Effects Of Ocean Currents Research Articles

Effect of Ocean Currents and Temperature Variability on Yellowfin Tuna Catch Rates of Sri Lankan Longline Fishery

Effect of Ocean Currents and Temperature Variability on Yellowfin Tuna Catch Rates of Sri Lankan Longline Fishery

Quantitative evaluation of motion performances of underwater gliders considering ocean currents

Underwater gliders (UGs) have attracted great attention for their low cost, long range, high endurance, and broad applications in oceanography. However, few studies have been conducted to research motion performances of UGs. In this study, to understand the effects of ocean currents on the motion performances of UGs, a dynamic model of UGs considering ocean currents was established. Based on the dynamic model, motion simulations of the Petrel-Ⅱ UG were conducted. The response time taken for the UG to return to the pitch angle of the undisturbed state, the relative rotation radius of steady spiral motion, and the UG's voyage in a single profile were used to quantitatively evaluate the stability of pitching motion, maneuverability, and cruising ability, respectively. The results show that UGs are self-stable in pitch degree after the disturbance disappears, and a positive axial ocean current or a negative vertical ocean current could remarkably improve UGs' cruising ability. This work provides a quantitative evaluation criterion for motion performances of UGs, enriching the comparative theory of UGs. The dynamic model considering ocean currents would also be useful in path planning and optimization of the control strategy of UGs, and it provides valuable guidance for engineering applications.

Enhanced Sinks of Polycyclic Aromatic Hydrocarbons Due to Kuroshio Intrusion: Implications on Biogeochemical Processes in the Ocean-Dominated Marginal Seas

The biogeochemical processes of polycyclic aromatic hydrocarbons (PAHs) in the South China Sea (SCS) are influenced by the exchanges of water masses, energies, and materials between this marginal sea and the Pacific Ocean. To investigate the impact of oceanic water intrusion on semivolatile compounds, we collected seawater samples in the Western Pacific, northern, and central SCS in 2017 and analyzed for dissolved PAHs. PAH concentrations in the water columns of the Pacific Ocean and SCS were 1.7-11 and 1.1-7.3 ng L-1, respectively, showing spatial distinctions in terms of the composition and source characteristics. A common depletion for three-ring PAHs was found in the northern SCS by comparing the modeling results of conservative mixing by Kuroshio intrusion. Kuroshio water increased the levels of temperature, dissolved oxygen, and nutrients when intruding into the northern SCS and was likely to enhance the bioavailability of PAHs and stimulate their biodegradation process. In the water column, the most effective layer under the Kuroshio intrusion impact is different for three- and four-ring PAHs, where the three-ring PAHs' depletion was most significant at the surface; however, for four-ring PAHs, that was at the deep chlorophyll maximum layer. This study highlighted the effect of ocean currents on PAHs for their water-column processes both from physical and biogeochemical perspectives.

Path planning method for unmanned underwater vehicles eliminating effect of currents based on artificial potential field

AbstractTo eliminate the effect of ocean currents for optimal path planning for unmanned underwater vehicles (UUVs) in the underwater environment, an intelligent algorithm is designed and proposed in this paper. The algorithm consists of two parts: an artificial potential field-based algorithm that derives the shortest path and avoids collision accidents; and an adjusting function that eliminates the effect of ocean currents. The planning results of the intelligent algorithm are presented in detail, and compared with the conventional algorithm that does not consider the effect of currents. The effectiveness of the optimised path planning method given in this paper is proved.

Robust Position Control of an Over-actuated Underwater Vehicle under Model Uncertainties and Ocean Current Effects Using Dynamic Sliding Mode Surface and Optimal Allocation Control.

