Increasing Water Depth Research Articles

Cooling water intake system safety analysis based on impingement probability

Invasion or aggregation of marine organisms in cooling water intake systems (CWIS) has gradually become an important problem affecting the safety of nuclear power plants with environmental and climate changes. In this study, a 3-dimensional numerical model (TELEMAC-3D) was used to determine the impingement probability in a typical nuclear power plant with a once-through cooling system, and the effect on CWIS safety. The factors controlling impingement probability were also analyzed. Results show that (1) impingement probability decreased rapidly with an increase in distance from the CWIS. In addition, the distance of the impingement effect of a nuclear power plant with six units was mainly within 1 km of the CWIS. (2) Impingement probability increased with water withdrawal, and as distance to the CWIS increased, the increase in probability increased. (3) Generally, an increase in tide strength led to a decrease impingement probability. (4) Near the CWIS, the impingement probabilities of areas upstream or downstream of the CWIS along the tidal flow direction were much higher than those not in those areas. (5) An increase in water depth significantly reduced impingement probability. When the water depth of the CWIS increased from 5 m to 15 m, impingement probability was reduced up to 30%. Based on the above findings, the following suggestions were made to minimize the impingement effects on CWIS safety: first, the CWIS of coastal nuclear power plants should be set in an area with low aquatic biomass, strong tides, deep water, and few surface species within the range of 1 km, and second, the amount of cooling water withdrawal or velocity should be reduced as much as possible.

Vertical patterns of leaf physiology and biofilm characteristics for Hydrilla verticillata in both single and mixed communities

Little is known about how community composition affects vertical patterns of leaf characteristics for submerged macrophytes in freshwater lakes. Here, after sampling Hydrilla verticillata in both single and mixed communities in shallow and deep areas in a shallow lake, we measured vertical patterns of leaf biofilm and physiology characteristics. Upper leaves of H. verticillata always had more attached abiotic biofilm matters, and all biofilm characteristics exhibited declining trends from top to bottom segments in deep areas. Moreover, the amount of attached biofilm matter in the mixed community was less than in the single community in shallow areas, but the reverse was true in deep areas. The vertical pattern of leaf physiology characteristics was obvious in the mixed community. In the shallow area, leaf pigment concentrations showed increasing trends with an increasing water depth, but the enzymatic specific activity of peroxidase (POD-ESA) was precisely the opposite. In the deep area, leaf chlorophyll concentrations were greatest in the leaves of bottom segments and lowest in top segments, while carotenoids and POD-ESA were greatest in the leaves of the middle segment-II. Light intensity and biofilm were found to play an important role in regulating the vertical patterns of photosynthetic pigments and POD-ESA. Our study highlighted the effect of community composition on the vertical pattern of leaf physiology and biofilm characteristics. HIGHLIGHTS: Biofilm characteristics always showed increasing trends with increasing water depth. Community composition changed the amount of attached biofilm matter. The vertical pattern of leaf physiology was more obvious in mixed communities. Light intensity and biofilm regulated the vertical pattern of leaf physiology.

From the Surface Ocean to the Seafloor: Linking Modern and Paleo‐Genetics at the Sabrina Coast, East Antarctica (IN2017_V01)

AbstractWith ongoing climate change, research into the biological changes occurring in particularly vulnerable ecosystems, such as Antarctica, is critical. The Totten Glacier region, Sabrina Coast, is currently experiencing some of the highest rates of thinning across all East Antarctica. An assessment of the microscopic organisms supporting the ecosystem of the marginal sea‐ice zone over the continental rise is important, yet there is a lack of knowledge about the diversity and distribution of these organisms throughout the water column, and their occurrence and/or preservation in the underlying sediments. Here, we provide a taxonomic overview of the modern and ancient marine bacterial and eukaryotic communities of the Totten Glacier region, using a combination of 16S and 18S rRNA amplicon sequencing (modern DNA) and shotgun metagenomics (sedimentary ancient DNA, sedaDNA). Our data show considerable differences between eukaryote and bacterial signals in the water column versus the sediments. Proteobacteria and diatoms dominate the bacterial and eukaryote composition in the upper water column, while diatoms, dinoflagellates, and haptophytes notably decrease in relative abundance with increasing water depth. Little diatom sedaDNA is preserved in the sediments, which are instead dominated by Proteobacteria and Retaria. We compare the diatom microfossil and sedaDNA record and link the weak preservation of diatom sedaDNA to DNA degradation while sinking through the water column to the seafloor. This study provides the first assessment of DNA transfer from ocean waters to sediments and an overview of the microscopic communities occurring in the climatically important Totten Glacier region.

