Seawater Depth Research Articles

An Envelope-to-Cycle Difference Compensation Method for eLoran Signals in Seawater Based on a Variable Step Size Least Mean Square Algorithm

The dispersion effect of seawater can cause the envelop distortion of underwater eLoran signals, which causes the envelope-to-cycle difference (ECD) to exceed the standard range. Furthermore, it results in incorrect cycle identification and significant positioning errors. However, few studies have focused on the distortion caused by the dispersion effect. In this study, we propose an accurate underwater eLoran ECD compensation method based on a variable step size least mean square (VSS-LMS) algorithm. First, a systematic modeling approach was employed to investigate the impact of dispersion effects on Loran signals. Second, the VSS-LMS algorithm was introduced to update the filter weight vector in response to discrepancies in the input signal. Finally, the input signal was subjected to an adaptive transversal filtering process, resulting in an output signal that adhered to the specifications of the ECD standard. The efficacy and superiority of the proposed algorithm were demonstrated by experimentation and simulation. When the depth of seawater exceeds 2 m, the ECD value of the original eLoran signal exceeds the standard range, precluding the possibility of cycle identification. However, when the depth of seawater reaches 4 m, the ECD of the signal compensated by the proposed algorithm adaptively compensates for the normal range, thereby enabling the accurate recognition of cycles.

Multi-proxy reconstructions of paleotemperature in the southern South China Sea since the last deglaciation

The accuracy of paleothermometers is a prerequisite for understanding the past sea surface temperature (SST) changes in the tropical seas. Here, we analyzed the SST estimates reconstructed by four lipid proxies with common linear and newly advanced models in parallel in a sediment core collected from the southern South China Sea (SCS). After excluding the impact of terrestrial input, all of the four proxies-inferred SSTs displayed a gradually warming pattern since 18.3 ka. Our long-chain alkenones-derived annual SST at seawater depth of 0–30 m (SST 0–30 m) record closely matched the regional synthetic SST record from the entire southern SCS, corresponding to high-latitude climate events during the deglaciation. The temperatures reconstructed by long-chain diols (LCDs) showed an upper limit of 27 °C, and we thus proposed that they reflected the optimal survival temperature for organisms producing LCDs when SST was higher than 27 °C. Isoprenoid and hydroxy glycerol dialkyl glycerol tetraethers (iGDGTs and OH-GDGTs)-derived temperatures likely reflected the subsurface temperature (subT) at seawater depth of 30–125 m and SST towards the warm season in the tropical sea, respectively.

Adaptive TLS-OQSM technology of a wireless optical MIMO communication system over an oceanic vertical turbulence channel.

In this paper, we construct a wireless optical MIMO system based on the ocean power spectrum in the vertical channels, which is suitable for any sea depth under the combined effects of ocean turbulence and pointing errors. Thereby, an adaptive transmit laser selection-optical quadrature spatial modulation (TLS-OQSM) technology is proposed to improve its effectiveness and reliability of communication. The adaptive TLS-OQSM employs the channel adaptive bit mapping (CABM) to grouping and spatial mapping for laser diode (LD) indices based on limited feedback bits for the adaptive signal modulation and power allocation (PA). Simulation results show that the average BER of the system can be efficiently reduced by applying the adaptive TLS-OQSM scheme at different depths in seawater where optical transceivers are deployed, with different pointing errors and different predefined spectral efficiencies.

Spatial Distribution of Physical and Chemical Properties of Deep Sea Water in Xisha, South China Sea

Deep sea water (DSW) is a globally utilized source of renewable energy and other resources. To understand the characteristics of DSW resources in the South China Sea, in July 2022, the Guangzhou Marine Geological Survey (GMGS) investigated temperature, salinity, pH, dissolved oxygen (DO), inorganic salts (DIN, PO43−-P, and SiO3-Si), heavy metals (Hg, Pb, As, and Cd), trace elements (Cu, Zn, Fe, Mn, Ni, Se, and Mo), and other related indicators. The results of this investigation elucidate the horizontal and vertical changes in the physical and chemical properties of deep sea water in the Xisha Sea. The surface seawater quality in Xisha was found to be excellent and to meet first-class seawater survey standards. However, the concentrations of various nutrient salts in the surface layer were relatively low. As the seawater depth increased, different trace elements and heavy metals exhibited variations, and the concentrations of various nutrients also gradually increased.

