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ObjectivesIn order to effectively broaden the beam width of the 3 dB axis ratio of a Beidou antenna, this paper proposes a slotted laminated microstrip patch antenna loaded with parasitic elements. MethodsThe Beidou dual frequency band feature is realized through a two-layer substrate structure. The bandwidth is widened by slotting. Circular polarized radiation is achieved by cutting corners at the edge of the patch. At the same time, L-shaped parasitic elements are loaded around the patch to broaden the 3 dB axial ratio beam width of the antenna.ResultsThe measured and simulated results are in good agreement. The relative bandwidths of the antenna in the Beidou B1 and B2 bands are 3% and 7.5%. The beam width of the 3 dB axis ratio can reach 180° and 176°, and the maximum gain can reach 6 dBi. In the Beidou receiver test, the number of antenna satellites can reach more than 17, and the positioning accuracy is within meters. ConclusionsThis paper proposes and validates a high-precision positioning dual band Beidou navigation antenna with wide axis ratio beam width. The results can provide references for the design of small Beidou navigation antennas.

ObjectiveThis paper aims to reveal the influence law of cushion pressure on the underwater noise radiation of air cushion vehicles (ACVs). MethodsAn ACV is taken as a computational example. First, the forming process of the skirt under cushion pressure is simulated according to the Newton–Raphson iteration method. Second, a numerical model considering skirt-air cushion-water coupling is established via the vibro-acoustic finite element method (FEM) and calibrated based on modal tests. Third, comparisons are made of the sound power level (SWL) of the ACV's underwater radiation noise under different pressure levels on the skirt and different cushion depression depths. ResultsUnderwater radiation noise is found to be positively correlated with air cushion pressure. The overall SWL increases by nearly 0.97 dB while the air cushion pressure increases by 1000 Pa. Increasing the stiffness of the skirt can effectively reduce the underwater radiation noise in the low frequency band, and increasing the cushion depression depth will increase the peak value of the SWL in the higher frequency band, and make the peak position shift to the low frequency direction. ConclusionThe influence law of air cushion pressure revealed in this paper has important guiding significance for evaluating and numerically predicting the acoustic performance of ACVs.

ObjectivesLow sampling rates on reconstruction surfaces cause high reconstruction error in near-field acoustic holography. Therefore, a deep learning-based approach which is applicable to planar sound sources and high-precision reconstruction with low sampling rates is put forward.MethodsA three-dimensional N-shaped convolution neural network for near-field acoustic reconstruction is established to extract features in the frequency dimension in order to make up for sparse sampling in the spatial dimension. A frequency focal mechanism, namely an adaptive frequency weight focus mechanism, is put forward to improve reconstruction precision in the natural frequency and high frequency. Moreover, this paper also raises frequency-scaled focal loss and frequency-scaled focal Kirchhoff–Helmholtz （KH） loss, which are considered regularization. To validate the proposed methods, datasets are created with COMSOL Multiphysics and Matlab.ResultsThe mean error range of 100–2 000 Hz of the algorithm proposed in this paper is only 4.96%, higher than those of SRCNN and PV-NN.ConclusionsThe proposed method is verified as having the potential to reconstruct the accurate velocity fields of sound sources under low sampling rates.

ObjectivesIn order to assess the vitality of shipborne equipment consists of important components of a warship system under the action of an anti-ship missile implosion load, this paper propose a response failure analysis method.MethodsThe shock response of a typical hull structure subjected to an internal explosion is numerically simulated, and the shock response spectrum is calculated to determine the impact environment of the location of the shipborne equipment. ResultsThrough the shock response spectrum of the typical position, the shock response parameters of shipborne equipment in different positions and at different installation frequencies are obtained, and a failure probability model is established through comparison with the shock design value, thereby forming a shock response failure analysis method for shipborne equipment. ConclusionsThe method proposed in this paper allows the calculation of the failure probability of typical shipborne equipment, and the results can provide references for the damage assessment and failure analysis of shipborne equipment under implosion load.

ObjectiveIn order to set or improve the lightning protection measures of ships, it is necessary to evaluate the strike risk of critical equipment and the protection effect of the lightning rod.MethodsIn this paper, a lightning leader fractal model is constructed and applied to a simulation study on the lightning attachment process of a ship. The configuration method of the simulation boundary of the model and the quantitative evaluation method of lightning strike risk are improved, and a quantitative study on the influence of different factors on the lightning strike risk of the ship is performed.ResultsThe simulation results show that the protection probability of the lightning rod in the middle of the ship is more than 75% under the basic configuration. The bow, stern and antenna far away from the lightning rod have a relatively large risk of circling strike. The lightning strike probability of the shipboard antenna is lower if the lightning initiation position is closer to the lightning rod, the lightning current is greater or the lightning rod is higher.Conclusions The lightning leader fractal model constructed in this paper can be used to investigate the weak links of direct lightning protection on the surface of ships, which can provide useful references for the direct lightning protection design of ships.

