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Fluid Mechanics (fluid + mechanic)
Terms modified by Fluid Mechanics Selected AbstractsThe formation of dunes, antidunes, and rapidly damping waves in alluvial channelsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 7 2001L.-H. Huang Abstract Under the effect of a constant current for a long time, a water channel of infinitely long and constant depth interacting with a uniform sandbed of infinite thickness is used to simulate the formation of dunes, antidunes and rapidly damping waves in alluvial channels. The theory of potential flow is applied to the channel flow, while Biot's theory of poroelasticity is adopted to deal with erodible bed material. The governing equations, together with free surface, bed surface, and far field boundary conditions, form a complete boundary-value problem without applying empirical sediment discharge formulas as in conventional researches. The comparison of the present result with Kennedy's (Journal of Fluid Mechanics, 1963; 16: 521,544) instability analysis not only indicates the appropriateness of the present work, but also reveals the advantage of the present study due to its ability to find all kinds of bed forms (including the rapidly damping waves that Kennedy could not find) and of solving for the unclear lagged distance , introduced in Kennedy's work. Copyright © 2001 John Wiley & Sons, Ltd. [source] Higher-order finite element discretizations in a benchmark problem for incompressible flowsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 8 2001Volker John Abstract We present a numerical study of several finite element discretizations applied to a benchmark problem for the two-dimensional steady state incompressible Navier,Stokes equations defined in Schäfer and Turek (The benchmark problem ,Flow around a cylinder'. In Flow Simulation with High-Performance Computers II. Notes on Numerical Fluid Mechanics, vol. 52, Hirschel EH (ed.). Vieweg: Wiesbaden, 1996; 547,566). The discretizations are compared with respect to the accuracy of the computed benchmark parameters. Higher-order isoparametric finite element discretizations turned out to be by far the most accurate. The discrete systems obtained with higher-order discretizations are solved with a modified coupled multigrid method whose behaviour within the benchmark problem is also studied numerically. Copyright © 2001 John Wiley & Sons, Ltd. [source] Advanced Fluid Mechanics By W. P. GraebelAICHE JOURNAL, Issue 11 2008Jan V. Sengers No abstract is available for this article. [source] Mechanobiology and the Microcirculation: Cellular, Nuclear and Fluid MechanicsMICROCIRCULATION, Issue 3 2010KRIS NOEL DAHL Microcirculation (2010) 17, 179,191. doi: 10.1111/j.1549-8719.2009.00016.x Abstract Endothelial cells are stimulated by shear stress throughout the vasculature and respond with changes in gene expression and by morphological reorganization. Mechanical sensors of the cell are varied and include cell surface sensors that activate intracellular chemical signaling pathways. Here, possible mechanical sensors of the cell including reorganization of the cytoskeleton and the nucleus are discussed in relation to shear flow. A mutation in the nuclear structural protein lamin A, related to Hutchinson-Gilford progeria syndrome, is reviewed specifically as the mutation results in altered nuclear structure and stiffer nuclei; animal models also suggest significantly altered vascular structure. Nuclear and cellular deformation of endothelial cells in response to shear stress provides partial understanding of possible mechanical regulation in the microcirculation. Increasing sophistication of fluid flow simulations inside the vessel is also an emerging area relevant to the microcirculation as visualization in situ is difficult. This integrated approach to study,including medicine, molecular and cell biology, biophysics and engineering,provides a unique understanding of multi-scale interactions in the microcirculation. [source] Fluid Mechanics, Cell Distribution, and Environment in Cell Cube BioreactorsBIOTECHNOLOGY PROGRESS, Issue 1 2003John G. Auni Cultivation of MRC-5 cells and attenuated hepatitis A virus (HAV) for the production of VAQTA, an inactivated HAV vaccine ( 1), is performed in the Cell Cube reactor, a laminar flow fixed-bed bioreactor with an unusual diamond-shaped, diverging-converging flow geometry. These disposable bioreactors have found some popularity for the production of cells and gene therapy vectors at intermediate scales of operation ( 2, 3). Early testing of the Cell Cube revealed that the fluid mechanical environment played a significant role in nonuniform cell distribution patterns generated during the cell growth phase. Specifically, the reactor geometry and manufacturing artifacts, in combination with certain inoculum practices and circulation flow