Search

Three-dimensional solid modeling of an OBS anti-trawl sinking coupling frame was carried out using the ANSYS, and modal simulation analysis of the overall structure of the anti-trawl sinking coupling frame was made through the ANSYS Workbench. The natural frequencies and mode shape contour diagrams of the first six modes were extracted. The displacement response spectrum was analyzed, and the equivalent stress and directional displacement contour diagrams were obtained. Simulation results show that the natural frequency of the anti-trawl sinking coupling frame evades the working frequency band of the OBS, which verifies the effectiveness of the anti-trawl structure design.

Natural rubber (NR) has poor mechanical properties, which limits its practical application. Filler blending is a simple method that improves the inherent properties of natural rubber and expand its applicability. Using the mechanical mixing process, the effects of graphene oxide (GO) and redox graphene (rGO) on the physical properties, electrical conductivity, thermal conductivity, and air permeability of styrene-butadiene rubber (SSBR)/NR composites were studied. The results show that rGO exhibits efficient filler properties in various aspects, for example, the optimal filling amount of rGO and GO was 1.5 phr. In addition, rGO filled SSBR/NR composites showed satisfactory filler dispersibility. Notably, the better dispersibility of rGO was because of fewer hydrophilic functional groups on the surface which were difficult to agglomerate. The increase of rGO and GO content increased the maximum torque (MH) and minimum torque (ML) of the composite material, and decreases tc90 and tc10. The Payne effect of GO/SSBR/NR composites is more obvious than that of rGO/SSBR/NR composites. In addition, we found that the content of rGO (GO) reached saturation at 2phr. Notably, rGO and GO improved the properties of rGO filled SSBR/NR composites such as the tensile strength of rGO/SSBR/NR composites to 23.9 MPa. This shows the potential application of SSBR/NR composites in wearable electronic devices.

According to the requirements of pressure resistance and sealing performance detection of deep-sea instruments and equipment under full sea pressure, a 120MPa deep-sea test chamber for ultra-high pressure environment simulation is designed in this paper. The structural dimensions of the test chamber were designed and calculated, including the cabin wall thickness, the cabin bottom head thickness, the sealing top cover, and the locking nut. The strength of the cylinder structure and the sealing cover of the test chamber were verified and analyzed through finite element analysis, which validates the reliability of the test chamber structure. The 120MPa deep-sea test chamber for ultra-high pressure environment simulation designed in this paper can provide important technical support for testing the pressure resistance and the sealing performance of deep-sea instruments and equipment.

A drogue is used to stabilise and straighten seismic arrays so that seismic waves can be well-received. To embed the effect of a cone-shaped drogue into the numerical modelling of the deep-towed seismic survey system, one surrogate model that maps the relationship between the hydrodynamic characteristics of the drogue and towing conditions was obtained based on data-driven simulations. The sample data were obtained by co-simulation of the commercial software RecurDyn and Particleworks, and the modelling parameters were verified by physical experiments. According to the Morison formula, the rotational angle, angular velocity, angular acceleration, towing speed, and towing acceleration of the drogue were selected as the design variables and drag forces and aligning torque were selected as the research objectives. The sample data of more than 8500 sets were obtained from virtual manoeuvres. Subsequently, both polynomial and neural network regression algorithms were used to study these data. Finally, analysis results show that the surrogate model obtained by machine learning has good performance in predicting research objectives. The results also reveal that the neural network regression algorithm is superior to the polynomial regression algorithm, its largest error of mean square is less than 0.8 (N2/N2 mm2), and its R-squared is close to 1.

Sparkers are the sound source widely used in marine seismic exploration to provide high-resolution vertical sections. Sparkers are relatively simple, inexpensive, high-frequency sources. In this study, the types of noise occurring in sparker source data were analyzed and attenuated by a processing technique. Frequency–wave number (f–k) filtering is used for attenuating the linear noise. Predictive deconvolution is used for attenuating the ghost waves and bubble effects. A complete processing workflow was designed for processing the data, and the migration section was obtained. The results show that the sparker source data are capable of achieving vertical sections with very high resolution. It is suggested as a necessary technique for high-accuracy gas hydrate exploration in the South China Sea.

The signal-to-noise ratio (SNR), vertical resolution and fidelity of marine seismic data are closely related to the characteristics of hydrophones, namely the sensitivity and the frequency band range. In this article, we analyzed and processed seismic data collected in 2017 from a towed marine streamer equipped with optical fiber cable and hydrophones. Results from a pre-stack time migration section revealed that the optical fiber seismic data yielded high SNR, vertical resolution and fidelity. For validation purpose, a comparison of these data with those acquired by classic piezoelectric hydrophones along a migration section located in a very close location was carried out. This comparison showed that the SNR, fidelity and vertical resolution from the two means of measurements were comparable.

