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Composite materials are increasingly utilized in engineering due to their superior properties such as strength, flexibility, and corrosion resistance. However, accurately predicting the buckling pressure of composite cylindrical shells under external loads remains challenging due to the complexities introduced by various stacking methods. This study addressed this challenge by integrating advanced machine learning techniques with simulation-based data generation through finite element analysis (FEA). A comprehensive dataset comprising 1369 simulation results was generated using ANSYS ACP, focusing on cylindrical shells modeled with an 8-mm-thick filament winding technique and T700 material. The stacking angles ranged from −90 degrees to 90 degrees in 5-degree increments. Stacking configurations (inputs) and their corresponding buckling strength (outputs) were generated using ANSYS ACP. Machine learning models, including linear regression, elastic net, polynomial regression, random forest, support vector regression, XGBoost regression, and artificial neural networks, were implemented using Python 3.8 and Scikit-learn (version 0.24.2). A comparative analysis of these methods revealed their model performance, providing insights into the most effective approaches. Additionally, the accuracy of these models was then evaluated on previously unseen input data, allowing for a comparison of their out-of-sample accuracy. The results demonstrated that the random forest model and XGBoost regression achieved superior accuracy with minimal prediction errors. The study highlights the critical role of machine learning in predicting buckling pressure, which is essential for ensuring structural integrity and optimizing performance in marine engineering and other applications involving composite materials. [ABSTRACT FROM AUTHOR]

Thermochemical conversions of nonedible biomass into energy are promising alternatives for ensuring a sustainable energy society. However, determining the optimum design and operating conditions of the processes remains a major challenge due to the laborious and costly experimental methods. Machine learning techniques are cost-effective and non-time consuming and have been widely utilized in thermochemical conversion process modelling with robust and accurate results and solutions. Nonetheless, no standard method has been proposed for applying ML models to biomass thermochemical processes. Consequently, the general development procedure for ML models with high accuracy and robustness remains unclear. This review provides a comprehensive review of machine learning techniques for predicting biofuel yield and composition. It is recommended that quality datasets be ensured to enable the development of more robust machine learning-aided models for practical engineering applications. Finally, solutions to the identified challenges and prospective future research directions on machine learning-based biomass thermochemical conversion processes are recommended to accelerate the optimization and large-scale deployment of these processes. [ABSTRACT FROM AUTHOR]

This paper presents the structural assessment of a 500-cbm liquefied natural gas bunker ship, which is operated as a ship-to-ship transporter in the coastal area of South Korea, under collision accidents by a numerical approach. Based on marine traffic data, it was assumed that an oil tank is the colliding ship and the bunker ship is the struck ship. A non-linear finite element analysis was conducted under credible scenarios to consider the hydrodynamic response on the struck ship. It was compared to the structural response of the struck ship in bunkering which does not consider the hydrodynamic effect. In addition, major collision parameters that lead to severe damage on the struck ship was observed, and the specific values for ship speed and displacement of a third-party colliding ship during bunkering were suggested to minimise the risk of structural failure. [ABSTRACT FROM AUTHOR]

Liquefied natural gas (LNG)-fuelled ships provide a good option for the air pollution problem. However, safety and reliability have to investigate in the design process. A hypothetical LNG-fuelled ship model is used as the target ship. The gas explosion parameters include the gas cloud volume for determining the gas cloud size and the gas cloud centre of gravity for specifying the gas cloud position and ignition point. Previously reported gas dispersion results are utilised to establish these parameters regarding both frequency and physical data. The Latin hypercube sampling is used to generate 50 gas explosion scenarios. The blast overpressure of vapour cloud explosion (VCE) is simulated by the ExSim computational fluid dynamics (CFD) code, and software validation is provided. Finally, the gas explosion frequency can be compiled with blast overpressure to produce the exceedance frequency diagram. Subsequently, this diagram can be used to determine the design accidental loads under VCE. [ABSTRACT FROM AUTHOR]

