International Journal of Naval Architecture and Ocean Engineering最新文献

The aim of the work is to evaluate different design alternatives to obtain criteria for the selection of the most effective design by fatigue strength assessment of the local cut-out as a result of the connection between the longitudinal or ordinary stiffener and the transverse web frame (longi-web) in the side hull structure (upper wing torsional box), very important area due to its high stress concentration, of a container vessel, one of the most important ships in terms of its influence on the world economy. Structural solutions and design guidelines are established, by means of numerical models validated by experimental tests, which allow alternative designs to be obtained that improve their fatigue behaviour. Standard cut-out geometries are studied under the presence of different variables (radius of curvature, longitudinal spacing, longitudinal stiffener cross-section, and flange arrangement) that are evaluated to determine their effect in the structural assessment (fatigue damage, stress concentration, and fracture mechanics) and the weight comparison between alternatives.

The prediction of the statutory attained subdivision index is a challenging issue for the initial design of ships due to the design freedom offered by a probabilistic damage stability assessment. To this end, optimisation techniques integrated with a parametric model of the internal layout may generate a preliminary subdivision design, fulfilling damage stability regulations and cargo volume requirements. The present study explores using a multi-objective constrained optimisation algorithm coupled with a parametric model of a single hold cargo vessel, first investigating two design goal alternatives and secondly performing a global sensitivity analysis on the design variables for the most promising solution. The adoption, in parallel, of state-of-the-art practices shows the validity of the obtained solutions and the time benefits for designers. Nonetheless, the non-linear nature of probabilistic damage stability does not allow for clearly identifying the most impactful parameters on the attained survivability index.

This study aims to present a practical practice to obtain a reliable numerical solution based on an Unsteady Reynolds Averaged Navier-Stokes (URANS) Computational Fluid Dynamics (CFD) to estimate the forces acting on moored ships during a passage of a ship in a confined waterway. The motion of the passing ship is implemented using an overset-grid method. The convergence of the numerical solutions depending on the spatial and temporal discretization are systematically analyzed, and the computational results are validated with a recent benchmark test data. In particular, the effect of the initial state of the passing ship in the unsteady simulation is dealt with in-depth. The simulation results when the passing ship departs at a constant speed and when it accelerates from a standstill are compared, and the influence of undesirable wave radiation generated with the departure of the passing ship at a constant speed is discussed.

This paper investigates the corrosion factor to the global strength of aging offshore jacket platforms in different marine zones. The time-dependent corrosion wastage model from Melchers, an active corrosion expert, by considering different marine zones, i.e., atmospheric, splash, and immersion. In addition, three aged jacket platform models of the originally installed platform were selected to investigate the effect of corrosion wastage on global strength. The jacket platform's global strength is calculated by the Reserve Strength Ratio (RSR) value. RSR is obtained via nonlinear static pushover analysis and is always used to estimate overall structure strength reserves. Safety assessment is evaluated by the PETRONAS Technical Standard (PTS). According to this study, immersion zone corrosion is the most influential zone after splash zone corrosion. Furthermore, the study also predicts the lifetime of each jacket platform, and it is useful for structural engineers to estimate corrosion allowance at the early design stage.

In this study, the motions of a moored buoy and its surrounding fluid flow are numerically studied. The solver is developed by coupling the computational fluid dynamics platform, OpenFOAM, with a lumped mass mooring line model, MoorDyn. The time marching interface to transfer the solution variables is developed for the robustness and accuracy of the solver. The developed coupled solver was validated against a moored cubic-shaped box model in waves. The different mesh configurations, mesh generation technique and mooring line discretization are considered in the numerical study. A cubic-shaped box attached with tensioned mooring lines in waves is simulated and the results are compared with the experimental results. Motion responses of a moored semi-submersible platform, which is designed by Korea Research Institute of Ship and Ocean Engineering (KRISO), in waves are predicted by the solver. The mooring line tensions acting on the body and anchor, the forces acting on the platform and the platform's motion performance are analyzed, and comparisons are made between simulation data and experimental data.

