In maritime safety research, risk is assessed usually within the framework of formal safety assessment (FSA), which provides a formal and systematic methodology to improve the safety of lives, assets, and the environment. A bespoke application of FSA to mitigate accidents in marine seismic surveying is put forward in this paper, with the aim of improving the safety of seismic vessel operations, within the context of developing an economically viable strategy. The work herein takes a close look at the hazards in North Sea offshore seismic surveying, in order to identify critical risk factors, leading to marine seismic survey accidents. The risk factors leading to undesirable events are analysed both qualitatively and quantitatively. A risk matrix is introduced to screen the identified undesirable events. Further to the screening, Fault Tree Analysis (FTA) is presented to investigate and analyse the most critical risks of seismic survey operation, taking into account the lack of historical data. The obtained results show that man overboard (MOB) event is a major risk factor in marine seismic survey operation; lack of training on safe work practice, slippery deck as a result of rain, snow or water splash, sea state affecting human judgement, and poor communication are identified as the critical risk contributors to the MOB event. Consequently, the risk control options are focused on the critical risk contributors for decision-making. Lastly, suggestions for the introduction and development of the FSA methodology are highlighted for safer marine and offshore operations in general.

This study developed a new methodology for analyzing the risk level of marine spill accidents from two perspectives, namely, marine traffic density and sensitive resources. Through a case study conducted in Busan, South Korea, detailed procedures of the methodology were proposed and its scalability was confirmed. To analyze the risk from a more detailed and microscopic viewpoint, vessel routes as hazard sources were delineated on the basis of automated identification system (AIS) big data. The outliers and errors of AIS big data were removed using the density-based spatial clustering of applications with noise algorithm, and a marine traffic density map was evaluated by combining all of the gridded routes. Vulnerability of marine environment was identified on the basis of the sensitive resource map constructed by the Korea Coast Guard in a similar manner to the National Oceanic and Atmospheric Administration environmental sensitivity index approach. In this study, aquaculture sites, water intake facilities of power plants, and beach/resort areas were selected as representative indicators for each category. The vulnerability values of neighboring cells decreased according to the Euclidean distance from the resource cells. Two resulting maps were aggregated to construct a final sensitive resource and traffic density (SRTD) risk analysis map of the Busan–Ulsan sea areas. We confirmed the effectiveness of SRTD risk analysis by comparing it with the actual marine spill accident records. Results show that all of the marine spill accidents in 2018 occurred within 2 km of high-risk cells (level 6 and above). Thus, if accident management and monitoring capabilities are concentrated on high-risk cells, which account for only 6.45% of the total study area, then it is expected that it will be possible to cope with most marine spill accidents effectively.

A series of tests of a full-scale river icebreaker was conducted to investigate the characteristics of ice-induced hull vibration. The test was conducted when the river icebreaker was operating in an ice-covered river at temperatures of -4 to 0 ℃ with ice thicknesses of 300 to 400 mm. In the tests, the ice condition and icebreaker speed were chosen as the main influence factors. By analyzing the measured test data, we identified some important points regarding ice-induced hull vibration. When the river icebreaker navigates in an area with complete ice coverage, the peak value of the acceleration amplitude spectrum is highest. Also, the vibration response excited by the icebreaking load in an area with complete ice coverage exhibits more frequencies. With an increase in icebreaker speed, the vibration acceleration response gradually increases. However, habitability of the bow region on the main and driving decks is maintained due to the harmless vibration levels. In addition, the icebreaking operation of the river icebreaker causes violent local vibration of the grillage on the main deck.

Welding residual stress in the engineering structure has a non-negligible influence on crack propagation, and crack closure is a significant factor affecting the crack propagation. Based on the elastoplastic finite element method and crack closure theory, we studied crack closure and residual compressive stress field of butt-welded plates under constant amplitude loading and overloading regarding the stress ratio, maximum load, overload ratio, and number of overloads. The results show that the welding residual tensile stress can decrease the crack closure because of a decrease in the residual compressive stress in the wake zone, but the effect is gradually reduced with increased stress ratio or maximum load. And the combined effect of welding residual tensile stress and overload can produce a stronger retardation effect on crack propagation.

Stealth security has always been considered as an important guarantee for the vitality and combat effectiveness of submarines. In accordance with the stealth requirements of submarines performing stealth voyage tasks, this paper proposes a stealth assistant decision system. Firstly, the submarine stealth posture is acquired. A fuzzy neural network inference engine based on improved simplified particle swarm optimization is designed. The auxiliary decision-making scheme for state control and maneuver avoidance of submarine and its equipment is automatically generated. Secondly, the simulation and deduction of the assistant decision-making scheme are realized by the calculation modules of sound source level, propagation loss, and stealth situation. The assistant decision-making scheme and simulation result provide decision support for the commander. Thirdly, the simulation experiment platform of the submarine stealth assistant decision system is constructed. The submarine stealth assistant decision system described in this paper can quickly and efficiently produce assistant decision-making schemes, including submarine and equipment control and maneuver avoidance. The scheme is in line with the combat experience and the results of the pre-model simulation experiments, whereas the simulation deduction evaluates the rationality and effectiveness of the selected scheme. The submarine stealth assistant decision system can adapt to a complex battlefield environment in addition to rapidly and accurately providing assistance in decision-making.