Effect of hyperbaric exposure on cognitive performance: an investigation conducting numerical Stroop tasks during a simulated 440 m sea water saturation diving

BackgroundSaturation diving (SD) is useful and safe in deep diving for long durations. Japan Maritime Self-Defense Force (JMSDF) Undersea Medical Center (UMC) maintained safely deep 45 ATA SDHowever, cognitive performance was reportedly impaired by hyperbaric exposure in over 31 atmosphere absolute (ATA) SD. This study investigated the effects of hyperbaric exposure during 45 ATA deep SD on expert divers’ cognitive function using Stroop tasks, a useful method to examine cognitive function, especially in narrow spaces such as SD chambers.MethodsTwo numerical Stroop tasks were utilized to create two magnitude comparisons of a pair of single-digit numerical and physical tasks. Both numerical Stroop tasks were examined twice, at 1 and 45 ATAs, during a simulated 440 m of sea water depth for SD. Participants were 18 male expert JMSDF SD divers (age 36.58 ± 4.89 years).ResultsIn the numerical task, reaction time (RT) was significantly delayed at 45 ATA compared with 1 ATA in the incongruent condition. In the physical task, RT at 45 ATA was significantly delayed under all the conditions (congruent, incongruent, and neutral). The correct rates (CR) in both numerical Stroop tasks significantly decreased at 45 ATA compared with 1 ATA in the incongruent condition.ConclusionsOur findings suggest that divers’ cognition is impaired during 45 ATA deep SD. These results emphasize the importance of monitoring cognition in deep sea SD and highlight the need to educate and train for SD. Further examination combining Stroop tasks with other analyses such as event-related potential (ERP) is expected.

Diversity and structure of pelagic microbial community in Kuroshio Extension

Kuroshio Extension (KE) is the most active region of oceanic change in the North Pacific Ocean, which provides an essential place for the survival of marine microorganisms. However, Vertical changes in microbial communities in the Kuroshio Extension and the mechanisms by which environmental factors drive vertical changes in community structure remain unclear. In this work, microbial diversity, abundance, and community structure of 12 water layers (from surface to bottom) at five stations were uncovered by 16S rRNA gene high–throughput sequencing. Microbial diversity and richness decreased with increasing seawater depth. Microorganisms in the euphotic zone can be well separated from other zones based on NMDS analysis. Proteobacteria (65.20%), Bacteroidota (8.48%), Actinobacteriota (5.76%), and Crenarchaeota (4.49%) accounted for a relatively large proportion and their distribution is similar in four zones. Most of microorganisms were significantly (Spearman test, p < 0.05) correlated with salinity, density, pressure, and temperature. This work enhances our understanding of vertical microbial diversity and provides insights into the pelagic microbial community structure.

Distribution and bioaccumulation of per- and polyfluoroalkyl substances (PFASs) in the Kuroshio Extension region of Northwest Pacific Ocean

