Hasil untuk "Naval architecture. Shipbuilding. Marine engineering"

Nguyen Thi Huyen Trang, Taiga Mitsuyuki, Yoshiaki Hirakawa et al.

Wind power generation ships (WPG ships), which combine rigid sails for propulsion and underwater turbines for onboard power generation, have attracted increasing attention as a promising concept for utilizing renewable energy at sea. This study presents an integrated assessment of a WPG ship by combining towing-tank experiments, CFD simulations using ANSYS Fluent, and theoretical analysis to evaluate the coupled performance of sails, hull, and underwater turbines. First, sail thrust and bare-hull resistance were quantified to identify the effective operating-speed range under Beaufort 6–8 wind conditions, and the optimal number of rigid sails was determined. Based on a thrust–resistance balance at a representative rated operating point, two turbine configurations (two and four turbines) were preliminarily sized. The results show that ten rigid sails can provide near-maximum thrust without excessive aerodynamic interference, and the installation of turbines significantly reduces the feasible operating range compared to the bare-hull case. For the two-turbine configuration, a common effective ship-speed range of 6.58–8.0 m/s is obtained, whereas the four-turbine configuration is restricted to 6.58–7.44 m/s due to wake losses, additional appendage drag, and near-free-surface effects. The four-turbine configuration exhibits approximately 30% lower total power output than the two-turbine configuration. These findings demonstrate that an integrated, system-level evaluation is essential for WPG ship design and indicate that the two-turbine configuration offers a more favorable balance between power generation capability and operational flexibility.

Guoshuai Li, Shimiao Wang, Xianku Zhang et al.

To ensure the safe navigation of ships in rough seas while reducing steering gear energy consumption and losses, a steering control system with small rudder output angles, low steering frequency, and high control performance was designed. A third-order closed-loop gain-shaping algorithm was employed in the development of the controller, with the ultimate control strategy derived by embedding a nonlinear compound function between the proportional derivative (PD) controller and the second-order oscillation link to enhance control effectiveness. A nonlinear Nomoto model of the “Yupeng” ship was employed for simulation validation. The simulation results illustrated a 14.5% improvement in overall control performance achieved by the proposed controller compared to a nonlinear feedback controller. The controller’s robustness was additionally validated through the application of the Norrbin ship model. The proposed controller enhances the stability of ships in rough seas, effectively limiting the maximum rudder angle during turns and reducing the average rudder angle and steering frequency during navigation. This design aligns with practical requirements for maritime operations in heavy weather, contributing significantly to the economic, safe, and efficient navigation of ships.

Tao Jiang, Weigang Lu, Linguang Lu et al.

The axial-flow pump system has been widely applied to coastal drainage pump stations, but the hydraulic performance optimization based on the contraction angles of the inlet passage has not been studied. This paper combined the computational fluid dynamics (CFD) method, machine learning (ML) algorithms and genetic algorithm (GA) to find the optimal contraction angles of the inlet passage. The 125 sets of comprehensive objective function were obtained by the CFD method. Three contraction angles and comprehensive objective function values were regressed by three ML algorithms. After hyperparameter optimization, the Gaussian process regression (GPR) model had the highest <i>R</i>² = 0.958 in the test set and had the strongest generalization ability among the three models. The impact degree of the three contraction angles on the objective function of the GPR model was investigated by the Sobol sensitivity analysis method; the results indicated that the order of impact degree from high to low was <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mrow><mi>θ</mi></mrow><mrow><mn>3</mn></mrow></msub><mo>></mo><msub><mrow><mi>θ</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>></mo><msub><mrow><mi>θ</mi></mrow><mrow><mn>1</mn></mrow></msub></mrow></semantics></math></inline-formula>. The optimal objective function values of the GPR model and corresponding contraction angles were searched through GA; the maximum objective function value was 0.963 and corresponding contraction angles were <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mrow><mi>θ</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>=</mo><mn>13.34</mn><mo>°</mo></mrow></semantics></math></inline-formula>, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mrow><mi>θ</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>=</mo><mn>28.36</mn><mo>°</mo></mrow></semantics></math></inline-formula> and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mrow><mi>θ</mi></mrow><mrow><mn>3</mn></mrow></msub><mo>=</mo><mn>3.64</mn><mo>°</mo></mrow></semantics></math></inline-formula>, respectively. The results of this study can provide reference for the optimization of inlet passages in coastal drainage pump systems.