Underwater vehicles (UVs) are subjected to various environmental disturbances due to ocean currents, propulsion systems, and un-modeled disturbances. In practice, it is very challenging to design a control system to maintain UVs stayed at the desired static position permanently under these conditions. Therefore, in this study, a nonlinear dynamics and robust positioning control of the over-actuated autonomous underwater vehicle (AUV) under the effects of ocean current and model uncertainties are presented. First, a motion equation of the over-actuated AUV under the effects of ocean current disturbances is established, and a trajectory generation of the over-actuated AUV heading angle is constructed based on the line of sight (LOS) algorithm. Second, a dynamic positioning (DP) control system based on motion control and an allocation control is proposed. For this, motion control of the over-actuated AUV based on the dynamic sliding mode control (DSMC) theory is adopted to improve the system robustness under the effects of the ocean current and model uncertainties. In addition, the stability of the system is proved based on Lyapunov criteria. Then, using the generalized forces generated from the motion control module, two different methods for optimal allocation control module: the least square (LS) method and quadratic programming (QP) method are developed to distribute a proper thrust to each thruster of the over-actuated AUV. Simulation studies are conducted to examine the effectiveness and robustness of the proposed DP controller. The results show that the proposed DP controller using the QP algorithm provides higher stability with smaller steady-state error and stronger robustness.

Station-Keeping Control of a Hovering Over-Actuated Autonomous Underwater Vehicle Under Ocean Current Effects and Model Uncertainties in Horizontal Plane

Nowadays, underwater vehicles (UVs) are applied to various tasks such as carrying objects or maintenance of underwater structures. To carry out well these tasks, UVs should keep the position and orientation in the water to perform the specified tasks. However, the systems used in underwater operations are always under the influence of disturbance such as ocean currents and model uncertainties. In this paper, the robust station-keeping (SK) control algorithm based on a sliding mode control (SMC) theory is designed to guarantee stability and better performance of a hovering over-actuated autonomous underwater vehicle (HAUV) despite the existence of model uncertainties and ocean current disturbance in the horizontal plane (HP). Using the Lyapunov theorem, the stability of the proposed controller is demonstrated. Besides, an optimal allocation control (AC) algorithm is also designed to keep the linear position and Euler angles of the HAUV in the presence of model uncertainties as well as ocean currents and to minimize the energy consumption of the system. Finally, a series of simulations and experiments for the HAUV system is conducted to demonstrate the superior performance of the proposed method.

Influence of the Coupling Effect of Ocean Currents and Waves on the Durability of Pier Structure of Cross-sea Bridges

Xie, Y.P. and Li, X.H., 2020. Influence of the coupling effect of ocean currents and waves on the durability of pier structure of cross-sea bridges. In: Al-Tarawneh, O. and Megahed, A. (eds.), Recent Developments of Port, Marine, and Ocean Engineering. Journal of Coastal Research, Special Issue No. 110, pp. 87–90. Coconut Creek (Florida), ISSN 0749-0208.In the marine environment, under the action of ocean currents and waves, the piers of cross-sea bridges face a series of durability problems such as salt erosion and salt freeze-thaw cycles. The durability of the pier structure directly affects the service life of cross-sea bridges, so the research and test on the durability are of important significance for the design of cross-sea bridges. Based on the coupling effect of ocean currents and waves in the marine environment, this paper explores its influence on the durability of the pier structure of cross-sea bridges. The research results show that the durability analysis includes environmental index calculation, durability index calculation and durability evaluation. The damage of the bridge pier concrete structure is related to the material composition and the deterioration of the macro performance of the microstructure under the action of special environment. The pier concrete of the target cross-sea bridge measured in the laboratory has a salt-freeze resistance greater than F300. This paper provides an important theoretical basis for the research on the safety of marine concrete structures.

