Hasil untuk "Naval architecture. Shipbuilding. Marine engineering"

Wan-Gu Kim, Byoung-Nam Kim, Yohan Chweh

The influence of station-to-station line orientation on sea current speed observations using Coastal Acoustic Tomography (CAT) was quantitatively investigated. For this purpose, we conducted CAT experiments at five stations in Yeosu Bay, South Korea. Through these experiments, the sea current speeds were estimated along a total of six tomographic observation lines with different orientations, and the results were compared with current speeds measured simultaneously by an Acoustic Doppler Current Profiler (ADCP). The comparison showed that the concordance between tomography-estimated sea current speed and ADCP-measured sea current speed tended to decrease as the acute angle between the predominant tidal current direction in Yeosu Bay and a tomographic observation line increased. This tendency is interpreted as arising because the smaller the difference between the two one-way travel times obtained during tomographic observations, the greater the effect of the travel time measurement error whose magnitude is relatively direction-independent. This interpretation was supported by a simple numerical simulation. Furthermore, quantitative analysis of these simulation results indicated that a smaller acute angle between the predominant sea current direction in the survey area and a tomographic observation line enhances the robustness of sea current speed estimation against travel time measurement errors. The results show that the station-to-station line in CAT should be arranged considering the predominant sea current direction in the survey area, which can provide an important guideline for selecting station locations.

Renfei Kuang, Jinhai Zhao, Tuo Zhang et al.

Offshore wind turbines are prone to structural damage over time due to environmental factors, which increases operational costs and the risk of accidents. Early detection of structural damage through monitoring systems can help reduce maintenance costs. However, under complex external conditions and varying structural parameters, existing methods struggle to accurately and quickly detect damage. Understanding the factors that influence structural health is critical for effective long-term monitoring, as these factors directly affect the accuracy and timeliness of damage identification. This study comprehensively analyzed 5 MW offshore wind turbine measurement data, including constructing a digital twin model, establishing a surrogate model, and performing a sensitivity analysis. For monopile-based turbines, sensors in x and y directions were installed at four heights on the pile foundation and tower. Via Bayesian optimization, the finite element model’s structural parameters were updated to align its modal parameters with sensor data analysis results. The update efficiencies of different objective functions and the impacts of neural network hyperparameters on the surrogate model were examined. The sensitivity of the turbine’s structural parameters to modal parameters was studied. The results showed that the modal flexibility matrix is more effective in iteration. A 128-neuron, double-hidden-layer neural network balanced computational efficiency and accuracy well in the surrogate model for modal analysis. Flange damage and soil degradation near the pile mainly impacted the turbine’s health.

Changui Lee, Seojeong Lee

The maritime sector is increasingly integrating Information and Communication Technology (ICT) and Artificial Intelligence (AI) technologies to enhance safety, environmental protection, and operational efficiency. With the introduction of the MASS Code by the International Maritime Organization (IMO), which regulates Maritime Autonomous Surface Ships (MASS), ensuring the safety of AI-integrated systems on these vessels has become critical. To achieve safe navigation, it is essential to identify potential risks during the system planning stage and design systems that can effectively address these risks. This paper proposes RA4MAIS (Risk Assessment for Maritime Artificial Intelligence Safety), a risk identification method specifically useful for developing AI-integrated maritime systems. RA4MAIS employs a systematic approach to uncover potential risks by considering internal system failures, human interactions, environmental conditions, AI-specific characteristics, and data quality issues. The method provides structured guidance to identify unknown risk situations and supports the development of safety requirements that guide system design and implementation. A case study on an Electronic Chart Display and Information System (ECDIS) with an AI-integrated collision avoidance function demonstrates the applicability of RA4MAIS, highlighting its effectiveness in identifying specific risks related to AI performance and reliability. The proposed method offers a foundational step towards enhancing the safety of software systems, contributing to the safe operation of autonomous ships.

Xuegang Li, Yang Shi, Cheng Zhao et al.