Yanli Guo, Yonghai Gao, Qingtao Gong et al.

Under shut-in conditions in deepwater drilling, the gas invading the bottomhole ascends along the wellbore and accumulates at the wellhead, forming a high-pressure trap, challenging wellbore pressure prediction and control. The accurate prediction of bottomhole pressure is essential for well control during shut-in conditions. In this study, a new bottomhole pressure prediction model that considers wellbore storage effects was developed to address gas invasion issues during shut-in conditions in deepwater drilling. This model incorporates factors such as the wellbore elasticity, fluid compressibility, and drilling fluid filtration loss. The calculated values show good agreement with experimental values, with the average absolute and relative errors of 2.095 × 10⁻² MPa and 3.71%, respectively. Meanwhile, the results indicate that the bottomhole pressure initially increases logarithmically over time and then transitions to a linear increase, and the residual flow and gas ascent significantly influence the bottomhole pressure. Finally, the effects of various parameters on the bottomhole pressure were evaluated. Larger initial pressure differential, exposed thickness, and formation permeability accelerate the increase in bottomhole pressure during residual flow stage, while smaller filter cake permeability and drilling fluid viscosity quicken its increase during gas ascent stage. Drilling fluid density affects the initial pressure and the residual flow duration. The findings of this study would provide theoretical support for well control operations in deepwater drilling.

Yuehua Gong, Shengxiong Yang, Jinqiang Liang et al.

Accurately identifying the Bottom Simulating Reflector (BSR) is a crucial and fundamental task in seismic exploration and the interpretation of gas hydrates in marine areas. During our seismic interpretation and inference work on a gas hydrate survey in the Qiongdongnan Sea area, we encountered a phenomenon that closely resembled the seismic reflection characteristics of BSR. By comparing and identifying various geological phenomena, we have determined that this unique seismic reflection phenomenon is, in fact, the reflection of the depositional bottom interface known as “mass transport deposits (MTDs)” as described by previous researchers. The physical properties of the MTDs developed on the shallow surface of the seafloor are similar to those of gas hydrate reservoirs in the seismic exploration of marine areas, particularly in the northern South China Sea’s Qiongdongnan Sea area. Due to the lack of active neotectonic movement in the area, most identified BSR reflection occurrences are parallel to the seafloor. Consequently, during the process of seismic interpretation of BSR in the Qiongdongnan Sea area, it may be confused with the bottom boundary reflection interface of MTDs. Accurately identifying MTDs’ sedimentary bodies in gas hydrate exploration activities in this area would greatly enhance the accurate identification of BSR and support the refined evaluation of gas hydrate resources. In this paper, the structural characteristics of MTDs are compared with the reflection characteristics of seismic profiles, the reflectors are identified as MTDs rather than BSR through analysis and interpretation, and the possible mechanism of hydrate accumulation in this region is discussed.

Naomasa Oshiro, Ana Gago-Martínez, Aurelia Tubaro

Marine biotoxins refer to bioactive natural products primarily produced by microalgae and bacteria and may affect aquatic organisms and human health [...]

Hongbo Li, Lin Ding, Qibiao Zang et al.