A Study on Local Scour of Large-Diameter Monopile under Combined Waves and Current

The complex-load environment of offshore monopile foundations makes the combination of waves and current, and the variation in water depth, important factors for local scour. A flume test model of flow–pile–soil coupling for large-diameter monopile foundations is established, which comprehensively considers the combined reciprocating action of wave/current and the influence of tide depth. The precision of the experiment is ensured by the extension method of series models. The results show that the local scour caused by tides and the wave–current combination is obviously different from the unidirectional wave–current combination. The equilibrium scour depth obtained by the test is found to have some deviation from the predicted scour-depth equation. The maximum scour depth decreased with the increase in water depth within the range of 3 to 6 times the pile diameter. The bed shear-stress equation was generally consistent with the scouring-depth rule measured by the model, which can be considered to evaluate the rationality of the test results.

Quantitative prediction of the hydraulic performance of free water surface constructed wetlands by integrating numerical simulation and machine learning

Quantitative prediction of the design parameter-influenced hydraulic performance is significant for optimizing free water surface constructed wetlands (FWS CWs) to reduce point and non-point source pollution and improve land utilization. However, owing to limitations of the test conditions and data scale, a quantitative prediction model of the hydraulic performance under multiple design parameters has not yet been established. In this study, we integrated field test data, mechanism model, statistical regression, and machine learning (ML) to construct such quantitative prediction models. A FWS CW numerical model was established by integrating 13 groups of trace data from field tests. Subsequently, training, test and extension datasets comprising 125 (5^3), 25 (L25(56)) and 16 (L16(44)) data points, respectively, were generated via numerical simulation of multi-level value combination of three quantitative design parameters, namely, water depth, hydraulic loading rate (HLR), and aspect ratio. The short circuit index (φ10), Morrill dispersion index (MDI), hydraulic efficiency (λ) and moment index (MI) were used as representative hydraulic performance indicators. Training set with large samples were analyzed to determine the variation rules of different hydraulic indicators. Based on the control variable method, φ10, λ, and MI grew exponentially with increasing aspect ratio whereas MDI showed a decreasing trend; with increasing water depth, φ10, λ, and MI showed polynomial decreases whereas MDI increased; with increasing HLR, φ10, λ, and MI slowly increased linearly whereas MDI showed the opposite trend. Finally, we constructed models based on multivariate nonlinear regression (MNLR) and ML (random forest (RF), multilayer perceptron (MLP), and support vector regression. The coefficients of determination (R2) of the MNLR and ML models fitting the training and test sets were all greater than 0.9; however, the generalization abilities of different models in the extension set were different. The most robust MLP, MNLR without interaction term, and RF models were recommended as the preferred models to hydraulic performance prediction. The extreme importance of aspect ratio in hydraulic performance was revealed. Thus, gaps in the current understanding of multivariate quantitative prediction of the hydraulic performance of FWS CWs are addressed while providing an avenue for researching FWS CWs in different regions according to local conditions.

Potamogeton crispus restoration increased the epiphytic microbial diversity and improved water quality in a micro-polluted urban river

