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An exact three-dimensional elastodynamic analysis for describing the acoustic resonance frequencies of an acoustic eccentric hollow sphere is derived. The Neumann boundary conditions for inner and outer sphere are considered. The translational addition theorem for spherical vector wave functions is employed to enforcing Neumann boundary conditions. The frequency equations in form of exact determinantal equations involving spherical Bessel functions and Wigner 3j symbols are obtained. Due to geometric symmetry for spherical cavity with inner concentric sphere, multiple degenerate acoustic resonance frequencies are occurred. According to the geometry parameters and frequency number, introduction of eccentricity has a different effect on the acoustic resonance frequency shift. Extensive numerical results have been carried out for acoustic resonance frequency of selected inner-outer radii ratios in a wide range of cavity eccentricities. The numerical results describe the imperative influence of cavity eccentricity and radii ratio on the resonance frequency of the acoustic hollow sphere. Some phenomena such as diminishing degenerate resonance frequency, increasing in the number of resonant frequencies through the splitting of degenerate modes and exchanging the mode of resonance frequencies are demonstrated and discussed.

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In giant magnetostrictive transducer, Young modulus of the core considerably alters with changing its magnetic level. Young modulus change in Terfenol-D core has the highest value. This effect, changes the resonance frequency and mode shapes of the transducer. This subject in Terfenol-D resonance transducer is studied in this paper. For this purpose, a resonance Terfenol-D transducer has been designed and fabricated. Node locations in the transducer are considered to add pre-load and bias mechanisms. Effect of Young modulus change on resonance frequency and mode shape were studied both analytically and by ANSYS FEM software. Range of resonance frequency change in the first mode is 1000 Hz and in the second mode is 100 HZ. Mode shapes changes are limited for both modes. In 40kA/m magnetic field bias, Results from analytical and FEM simulation were verified with experimental results. Resonance frequency in this bias is 3100 Hz for the first mode and 8252 Hz for the second mode. Results have acceptable agreement with experimental results. Moreover, in this bias magnetic field, impedance responses between first and second modes are compared. Results show that selecting second mode is preferable for reducing disturbance of Young Modulus change on vibrational behavior.

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Knowledge of broadband transducers is a new technology in the field of sonar science. Considering that Iran has sea water resources, its importance becomes more and more. In this article, after studying the performance of the kinds of transducers in the field of sonar transducers, a proper broadband transducer with the specific impedance and acoustical characteristics that can send and receive signals, is designed, simulated, fabricated and tested. At first, overall dimension of a broadband transducer with lumped parameter model and electrical equivalent circuit model was approximated and then, with increasing the degrees of freedom of analytical models, all characteristics of the optimum transducer parts were obtained in order to have a large bandwidth. By using a finite element software (COMSOL Multiphysics), the designed model was simulated and the obtained results have been compared with analytical design solution. Finally, the transducer was fabricated and tested in order to the modeled and simulated data be validated with practical ones. The obtained experimental results showed that the simulation with COMSOL Multiphysics can predict the resonance frequency and maximum transmitting voltage response (TVR) of the broad bandwidth transducer with a reasonable precision. The prediction error of resonance frequency and maximum TVR by COMSOL is 3.8% and 5.7%, respectively. The use of lumped parameter and electrical equivalent circuit models, however, gives an initial approximation for transducer dimensions, but in determination of the resonance frequency and the frequency of maximum TVR has a higher error in comparison with the finite element method.

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Hartmann-Sprenger tube is a device in which an under-expanded jet enters a closed-end tube which is placed in a specific distance from the nozzle. By producing an intensive heat inside the tube in some specific modes of operation, the device could be used for some important engineering applications such as acoustic igniters. In present study, thermal performances of a set of six different case studies with conical tubes and different physical specifications are investigated. The variable parameters are the pipe material, the pipe length, the gap distance and the end wall condition which could be closed or perforated. The experimental tests in conjunction with numerical analysis are performed to evaluate the effect of changes in physical parameters on temperature rise inside the tube. The oscillatory flow with strong shock waves is the major reason of temperature rise inside the tube. As the gap distance changes, no oscillatory flow and no sensible temperature rise could be observed. Existence of a tiny hole on the tube end wall reduces the temperature rise, as the shorter tube does. The frequency of oscillations is near the tube resonance frequency for longer tubes. Tubes which made of materials with lower thermal conductivity could produce higher temperatures.

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At the outlet of a converging nozzle connected to a high-pressure gas source, based on its input pressure, an under-expanded and ultrasonic flow is created, accompanied by a shock wave. A simple design of the Hartmann-Sprenger resonance tube device is made by placing a closed-end tube in front of this converging nozzle. The impact of the shock wave and nozzle outflow jet on the tube causes intense heating in the trapped gas inside the tube. This research investigated the functional cycle of the resonance tube and the fluctuating nature of the flow inside it. The main parameters of the problem in the form of the inlet pressure to the nozzle and the distance between the tube and the nozzle, the determination and the effect of changing their value on the fluctuating performance of the flow inside the tube, and the fluctuations of the pressure at the end of the tube were shown. The dominant frequencies of these oscillations were determined and shown that in the range of input pressure from one to ten bar, the range of dominant frequencies is between 600 and 933 Hz, which are slightly different from the resonant frequency of the tube. The intensification of oscillations and dominant frequencies can only be seen in a certain number of values of the main parameters, and the intended heating is created only in these conditions.