Air entrainment and self-aeration flow are phenomena that can generate fluctuation in pressure and induce disadvantages in piping systems. In this study, the mechanism of air bubble formation in Partially Filled Pipe Flow (PFPF) is investigated through a series of experiments on a butterfly valve with flow visualization and pressure measurement. This paper provides a description of the formation of bubbles induced by a butterfly valve and analyzes the characteristics of the pressure and flow coefficient of the valve. The pressures at various locations on the pipeline adjacent to the valve were measured to compare with the positions recommended by the International Society of Automation standard. The results indicated that in PFPF, the differences in the pressure between measured points downstream are noticeable, notably at valve openings less than 50°. The bubbles created at the valve, which lead to the highly-disordered aerated flow downstream, might induce the differences. The pressure drop and the flow rate across the butterfly valve in 100% water fraction flow are respectively 3–7.5 and 2–9 times higher than those in 90% WF. The flow coefficient of the 3-inch butterfly valve was found to increase linearly with the Reynolds number before leveling off when the Reynolds number exceeds $6\times {10}^4$. Besides, the flow coefficients in 100% water fraction flow are double those in 90% water fraction flow.

In this study, the dieless bulging and nonlinear buckling behaviours of a stainless longan-shaped pressure hull were investigated. According to the Cassini oval equation, the longan shape has a shape index of 0.1. The lengths of the major and minor axes of the designed longan-shaped pressure hull were approximately 400 and 396 mm, respectively. The wall thickness of this pressure hull was 1 mm. The Huber–von Mises stress and first yielding load of the designed longan-shaped shell and its inscribed polyhedral preform were investigated analytically and experimentally. Moreover, the dieless bulging of the designed longan-shaped pressure hull was investigated numerically and experimentally by using the nonlinear finite element method and a hydrostatic test, respectively. The analytical, experimental, and numerical results exhibited good agreement with each other.

IMO suggests Second-Generation Intact Stability Criterion (SGISC), which consists of five failure modes, because of continuous accidents due to a lack of ship stability. In this study, Level 1 and Level 2 stability of SGISC were evaluated for three stability failure modes (Dead Ship Condition, Surf-riding, and Excessive Acceleration). Level 1 was calculated in the same way as the second-generation intact stability calculation method, and Level 2 was calculated in a deterministic manner by using a real-time maritime environment rather than a probabilistic approach for all maritime environments. Based on this, a program was developed to visualize dangerous and safe areas on a map. Using the developed program, it is expected that SGISC can be used not only in the design stage, but also in the operation stage of ships, such as route planning or selection of operating locations in the ocean.

A well-balanced naval ship design to enhance the survivability from the initial design stage in parallel with other designs focusing on the major function and its inherent mission is considered as a desirable design trend in ROK navy since Cheonan sinking accident. Because it is difficult to estimate a hit location of a given threat for survivability evaluation, a statistical approach based on multiple-hit scenarios is frequently addressed, and it is necessary to accomplish rapid analyzes considering the tight design schedule. In addition, accurately estimating the extent of damage caused by the given threat is also an important matter to secure the reliability of evaluation. In particular, the empirical formula-based damage extent estimation method, which is frequently used for initial rapid vulnerability analysis, has limitations in not faithfully reflecting the latest technology advances such as hull design changes and diversification of threats, so researches on this have been continuously accomplished. In this study, a method for analyzing the extent of damage was developed considering the structural response of a ship to damage under a blast load. The proposed method quickly and easily calculates the extent of damage using physical design parameters together with the accurate analysis results and is also very effective at the initial design stage of the naval ship (e.g., in evaluating various design candidates for structural configurations). To show the effectiveness of suggested method, FLACS, a well-known commercial program for explosion analysis, is used for the analysis of nine representative scenarios together with the stepwise validations of the suggested procedure; the analysis results are observed the same in most cases with the developed program based on the proposed procedure, with a difference of approximately 15% for one scenario.

The research examines the motion response and hydrodynamic wave loads of a deep-water Tension Leg Platform (TLP), emphasising the impacts of the wave sum frequency on the restrained modes of heave, roll, and pitch. The stochastic TLP structural reaction in a random sea state was precisely computed using a Volterra series representation of the TLP corner vertical displacement, which was selected as a response process. The wave loading was evaluated using the second-order diffraction code WAMIT and applied to a linear damped mass-spring model representing the dynamic system. Then, platform displacement response at the design low probability level has been determined using a novel deconvolution approach. Since the Volterra series represented the analytical solution, the exact Volterra and the approximated predictions have been compared in this study. The latter provided an accurate way to validate the effectiveness and precision of the proposed novel deconvolution method. Compared to existing engineering techniques, the most attractive advantage of the proposed deconvolution method is that it does not rely on any pre-assumed asymptotic probability distribution class. The latter may be an attractive point for practical engineering design. Thus the primary objective of this work was to validate a novel deconvolution approach using exact quasi-analytical solutions. This work also highlights the limitations of mean up-crossing rate-based extrapolation methodologies for the situation of narrowband effects, including clustering, which are often included in the springing type of response.