Special characterization and assembly of epiphytic microbial communities remain unclear in micro-polluted water column during submersed macrophytes restoration. In this study, an in-situ enclosure area sowing with turions of Potamogeton crispus (P. crispus) was conducted in a micro-polluted urban river to investigate the characterization of P. crispus and epiphytic microbial communities and their response to water environment under different water depths. Turions completely germinated in water column with <90 cm water depth and the germination speed decreased with increasing water depth within 18 days. There were obvious differences in morphological characteristics of P. crispus between deep and shallow water layers. P. crispus restoration decreased by 12–32%, 13–36%, 9–43% and 5–36% of COD, NH4+-N, TN and TP concentration, respectively, in enclosed overlying water compared to the river (P < 0.05) during 5 months of experiment. Illumina sequencing was employed to explore the epiphytic bacterial and microeukayotic communities at water depth 25–35 cm (shallow area) and 80–90 cm (deep area). A total of 9 bacterial and 12 microeukayotic dominant phyla were obtained in eight samples. It should be noted that the algae abundances were higher in shallow area than deep area but a reverse trend was observed for methanotrophs. Null model analysis revealed that dispersal limitation and undominated process was the most important assembly process, whereas stochastic processes gained more importance in shallow area than deep one. According to cooccurrence analysis (|r| > 0.6, P < 0.05), there were more strongly correlated edges in shallow area (456 edges) than deep area (340 edges). These results highlight that submerged macrophytes restoration can increase microbial diversity and improve water quality, and provide a “summer disease cured in winter” way by using could-resistant P. crispus for water purification in micro-polluted rivers in low-temperature season.

Water and Handwashing in a Drought-Prone Region of Southern Niger: How Environment, Household Infrastructure, and Exposure to Social and Behavior Change Messages Interact.

This study aims to inform multisectoral development programs by exploring the extent to which social and behavior change (SBC) messages, environment, and household infrastructure are associated with knowledge and practice of handwashing behaviors. A cross-sectional survey of 2,708 households in the Maradi and Zinder districts of Niger was collected in April 2021. Household data were integrated with two local environmental measures: 1) water level at the nearest waterhole point, and 2) anomalous rainfall for the previous rainy season derived from climate hazards infrared precipitation with station rainfall (CHIRPS) data. Logistic regression models were constructed to explore how environment, household infrastructure, and exposure to SBC messages were associated with two hygiene-related outcomes: 1) observed water and soap available at household handwashing stations, a behavior, and 2) knowledge of critical moments for handwashing, a behavioral determinant. We find that in households near a water point with higher water depth, households were statistically significantly more likely (odds ratio [OR] = 1.25); (confidence interval [CI] = 1.12-1.49) to have water and soap observed at the handwashing station. Women in households near a water point with increased water depth (more water) were more likely to know three or more critical handwashing moments (OR = 1.07; CI = 1.03-1.11). Exposure to messages about the importance of handwashing was significantly associated with knowledge of critical handwashing moments and having water and soap observed at a handwashing station. Multisectoral programming should consider layering efforts so that development projects that increase access to water sources are complemented with SBC approaches focused on hygiene.

A novel three-phase mixture approach for the numerical modeling of self-aerated flows

This work presents a novel theoretical/numerical model for the simulation of self-aerated flows under a Reynolds-Averaged Navier-Stokes (RANS) framework. The new formulation is based on a three-phase mixture approach composed of a continuous air phase, a bubble phase, and a continuous water phase. A mass transfer mechanism that does not depend on an entrainment function and does not require calibration accounts for the incorporation of air into the flow. A modification in the formulation of the Volume-of-Fluid algorithm (used to track the free surface) allows one to capture the increase in water depth due to the presence of bubbles. The proposed formulation recovers the traditional Volume-of-Fluid formulation for free surface flows in the absence of bubbles, allowing the model to represent simultaneously the aerated and not aerated regions of a flow. Governing equations for the mixture are derived from mass and momentum conservation equations for each phase, and a numerical algorithm that ensures the boundedness of the numerical solution is proposed. The model is tested and validated using four experimental cases: a degassing tank, a bubble plume, a plunging jet, and a stepped spillway, showing very satisfactory results. The new methodology provides a significant advance in the current capabilities for simulating self-aerated flows.

Shifts in composition and function of bacterial communities reveal the effect of small barriers on nitrous oxide and methane accumulation in fragmented rivers.

