2,360 research outputs found
Single Curved Fiber Sedimentation Under Gravity
Dynamics of single curved fiber sedimentation under the gravity are simulated by using lattice Boltzmann method. The results of migration and rotation of the curved fiber at different Reynolds numbers are reported. The results show that the rotation and migration processes are sensitive to the curvature of the fiber
The sedimentation of flexible filaments
The dynamics of a flexible filament sedimenting in a viscous fluid are
explored analytically and numerically. Compared to the well-studied case of
sedimenting rigid rods, the introduction of filament compliance is shown to
cause a significant alteration in the long-time sedimentation orientation and
filament geometry. A model is developed by balancing viscous, elastic, and
gravitational forces in a slender-body theory for zero-Reynolds-number flows,
and the filament dynamics are characterized by a dimensionless
elasto-gravitation number. Filaments of both non-uniform and uniform
cross-sectional thickness are considered. In the weakly flexible regime, a
multiple-scale asymptotic expansion is used to obtain expressions for filament
translations, rotations, and shapes. These are shown to match excellently with
full numerical simulations. Furthermore, we show that trajectories of
sedimenting flexible filaments, unlike their rigid counterparts, are restricted
to a cloud whose envelope is determined by the elasto-gravitation number. In
the highly flexible regime we show that a filament sedimenting along its long
axis is susceptible to a buckling instability. A linear stability analysis
provides a dispersion relation, illustrating clearly the competing effects of
the compressive stress and the restoring elastic force in the buckling process.
The instability travels as a wave along the filament opposite the direction of
gravity as it grows and the predicted growth rates are shown to compare
favorably with numerical simulations. The linear eigenmodes of the governing
equation are also studied, which agree well with the finite-amplitude buckled
shapes arising in simulations
Three-dimensional cell to tissue assembly process
The present invention relates a 3-dimensional cell to tissue and maintenance process, more particularly to methods of culturing cells in a culture environment, either in space or in a gravity field, with minimum fluid shear stress, freedom for 3-dimensional spatial orientation of the suspended particles and localization of particles with differing or similar sedimentation properties in a similar spatial region
Microgravity: a Teacher's Guide with Activities, Secondary Level
This NASA Educational Publication is a teacher's guide that focuses on microgravity for the secondary level student. The introduction answers the question 'What is microgravity?', as well as describing gravity and creating microgravity. Following the introduction is a microgravity primer which covers such topics as the fluid state, combustion science, materials science, biotechnology, as well as microgravity and space flight. Seven different activities are described in the activities section and are written by authors prominent in the field. The concluding sections of the book include a glossary, microgravity references, and NASA educational resources
Dynamics of flexible fibers in viscous flows and fluids
International audienceThe dynamics and deformations of immersed flexible fibers are at the heart of important industrial and biological processes, induce peculiar mechanical and transport properties in the fluids that contain them, and are the basis for novel methods of flow control. Here we focus on the low Reynolds number regime where advances in studying these fiber-fluid systems have been especially rapid. On the experimental side this is due to new methods of fiber synthesis, microfluidic flow control, and of microscope based tracking measurement techniques. Likewise, there have been continuous improvements in the specialized mathematical modeling and numerical methods needed to capture the interactions of slender flexible fibers with flows, boundaries, and each other
The First United States Microgravity Laboratory
The United States Microgravity Laboratory (USML-1) is one part of a science and technology program that will open NASA's next great era of discovery and establish the United States' leadership in space. A key component in the preparation for this new age of exploration, the USML-1 will fly in orbit for extended periods, providing greater opportunities for research in materials science, fluid dynamics, biotechnology, and combustion science. The major components of the USML-1 are the Crystal Growth Furnace, the Surface Tension Driven Convection Experiment (STDCE) Apparatus, and the Drop Physics Module. Other components of USML-1 include Astroculture, Generic Bioprocessing Apparatus, Extended Duration Orbiter Medical Project, Protein Crystal Growth, Space Acceleration Measurement System, Solid Surface Combustion Experiment, Zeolite Crystal Growth and Spacelab Glovebox provided by the European Space Agency
Obstacle-induced lateral dispersion and nontrivial trapping of flexible fibers settling in a viscous fluid
The motion of flexible fibers through structured fluidic environments is
ubiquitous in nature and industrial applications. Most often, their dynamics
results from the complex interplay between internal elastic stresses, contact
forces and hydrodynamic interactions with the walls and obstacles. By means of
numerical simulations, experiments and analytical predictions, we investigate
the dynamics of flexible fibers settling in a viscous fluid embedded with
obstacles of arbitrary shapes. We identify and characterize two types of
events: trapping and gliding, for which we detail the mechanisms at play. We
observe nontrivial trapping conformations on sharp obstacles that result from a
subtle balance between elasticity, gravity and friction. In the gliding case, a
flexible fiber reorients and drifts sideways after sliding along the obstacle.
The subsequent lateral displacement is large compared to the fiber length and
strongly depends on its mechanical and geometrical properties. We show how
these effects can be leveraged to propose a new strategy to sort particles
based on their size and/or elasticity. This approach has the major advantage of
being simple to implement and fully passive, since no energy is needed.Comment: 18 pages, 9 figure
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