Reservoir sensitivity is a parameter that is used to evaluate the degree of change in reservoir permeability under the influence of external fluids. Accurate evaluation of reservoir sensitivity is conducive to the optimization of fluid parameters during exploration and development. Taking the Wenchang Formation and Enping Formation of the Paleogene in the Huilu area of the Pearl River Mouth Basin as the research object, reservoir sensitivity experiments were carried out. Combined with the corresponding experimental results obtained using methods such as thin section identification, scanning electron microscopy (SEM), X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), and screening analysis, based on mineral sensitization and pore structure sensitization, qualitative and quantitative evaluations of reservoir sensitivity were carried out, and factors affecting sensitivity and sensitization mechanisms were analyzed. This work shows the following: (1) The sandstone reservoirs in the two areas have the same clay type, but the total clay content of the Wenchang Formation is greater than that of the Enping Formation. The porosity of the Wenchang Formation is less developed than the Enping Formation. (2) The Wenchang Formation has weak or moderately weak water sensitivity and moderately weak or moderately strong flow velocity sensitivity. The water sensitivity of the Enping Group samples is moderately weak or moderately strong, the flow rate sensitivity is moderately weak, the alkali sensitivity is weak, the acid sensitivity is moderately weak, and the salinity sensitivity is moderately weak or moderately strong. (3) The sensitivity of the Wenchang Formation is mainly affected by the content of clay minerals. The sensitivity of the Enping Formation is also affected by the clay content and type. Although the clay content is not high, the permeability is more susceptible to sensitivity due to the pore structure and debris particle distribution characteristics. These conclusions are beneficial for the selection of fluid parameters and efficient reservoir development.

Chaoyue Zhang, Bin Lin, Chao Li et al.

Mobile edge computing is envisioned as a prospective technology for supporting time-sensitive and computation-intensive applications in marine vehicle systems. However, the offloading performance is highly impacted by the poor wireless channel. Recently, an Unmanned Aerial Vehicle (UAV) equipped with an Intelligent Reflecting Surface (IRS), i.e., UIRS, has drawn attention due to its capability to control wireless signals so as to improve the data rate. In this paper, we consider a multi-UIRS-assisted marine vehicle system where UIRSs are deployed to assist in the computation offloading of Unmanned Surface Vehicles (USVs). To improve energy efficiency, the optimization problem of the association relationships, computation resources of USVs, multi-UIRS phase shifts, and multi-UIRS trajectories is formulated. To solve the mixed-integer nonlinear programming problem, we decompose it into two layers and propose an integrated convex optimization and deep reinforcement learning algorithm to attain the near-optimal solution. Specifically, the inner layer solves the discrete variables by using the convex optimization based on Dinkelbach and relaxation methods, and the outer layer optimizes the continuous variables based on the Multi-Agent Twin Delayed Deep Deterministic Policy Gradient (MATD3). The numerical results demonstrate that the proposed algorithm can effectively improve the energy efficiency of the multi-UIRS-assisted marine vehicle system in comparison with the benchmarks.

Gajalakshmi G, Meenakshi S

This paper explores the intricate relationship between man and nature in Ernest Hemingway’s The Old Man and the Sea through the lens of deep ecology. It challenges the traditional anthropocentric interpretation of the novella, proposing that the protagonist Santiago’s struggle is not merely a tale of human triumph over nature but a journey towards understanding and coexisting with the natural world. By applying the principles of deep ecology, the study reveals how Santiago’s evolving relationship with the marlin and other sea elements reflects a broader ecological consciousness. The analysis also draws parallels between Santiago’s experience and the Biblical narrative of Jonah, suggesting that Santiago’s success is not solely due to his physical endurance but also the cosmic forces that aid him. This paper ultimately rethinks the themes of struggle and victory in the novella, emphasising the need for a harmonious relationship between humanity and the environment.

Dejene Tadesse Banjaw, Habtamu Gudisa Megersa

Garlic is a versatile vegetable commonly grown in subtropical and highland agroecosystems, which is utilized for its culinary, medicinal, and spice properties. The use of garlic as a medicinal aid can be traced back to ancient times. The health benefits of garlic production are attributed to its antiviral, antibacterial, and antifungal properties. The use of garlic is prevalent in both traditional and modern healthcare systems, where it is used to treat a wide range of conditions. Numerous studies have reported the therapeutic properties of garlic, and its effectiveness has been demonstrated in clinical trials. The growing global interest in health and wellness, the widespread use of garlic as a spice, and its potential economic, social, and health benefits have contributed to a surge in its demand worldwide. This review aims to provide a comprehensive overview of the scientific literature on the morphological descriptions of garlic and its nutritional and health significance.

