International Journal of Naval Architecture and Ocean Engineering最新文献

In ship design, the matching of engine, propeller, and hull is an analytical process to establish the optimal operating mode so that the engine works safely with full power and the lowest fuel consumption, and a ship reaches desired speed. In theory, the operating process of the engine, hull, and propeller is usually expressed by their characteristics, and the matching problem is solved by finding the intersection of these characteristics. The problem here is that the above characteristics are determined under design conditions, corresponding to the standard technical conditions of the engine, hull, and propeller, however, all of these will be changed under actual service conditions, leading to a change in the position of the defined design match points and thereby greatly affect the safety and performance of the ships. This paper presents a new approach to determining the actual characteristics of the engine, hull, and propeller and how to use them to solve the matching problem under service conditions. This study was verified and validated on three study ships and was also applied to solve the matching problem of the Glory Star tanker. All the obtained results are in good agreement with the published real experimental data for this ship with a power loss of 21.5% under current service conditions, including 6.5% due to changes in propeller characteristics by changing technical conditions of propeller and hull surface, 6.3% due to engine deterioration, and 8.7% due to the engine - propeller mismatch after 5 years of operation.

Composite small crafts are manufactured in a job-shop system that prioritizes delivery times and creates various small-scale products using flexible equipment and worker operations. The process involves layering composite materials onto a mold to form the product through molding. Three intermediate stages must be completed before the final product, including mock-up, mold, and small craft. The stability and performance of the small craft rely on the accuracy of the mock-up and mold production. However, repeated molding can cause deformation and worker skill level affects product quality, leading to inconsistent results. This study aimed to improve the quality control of composite small crafts in leisure boat shipyards. We propose developing a high-precision digital shape model using 3D scanning of intermediate products such as the ship body frame, finished mold, and shaped hull of the FRP small craft to enable quantitative quality control and identify shape deviations.

As the reduction of greenhouse gas emissions has become an important issue, measures and devices to reduce energy consumption are in increasing demand. In this study, the potential energy saving due to the application of air lubrication technology in merchant ships is analyzed. We propose a simplified empirical model, covering three different air lubrication technologies, based on the experimental results and assumptions taken in the existing studies. The bottom surface area covered with air is important for the efficiency of the air lubrication system, according to the sensitivity analysis. From the global fleet analysis, net-percentage power saving varies according to the operational profile as well as the technology. Net-percentage power savings of 2–5% from air bubble, 8–14% from air layer, and 16–22% from air cavity technology were obtained assuming calm-water conditions. The methodology can be adopted in early design stage and fleet-wide analyses of various energy-saving measures.

This study proposes an automatic gain-tuning algorithm for ships. The proposed algorithm is designed to tune the gains of the ship controller automatically, rather than using trial and error. The forward speed and steering models were derived by linearizing and simplifying the 3-degrees of freedom (DOF) nonlinear equation of motion of the ship. The initial control gains were calculated using an error dynamics model constructed by combining the steering and system models of the controller. The maneuvering simulations and sensitivity analysis of the control performance at various control gains were performed for gain-tuning. System identification was conducted based on derived dynamics models and free-running test data. The tests verified that the gain-tuning algorithm corrects the gains more accurately and rapidly than trial and error. In addition, the algorithm reduced overshoot by 85% compared to the initial control gains.

The hydrodynamic performance of a sea-going ship can be analyzed using data from different sources, like onboard recorded in-service data, AIS data, and noon reports. Each of these sources is known to have its inherent problems. The current work highlights the most prominent issues, explained with examples from actual datasets. A streamlined semi-automatic approach to processing the data is finally outlined, which can be used to prepare a dataset for ship performance analysis. Typical data processing steps like interpolating metocean data, deriving additional features, estimating resistance components, data cleaning, and outlier detection are arranged in the best possible manner not only to streamline the data processing but also to obtain reliable results. A semi-automatic implementation of the data processing framework, with limited user intervention, is used to process the datasets here and present the example plots for various data processing steps, proving the effectiveness of the proposed approach.

The Large Eddy Simulation (LES) method coupled with a Schnerr and Sauer cavitation model was adopted to simulate the unsteady cavitating flow around a Delft Twist 11 (Twist11) hydrofoil. We proposed a novel aggressiveness indicator to predict the risk of cavitation erosion on the hydrofoil surface by utilizing LES simulations as input. The proposed aggressiveness indicator introduces the time-averaged pressure, the hypotheses of Nohmi et al. and the concept of the power exponent into the energy balance approach. The results show that the current numerical method integrally reproduces the evolution of the cloud cavity observed in the cavitation tunnel. The cavitation erosion risk predicted by the aggressiveness indicator ${⟨e_1⟩}_{n=5}^{\prime }$ agrees well with the erosion pattern obtained from the paint test. The predicted erosion risk regions are located in the “hoof” positions (region 2 and region 3) of the horse-shoe-shaped cloudy cavity and the positions (region 1) near the cavity closure line.

To study the performance of partial air cushion-supported catamaran (PACSCAT), which is sailing with a flexible air seal in waves, this paper uses the model tests, and research the motion characteristics of PACSCAT at different wavelengths, by monitoring the boundaries of heave, pitch, acceleration, air cushion pressure. Firstly this paper introduces the test situation of PACSCAT in the towing tank and introduces the test method, equipment, and test conditions. Second, this paper extracts the test data, analyzes the features of heave, pitch, acceleration, and air cushion pressure, and studies their linear and nonlinear changes in regular waves. Thirdly this paper analyzes the nonlinear air leakage flow of the bow of PACSCAT in detail under the test conditions and studies the internal and external free liquid surface under different conditions.

The present study concerns an open water performance of a partially submerged propeller. To investigate the free surface effects on the propulsion performance, the force and moment were measured, and the ventilation phenomena were visualized with respect to submergence ratios and advance coefficients. The thrust loss in heavy load conditions due to ventilation at the suction side of the propeller blade was observed. The extent of the ring-shaped ventilation phenomena increased as the advance coefficients decreased, resulting in thrust loss. Using the underwater camera and the fast Fourier transform results of the thrust, the ventilation phenomena were classified into five types. Also, the shaft excitation force of the propeller was analyzed. The shaft-bearing load was approximately 100% greater than the propeller weight in the ballast draft condition. A larger load was applied to the shaft due to the movement of the thrust eccentricity near the free surface.

The measurement of wave height is essential for weather analysis, safe navigation of ships, and ship design. This study proposes a low-cost and direct method for measuring wave height using ocean wave images. The proposed scheme comprises a Wave Detector based on Convolutional Neural Networks that takes two-dimensional ocean images as input, and a PPM Calculator that measures the size of an object in the image. The study explains the configuration and implementation of the Wave Detector and the basic principle of the PPM surface generating method for the PPM Calculator, with support from ground experiments. The proposed scheme is validated using two types of wave height measurement sensors and three types of real ocean images for the Wave Detector, as well as two rounds of ground experiments for the PPM Calculator.

The results show that the wave height values measured by the proposed scheme are highly consistent with the values from the measurement sensors.