To study the rapid estimation method and characteristics of low-frequency ambient sea noise generated by far-field ships, firstly, based on the reciprocity principle of sound fields and the fact that the number of noise sources significantly exceeds the number of receiving array elements, the positions of noise sources and receiving array elements were swapped to effectively reduce the sound field estimates and the running time. Secondly, a vertical directionality analysis method for ambient noise generated by ship noise was derived. And lastly, the ambient sea noise generated by ship noise in the Philippine Sea was estimated and analyzed, and the validity of the estimation method was verified based on measured data in the region. The estimation method presented in this paper can be used to predict the level and directionality of ambient noise generated by ship noise in a large area of sea, and acts as technical support for the meaningful use of sonar arrays in the actual marine environment.

Zhiwei Zhang, Dawei Pan, Yan Liang et al.

Field determination and ecological risk assessment of dissolved lead (Pb) were performed at two Yellow Sea sites in China using a continuous automated electrochemical system (CAEDS). This CAEDS instrument includes an automatic triple filter sampler and an electrochemical detection water quality analyzer, which might be operated automatically four times daily. The dissolved Pb concentrations varied from 0.29 to 1.57 μg/L in the South Yellow Sea over 16 days and from 0.32 to 2.28 μg/L in the North Yellow Sea over 13 days. During the typhoon and algal bloom periods, the Pb concentration was as high as ten times greater than usual. According to the calculation of contamination factors (C_f) and subsequent analysis, seawater quality was classified as Grade II. Through species sensitivity distribution (SSD) method experiments and ecological risk analysis, an average risk quotient (RQ) below 1 for both areas was obtained, indicating a low-to-moderate ecological risk. This system will be helpful for Pb monitoring and assessment in seawater and contribute to the biogeochemical cycling study of Pb.

Jilong Chen, Xing Chen, Wenjin Li et al.

In deep-sea mining hydraulic lifting systems, centrifugal pumps are very important as power units. In the process of transportation, the fluid prewhirl phenomenon in the impeller inlet will lead to changes in the state of motion of the particles and fluid and cause the wear of the inlet pipe, which can lead to centrifugal pump failure in serious cases. In this paper, a numerical simulation of the centrifugal pump is carried out based on the CFD-DEM coupling method to analyze the influence of the prewhirl on the wear of the inlet pipe. The results show that the velocity streamline near the impeller inlet position changes significantly. The flow field velocity increases along the radial direction of the inlet pipe, and it has a maximum value at <i>r/R</i> = 0.98. The prewhirl flow pulls the particles to change their original motion direction, and the area where the particles are subjected to high fluid force is concentrated between 0.5 <i>d/D</i> and 1 <i>d/D</i>, about 0.015 to 0.018 N, resulting in the uneven distribution of particles. The high-wear area appears in the bottom-left area (specifically, L4, L9, and L13), and this is also the location of the largest cumulative force; the high-wear area shows a triangle. The collision energy loss of particles increases due to the influence of the prewhirl, which leads to an increase in wear.

Xinhui Zheng, Qiyan Tian, Qifeng Zhang

Recently, as humans have become increasingly interested in ocean resources, underwater vehicle-manipulator systems (UVMSs) have played an increasingly important role in ocean exploitation. To realize precise operation in underwater narrow spaces, the fly arm underwater vehicle manipulator system (FAUVMS) is proposed with manipulators as its core. However, this system suffers severe dynamic coupling effects due to the combination of small vehicle and big manipulators. To resolve this issue, we propose a robust adaptive controller that contains two parts. In the first part, the extended Kalman filter (EKF) is designed to estimate the system states and predicts external disturbances to achieve adaptive control. In the second part, a chattering-free sliding mode control (SMC) is designed to converge the tracking errors to zero, thus guaranteeing the robustness of the controller. We constructed the simulation platform based on the geometric model of FAUVMS, and various simulations are carried out under different situations. Compared to the traditional methods, the proposed method has a faster convergent speed, a better robustness and adaptiveness to external disturbances, and the tracking errors of positions of the vehicle and each end-effector are much smaller.