LI Qian, JIANG Xin, ZHANG Junzhao, DUAN Shijie, JIN Yang

In this paper, large-scale energy storage system(ESS) is taken as the research object to conduct study of business models on the participation of ESS in electricity spot market with liberalization. First, based on the typical market clearing mechanism at home and abroad, the clearing method, clearing calculation process and so on in day-ahead market and real-time balance market are analyzed, and a joint clearing mechanism suitable for large-scale ESS to participate in the spot market is proposed, including bidding method, billing method and clearing method, etc. Then, in order to fully explore the market value and other added value of large-scale ESS, to enhance cluster effect and to solve the problem of idle ESS capacity, business models suitable for large-scale ESS to participate in the spot market are proposed, including independent (single investment entity, single service model), alliance (diversified investment entities, single service model), and shared (diversified investment entities, diversified service models) models. The game relationship in the market transaction chain is analyzed, of which the electric energy value, the ancillary service value, and other added value are quantified. On this basis, a bilevel clearing model paradigm for ESS to participate in the spot joint market of different business models is constructed based on the master-slave game. In the upper-level model, large-scale ESS is the leader to participate in market competition with the goal of maximizing profits, while the dispatching and trading center in the lower-level model are followers to jointly clear the market with the goal of maximizing social welfare. Finally, the validity and feasibility of the proposed business models are verified by taking typical transaction scenarios as examples based on the improved IEEE30 node system.

Eetu Heikkilä, Timo Malm, Risto Tiusanen et al.

Increasing automation is a major trend in container terminals. In automated container handling systems, safety has been previously ensured by segregating the automated machinery from other traffic and workers moving on foot. Currently, further increases in flexibility are sought by developing autonomous systems that are capable of mixed-traffic operations without the need for separate operating areas. This increases the complexity of the systems and introduces new safety hazards. In addition to traditional hazard analysis methods, new approaches are needed to address the emergent risks related to autonomous operations. This paper studies the applicability of the STPA (system-theoretic process analysis) method in hazard analysis of an autonomous machine system. To support the evaluation, we define evaluation categories for comparison of the analysis methods. We also compare STPA with an established method, HAZOP (hazard and operability study). To perform the comparison, both STPA and HAZOP are applied to an autonomous container handling system concept. The study suggests that both STPA and HAZOP are well suited to support the development of autonomous machinery. However, we also highlight some notable differences in the methods, mostly related to the different underlying accident models that they utilise. HAZOP is an established method with tools and standards available. STPA, on the other hand, provides a well-defined syntax to ensure the analysis quality and a system modelling approach that supports the system development.

Mikel Serrano-Antoñanazas, Jesús-Enrique Sierra-Garcia, Matilde Santos et al.

Compared to onshore turbines, floating offshore wind turbines (FOWTs) take advantage of the increased availability of offshore wind while causing less environmental impact. However, the strong winds, waves, and currents to which they are subjected trigger oscillations that can cause significant damage to the entire structural system and reduce its useful life. To reduce these loads, active tower damping techniques such as filter banks can be used. These filters must be carefully tuned to block specific vibration frequencies. Therefore, it is essential to analyze the nature of the oscillations in the FOWT and to understand how the frequencies vary in time. This topic is usually approached from a point of view very focused on a specific turbine. What is proposed here is a general method, which can be applied to any type of wind turbine, to automatically study the relationship between vibration frequencies and the degrees of freedom (DOF) of the turbine, which facilitates the design of structural control. Each frequency is associated with the DOF of the FOWT that produces it. This methodology has been successfully validated in simulation experiments with the NREL 5 MW ITI Barge FOWT. Under the wind conditions of the experiments, the main frequency found is 0.605 Hz. This frequency coincides with the 3P theoretical frequency of the FOWT. This proposal may help to design structural control systems able to damp these vibration frequencies with accuracy and efficiency.

