Deep-water Experiments Research Articles

A novel full-process test bench for deep-sea in-situ power generation systems

A novel full-process test bench was developed to replace lengthy and costly deep-water experiments. This platform can accurately simulate the dynamic characteristics of hydrokinetic turbines and can be used to evaluate their power-supply capabilities under various conditions. The hydrokinetic turbine power model was established by obtaining discrete performance data through experimentally validated computational fluid dynamics simulations and building surrogate models using the response surface methodology. This approach offers higher accuracy and broader applicability than empirical models. Moreover, a stepper motor platform based on a speed control scheme is proposed for the first time that can achieve high-precision transient simulation with a simplified control mechanism. This platform was employed to assess the power supply capacity of two hydrokinetic turbines under constant and typical deep-sea flow speeds. The ductless Archimedes screw hydrokinetic turbine was found to be more suitable for the deep water application than the high-solidity horizontal axis turbine due to its high self-start capacity and power coefficient. Furthermore, a case study was conducted on the design of a deep-sea in-situ power generation system at Luzon Undercurrent. Results suggest that a ductless Archimedes screw hydrokinetic turbine with a 1000 mm radius can comfortably cater to the energy demands of miniature AUVs.

Development of a high-resolution deep-towed multi-channel seismic exploration system: Kuiyang ST2000

When the traditional sea surface towed multi-channel seismic technology is applied to the deep-water stratum exploration, the Fresnel radius of the target stratum is large due to the large-depth water bodies, greatly reducing the horizontal resolution. Hence, it is difficult to achieve high-resolution exploration with the traditional technology and cannot meet the requirements for high-precision exploration and orebody description of such deep-water seabed resources as natural gas hydrate (NGH). The near-seabed deep-towed seismic exploration technology was proposed to solve this problem. This paper introduces a set of high-resolution deep-towed seismic system being developed in China, Kuiyang ST2000. The remarkable difference between the equipment and foreign counterpart is that this equipment uses a deep-towed sparker instead of a resonator source. We systematically describes the system composition of the deep-towed system, and primarily discusses the technical design of the deep-towed sparker which can still have relatively large stratum penetration depth in deep-water and high-static-pressure environment. In addition, we also introduces the unique continuous acquisition technology possessed by the system. At present, the experiment of 2000 m deep-water depth has been carried out for this system, and the experimental and related data processing results show that this equipment has had fundamental functions. Several deep-water experiments will be carried out in the next step.

Prediction uncertainty of wind-generated noise spectra from wind speed.

The prediction of wind-generated noise spectral levels at one frequency is typically based on a linear regression function, which is defined over the logarithm of the 10-m wind speed. However, despite its widespread success, the linear regression model does not pay attention to its prediction uncertainty because it makes point predictions. The main reasons for the uncertainty in the predicted value of the wind-generated noise level are that it cannot be uniquely determined by 10-m wind speed and its measurements may be corrupted by other sources of ambient noise. To quantify the uncertainty in predictions in this scenario, a Bayesian treatment of linear regression models and its associated predictive distribution are applied, making distribution predictions instead of point predictions. Once the predictive distribution for one frequency has been fixed, its linear variants are used to obtain predictive distributions for other frequencies. The data for the ocean ambient noise and 10-m wind speed are collected from two deep-water experiments, conducted in the South China Sea, and reanalysis data sets of the European Centre For Medium-Range Weather Forecasts, respectively. Empirical expressions for the predictive distribution of noise spectra (0.5-10 kHz) at wind speeds from 3.3 to 14 m/s have been developed. The results indicate decreasing uncertainties with an increasing wind speed.

Mapping sea surface observations to spectra of underwater ambient noise through self-organizing map method.

This letter presents a model for mapping sea surface observations to the spectra of underwater ambient noise through the self-organizing map method (SOM). The data used to train and test the proposed model include observations of wind speed, atmospheric pressure, and significant wave height from public databases, as well as observations of ambient noise from two deep-water experiments. SOM extracts nonlinear relations from the data and is more suitable for the study of nonlinear dynamics in the ocean than conventional methods. Results indicate the proposed model is reliable with coefficients of determination above 0.9 and root-mean-square errors below 1 dB.

