Variation Of Sound Velocity Research Articles

Sound Velocity of Seafloor Sediment and its Response under Axial Stress-Strain

The results of axial stress-strain measurements made from short columnar samples of seafloor shallow surface sediment in the southern South China Sea area indicate that there are three kinds of variations in the longitudinal wave sound velocity, which are related to such characteristics as physical-mechanical properties, grain contact status and grain structure and microstructure of the submarine shallow surface sediment. This study may make theoretical contributions to further understanding the reliability of various submarine sediments in the southern South China Sea as bearing interfaces and such scientific objectives as phonotelemetering and remote sensing of the engineering mechanical properties of seafloor sediment.

Use of the transmission line matrix method for the sound propagation modeling in urban area

This paper deals with the sound propagation modeling in urban area. This problematic requires to take into account many phenomena that can have a substantial impact as well in semienclosed spaces as on long-range outdoor sound propagation, such as reflections and absorption on the frontages and on the ground, atmospheric attenuation, sound velocity variations related with wind and temperature vertical gradients, atmospheric turbulences. The numerical method used is the TLM (transmission line modeling), which has been originated in electromagnetism and adapted for acoustics applications. It consists in a physical rendering of the waves propagation based on the Huygens' principle. It is established on a spatiotemporal discretization of the domain using an iterative temporal process for sound pressure propagation, instead of the resolution of mathematical equations. The TLM model has then been developed in two and three dimensions allowing to combine all the phenomena affecting the sound propagation in urban area. Numerical simulations are given for canyon streets.

Remote measurements of sound velocity variations in bottom sediments based on acoustic profiling data

Remote measurements of sound velocity variations in bottom sediments based on acoustic profiling data

Correlated shear and bulk moduli to 1400 km beneath the Mediterranean region

We present a new model for the shear and compressional wave velocity structure of the Mediterranean plate boundary region. The model is obtained by a combined inversion of S and P data, where we solve in one single step for shear wave and bulk sound velocity variations. The ratios between the types of seismic velocities inferred from the combined inversion constrain the origin of heterogeneity. Our model is dominated by fast anomalies from subducted oceanic lithosphere. We found that only a slight amount of bulk sound velocity heterogeneity is required to explain the combined set of P and S data. Thus, compressional wave velocity anomalies are dominated by shear modulus heterogeneity and the ratio between bulk sound and shear wave velocity heterogeneity suggests a predominantly thermal origin.

The Effect of Internal Waves on the Sound Propagation in the Shelf Zone of the Sea of Japan in Different Seasons

Results of the observation of seasonal variations in the vertical distribution of water temperature in the shelf zone of the Sea of Japan are presented, and the effect of this variability on the parameters of internal waves and on sound propagation is studied. The measurements were carried out in different seasons using a vertical acoustical-hydrophysical measuring system. The propagation of sound (tone and noise signals) was studied on a 510-m-long track at a constant depth of 38 m. Using a self-contained resonance (320 Hz) transmitter of the electromagnetic type, which was bottom-moored at a depth of 65 m, a 10.6-km-long stationary acoustic track crossing the shelf was set up. During the in-sea experiments, the spatial characteristics of internal waves were measured along with the distributions of temperature, salinity, sound velocity, and sea level variations.

Low Temperature Acoustic Properties of Poly-Crystalline Aluminium

As in other structurally disordered solids, the low temperature acoustic properties of poly-crystalline aluminium are governed by atomic two-level tunneling systems. The particular temperature variation of sound velocity and internal friction depends on the dynamical behaviour of these tunneling systems, which is expected to be determined by interaction with thermal phonons and conduction electrons as in metallic glasses. In earlier measurements on aluminium-wires no significant difference was found whether the sample was superconducting or kept in the normal state by a sufficiently high magnetic field and the concluding claim was ‘absence of electron-assisted relaxation for tunneling systems in poly-crystalline metals’. In this report, vibrating reed measurements are presented of pure poly-crystalline Al with a special sample shape that reduces the influence of the clamping. We in fact find significant differences between the sample being normal conducting or superconducting. The overall behaviour indeed resembles very closely that of metallic glasses and clearly demonstrates that also in Al tunneling systems couple to conduction electrons as expected. As a quantitative result we may state that the density of states of tunneling systems in poly-crystalline Al is considerably smaller than in metallic glasses. PACS numbers: 61.43.-j, 62.65.+k, 63.50.+x

