Franco Antonio Rocha-Díaz, María Adela Monreal-Gómez, Erik Coria-Monter
et al.
This study evaluated how the summer circulation pattern in the Southern Gulf of California influences copepod communities. The evaluation was based on hydrographic data and zooplankton samples collected during a multidisciplinary research cruise conducted in June and July of 2019. The results revealed the presence of a cyclonic circulation with a diameter of approximately 100 km, located near the entrance of the Gulf, affecting the upper 200 m layer. A total of 30 copepod species were identified, including 20 from the order Calanoida and 10 from Cyclopoida. The most abundant Calanoida species were <i>Canthocalanus pauper</i>, <i>Clausocalanus furcatus</i>, and <i>Subeucalanus subcrassus</i>, with respective densities of 2316.80, 1593.60, and 1584.64 ind m<sup>−3</sup>. The most abundant Cyclopoida species were <i>Oithona setigera</i>, <i>Dioithona rigida</i>, and <i>Oncaea venusta</i>, which had densities of 963.44, 290.56, and 235.52 ind m<sup>−3</sup>, respectively. The horizontal distribution of these species showed variations influenced by the cyclonic circulation. Specifically, low abundance values were observed at the center of cyclonic circulation, while higher values were found at its periphery. This pattern was consistent among the dominant species, indicating that they do not benefit from the cold subsurface waters induced by circulation. In fact, the distribution of some species was higher in a band of warm water located in the eastern portion of the study area. Overall, our findings shed light on how the summer cyclonic circulation in the Southern Gulf of California affects the copepod community, an aspect that has not been previously explored. This research enhances our understanding of the processes influencing this group of organisms in a highly dynamic environment.
Marine gas hydrates are recognized as a promising offshore energy resource. Self-heat fluid injection is an innovative thermal-enhanced gas recovery technique for hydrate exploitation engineering. This study numerically investigates hydrate saturation during the self-heating reagent injection process in a sub-sea hydrate reservoir, decoupled from gas production interference. This process employs two consecutive stages: reactive chemical flow stage followed by non-reactive flow stage. The simulation output parameters encompass reservoir temperature, fluid saturation, thermal conductivity, and heat flow rate. The base case demonstrates that fluid injection elevates reservoir temperature from 13.0 °C to 29.3 °C and reduces hydrate saturation from 0.40 to 0.21 through coupled heat–mass transfer mechanisms during the reactive flow stage. In the consequent non-reactive flow stage, hydrate saturation decreases to zero. Sensitivity analysis reveals that initial permeability variation governs the hydrate saturation and temperature during the non-reactive phase. The permeability range of less than 15 mD is the optimal threshold preventing hydrate reformation during fluid injection. 55–70 mD permeability triggers severe secondary hydrate generation, which decreases the fluid application feasibility. Fluid flooding demonstrates superior hydrate dissociation efficacy compared to in situ thermal stimulation. This study develops a novel simulation approach to characterize marine hydrate saturation dynamics.
Inland LNG-fuelled liner shipping is emerging as a significant trend, yet limited refueling infrastructure presents operational challenges. The complexity of inland navigation requires frequent speed adjustments to meet scheduled arrivals, which directly affects fuel consumption and refueling strategies. Additionally, imbalances in domestic and foreign trade container flows further increase operating costs for liner shipping companies. Given estimated weekly demands, considering navigational restrictions such as water depth and bridge clearance, as well as streamflow velocity, port time windows, empty container repositioning, port selection, speed adjustment, and uncertain fuel consumption, two novel models based on empty container arc variables and node variables are formulated, aiming to maximize voyage profit. These models are extended from divisible demand to indivisible demand cases. The explicit expression for the maximum fuel consumption under the worst-case speed deviation is derived, and an external linear approximation algorithm is proposed to linearize the nonlinear models while controlling approximation errors. Furthermore, the NP-hardness of the problem, the strict equivalence of the two modeling approaches, and the solution properties are proved. A case study of LNG-fuelled liner shipping on the Yangtze River shows the following: (1) for divisible demand, both models achieve optimal solutions within seconds, while for indivisible demand, the node-variable model outperforms the arc-variable model; (2) tactical strategies should be flexibly adjusted based on seasonal water depth, fuel prices, carbon taxes, speed deviations, and expected lock passage times; and (3) increasing fuel prices and carbon taxes generally reduce port calls and sailing speeds, suggesting that stricter fuel price and carbon tax policies can support the transition to green shipping. This study provides both theoretical guidance and managerial insights, supporting shipping companies in optimizing operations and promoting the development of sustainable inland shipping.