rates, can create cell growth behavior that is not simply explained. Via experimentation and computational fluid dynamics simulations we can account for practically all of the observed cell growth behavior, which appears to be due to a complex mixture of flow distribution, particle deposition under gravity, fluid shear, and possibly nutritional microenvironment. [source] Teaching differential equations in different environments: A first approachCOMPUTER APPLICATIONS IN ENGINEERING EDUCATION, Issue 3 2010Filipa Carneiro Abstract The use of specific softwares was the basis for a new approach for teaching ordinary and partial differential equations, in the field of heat transfer and fluid mechanics. The main objective was to enhance learning effectiveness of Numerical Methods in the post-graduate course of Polymers Engineering at the University of Minho. This degree takes place into two different environments: at the university campus and at the industrial field. Different commercial codes were used, namely EXCEL, MATLAB, and FLUENT, as well as two tools developed in house at University of Minho: CoNum and a graphics application PDE v.1. Lectures were based on videoconferencing and other web utilities. The teaching methodology presented and discussed in this article was well received and accepted by the post-graduate students, motivating teachers to improve their teaching/learning strategies. © 2009 Wiley Periodicals, Inc. Comput Appl Eng Educ 18: 555,562, 2010; View this article online at wileyonlinelibrary.com; DOI 10.1002/cae.20231 [source] Joule heating in electrokinetic flowELECTROPHORESIS, Issue 1 2008Xiangchun Xuan ProfessorArticle first published online: 30 NOV 200 Abstract Electrokinetic flow is an efficient means to manipulate liquids and samples in lab-on-a-chip devices. It has a number of significant advantages over conventional pressure-driven flow. However, there exists inevitable Joule heating in electrokinetic flow, which is known to cause temperature variations in liquids and draw disturbances to electric, flow and concentration fields via temperature-dependent material properties. Therefore, both the throughput and the resolution of analytic studies performed in microfluidic devices are affected. This article reviews the recent progress on the topic of Joule heating and its effect in electrokinetic flow, particularly the theoretical and experimental accomplishments from the aspects of fluid mechanics and heat/mass transfer. The primary focus is placed on the temperature-induced flow variations and the accompanying phenomena at the whole channel or chip level. [source] Development of equine upper airway fluid mechanics model for Thoroughbred racehorsesEQUINE VETERINARY JOURNAL, Issue 3 2008V. RAKESH Summary Reason for performing study: Computational fluid dynamics (CFD) models provide the means to evaluate airflow in the upper airways without requiring in vivo experiments. Hypothesis: The physiological conditions of a Thoroughbred racehorse's upper airway during exercise could be simulated. Methods: Computed tomography scanned images of a 3-year-old intact male Thoroughbred racehorse cadaver were used to simulate in vivo geometry. Airway pressure traces from a live Thoroughbred horse, during exercise was used to set the boundary condition. Fluid-flow equations were solved for turbulent flow in the airway during inspiratory and expiratory phases. The wall pressure turbulent kinetic energy and velocity distributions were studied at different cross-sections along the airway. This provided insight into the general flow pattern and helped identify regions susceptible to dynamic collapse. Results: The airflow velocity and static tracheal pressure were comparable to data of horses exercising on a high-speed treadmill reported in recent literature. The cross-sectional area of the fully dilated rima glottidis was 7% greater than the trachea. During inspiration, the area of highest turbulence (i.e. kinetic energy) was in the larynx, the rostral aspect of the nasopharynx was subjected to the most negative wall pressure and the highest airflow velocity is more caudal on the ventral aspect of the nasopharynx (i.e. the soft palate). During exhalation, the area of highest turbulence was in the rostral and mid-nasopharynx, the maximum positive pressure was observed at the caudal aspect of the soft palate and the highest airflow velocity at the front of the nasopharynx. Conclusions and clinical relevance: In the equine upper airway collapsible area, the floor of the rostral aspect of the nasopharynx is subjected to the most significant collapsing pressure with high average turbulent kinetic during inhalation, which may lead to palatal instability and explain the high prevalence of dorsal displacement of the soft palate (DDSP) in racehorses. Maximal abduction of the arytenoid cartilage may not be needed for optimal