Sound velocity in shallow water bodies with gas-saturated water-bottom (ice) interfaces

Sound velocity variations in shallow water bodies with gas-saturated water-bottom (ice) interfaces are investigated. The effect of air inclusions in water and water-like bottoms (ice) on the velocity of longitudinal sound waves is qualitatively and quantitatively estimated. It is shown that changes in the sound velocity are mainly governed by the radial resonance, which at low frequencies depends on the quality factor of the zeroth mode of bubble oscillation. For real concentrations of bubbles, the velocity of longitudinal waves may become very low. This may lead to considerable distortions of boundary conditions at rough surfaces and, hence, to enhancement of scattering and absorption of sound waves and additional leakage of acoustic energy into the bottom (ice), as well as considerable changes in the sound velocity profile in surface layers with a change of sign of the velocity gradient from negative to positive, which results in the formation of a subsurface channel or an increase in its power. It is found that water-like bottoms (sediments) and ice (“liquid” ice), which are characterized by shear wave velocities of an order of 15 m/s or less, behave in the kilohertz range almost as a vacuum (Cl → 0) when the air content in them reaches several percent. As a result, the propagation of first normal modes in shallow water or in subsurface layers of arctic and oceanic waveguides noticeably changes.

Estimation and correction for the effect of sound velocity variation on GPS/Acoustic seafloor positioning: An experiment off Hawaii Island

A GPS/Acoustic experiment on the southeastern slope of Hawaii Island presented precise seafloor positioning in the condition of large water depth (2.5—4.5 km) and large velocity variations. We estimated sound velocity variations from acoustic ranging, and found that temperature variation can well explain the velocity variation. The effect of daily variation in the sound velocity amounted to +/- 0.7 m on acoustic ranging of 4—7 km with a fixed velocity structure. CTD data observed about every 3 hours could decrease the range residuals to +/- 0.4 m. These large residuals were fairly well canceled in the positioning of the array center of three acoustic transponders. The estimated precision of the array center positioning was about 3 cm in latitude and longitude.

Vertical Variations of Core Sound Velocity: Evidence of Paleooceanographic History Since the Pleistocene Epoch

The vertical variations in the borehole core sound velocity (Cp) of the submarine sediments are related to the events of marine transgression and regression in the geologic history. This article establishes the vertical variation of Cp curve for the borehole sound velocity in the northern South China Sea continental shelf and the East China Sea continental shelf, thus providing evidence for revealing at least (3) sedimentary cycle events of marine transgression and regression occurring in the west Pacific marginal sea since the Pleistocene Epoch. The sound velocity of marine sediments brought in the course of marine transgression is lower (1450-1510 m/s) while that of continental sediments formed in the course of marine regression is higher (1650-1720 m/s).

LOCALISING BITTERNS BOTAURUS STELLARIS WITH AN ARRAY OF NON-LINKED MICROPHONES

ABSTRACT Some animals emit sounds usable for acoustic monitoring of their population size. Such signals should be loud, omni-directional and easy to recognise and localise. Eurasian Bittern Botaurus stellaris mating calls (booms) are known to be loud and probably omni-directional but there is no data on acoustic localisation of this species. We made recordings of bittern booms with a 4-element GPS-linked microphone array, calibrated for absolute sound pressure level measurements. Receiver spacing was 65 to 294 m. The source level was 101 ± 3 dB re 20 μPa @ 1 m. The source level did not vary more than 7 dB for the same boom recorded at two different locations, with angular separations of 3°-27° as seen from the source. The geometric transmission loss was close to spherical, and the excess attenuation was much smaller than what was expected from the prevailing temperature and humidity conditions. The prevailing wind conditions caused sound velocity variations of up to 3%. The source location error was 104 ± 113 m (mean ± 1 s.d.). The prevalence of large location errors was probably caused by problems of discerning the direct path from multipath arrivals of the signal at the receivers and by sound velocity variations.