Objectives To overcome the challenges of tracking small targets in unmanned surface vehicle vision under the conditions of low feature resolution and similar environmental information, a multi-feature fusion-based continuous convolution operator tracking （MCCOT） algorithm is proposed. Methods The resolution of multi-feature maps is enhanced using bicubic interpolation techniques to enable sub-pixel-level localization. Efficiencies in target tracking are achieved through feature projection and sample space generation to mitigate filter overfitting. Furthermore, interference arising from similar environmental features on the filter is addressed by developing an update strategy for high-confidence models. Results As the experimental results show, compared to traditional continuous convolution operator tracking algorithms, the proposed algorithm achieves an average success rate increase of 17.4%, average distance precision increase of 17.8%, and expected average overlap rate increase of 5.1%. Conclusions The proposed algorithm can deal with the problem of small target tracking confusion in marine environments, providing key technical support for improving the intelligent sensing capability of unmanned boats and marine robots.
Solar radiation, particularly ultraviolet radiation (UVR, 280–400 nm), is known to play a significant role in driving primary production in marine ecosystems. However, our understanding of the specific effects of UVR on the primary production of natural phytoplankton communities is still limited. We utilized the <sup>13</sup>C stable isotope to quantify primary production and conducted experiments using different types of incubation bottles (polycarbonate and quartz bottles) to compare the primary production in the absence and presence of UVR. Although we observed a weak inhibitory effect at the surface of the water column, UVR exposure resulted in an approximately 1.5-fold increase in primary production over the euphotic zone. The enhanced primary production during the study period can be attributed to the combined effect of low UVB (280–320 nm) dose and abundant nutrient conditions. Notably, our size-fractionated measurements revealed that UVR exposure led to a two-fold increase in primary production in large cells (>2 μm) compared to the exposure of solely photosynthetically active radiation (PAR). In contrast, there was no significant difference in the primary production of small cells (<2 μm) between the absence and presence of UVR. These findings highlight the advantages of large cells when exposed to UVR, emphasizing the importance of phytoplankton cell size in determining their response to UVR. However, it is important to note that the effects of UVR on phytoplankton are influenced by various environmental factors, which interact with solar radiation, shaping the dynamics of phytoplankton responses to UVR.
Guilherme Muricy, Anaíra Lage, Joana Sandes
et al.
Submarine caves are important biodiversity reservoirs, but there is little information about the biota of marine caves in the Southwestern Atlantic. Here, we describe three submarine cavities and their sponge communities on the Fernando de Noronha Archipelago, Northeast Brazil. The underwater cavities were explored and collections were made through scuba diving from 5 to 18 m depths. Sapata Cave has a wide semi-dark zone near the entrance, a narrow transition zone, and a dark chimney, which is closed at the top. Ilha do Meio Cave is narrower and shallower than Sapata Cave, but has a long passage that leads to two completely dark rooms. Pedras Secas Tunnel has only a semi-dark zone with high water movement. The sponge communities in the semi-dark zones of the three cavities are rich and dominated by the classes Demospongiae and Homoscleromorpha, but Calcarea are also common. The transition zones of both caves are dominated by a desma-bearing sponge, thinly encrusting spirastrellids, and small Homoscleromopha and Calcarea. The dark zone in Ilha do Meio Cave is almost azoic, with only three species. This study has increased the number of sponge species known in submarine cavities on Fernando de Noronha from 29 to 69, highlighting the great richness of the sponge communities in these cryptic environments.
ObjectivesThe aim of this paper is to obtain test scenarios of autonomous collision avoidance for inland waterway ships by modeling. MethodsStarting with the automatic identification system (AIS) and radar data collection and fusion method, a ship navigation data collection and fusion system is established. Taking the inland waterway between the Three Gorges Dam and Gezhouba Dam as an example, ship scenario elements are collected and analyzed, and a parametric generation method of inland waterway collision avoidance test scenarios is proposed which can automatically generate a ship collision avoidance test scenario by setting a series of parameters. Taking two-ship and multi-ship encounters scenario as examples, a series of test scenarios are generated and simulated. ResultsThe collision avoidance simulation tests results show that the parameterized test scenario generation method proposed herein can effectively test the autonomous ship collision avoidance algorithm. ConclusionsThe research providing a basis for improving the pertinence and practicality of inland river smart ship collision avoidance testing.
The compression deformation of the measuring membrane of the differential pressure capacitance sensor is studied. The classical von Kármán thin plate theory is applied to the elastic circular thin plate subjected to pretension, and the approximate analytical solution is given by adopting the homotopy analysis method. The results are compared with the simulation results of the finite element software ANSYS, which shows that they have a high degree of agreement. The magnitude of pretension has a great influence on the deformation of the membrane under compression, thus affecting the capacitance output characteristics of the sensor. The effect of pretension on the nonlinear characteristic of the sensor is verified by the sensor performance test. The results suggest that the linearity of the sensor can be effectively improved by selecting the appropriate pretension, and the sensitivity of the output can be improved by appropriately reducing the membrane thickness. The analysis results have an important reference value for the design of membrane of differential pressure capacitance sensors.