As ship collisions and grounding accidents lead to human injury and damage to the environment and property, more accurate predictions of structural damage to ships under impact loads are needed. Currently, to determine structural behaviors, finite element analysis (FEA) is frequently adopted. However, it is recommended to pay attention to material properties in FEA because structural damage is sensitive to material properties such as yield strength, fracture strain, etc. While the strain rate (impact speed) is automatically considered for dynamic yield stress using the Cowper–Symonds equation or other methods, the pre-defined fracture strain is generally used as the dynamic fracture strain (DFS), which is not dependent on strain rate during the simulation. This assigned value of fracture strain may affect the extent of damage and structural response. In this study, the effect of the DFS on the structural damage from collisions was investigated to determine the relationship between the DFS and damage. Empirical formulas based on predictions of damage by various events were developed as a function of the DFS and initial impact speed. The results of this study explained the effect of the DFS on the structural damage and determined the upper and lower bounds of damage by collisions. [ABSTRACT FROM AUTHOR]

The growing demand for liquefied natural gas (LNG)-fueled ships necessitates the establishment of an LNG bunkering facility. Ship-to-ship (STS) is one of the most practical forms of LNG bunkering systems. Although there are benefits to the LNG bunkering of ships, risk and safety issues are a concern due to the volatile cargo. Ship collision could result in accidental LNG release. The purpose of this study was to build LNG leakage scenarios, establish critical zones based on gas concentrations, and estimate the temperature reduction in a bunkering ship's structure resulting from the use of cryogenic fluid. The condition of a target ship's structure, both intact and when damaged due to collision, was considered. Leak size, leak direction, leak position, release rate, and reservoir pressure were included as leak parameters, and environmental parameters, such as the wind direction, wind speed, and ambient temperature, were also included. The release duration was set based on the shutdown duration of the emergency shutdown valve (ESD). A total of 72 leakage scenarios were generated for the main CFD analysis. Convergence tests were conducted to determine the appropriate grid and iteration numbers for a computational fluid dynamics (CFD) simulation. The gas dispersion characteristics and the cryogenic flow impact on the LNG bunkering ship's structure are discussed through a parametric study. [ABSTRACT FROM AUTHOR]

Submarine hulls are pressure vessels for which excellent structural integrity under underwater pressure loads is essential. The use of light-weight materials contributes to reduced fuel consumption, improved speed, and increased payload while strength properties are retained. The focus of this paper is on the collapse behavior of a filament-wound cylindrical structure that serves as the main hull of a submarine subject to hydrostatic pressure loads. This paper presents a computational modelling approach for the prediction of the collapse behavior mechanism using a commercial finite element (FE) solver. The collapse strength obtained from the numerical model corresponded closely to available experimental data. The composite and aluminum material models were compared and the effects of stacking angle and thickness portion in the ply sequence on collapse strength were investigated. The advantages and disadvantages of available design codes (i.e., American Society of Mechanical Engineers (ASME) BPVC-X and National Aeronautics and Space Administration (NASA) SP-8007) were reviewed by direct comparison with numerical results. It is concluded that the application of effective engineering constants for the prediction of the collapse pressure of submarine hulls may be feasible. [ABSTRACT FROM AUTHOR]

The structural damage of ships in navigational accidents is influenced by the hydrodynamic properties of surrounding water. Fluid structure interactions (FSI) in way of grounding contact can be idealized by combining commercial FEA tools and specialized hydrodynamic solvers. Despite the efficacy of these simulations, the source codes idealizing FSI are not openly available, computationally expensive and subject to limitations in terms of physical assumptions. This paper presents a unified FSI model for the assessment of ship crashworthiness following ship hard grounding. The method uses spring elements for the idealization of hydrostatic restoring forces in 3 DoF (heave, pitch, roll) and distributes the added masses in 6 DoF on the nodal points in way of contact. Comparison of results against the method of Kim et al. (2021) for the case of a barge and a Ro–Ro passenger ship demonstrate excellent idealization of ship dynamics. It is concluded that the method could be useful for rapid assessment of ship grounding scenarios and associated regulatory developments. [ABSTRACT FROM AUTHOR]