P3-D-58 Feasibility study for measuring sound velocity variation along the wave path in a plate

P3-D-58 Feasibility study for measuring sound velocity variation along the wave path in a plate

Tunneling state anisotropy in a single grain decagonal quasicrystal.

We present low-temperature measurements, between 20 mK and 20 K, of the sound velocity variations in a single grain of the decagonal quasicrystal Al-Ni-Co. We have used acoustic shear waves of frequency 70 MHz propagating in the quasicrystalline planes with two different polarizations: parallel and perpendicular to the quasicrystalline planes. Our results show the presence of tunneling states (TSs) with a strong difference of the phonon-TS coupling for the two polarizations, which reveals a strong anisotropy of distribution of the orientations of the TSs in the sample. This result gives direct evidence that TSs are generated by the quasicrystalline structure itself.

Long-term stability of the sound field structure in the central part of the eastern Atlantic

Results of studying the angular and energy structures of the sound field formed in the first convergence zone as a result of the transmission of a continuous pseudonoise signal in the frequency range 0.8–1.5 kHz are presented for the case of the corresponding points lying in the upper ocean layer at depths between 150 and 500 m. The sound field characteristics were studied with the use of omnidirectional and narrow-beam (∼2°) reception in the vertical plane. The variability of the basic experimental parameters of the field structure is analyzed using the data of three experiments carried out in the eastern part of the Atlantic Ocean, near the Canary Islands, over a period of 11 years. The experimental results are compared with ray calculations. It is shown that, in the region under investigation, the experimental characteristics of the field structure are relatively stable and the extent to which they agree with the calculated parameters is also stable. In addition, some data are presented to illustrate the effect of a small lens of Mediterranean water, which manifests itself in sound velocity variations at the channel axis, on certain field characteristics.

Sound velocity variations and melting of vanadium under shockcompression

The sound velocities of vanadium at shock pressure ranging from 154to 250 GPa were determined using transparent-window optical analysertechniques. A discontinuity in sound velocities at about 225 GPa may mark thepartial melting under shock compression. The comparison between the measuredsound velocity data sets above ~225 GPa and calculated values yieldsγ0≈2.0 and the empirical expression γρ = γ0ρ0is basically tenable. Additionally, shock temperatures along the principalHugoniot of vanadium were also determined from interfacial radiationintensities according to Grover's ideal interface model. Thus the temperatureat this solid-liquid phase transition was constrained to be round about7800(±800) K on the basis of the measured Hugoniot temperatures, meltingtemperatures, and high-pressure sound velocity variations with pressure.

Non‐adiabaticity in mantle convection

Seismic observations indicate that Earth's lower mantle is homogeneous as revealed by smooth depth variations of the bulk sound velocity and Bullen's inhomogeneity parameter η being close to one. Here we show with 3D spherical convection simulations that it should also be non‐adiabatic because a significant proportion of mantle heat sources is internal. The computer simulations predict non‐adiabaticity of 100–300 degrees for the lower mantle geotherm, with η ∼ 1.01 implying that the temperature drop across the Core Mantle Boundary exceeds 1000 degrees.