Surface Gravity Waves and Their Role in Ocean‐Atmosphere Coupling in the Gulf of Mexico

AbstractThis study provides an overview of the surface gravity wave dynamics in the Gulf of Mexico (GoM) using numerical simulations. The focus is on the effects of ocean currents on waves, and the geographic distribution of wave statistics and parameters related to the role of waves on both sides of the ocean‐atmosphere interface. Simulations are performed using the Simulating WAves Nearshore (SWAN) model with and without coupling with the Regional Ocean Modeling System (ROMS) model within the Coupled Ocean Atmosphere Wave Sediment Transport (COAWST) framework. In the GoM, currents alter the climatological significant wave heights by up to 0.18 m (±15%), reducing wave heights in the southwestern GoM and generally increasing wave heights in other regions. In two instantaneous snapshots representing the Loop Current variability in terms of its northward extension into the GoM, significant wave heights are modulated by as much as 0.30 m (±35%) by the currents. Probability density of wave height modulation covers a wider range of values and is skewed toward positive values over the eastern flank of the Loop Current. In winter, spring, and fall, swell fraction of wave energy increases from east to west in the GoM and reaches as high as 0.8 in the southwestern GoM, off the coast of Mexico. The dominance of swell in this region combined with weak wind results in a higher prevalence of the wave‐driven wind regime throughout the year. The interannual variability of significant wave height and swell fraction shows signals of major storms in the GoM.

Online AUV Path Replanning Using Quantum-Behaved Particle Swarm Optimization with Selective Differential Evolution

This paper presents an online AUV (autonomous underwater vehicle) path planner that employs path replanning approach and the SDEQPSO (selective differential evolution-hybridized quantum-behaved particle swarm optimization) algorithm to optimize an AUV mission conducted in an unknown, dynamic and cluttered ocean environment. The proposed path replanner considered the effect of ocean currents in path optimization to generate a Pareto-optimal path that guides the AUV to its target within minimum time. The optimization was based on the onboard sensor data measured from the environment, which consists of a priori unknown dynamic obstacles and spatiotemporal currents. Different sensor arrangements for the forward-looking sonar and horizontal acoustic Doppler current profiler (H-ADCP) were considered in 2D and 3D simulations. Based on the simulation results, the SDEQPSO path replanner was found to be capable of generating a time-optimal path that offered up to 13% reduction in travel time compared to the situation where the vehicle simply followed a path with the shortest distance. The proposed replanning technique also showed consistently better performance over a reactive path planner in terms of solution quality, stability, and computational efficiency. Robustness of the replanner was verified under stochastic process using the Monte Carlo method. The generated path fulfilled the vehicle’s safety and physical constraints, while intelligently exploiting ocean currents to improve the vehicle’s efficiency.

Phylogeographic analysis of the genus Platycephalus along the coastline of the northwestern Pacific inferred by mitochondrial DNA

BackgroundFlathead fishes of the genus Platycephalus are economically important demersal fishes that widely inhabit the continental shelves of tropical and temperate sea waters. This genus has a long history of taxonomic revision, and recently four Platycephalus species (Platycephalus sp. 1, Platycephalus sp. 2, P. indicus, and P. cultellatus) in the northwestern Pacific Ocean (NWP) have been recognized and redescribed. However, many aspects of their systematics and evolutionary history are unclear.ResultsA total of 411 individuals were sampled from 22 different sites across their distributions in the NWP. Three mitochondrial loci were sequenced to clarify the phylogeny and phylogeographic history of the fishes. The results showed significant differentiation of four Platycephalus species in the NWP with well-supported clades in which Platycephalus sp. 1 and Platycephalus sp. 2 were the closest, clustered with P. cultellatus, while their genetic relationship with P. indicus was the furthest. There were significant genealogical branches corresponding to P. indicus but not to other Platycephalus lineages. We further examined the phylogeographic patterns of 16 Platycephalus sp. 1 populations along the coastlines of China and Japan. A total of 69 haplotypes were obtained, with 23 shared among populations. One dominant haplotypic group, with a modest lineage structure and low levels of haplotype diversity and nucleotide diversity, was observed among Platycephalus sp. 1 populations. The demographic history reconstruction suggested a Platycephalus sp. 1 population expansion event dating back to the late Pleistocene.ConclusionsDistributional rang variations may be the crucial factors shaping the genetic relationships of the genus Platycephalus. Reproductive schooling and potential egg/larval dispersal ability, coupled with the effects of ocean currents, are responsible for the present phylogeographic pattern of Platycephalus sp. 1.

