International Journal of Naval Architecture and Ocean Engineering最新文献

The present study aims to improve the mean extracted power of a Wave Energy Converter (WEC) by mapping the parameters of its ballast weight and position, wave frequency, viscosity, and Power Take-Off (PTO) damping using an Artificial Neural Network (ANN) model. A total of 25 types of WEC rotors are designed with varying ballast weights and positions. The hydrodynamic coefficient and response of each rotor are determined using linear potential theory and viscous damping is estimated using computational fluid dynamics. The optimal design parameters are obtained by applying the trained model to a large randomly generated input dataset and the prediction output is evaluated to determine the best design parameters. According to the findings of the study, a well-trained model can predict and adopt to the nonlinear behavior of the given dataset as well as provide the optimal design parameters for the selected pitch-type WEC rotor.

This paper presents a procedure model that allows for a systematic analysis of execution risk in ship production by using stochastic risk simulation. Hence, planners can increase the depth of production planning to reduce disruptions and delays even with insufficient information density. The derived four-step model was then applied to the planning process at a German shipyard. Effects and probabilities of risks were estimated using stochastic distribution functions for two exemplary work packages in outfitting. Simulating the risk profiles for all work steps, the critical work steps and accordingly proposed planning tasks to increase the depth of production planning were identified. The application showed altogether that the Monte Carlo method can be used to mitigate the overall execution risk. In addition to increasing objectivity in the production planning process, the approach offers automation possibilities for future use cases and integration into planning software.

In this paper, we present a numerical experiment on a new piston-type wavemaker using a recently proposed piston-type wavemaker theory. The theory was primarily derived from the classical Boussinesq equation, based on the Pseudo-parameter Iteration Method (PIM). We first use the new theory to observe low amplitude propagating solitary waves and cnoidal waves, whereby we see the workability and validity of the theory. We further succeed in obtaining the graph of a mean power characteristic, in the range of 0.4 $\le kh\le$ 1.0, of the new piston-type wavemaker from the new theory.

In this study, the proportional, integral, and differential control constants for a self-propulsion point search were investigated using free running Computational Fluid Dynamics (CFD) simulations. The experimental data obtained using a 1/100 scale model of KVLCC2 were used to verify the calculation results. A range of initial propeller rotational speeds from 30% to 140% of the self-propulsion point of the experiment was considered. The controller constants were estimated using the trial-and-error and the Ziegler-Nichols methods, and the two results were similar. As a result, a robust numerical result was obtained within a 0.01% difference of the target speed, and a 0.5% difference of the self-propulsion point of the experiment with P and I constants of 180/m and 30 RPS/m, respectively, for a straight-ahead time of 12.5 L/V. Under the straight-ahead condition, a time step of 0.005 L/V was sufficient. However, in the turning simulation, a time step of 0.0025 L/V or less was required. The key findings obtained from this study are believed to provide a practical guideline for self-propulsion and maneuvering simulation using CFD.

In this study, a system integrating Solid Oxide Fuel Cells (SOFC) fueled by Liquefied Natural Gas (LNG) for marine vessels is proposed and analyzed. The system comprises Proton Exchange Membrane Fuel Cells (PEMFC), Organic Rankine Cycle (ORC), Gas Turbine (GT), Steam Rankine Cycle (SRC), and Waste Heat Boiler (WHB) combined with the SOFC system to enhance power generation and system performance. The PEMFC is particularly important for maritime applications, compensating for the disadvantage of the SOFC in terms of starting and response time according to the vessel's demand. The CO₂ capture system designated in this proposal not only helps to comply with international regulations and standards on emission control but also reduces the power consumption requirement for traditional CO₂ capture. To simulate and optimize the system's design, the Aspen HYSYS V12.1 process modelling software is employed. The thermodynamic models and equations for this proposed system are based on the first and second laws of thermodynamics. The exergy destruction equations and calculations for the main components are established and estimated to optimize the system's design and operation. The predicted performance of the proposed system is 68.76% for energy efficiency and 33.58% for exergy efficiency. The combined system for cold energy utilization and waste heat recovery generates more than 2100.42 kW equivalent, representing 35.6% of the total system generation. The results of the analysis indicate that when the current density is increased from 930 to 1930 A/m², performance of system experience a reduction of 33.18% and 16.2% for the energy and exergy efficiencies, respectively.