ObjectivesIn order to improve ship propulsion performance and efficiency, and overcome such obstacles as numerous propeller parameters, complicated modeling, slow convergence of hydrodynamic numerical calculations and turbulent wake field effects, this paper proposes an efficient propeller optimization method.MethodsA parameterized propeller constructed with non-uniform rational B-spline based free form deformation (NFFD) technology is used as the output. The CFD numerical simulation is applied to predict its performance characteristics and the Gaussian approximate prediction model of the propeller performance is established based on the simulation data. The optimization model aims to improve efficiency and reduce the torque coefficient by using the second-generation non-dominated sorting genetic algorithm (NSGA-II) method to obtain the optimal solution.ResultsThe results show that under the uniform flow field and wake field behind the ship, the optimization results of the propeller have similar laws; that is, the blade width and thickness of the propeller show a decreasing trend, while the inclination angle shows an increasing trend. The flow velocity decreases in the wake field behind the ship, so the reduction in width and thickness and increase in inclination angle of the propeller blade are smaller than those in the uniform flow field. ConclusionThe method proposed in this paper can be used to achieve the more efficient optimization design of propellers under uniform flow fields and wake fields behind ships.

ObjectiveThis paper analyses the fatigue life of weld cracks in a large opening coaming with a conical shell under uniform pressure load. MethodsFirst, a finite element model of an underwater pressure-hull structure is built. Next, the peril point and its fatigue life are calculated using the structural strain method. Finally, the accuracy of the structural strain method used in the fatigue life evaluation of the underwater pressure-hull structure is verified through a comparison with the calculated results of the experimental data model.ResultsThe results show that the maximum structural stress is located at the weld of the coaming near the large end, which is the same as the appearance location of fatigue cracks in the experiment. The fatigue life calculated using the structural strain method shows good agreement with the experimental results, and the data of the model fatigue experiment is located in a narrow band of the master e-N curve. The normal structural stress is far greater than the shear structural stress at the peril point of the coaming weld. ConclusionsThe structural strain method can effectively solve problems with the fatigue life of weld cracks in a large opening coaming with a conical shell. Under the load conditions of this paper, the initial crack at the peril point should be type one.

ObjectiveThis paper aims to analyze the explosion loading characteristics in a confined ship cabin with a pressure relief hole, and the impact of the pressure relief hole in propagating shock loads from the explosion affected cabin to the adjacent cabin.MethodFirst, a numerical simulation of the explosion venting effect on a double cabin is conducted, and the pressure drop of the explosion affected cabin is analyzed with the Baker empirical formula. On the basis of the pressure distribution characteristics in the adjacent cabin, the empirical formula for the initial peak pressure in the adjacent cabin is deduced using the least squares principle.ResultsThe results indicate that the increase in the size of the pressure relief hole will change the initial state of the pressure field in the explosion affected cabin and adjacent cabin during the explosion venting process, weakening the pressure convergence and superposition in the explosion affected cabin, and strengthening the pressure propagation in the adjacent cabins. Without considering the influence of structural deformation, the shock wave presents a peach-shaped and jellyfish-shaped pressure distribution after passing through the pressure relief hole, and the phenomenon of pressure stratification and attenuation with angle occurs.ConclusionThe results of this paper can provide references for the study of explosion load characteristics in cabins.

This paper starts with the importance and basic physical phenomena of underwater explosion, explaining the background and significance of ship damage and protection research under underwater explosion loads, research progress and status, as well as key challenges. To address these challenges, the paper elaborates on popular underwater explosion theories, models and methods. In terms of theoretical and computational research, a unified theory of bubble dynamics is presented, as well as a transient strong non-linear gas-liquid-solid fully coupled model and numerical method for underwater explosion, which have been used to develop a fundamental industrial software FSLAB capable of solving practical problems in fluid-structure interaction. In terms of experimental research, underwater explosion surrogate experimental methods and model testing methods are elaborated. Based on this, theoretical analysis, computational and experimental results in the field of ship damage and protection under underwater explosion loads are presented and discussed, aiming to provide references for underwater explosion-related research.

