Numerical investigation of geometrical parameters on the hydrodynamic noise characteristics of submerged bodies and comparisons with experiments

The effects of the geometrical parameters on the hydroacoustic characteristics of the flow over rectangular, square and circular cylinders are investigated by numerical analyses and experiments. The numerical simulations are carried out by using a hybrid method which combines RANS with FWH equation. In order to validate the numerical results, the hydroacoustic measurements are also performed for the circular cylinders. The circular cylinders with diameters of 9.5, 19.0, 38.0 and 65.0 mm and aspect ratios of 2.5, 5.0 and 10.0 are employed for the hydroacoustic measurements and analyses. The rectangular cylinders with side ratios of 0.3, 0.6, 1.8 and 3.0, and also square cylinder with the side ratio of 1.0 are considered in hydroacoustic analyses. The Reynolds numbers are in the range of 2.25 × 104 and 1.7 × 105. The hydroacoustic characteristics of the cylinders are obtained to be completely different due to the differences in the shear layer separation, reattachment mechanism and the intensity of disturbance. The shape of the noise spectrum significantly changes with the geometrical shapes of the cylinders. The spectrum becomes narrower by an increase in the side ratio. The main peak frequency reduces when the side ratio increases. The highest value of the maximum sound pressure level, SPLmax are observed for the square cylinder and the lowest value for the rectangular cylinder with the side ratio of 0.6. The peak spectrum becomes like a line spectrum as the cylinder diameter decreases. The main peak frequency decreases when the cylinder diameter increases but it is almost constant with the aspect ratio. At the constant Reynolds number, the broadband noise level and SPLmax decrease with an increase in the cylinder diameter and decrease in the aspect ratio. A good agreement between the numerical and experimental results are obtained.

DETERMINING OF OPERATIONAL PARAMETERS FOR TRAWL SYSTEM TAKING INTO ACCOUNT EXPERIMENTAL DATA ON SHAPE OF THE ROPE-NET SHELL OF MIDWATER TRAWLS

Calculating of horizontal opening for a trawl mouth using the mathematical model of midwater trawl system developed by V.I. Gabryuk gives the errors 25.4 and 32.9 %, on average, for the trawls RT 57/360 m and RT 80/396 m, respectively. The significant errors cause doubts about correctness of this model equations application for calculation of the catch zone that is necessary for assessment of abundance and biomass of marine biological resources. New empirical equations are proposed on the basis of experimental data on shape of the rope-net shell of a midwater trawl, which allow to calculate the horizontal opening for its certain sections. The errors of the horizontal opening calculation with these new equations are 13.7 and 6.1 %, on average, for the trawls RT 57/360 m and RT 80/396 m, respectively, that is satisfactory for using them for calculating operational parameters of a midwater trawl system. The operational parameters of the midwater trawls RT 57/360 m and RT 80/396 m are calculated using Baranov’s approach with these new empirical equations, and their good adequacy is shown in the experiment with hydroacoustic measurements of the trawls mouth horizontal opening and the distance between the trawl doors conducted aboard RV TINRO and RV Professor Kaganovsky in the Okhotsk Sea in 2012–2015.

Hydroacoustic measurements of the 2004 submarine eruption near Nightingale Island, Tristan da Cunha

<p>Little is known about active volcanism in the remote regions of the global ocean. Here, we resort to long‐range acoustic measurements to study the July/August 2004 eruption at Isolde, a submarine volcanic cone in the Tristan da Cunha archipelago, South Atlantic Ocean. Underwater sound phases associated with the event were recorded as far as Cape Leeuwin, Western Australia, where a bottom-moored hydrophone array is operated as part of the International Monitoring System (IMS). IMS hydrophone data in combination with local seismic observations suggest that the center of activity is located east of Nightingale Island, where a recent seafloor mapping campaign aboard R/V Maria S Merian (MSM20/2) has revealed a previously unknown, potentially newly formed stratocone. Transmission loss modeling via the parabolic equation approach indicates that low-frequency sound phases travel at shallow depths near and within the Antarctic Circumpolar Current, thereby avoiding bathymetric interference along the 10,265 km source-receiver path. Our study highlights the potential of the IMS network for the detection and study of future eruptions both at Isolde and elsewhere. Implications for test-ban treaty monitoring and volcano early warning will be discussed.</p>

Determination of Survey Boat “Heave” Motion with the Use of RTS Technique

The paper presents analysis of determination of vertical movement of the surveying boat called “heave” with the use of Robotized Total Station (RTS) technique. The classical geodetic Total Station was used for sub-centimeter calculation of water level changes during hydroacoustic measurements on the fragment of Vistula river behind the dam and hydropower in Włocławek in Poland. The power station work causes up to 1.7 m movement of vertical reference water surface in aspect of local bathymetric survey. The experimental, hydrographic surveys on the river were conducted where the water level was changing significantly over time depending on the operational schedule of the power plant. Verified hydrographic data had to be brought to the common water level. To determine the final water level, data on the height of the Robotized Total Station prism positioned on the boat during sounding was considered. The RTS technique with 0.02–0.05 m vertical accuracy proved to be very useful and essential in engineering inland bathymetric measurements.