Selçuk Nas

Xiaolong Tang, Changjie Wu, Xiaoyan Xu

The steering mechanism of ship steering gear is generally driven by a hydraulic system. The precise control of the hydraulic cylinder in the steering mechanism can be achieved by the target rudder angle. However, hydraulic systems are often described as nonlinear systems with uncertainties. Since the system parameters are uncertain and system performances are influenced by disturbances and noises, the robustness cannot be satisfied by approximating the nonlinear theory by a linear theory. In this paper, a learning-based model predictive controller (LB-MPC) is designed for the position control of an electro-hydraulic cylinder system. In order to reduce the influence of uncertainty of the hydraulic system caused by the model mismatch, the Gaussian process (GP) is adopted, and also the real-time input and output data are used to improve the model. A comparative simulation of GP-MPC and MPC is performed assuming that the interference and uncertainty terms are bounded. Consequently, the proposed control strategy can effectively improve the piston position quickly and precisely with multiple constraint conditions.

Kazuo Hiekata, Zhinan Zhao

The maritime industry is trying to utilize new technology for enhancing its competitiveness to overcome today’s severe economic situation, and some interact effects, or potentially emergent effects, will emerge during the introduction of these technologies. In this study, various simulations that relate to marine logistics and shipping were performed. By contrast, a detailed method that can reproduce emergent effects is required to some extent. This study utilized a Monte Carlo simulation for uncertainties, such as market and failure uncertainties. To evaluate and explore the emergent effect correctly and accurately when multiple technologies are introduced, an evaluation methodology was developed, which can evaluate the interact effect from the perspective of profit improvement and CO₂ reduction during the transportation period. As a case study, decision making for introducing 28 technology combinations to the maritime industry was conducted, and the utility of the proposed methodology was assessed.

Аnna Rodkina, Olga Ivanova, Vadim Kramar et al.

The requirements of the rules and regulations of the Classification Societies are based on the assumption that during the construction and operation of ships the hull corrosion protection measures are implemented according to the standards and other regulatory documents currently in force. For the purposes of designing the ship hull structures, the load components for different corrosion protection types have been obtained in the paper. There have been collected the data on the relationship between the corrosion protection weight load and the ship displacement, which enables to select the lowest corrosion protection type by weight. Technical and economic parameters of corrosion protection of ship hull structures have been analyzed. To achieve the objective of the paper a cumulative simplified approach of economic feasibility of selecting the corrosion protection type for ship hull structures has been employed. It has been determined that a total cost of protection from stress-corrosion fractures decreases for the ships with a displacement of more than 6000 [t] in the case of usage of the impressed current cathodic protection instead of the sacrificial anode cathodic one. The results of the investigation can be used by shipbuilders at the ship design stage, which enables to make a correct selection of a corrosion protection type and decreases its total cost.

Jinghui Li, Wei Shi, Lixian Zhang et al.

There is a huge energy demand from offshore renewable energy resources. To maximize the use of various renewable energy sources, a combined floating energy system consisting of different types of energy devices is an ideal option to reduce the levelized cost of energy (LCOE) by sharing the infrastructure of the platform and enhancing the power production capacity. This study proposed a combined concept of energy systems by combing a heave-type wave energy converter (WEC) with a semisubmersible floating wind turbine. In order to investigate the power performance and dynamic response of the combined concept, coupled aero-hydro-servo-elastic analysis was carried out using the open-source code F2A, which is based on the coupling of the FAST and AQWA tools by integrating all the possible environmental loadings (e.g., aerodynamic, hydrodynamic). Numerical results obtained by AQWA are used to verify the accuracy of the coupled model in F2A in predicting dynamic responses of the combined system. The main hydrodynamic characteristics of the combined system under typical operational conditions were examined, and the calculated responses (motions, mooring line tension and produced wave power) are discussed. Additionally, the effect of aerodynamic damping on the dynamic response of the combined system was examined and presented. Moreover, a second fully coupled analysis model was developed, and its response predictions were compared with the predictions of the model developed with F2A in order for the differences of the calculated responses resulted by the different modeling techniques to be discussed and explained. Finally, the survivability of the combined concept has been examined for different possible proposed survival modes.