Liquefied natural gas (LNG) exhibits significant environmental advantages. However, the hazards of LNG-fuelled ships need to be investigated in their early design stages, particularly with regard to accidental fuel leakage. In this study, a hypothetical oil tanker model was used with a fuel gas supply system installed on the main deck; the objective was to establish a critical zone for natural gas dispersion. A probabilistic approach was applied to determine credible scenarios, and leak size, location, and direction were considered as parameters along with environmental parameters such as wind direction and speed. Computational fluid dynamics was used to present the critical zone in terms of the contours of the natural gas concentration. The simulation results indicated that the leak size and wind speed significantly influence the size of the critical zone. [ABSTRACT FROM AUTHOR]

In this study, the genetic algorithm (GA) was implemented for the multi-objective optimization of the structural design of a pressure hull. The objective functions sought the maximum ultimate strength of the ring-stiffened cylindrical shell structure with minimum structural weight and maximum volume of the configured structural member. First, the evaluation models of several design variables of submarine structures were studied. Subsequently, a multi-objective GA algorithm was introduced. To improve the quality of the new population, several design constraints are applied. The final candidate structures were recomputed by non-linear finite element analysis (FEA) to observe the failure modes and compared with the initial design model. The results suggest that a lightweight construction would be achieved when a material with higher strength is used, especially for greater design depths [ABSTRACT FROM AUTHOR]

In the last ten years, reducing CO2 emissions has been a very important focus across all industries. To efficiently achieve carbon reduction in the power generation sector, various policies, regulations, and legislation have been proposed. In addition, new energy sources and technologies have been developed and widely adopted. In this study, current and future CO2 emissions from the domestic power generation sector were calculated and predicted based on two national power generation plans. The overall power plant efficiencies, operation rate of power plants, power capacities, and CO2 emissions for 2030 were predicted based on the 7th and 8th basic plan for long-term electricity supply and demand in Korea. In addition, the CO2 emissions policies of several major countries announced in accordance with the Paris Climate Agreement were identified and compared with Korea's climate change policy. Finally, the improvement of power generation efficiencies and co-combustion of biomass with coal is recommended to help the reduction of the BAU-based CO2 emissions by 19.4%. [ABSTRACT FROM AUTHOR]

Purpose: In Southeast Asia, the renewable energy produced from hydropower systems has significant potential. Therefore, adequate development is needed to prevent future energy-related crises. This study, therefore, aims to determine the variations effects in geometry and the geometrical factors on turbine performance. Design/methodology/approach: The developed aspects are selected to determine the blade shape, its number and multistage requirements. The study was conducted in 3D simulation, with Ansys software used to calculate a series of computational fluid dynamic problems. The aspect ratio applied in this study utilized the ratio of the overall diameter of the rotor height (D / H), which is 1. Findings: The results showed that the highest Cp-max value, number of blades and stages were 0.2, two and three, respectively. Furthermore, these attributes combined to improve the performance of hydroturbines. Research limitations/implications: The research was fully conducted using numerical simulation, which requires sustainable research in the form of laboratory experiments. Also, pioneer experiments were conducted using benchmarking to ensure the results obtained are reliable. Practical implications: Hydropower is one of the best renewable energy sources in Indonesia with a large potential in the archipelago and tropical countries due to rivers and various water sources. The current generated is a useful reference for Savonius design. Originality/value: The originality of this study is to examine the three aspects of the geometry of the rotor, such as the number and shape of blades, as well as the stages in the same boundary conditions. Therefore, the comparison of the effects of changes in geometry on turbine performance is more acceptable and complete compared to the pioneer works, which focused on a parameter. This research combines several aspects to determine the effect of rivers and various water sources on the hydroturbine. [ABSTRACT FROM AUTHOR]

