2. Basic Research in Hydrodynamics |
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(1) Research on bubble plume |
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The sea surrounds the Taiwan. So ocean is an important resource
to our country. It is known that there is abundant in natural gas under
Taiwan west offshore. The Chinese Petroleum Corporation set up the platform
ship in the southwest offshore to drilling well for exploring natural gas.
The gas blowout may be occurred in accident. Due to the gas containing of
hydrocarbon that is harmful to marine life, the spread and diffusion of
gas will cause offshore environment pollution. Thus, spread and diffusion
of gas blowout are worth to investigate thoroughly. We are trying to do
the experimental study on the bubble plume that is conducted in a tank filled
with density stratified water. The laser light sheet is created to illuminate
the flow field. A CCD (Charge-Coupled Detector) is applied to take the picture.
The digital image process skill is employed to analyze the picture to obtain
the spread characteristics of the bubble plume in stratified water. The
effects of the gas flow rate and ambient water stratification on the bubble
plume behaviors are also investigated. Experimental results are used to
compare the numerical model calculation. The developed numerical model and
experimental method will be applied to investigate gas blowout in Taiwan
southwest offshore gas well blowout. The results can be used as references
for offshore environment pollution assessment and control. (Bao-Shi Shiau) |
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(2) Numerical simulations of surface
wave propagation over a submerged obstacle |
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This study is to propose a numerical model simulating free
surface flows. It will be used to investigate the interaction of travelling
waves with a submerged obstacle, especially the vortex generation in the
vicinity of the obstacle. The finite analytical method is the main numerical
scheme employed. Ursell number and Keulegan-Carpenter (KC) number are two
parameters of the free surface flows. Their effects will be explored in
the study. (Robert R. Hwang, Ming-Jyh Chern) |
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(3) Direct Numerical Simulation study
from laminar to chaotic flows |
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Following the rapid development of the chaos theory and computational
methods, it is the best time to investigate phenomena of fluid dynamical
system from transition to chaos in terms of direct numerical simulation.
Transition processes in benchmark flow fields will be explored in terms
of various Reynolds numbers. Cavity flows are currently being studied and
some results are obtained. Channel flows and flow past a obstacle such as
a square or cylindrical cylinder will be considered. (Robert R. Hwang, Yin-Ferng
Peng, You-Shien Shiau) |
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(4) Two-dimensional soap film tunnel |
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A soap film tunnel is planed to establish for observation
of two-dimensional turbulent flows. The soap film is extremely thin (about
1 mm). The drag reduction theory is planed to be investigated in the soap
film tunnel. The main work of the study includes the measurement of the
thickness of the soap film, flow visualization, the measurement of velocity
field. (Robert R. Hwang, Ming-Jyh Chern) |
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(5) Effects of tidal variability and
continuous stratification at estuary |
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Several effects in the flow field of an estuary including
interaction of river current and ocean current has been studied. Other important
mechanism such as density stratification and tidal variation are not touched.
Hence, it is worth paying more attentions in these topics. This project
is conducted using numerical simulation. The main goal is to establish a
3-D numerical model. The vertical density stratification and tidal variation
will be considered. (Robert R. Hwang, Wen-Chang Yang) |
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(6) Liquid encapsulated floating zone |
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In liquid encapsulated floating zone configuration, the liquid
column is concentrically surrounded by immiscible liquid encapsulant and
creates a column of two concentric immiscible liquid. The shape of the volume
of fluid is held between equal diameter solid disks by surface tension.
The liquid bridge has been extensively investigated since the early publication
of Rayleigh and Plateau more than a century. Recently, with the availability
of the reduced gravity environment and the potential of containless processing,
the problem has been widely studied and applied in industry applications.
We have simulated the encapsulated floating zone by volume of fluid model
with continuum surface formulation to take care liquid/liquid or liquid
air interface. The two fluids, inner cylinder filled with FC-40 and outer
2 cSt silicon oil, are handled by unique system of governing equations and
solved like single fluid problem with pressure based algorithm. The flow
characteristics and the thermal properties of the liquid encapsulated floating
zone in various gravity conditions are obtained. The micro-gravity effects
on the crystal growth in liquid encapsulated floating zone process are simulated.
(Lai-Chen Chien) |
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3. Physics of Complex Fluids |
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(1) Electromagnetic effects
on material growth |
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Solidification material processes can be controlled by heat
transfer, mass transfer, convection, thermodynamic and dynamic technique.
The most popular one is applying an electromagnetic field during material
processes. Besides the computational fluid dynamic equations, the Maxwell
equations are coupled for the crystal growth facilities. The Maxwell equations
are cast into conservative form similar to those of computation fluid dynamics.