The hydrodynamic derivatives are necessary for assessing the dynamic characteristics, such as dynamic stability and maneuverability which are crucial in evaluating navigation safety and operational efficiency. Hence, it is required to compute the hydrodynamic derivatives precisely. This study nominates the new empirical formulae for predicting the hydrodynamic derivatives of a submarine. The proposed empirical formulae are derived from hydrodynamic forces and moments which are measured using Computational Fluid Dynamic (CFD) approach. Because the BB2 generic submarine is designed with an appropriate geometry and outstanding features, especially directionally stability, so, it is designated to establish the empirical formulae. The design parameters that have a significant impact on the maneuverability of the BB2 submarine, such as the length-to-diameter ratio, sail position, and sail height, are altered to fit different types of submarines for various purposes. Then, hydrodynamic derivatives of each change factor of the design parameter are taken using the least square method and assessed in relationship with the design parameters through correlation analysis. The high correlation values determine the independent variables which are the design parameters to form the empirical formulae for each hydrodynamic derivative based on multiple regression analysis. The applicability of the established empirical formulae is confirmed by applying them to calculate the hydrodynamic derivatives of BB2 and 2000 tons submarines, and comparing the calculation with the available data. The high precision implies that the established empirical formulae can be used to predict the hydrodynamic derivatives of similar profile submarines to the BB2 and 2000 ton submarines, and they can be extended to submarines in general at the designing phase.

Recently, the evaluation of vortex-induced vibration has emerged as a significantly important issue owing to the development of high-speed and lightweight ships and submarines. To derive an accurate vortex-induced vibration response, it is essential to consider the fluid-structure interaction. Moreover, it is necessary to evaluate the generation of the fluid-structure interaction to effectively prevent catastrophic failure in the structures. In this study, a hydrofoil wake oscillator model was developed based on a near-vortex strength that considers the fluid-structure interaction. The near-vortex strength was calculated from the boundary layer on a trailing edge to overcome the empirical parameter of lift fluctuation in conventional wake oscillator models. To predict the vortex-induced vibration on a hydrofoil, procedures for calculating the near-vortex strength and coupling the structural equations and fluid equation were introduced. The vortex-induced vibration derived using the developed hydrofoil wake oscillator model was verified by comparison it against the experimental results. The results reveal that the derived amplitude and lock-in range of the vortex-induced vibration were consistent with the experimental results. In addition, the extent of occurrence of the fluid-structure interaction and its contribution to vortex-induced vibration were evaluated using a non-dimensional wake parameter.

Design

rationale is a promising way of capturing design decisions and considerations for later retrieval and traceability to improve collaborative design decision-making. To achieve these perceived benefits for early-stage complex ship design, this paper first elaborates on the development of a proof-of-concept design rationale method. The method aims to aid ship designers in the continuous capturing and reuse of design rationale during the collaborative concept design process. Second, the setup and results of an experiment conducted with marine design students and with experts are discussed. This experiment shows how the developed design rationale method benefits collaborative design decision-making such that it leads to improved insight into design issues across the design team during a single design session.

This study presents a novel ship route planning algorithm that takes into account both operational economy and safety by integrating the A∗ algorithm with a collision avoidance algorithm that evaluates the Collision Risk Index (CRI) between the own ship and the target ship. The CRI-based A∗ algorithm defines a penalty zone, allowing the own ship to explore safe routes based on the International Regulations for Preventing Collisions at Sea 1972 (COLREGs) and performs an adaptive and effective node search on an extended local map grid according to various encounter situations. The proposed algorithm is validated through simulations of head-on, fine-broad crossing, converging crossing, and overtaking encounters, indicating an economical and safe optimum route compared to conventional ship domain-based route planning.

A transporter is a means of transportation that is widely used in heavy industries to move heavy loads called blocks. Because the transporter has a more complex operating system compared to the regular car, it takes a lot of time to become familiar with its operation. However, it is not easy to find a proper place and a transporter for training operators. As a result, the number of accidents caused by the operator's inexperience, such as block drops or collisions, is increasing every year. Therefore, in this study, a transporter training simulator based on virtual reality is developed to allow transporter operators to be trained anytime, anywhere without considering actual transporter and a special training place. This training simulator is composed of five modules. The first module is models of the transporter and the shipyard to be displayed in virtual reality. The second is implementation of the transporter operations such as lifting, lowering, and moving wheels. The third is vehicle dynamics model to implement realistic movement of the transporter. The fourth is the network function to simulate collaboration among workers. The fifth is the scenario module to simulate work situations that are similar to actual ones. By using the developed simulator, a scenario where the signalman and the operator collaborate to transport a block is successfully conducted.