Tao Song, Jiarong Wang, Danya Xu et al.

Physical oceanography models rely heavily on grid discretization. It is known that unstructured grids perform well in dealing with boundary fitting problems in complex nearshore regions. However, it is time-consuming to find a set of unstructured grids in specific ocean areas, particularly in the case of land areas that are frequently changed by human construction. In this work, an attempt was made to use machine learning for the optimization of the unstructured triangular meshes formed with Delaunay triangulation in the global ocean field, so that the triangles in the triangular mesh were closer to equilateral triangles, the long, narrow triangles in the triangular mesh were reduced, and the mesh quality was improved. Specifically, we used Delaunay triangulation to generate the unstructured grid, and then developed a K-means clustering-based algorithm to optimize the unstructured grid. With the proposed method, unstructured meshes were generated and optimized for global oceans, small sea areas, and the South China Sea estuary to carry out data experiments. The results suggested that the proportion of triangles with a triangle shape factor greater than 0.7 amounted to 77.80%, 79.78%, and 79.78%, respectively, in the unstructured mesh. Meanwhile, the proportion of long, narrow triangles in the unstructured mesh was decreased to 8.99%, 3.46%, and 4.12%, respectively.

Herman D. Haustein, Alon Gany, Ezra Elias

An innovative variant of a multiphase marine ramjet is investigated analytically and experimentally. Pressure liquefied gas (LG) is injected, boiling under superheat conditions in the water stream within the propulsion unit, and serving as an on-board bubble source necessary for the ramjet operation. Experiments were conducted in a 10 m diameter tow pool at a speed range of 7–18 m/s (approximately 14–35 knots). For the laboratory concept demonstration and process characterization, two liquefied gases, butane and R134a (synthetic refrigerant gas), were employed. In practical applications, non-polluting LGs such as liquid air may be used. The results reveal the overall performance comparable to the operation with pressurized air, with some thrust advantage of the LG at high-speed tests, attributed to the volume increase of gas during phase change, in accordance with the thermodynamic power cycle analysis.

Abbasali Rezapour, Fazlolah Saghravani, Alireza Ahmadyfard et al.

Saltwater intrusion is a transient process that affects the coastal aquifers quality and hydrodynamics. The transient behavior of the saltwater wedge (SW) and mixing zone (MZ) due to the changes of the inland freshwater head was investigated through experimental and numerical approaches using image processing technique and the numerical code SUTRA. To acquire data in the transient conditions, automated algorithms were designed and employed for both methods. Numerical simulations were extended to a reference problem of field scale for further study of the transient aspect of the saltwater intrusion phenomena. The results demonstrated that the behavior of SW area is significantly similar to the behavior of SW toe length in transient conditions. Also, in the advancing case, the SW height reaches the steady state condition much sooner than the SW toe length and the SW area, while in the receding case, all the three indicators are stabilized almost simultaneously. Furthermore, the results showed that the MZ expanded at early stages of the receding and after a while condensed again gradually until it finally reaches to its original state at the beginning of the advancing case. Although local velocity of brackish water toward sea boundary in the dilute region of the MZ is more than in the dense region, the flushing and mixing process causes to increase the MZ in the receding case. Sensitivity analyzes showed that the speed of SW advancing or receding does not affect the MZ thickness in a steady state condition.