Comprehensive Detection of Gas Plumes from Multibeam Water Column Images with Minimisation of Noise Interferences.

Multibeam echosounder systems (MBES) can record backscatter strengths of gas plumes in the water column (WC) images that may be an indicator of possible occurrence of gas at certain depths. Manual or automatic detection is generally adopted in finding gas plumes, but frequently results in low efficiency and high false detection rates because of WC images that are polluted by noise. To improve the efficiency and reliability of the detection, a comprehensive detection method is proposed in this paper. In the proposed method, the characteristics of WC background noise are first analyzed and given. Then, the mean standard deviation threshold segmentations are respectively used for the denoising of time-angle and depth-angle images, an intersection operation is performed for the two segmented images to further weaken noise in the WC data, and the gas plumes in the WC data are detected from the intersection image by the morphological constraint. The proposed method was tested by conducting shallow-water and deepwater experiments. In these experiments, the detections were conducted automatically and higher correct detection rates than the traditional methods were achieved. The performance of the proposed method is analyzed and discussed.

Estimating sea-water volume attenuation coefficients from mid-frequency, deep-water experiments in the Atlantic and Pacific

A collection of mid-frequency deep-water experiments were performed off the U.S. Pacific coast and in the northeastern Atlantic using a short vertical array cut for 7.5 kHz. Previously presented analysis of a Pacific experiments have shown agreement between experimental estimates of attenuation coefficients to the decades old attenuation models. We present the comparison of experimental attenuation coefficient estimates from additional Pacific and Atlantic data and discuss the methodology for inverting for depth-dependent ocean properties using acoustic amplitude measurements. The data and methodology are also used to explore the feasibility of ocean acoustic attenuation tomography for determining the individual chemical attenuation coefficient terms strictly from in situ measurements.

A reformulation of the ΛΦ diagram for the prediction of ocean acoustic wave propagation regimes

The ΛΦ diagram was a tool introduced in the late 1970s to predict ocean acoustic fluctuation regimes termed unsaturated, partially saturated, and fully saturated, where internal wave sound-speed fluctuations play a dominant role. The ΛΦ parameters reflect, respectively, the strength of diffraction and the root mean square phase fluctuation along a ray path. New oceanographic knowledge of the small scale part of the internal wave spectrum, and high angle Fresnel zone formulations now allow a more stable and accurate calculation of these parameters. An empirical relation between the variance of log-intensity and ΛΦ provides a more accurate border between the unsaturated regime and stronger fluctuations. The new diagram is consistent with six short-range, deep-water experiments in the Pacific, Atlantic, and Arctic oceans with frequencies ranging from 75 to 16 000 Hz. The utility of the ΛΦ diagram is that it provides one of the few means to inter-compare experiments at different geographic locations, differen...

Mid-frequency attenuation estimates from deep-water experiments using eigenrays

A collection of deep-water experiments were recently performed using a short vertical array cut for 7.5 kHz and a source transmitting tonals as well as chirps. Eigenray arrivals out to the first convergence zone were identified through matching the processed data to ray-tracing models, using environmental parameters measured during the experiments. The ray path and transmission loss information were used to produce an ocean-average attenuation result, and compared to decades-old attenuation models. Attempts were made at producing a layered estimate of attenuation using the experimental-simulation ray-matching — a technique previously proposed for inverting for ocean acidity. We present our ocean-average mid-frequency attenuation estimates, and our initial results for a layered attenuation inversion.

