Volume 135, Issue 3, March 2014
Index of content:
- ULTRASONICS, QUANTUM ACOUSTICS, AND PHYSICAL EFFECTS OF SOUND 
135(2014); http://dx.doi.org/10.1121/1.4864303View Description Hide Description
In this paper a numerical approach is presented to compute dispersion curves for solid waveguides coupled to an infinite medium. The derivation is based on the scaled boundary finite element method that has been developed previously for waveguides with stress-free surfaces. The effect of the surrounding medium is accounted for by introducing a dashpot boundary condition at the interface between the waveguide and the adjoining medium. The damping coefficients are derived from the acoustic impedances of the surrounding medium. Results are validated using an improved implementation of an absorbing region. Since no discretization of the surrounding medium is required for the dashpot approach, the required number of degrees of freedom is typically 10 to 50 times smaller compared to the absorbing region. When compared to other finite element based results presented in the literature, the number of degrees of freedom can be reduced by as much as a factor of 4000.
Characterization of the shock pulse-induced cavitation bubble activities recorded by an optical fiber hydrophone135(2014); http://dx.doi.org/10.1121/1.4863199View Description Hide Description
A shock pressure pulse used in an extracorporeal shock wave treatment has a large negative pressure (<−5 MPa) which can produce cavitation. Cavitation cannot be measured easily, but may have known therapeutic effects. This study considers the signal recorded for several hundred microseconds using an optical hydrophone submerged in water at the focus of shock pressure field. The signal is characterized by shock pulse followed by a long tail after several microseconds; this signal is regarded as a cavitation-related signal (CRS). An experimental investigation of the CRS was conducted in the shock pressure field produced in water using an optical hydrophone (FOPH2000, RP Acoustics, Germany). The CRS was found to contain characteristic information about the shock pulse-induced cavitation. The first and second collapse times (t 1 and t 2) were identified in the CRS. The collapse time delay (tc = t 2 – t 1) increased with the driving shock pressures. The signal amplitude integrated for time from t 1 to t 2 was highly correlated with tc (adjusted R 2 = 0.990). This finding suggests that a single optical hydrophone can be used to measure shock pulse and to characterize shock pulse-induced cavitation.
135(2014); http://dx.doi.org/10.1121/1.4863307View Description Hide Description
A one-dimensional (1D) laminar oscillating flow heat transfer model is derived and applied to parallel-plate thermoacoustic heat exchangers. The model can be used to estimate the heat transfer from the solid wall to the acoustic medium, which is required for the heat input/output of thermoacoustic systems. The model is implementable in existing (quasi-)1D thermoacoustic codes, such as DeltaEC. Examples of generated results show good agreement with literature results. The model allows for arbitrary wave phasing; however, it is shown that the wave phasing does not significantly influence the heat transfer.