Magnetic mineral tracing of sediment provenance in the central Bengal Fan

We present a comprehensive magnetic mineral analysis of surface sediments from 110 sites in the central Bengal Fan to trace sediment provenance. Multiple magnetic parameters, including magnetic mineralogy, concentration, and grain size were generated. Rock magnetic measurements indicate that the dominant magnetic minerals within the studied sediments are detrital magnetite and titanomagnetite, which is further confirmed directly by scanning electron microscope (SEM) and transmission electron microscope (TEM) observations on magnetic extracts. Fuzzy c-means clustering analysis of magnetic parameters indicates that the study area can be divided into three clusters. Considering the position of ‘active valley’, we further divide cluster 1 into clusters 1A and 1B. Cluster 1A primarily covers the west side of the ‘active valley’ with relatively high magnetic concentrations and dominantly coarse-grained magnetic minerals, which likely correspond to basaltic materials derived from the Deccan Plateau. From the Godavari river mouth to the inner Bay of Bengal, magnetic concentration gradually decreases with a fining trend of magnetic grain size. Clusters 1B, 2, and 3 are on the east side of the ‘active valley’, where magnetic concentration and magnetic grain size decrease with increasing distance to the ‘active valley’. Combined with published data in the Indian region and the upper Bengal Fan, we suggest that the main provenances are the Himalayan and the Deccan Plateau, whose contributions to sediment distribution are quantitatively assessed. Our analysis suggests that the position of ‘active valley’ plays a key role in sediment distribution in the central Bengal Fan, while the effect of ocean currents is negligible.

Lagrangian pathways in the southern Benguela upwelling system

The effect of ocean currents on fish eggs and larvae during their journey from spawning to nursery grounds in the Southern Benguela upwelling system is poorly understood. The survival and successful transport of fish eggs and larvae results from complex biological and physical processes. This study focuses on the advective processes, more specifically on how the dynamics and characteristics of the ocean currents shape the Lagrangian pathways in the Southern Benguela. A mesoscale eddy resolving interannual (1989–2010) simulation of the region, with a horizontal resolution of 7.5 km, is used to study processes impacting the connectivity between the western edge of the Agulhas Bank and the west coast upwelling region. A set of Lagrangian experiments are conducted with particles being released within the top 100 m of the water column along an across-shore transect off Cape Point (34∘ S). Transport success is given by the ratio of the number of particles that reach St Helena Bay (32∘ S) over the total number of particles released. The model results show a strong seasonal cycle in transport success which is governed by the complex three-dimensional structure of the along-shore jets, their variability, together with the wind-induced Ekman drift. Transport success is most efficient in spring when the Benguela Jet consists of one coherent intensified single-core branch that flows over the 300 m isobath, and when wind-induced Ekman transport favours the retention of particles within the jet. At this time of the year, the pathway leading to successful transport is located inshore, with 90% of particles released inshore the 300 m isobath being successfully transported to St Helena Bay in <15 days. This pathway is also characterized by low eddy kinetic energy values. During the upwelling season (December–March), transport success becomes less efficient, and less sensitive to the initial across-shore position of the particles. The inshore route no longer dominates, as the majority of particles follow offshore pathways. The Benguela Jet shifts offshore and splits into several branches due to the shoaling of the poleward undercurrent. The entrainment of particles within the offshore branch of the jet is favored by the dominating offshore wind-induced Ekman transport. Particles trapped in the offshore branch get exposed to higher mesoscale variability. Their northward progression is slower, which leads to journeys generally exceeding 20 days. This study shows that successful transport from the Agulhas Bank to the west coast upwelling region cannot be attributed to only a simple wind induced modulation of the jet. It explores how the seasonal modulation of the Benguela Jet, poleward undercurrent and offshore Ekman transport combine together with the turbulent off-shelf eddy field to set-up the characteristics of transport success.

