Controllable acoustic media having anisotropic mass density and tunable speed of sound

Context. The reduced speed of sound technique (RSST) has been used for efficient simulation of low Mach number flows in solar and stellar convection zones. The basic RSST equations are hyperbolic and are suitable for parallel computation by domain decomposition. The application of RSST is limited to cases in which density perturbations are much smaller than the background density. In addition, nonconservative variables are required to be evolved using this method, which is not suitable in cases where discontinuities such as shock waves coexist in a single numerical domain. Aims. In this study, we suggest a new semiconservative formulation of the RSST that can be applied to low Mach number flows with large density variations. Methods. We derive the wave speed of the original and newly suggested methods to clarify that these methods can reduce the speed of sound without affecting the entropy wave. The equations are implemented using the finite volume method. Several numerical tests are carried out to verify the suggested methods. Results. The analysis and numerical results show that the original RSST is not applicable when mass density variations are large. In contrast, the newly suggested methods are found to be efficient in such cases. We also suggest variants of the RSST that conserve momentum in the machine precision. The newly suggested variants are formulated as semiconservative equations, which reduce to the conservative form of the Euler equations when the speed of sound is not reduced. This property is advantageous when both high and low Mach number regions are included in the numerical domain. Conclusions. The newly suggested forms of RSST can be applied to a wider range of low Mach number flows.

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Ultrasonic Setup for Testing Hydrogels: Preliminary Experiments on Collagen Gels

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.409.146 ◽

2011 ◽

Vol 409 ◽

pp. 146-151 ◽

Cited By ~ 1

Author(s):

Ramiro M. Irastorza ◽

Matteo Achilli ◽

Marta Amadei ◽

Eugenia Blangino ◽

Bernard Drouin ◽

...

Keyword(s):

Mechanical Properties ◽

Speed Of Sound ◽

Mass Density ◽

Acoustic Properties ◽

Collagen Gels ◽

Experimental Conditions ◽

Collagen Concentration ◽

Bulk Compressibility ◽

Acoustic Transducer ◽

Pulse Echo

The assessment of mechanical properties of highly hydrated natural materials remains a challenge because, in general, their mechanical evaluation implies invasive and finally destructive methods. Acoustic-based tests may represent the appropriate tools to investigate the mechanical properties of such materials, particularly collagen gels, whose acoustic properties are poorly understood. The objective of this work is to develop two experimental setups for the assessment of acoustic properties of such a hydrogels. In the first one, a typical pulse echo reflectometer was implemented. The acoustic parameters were measured at controlled temperature in an especially designed chamber. In the second one, the previous configuration was combined with a setup for compressive tests, allowing to interrogate simultaneously both the acoustic and mechanical properties of the sample under test. The frequency of the acoustic transducer was 10MHz. The acoustic and mechanical properties of collagen gels prepared according to different experimental conditions (pH and collagen concentration) were evaluated. The first set of experiment was useful to accomplish estimation of the speed of sound, attenuation and acoustic impedance. The second one allowed us to monitor the speed of sound during the evolution of the compression test. This approach could be a potential tool to study the changes in hydrogels mass density and bulk compressibility.

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Inverse scattering for geophysical problems. III. On the velocity-in version problems of acoustics

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1985.0052 ◽

1985 ◽

Vol 399 (1816) ◽

pp. 153-166 ◽

Cited By ~ 8

Keyword(s):

Speed Of Sound ◽

Three Dimensional ◽

Acoustic Medium ◽

Inversion Problem ◽

Dimensional Problem ◽

Velocity Inversion ◽

One Dimensional ◽

Time Harmonic ◽

Acoustic Media ◽

Unknown Region

A bounded inhomogeneity D is immersed in an acoustic medium; the speed of sound is a function of position in D , and is constant outside. A time-harmonic source is placed at a point y and the pressure at a point x is measured. Given such measurements at all for all x ∈ P , for all y ∈ P where P is a plane that does not intersect D , can the speed of sound (in the unknown region D ) be recovered? This is a velocity-inversion problem. The three-dimensional problem has been solved analytically by Ramm ( Phys. Lett . 99A, 258-260 (1983)). In the present paper, analogous one-dimensional and two-dimensional problems are solved, as well as the problem where the plane P is the interface between two different acoustic media.

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