ObjectivesThis papers aims to analyze the impact resistance of honeycomb structure with different Poisson's ratio. MethodsBased on the explicit dynamic finite element method, this paper analyzes the dynamic mechanical properties of honeycomb structures with different Poisson's ratios under in-plane impact load, and explores the influence laws of Poisson's ratios on their impact resistance. Three typical honeycomb structures with negative/zero/positive Poisson's ratios (reentrant hexagon, hexagon and semi-reentrant hexagon) are selected, their geometric parameters are changed to give them the same relative density and different Poisson's ratios (−2.76 – +3.63), and their dynamic mechanical properties under low/medium/high-speed dynamic displacement loads are analyzed. ResultsThe results show that the zero Poisson's ratio semi-reentrant honeycomb structure has the best structural stability without transverse deformation under compression deformation; without structural instability, the platform stress has little correlation with the Poisson's ratio; and the compact strain and total energy absorbtion increases with the absolute value of the Poisson's ratio. Negative Poisson's ratio honeycomb structures with large t/l and small θ are suitable for applications with high platform stress (strong deformation resistance), and negative Poisson's ratio honeycomb structures with small t/l and small θ are suitable for high total energy absorbtion applications, while zero Poisson's ratio semi-reentrant honeycomb structures are suitable for applications with high platform stress (strong deformation resistance). ConclusionsThis study can provide references for the type selection and geometric parameter design of side impact honeycomb structures.

Objective This paper carries out an experimental study of a multi-function dirllship model with moonpool structure in towing tank, aiming at analyzing the effects of the moonpool structure on the ship resistance in open and closure condition.MethodsTaking a dirllship as the research object, the ship motion response in regular and irregular waves is investigated. The resistance of the ship in hydrostatic water and waves is measured with tension sensors, and the acceleration characteristics of the bow, midship and stern are analyzed by acceleration sensors.ResultsThe results indicate that hull resistance under light load conditions is greater when open moonpool, while hydrostatic water resistance with closed moonpool is greater under design load conditions. The closed moonpool in regular waves reduces stern acceleration by 58.2%, bow resistance by 46.7% and heave response by 41.8%. The peak of resistance at the bow in irregular waves is about ten times higher than that at the stern, and the peak of resistance occurs more often when the moonpool is open at the same time.ConclusionsThe experimental study shows that the difference in load conditions changes the waterplane area and affects the hull resistance in hyrostatic water. In contrast, the closure of the moonpool not only reduces acceleration and resistance, but also improves surge and heave. As such, this paper can provide references for the structural design of drillships with moonpools.

ObjectivesThis paper aims to study the problems that the external electrical characteristics of a hydrogen fuel cell are soft, its dynamic characteristics are poor and its system stability is susceptible to the influence of propulsion load in marine hydrogen storage DC electric propulsion systems. MethodsFirst, an analysis is performed of the output external electrical characteristics of the hydrogen fuel cell and the propeller load conditions of the marine electric propulsion system, then a ship-engine-propeller model and a frequency-domain model of drive control system for a permanent magnet synchronous motor (PMSM) are set up. Next, a speed-loop bandwidth design method is proposed, considering the external electrical characteristics of hydrogen fuel cell and propeller load conditions. Finally, on basis of the parameters of a mother ship, an electric propulsion system for a hydrogen-battery DC electric propulsion ship in a hardware-in-loop experimental platform is established to verify the proposed method.ResultsThe experimental results show that the speed response of the motor has no overshoot under this method, and the speed-loop fluctuation is reduced by 5 r/min when the load torque disturbance occurs. ConclusionsThe speed-loop bandwidth design method proposed in this paper improves the comprehensive characteristics of the ship hydrogen storage DC electric propulsion system, and is easy to implement in engineering.

ObjectiveThis paper aims to evaluate the impact of flow-induced vibration on the receiver performance of low-frequency magnetic antenna in an underwater environment, investigating the electromagnetic-induced noise of antenna under different vibration conditions. MethodsFirst, a fluid excitation antenna vibration model is established using COMSOL software, then an antenna vibration-induced noise model is constructed to simulate electromagnetic-induced noise. Finally, outdoor experiments to measure the antenna vibration-induced noise are carried out. Results The results show that the stronger the antenna vibration is, the greater the electromagnetic-induced noise is. When the antenna vibration acceleration reaches 0.029 4 m/s², the electromagnetic-induced noise above the pT level will be caused, and the normal communication signal will be submerged. ConclusionThe results show that the proposed model in this paper can be used to evaluate the vibration-induced noise of low frequency magnetic antenna.

ObjectiveCargo loading and unloading plan generation time and safety evaluation have a great influence on the handling efficiency. To this end, this paper introduce weight coefficient searching genetic algorithm into the plan generation. MethodsLoading safety status mainly involves draft limitation, intact stability checking, hyrostatic strength checking and compatibility between the generated loading and unloading plan and preset process. In this study, a non-deterministic polynomial and corresponding optimization objective functions are established to solve the loading and unloading scheme generation problem of liquid cargo carriers. The weight of each influence factor in the objective function is changed and recorded in sequence to form an optimal objective function cluster. The optimal solution of each member in the cluster is then carried out through an elitist preservation genetic algorithm in order to provide an optimal solution set. On this basis, a comparison is made with the loading and unloading plan of a very large crude oil carrier (VLCC) generated by the linear fitting methodResultsThe ship draft status is more consistent with the target, and the stability state is obviously better than that of the user preset plan in each loading/unloading step generated by this algorithm. ConclusionThe weight coefficient searching genetic algorithm based on elitist preservation proposed in this paper can improve the accuracy and reliability of the liquid cargo carrier loading sequence.

