International Journal of Naval Architecture and Ocean Engineering最新文献

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.

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.

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 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.

In the present study, the hull form of an 1,800 TEU containership was developed to reduce fuel consumption under real operation conditions. Contrary to the conventional hull form design practice in terms of the calm-sea performance, the hull form design in this study was aimed at improving the performance of a ship under in-service condition, which is closely associated with the added resistance due to waves. In order to reduce the added resistance due to waves, the bow hull form was modified to have sharper entrance with increased length between perpendicular. This enabled the waves to follow the bow part more smoothly. The added resistance of the developed hull was predicted by means of a series of CFD simulations in regular waves with wavelengths $\lambda /L_{pp}=0.5\sim 2.0$. The added resistance at irregular waves was calculated by frequency integration. The Daily Fuel Oil Consumption (DFOC) was subsequently calculated based on the wave statistics on the operating route. The significance of the present study lies in the point that the performance evaluation was carried out by means of the free-surface CFD simulation in the presence of regular waves. Final performance verification was made through a series of model tests. The resulting DFOC and daily CO₂ emission for the optimal hull form under the in-service conditions was found to be reduced by 7.65%. Furthermore, the calm-sea DFOC and CO₂ emission were also improved by 3.43%.

As the exploration and exploitation of deep-sea oil and gas, along with promising polymetallic nodule&sulfides mining, have been developing toward ultra-deep waters, some innovative concepts of marine cable configuration suitable for ultra-deepwater are proposed, such as stepped cable, hybrid cable and double-stepped cable. For deep-water cables with complex configurations, the structural responses become more complicated due to their non-uniform structural properties. Because the distributed buoyancy modules along cable length might introduce more significant local bending segments. Moreover, the impacts of moving boundary, caused by the motions of top vessel and bottom mining vehicle, should be considered. Through combing the finite element simulations with the hydrodynamic models, the dynamic response analysis approach of ultra-deepwater cables is established in this study. Then the double-stepped cable responses, including axial tension, displacement along with the change of overall configurations caused by moving top vessel and bottom mining vehicle, are calculated. Moreover, wave propagation behaviors during cable response are comprehensively examined, and the influences of non-uniform structural properties on cable response and wave propagation are analyzed using the wave propagation theory of structure with axially varying properties based on the Bessel function. The results show that the presented double-stepped cable can provide suitable configurations during the dynamic response, which has good compliance performance and can effectively buffer its response caused by moving boundary excitation. Finally, we found that the response spatial-temporal evolutions present some interesting phenomena, such as the axially non-uniform characteristics lead to non-monotonic changes in response amplitude and wavelength, with local peaks occurring in the low-tension region, owing to the distributed buoyancy modules, along with axially-varying and discontinuous structural properties. And, there exists significant mixed effect coming from both standing waves and traveling waves.

The towing stability of a towed underwater object was investigated through towing tank model tests. Three types of towing cables were employed, and the attitude of a towed object was measured by an inertial measurement unit. The towed object's geometry and the position of the towing point were fixed. The lower center of gravity enabled the positive pitch moment due to the increased moment arm and reduced the fluctuation of pitch motion. Three types of appendages, which were vanes, a streamlined bracket, and a spoiler, were employed. The magnitude of the damping force by the vanes and the resulting towing stability depended on the vanes' exposed area to the inflow. The damping force by the streamlined bracket enhanced the pitch stability. On the other hand, the spoiler deteriorated the towing stability as the tilted spoiler resulted in a stall and thereby nonlinear and unfavorable damping force.

The adverse human contribution to global climate change has forced the yachting industry to acknowledge the need to reduce its environmental impact due to the client's increasing pressure and potential future regulations to limit the ecological effects. Unfortunately, current real-world data presents a significant disparity between predicted and actual gathered energy consumption results. Thus, this research aims to develop an approach to accurately predict total dynamic Energy Consumption (EC) using real operation voyage data for the improved early-stage design of future yachts. A Grey-Box Modelling (GBM) solution combines: physics-based White-Box Models (WBM); and Black-Box Model (BBM) artificial neural networks to provide estimations with high accuracy and improved extrapolation capacity. The study utilizes ten months of onboard continuous monitoring data, hindcasted weather, and voyage information from a Feadship fleet yacht. Upon applying a sequential modelling methodology, predictions are compared between the three model categories, indicating propulsion and auxiliary estimates fall within 3% and 7% error of operational conditions. The study is then continued using external range datasets to evaluate the extrapolation potential. While GBM improvements are seen over the BBM, limitations were directly related to the strength between dynamic WBM input-output correlations. Ultimately, GBM's have the potential to improve both accuracy and extrapolation ability over existing WBM and BBM's; however, much is dependent on the strength of the input-output relationships.