Acoustic properties of amorphous PdSiCu at very low temperatures

We have studied in detail the temperature and strain dependence of the acoustic properties of the metallic glass PdSiCu in the temperature range 0.2 mK ⩽T⩽ 200 mK with the vibrating reed technique at 980 Hz. At very low temperatures the sound velocity variation Δ v/ v deviates from the expected logarithmic dependence with increasing acoustic intensity. Strikingly, the internal friction Q −1 shows also a logarithmic decrease with decreasing temperature, instead of the plateau predicted in the kHz range by the standard tunneling model. We show that the extrapolated data to zero strain unveil the behaviour expected within the tunneling model.

Positioning accuracy of a large-aperture hydrophone array for sperm whale research

Source positioning accuracy of a large-aperture (1 km) hydrophone array was investigated, using 2-D and 3-D algorithms. The array was used for positioning and SL determination of sperm whales off the coast of Northern Norway during the summers of 1997 and 1998 (see Mo/hl, this volume). Positioning accuracy is dependent on mainly four factors: (1) positioning accuracy of the hydrophones, (2) variation in sound velocity of the medium, (3) inaccuracies in the measurements of the time-of-arrival differences, and (4) choice of algorithm (errors associated with geometric over-simplification). Errors introduced by the factors (1) and (3) had small effects compared with errors introduced by the factors (2) and (4). The total estimated error varied considerably in different areas covered by the array and for different array configurations. Sound velocity showed only modest variation with depth, except for a −0.2-m/s per meter gradient in the 0–100-m depth interval caused by summer heating of the surface water. For a sound source close to the surface, this sound velocity gradient causes a shadow zone starting some hundred meters from the source. Such a shadow zone may lead to underestimates of source level estimates from 2-D algorithms. [Work supported by the Danish National Research Foundation.]

ULTRASONIC METHODS TO DETECT AND EVALUATE DAMAGE IN STEEL

Porosity, microcracks, or secondary phase inclusions alter the sound velocities of materials, Ultrasonic scattering at grain and phase boundaries in polycrystalline, multi-phase, or porous media causes attenuation of sound waves and dispersive sound velocities. These effects and also the amplitudes of the scattered waves can be exploited for materials characterization if their dependence on the structure properties is known quantitatively. In this paper the usefulness of sound velocity, attenuation, and backscattering measurements to detect and value damage in steel e.g caused by hydrogen attack is discussed. Numerical evaluations of theoretical results and experimental investigations are presented. It turns out that in most cases velocity measurements do not yield sufficient quantitative information about damage because the variations in sound velocity caused by slight differences of the undamaged material are often larger than those caused by damage. Sound attenuation and back scattering amplitude measurements are more appropriate to estimate damage in steel.

Viscoelastic behavior of antibody films on a shear horizontal acoustic surface wave sensor.

To study the viscoelastic behavior of antibody films on a surface acoustic wave device, we have measured the influence of multiple layers of antibodies onto the propagation of the wave. Attenuation and sound velocity variation caused by up to 20 layers have been measured. The results can be interpreted with the propagation of a viscously damped Love wave in a film with an extremely low velocity of sound. From our results, we conclude that, for the one- or two-layer films normally used in acoustic wave immunosensing, a pure mass effect is dominant. For thick films, a saturation of the sensor response is observed.

Dynamic control of elasticity by means of ultrasound excitation in antiferromagnets

Sound velocity control by resonance ultrasonic oscillations in a magnetoordered medium is demonstrated experimentally on a sample of α-Fe 2O 3 single crystal. The phenomenon is caused by giant nonlinearity introduced by the crystal magnetic subsystem into the elastic one. The sensitivity of the dynamic elasticity control obtained in the experiment is ( Δν/ν)/a 2 p =10 −5 ppm −2 , where Δ ν is the variation of sound velocity under an ultrasonic deformation of the amplitude a p. From another side, the acoustically induced static deformation caused by the magnetoelastic nonlinearity is estimated, for the same experimental conditions, as 0.64 ppm when an alternative deformation of amplitude a p=20 ppm is applied. As it is shown both values are coupled in agreement with the theory.