ObjectiveThe purpose of this paper is to explores the water-entry slamming load distribution of a trimaran connecting bridge.MethodsBased on OpenFOAM open source software and starting with the continuity equation and N-S equation, this paper establishes a free entry slamming numerical model of a trimaran connecting bridge. The dynamic changes of velocity, slamming pressure and free surface during the free entry slamming process of the trimaran connecting bridge are simulated. The convergence analysis of the grid is carried out, and the numerical solution is compared with the experimental solution to verify the accuracy of the numerical calculation method. ResultsThe results show that this method can effectively predict the falling body slamming load of a trimaran connecting bridge structure. It is found that the slamming pressure coefficient of the connecting bridge is largest near the outer corner. The peak value of the slamming pressure on the lower surface of the connecting bridge and the relationship between the slamming pressure coefficient and velocity are then obtained.ConclusionsThis study presents the characteristics and range of slamming pressure on a trimaran connecting bridge, providing a numerical basis for the structural strength evaluation and design of trimarans.

ObjectivesIn order to solve problems such as bad weather conditions, remote routes, long rescue time and no suitable port of call for rescue supplies, which are unique to polar routes and not conducive to personnel safety, this paper presents a design concept in which the polar cruise ship itself is the best lifeboat in the event of fire or flooding, and discusses an electrical system design method for realizing this concept.MethodsThis paper analyzes the characteristics of the polar route environment, summarizes risks and countermeasures, combines the Safe Return to Port (SRtP) concept and proposes the functional goals of important electrical systems in order to guarantee the power and personnel safety of polar cruise ships. It then provides the topology for the design of redundant electrical systems and analyzes the design scheme of typical systems combined with the realized design objectives and philosophy. Results In the design and construction of small polar cruise ships, the design principle of double redundancy or isolation should be adopted as far as possible in order to achieve the design goal of maintaining the operation of important electrical systems after accidents, thereby greatly improving the life safety guarantee of cruise ship personnel. ConclusionThis paper can provide ideas and references for the electrical system design of small polar cruise ships.

ObjectiveThe prediction of supporting resources has always been a focus and difficulty of naval ship comprehensive support. In this paper, a prediction model and method are proposed for the support needs of naval ship maintenance docks. MethodThe Markov process is introduced and applied to the prediction of ship dock demand. By analyzing the system characteristics of ship dock use, a Markov forecasting model and evaluation index of dock demand are established, and the validity of the prediction method is verified by case analysis. ResultsThe calculation example shows that the prediction model can better reflect the influence of ship maintenance intensity and the number of docks on the system state, and the optimal dock requirements reflected by the evaluation index are in good agreement with the actual engineering. ConclusionThe prediction model of ship repair dock demand proposed in this paper can better reflect the physical process and engineering practice, and provide theoretical support for decision analysis, giving it good practical significance.

ObjectiveThe exhaust ejection device is an important part of a ship's gas turbine intake and exhaust system. It is very important to ensure the exhaust and ejection performance of the exhaust ejection device for the normal operation of the ship. MethodsAccording to the characteristics of this type of gas turbine exhaust ejection device, this paper selects eight relevant structural parameters and two objective functions in order to analyze the parameter correlation, and determines the two design variables that have the greatest correlation with the objective function. On this basis, the design parameters are optimized based on the multi-objective optimization genetic algorithm NSGA-II, and the selected optimization scheme is applied to a gas turbine intake and exhaust system assembly model for verification. Results The results show that, compared with the original scheme, the optimized exhaust ejection device has a significantly improved ejection flow rate of the gas turbine casing, meeting the design requirements of the exhaust ejection amount, but this also leads to an increase in exhaust back pressure. ConclusionThe research approaches and results obtained in this paper have certain reference value for the design and optimization of gas turbine exhaust ejection devices.

ObjectiveA ship's system is a complex mechanism composed of multiple pieces of equipment. Due to the dynamic and non-linear characteristics of the parameters of each component, fault diagnosis is complicated. This paper proposes a dynamic feature fusion method for performing efficient fault diagnosis on the system.MethodsFractal theory, dynamic theory and the kernel principal component analysis (KPCA) method are used to reconstruct, map and filter the system state data, and obtain the principal component characteristic data matrix, square prediction error (SPE) and corresponding control limits. An offline monitoring model based on the health data of a marine diesel engine intake and exhaust system is then constructed and used to diagnose and analyze ship system faults. In order to verify the validity of the model, the fault data of the intake and exhaust system of a marine diesel engine is selected for verification and analysis. ResultsThe results show that this method can effectively realize the accurate analysis of a system's dynamic nonlinear state data and efficient analysis and diagnosis of faults, with better fault diagnosis performance than the KPCA and support vector machine (SVM) method.ConclusionsThe method proposed in this paper can realize the detection and diagnosis of marine diesel engine intake and exhaust system failures, and improve the reliability and safety of system operation.

