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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 10 (1998), S. 760-774 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We study the dynamics of a compound liquid drop which is comprised of an outer membrane surface, a shell layer, and a core. The deformation due to an imposed extensional flow and the subsequent recovery are investigated computationally employing a combined Eulerian–Lagrangian technique. The numerical method allows for large viscosity and capillarity differences between layers. The present study reports several findings which provide direct insight into developing a dynamic model for leukocytes. A compound drop behaves like a homogeneous, simple liquid drop if the core is sufficiently deformed and the time scale of the core, related to the combination of its viscosity and capillarity, is comparable to that of the shell layer. Disparate time scales between the core and shell layer result in a rapid initial recoil of the drop during which the shell fluid is the primary participant in the hydrodynamics, followed by a slower relaxation period during which the core and shell layer interact with each other. Consequently, the apparent viscosity of the drop depends not only on the rheological properties of the drop, but also on the flow dynamics surrounding it. The findings obtained with the three-layer compound drop model can explain several main characteristics of leukocytes reported in the literature. Furthermore, our study suggests that unless the presence and possible deformation of the nucleus are explicitly accounted for, neither Newtonian nor non-Newtonian models for leukocytes can adequately predict the hydrodynamics of leukocytes. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 8 (1996), S. 3346-3353 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the present paper an aeroelastic model of flexible membrane wing aerodynamics which incorporates the Reynolds-averaged Navier–Stokes equations is presented. The Reynolds stresses are prescribed by the k–ω shear-stress transport eddy-viscosity model recently proposed by Menter. The computed coefficients are compared with classical inviscid membrane airfoil theory and with a portion of the available experimental data for membrane wings. The results indicate that classical potential-based membrane airfoil theory can provide a meaningful description of membrane wing aerodynamics only for a small range of incidence angles near ideal and then only for membrane airfoils with small excess length ratios. For larger excess lengths and incidence angles viscous effects dominate the aerodynamics. The agreement of the computed results with the experimental data is mixed. The current status of the available experimental data for membrane airfoils is also reviewed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 9 (1997), S. 2769-2788 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In modeling the effect of compressibility on the turbulence structure, additional physical mechanisms arise in production and dissipation of turbulent kinetic energy. Several proposed treatments dealing with the dilatation dissipation and the pressure dilatation correlation are discussed in the context of the k−cursive-epsilon two-equation model. Modifications accounting for the turbulent mass flux, enthalpic production, and baroclinic torque are also assessed along with the nonequilibrium treatment. These compressibility models are evaluated with the aid of experimental data for supersonic flow over an axisymmetric afterbody. With the free-stream Mach number of 2.46, the compressibility and nonequilibrium modifications give marginally better results for the turbulence structure and offer added insight into the mean and fluctuating flow fields. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 2592-2607 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Numerical calculations are conducted for two-dimensional steady-state double-diffusive flow in enclosures, where both the temperature and solute gradients are imposed horizontally, and the two buoyancy effects can either augment or counteract each other. Important controlling parameters including the thermal and solutal Grashof numbers, Schmidt number, and Prandtl number, are varied and new insights into the solutions of both the augmenting and counteracting modes gained. Even though the relative directions of the two buoyancy mechanisms reverse between the augmenting and counteracting modes, qualitative similarities in convection characteristics emerge. For both modes, with fixed thermal and solutal Grashof numbers, convection strength increases as the ratio between the Schmidt and Prandtl numbers, i.e., the Lewis number, becomes higher. With appropriate combinations of the Grashof number and buoyancy ratio, multiple-cell flow patterns also appear in both modes, where the length scale disparity due to a large Lewis number causes the convection to be largely controlled by the temperature field within the primary convection cell, and by the solute field either in the region across the cell interface or in the secondary cells. Effects of irregular geometry of the enclosure on the transport processes are also assessed.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 1712-1719 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A three-dimensional theoretical model based on first principles has been developed to predict the characteristics of mass, momentum, energy, and electrostatic potential transport in high-pressure mercury arcs confined in a quartz arctube. The model is utilized to systematically investigate the impact of convection on the transport process by including and excluding the gravity effect. Strong three-dimensional convection flows with multiple contrarotating vortices have been identified. These vortices substantially change the energy balance within the arc, causing highly nonuniform gas temperature distribution and lowering the maximum gas temperature. Geometrical modifications of the arctube such as wall contour curvature and electrode offsets do not change the strength of convection but can produce better overall temperature uniformity within the arctube by accommodating the upward-moving tendency of temperature contours caused by convection. In agreement with the experimental measurement, the model predicts that the arctube curvature can cause large differences of wall temperature profiles, including shape, level, and locations of peak values.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 7 (1995), S. 2175-2184 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Computations of the harmonically forced, unsteady viscous flow over a flexible, two-dimensional membrane wing are presented. The aeroelastic problem is nondimensionalized and a set of six basic dimensionless parameters is derived that govern the physical problem. The computational investigation is facilitated by distinguishing three distinct classes of problems—the constant tension, elastic, and inextensible membrane problems—which are associated with limiting cases of the dimensionless parameter set. A pressure-based method for the incompressible Navier–Stokes equations written in general time-dependent curvilinear coordinates is adopted as the flow solver. The computations were performed at a Reynolds number of 4×103, which is near the upper limit of the laminar flow regime. The periodic appearance and collapse of recirculation zones, along with an attendant adjustment in membrane configuration, results in an aeroelastic response, which may not be characterized as a simple harmonic response at the free-stream forcing frequency. Ostensibly, the computations are designed to simulate the behavior of a marine sail in a wind gust; however, the simulation of a harmonically forced free-stream flow also proves to be a useful vehicle for demonstrating some of the more generic features of membrane wing mechanics. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Bradford : Emerald