Per- and polyfluoroalkyl substances (PFASs) are prevalently present in oceans, posing potential health risks to organisms and humans. However, information of PFAS distribution in remote open oceans is limited. In the Kuroshio Extension region of Northwest Pacific Ocean (6 stations), samples of 84 seawater (0–5800 m), 9 sediments, and 9 organisms were taken, and 25, 10, and 15 out of 29 PFASs were identified, respectively, with perfluorooctanoic acid (PFOA) and perfluorooctane sulfonates (PFOS) as the most dominant PFASs. In seawater, ΣPFASs concentration decreased from the Kuroshio region (4.47 ng/L) to the Oyashio region (3.15 ng/L), and decreased with increasing seawater depth under the function of biological and physical pumps. Additionally, 12 precursors and emerging PFASs, including perfluorooctane sulfonamide (FOSA, 0.20 ng/L), were detected. In sediment, PFASs (5.92–12.97 pg/g) were identified at depths exceeding 5000 m, including 3 precursors (e.g., FOSA, 0.82 pg/g). ΣPFASs contents were 27.12, 31.47 and 36.97 ng/g (dry weight) in brown algae (Phaeophyceae), barnacles (Balanus), and lanternfish (Myctophiformes), respectively, in which two precursors (e.g., FOSA, 0.09–0.12 ng/g) were also identified. A correlation with the trophic position was found for PFOA bioaccumulation. These findings provide useful information on PFAS distribution in the global open ocean environments.

An adaptive stratification algorithm based on gradient fitting deviation and its application to acoustic ray-tracing algorithm

Accurate underwater positioning is a challenging task for complex marine environments where the study of sound velocity profiles (SVPs) is essential. To overcome the problem that the original SVP reduces the computational efficiency of the ray-tracing algorithm due to great capacity of data, this paper simplifies the SVP. The nature of the SVP and its influence on accurate underwater positioning are discussed. An adaptive stratification algorithm applicable to the ray-tracing algorithm is proposed, based on the gradient fitting deviation and characterized by the fitting treatment of the sound velocity gradient by the Fourier method. Measured SVP data and acoustic positioning data were used to validate this algorithm in the context of acoustic ray-tracing algorithm, to analyze and compare the simplification rates before and after SVP simplification, and the effect on the positioning accuracy. The experimental results in the shallow sea (water depth of 60 m) show that the simplification rate of the SVP is more than 95.56%, and the RMS of the deviation of the ray-tracing algorithm is better than 0.0112 m when determining the optimal number of unfolding levels and threshold; the experimental results in the deep sea (water depth of 1900 m) show that the simplification rate of the SVP is more than 99%, and the RMS of the deviation of the ray-tracing algorithm is better than 0.5 m. This indicates that, the algorithm can reconstruct the original SVP well and implement the automatic hierarchical simplification of the SVP while ensuring the positioning accuracy.

Thermo-economic examination of ocean heat-assisted pumped thermal energy storage system using transcritical CO2 cycles

In response to the challenges posed by the growth of renewable energy electricity to the security of the power grid, energy storage technology has rapidly developed in recent years. Pumped thermal energy has been recognized as an attractive massive energy storage technology with the superiority being independent of site. An ocean heat-assisted pumped thermal energy storage system using transcritical CO2 cycles is proposed in this study. State-of-the-art thermo-economic models are developed and described to simulate the system processes and conduct cost estimates. The originality of this system lies in the ability to effectively improve its efficiency by configuring seawater at different depths at the low temperature end of the system. Research has found that, if the seawater used in the charge process always comes from the surface of the ocean, the system efficiencies are 48.1 %, 61.3 % and 66.4 % respectively when the depth of seawater during the discharge process are 50 m, 100 m and 1000 m. When the seawater employed in the entire system comes from 1000 m underwater, the efficiency of the system is only 53.5 %. In addition, for the 50 MW/10 h system, the minimum value of levelized cost of storage is 0.143 $/kWh. The uncertainty analysis of cost for the proposed system is carried out using the Monte Carlo method. Results show that with the charge/discharge duration ratio rising from 4 h/10 h to 10 h/4h, the total capital cost falls from 245 ± 76 M$ to 102 ± 34 M$ and the levelized cost of storage reaches the minimum value when this ratio is 1. The larger the energy storage capacity, the lower the levelized cost of storage. In summary, the system has shown satisfactory results in both thermodynamics and economic performance, and further research is worthwhile in the future.