Most wind turbine blades are assembled piece-by-piece onto the hub of a monopile-type offshore wind turbine using jack-up crane vessels. Despite the stable foundation of the lifting cranes, the mating process exhibits substantial relative responses amidst blade root and hub. These relative motions are combined effects of wave-induced monopile motions and wind-induced blade root motions, which can cause impact loads at the blade root’s guide pin in the course of alignment procedure. Environmental parameters including the wind-wave misalignments play an important role for the safety of the installation tasks and govern the impact scenarios. The present study investigates the effects of wind-wave misalignments on the blade root mating process on a monopile-type offshore wind turbine. The dynamic responses including the impact velocities between root and hub in selected wind-wave misalignment conditions are investigated using multibody simulations. Furthermore, based on a finite element study, different impact-induced failure modes at the blade root for sideways and head-on impact scenarios, developed due to wind-wave misalignment conditions, are investigated. Finally, based on extreme value analyses of critical responses, safe domain for the mating task under different wind-wave misalignments is compared. The results show that although misaligned wind-wave conditions develop substantial relative motions between root and hub, aligned wind-wave conditions induce largest impact velocities and develop critical failure modes at a relatively low threshold velocity of impact.

Heavy fuel oils require heated tanks to facilitate their transportation and processing. This paper proposes and investigates threeand four-level heating coil bundles. Numerical study revealed that powerful large-scale circulation of the heated fluid enhances heat transfer, delivering 16.7% and 23% improvements to the average heat transfer coefficient for the three- and four-level bundles, respectively. Furthermore, this circulation improves oil mixing and limits the variation in bulk oil temperature to - 0.3 to + 1.3 ℃ from the average. The study also quantified oil flow velocity near the bottom of the tank. The time-averaged horizontal components of velocity, estimated 25 mm and 50 mm above the bottom of the tank, exceed 2 mm/s and 4 mm/s, respectively. The proposed heating coil bundles feature a compact design that reduces the material and labor costs of construction and that, by occupying only a small portion of the bottom of the tank, improves accessibility, maintenance, and cleaning.

Economic factors along with legislation and policies to counter harmful pollution apply specifically to maritime drive research for improved power generation and energy storage. Proton exchange membrane fuel cells are considered among the most promising options for marine applications. Switching converters are the most common interfaces between fuel cells and all types of load in order to provide a stable regulated voltage. In this paper, a method using artificial neural networks (ANNs) is developed to control the dynamics and response of a fuel cell connected with a DC boost converter. Its capability to adapt to different loading conditions is established. Furthermore, a cycle-mean, black-box model for the switching device is also proposed. The model is centred about an ANN, too, and can achieve considerably faster simulation times making it much more suitable for power management applications.

This paper aims to evaluate the feasibility of pressure-dependent models in the design of ship piping systems. For this purpose, a complex ship piping system is designed to operate in firefighting and bilge services through jet pumps. The system is solved as pressure-dependent model by the piping system analysis software EPANET and by a mathematical approach involving a piping network model. This results in a functional system that guarantees the recommendable ranges of hydraulic state variables (flow and pressure) and compliance with the rules of ship classification societies. Through this research, the suitability and viability of pressure-dependent models in the simulation of a ship piping system are proven.

More than 10 000 different types of ship ply the waters of Bangladesh all year round, but the performance of these ships in terms of CO₂ emission is not known and regulations related to energy efficiency of inland waterway ships remain nonexistent. This paper attempts to assess the present situation of inland class vessels in terms of Energy Efficiency Design Index (EEDI). With the use of a developed database of inland vessels in Bangladesh, EEDI reference lines for different types of inland vessels in Bangladesh were established and then compared with those of other countries. The present EEDI of existing inland vessels was investigated. Results indicate that most of the existing vessels do not meet the current EEDI baseline. Hence, new guidelines are necessary to achieve EEDI compliance in the near future. Some recommendations were proposed for improving CO₂ emissions, with the socioeconomic and technical factors in Bangladesh taken into consideration.

The outer-product decomposition algorithm (OPDA) performs well at blindly identifying system function. However, the direct use of the OPDA in systems using bandpass source will lead to errors. This study proposes an approach to enhance the channel estimation quality of a bandpass source that uses OPDA. This approach performs frequency domain transformation on the received signal and obtains the optimal transformation parameter by minimizing the p-norm of an error matrix. Moreover, the proposed approach extends the application of OPDA from a white source to a bandpass white source or chirp signal. Theoretical formulas and simulation results show that the proposed approach not only reduces the estimation error but also accelerates the algorithm in a bandpass system, thus being highly feasible in practical blind system identification applications.

Breakwaters have been built throughout the centuries for the coastal protection and the port development, but changes occurred in their layout and criteria used for the design. Quarter circle breakwater (QBW) is a new type evolved having advantages of both caisson type and perforated type breakwaters. The present study extracts the effect of change in the percentage of perforations on the stable conditions of seaside perforated QBW by using various physical models. The results were graphically analyzed using dimensionless parameters and it was concluded that there is a reduction in dimensionless stability parameter with an increase in steepness of the wave and change in water depth to the height of breakwater structure. Multiple non–linear regression analysis was done and the equation for the best fit curve with a higher regression coefficient was obtained by using Excel statistical software—XLSTAT.

This study presents the results of a 2D numerical modeling investigation on the performance of non-reshaping berm breakwaters with a special look at the spatial distribution of irregular wave overtopping using FLOW-3D CFD code. The numerical model is based on Reynolds-Averaged Navier-Stokes solver (RANS) and volume of fluid (VOF) surface capturing scheme (RANS-VOF). The numerical model has been validated using experimental data. The armor and core porosities have been used as calibration factors to reproduce the wave overtopping distribution. The computed distributions of wave overtopping behind the structure agree well with the measurements for a non-reshaping berm breakwater. A formula is derived to relate the spatial distribution of wave overtopping water behind non-reshaping berm breakwaters to non-dimensional forms of wave height, wave period, berm width, berm height, and armor freeboard based on numerical results. This formula model agreed reasonably well with numerical model results.