The acoustic bottom backscattering strength was measured at the frequency range of 6–24 kHz on a typical sandy bottom in the South Yellow Sea by using omnidirectional sources and omnidirectional receiving hydrophones. In the experiment, by avoiding disturbances due to scattering off the sea surface and satisfying the far-field condition, we obtained values of acoustic bottom backscattering strength ranging from −41.1 to −24.4 dB within a grazing angle range of 18°–80°. In the effective range of grazing angles, the acoustic scattering strength generally increases with an increase in the grazing angles, but trends of the variation were distinct in different ranges of frequency, which reflect different scattering mechanisms. The frequency dependence of bottom backscattering strength is generally characterized by a positive correlation in the entire frequency range of 6–24 kHz at the grazing angles of 20°, 40° and 60° with the linear regression slopes of 0.222 9 dB/kHz, 0.513 0 dB/kHz and 0.174 6 dB/kHz, respectively. At the largest grazing angle of 80°, the acoustic backscattering strength exhibits no evident frequency dependence.

A method of obtaining bottom backscattering strength by employing an omnidirectional projector and omnidirectional hydrophone is proposed. The backscattering strength is extracted from monostatic backscattering data. The method was adopted in an experiment conducted in the South Yellow Sea of China. The seafloor surface was relatively smooth and covered by a small quantity of shell fragments, as observed through a digital camera system. Sampling data showed that the main component of the sediment at this experimental site was fine sand. In this paper, we detail the calculation method. Preliminary results of backscattering strength as a function of grazing angle (20°–70°) in the frequency range of 6–24 kHz are presented. The measured backscattering strength increased with the grazing angle and changed more rapidly at large grazing angles (60°–70°). A comparison of the data at different frequencies reveals that the measured backscattering strength substantially rises with the increase of acoustic frequency. A fitting curve of Lambert’s law against the measured data shows that the backscattering strength deviates from Lambert’s law at large grazing angles.

For shallow water environments, reverberation disturbance mainly derives from the bottom scattering. Although acoustic scattering strength is a feature of the bottom, scattering characteristics are different for various sediment types and areas. Backscattering strength at a grazing angel range of 20°–70° over a broad band of 6–24 kHz from a sand bottom in the area of the South Yellow Sea was measured, utilizing a pair of omnidirectional transmitter and hydrophone. The backscattering strength depends on the grazing angle with a positive gradient and performs a faster rate at grazing angle range of 60°–70°. For frequency dependence, the backscattering strength overall enhances with the frequency. Fitting curves of Lambert’s law to the measured data indicate that Lambert’s law departs from the data at grazing angle range of 60°–70°. Fitting curves of a scattering model on the basis of that of Jackson et al. against the data indicate that the seafloor roughness scattering is primary relative to the sediment volume scattering for frequency lower than 10 kHz and at grazing angle range of 60°–90° for high frequency.

Acoustic bottom scattering is the main source of reverberation background in target detection and recognition near the seafloor. Accurate estimation of bottom scattering strength is necessary for prediction of sonar performance in the presence of reverberation in shallow-water environments. A measurement of bottom backscattering strength at midfrequency in a shallow-water environment of the South Yellow Sea of China was carried out in April 2016, where the water depth was 39 m. The surface of the seafloor was relatively flat and covered by some shell fragments observed through a digital camera system. Core data showed that the main component of sediment at this experiment site was fine sand. The backscattering strength as a function of grazing angle (20°–70°) in the frequency range of 6–12 kHz was extracted from monostatic backscattering data, employing an omni-directional source and an omni-directional hydrophone. The measured backscattering strength increases with the increase of the grazing angle, and changes more rapidly at large grazing angles (60°–70°). Comparing the data at different frequencies, it is found that the measured backscattering strength slightly increases with the increase of the acoustic frequency. A fit of Lambert's law to the measured data shows that the backscattering strength deviates from the Lambert's law at large grazing angles. Finally, the fitted result of a scattering model to the measured data suggests that seafloor roughness scattering is larger than that from sediment volume heterogeneity in the measurement frequency band.