The applied electromagnetic forces reduces the convection. Thus the temperature
distribution is more uniform compared with that of general condition. Furthermore,
the effects of Lorentz force on micro-gravity material process can improve
the product quality. (Lai-Chen Chien) |
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(2) Surfactant driven instability in
a Hele-Shaw Cell |
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The interfacial instability of a moving air-liquid interface
moving in a Hele-Shaw cell is studied. From the classical Saffmann-Taylor
result, the interface will become unstable only when the less viscous air
is pushing on the more viscous liquid. However, in our experiment, we have
observed that an instability will develop even when the liquid is pushing
the air if the liquid used in an aqueous surfactant solution. Detailed analysis
of the experiment has revealed that a wetting layer on the air side of the
interface on the all of the Hele-Shaw cell is needed to produce the observed
instability. Based on this observation, a phenomenological model is constructed
to explain the observed experimental results. The main hypothesis of the
model is that surfactants accumulated on the advancing interface will either
dissolve into the bulk to form micelles or diffuse into the wetting layer
on the wall. Instability of the interface will occur when the diffusing
front of the surfactants in the wetting layer becomes unstable. In this
aspect, the surfactant driven instability is very similar to that observed
in directional solidification where the instability of the solidification
front is controlled by the diffusion of impurities ahead of the front. Experiments
are planned in the future to observe this diffusion front directly. (Chi-Keung
Chan) |
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(3) Collapse of a granular pile |
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Usually, avalanches in granular systems are studied
on granular piles by adding the granular material on the top of the piles
either randomly or at a particular location to induce avalanches. However,
in actual situations, another type of avalanches can also be produced in
granular system by the removal of grains or collapse of structure close
to the bottom of the pile. For example, in the landslide close to rivers,
the collapses of nearby slopes are mainly due to the erosions of the river
bed. Despite the practical importance of these avalanches, very little is
known about the properties of these avalanches. An experimental investigation
of the scaling properties of a collapsing rice pile induced by reducing
the length of the base support of the pile is carried. It is found that
two angles of repose are needed to describe the shape of the collapsing
granular pile. Corresponding to these two angles of repose, the collapse
of the granular pile can be characterized by local and global avalanches.
Furthermore, it is found that the probability distributions of the avalanches
depend on the sizes of the avalanches under consideration. (Pei-Yen Lai,
Chi-Keung Chan) |
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(4) Nonlinear phenomena in chemical
and biological systems |
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As it is generally observed, nonlinear phenomena is a cross-discipline
study. With the new laboratory facilities which will be finished next year
in place of the old library, we will be able to conduct experiments in systems
of chemical and biological nature. The chemical system we have in mind is
the Belousov-Zhabotinsky (BZ) reaction in which nonlinear temporal and spatial
behaviors can be observed. We will be interested in the dynamic control
of the pattern formation properties of such a system. As for the biological
system, we will begin by carrying out preliminary studies in the aggregation
behaviors of the slime mold (Dictyostelium). Similar to other pattern formation
systems, interesting patterns can be created during the aggregation of the
slime mold. We are interested in the non-linear dynamics of the collective
behaviors of the individual ameoba in the slime mold. (Chi-Keung Chan) |
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(5) Effect of polymer on the critical
behavior of binary liquid mixture |
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We studied the effects of a high molecular weight polymer
(Polyacrylic Acid, PAA) on the critical behavior of a binary liquid mixture
(Lutidine + Water, LW). A high precision refractometer was built to measure
the temperature dependence of the refractive indexes of the two coexisting
phases after the sample has phase separated. From the refractive indexes
we mapped out the coexistence curve in which composition difference Dc ~
(T - Tc)£]. Here£]and Tc are, respectively, the sample temperature and the
critical temperature of the sample. We found £] = 0.40¡Ó0.01 for the LW with
0.7 mg/cc PAA which is different from that (£]= 0.31¡Ó0.01) of pure LW. (Kiwing
To) |
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(6) Flow properties of semi-conducting
electrorheological fluids |
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An electrorheological (ER) fluid is one that exhibits reversible
changes in rheological properties when acted upon by an electric field.
Such fluids are usually made of particle suspension with large dielectric
constant mismatch between the particles and the fluid in which the particles
are dispersed. Because of the controllable viscosity and fast response,
ER fluid is regarded as a smart material for active devices which transform
electric energy to mechanical energy. It has been widely accepted that the
ER effect is the result of the formation of internal structures such as
chains and columns of the suspended particles in the presence of an electric
field. We have conducted experimental study of semi-conducting polyaniline
ER fluids and found that the flow curves follow a scaling behavior at different
applied electric field strength. We are trying to develop a model based
on the electrical conductivity differences between different kind of polyaniline
derivatives. (Hyoung J. Choi, Kiwing To) |
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