Qiang Zhang, Shunhao Pu, Ming Yin

Transshipment hubs are important components of the global container shipping network. Nowadays, hybrid ports are emerging, handling both gateway and transshipment container traffic depending on their significant maritime connectivity. Effectively identifying transshipment hubs, including traditional transshipment hubs with high transshipment incidences and hybrid ports with sufficient transshipment capabilities, is crucial to gain a good understanding of container shipping networks. The method of reinforced structural holes (RSHs) has been introduced from the sociology to detect transshipment hubs at the global level, as it can fully consider the existence of separated cohesive port communities. The results show that the RSH-based approach is feasible to identify those hubs playing the role of bridges across different port communities worldwide, which is demonstrated from the perspective of maritime connectivity. The higher ranked hubs with higher RSH values generally have better maritime connections with ports from various port communities. Several policy implications have been further elaborated for relevant decision makers, such as liner companies and port operators.

Marek T. Hartman

According to the definition the effective value of voltage V is equal to Vrms as to the mean value of u(t) during the energy transfer time T or kT, where k may be 1, 2, 3, 4 etc. However, in power electronics circuits (e.g. rectifiers, choppers, converters, inverters) the energy transfer time, Δt, in many situations is less than the functions period, T (Δt < T). In such a situation the author asks a question – how can we calculate the effective value of voltage V?

Ming Ze Lee, Fatemeh Mekanik, Amin Talei

El Niño Southern Oscillation is one of the significant phenomena that drives global climate variability, showing a relationship with extreme events. Reliable forecasting of ENSO phases can minimize the risks in many critical areas, including water supply, food security, health, and public safety on a global scale. This study develops an ENSO forecasting model using the dynamic evolving neural fuzzy inference system (DENFIS), an artificial intelligence-based data-driven algorithm. To forecast ENSO phases for 1, 2, and 3 months ahead, 42 years (1979–2021) of monthly data of 25 oceanic and continental climatic variables and ENSO-characterizing indices are used. The dataset includes 12 El Niño and 14 La Niña events, of which the latest 2 El Niño and 4 La Niña events are reserved for testing while the remaining data are used for training the model. The potential input variables to the model are short-listed using a cross-correlation analysis. Then a systematic input selection procedure is conducted to identify the best input combinations for the model. The results of this study show that the best performing combination of such climate variables could achieve up to 78.57% accuracy in predicting short-term ENSO phases (up to 3 months ahead). Heat content at 0 to 300 m of central equatorial Pacific shows promising performance in forecasting ENSO phases. Moreover, DENFIS was found to be a reliable tool for forecasting ENSO events using multiple oceanic and continental climate variables.

Mathijs Carmen, Simon D. Berrow, Joanne M. O’Brien

The Shannon Estuary in Ireland is home to a resident population of bottlenose dolphins (<i>Tursiops truncatus</i>) and is designated as a Special Area of Conservation under the EU Habitats Directive. It is an important industrial area, with numerous deep-water berths for shipping. Despite its high conservation value, there are few published studies on habitat use or foraging behavior of the Shannon dolphins throughout the year. The present study assessed the year-round presence and foraging activity of bottlenose dolphins at different locations in the middle and inner estuary using static acoustic monitoring. Dolphin presence was found to decrease with increased distance from the estuary mouth, i.e., where the estuary meets the Atlantic Ocean, while at the same time, foraging was found to be considerably higher in the upriver areas, suggesting the inner estuary was an important foraging area. Model predictions for seasonal, tidal and diel foraging were highly variable across locations, indicating that changes in dolphin behavior occurred over relatively small geographical scales. These results indicate that conservation efforts should consider the Shannon Estuary as a dynamic aggregation of habitats and future development initiatives should attempt to mitigate disturbance to the dolphins during important foraging periods on seasonal and diel scales.

Ximun Lastiri, Stéphane Abadie, Philippe Maron et al.