With the constant development of power, information and other technologies, the advantages of unmanned ships are emerging in anti-mine, anti-submarine, electronic warfare, maritime security, maritime interception, and other military fields. This paper describes the development of unmanned ships and power technology and clarifies that the integrated power system has become a major trend of medium and large-sized unmanned ships. It also introduces the application of integrated power system in manned and unmanned platforms, and proposes that issues like size, weight, and control of vibration and noise are of essential for the integrated power system for unmanned platforms. In the end, this paper summarizes the trend of integrated power technology for unmanned platforms and identifies the key scientific problems of integrated power technology on unmanned platform, namely the intelligent operation of integrated power system, high-performance motor materials, information perception of complex motor system, power electronic device and system, high-performance power conversion and efficient energy storage.

ObjectivesThis paper aims to address the numerical simulation problems of the dynamic response of ships subject to near-, medium- and far-field underwater explosions by establishing several numerical methods and calculation models. MethodsFirst, load and fluid-structure interaction models are established on the basis of the Eulerian finite element method and acoustic finite element method using the field-split technique, and FSLAB fluid-structure interaction software is developed. Next, near-, medium- and far-field underwater explosions are numerically simulated respectively. The shock wave propagation law, bubble shape and load evolution characteristics of near free-surface and near-wall underwater explosions are obtained, and the shock response characteristics of a spherical shell and ship subject to far-field underwater explosions are analyzed. Finally, the FSLAB software results are compared with the analytical solutions, reference solutions and experimental data. ResultsThe results show that the FSLAB fluid-structure interaction software developed in this paper is effective and accurate in simulating the impact damage of underwater explosions on warships. ConclusionThis study can provide a basis and support for the power assessment of underwater anti-explosion and shock design of warships.

ObjectivesAiming at the operation support scheduling of carrier-based aircraft, this paper proposes a scheduling optimization algorithm based on apprenticeship learning which can quickly generate a operation support schedule for a carrier-based aircraft fleet. MethodsUsing the apprenticeship learning method, the executed and unexecuted tasks in expert demonstrations are compared in pairs to construct a sample set, and the support task scheduling classifier is trained based on the deck features of aircraft carrier. On this basis, a support task apprenticeship learning algorithm for a carrier-based aircraft fleet is designed and compared with the traditional genetic algorithm （GA） in terms of solving solution, solving time and resource allocation. ResultsThe results show that the operation support schedule obtained by the apprenticeship scheduling algorithm is equivalent to that by the traditional GA, but the rate of convergence is increased nearly fourfold, and the support resources are more evenly distributed. ConclusionsThe apprenticeship scheduling algorithm proposed in this paper can adequately learn from expert experiences and solve the problem of static single-objective carrier-based aircraft support scheduling. As such, this study provides references for further research in the field of dynamic multi-objective carrier-based aircraft support scheduling.

Objectives With the development of intelligent ships, it has been difficult for traditional crack damage detection methods to meet the detection requirements. This paper proposes a real-time crack damage detection method for box girders based on a gated recurrent unit (GRU) neural network. MethodsUsing the secondary development technology of Abaqus based on the Python language, a box girder crack damage model is built, and its acceleration response under dynamic Gaussian white noise excitation is calculated. A dataset is generated by expanding the original data using the data cropping method, and the influence of noise is considered. A box girder crack damage detection model based on GRU is established, the acceleration response dataset is directly used as input and the minimum loss function value is used as a target to train the model. This method is then compared to the wavelet packet transform-based multi-layer perceptron (WPT-MLP) model. ResultsThe comparison shows that the GRU model proposed in this paper has higher detection accuracy than the WPT-MLP model in damage location and extent detection. It is less sensitive to noise and has higher accuracy in approximate prediction. ConclusionsThe results of this study verify the applicability of GRU neural networks in the crack damage detection of box girders containing multiple plates.

Unmanned surface vessel (USV) based cross-domain heterogeneous formation cooperative navigation is an important method for overcoming the difficulties of navigation and positioning facing in the three areas of water surface, underwater and air in the future. This paper reviews related issues in the field of USV based cross-domain heterogeneous formation cooperative navigation from three aspects. First, this paper describes the development of USV at home and abroad, the concept and research progress of USV based cross-domain heterogeneous formation, and analyzes the cooperative navigation methods of USV based cross-domain heterogeneous formation, and summarizes them from three aspects: surface/underwater co-location, air-sea visual navigation, and path planning. Finally, it points out the key technologies and future development trends of USV based cross-domain heterogeneous formation.