performance, since the trachea cross-sectional area is 7% smaller than the rima glottidis. [source] Local volume-conserving free surface smoothingINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 2 2007F. S. Sousa Abstract Removing high-frequency undulations in surfaces is a problem that appears in different fields, such as computer graphics and computational fluid mechanics. This problem is typically handled by surface smoothing techniques, such as Laplacian filters, that eliminate high-frequency undulations but degrade the volume encompassed by the surface. The need for conserving volume (or mass) rules out the use of such techniques in several application, as for example incompressible flows. In this work we present a smoothing technique that suppresses undulations while conserving local volumes, ensuring that the global mass is conserved. The effectiveness of the proposed technique is illustrated in synthetic datasets as well as in free surface flows simulation. Comparisons between our smoothing approach and the well-known Laplacian filter are also presented. Copyright © 2006 John Wiley & Sons, Ltd. [source] FLEXMG: A new library of multigrid preconditioners for a spectral/finite element incompressible flow solverINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2010M. Rasquin Abstract A new library called FLEXMG has been developed for a spectral/finite element incompressible flow solver called SFELES. FLEXMG allows the use of various types of iterative solvers preconditioned by algebraic multigrid methods. Two families of algebraic multigrid preconditioners have been implemented, namely smooth aggregation-type and non-nested finite element-type. Unlike pure gridless multigrid, both of these families use the information contained in the initial fine mesh. A hierarchy of coarse meshes is also needed for the non-nested finite element-type multigrid so that our approaches can be considered as hybrid. Our aggregation-type multigrid is smoothed with either a constant or a linear least-square fitting function, whereas the non-nested finite element-type multigrid is already smooth by construction. All these multigrid preconditioners are tested as stand-alone solvers or coupled with a GMRES method. After analyzing the accuracy of the solutions obtained with our solvers on a typical test case in fluid mechanics, their performance in terms of convergence rate, computational speed and memory consumption is compared with the performance of a direct sparse LU solver as a reference. Finally, the importance of using smooth interpolation operators is also underlined in the study. Copyright © 2010 John Wiley & Sons, Ltd. [source] A CBS-type stabilizing algorithm for the consolidation of saturated porous mediaINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 4 2005V. A. Salomoni Abstract The presented method stems from the works by Zienkiewicz and co-workers for coupled fluid/thermal problems starting from the early 1990s. They propose algorithms to overcome the difficulties connected to the application of the FEM to the area of fluid mechanics, which include the problems of singular behaviour in incompressibility and the problems connected to convective terms. The major step forward was to introduce the concept of characteristic lines (the particle paths in a simple convection situation): for a class of problems with a single scalar variable, the equations in the characteristic co-ordinates regain self-adjointness. The procedure is called characteristic based split algorithm (CBS). We use here a CBS-type procedure for a saturated deformable elastic porous medium, in which the fluid velocity is governed by Darcy's equation (which comes directly from Navier,Stokes ones). The physical,mathematical model is a fully coupled one and is here used to study an incompressible flow inside a continuum with incompressible solid grains. The power of the adopted algorithm is to treat the basic equations in their strong form and to transform a usual ,u,p' problem into a ,u,v,p' one, where u generally indicates the displacement of the solid matrix and p and v the pressure and velocity of the fluid, respectively. Attention is focused on the expression of Darcy's velocity which is considered as the starting point of the algorithm. The accuracy of the scheme is checked by comparing the present predictions in a typical consolidation test with available analytical and numerical u,p solutions. A good fitting among different results has been obtained. It is further shown that the procedure eliminates the oscillations at the onset of consolidation, typical for many schemes. The FEM code Ed-Multifield has been used for implementing and testing the procedure. Copyright © 2005 John Wiley & Sons, Ltd. [source] How Views about Flow Adaptations of Benthic Stream Invertebrates Changed over the Last CenturyINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 