Plane SV-waves scattering by seawater convex surface topography and underlying lined tunnel in a saturated half-space

Analytical solutions of boundary-valued problems for aboveground topography and underground buried structures, especially for sites with overlying seawater, have always been challenging. Based on the region decomposition technique (RDT) and Hankel integral transform method (HITM), SV-waves scattering by the convex circular topography with seawater and underlying tunnel in a saturated half-space is solved. The primary problem is tackling additional scattered waves introduced by the water–soil interface and convex topography, while ensuring boundary conditions are all met. To this end, scattering wave potential functions in cylindrical coordinates are first transformed into the Hankel integral form in Cartesian coordinates. This greatly facilitates the straightforward application of free boundary conditions at the soil–seawater flat interface, rather than making a large circular arc approximate assumption, which, in turn, avoids the resultant accumulating errors. Secondly, scattering problem to be solved is mathematically and analytically formulated as solving a 5 × 5 linear equation system comprised of wave functions inside the convex topography and lining tunnel while satisfying all physical continuous boundary conditions. This is the main innovation and resulting consequence from the theoretical derivation process. Finally, validation of numerical examples between this paper, existing studies and theoretical analysis further demonstrates the reliability and general adaptability of solutions. Parametric studies of the incident SV waves are conducted to investigate the spatially varying seismic response. The effects of SV-waves incident angles and frequencies, tunnel burial depth, tunnel lining thickness, saturated soil porosity, and seawater depth are investigated and analyzed in detail. This study provides a feasible scheme of investigating the dynamic response of complex submarine sites, which is of great significance for both theoretical value and engineering purposes.

Multi-segmented fifth-order polynomial–shaped shells under hydrostatic pressure

The design and construction of submerged complex shells for new applications in offshore structures are increasingly popular. Therefore, the purpose of this study is to present the analytical model and Lagrange multipliers associated with the constraint equation for large displacement analysis of a fifth-order polynomial–shaped shell under hydrostatic pressure for the first time. The shell geometry can be computed using differential geometry with a fifth-order polynomial. The energy functional of the fifth-order polynomial–shaped shell is derived based on the principle of virtual work and written in the appropriate form. The nonlinear static responses of the fifth-order polynomial–shaped shell under hydrostatic pressure can be calculated using the nonlinear finite element method via the fifth-order polynomial shape function. This study develops the model using one-dimensional beam elements divided along the shell radius. To avoid the slope of a meridian curve at the equatorial plane approaching infinity, the shell is divided into two regions defined by different surface parameters. At the junction of two adjacent regions, the continuity requirements are established as the constraint conditions using Lagrange multipliers. The numerical results from the proposed methods are demonstrated and discussed, along with the effects of varied seawater depth, thickness, and elastic modulus on the deformed configuration and principal curvature at the deformed state. The results show that the nonlinear displacement is higher than the linear one in the case of the hydrostatic pressure, whereas the case of the internal pressure has an opposite result. For principal curvatures at the apex, the principal curvatures increase as the seawater depth increases, whereas the principal curvatures decrease when the thickness and elastic modulus increase.

Mineralogy, ore genesis and zircon U[sbnd]Pb age characteristics of the Cerattepe Cu[sbnd]Au (±Zn) deposit (Artvin, NE Turkey)