An inversion method using backscattering strength is used to obtain bottom parameters. A backscattering model based on the effective density fluid approximation was established as the forward model. The objective function used to scale the mismatch between the model predictions and the measured data (obtained by employing two monostatic transducers with narrow directivity) was established on the assumption that the data errors follow a Gaussian distribution. The maximum a posteriori estimations of inversion parameters were obtained by using a two-step hybrid optimization algorithm combining the differential evolution algorithm and the particle swarm optimization algorithm. The uncertainty and the correlation of inversion parameters were presented using marginal probability distributions and a covariance matrix through Bayesian inversion. Using this method, we can acquire not only geoacoustic parameters (including sound speed and attenuation) but also partial physical parameters of marine sediments and statistical character parameters of seafloor roughness and sediment heterogeneity. Finally, the efficiency of this inversion method was verified through comparison between inversion results and sampling data from sand sediment at the bottom of a water tank.

In this paper, a thermal insulation structure with silica aerogel felt as filler material was designed for the requirements of deep-sea fluid thermal insulation sampling technology for Jiaolong human occupied vehicle. Simulation analysis of thermal insulation performance was carried out and an experimental prototype was developed for the thermal insulation structure. Experimental study on thermal insulation performance was conducted with the variation characteristics of the operation environment for Jiaolong human occupied vehicle being taken into account. Results show that the silica aerogel felt with a thickness of 30 mm filled in the radial space between the inner and outer cylinders can achieve the expected thermal insulation effect during the diving-sampling-transferring process, with maximum temperature rise of 8.5 °C, and can meet the requirements of deep-sea fluid thermal insulation sampling technology.

In order to predict the bottom backscattering strength more accurately, the stratified structure of the seafloor is considered. The seafloor is viewed as an elastic half-space basement covered by a fluid sediment layer with finite thickness. On the basis of calculating acoustic field in the water, the sediment layer, and the basement, four kinds of scattering mechanisms are taken into account, including roughness scattering from the water-sediment interface, volume scattering from the sediment layer, roughness scattering from the sediment-basement interface, and volume scattering from the basement. Then a backscattering model for a stratified seafloor applying to low frequency (0.1–10 kHz) is established. The simulation results show that the roughness scattering from the sediment-basement interface and the volume scattering from the basement are more prominent at relative low frequency (below 1.0 kHz). While with the increase of the frequency, the contribution of them to total bottom scattering gradually becomes weak. And the results ultimately approach to the predictions of the high-frequency (10–100 kHz) bottom scattering model. When the sound speed and attenuation of the shear wave in the basement gradually decrease, the prediction of the model tends to that of the full fluid model, which validates the backscattering model for the stratified seafloor in another aspect.

The bottom is a significant boundary of the ocean, whose properties have always been concerned by oceanographers and geologists, and achieved considerable attention in civil and military applications. To realize estimation of bottom parameters efficiently and accurately, a remote sensing method of bottom parameters based on acoustic backscattering characteristics is proposed in this paper. The bottom backscattering strength was measured in a wide band (6–24 kHz) and grazing angle range (20°-70°), employing an omnidirectional projector and an omnidirectional hydrophone. The bottom parameters is efficiently obtained according to a wealth of information of backscattering strength at different frequencies and grazing angles, through fitting of a scattering model to the measured data, including geophysical parameters (geoacoustic parameters and physical parameters) of the marine sediment, and statistic character parameters of the seafloor roughness and the sediment heterogeneity. Finally, the estimate accuracy of some parameters is analyzed by comparing with direct measurement results. The method is hopeful to be a new approach of remote sensing of the bottom properties, which will improve the efficiency in conventional marine environment surveys.

In order to study the properties of sound-speed dispersion in a sandy sediment, the sound speed was measured both at high frequency (90–170 kHz) and low frequency (0.5–3 kHz) in laboratory environments. At high frequency, a sampling measurement was conducted with boiled and uncooked sand samples collected from the bottom of a large water tank. The sound speed was directly obtained through transmission measurement using single source and single hydrophone. At low frequency, an in situ measurement was conducted in the water tank, where the sandy sediment had been homogeneously paved at the bottom for a long time. The sound speed was indirectly inverted according to the traveling time of signals received by three buried hydrophones in the sandy sediment and the geometry in experiment. The results show that the mean sound speed is approximate 1710–1713 m/s with a weak positive gradient in the sand sample after being boiled (as a method to eliminate bubbles as much as possible) at high frequency, which agrees well with the predictions of Biot theory, the effective density fluid model (EDFM) and Buckingham’s theory. However, the sound speed in the uncooked sandy sediment obviously decreases (about 80%) both at high frequency and low frequency due to plenty of bubbles in existence. And the sound-speed dispersion performs a weak negative gradient at high frequency. Finally, a water-unsaturated Biot model is presented for trying to explain the decrease of sound speed in the sandy sediment with plenty of bubbles.