Engineering (General). Civil engineering (General), Chemical engineering
The load resistance factor according to the target reliability level was proposed using 16 vertical breakwaters constructed along the coast of Korea. Limit state functions for sliding and overturning limit states were defined. Reliability analysis was performed to obtain the sensitivity of the limit state function to the design variables. The partial safety factors of the design variable were obtained using the sensitivity, and the load resistance factor was calculated in turn. The representative value of load resistance factors was obtained by optimizing the load resistance factors for 16 vertical breakwaters, and it was verified that the breakwater designed using the representative value had a reliability index greater than the target value.
Applying fin stabilizers is an effective solution for ship rolls on waves in a seaway. They generally consist of one or two pairs of retractable fins that are symmetrically mounted to both sides of the ship, effectively reducing the roll motion at low or moderate speeds. Fin stabilizers are commonly used by cruise ships for the comfort and safety of passengers. However, there is still little experimental and numerical analysis of the fins’ effect on hydrodynamic performance. In this study, the resistance performance of a cruise ship was investigated with/without fin stabilizers at different fin angles and ship velocities by model tests and numerical analysis. The CFD analysis provides a flow-detailed interpretation of the physical phenomenon, especially at an asymmetric maximum fin angle. The significant fin-induced resistance is newly discovered and averages up to 19% in calm water conditions, while the added resistance in waves is evaluated with a smaller increment up to 1.31%. By comparing the numerical and experimental results, this study provides insight into the resistance induced by overhanging fins, which provides an accurate prediction reference for cruise ship performance and benefits the fin stabilizers’ design and selection.
This paper investigates the automatic berthing problem of underactuated surface vessels in the case of uncertain dynamics and yaw rate limitation, given the importance of yaw rate control and the unmeasurable hydrodynamic parameters of the vessel at low speeds. First, we use the differential homeomorphism coordinate transformation to solve the problem of underactuation. Second, a radial basis function network (RBF) is introduced to approximate unknown nonlinear functions. Third, we apply the barrier Lyapunov function (BLF) approach to limit the yaw rate within a safe range. Fourth, we use dynamic surface control (DSC) technology and minimum learning parameters (MLP) to tackle the differential explosion problems in backstepping and computational complexity. Finally, Lyapunov stability theory proves that signals produced by the designed control scheme are bounded and effective. The simulation results show that, compared with the control scheme without BLF, the proposed method can effectively limit the yaw rate within a specific range and effectively solves the influence of the model uncertainly.
Kai Ziervogel, Manoj Kamalanathan, Antonietta Quigg
Biological oil weathering facilitated by specialized heterotrophic microbial communities plays a key role in the fate of petroleum hydrocarbon in the ocean. The most common methods of assessing oil biodegradation involve (i) measuring changes in the composition and concentration of oil over time and/or (ii) biological incubations with stable or radio-labelled substrates. Both methods provide robust and invaluable information on hydrocarbon biodegradation pathways; however, they also require extensive sample processing and are expensive in nature. More convenient ways to assess activities within microbial oil degradation networks involve measuring extracellular enzyme activity. This perspective article synthesizes previously published results from studies conducted in the aftermath of the 2010 Deepwater Horizon (DwH) oil spill in the northern Gulf of Mexico (nGoM), to test the hypothesis that fluorescence assays of esterases, including lipase activity, are sensitive indicators for microbial oil degradation in the ocean. In agreement with the rates and patterns of enzyme activity in oil-contaminated seawater and sediments in the nGoM, we found close correlations between esterase activity measured by means of methylumbeliferyl (MUF) oleate and MUF butyrate hydrolysis, and the concentration of petroleum hydrocarbons in two separate laboratory incubations using surface (<1 m) and deep nGoM waters (>1200 m). Correlations between esterase activities and oil were driven by the presence of chemical dispersants, suggesting a connection to the degree of oil dissolution in the medium. Our results clearly show that esterase activities measured with fluorogenic substrate proxies are a good indicator for oil biodegradation in the ocean; however, there are certain factors as discussed in this study that need to be taken into consideration while utilizing this approach.