LU Conghong, BAI Huizhe, WANG Yunlong

<b>[Objectives]</b> In order to define the advanced grade of the existing Semi-Submersible Crane Vessel (SSCV), evaluate whether the ship design achieves the expected effect,and find out the existing problems to guide the future work,<b>[Methods]</b> an advanced grade evaluation index system and an evaluation method suitable for SSCV in service is proposed with reference to national standards and combined with characteristics and functions of SSCV. And the applicability and feasibility of this evaluation method are determined through the actual calculations.<b>[Results]</b> The calculation results show that the proposed advanced grade evaluation index system and evaluation method are applicable to the evaluation of SSCV in service,and the evaluation results are in line with the engineering practice.<b>[Conclusions]</b> The proposed method herein can provide a reference for the advanced grade evaluation of SSCV under design.

DONG Jiuting, LIU Jianhu, WANG Jun et al.

<b>[Objectives]</b> The shock environment of a warship in an underwater explosion is the basic input for the design and shock resistance ability evaluation of ship equipment. <b>[Methods]</b> In this paper, a numerical simulation is used to analyze the shock environment in different regions of a ship, and the Second-order Doubly Asymptotic Approximation(DAA₂)is used to solve the fluid-structure interaction. First, the appropriate calculating parameters are chosen, such as damping ratio, and then a series of Single-Degree-of-Freedom(SDOF) systems are attached at various deck locations to simulate flexible equipment. <b>[Results]</b> The accuracy and reliability of DAA₂ is verified by the fact that the calculated shock spectrums at classic regions perfectly match the data of the ship shock trial. The shock response of the SDOF systems under the same shock input are then calculated and transformed into the shock environment. Finally, the results of shock environments in different regions are compared. <b>[Conclusions]</b> The conclusions of this paper can provide design reference data for the subsequent anti-shock design of equipment.

Elisabeta Burlacu, Remus Zagan

For several decades fatigue cracks and damages have been a problem for the ship designers. Detail design was initially the obvious remedy to improve and solve a part of the fatigue problem given by stainless steels with higher tensile strength used in ship construction parts. The hull and ship deck and also bottom structure are improved with the aim of increasing the strength of hull girder. In the following paper, the fatigue tools results of ANSYS Workbench 16.2 are represented for a double bottom unit model of a Deep Water Installation Vessel.

Paszota Zygmunt

In a motor or a drive system the quantity of power increases in the direction opposite to the direction of power flow. Energy losses and energy efficiency of a motor or drive system must be presented as functions of physical quantities independent of losses. Such quantities are speed and load. But the picture of power stream in a motor or drive system is presented in the literature in the form of traditional Sankey diagram of power decrease in the direction of power flow. The paper refers to Matthew H. Sankey’s diagram in his paper „The Thermal Efficiency of Steam Engines“ of 1898. Presented is also a diagram of power increase in the direction opposite to the direction of power flow. The diagram, replacing the Sankey’s diagram, opens a new prospect for research into power of energy losses and efficiency of motors and drive systems.

Sime Malenica, Quentin Derbanne

ABSTRACT: The structural design of the ships includes two main issues which should be checked carefully, namely the extreme structural response (yielding & buckling) and the fatigue structural response. Even if the corresponding failure modes are fundamentally different, the overall methodologies for their evaluation have many common points. Both issues require application of two main steps: deterministic calculations of hydro-structure interactions for given operating conditions on one side and the statistical post-processing in order to take into account the lifetime operational profile, on the other side. In the case of ultra large ships such as the container ships and in addition to the classical quasi-static type of structural responses the hydroelastic structural response becomes important. This is due to several reasons among which the following are the most important: the increase of the flexibility due to their large dimensions (Lpp close to 400 m) which leads to the lower structural natural frequencies, very large operational speed (20 knots) and large bow flare (increased slamming loads). The correct modeling of the hydroelastic ship structural response, and its inclusion into the overall design procedure, is significantly more complex than the evaluation of the quasi static structural response. The present paper gives an overview of the different tools and methods which are used in nowadays practice. KEY WORDS: Hydro-structure interactions, Hydroelasticity, Springing, Whipping, Slamming, Potential flow, Boundary integral equation method, Finite element method, CFD, Model tests, Full scale measurements