Rivers are often blocked by barriers to form different habitats, but it is not clear whether this change will affect the accumulation of N2O and CH4 in rivers. Here, low barriers (less than 2 m, LB) increased N2O concentration by 1.13 times and CH4 decreased by 0.118 times, while high barriers (higher than 2 m, less than 5 m high, HB) increased N2O concentration by 1.19 times and CH4 by 2.76 times. Co-occurrence network analysis indicated LB and HB can promote the enrichment of Cyanobium and Chloroflexi, further limiting complete denitrification and increasing N2O accumulation. The LB promotes methanotrophs (Methylocystis, Methylophilus, and Methylotenera) to compete with denitrifiers (Pseudomonas) in water, and reduce CH4 accumulation. While the HB can promote the methanotrophs to compete with nitrifiers (Nitrosospira) in sediment, thus reducing the consumption of CH4. LB and HB reduce river velocity, increase water depth, and reduce dissolved oxygen (DO), leading to enrichment of nirS-type denitrifiers and the increase of N2O concentration in water. Moreover, the HB reduces DO concentration and pmoA gene abundance in water, which can increase the accumulation of CH4. In light of the changes in the microbial community and variation in N2O and CH4 accumulation, the impact of fragmented rivers on global greenhouse gas emissions merits further study.

Spatiotemporal distribution of seabed litter in the SE Levantine Basin during 2012–2021

This study explores the first record of spatiotemporal distributions of macro and micro-litter on the seafloor in the Southeastern (SE) Levantine Basin (LB) during 2012–2021. Macro-litter was surveyed by bottom trawls in water depths of 20-1600 m and micro-litter by sediment box corer/grab at a depths range of 4-1950 m. Maximal macro-litter concentrations were recorded at the upper continental slope (200 m), averaging 4700 ± 3000 items/km2. Plastic bags and packages were the most abundant items (77 ± 9 %) with a maximum of 89 % at 200 m depth, and their size decreased with increasing water depth. Micro-litter debris were found mainly in shelf sediments (≤30 m water depth) with an average concentration of 40 ± 50 items/kg, while shit particles transferred to the deep sea. These findings suggest an extensive distribution of plastic bags and packages in the SE LB, predominantly accumulating in the upper continental slope and deeper, based on their size.

Holocene Paleoenvironmental Implications of Diatom, Non-Pollen Palynomorph, and Organic Carbon Records from the Kandalaksha Bay of the White Sea (European Arctic)

Variations in sea surface conditions and sea level through the Holocene in the Kandalaksha Bay, the White Sea, were reconstructed based on the study of core sediments from the outer Kandalaksha Bay, using the modern analog technique applied to dinocysts in addition to diatoms, TOC, δ13Corg, CaCO3, and grain size data. The chronostratigraphy of the core sediments was defined from accelerator mass spectrometry 14C dates on mollusk shells. The results indicated an increase in water depth in the outer Kandalaksha Bay and in the central Dvina Bay until the late Holocene. From about 9.5 to 7.5 cal kyr BP, the data suggested a general trend of increasing sea surface temperatures (up to 14 °C), at least in areas with inflow of Atlantic waters. The last 2.5 kyr were characterized by increased freshwater runoff to the White Sea.

Propagation Mechanism of Deep-Water Impulse Waves Generated by Landslides in V-Shaped River Channels of Mountain Valleys: Physical Model of Regular Rigid Block

Landslide-induced impulse waves in alpine valleys are a significant risk to large-scale dam and reservoir engineering projects in the surrounding area. In this study, a 1 : 200-scale physical model of landslide-induced impulse waves in a V-shaped river channel was established, and 18 groups of tests were conducted to evaluate the influence of different parameters, such as the volume and shape of the landslide body, water entry velocity, and water depth of the reservoir. Based on the test results, a dimensionless formula was established for the first wave height of impulse waves caused by a deep-water landslide in a V-shaped channel. An energy conversion law was determined for the impact of landslide-induced impulse waves on the reservoir bank. Finally, a distribution law was obtained for the initial maximum pressure caused by landslide-induced impulse waves along the water depth on the opposite bank. The theoretical predictions of the dimensionless formula showed good agreement with the experimental results, and the energy conversion rate of the landslide-induced impulse waves initially increased and then decreased with an increasing Froude number. The maximum dynamic water pressure showed a triangular distribution with increasing water depth below the surface of the still water body. The impact pressure of the impulse waves on the slope on the opposite bank increased with the water entry velocity. This study provides a scientific basis for the risk prevention and control of landslide-induced impulse waves in river channels feeding into reservoirs.