In recent years, oil and gas pipes and risers in deep sea reservoirs are required to have high resistance to collapse. This paper reports the comprehensive investigation of the residual stress distributions in a recently developed seam-welded offshore gas transmission riser of high-strength steel. Experimental hole drilling methods are applied to understand the residual stress distribution in the real scaled riser. Then, FE modelling on double-V groove is performed for a systematic parametric residual stress analysis of the riser components with consideration of parameters including the ratio of component radius to wall thickness (r/t), joint preparation, pass size, and heat input. Through the use of a residual stress decomposition technique, the thickness-through-thickness residual stress is partitioned into membrane and bending stresses. According to the results of the parametric study, a method for prediction of residual stress in circumferential direction is developed based on simplified empirical formulas for existing riser configurations with varying welding conditions. [ABSTRACT FROM AUTHOR]

Ship–ship collisions continue to occur regardless of efforts to prevent them. The collisions involve highly nonlinear characteristics associated with structural crashworthiness, including crushing and fracture as well as buckling and plastic collapse. When applying nonlinear finite element analysis (NLFEA) to solve these problems, a reliable critical fracture strain accounting for strain-rate effects due to collision speed must be implemented. This study proposes a practical method to estimate the dynamic fracture strain to be used for the structural crashworthiness analysis associated with the collisions. For this purpose, the strain-rate characteristics in struck ship were investigated by NLFEA, in which the striking vessel was assigned various velocities in the range of practical ship speeds. Based on computations, an empirical formula was developed to calculate the strain rate at a given collision speed, allowing for a practical estimation of the dynamic fracture strain. The formula is validated by a comparison with experiment. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to review and examine the effects of the selected collision parameter values on the characteristics of collision energy in several ship collision scenarios. The benchmarking particulars were taken from the ship-to-ship collision case on Sunda Strait in 2014, while the collision process was modeled with non-linear simulations using the finite element (FE) method to determine the predicted damage and internal energy in the collision process. In the first phase, the verified model for the numerical simulation was built based on the benchmarks and other previous findings by researchers. The study of parameters during the collision process was performed in a later stage. The location of the target point in the vertical axis and the effect of the collision angle were the primary main focuses. The characteristics of damage and energy tendencies will be presented. One remarkable findings was that the structure of the car deck showed a better resistance and was more difficult to destroy than the other proposed locations. The angle position between the two objects during the impact process significantly contributed to the damage pattern on the side hull. The final results also indicated that the cross-section of the target point's location influenced the observed parameters. [ABSTRACT FROM AUTHOR]

Offshore structures are installed in a variety of water depths, under harsh environments, for long stretches of time, and waves are the most interrelated factor directly affecting their structural integrity. Thus, such structures should be designed to satisfy the demands of wave characteristics. In the preliminary structural design phase, a method for predicting non-linear random wave characteristics and extreme wave conditions must be determined. A structural response is not a linear value corresponding to maximum wave height, due to the related periods; that is, certain waves of less than maximum height may have greater effects on a structure depending on the wave period. This study focuses on selecting design conditions that generate a significant hydrodynamic load on a floating pendulum wave energy converter (FPWEC). For this purpose, it finds an equivalent regular wave height capable of generating the same hydrodynamic load, critical wave period and wave direction by conducting a response analysis. Generally, the subsequent equivalent design wave conditions are used to investigate an FPWEC's global strength. This study also applies a global structural analysis for the FPWEC using the determined equivalent design wave. The obtained results should be useful for understanding the global structural responses of FPWECs. [ABSTRACT FROM PUBLISHER]

Offshore installations are exposed to hydrocarbon explosions and/or fire accidents. Especially, explosions lead to serious damages to human, safety, and environment. To minimise and prevent the damage from explosions, blast walls are generally installed in oil and gas production structures. Typical blast walls are classified into flat, corrugated, and stiffened types. Among them, corrugated blast walls are frequently used for reasons such as construction, cost, and energy absorption. However, it has been known that a corrugated type of blast wall buckles between the web and flange under the explosion loads, and loses its stiffness. It means that the buckling phenomenon of a blast wall is closely related to the structural strength. This study investigates on the structural characteristics of a blast wall under quasi-static and dynamic (explosion) loads with or without a flat-plated stiffener. Finally, it can be concluded that the flat type of stiffeners are located at the buckling region to delay the buckling and improve the strength of blast walls. [ABSTRACT FROM AUTHOR]