4-5 2008Bernhard StatznerArticle first published online: 15 OCT 200 Abstract Throughout the last century, stream ecologists tried to answer the question: how do benthic invertebrates cope with the flows prevailing in streams? Whereas the pioneers frequently sought answers using imagination and speculation in a hefty debate, subsequent research on flow adaptations of stream invertebrates relied increasingly on the transfer of concepts (from fluid mechanics to stream ecology) and technological innovations. Correspondingly, views about flow adaptations of stream invertebrates changed considerably over the last century. However, stream ecologists are still far from understanding how stream invertebrates are adapted to the many different flow conditions they face during their life, because the near-bottom flows they experience are extremely complex and create so diverse constraints that adaptation to all of them is physically impossible. This instance shows how ignorant we are of the physical factors in the environment which ultimately shape the organisms, and how difficult it is to understand the utility of a structure without knowing the requirements for which it is produced Sunder Lal Hora, 1930 (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Smart blending technology enabled by chaotic advectionADVANCES IN POLYMER TECHNOLOGY, Issue 3 2006D. A. Zumbrunnen Abstract Polymer blending has been typically regarded as a mixing process rather than a structuring process so polymer blends and composites are not necessarily optimized with regard to structure, properties, and composition. In this article, a new smart blending technology is described whereby melt components and solid additives are more controllably organized into micrometer-scale and sub-micrometer-scale shapes and arrangements to improve properties or impart functionality to extruded plastics. Chaotic advection is an enabling recent subfield of fluid mechanics for smart blending. It provides a method to controllably stretch and fold melt domains and evolve a multilayered structure leading to derivative morphologies, or indirectly manipulate solid additives. Recent advances in fluid mechanics have thereby been implemented to reconsider how blending is done. A variety of structured plastic materials are producible with a single smart blending device with no device alterations. Several examples and their improved physical properties are shown or discussed. © 2006 Wiley Periodicals, Inc. Adv Polym Techn 25:152,169, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20073 [source] The effect of viscosity on surface tension measurements by the drop weight methodJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2007T. Kaully Abstract Viscosity is one of the parameters affecting the measured surface tension, as fluid mechanics affects the measurement process using conventional methods. Several methods including the selected planes (SPM) and WDSM which combines the weight drop method (WDM) and SPM, are applied to surface tension measurement of high viscous liquids. Yet, none of them treats the viscosity effect separately. The current publication presents a simple, easy to apply empirical approach of satisfactory accuracy, for evaluation of surface tension of liquids having wide range of viscosities up to 10 Pa s. The proposed method is based on Tate's law and the "drop weight" method using calibration curves of known liquids having similar surface tensions but different viscosities. Drop weight of liquids having viscosity ,0.05 Pa s, was found to be significantly affected by the liquid viscosity. The shape factor, f, of high viscosity liquids was found to correlate linearly with the logarithm of viscosity, pointing the importance of viscosity correction. The experimental correlation presented in the current work can be used as a tool for the evaluation of surface tension for high viscosity liquids such as prepolymers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 [source] Simulation of polymer melt processingAICHE JOURNAL, Issue 7 2009Morton M. Denn Abstract Polymer melt processing requires an integration of fluid mechanics and heat transfer, with unique issues regarding boundary conditions, phase change, stability and sensitivity, and melt rheology. Simulation has been useful in industrial melt processing applications. This brief overview is a personal perspective on some of the issues that arise and how they have been addressed. