Bubble motion in an acoustic resonator with flowing liquid

This work describes results of theoretical study of bubble dynamics in an acoustic field. It is known that there is a radiation force on a bubble in an acoustic resonator. This force can provide conditions of bubble levitation. We consider forces acting on a bubble in a resonator with flowing liquid. It is described in the paper bubble motion in such a condition for different parameters. Results of calculations are discussed

Feasibility of a nonlinear acoustic method for monitoring of bubbles and fishes

A problem of remote counting of bubbles and fishes in shallow waters is complicated due to strong reverberation. Traditional way to solve this problem is the use of narrow acoustic beams and short pulse signals, but it is not applicable for all the situations, in particular, in rivers. Reverberation can be suppressed by methods of nonlinear acoustics, since signals scattered by nonlinear targets contain frequencies which are different from primary emitted ones. Bubble-like objects (free bubbles or swimbladder fishes) have strong nonlinear responses. In the present paper a difference frequency method of counting of bubble-like objects is theoretically considered. Since such a nonlinear scattering is resonant bubble and fish sizing becomes possible. For moving targets nonlinear acoustic response exhibits a specific frequency shift, which can be used for velocity estimation

Acoustical properties of plankton

Plankton is distributed in all oceans and seas, and therefore its acoustic properties can be essential for underwater acoustics. A sound scattering cross section of plankton can increase due to gas cavities associated with plankton cells. Such gas cavities has been found in many kinds of phyto- and zoo- plankton. The present paper gives results of investigation of plankton gas cavities with different methods. II was found in particular that sound velocity in phytoplankton suspensions varies bofh up and down compared to the sound velocity in pure water. A response of phyto- and zoo- plankton on compression and decompression is studied. It was found that species of euphausiids having long range vertical daily migration use bubbles (swimbladders) lo control their buoyancy, while species living without long vertical migration do nof have swimbladders

Bubble diagnostics with the nonlinear acoustic scattering method

The highly nonlinear response of a bubble to an acoustic excitation makes nonlinear methods possible for bubble observation and sizing. There are various nonlinear acoustic methods of bubble detection. The difference frequency method is described, with application to the bubble concentration measurements in the sea. The results of observations on bubble populations of different sizes with a nonlinear acoustic bubble counter are given. The bubble counter was put in the subsurface ocean layer from the drifting vessel. The unit detected single bubbles of known sizes when they passed through the working volume created by the intersection of high-frequency acoustic beams. Data on bubble concentration are presented and discussed. Experiments on bubble motion diagnostics in the cavitation water jet are also described

Acoustic tomography of a turbulent water jet

Measurement of parameters of flowing liquid is one of problems, which have many applications. in the present paper we describe linear and nonlinear acoustic tomography methods for reconstruction of parameters of a turbulent water jet with gas bubbles. Experiments on both techniques are described. in the linear acoustic method it was measured fluctuations of acoustic signal passed through the jet. In the nonlinear acoustic technique it was measured spectra of combination scattering signals in the jet. Experiments were done in a water tank with a submerged water jet. The results of the work demonstrate the possibility of the tomography of flowing bubble liquids