To achieve rapid and flexible vertical profile exploration of deep-sea hybrid structures, a multi-joint autonomous underwater vehicle (MJ-AUV) with orthogonal joints was designed. This paper focuses on the 3-dimensional (3D) modeling and attitude control of the designed vehicle. Considering the situation of gravity and buoyancy imbalance, a 3D model of the MJ-AUV was established according to Newton’s second law and torque balance principle. And then the numerical simulation was carried out to verify the credibility of the model. To solve the problems that the pitch and yaw attitude of the MJ-AUV are coupled and the disturbance is unknown, a linear quadratic regulator (LQR) decoupling control method based on a linear extended state observer (LESO) was proposed. The system was decoupled into pitch and yaw subsystems, treated the internal forces and external disturbances of each subsystem as total disturbances, and estimated the total disturbances with LESO. The control law was divided into two parts. The first part was the total disturbance compensator, while the second part was the linear state feedback controller. The simulation results show that the overshoot of the controlled system in the dynamic process is nearly 0 rad, reaching the design value very smoothly. Moreover, when the controlled system is in a stable state, the control precision is within 0.005%.
Dynamic collision avoidance between multiple vessels is a task full of challenges for unmanned surface vehicle (USV) movement, which has high requirements on real-time performance and safety. The difficulty of multi-obstacle collision avoidance is that it is hard to formulate the optimal obstacle avoidance strategy when encountering more than one obstacle threat at the same time; a good strategy to avoid one obstacle sometimes leads to threats from other obstacles. This paper presents a dynamic collision avoidance algorithm for USVs based on rolling obstacle classification and fuzzy rules. Firstly, potential collision probabilities between a USV and obstacles are calculated based on the time to the closest point of approach (<i>TCPA</i>). All obstacles are given different priorities based on potential collision probability, and the most urgent and secondary urgent ones will then be dynamically determined. Based on the velocity obstacle algorithm, four possible actions are defined to determine the basic domain in the collision avoidance strategy. After that, the Safety of Avoidance Strategy and Feasibility of Strategy Adjustment are calculated to determine the additional domain based on fuzzy rules. Fuzzy rules are used here to comprehensively consider the situation composed of multiple motion obstacles and the USV. Within the limited range of the basic domain and the additional domain, the optimal collision avoidance parameters of the USV can be calculated by the particle swarm optimization (PSO) algorithm. The PSO algorithm utilizes both the characteristic of pursuance for the population optimal and the characteristic of exploration for the individual optimal to avoid falling into the local optimal solution. Finally, numerical simulations are performed to certify the validity of the proposed method in complex traffic scenarios. The results illustrated that the proposed method could provide efficient collision avoidance actions.
The research problem discussed in this paper is of relevance to floating offshore wind turbine design, where heave plates are attached to the columns of a semi-submersible in order to improve vertical plane stability and the power output. Because of the shallow draft of these structures, the heave plates are proximal to the water surface. When subject to vertical plane motions the flow around a plate is altered by the presence of the free surface, resulting in changes in added mass and damping forces. In this paper, we present the experimental results for the added mass and damping coefficients for circular heave plates attached to a column, when oscillating in heave in the presence of oncoming waves. The results tend to indicate that applying the hydrodynamic coefficients obtained from still water experiments for a structure moving in waves may only be an approximation. For different relative phases of the wave and the motion, large variations could occur. We define a modified Keulegan—Carpenter (<inline-formula><math display="inline"><semantics><mrow><mi>K</mi><mi>C</mi></mrow></semantics></math></inline-formula>) number that depends on the relative amplitude of motion with respect to the wave. With this definition, the added mass and damping values are seen to be closer to the still water trends. However, at lower <inline-formula><math display="inline"><semantics><mrow><mi>K</mi><mi>C</mi></mrow></semantics></math></inline-formula> values, the added mass coefficients could differ by 30%, which can affect natural frequency estimates. Thus, caution needs to be exerted in the selection of hydrodynamic coefficients for heave plates oscillating in proximity to the free surface.
Izabela Michalak, Katarzyna Chojnacka, Daniel Korniewicz
In the present study, the effect of macroalga <i>Enteromorpha</i> sp. enriched with Zn(II) and Cu(II) ions on daily amounts of feces and urine excreted by growing pigs, apparent fecal nutrient digestibility and daily nitrogen balance and retention, meat quality and the slaughter value of carcasses was examined. The duration of feeding experiments was 87 days. In the control group, the requirement for zinc and copper was covered by inorganic salts, whereas in the experimental group algae enriched with these elements via biosorption were supplemented. No effect of <i>Enteromorpha</i> sp. on the increase in digestibility of dry matter, dry organic matter, crude protein, crude fat and nitrogen-free extractives was observed. Statistically significant differences concerned only the digestibility of crude ash. The daily amount of excreted feces and urine did not differ significantly between groups. Meat from pigs in the algal group was characterized by a lower water absorption and drip loss and contained less fat and more protein than meat from the control group. Furthermore, a slight darkening of the meat was observed. The weight of the liver was lower in pigs from the algal group. Enriched macroalga <i>Enteromorpha</i> sp. may be introduced into pig nutrition as a feed material as an alternative to inorganic salts.