Oceanographic studies were carried out from August 1994 to March 1995 on the intrusion of the Fly River plume in Torres Strait. Measurements at offshore coral reefs revealed an event of decreased ...salinity (≈24) while salinity of the water over the reefs fluctuated between 30–34 the rest of the time. Modelling suggests that this event resulted from the reversal of longshore currents advecting old river plume water back past the river mouth. There the new river water mixed with the old river plume water generating a patch of low-salinity water. While such events may be infrequent, they have the potential to leave a terrestrial signature on offshore coral reefs, in terms of (1) an input of terrigenous sediment and (2) the possible incorporation of riverine particulate metal into the food chain. The impact during an intrusion event may be significant. In the long term the riverine material is diluted in calcareous sediment produced throughout the year by bio-erosion of coral reefs.
The two-fluid model with bubble oscillations, proposed by Egashira et al. (2004), can explain the properties of cavitating bubbly flow and pressure wave propagation in the bubbly liquid. However, the ...viscous effect as well as energy conservation leading to temperature changes inside the bubble with bubble oscillations have not yet been considered. Hence, this study aimed to incorporate the viscous (bulk viscosity and drag) and thermal effects to the previously proposed two-fluid model with bubble oscillations. Bulk viscosity was considered by averaging the shear stress term in the single-phase momentum conservation for a Newtonian fluid, and the drag was introduced by transforming the interfacial shear stress. We derived the averaged energy conservation for a general two-phase flow with a thermal conduction inside bubbles and heat transfer between the two phases, and limited this equation to that for a bubbly flow by closing the interfacial temperature gradient term via constitutive equations for a single bubble. Furthermore, we investigated the stability of our proposed one-dimensional model equations using the dispersion analysis. This analysis provided the following insight: (i) The difference in the temperature gradient models had a slight effect on the stability of the proposed model equations; (ii) the thermal conduction inside the bubbles was dominant in the thermal damping in bubbly flows rather than the heat transfer between the two phases; (iii) incorporating both the bulk viscosity and drag stabilized the proposed model equations. Our results provide insights into the development of mathematical models to investigate the thermal effects in bubbly flow with bubble oscillations, such as cavitating bubbly flow and wave propagation in bubbly liquids.
•Two-fluid model with bubble oscillations was analytically derived by volume average.•Interfacial term of energy conservation was closed by temperature gradient model.•Stability analysis revealed that thermal conduction inside bubble was dominant.•Viscosity and drag play an important role in stability of our derived two-fluid model.
•Extension of acoustic theory for single encapsulated bubble to multiple bubbles.•Bubble encapsulated by a visco-elastic shell with compressibility.•Presence of shell affected advection, ...nonlinearity, and dissipation of ultrasound.•Ultrasound dissipation by compressibility and viscosities of shell and liquid.•Dissipation due to shell compressibility was the highest.
Owing to its potential for application in ultrasound-based diagnosis and therapy, the dynamics of a microbubble encapsulated by shells has long been theoretically investigated. However, outside of our research group, previous theories have been restricted to the case of single encapsulated bubble, whereas in practical diagnostic scenarios, multiple encapsulated bubbles are used as ultrasound contrast agents. In this study, the most recent theory for a single encapsulated bubble incorporating shell compressibility was extended for multiple encapsulated bubbles. Using the method of multiple scales, weakly nonlinear wave equation for one-dimensional ultrasound in liquids containing multiple encapsulated microbubbles was derived from the set of volumetric averaged equations for bubbly flow. It was found that the shell compressibility significantly increased the advection and dissipation effects of ultrasound. Further, five types of dissipation effects were compared with each other, and showed that the dissipation effects corresponding to shell compressibility were the highest.
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