Before analyzing the distribution of submarine minerals, the positions of hydrophones installed in seismic array cables must be known. Generally, the hydrophone positions are computed through inversion calculation based on assumptions that conflict with the facts, and some assumed parameters are adjusted repeatedly to reduce the spatial aliasing in seismic reflection profiling. Furthermore, the inversion calculation cannot study the relations between the cable shape and working conditions. Dynamic analysis is proposed to predict the hydrophone positions and investigate these relations herein. The array cable is modeled by the lumped mass method with respect to the relative-velocity-element-frame. The results of the dynamic analysis and inversion calculation are verified using the recorded depth data. Although the cable shape by inversion calculation is the same as that by dynamic analysis, the cable depth by inversion calculation demonstrates an obvious shift in comparison with the depth data; meanwhile, the results obtained via dynamic analysis match well with the depth data. Additionally, three virtual maneuvers—diving and rising, depth change, and lateral current—are designed to study the relation between the cable shape and working conditions. The obtained results may help guide exploration and promote the development of exploration equipment.

This study sought to improve the interfacial bonding force between aramid fiber (AF) and a rubber matrix. We pretreated the aramid fiber with anhydrous calcium chloride (CaCl2) and sodium hydroxide (NaOH) solutions. We then performed a separate modification using two different methods, first, grafting the aramid fiber with silane coupling agent γ-Methacryloxypropyl trimethoxy silane (KH570) and secondly in situ formation of silica on the surface of aramid fiber. In addition, mechanical blending was adopted to prepare natural rubber/cis-1,4-polybutadiene rubber/aramid fiber (NR/BR/AF) composites. Finally, aramid fibers were characterized via Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and scanning electronic microscopy (SEM), then the mechanical properties of the corresponding composites analyzed. Results revealed that the synergistic action of anhydrous CaCl2 and NaOH solutions caused an increase in surface roughness and the contact area of the aramid fiber. The Sol-gel method allowed successful coating of the secondary modified aramid fiber surface with a layer of in situ-generated silica. Consequently, this improved surface reactivity of the fiber and the rubber matrix, thus promoting their combination. Moreover, we successfully grafted KH570 onto the surface of the aramid fiber through an oxygen-containing group on the surface of the pretreated aramid fiber. Tensile properties of AF composites exhibited a 31.9% increase after secondary modification with KH570 whereas their DIN abrasion performance increased by 16.2%. Notably, a significant improvement in interfacial adhesion was recorded in modified AF prepared NR/BR composites, which further improved the mechanical properties of NR/BR composites.

Seismic reflectivity inversion using basis pursuit de-noising algorithm (BPDN) produces sparse solutions by applying l1-norm regularization. Due to the presence of the regularization term, there is always a deviation between the solution obtained by BPDN and the true one. A debiasing step of “adding back the residual” was introduced into seismic reflectivity inversion using BPDN to reduce the deviation, so that the accuracy of seismic reflectivity inversion using BPDN is improved. The debiasing step is carried out using a moderately large trade-off factor by iteratively performing the fast iterative soft thresholding algorithm (FISTA) to solve the objective function of BPDN with the input updated by adding back the residual to the initial input. The solution obtained by using FISTA with incorporation of the debiasing step of “adding back the residual” is a better approximation of the true solution than the result obtained by using FISTA a single time. In addition, the debiasing step of “adding back the residual” is not limited to the number of nonzero components in the solution and can be used in a low signal-to-noise ratio circumstance. A multichannel inversion method was adopted to recover the acoustic impedance from the inverted reflection coefficient, and it gained good results both in numerical and field examples.

Acoustic bottom scattering is the main source of reverberation background in the shallow water environment. Backscattering characteristics of a sand and a mud bottom in the South Yellow Sea of China were compared. The backscattering strength in the grazing angel range of 20°–70° over a wide band (6–24 kHz) was measured employing an omnidirectional projector and an omnidirectional hydrophone. For the sand site, the backscattering strength enhances with the increase of grazing angle and has a high variation rate at large grazing angles (60°–70°). For the mud site, it decreases with the grazing angle in the range of 50°–70°. A comparison of the data at different frequencies reveals that the backscattering strength in general slightly rises at the sand site, while it somewhat declines at the mud site, with the increase of frequency. A fitting curve of Lambert's law against the backscattering strength indicates that the measured data depart from Lambert's law at large grazing angles. Fitted results of a scattering model based on that of Jackson et al. to the backscattering strength suggest that seafloor roughness scattering is the main scattering mechanism at low frequency (