris Degroote Abstract Partitioned fluid,structure interaction simulations of the arterial system are difficult due to the incompressibility of the fluid and the shape of the domain. The interface artificial compressibility (IAC) method mitigates the incompressibility constraint by adding a source term to the continuity equation in the fluid domain adjacent to the fluid,structure interface. This source term imitates the effect of the structure's displacement as a result of the fluid pressure and disappears when the coupling iterations have converged. The IAC method requires a small modification of the flow solver but not of the black-box structural solver and it outperforms a partitioned quasi-Newton coupling of the two black-box solvers in a simulation of a carotid bifurcation. Copyright © 2009 John Wiley & Sons, Ltd. [source] The buckling mode extracted from the LDLT -decomposed large-order stiffness matrixINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 7 2002Fumio Fujii Abstract The present study proposes an innovated eigenanalysis-free idea to extract the buckling mode only from the LDLT -decomposed stiffness matrix in large-scale bifurcation analysis. The computational cost for extracting the critical eigenvector is negligible, because the decomposition of the stiffness matrix will continually be repeated during path-tracing to solve the stiffness equations. A numerical example is computed to illustrate that the proposed idea is tough enough even for multiple bifurcation. Copyright © 2002 John Wiley & Sons, Ltd. [source] Bifurcation and stability analysis of laminar flow in curved ductsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2010Werner Machane Abstract The development of viscous flow in a curved duct under variation of the axial pressure gradient q is studied. We confine ourselves to two-dimensional solutions of the Dean problem. Bifurcation diagrams are calculated for rectangular and elliptic cross sections of the duct. We detect a new branch of asymmetric solutions for the case of a rectangular cross section. Furthermore we compute paths of quadratic turning points and symmetry breaking bifurcation points under variation of the aspect ratio , (,=0.8,1.5). The computed diagrams extend the results presented by other authors. We succeed in finding two origins of the Hopf bifurcation. Making use of the Cayley transformation, we determine the stability of stationary laminar solutions in the case of a quadratic cross section. All the calculations were performed on a parallel computer with 32×32 processors. Copyright © 2009 John Wiley & Sons, Ltd. [source] A two-grid fictitious domain method for direct simulation of flows involving non-interacting particles of a very small sizeINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2010A. Dechaume Abstract The full resolution of flows involving particles whose scale is hundreds or thousands of times smaller than the size of the flow domain is a challenging problem. A naive approach would require a tremendous number of degrees of freedom in order to bridge the gap between the two spatial scales involved. The approach used in the present study employs two grids whose grid size fits the two different scales involved, one of them (the micro-scale grid) being embedded into the other (the macro-scale grid). Then resolving first the larger scale on the macro-scale grid, we transfer the so obtained data to the boundary of the micro-scale grid and solve the smaller size problem. Since the particle is moving throughout the macro-scale domain, the micro-scale grid is fixed at the centroid of the moving particle and therefore moves with it. In this study we combine such an approach with a fictitious domain formulation of the problem resulting in a very efficient algorithm that is also easy to implement in an existing CFD code. We validate the method against existing experimental data for a sedimenting sphere, as well as analytical results for motion of an inertia-less ellipsoid in a shear flow. Finally, we apply the method to the flow of a high aspect ratio ellipsoid in a model of a human lung airway bifurcation. Copyright © 2009 John Wiley & Sons, Ltd. [source] Study on flow past two spheres in tandem arrangement using a local mesh refinement virtual boundary methodINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 5 2005Jian-Feng Zou Abstract A local mesh refinement virtual boundary method based on a uniform grid is designed to study the transition between the flow patterns of two spheres in tandem arrangement for Re=250. For a small gap (L/D=1.5), the flow field is axisymmetric. As the spacing ratio increases to 2.0, the pressure gradient induces the circumferential fluid motion and a plane-symmetric flow is constructed through a regular bifurcation. For L/D,2.5, the vortices are periodically shed from the right sphere, but the planar symmetry remains. The case for L/D=3.0 is picked up to give a detail investigation for the unsteady flow. The shedding frequency of vortical structure from the upper side of the right sphere is found to be double of the frequency of the lower side. With the flow spectra of various gaps given, the underlying competitive mechanism between the two shedding frequencies is studied and a critical spacing gap is revealed. Copyright © 2005 John Wiley & Sons, Ltd. [source] Linear stability analysis of flow in a periodically grooved channelINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6 2003T. Adachi1 Abstract We have conducted the linear stability analysis of flow in a channel with periodically grooved parts by using the spectral element method. The channel is composed of parallel plates with rectangular grooves on one side in a streamwise direction. The flow field is assumed to be two-dimensional and fully developed. At a relatively small Reynolds number, the flow is in a steady-state, whereas a self-sustained oscillatory flow occurs at a critical Reynolds number as a result of Hopf bifurcation due to an oscillatory instability mode. In order to evaluate the critical Reynolds number, the linear stability theory is applied to the complex laminar flow in the periodically grooved channel by constituting the generalized eigenvalue problem of matrix form using a penalty-function method. The critical Reynolds number can be determined by the sign of a linear growth rate of the eigenvalues. It is found that the bifurcation occurs due to the oscillatory instability mode which has a period two times as long as the channel period. Copyright © 2003 John Wiley & Sons, Ltd. [source] Numerical investigation of the first instabilities in the differentially heated 8:1 cavityINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 8 2002F. Auteri Abstract We present a new Galerkin,Legendre spectral projection solver for the simulation of natural convection in a differentially heated cavity. The projection method is applied to the study of the first non-stationary instabilities of the flow in a 8:1 cavity. Statistics of the periodic solution are reported for a Rayleigh number of 3.4×105. Moreover, we investigate the location and properties of the first Hopf bifurcation and of the three successive bifurcations. The results confirm the previous finding in the range of Rayleigh numbers investigated that the flow instabilities originate in the boundary layer on the vertical walls. A peculiar phenomenon of symmetry breaking and symmetry restoring is observed portraying the first steps of the transition to chaos for this flow. Copyright © 2002 John Wiley & Sons, Ltd. [source] Bifurcation behaviour in parallel-connected boost convertersINTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONS, Issue 3 2001H. H. C. Iu Abstract This paper describes the bifurcation phenomena of a system of parallel-connected d.c./d.c. boost converters. The results provide important information for the design of stable current sharing in a master,slave configuration. Computer simulations and experiments are performed to capture the effects of variation of some chosen parameters on the qualitative behaviour of the system. In particular, it is found that variation of some parameters leads to Neimark,Sacker bifurcation. Analysis is presented to establish the possibility of the bifurcation phenomena. Copyright © 2001 John Wiley & Sons, Ltd. [source] Homoclinic bifurcation and global indeterminacy of equilibrium in a two-sector endogenous growth modelINTERNATIONAL JOURNAL OF ECONOMIC THEORY, Issue 1 2009Paolo Mattana C62; E32; O41 This paper considers an endogenous growth model that belongs to the same family as the Lucas model. In the Lucas model an external effect appears in the physical-goods sector, whereas in our model, it appears in the educational sector. In our model, this external effect yields multiple balanced growth paths. Our model undergoes a homoclinic bifurcation and exhibits global indeterminacy of equilibrium. 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