ObjectivesOver millions of years of natural selection, fish have evolved various types of swimming modes with various advantages in efficiency, motility and tranquility, making them ideal biological objects on which autonomous underwater vehicles (AUVs) can be modelled. In order to develop a brand new AUV with lower noise and higher mobility, this paper puts forward a design for a myliobatid-inspired robot actuated by pairs of flexible pectoral fins.MethodsThe manufacturing process and actuating method of the prototype are illustrated in detail. In order to test the maximum speed and mobility of the prototype, a series of swimming tests is carried out.ResultsThe experimental results show that the prototype can complete a variety of maneuvers in water, including rolling, small radius steering and hovering, and its maximum swimming speed can reach 1.9 body lengths per second (about 0.73 m/s).ConclusionsThis paper outlines the preliminary design and swimming test of a myliobatid-inspired robot, giving it reference value as an indicator for the next generation of AUVs.

ObjectiveIn order to forecast a ship's maneuverability more realistically, it is necessary to conduct the direct simulation of the full-scale ship's maneuver. MethodsIn this paper, based on overset grid technology, calculations of the full-scale ship towing, supporting propeller open water and full-scale ship self-propulsion are first produced, and the calculations are then compared with the experimental results. On this basis, numerical simulations of the full-scale ship's 10/10 standard zigzag maneuvers are carried out to analyze changes in the ship's motion, hydrodynamics, flow field and vortex structure. ResultsThe self-propulsion results show that the numerical method used in this paper is reliable. The torque coefficient decreases due to the propeller scale effect. When maneuvering, the ship's motion is more intense. Due to the interference of the ship-rudder system, the post-propeller vortex structure is more complicated and produces a certain angle of offset with the change in drift angle. ConclusionsThe ship's motion, hydrodynamic characteristics and flow field information can be accurately obtained using this numerical method to simulate full-scale ship maneuvers, it can be used as an effective pre-evaluation tool and provide references for ship design.

ObjectiveThis paper aims to explore the hydrodynamic characteristics of underwater vehicles under the action of internal solitary waves.MethodsBased on the internal solitary wave mKdV theory under the strong stratification assumption, the incompressible Navier-Stokes （N-S） equation is discretized by the finite volume method. Combining the velocity entrance wave-making and overset grid methods, a numerical model of an underwater vehicle coupled with internal solitary waves in stratified flow is established. Through this model, the coupling process of internal solitary waves and fixed and suspended vehicles in different internal wave environments is simulated, and the variation law of the hydrodynamic load is obtained by numerical solution. ResultsThe amplitude of the force and moment of the underwater vehicle increases with the increase in wave amplitude. When the position of the fixed vehicle is close to the interface of two layers of fluid, it is more severely affected. When the suspended vehicle is close to the wave trough, the impact is more significant. The increase in the initial pitch angle will lead to a sharp increase in the horizontal force amplitude of the vehicle. In addition, the "falling depth" phenomenon occurs when a vehicle with initial speed is affected by the main wave and coda wave of an internal solitary wave.ConclusionThe results obtained in this paper have reference value for safe operation of underwater vehicles.

ObjectiveThis paper aims to analyze the horizontal trajectory tracking of an underwater vehicle.MethodsFirst, the 3-DOFs motion equation is derived based on the plane trajectory tracking control target of the underwater vehicle, and the damping term parameters and additional mass term parameters of the vehicle are obtained through the commercial CFD software STAR-CCM+ and ANSYS AQWA respectively. Combined with the dynamic configuration of the vehicle and calculated hydrodynamic parameters, a control strategy is designed on the basis of backstepping and sliding mode control technology. Finally, using the designed control strategy, the trajectory tracking simulation calculation is carried out on the Matlab/Simulink platform for both the linear and nonlinear motion trajectories of the vehicle on the horizontal plane.ResultsThe numerical simulation results show that the underwater vehicle can achieve good tracking effects for both kinds of motion trajectories, and the propeller thrust changes smoothly.ConclusionsThe controller designed in this paper can enable an underwater vehicle to track its target trajectory quickly and maintain a good continuous tracking effect.