NUMERICAL SIMULATION OF THE VISCOUS FLOW AROUND SHIPS TURNING IN SHALLOW WATER

Due to the effect of water depth, hydrodynamic characteristics of ships manoeuvring in shallow waters are quite different from those in deep water. In the present study, the CFD method is used to investigate the hydrodynamic behaviour of the ESSO OSAKA model in model-fixed condition in deep and shallow waters by solving RANS equations, which performs steady turning motion with the effect of free surface considered. The governing equations are discretized by the finite volume method (FVM) and the free surface is captured by applying the volume of fluid (VOF) method. Viscous hydrodynamic characteristics and flow fields in a series of cases at different water depths and speeds are investigated respectively. By comparing the numerical results in shallow water with those in deep water, it was found that effects of water depth and free surface are significant on ship’s hydrodynamic forces. The coefficients of drag, lateral force and yaw moment all increase with the decrease of water depth. The drag coefficient in shallow water is about 45% larger than that in deep water. However, effect of water depth on the lateral force coefficient is small, it is about 15% larger in shallow water than that in deep water. While, it has significant effect on the yaw moment coefficient, which is about 25% larger in shallow water than in deep water. And as the water depth increases, the effect of the free surface gradually becomes smaller. Both coefficient of pressure component of drag force and drag coefficient in the present simulation are about 7% smaller than the case without considering the free surface at h/d ≥ 3.0, while that of frictional component is almost the same. When h/d ≥ 3.0, the lateral force and yaw moment coefficients are almost the same as when the free surface is not considered. The error between the present numerical result and the measurements is within 10%, which indicates that RANS method has promising capability to predict the hydrodynamic forces on ships manoeuvring in shallow water.

Assessment of Dynamic Effects of Wave Loads in Fatigue Analysis for Fixed Steel Offshore Structures

This paper presents an algorithm and develops a formula to evaluate the dynamic effect of wave loading on fixed steel offshore structures (jacket structures) through the fatigue damage ratio. Applying the algorithm and formula proposed in this paper to evaluate the dynamic effect of wave loads in fatigue analysis for 03 Jacket structures built at increasing water depth under one specific marine condition and provide specific recommendations on the limits of application of quasi-static and dynamic methods in the fatigue analysis of the jacket structures. This research is really necessary because currently, the current standards (API, DnV) only stop at evaluating the dynamic effects of wave loads acting on the Jacket structure in the strength analysis. These standards propose a limit for quasi-static or dynamic analysis based on the "3.0 s or 2.5 s rule" (use the quasi-static method when Tmax≤ 3.0 s or ≤ 2.5 s), and it is advised that they only apply to waters within the North Sea and the Gulf of Mexico. This paper has demonstrated that it is not appropriate to use the specified standards for the North Sea and the Gulf of Mexico to select the method of fatigue analysis of the jacket structure in marine conditions outside the study area of the standard. Hoped that this paper will be a reference for engineers when choosing a fatigue analysis method for jacket structures in specific marine conditions at the location where the jacket structure has been installed. Doi: 10.28991/CEJ-2023-09-02-016 Full Text: PDF

Efficient optimization design method of jacket structures for offshore wind turbines

With the gradual implementation of offshore wind energy production, the future tendency is to expand into the deeper water. The jacket foundations will take the place of the present monopile foundations when the water depth increases. The foundations account for the majority of the construction cost for offshore wind farms, and the structural optimization of jackets will bring lucrative economic benefits. Structural optimization is a complex iterative process that requires huge computing costs. Therefore, this paper proposes a structural optimization method based on surrogate models to solve this problem effectively and swiftly obtain optimized design schemes of lightweight jackets for offshore wind turbines. The structural responses of jacket wind turbine systems under the equivalent static extreme loads with a recurrence period of 50 years are mainly considered in structural optimization design, and the key optimization variables of jackets are determined by parameter sensitivity analysis. The finite element models of jackets are transformed into surrogate models, and the genetic algorithm is employed to optimize the surrogate models directly. The optimized jackets are additionally verified through coupled dynamic analysis, besides, buckling strength and fatigue life are also checked. And local refined optimizations are carried out for the failure members. According to the optimized design schemes of lightweight jackets for 30 m, 50 m and 70 m water depths, it is demonstrated that the structural optimization design method is adequate and efficient for jackets of wind turbines. Parameter sensitivity analysis can cut the number of optimization variables in half to improve the optimization efficiency. Furthermore, the application of surrogate models can significantly speed up the optimization process by saving about 98.61% of the original time consumed. The optimization design method of the jackets for offshore wind turbines proposed in this paper is suitable for practical engineering, with high precision and efficiency.