The Cerattepe deposit is associated with bimodal felsic volcanics of the Kızılkaya Formation, which hosts the majority of VMS deposits in the Eastern Pontide Orogenic Belt. Pyrite, chalcopyrite, sphalerite, and bornite are the main sulfides, with minor galena, fahlores, marcasite, idaite, covellite, and chalcocite. Barite and quartz are the primary gangue minerals, with minor calcite and gypsum. Hematite, limonite, goethite, jarosite, and lepidocrocite are common oxide minerals. The sulfide ore is shaped by rapid cooling, zone refinement, replacement, and local deformation processes, which affect textural relationships and mineral paragenesis.Fluid inclusion studies have shown that the early stages of the ore were formed by boiling at temperatures of 250–355 °C and approximately 1900 m depth of sea water, while the later stages developed at temperatures as low as 148 °C. The Te temperatures imply that NaCl-dominated solutions with partial mixing of CaCl2 may be responsible for mineralization. The CO2 phase present in the early stages of the ore may have been derived from the interaction of hydrothermal solutions with the underlying carbonate rocks. Salinity values of 0.2–7.62 wt% NaCl equ., compatible with the average salinity of Kuroko type VMS deposits, indicate that the Cerattepe deposit was formed in a marine environment.The Co/Ni of pyrites (1–12, with an average of ∽2) and Zn/Cd of sphalerites (127–383) indicate an acidic source and magmatic source of acidic-andesitic for the ore-forming fluids, respectively. The δ34S values −4.4 ‰ – +9.63 ‰ indicate a magmatic sulfur source, with partial sulfate-reduced sulfur. A magmatic-related source is also inferred from δ18O values (+8.5 and + 9.5 ‰.) for the Cerattepe deposit. The leaching, zone refinement, and replacement processes, followed by remobilization and precipitation of the metals, resulted in gold enrichment in the oxide zone. The new zircon UPb dating constrains the formation age of the Cerattepe deposit into a time span from 79 ± 1–76.8 ± 1 Ma, a younger age compared to other VMS deposits in the eastern Pontide region.

A study of the temperature distribution in the OTEC cold water pipe using a heat and mass transfer approach

Abstract The difference between sea water temperature at a depth of around 1000 m and sea water temperature at sea level is generally used as a parameter in the design of Ocean Thermal Energy Conversion (OTEC). In practice, electricity generation is determined by the difference between the temperature of the cold seawater coming out of the Cold Water Pipe (CWP) and the temperature of the seawater at the surface. The temperature of cold sea water increases due to heat transfer experienced by cold sea water flowing through the CWP, which comes into contact with surrounding sea water which has a higher temperature. This in turn provides a lower actual temperature difference, and therefore reduces the design power capacity. However, many previous studies did not consider these lower temperature differences. This may be acceptable for cases with practically small heat transfer such as CWP with low thermal conductivity combined with good insulation used in 1000 m CWP vertical floating systems. Unfortunately, this may not be the case for many of OTEC’s proposed alternative sites, which are located on land systems that require CWP lengths of five km or more. This raises the need for careful investigation to determine the temperature of the sea water coming out of the CWP, where it is necessary to calculate the temperature distribution of the cold sea water flowing through the CWP. This paper aims to estimate the temperature distribution of cold sea water flowing through the CWP and the increase in temperature of cold sea water leaving the CWP. Analysis based on the principles of mass and heat transfer was carried out in this research, where modelling was carried out numerically using a finite volume approach. For the case considered, the change in sea water temperature at CWP from depth to the surface occurs 1-3°C, which is the accumulation of each change in sea water depth. The results of this research illustrate that designing an OTEC system with a long CWP must consider the temperature distribution of cold sea water flowing through the CWP to produce a more realistic design.

Brackish Water Phytodesalination by the Euhalophyte Sesuvium portulacastrum

In the Middle East and North Africa as well as in numerous countries in South America and Southeast Asia, water scarcity is a real concern. Therefore, water desalination has become a key solution and an important source of freshwater production. Solar stills are used for water desalination but they require low depth of sea or brackish water and sufficient solar radiation to evaporate water. In this investigation, a phytodesalinator is presented for the first time. The halophyte used in this work is Sesuvium portulacastrum L., a heat-tolerant euhalophyte. The presented phytodesalinator can replace basic solar stills during cold seasons if there is sufficient sunlight to ensure the transpiration process in the plant. The euhalophyte S. portulacastrum was tested for its ability to desalinate reject brine as grown for two subsequent phytodesalination cycles. Several factors were found to affect the productivity of the phytodesalinator, in particular, solar radiation, phytodesalination duration, and plant density. Nevertheless, it exhibited an average productivity of 2.44 kg/m2/d and showed several advantages in comparison with basic solar stills.