Investigation of the mechanical response of a deep-water drilling riser to ocean currents and waves

The drilling riser is an important piece of equipment used to link the subsea wellhead with the drilling platform. Its operating environment is extremely complex because of the effects of ocean currents, which can cause riser overload, fatigue, leading to economic loss. Therefore, in order to improve design and prevent premature failure of drilling riser, it is important to research the mechanical response to ocean currents. The effects of tension ratio and platform deflection on the lateral displacement, bending moment, and the stress of the drilling riser are analyzed, under actual working conditions and shear flow. The results show that the bending moment and lateral displacement of the drilling riser decrease significantly and the stress of the riser increases with increasing tension ratio. There is an increase in the lateral displacement of the drilling riser and the bending moment at the lower end of the drilling riser, with an increase in the initial offset of the offshore drilling platform. However, the initial offset of the offshore drilling platform has little effect on the stress of the riser. Under shear flow conditions, the lateral displacement, bending moment, and stress initially increase, then decrease, and finally stabilize. These results can be used to improve the design of drilling riser.

Dispersal traits interact with dynamic connectivity to affect metapopulation growth and stability

Many marine benthic species undergo a pelagic larval stage during which larvae are transported by ocean currents over a broad range of spatial and temporal scales. Although metapopulation theory predicts how stochastic dispersal can alter the stability of metapopulations, little is known about how dispersal-related traits such as spawning time and larval duration interact with spatiotemporal connectivity to affect metapopulation growth and stability. We used stochastic models and stage-structured metapopulation dynamics to study the interacting effects of ocean currents and dispersal traits on regional growth and stability. We derived stochastic metapopulation growth and stability, which predict the strong impact of local density regulation on the response of metapopulation to dynamic connectivity: temporal variance, positive (negative) covariance, and negative (positive) autocorrelation in connectivity deflate (inflate) density-independent growth. Yet, stability decreases (increases) with temporal variance and positive (negative) covariance of connectivity. We applied our derived metrics to simulated connectivity along the coast of British Colombia (Canada) over a range of spawning time (ST) and pelagic larval duration (PLD). Our analysis shows strong interactions between statistical components of connectivity, dispersal-related traits, and metapopulation growth and stability. The non-monotonic response of metapopulation stability to PLD was driven by mean of connectivity over short PLDs ( 36 days. We therefore use a trait-based framework and partitioning the relative importance of spatial and temporal components of stochastic marine dispersal, to inform species response through climate-induced changes in larval transport and in dispersal-related traits.

Particle swarm optimization-based receding horizon formation control of multi-agent surface vehicles

This paper proposes a novel receding horizon control (RHC) algorithm for formation control of a swarm of unmanned surface vehicles (USVs) using particle swarm optimization (PSO). The proposed control algorithm provides the coordinated path tracking of multi-agent USVs while preventing collisions and considering external disturbances such as ocean currents. A three degrees-of-freedom kinematic model of the USV is used for the RHC with guaranteed stability and convergence by incorporating a sequential Monte Carlo (SMC)-based particle initialization. An ocean current model-based estimator is designed to compensate for the effect of ocean currents on the USVs. This method is compared with the PSO-based RHC algorithms to demonstrate the performance of the formation control and the collision avoidance in the presence of ocean currents through numerical simulations.

Experimental Investigation on Vortex-Induced Vibration of a Free-Hanging Riser Under Vessel Motion and Uniform Current

A model test of a free-hanging riser under vessel motion and uniform current is performed in the ocean basin at Shanghai Jiao Tong University to address four topics: (1) confirm whether vortex-induced vibration (VIV) can happen due to pure vessel motion; (2) to investigate the equivalent current velocity and Keulegan–Carpenter (KC) number effect on the VIV responses; (3) to obtain the correlations for free-hanging riser VIV under vessel motion with VIV for other compliant risers; and (4) to study the similarities and differences with VIV under uniform current. The top end of the riser is forced to oscillate or move, in order to simulate vessel motion or ocean current effects. Fiber Bragg Grating (FBG) strain sensors are used to measure the riser dynamic responses. Experimental results confirm that the free-hanging riser will experience significant out-of-plane VIV under vessel motion. Meanwhile, vessel motion-induced VIV responses in terms of response amplitude, response frequency, and cross section trajectories under different test cases are further discussed and compared to those under ocean uniform current. Most importantly, the correlation among VIV response frequency, vortex shedding pairs, and maximum KC number KCmax is revealed. The presented work is supposed to provide useful references for gaining a better understanding on VIV of a free-hanging riser and for the development of future prediction models.

