HYDRODYNAMICS AND ATMOSPHERIC PHYSICS
Weekly Schedule of Softmatter and Biophysics Journal Club



1. Atmospheric Physics
¡@ (1) Atmospheric corrections for the resources satellite images
(2) Application of the semi-Lagrangian method to cloud model
2. Basic Research in Hydrodynamics
¡@ (1) Research on bubble plume
(2) Numerical simulations of surface wave propagation over a submerged obstacle
(3) Direct Numerical Simulation study from laminar to chaotic flows
(4) Two-dimensional soap film tunnel
(5) Effects of tidal variability and continuous stratification at estuary
(6) Liquid encapsulated floating zone
3. Physics of Complex Fluids
¡@ (1) Electromagnetic effects on material growth
(2) Surfactant driven instability in a Hele-Shaw Cell
(3) Collapse of a granular pile
(4) Nonlinear phenomena in chemical and biological systems
(5) Effect of polymer on the critical behavior of binary liquid mixture
(6) Flow properties of semi-conducting electrorheological fluids

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1. Atmospheric Physics
(1) Atmospheric corrections for the resources satellite images
¡@ ¡@ Satellite visible images are unavoidably masked by the cloud, aerosol and water vapor existing in the atmosphere. These effects may be removed by some means, except the cloud. This is the so-called atmospheric correction. In this project we will estimate the atmospheric correction parameters for the resource satellite images by using the multi-spectral data from multiple satellites. Of all the meteorological parameters the aerosol optical thickness is believed to be the most important one for the atmospheric correction. The aerosol optical thickness may be retrieved from the VISSR visible channels data aboard the operational meteorological satellite GMS and the ocean color imager data of the ROCSAT-1. The latter is launched in December 1998. We developed new method of extracting the aerosol optical thickness and test its validity. (Chung-Yi Tseng)
(2) Application of the semi-Lagrangian method to cloud model
¡@ ¡@ Recently the use of semi-Lagrangian method is extended to the meso- and small- scale models. The numerical efficiency in its application to the non-hydrostatic models is limited by fast moving acoustic and gravity waves. Furthermore, there exist overshoot and undershoot of the forecast variables during the integration formula used in the semi-Lagrangian scheme. Modified schemes have been proposed to improve the performance and efficiency. In this study we apply a quasi-monotone semi-Lagrangian scheme to a three-dimensional non-hydrostatic cloud model. The ice phase is considered in the microphysical parameterization in order to investigate its effects on the precipitation structure. The results indicate that the monotone scheme can suppress efficiently the noise generated in the model and simulate correctly the time change of water substances without increasing the computation time. In addition, the new model can simulate some important features of the development of a cumulus cloud. (Chung-Yi Tseng)
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2. Basic Research in Hydrodynamics
(1) Research on bubble plume
¡@ ¡@ 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)
(2) Numerical simulations of surface wave propagation over a submerged obstacle
¡@ ¡@ 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)
(3) Direct Numerical Simulation study from laminar to chaotic flows
¡@ ¡@ 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)
(4) Two-dimensional soap film tunnel
¡@ ¡@ 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)
(5) Effects of tidal variability and continuous stratification at estuary
¡@ ¡@ 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)
(6) Liquid encapsulated floating zone
¡@ ¡@ 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
(1) Electromagnetic effects on material growth
¡@ ¡@ 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)
(2) Surfactant driven instability in a Hele-Shaw Cell
¡@ ¡@ 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)
(3) Collapse of a granular pile
¡@ ¡@ 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)
(4) Nonlinear phenomena in chemical and biological systems
¡@ ¡@ 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)
(5) Effect of polymer on the critical behavior of binary liquid mixture
¡@ ¡@ 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)
(6) Flow properties of semi-conducting electrorheological fluids
¡@ ¡@ 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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