About transformation of the deep-water methane bubbles into hydrate powder and hydrate foam

During the Russian Academy of Sciences “MIRI na Baikale, 2008–2010” expedition, deep-water experiments with the bubbles of methane seeping from the bottom at depths 405, 860 and 1400 meters were carried out. These depths correspond to gas hydrate stability zone. Bubbles were caught by the trap which was looked like an inverted glass. It was found that the behavior of bubbles in a trap depends on the depth. At depth of 405 meters formation of hydrates was not observed. Having got to a trap at the depth of 860 meters, bubbles became covered by solid hydrate envelope, kept the initial form, and after a time period collapsed in a number of hydrate fragments which showed all properties of a granular matter. No visible changes in the hydrate granular matter were observed in the course of lifting it to a depth of 380 meters. Shallower, the decomposition of the hydrate granular matter into methane gas was observed. In the experiments at depth of 1400 meters the caught bubbles, becoming covered by hydrate envelope formed solid hydrate foam in the trap. At lifting this foam structure was deformed slightly but simultaneously a free gas left the foam and filled the trap. The volume of free gas in the trap at lifting varied according to the Boyle-Mariotte law.

The first experience the transportation of deep-water methane hydrates in a container

Deep-water experiments on the transportation of collected samples of methane hydrates from a lake’s bottom to a support container were carried out as part of the MIRY na Baikale (2008–2009) expedition run by the Russian Academy of Sciences. High pressures and low temperatures are necessary for gas hydrates stability. As a sample of the hydrate is lifted to the water’s surface, it intensively decomposes into water and methane gas. To reduce the decomposition, we used a container in which the hydrate’s sample occurs in a gas medium rather than in water, which results in a substantial reduction in the rate of the heat exchange. At that, the gas for the container’s filling was supplied by the hydrate itself due to its partial decomposition. To estimate the method’s efficiency, we observed the hydrate’s decomposition during lifting from a depth of 1400 m using different transportation techniques such as gas- or water-filled containers or fixing the sample in the manipulator’s arm of the submersible. The sample in the gaseous medium was the only one that was safely delivered on board the support container, while the two others completely decomposed during the transportation. It is remarkable that all the samples started to decompose simultaneously at a depth of 380 m but their decomposition occurred at different rates.

Breakup of deep-water methane bubbles

During the Russian Academy of Sciences “MIRI na Baikale. 2008–2009” expedition, deep-water experiments on methane bubbles emerging from the lake bottom at depth of 1400 and 860 meters were carried out. Bubbles escaping the seabed were caught by a trap, which was an inverted glass. Entering in the trap, bubbles became covered by a gas hydrate envelope and then after a time period collapsed into a number of gas hydrate solid fragments. Due to positive buoyancy, fragments remained in the top part of a trap, exhibiting properties of a powder. The glass’s bottom was replaced with a 1 mm mesh grid, allowing the finest gas hydrate particles to sift through the grid, rising upwards. It is proposed that bubble collapse into fragments is related to the pressure drop in the bubble in the course of formation of the gas hydrate envelope. No visible changes in the gas hydrate powder were observed in the course of lifting it to a depth of 380 meters. Shallower than 380 meters, i.e., outside the zone of gas hydrate stability, decomposition of the gas hydrate powder into methane gas was observed.

Experiments and Numerics of Bichromatic Wave Groups

This paper reports on extensive experiments on nonlinear wave groups that evolve in a hydrodynamic laboratory over long distances (200 m) from the generation of simple bichromatic waves. The deepwater experiments show large deformations of the wave group, with large increase of wave heights, depending on the value for the quotient of wave amplitude and frequency difference. The experimental results show little dissipation and reflections are virtually absent. A very efficient and accurate numerical code based on the full nonlinear surface wave equations, which has been developed for this purpose, reconstructs the experiments and enables one to investigate the evolution over much longer distances (reported here until 1,200 m) than in the laboratory.

Acoustic mapping of the ocean bottom and requirements of the initial data

The amount and degree of detail of the initial information are analyzed as applied to the new method of ocean bottom mapping on the basis of the fine structure of the bottom-reflected sound field at normal incidence. For the mapping data obtained with a planar multielement receiving array, the distortions caused by insufficiently detailed information derived from discrete measurements of the bottom-reflected amplitude are considered. The relations between the number of receivers, the receiver spacing, the array aperture, and the horizontal correlation length of the sound field are determined. The problem is solved by computer simulation with the use of generalized quantitative data obtained in deep-water ocean experiments.