Publication Details

A model has been developed to simulate cavitation on a blunt body moving through water. The model is implemented into a mrmerica. l code using a coupled vortex element/boundary element method that solves the poteatial flow around the cavitating body. The code is applied io a solid sphere moving through the liquid.

Because the components of a multiphase flow often exhibit different electrical properties, a variety of probes have been developed to study such flows by measuring impedance in the region of interest. Researchers are now using electric fields to reconstruct the impedance distribution within a measurement volume via Electrical Impedance Tomography (EIT). EIT systems employ voltage and current measurements on the boundary of a domain to create a representation of the impedance distribution within the domain. The development of the Sandia EIT system (S-EIT) is reviewed The construction of the projection acquisition system is discussed and two specific EIT inversion algorithms are detailed. The first reconstruction algorithm employs boundary element methods, and the second utilizes finite elements. The benefits and limitations of EIT systems are also discussed. Preliminary results are provided.

In recent years, an effective medium theory has been applied to model the contribution of bubbles for low-frequency oceanic backscattering [Prosperetti et al. and Sarkar and Prosperetti, both submitted to J. Acoust. Soc. Am.] This approach differs from the more traditional one used to account for the effect of bubbles at higher frequencies, in which bubbles are treated as individual scatterers. Here, the relationship between these two apparently different approaches is clarified and a unified theory is presented. In this way, a better understanding of the rationale and limitations for the older theory is achieved. Applications to scattering and bubble counting are described.

It has been shown in earlier studies [Prosperetti, Lu, and Kim; Sarkar and Prosperetti, both submitted to J. Acoust. Soc. Am.] that bubble clouds produced by breaking waves at the ocean’s surface can explain the unexpectedly high backscattering levels observed experimentally by Chapman and Harris [J. Acoust. Soc. Am. 34, 1592 (1962)] and others at low grazing angles. Gas volume fractions of the order of 1%, linear dimensions of the order of 1 m, and surface coverage of the order of 1% (the latter of which agrees with the experimentally measured values for 10 m/s winds) are sufficient to give an excellent match of the data as a function of frequency in the range 0.1–2 kHz and wind speeds from 5 to 25 m/s. In the previous work the clouds were treated as independent scatterers. In the present work the previous results are refined to include lowest order multiple scattering effects along the lines of Foldy [Phys. Rev. 67, 107 (1945)] and Biot [J. Acoust. Soc. Am. 44, 1616 (1968)].

Microbubbles are gas-filled contrast increasing agents used in ultrasound imaging, typically ranging from 1 to 10 μm in size. They are encapsulated by a protective shell to improve stability and prevent coalescence. Ensuring a stable size distribution and reliable performance over time is becoming increasingly important for their effectiveness. In this study, we explore the long-term stability and acoustic performance of our homemade microbubbles. These microbubbles are created using a mechanical agitation method, with a gas core of perfluorobutane (C4F10) and a shell made from a lipid mixture of DPPC and DPPE-PEG-2000 in a 9:1 ratio. We measure the size distribution, scattering, and attenuation of these microbubbles at regular intervals over 4 weeks. Additionally, we analyze the bubble shell properties by using the size and attenuation data. This research provides insights into the lifespan and stability of polydisperse microbubbles over expanded periods, highlighting their potential as efficient ultrasound contrast agents.