C20-C21-C23 tricyclic terpanes abundance patterns: Origin and application to depositional environment identification

Reconstruction of paleo-depositional environments in a sedimentary basin is often obstructed by the absence of typical environmental indicators in sedimentary rocks. Here, we propose a biomarker method using C20-C21-C23 tricyclic terpanes (TTs) as a tracer, which is simple in analysis but robust to provide reliable and detailed environmental information. Based on the analysis of 271 C20-C21-C23TT data from 32 basins in 18 countries, we observed a relationship between C20-C21-C23TT abundance patterns and depositional environments. This relationship was attributed to the control of depositional environments on the input proportions of plankton and terrigenous plants, which act as two end-member precursors for the TTs in a depositional system. The various mixing proportions between these two end-members result in different C20-C21-C23TT abundance patterns associated with different depositional environments, e.g., C20&amp;gt;C21&amp;gt;C23TT in river-lake transitional, C20&amp;lt;C21&amp;lt;C23TT in marine or saline lacustrine environments, C20&amp;lt;C21&amp;gt;C23TT in freshwater lacustrine and C20&amp;gt;C21&amp;lt;C23TT in marine-continental transitional environments. In addition, the C23/C21TT ratio increases with elevated salinity of depositional water, and the C21/C20TT ratio increases with increasing water depths. Based on these observations, a discrimination diagram using C23/C21TT vs. C21/C20TT was developed for environmental identification. The validity of this C20-C21-C23TT biomarker method is well demonstrated by the rock samples with typical environmental indicators. This method is applicable in a broad spectrum of rocks and in maturities up to 2.4%Ro. Its strength was shown by a case study of a complex depositional system in the East China Sea Basin, which has been strongly affected by eustasy.

Spatiotemporal distribution and prediction of chlorophyll-a in Ulansuhai lake from an arid area of China

Lake Ulansuhai, a typical shallow lake in an arid area that is economically and ecologically important along the Yellow River, is currently eutrophic. Long-term (2010–2020) data on chlorophyll-a, nutrient, and environmental factors were obtained from three Lake Ulansuhai monitoring stations. The temporal and spatial distribution characteristics of Chl-a were analyzed. Additionally, a hybrid evolutionary algorithm was established to simulate and predict Chl-a, and sensitivity analysis revealed the interaction between environmental factors and eutrophication. The results indicated that (1) the seasonal variation of eutrophication showed an obvious trend of spring &amp;gt; summer &amp;gt; autumn &amp;gt; winter, and the concentration of Chl-a in the inlet was significantly higher than that in the outlet; (2) The inlet, center, and outlet of Ulansuhai Lake are satisfactorily affected by HEA in the best suited method. The fitting coefficients (R2) of the optimal models were 0.58, 0.59, and 0.62 for the three monitoring stations, and the root mean square errors (RMSE) were 3.89, 3.21, and 3.56, respectively; (3) under certain range and threshold conditions, Chl-a increased with the increase of permanganate index, water temperature, dissolved oxygen concentration, and ammonia nitrogen concentration, but decreased with the increase of water depth, Secchi disk depth, pH, and fluoride concentration. The results indicate that the HEA can simulate and predict the dynamics of Chl-a, and identify and quantify the relationships between eutrophication and the threshold data. The research results provide theoretical basis and technical support for the prediction and have great significance for the improvement of water quality and environmental protection in arid and semi-arid inland lakes.