    International journal of numerical methods for heat & fluid flow 14 (2004), S. 98-115 
    ISSN: 0961-5539
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Multiphase flow computations involve coupled momentum, mass and energy transfer between moving and irregularly shaped boundaries, large property jumps between materials, and computational stiffness. In this study, we focus on the immersed boundary technique, which is a combined Eulerian-Lagrangian method, to investigate the performance improvement using the multigrid technique in the context of the projection method. The main emphasis is on the interplay between the multigrid computation and the effect of the density and viscosity ratios between phases. Two problems, namely, a rising bubble in a liquid medium and impact dynamics between a liquid drop and a solid surface are adopted. As the density ratio increases, the single grid computation becomes substantially more time-consuming; with the present problems, an increase of factor 10 in density ratio results in approximately a three-fold increase in CPU time. Overall, the multigrid technique speeds up the computation and furthermore, the impact of the density ratio on the CPU time required is substantially reduced. On the other hand, the impact of the viscosity ratio does not play a major role on the convergence rates.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Bradford : Emerald
    International journal of numerical methods for heat & fluid flow 14 (2004), S. 851-865 
    ISSN: 0961-5539
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The geometric conservation law (GCL) is an important concept for moving grid techniques because it directly regulates the treatments of the fluid flow and grid movement. With the grid movement at every time instant, the Jacobian, associated with the volume of each element in curvilinear co-ordinates, needs to be updated in a conservative manner. In this study, alternative GCL schemes for evaluating the Jacobian have been investigated in the context of a pressure-based Navier-Stokes solver, utilizing moving grid and the first-order implicit time stepping procedure as well as the PISO scheme. GCL-based on first and second-order, implicit as well as time-averaged, time integration schemes were considered. Accuracy and conservative properties were tested on steady-state, laminar flow inside a 2D channel and time dependent, turbulent flow around a 3D elastic wing; both treated with moving grid techniques. It seems that the formal order of accuracy is not a decisive indicator. Instead, the speed of grid movement and the interplay between the flow solver and the GCL treatments make a more noticeable impact.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Annals of biomedical engineering 27 (1999), S. 648-655 
    ISSN: 1573-9686
    Keywords: Leukocyte model ; Computational cellular dynamics ; Cell recovery
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The rheological properties of a leukocyte significantly affect its biological and mechanical characteristics. To date, existing physical models of leukocyte are not capable of quantitatively explaining the wide range of deformation and recovery behaviors observed in experiment. However, a compound drop model has gained some success. In the present work, we investigate the effect of nucleus size and position, and the relative rheological properties of cytoplasm and nucleus, on cell recovery dynamics. Two nucleus sizes corresponding to that of neutrophil and lymphocyte are considered. Direct comparison between numerical simulations and experimental observation is made. Results indicate that the time scale ratio between the nucleus and cytoplasm plays an important role in cell recovery characteristics. Comparable time scales between the two cell components yield favorable agreement in recovery rates between numerical and experimental observations; disparate time scales, on the other hand, result in recovery behavior and cell shapes inconsistent with experiments. Furthermore, it is found that the nucleus eccentricity exhibits minimum influence on all major aspects of the cell recovery characteristics. The present work offers additional evidence in support of the compound cell model for predicting the rheological behavior of leukocytes. © 1999 Biomedical Engineering Society. PAC99: 8717-d, 8719Tt
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 40 (1997), S. 1231-1261 
    ISSN: 0029-5981
    Keywords: float zone ; crystal growth ; solidification ; moving boundary ; thermocapillary transport ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A computational capability has been developed to predict the free surface shape, heat transfer and melt-crystal interface shapes in float-zone processing. A moving boundary, second order, finite volume, incompressible Navier-Stokes solver has been developed for the fluid flow and heat transfer calculations. The salient features of the approach include solving the dynamic form of the Young-Laplace equation for the free surface shape, dynamic remeshing to fit the free boundary, a flexible, multi-block, grid generation procedure and the enthalpy method to capture the melt-crystal and the melt-feed interfaces without the need for explicit interface tracking. Important convective heat transfer modes; natural convection and thermocapillary convection have been computed. It is shown that, whereas the overall heat transfer is not substantially affected by convection, the melt-crystal interface shape acquires significant distortion due to the redistribution of the temperature field by the thermocapillary and buoyancy-induced convective mechanisms. It is also demonstrated that the interaction of natural and thermocapillary convection can reduce the melt-crystal interface distortion if they act in opposing directions. It is found that the meniscus deformation can cause the height of the zone to increase but the qualitative nature of the melt-solid interface shapes are not significantly affected. Results are compared with literature to validate the predictive capability developed in this work. © 1997 by John Wiley & Sons, Ltd.
    Additional Material: 23 Ill.
    Type of Medium: Electronic Resource
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