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Simulations of grafting monomers and associated degradation of polypropylene in a modular co-rotating twin screw extruderJOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 4 2005Jongmin Keum Kinetic models of grafting maleic anhydride (MAH) and methyl methacrylate (MMA) on polypropylene (PP) were developed for screw extrusion. However, the kinetic models were insufficient to explain the grafting reactions along the length of modular co-rotating twin screw extruders because the rheological properties and the residence time of PP changed owing to degradation of PP during the grafting reaction. In order to model this system for a modular co-rotating twin screw extruder, the kinetic model of grafting reaction and models for degradation of PP were combined with fluid mechanics and heat transfer. Given the geometrical configurations of the screw, the operating conditions, and the physical properties of the polypropylene, the simulations predicted variation of molecular weight and mean residence time due to degradation of PP. The weight percent of grafted MAH or MMA on PP profiles along the screw axis was also calculated in the simulation. These predictions were compared with experimental data for various operating conditions. J. VINYL. ADDIT. TECHNOL. 11:143,149, 2005. © 2005 Society of Plastics Engineers. [source] Coupling finite difference methods and integral formulas for elliptic problems arising in fluid mechanicsNUMERICAL METHODS FOR PARTIAL DIFFERENTIAL EQUATIONS, Issue 2 2004C. Albuquerque Abstract This article is devoted to the numerical analysis of two classes of iterative methods that combine integral formulas with finite-difference Poisson solvers for the solution of elliptic problems. The first method is in the spirit of the Schwarz domain decomposition method for exterior domains. The second one is motivated by potential calculations in free boundary problems and can be viewed as a numerical analytic continuation algorithm. Numerical tests are presented that confirm the convergence properties predicted by numerical analysis. © 2003 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 20: 199,229, 2004 [source] A study of the Coriolis effect on the fluid flow profile in a centrifugal bioreactorBIOTECHNOLOGY PROGRESS, Issue 4 2009Christopher J. Detzel Abstract Increasing demand for tissues, proteins, and antibodies derived from cell culture is necessitating the development and implementation of high cell density bioreactors. A system for studying high density culture is the centrifugal bioreactor (CCBR), which retains cells by increasing settling velocities through system rotation, thereby eliminating diffusional limitations associated with mechanical cell retention devices. This article focuses on the fluid mechanics of the CCBR system by considering Coriolis effects. Such considerations for centrifugal bioprocessing have heretofore been ignored; therefore, a simpler analysis of an empty chamber will be performed. Comparisons are made between numerical simulations and bromophenol blue dye injection experiments. For the non-rotating bioreactor with an inlet velocity of 4.3 cm/s, both the numerical and experimental results show the formation of a teardrop shaped plume of dye following streamlines through the reactor. However, as the reactor is rotated, the simulation predicts the development of vortices and a flow profile dominated by Coriolis forces resulting in the majority of flow up the leading wall of the reactor as dye initially enters the chamber, results are confirmed by experimental observations. As the reactor continues to fill with dye, the simulation predicts dye movement up both walls while experimental observations show the reactor fills with dye from the exit to the inlet. Differences between the simulation and experimental observations can be explained by excessive diffusion required for simulation convergence, and a slight density difference between dyed and un-dyed solutions. Implications of the results on practical bioreactor use are also discussed. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source] Empirical Challenges and Concept Formation in the History of HydrodynamicsCENTAURUS, Issue 3 2008Olivier Darrigol Abstract Although the fundamental equations of hydrodynamics were known at an early stage of its history, this theory long remained irrelevant to most of the practical problems of flow. The advent of a more efficient fluid mechanics in the early twentieth century depended on conceptual schemes that could not be read directly from the basic equations. Attention to concrete problems of flow, rather than purely mathematical deduction or purely intuitive guessing, permitted the gradual introduction of relevant substructures and their ultimate combination in powerful approximation schemes. This history is in part singular, owing to the extreme difficulty of dealing with non-linear systems with infinitely many degrees of freedom. But it is also typical as an illustration of the futility of reducing a physico-mathematical theory to its fundamental equations. Any advanced theory of physics must include an evolving modular structure that plays an essential role in melding the formal with the empirical. [source] | ||||||||||||||||||||||