Marine Reserve Design with Ocean Currents and Multiple Objectives

There is a growing tendency to consider marine reserves as a management and conservation tool. We investigate a spatial bio-economic model to determine fishery profits under conservation efforts. Rather than imposing a marine reserve on our model, we ask, “When and where should a marine reserve be implemented ?” For one-dimensional habitat, we determine conditions under which marine reserves emerge as a part of the optimal policy. Depending upon the size of the habitat, the optimal strategy is either to avoid fishing or to fish at maximum rate. The effect of ocean currents is analyzed through numerical simulations. We find that in the presence of strong currents, a marine reserve may become ineffective. If the currents are at low rate, a marine reserve could emerge as a variable management tool.

Ocean currents determine functional connectivity in an Antarctic deep‐sea shrimp

AbstractThe coherency among larval stages of marine taxa, ocean currents and population connectivity is still subject to discussion. A common view is that organisms with pelagic larval stages have higher dispersal abilities and therefore show a relatively homogeneous population genetic structure. Contrary to this, local genetic differentiation is assumed for many benthic direct developers. Specific larval or adult migratory behavior and hydrographic effects may significantly influence distribution patterns, rather than passive drifting abilities alone. The Southern Ocean is an ideal environment to test for the effects of ocean currents on population connectivity as it is characterized by several well‐defined and strong isolating current systems. In this study we studied the genetic structure of the decapod deep‐sea shrimp Nematocarcinus lanceopes, which has planktotrophic larval stages. We analysed 194 individuals from different sample localities around the Antarctic continent using nine microsatellite markers. Consistent with a previous study based on mitochondrial DNA markers, primarily weak genetic patterns among N. lanceopes populations around the continent were found. Using ocean resistance modeling approaches we were able to show that subtle genetic differences among populations are more likely explained by ocean currents rather than by geographic distance for the Atlantic Sector of the Southern Ocean.

Path optimization for marine vehicles in ocean currents using reinforcement learning

This study proposes a path planning algorithm for marine vehicles based on machine learning. The algorithm considers the dynamic characteristics of the vehicle and disturbance effects in ocean environments. The movements of marine vehicles are influenced by various physical disturbances in ocean environments, such as wind, waves, and currents. In the present study, the effects of ocean currents are the primary consideration. A kinematic model is used to incorporate the nonholonomic motion characteristics of a marine vehicle, and the reinforcement learning algorithm is used for path optimization to generate a feasible path that can be tracked by the vehicle. The proposed approach determines a near-optimal path that connects the start and goal points with a reasonable computational cost when the map and current field data are provided. To verify the optimality and validity of the proposed algorithm, a set of simulations were performed in simulated and actual ocean current conditions, and their results are presented.

Quasi-Static Analysis of the Multicomponent Mooring Line for Deeply Embedded Anchors

Multicomponent taut mooring lines are widely used to secure floating facilities to anchors embedded in the seabed to restrict motions. Optimal design of the mooring line system requires a realistic model of the combined performance of all segments of the mooring line, including the separate segments contained within both the water column and the soil column. This paper presents a two-dimensional quasi-static model, which can analyze mooring lines comprising multiple types of mooring lines or chains, taking into account the effects of ocean currents, soil resistance, and elastic elongation of mooring line. An example analysis is carried out to predict the responses of multicomponent mooring line during pretension and under service conditions. The example analysis puts special focus on conditions where the floating facility undergoes a series of motion away from its original position to assess the effect of the vertical offset is studied in detail. Finally, based on the presented model, the performances of different components of the mooring system are thoroughly investigated and some useful conclusions are drawn.