Cost-Efficient Oceanographic Instrument with Microfabricated Sensors for Measuring Conductivity, Temperature and Depth of Seawater.

The design, fabrication and characterization of a cost-efficient oceanographic instrument with microfabricated sensors for measuring conductivity, temperature and depth of seawater are presented. Conductivity and temperature sensors were fabricated using MEMS technology, which allows for customized small footprints and low production costs. Dedicated electronics for reading, processing and storing acquired sensor data are described. The developed instrument enables the measurement of seawater conductivity in a range from 4 mS/cm to 70 mS/cm. The conductivity measurement is temperature-compensated in the range from 2 °C to 40 °C, with an accuracy of ±0.1 mS/cm. The temperature sensor's stability is 0.025 °C. The depth/pressure measurement range is up to 2000 m/200 bar, with a resolution of 0.1 bar. Temperature and conductivity sensor performance was assessed using laboratory equipment and designed electronics. The conductivity sensor was temperature-compensated to 0.01 mS/cm. The conductivity sensor electrode corrosion effect is presented below and was eliminated through adaptation of a signal acquisition circuit. Custom software was developed for monitoring critical conductivity sensor parameters (currents, voltages). A variation of 0.4% between cell conductance currents and voltages was established as a criterion for stable conductivity sensor operation.

Effects of internal waves on bottom thermal structures and turbulent mixing in the Xisha Islands

Using velocity and high-resolution temperature mooring data from the fore-reef slope of Yongxing Island in the northwest South China Sea (water depth of 69 m), we examine the effects of internal waves on the temporal variations in temperature, bottom mixed layer (BML) and turbulent mixing. The diurnal tide is found to be the dominant tidal force and the baroclinic tide is highly active, which would account for the 11 d abnormal spring-neap cycle in the barotropic tidal current. During the ebb period (tidal elevation decreases), the bottom diurnal baroclinic current transports cold water upslope, resulting in a decrease in temperature, and vice versa during the flood period. The BML thickness Hbml widely varies around 1.5m, approximately 2% of the water depth. The bottom turbulent mixing is not so active, indicated by the bulk dissipation Eɛ of 10 mWm−2 and turbulent diffusivity κz of 2×10−4m2s−1. Both Hbml and Eɛ approximate a log-normal distribution, demonstrating strong intermittency. The high-frequency (ω) internal bores can increase Hbml by four times and enhance the turbulent mixing by one order, which should be responsible for the slow cascade of Hbml(∼ω−1.5) and Eɛ(∼ω−1.0). In the downslope phase, Hbml is about 30% thicker, and turbulent mixing is enhanced by 3 times stronger than those in the upslope phase. It is revealed that under the forcing of internal waves, turbulent mixing corresponds to a thick BML with Hbml∼〈κz〉0.25, and stratification (N) has a significantly negative correlation with the development of BML, Hbml∼〈N〉−1.8.

Mathematical Modelling and Optimisation in Multibeam Bathymetry: A Study of Coverage Width, Overlap Rate and Course Optimisation

This paper focuses on the field of multibeam bathymetry, firstly, a two-dimensional mathematical model with coverage width, overlap rate, and seawater depth as the objectives is established by using the trigonometric properties, the terrain slope factor and the effect of different survey line distances from the centre on multibeam bathymetry. Matlab software was used to solve the model, and the expressions for the coverage width and the overlap rate of adjacent strips were obtained. Secondly, for the multibeam bathymetry along a certain direction, based on the three-dimensional geometric seawater depth model, the coverage width model corresponding to different survey line directions was obtained by using the classification discussion method. Finally, through the optimisation model and traversal algorithm, the optimisation model that meets the requirement of the overlap rate of adjacent strips is established with the objective of minimising the total routes, and solved by the cyclic traversal idea. This study provides a comprehensive mathematical model and optimisation method for multibeam bathymetry, and lays a theoretical foundation for practical applications in related fields.