Wave resource assessment is the first step toward the installation of a wave energy converter (WEC). To support initiatives for wave energy development in the southwest of France, a coastal wave database is built from a 44-year hindcast simulation with the spectral wave model SWAN (Simulating WAve Nearshore) run on a high-resolution unstructured grid. The simulation includes shallow-water processes such as refraction, shoaling, and breaking. The model is validated against a five-year coastal wave buoy recording. The study shows that most of the resource is provided by sea states with wave heights ranging from 2 to 5 m, with wave periods from 10 and 15 s, and coming from a very narrow angular sector. The long hindcast duration and the refined unstructured grid used for the simulation allow assessment of the spatiotemporal distribution of wave energy across the coastal area. On the one hand, large longshore variations of the resource caused by steep bathymetric gradients such as the Capbreton submarine canyon are underlined. On the other hand, the study highlights that no specific long-term trend can be extracted regarding the coastal wave energy resource evolution. The provided downscaled local wave resource information may be used to optimize the location and design of a future WEC that could be deployed in the region.

Fotini Botsou, Aristomenis P. Karageorgis, Vasiliki Paraskevopoulou et al.

The Antinioti Lagoon is a karstified, rather pristine, and shallow coastal lagoon located in the northern part of Corfu Island in NW Greece. The present study examines the levels of metals (Al, Fe, Mn, Cd, Cu, Pb, and Zn) in the dissolved and particulate phase, as well as in surface and core sediments, and identifies the critical processes that define their behavior. The major transport pathway of dissolved Mn, Cd, and Pb, and particulate Mn, Cd, and Zn into the lagoon is through freshwater springs, whereas surface runoff dominates the transport of particulate Al, Fe, and Cu. Interestingly, large particles (&gt;8 &#956;m) contain higher amounts of Al, Fe and Mn than the finer ones (&lt;8 &#956;m), due to flocculation of oxyhydroxides that, eventually, scavenge other metals, as well. Cadmium and Zn bound to the large particles were found to be less prone to desorption than the smaller ones and were effectively captured within the lagoon. In the sediments, diagenetic processes are responsible for post-depositional changes in the forms of metals (particularly Fe, Mn and Cd). Enrichment factors (EFs) based on local background showed that sediments are enriched in restricted areas in Cd and Pb by maximum factors 4.8 and 10, respectively. These metals were predominantly found in potentially labile forms. Thus, any interventions introducing changes in the physico-chemical conditions may result in the release of metals, with negative implications on the lagoon&#8217;s ecological quality.

Isabel Cardoso, João Cotas, Ana Rodrigues et al.

Nowadays, the development of new drugs only relies on a small number of molecules and 50% of all existent drugs are extracted or synthetically obtained. This work intends to evaluate the antibacterial potential of the ethanolic and polysaccharide extracts obtained from <i>Grateloupia turuturu</i> and to characterize the composition of the alga&#8217;s polysaccharides by FTIR-ATR. We used sequential extraction to obtain the extracts that were tested against <i>S. aureus</i> and <i>E. coli</i>. The ethanolic extracts in <i>E. coli</i>, at the highest concentration used (15 mg mL^&#8722;1) showed 45.7% (Tetrasporophyte extract) and 55.1% (Carposporophyte extract) of growth reduction and in <i>S. aureus</i> 56.2% (T extract) and 51.8% (C extract). Polysaccharide extracts started showing significant reduction effect on <i>E. coli</i> and <i>S. aureus</i> growth at 7.5 mg mL^&#8722;1 with a reduction of 54.9% and 39.5%, respectively. At 15 mg mL^&#8722;1 the reduction observed was 88.5% and 85.4%. The FTIR-ATR allowed to characterize <i>G. turuturu</i>&#8217;s polysaccharides concluding that it is composed by a hybrid kappa/iota carrageenan with traces of agar, in both phases of the life cycle. This work allows us to conclude about the antibacterial properties of this alga and the compounds that might be behind this activity, showing that there&#8217;s a lot more than a small number of molecules that can be used as natural drugs.