89,342 research outputs found
Simulation of bubbles
International audienceWe present a novel framework based on a continuous fluid simulator for general simulation of realistic bubbles, with which we can handle as many significant dynamic bubble effects as possible. To capture a very thin liquid film of bubbles, we have developed a regional level set method allowing multi-manifold interface tracking. Based on the definitions of regional distance and its five operators, the implementation of the regional level set method is very easy. An implicit surface of liquid film with arbitrary thickness can be reconstructed from the regional level set function. To overcome the numerical instability problem, we exploit a new semi-implicit surface tension model which is unconditionally stable and makes the simulation of surface tension dominated phenomena much more efficient. An approximated film thickness evolution model is proposed to control the bubble's lifecycle. All these new techniques combine into a general framework that can produce various realistic dynamic effects of bubbles
Cosmological HII Bubble Growth During Reionization
We present general properties of ionized hydrogen (HII) bubbles and their
growth based on a state-of-the-art large-scale (100 Mpc/h) cosmological
radiative transfer simulation. The simulation resolves all halos with atomic
cooling at the relevant redshifts and simultaneously performs radiative
transfer and dynamical evolution of structure formation. Our major conclusions
include: (1) for significant HII bubbles, the number distribution is peaked at
a volume of at all redshifts. But, at ,
one large, connected network of bubbles dominates the entire HII volume. (2)
HII bubbles are highly non-spherical. (3) The HII regions are highly biased
with respect to the underlying matter distribution with the bias decreasing
with time. (4) The non-gaussianity of the HII region is small when the universe
becomes 50% ionized. The non-gaussianity reaches its maximal near the end of
the reionization epoch . But at all redshifts of interest there is a
significant non-gaussianity in the HII field. (5) Population III galaxies may
play a significant role in the reionization process. Small bubbles are
initially largely produced by Pop III stars. At even the largest HII
bubbles have a balanced ionizing photon contribution from Pop II and Pop III
stars, while at Pop II stars start to dominate the overall ionizing
photon production for large bubbles, although Pop III stars continue to make a
non-negligible contribution. (6) The relationship between halo number density
and bubble size is complicated but a strong correlation is found between halo
number density and bubble size for large bubbles.Comment: 10 pages, 14 figures; accepted version; higher resolution figures and
supplementary material can be found at
http://www.astro.princeton.edu/~msshin/reionization/web.ht
Vortex-Antivortex Pair Production in a First Order Phase Transition
We carry out numerical simulation of a first order phase transition in 2+1
dimensions by randomly nucleating bubbles, and study the formation of global
U(1) vortices. Bubbles grow and coalesce and vortices are formed at junctions
of bubbles via standard Kibble mechanism as well as due to a new mechanism,
recently proposed by us, where defect-antidefect pairs are produced due to
field oscillations. We make a comparative study of the contribution of both of
these mechanisms for vortex production. We find that, for high nucleation rate
of bubbles, vortex-antivortex pairs produced via the new mechanism have
overlapping configurations, and annihilate quickly; so only those vortices
survive till late which are produced via the Kibble mechanism. However, for low
nucleation rates, bubble collisions are energetic enough to lead to many well
separated vortex-antivortex pairs being produced via the new mechanism. For
example, in a simulation involving nucleation of 20 bubbles, a total of 14
non-overlapping vortices and antivortices formed via this new mechanism of pair
creation (6 of them being very well separated), as compared to 6 vortices and
antivortices produced via the Kibble mechanism. Our results show the
possibility that in extremely energetic bubble collisions, such as those in the
inflationary models of the early Universe, this new mechanism may drastically
affect the defect production scenario.Comment: 8 pages, Revtex, 14 figures. Figs.1a,b and 5a,d are included, rest
are availaible on reques
Slip flow over structured surfaces with entrapped microbubbles
On hydrophobic surfaces, roughness may lead to a transition to a
superhydrophobic state, where gas bubbles at the surface can have a strong
impact on a detected slip. We present two-phase lattice Boltzmann simulations
of a Couette flow over structured surfaces with attached gas bubbles. Even
though the bubbles add slippery surfaces to the channel, they can cause
negative slip to appear due to the increased roughness. The simulation method
used allows the bubbles to deform due to viscous stresses. We find a decrease
of the detected slip with increasing shear rate which is in contrast to some
recent experimental results implicating that bubble deformation cannot account
for these experiments. Possible applications of bubble surfaces in microfluidic
devices are discussed.Comment: 4 pages, 4 figures. v2: revised version, to appear in Phys. Rev. Let
Growth and anisotropy of ionization fronts near high redshift quasars in the MassiveBlack simulation
We use radiative transfer to study the growth of ionized regions around the
brightest, z=8 quasars in a large cosmological hydrodynamic simulation that
includes black hole growth and feedback (the MassiveBlack simulation). We find
that in the presence of the quasar s the comoving HII bubble radii reach 10
Mpc/h after 20 My while with the stellar component alone the HII bubbles are
smaller by at least an order of magnitude. Our calculations show that several
features are not captured within an analytical growth model of Stromgren
spheres. The X-ray photons from hard quasar spectra drive a smooth transition
from fully neutral to partially neutral in the ionization front. However the
transition from partially neutral to fully ionized is significantly more
complex. We measure the distance to the edge of bubbles as a function of angle
and use the standard deviation of these distances as a diagnostic of the
isotropy of ionized regions. We find that the overlapping of nearby ionized
regions from clustered halos not only increases the anisotropy, but also is the
main mechanism which allows the outer radius to grow. We therefore predict that
quasar ionized bubbles at this early stage in the reionization process should
be both significantly larger and more irregularly shaped than bubbles around
star forming galaxies. Before the star formation rate increases and the
Universe fully reionizes, quasar bubbles will form the most striking and
recognizable features in 21cm maps.Comment: 11 pages, 10 figures. Updated after referee repor
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