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the bubble approaches that of a liquid, thereby invalidating a key assumption
of Rayleigh-type modeling. During these brief stages of high bubble density
when acoustic emission occurs, the energetics of vapor bubble evolution can
be significantly impacted.
Recently, one-dimensional (1-d) hydrodynamic simulations have begun to be
used for a more sophisticated treatment of bubble evolution, including the
emission of acoustic radiation.11-13 These studies have attempted to model
the generation of vapor bubbles in experiments where the short-pulse laser
energy is delivered via an optical fiber immersed in liquid.14 Two key
parameters in characterizing the bubble evolution are peak bubble size and
time of peak expansion. Although -the shape of the vapor bubble at maximum
expansion is nearly round, the bubble evolution begins quite asymmetrically,
due to the presence of the fiber behind the growing bubble. Comparing the
simulated 1-d bubble growth with experiment is problematic because of the
intrinsic, non-spherical geometry of the growing bubble. In this case, a two-
dimensional (2-d) simulation is preferred in order to capture the strong
deviations from spherical symmetry, particularly at early time.
The majority of experiments exploring vapor bubble evolution near a laser-
irradiating fiber tip are conducted so that physical boundaries are well re-
moved from the fiber tip.14 In this way, the evolution of the vapor bubble is
unaffected by reflecting shocks or acoustic waves for the duration of at least
several cycles of bubble expansion and collapse. However, the evolution of
vapor bubbles in a channel-like geometry such as an artery or large vessel can
be susceptible to important 2-d effects which may appreciably affect bubble
evolution. Use of a 2-d simulation code, such as LATIS15, to investigate
channel effects can be an important tool for understanding bubble dynamics
in a realistic geometry.
In these Proceedings we review the status of 1-d modelling of bubble
experiments for an effectively unbounded geometry. After comparing with
experiment and noting some discrepancies, we turn our attention toward 2-d
simulations. We find that the inclusion of non-radial flows in a 2-d
calculation helps to reduce bubble expansion and to effect better agreement
with the experiment. Finally, we discuss some preliminary work on
simulating 2-d bubble evolution in a channel or vessel-like geometry.
2. One-dimensional modelling
A useful procedure for understanding observed vapor bubble behavior and
deriving bubble scaling laws is through the use of 1-d hydrodynamic
simulations.12,13 The experiment that we concentrate on modelling consists
of a 100 pm radius fiber optic tip immersed in an aqueous dye solution [See
figure (1)]. The delivered half-micron wavelength energy is 0.317 mJ in 5 ns
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Amendt, P.A.; London, R.A. & Strauss, M. Modeling of bubble dynamics in relation to medical applications, report, March 12, 1997; California. (digital.library.unt.edu/ark:/67531/metadc694349/m1/4/: accessed February 22, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.