ObjectiveIn order to reduce the wave-making resistance of high-speed ships, this paper proposes an innovative hydrofoil appendage with a drag reduction effect. MethodsAn NACA 0012 airfoil is selected for the hydrofoil appendage cross-section, and a series of studies on the drag reduction effects of bow-mounted hydrofoil appendages of different sizes and installation positions is carried out using the numerical calculation method verified by convergence and reliability tests. The drag reduction effect of adding a T-wing to the stern of a ship is further studied. ResultsThe results show that the maximum drag reduction is 7.38% and 6.82% at high speeds of Froude number 0.45 and 0.494 when the hydrofoil appendage is only installed at the bow. The drag is further reduced after adding the T-wing to the stern, and the total drag reduction is 9.35% and 11.13% at high speeds of Froude number 0.45 and 0.494. Conclusions The hydrofoil appendage with a drag reduction effect proposed in this paper greatly reduces the total drag of high-speed ships, improves their speed and provides new technical means for further improving their navigation performance.

High-speed hydrodynamics and its corresponding complex fluid-structure interactions (FSI) are challenging topics associated with naval architecture and ocean engineering, typically characterized by large deformations, moving boundaries, strong convection and multiple fluid media. Since traditional mesh-based numerical methods possess limited ability to accurately simulate such strongly nonlinear problems, it is imperative to develop meshless numerical schemes with high fidelity and robustness to tackle this dilemma. As one of the most promising truly meshless methods, smoothed particle hydrodynamics (SPH) shows apparent advantages in high-speed hydrodynamics problems thanks to its Lagrangian nature. In the present paper, the attention is particularly focused on the latest advances of several SPH techniques with respect to the following high-speed hydrodynamics problems: vessel-induced waves and wakes, the water entry process of projectiles, and underwater explosion and its resulting structural damage; in addition, the future prospects of SPH are provided in the last part of the paper.

ObjectiveAs there is still no complete set of rules regarding the general engineering design process for towed array sonar system installation aboard a submarine, it is necessary to analyze approaches to the overall engineering design of the system and systematically ascertain the key points.MethodsOn the basis of a literature review, this paper carries out an in-depth analysis of the aforementioned issue in terms of the sensor system and retraction/release system respectively, covering design scheme selection (i.e., number of towed array sonars, types of sensing element and length of towed cable-array) and device design (i.e., winch, spooling gear, conduit, driving mode and release port location). ResultsThis review derives the basic process and method of engineering design and computational formulae (i.e., calculation of cable array’s length) for a towed array sonar installation adaptable to a submarine.ConclusionsThrough striking a good balance of desirable properties and trading-off among many elements while considering the actual state of the submarine and the technical characteristics of towed array sonar hardware, submarine designers can flexibly use the relevant engineering design points discussed in this paper to achieve optimal installation schemes.

ObjectivesThe superstructure participates in the overall longitudinal bending of a ship, which leads to stress concentration in certain parts and threatens the safety of the ship's structure. The large-scale steel model test can truly reflect the structural response characteristics of superstructures. MethodsThis paper studies the structural strength of a certain ship's superstructure. Through the equivalent simplification of the main hull structure, a large-scale steel model including the superstructure and main body is designed, and structural strength model testing is carried out under hogging moment load. ResultsThe test and finite element calculation results show obvious stress concentration phenomena in the corners of the side opening groups of the superstructure and the edges of the round transitions between the sidewall and main deck. The bending efficiency of the superstructure is 0.315. ConclusionsThe results of this study can provide references for the local structural strengthening and optimal superstructure design of target ships. The simplified design method of the ship hull model provided in this paper can also serve as a reference for the design of large-scale ship models.

ObjectivesThis paper proposes a theoretical calculation method for obtaining the impact load and dynamic response of shafting during the rapid engagement process of a combined gas turbine and gas turbine (COGAG) power plant. MethodsAccording to the mechanical relationships between various components in the meshing process of a synchro-self-shifting (SSS) clutch, a dynamic analysis model of the clutch is established, and the dynamic simulation and bench test during the rapid engagement of COGAG are carried out. ResultsAs the simulation results show, when the damping dashpot functions, a significant torque impact occurs on the clutch spiral spline which can result in a strong dynamic response on the shafting. It is also found that the relative position of the ratchet and pawl is random, which can cause the peak torque impact and dynamic response of the shafting to fluctuate within a certain range. Through a power plant experiment, the accuracy of the impact load calculation method and the randomness of the impact amplitude are verified, and the errors of the maximum and minimum torque response amplitudes are 3.56% and 8.86% respectively. ConclusionsThis paper finds that the rapid engagement of COGAG can produce an obvious torque impact which can affect the safety of the power plant. As such, it can provide references for the operation safety evaluation of COGAG power plants.

The design and construction of luxury cruise ships is currently a hot topic in the domestic shipbuilding industry, but the design skills are insufficient due to a lack of practical experience derived from real projects. First, based on a survey of the internal R&D and refitting design of luxury cruise ships and ferry/passenger ship projects with gross tonnages of 15 000–75 000, as well as referring to the latest developments in rules regarding cruise and passenger ships, and the design features of delivered ships across the world, this paper seeks to review the relevant advanced technologies employed in the international design and construction of luxury cruise ships, with a focus on 3D modelling, flexible design throughout the full life cycle, holistic ship performance optimal design and alternative design application. Moreover, the effects of the application of green fuel, digital and intelligent design, and health and hygiene safety requirements on the future design of cruise ships are discussed. It is hoped that this paper can provide valuable references for improving the domestic design level of luxury cruise ships.