Large freshwater-influx-induced salinity gradient and diagenetic changes in the northern Indian Ocean dominate the stable oxygen isotopic variation in Globigerinoides ruber

Abstract. The application of stable oxygen isotopic ratio of surface-dwelling planktic foraminifera Globigerinoides ruber (white variety; δ18Oruber) to reconstruct past hydrological changes requires a precise understanding of the effect of ambient parameters on δ18Oruber. The northern Indian Ocean, with its huge freshwater influx and being a part of the Indo-Pacific Warm Pool, provides a unique setting to understand the effect of both the freshwater-influx-induced salinity and temperature on δ18Oruber. Here, we use a total of 400 surface samples (252 from this work and 148 from previous studies), covering the entire salinity end-member region, to assess the effect of freshwater-influx-induced seawater salinity and temperature on δ18Oruber in the northern Indian Ocean. The analysed surface δ18Oruber mimics the expected δ18O calcite estimated from the modern seawater parameters (temperature, salinity, and seawater δ18O) very well. We report a large diagenetic overprinting of δ18Oruber in the surface sediments, with an increase of 0.18 ‰ per kilometre increase in water depth. The freshwater-influx-induced salinity exerts the major control on δ18Oruber (R2=0.63) in the northern Indian Ocean, with an increase of 0.29 ‰ per unit increase in salinity. The relationship between temperature- and salinity-corrected δ18Oruber (δ18Oruber−δ18Osw) in the northern Indian Ocean [T=-0.59⋅(δ18Oruber-δ18Osw)+26.40] is different than reported previously, based on the global compilation of plankton tow δ18Oruber data. The revised equations will help create a better palaeoclimatic reconstruction from the northern Indian Ocean by using the stable oxygen isotopic ratio. The entire data set (newly generated and previously published) used in this work is available both as a Supplement to this article and at PANGAEA (https://doi.org/10.1594/PANGAEA.945401; Saraswat et al., 2022).

Study on dynamic characteristics of drill string in deep-water riserless drilling

The cost and security of ocean drilling are directly related to the efficient exploration and development of ocean resources. The riserless drilling system is usually adopted in the ocean drilling. With the consideration of marine environment load, a dynamic analysis model of drill string in deep-water riserless drilling is established. This model aims to analyze the dynamic characteristics of drill string in the water and down hole during the process of deep-water riserless drilling. The research results are as follows. For the drill string in water, its displacement increase with the increase of ocean current velocity, water depth, rotation speed, and WOB. But the rotation speed and WOB have less influence. The drill string in down hole shows the same pattern. However, the drill string in down hole is only affected near the mud line and the bit, and the rest of the drill string is almost unaffected. In deep-water riserless drilling, stress on the drill string at the wellhead, near the mudline, and at the bottom hole assembly (BHA) is complex. The safety of drill string at these locations should be given great attention.

Water wave cloaking using a floating composite plate

The trajectory of surface gravity waves in the potential flow regime is affected by the gravitational acceleration, water density and sea bed depth. Although the gravitational acceleration and water density are approximately constant, the effect of water depth on surface gravity waves exponentially decreases as the water depth increases. In shallow water, cloaking an object from surface waves by varying the sea bed topography is possible, however, as the water depth increases, cloaking becomes a challenge because there is no physical parameter to be engineered and subsequently affects the wave propagation. In order to create an omnidirectional cylindrical cloaking device for finite-depth/deep-water waves, we propose an elastic composite plate that floats on the surface around a to-be-cloaked cylinder. The composite plate is made of axisymmetric, homogeneous and isotropic annular thin rings which provide adjustable degrees of freedom to engineer and affect the wave propagation. We first develop a pseudo-spectral method to efficiently determine the wave solution for a floating composite plate. Next, we optimise the physical parameters of the plate (i.e. flexural rigidity and mass of every ring) using an evolutionary algorithm to minimise the energy of scattered waves from the object and therefore cloak the inner cylinder from incident waves. We show that the optimised cloak reduces the energy of scattered waves as high as 99 % for the target wave number. We quantify the effectiveness of our cloak with different parameters of the plate and show that varying the flexural rigidity is essential to control wave propagation and the cloaking structure needs to be at least made of four rings with a radius of at least three times of the cloaked region. We quantify the wave drift force exerted on the structures and show that the optimised plate reduces the exerted force by 99.9 %. The proposed cloak, due to its structural simplicity and effectiveness in reducing the wave drift force, may have potential applications in cloaking offshore structures from water waves.