Identification of Groundwater Potential on Katela Island, West Muna Regency Using the Geoelectric Resistivity Method

Island Katela has a population of 957 people. Currently, the community has difficulty getting clean water. Activities to identify potential groundwater resources on Katela Island need to be carried out to solve this problem. The purpose of this research activity is to identify the subsurface of the land on Katela Island, West Muna Regency using the geoelectric resistivity method to obtain information on the potential of the groundwater layer. The main objective is to determine the existence of groundwater resources on Katela Island where the presence of groundwater is depicted in 2-dimensional (2D) and 1-dimensional (1D) subsurface resistivity cross-sectional models. The results obtained show that the structure of the subsurface layers in the survey area consists of layers of clay, sand, sandstone, limestone, salt water layers and groundwater (fresh) layers. The potential existence of a groundwater layer (fresh) is at a depth of 31.25 m at Site 1, with a resistivity value above 0.2 Ωm to 1 Ωm. This layer is thought to be a fresh water layer because above it there is a layer of clay which is impermeable so it is difficult for sea water to intrude. Based on resistivity data, at shallow depths (at the surface to a depth of 25 m) in the survey area sea water has been intruded.

A variable pressure water-sealed compressed air energy storage (CAES) tunnel excavated in the seabed: Concept and airtightness evaluation

For compressed air energy storage (CAES) caverns, the artificially excavated tunnel is flexible in site selection but high in sealing cost. A novel concept of building a water-sealed CAES tunnel in the seabed is proposed in this study, and the airtightness of the system is preliminarily evaluated. Based on the proposed variable pressure water-sealed CAES tunnel excavated in the seabed and combined with the actual operation of the system, a multifield and multiphase coupling calculation model for the airtightness calculation of water-sealed CAES tunnel under pressure changes was constructed, and the rationality of the model was confirmed by a case study. The airtightness analysis of the water-sealed CAES system is carried out. It is an effective method to excavate a tunnel in the seabed, and sealing the CAES system by utilizing the water head pressure in the pores of the rock mass and the low permeability of the rock mass. To satisfy the sealing requirements of the CAES system, the seawater depth of the tunnel should be deeper than 190 m if the gas pressure inside the tunnel is 4.5–10.0 MPa with the rock mass permeability of 1.0 × 10-16 m2 and the overlying rock thickness of 100 m, When the gas pressure inside the tunnel is 4.5–10.0 MPa, the overburden thickness is 100 m and the seawater depth is 50 m; the rock mass permeability should be less than 7.32 × 10-17 m2.

Dispersion of waves propagating in the ice-covered Arctic Ocean

The Arctic Ocean was modeled as an ice–seawater–sediment system, where the ice cover and seawater were assumed to be inhomogeneous solid and liquid, respectively, while the sediment was assumed to be homogeneous liquid. Transfer matrixes relating the displacements and stresses at the lower surface and those at the upper surface for a thin solid layer, and a thin liquid layer were derived. Furthermore, a dispersion equation for waves propagating in the ice-covered Arctic Ocean was derived using the transfer matrix technique. The phase- and group-velocity dispersion curves were obtained by solving the dispersion equation numerically. The results show that the dispersion curves for the Arctic Ocean with ice cover are much more complex than those without ice cover. Except for the new mode, the phase-velocity curve for the n-th (n > 2) mode exhibited a slight distortion, which caused a sharp peak in the group-velocity curve. These peak values, which depend on the order of the mode, may be significantly higher than the speed of sound in seawater. The variation of the ice cover thickness had significant influence on the dispersion curves of the first and second modes. Moreover, the influence of the seawater depth on the dispersion curves were investigated.