ObjectivesAiming at the vibration control problem, this paper puts forward a design approach involving longitudinal two-stage vibration isolation technology for ship propeller-shaft systems. MethodsFirst, a mathematic vibration model of a ship propeller-shaft longitudinal two-stage vibration isolation system is established. The effects of design parameters such as mass ratio, stiffness ratio and damping ratio on the vibration characteristics of the system are analyzed. The design is then optimized by using a ship propeller-shaft system as an example.ResultsThe results show that, for a ship propeller-shaft longitudinal two-stage vibration isolation system, the lowest natural frequency ratio control can be obtained according to the formula given in this paper under the given mass ratio or stiffness ratio. With the increase in damping ratio \begin{document}${\xi _1} $\end{document}, the attenuation of the vibration transmissibility at the second order natural frequency is more obvious. The optimized ship propeller-shaft longitudinal two-stage vibration isolation system has a better isolation effect than the single-stage vibration isolation system. ConclusionsThe results of this study have important reference value for the design of ship propeller-shaft longitudinal vibration isolation technology.

ObjectivesThis paper presents a non-singular terminal sliding mode track control method based on a finite-time disturbance observer to solve the problem of accurately tracking and controlling an the 3D trajectory of an unmanned underwater vehicle under complex external disturbances.MethodsA non-singular terminal sliding mode track controller is designed to ensure that the tracking error converges to zero accurately within a limited time. A finite-time disturbance observer is designed to improve the anti-jamming ability of the system under external multidimensional time-varying disturbances.ResultsThe Lyapunov function is used to prove that the designed control strategy can remain stable for a limited time. MATLAB is used for the simulation experiment, and a comparison with the backstepping sliding mode control method under step disturbance shows that the method presented in this paper achieves accurate trajectory tracking.ConclusionsThe results of this paper can provide a solution for accurately tracking the 3D trajectories of unmanned underwater vehicles.

ObjectivesThe effects of the key parameters of the inlet duct of a waterjet propulsor on its hydrodynamic performance are studied, providing references for the design of waterjet propulsors. MethodsBased on STAR-CCM+ software, the influence of the axis height and inlet angle of a waterjet inlet duct on its hydrodynamic performance under different intake velocity ratio (IVR) conditions is studied using steady Reynolds-averaged Navier-Stokes equations (RANS) numerical simulation. Numerical uncertainty analysis is carried out according to the international towing tank conference (ITTC) uncertainty analysis procedure. In this paper, the computational domain is discretized with hexahedral structured grids. The set of governing equations is closed using the Realizable k-ε two-layer turbulence model, and the discretization schemes are second-order accurate. The semi-implicit method for pressure linked equations (SIMPLE) algorithm is applied in the pressure-velocity coupling calculation. ResultsThe results show that the numerical uncertainty is less than 4%, indicating that the grids used in this paper yield well-converged and reliable numerical results. ConclusionsThe efficiency of the inlet duct is higher in the range of IVR = 0.7~1.1. For large IVR, the inlet angle should be reduced. For small IVR, the axis height can be appropriately increased to improve the homogeneity of flow at the exit of the inlet duct.

ObjectiveThis paper aims to study the influences of different allowable stresses of ribs in cylindrical shell design.MethodsTo this end, this paper uses full factorial experimental design and information entropy method to establish a multi-objective optimization model of ring-stiffened cylindrical shells based on the weighted-sum method, then uses the tolerance ranking method to optimize the solution of the model. Through changing the safety factor of allowable stress of ribs, the influences of them on the uniformity of the attributes of the cylindrical shell are analyzed. ResultsThe results show that the rib stress is the main constraint in design. When the safety factor of the allowable stress of ribs is 0.675, the margins of each attribute value are more uniform at about 15%, and the structural weight is relatively small at this time. ConclusionsTherefore, properly extending the allowable stress can solve the problem being the main constraint in structural design, and make the margins of each attribute value of the optimal solution more uniform.

ObjectiveThe aim of this paper is to proposes new methods for modelling a very large floating structure (VLFS) with complex connections in the framework of the discrete-module-beam (DMB) hydroelasticity theory, and makes a comparison with the existing methods. MethodFirst, a brief introduction of the DMB-based hydroelasticity analysis method is given, followed by procedures for calculating the dynamic response of VLFS under regular waves. A structural stiffness matrix is then defined to model connections with complex forms in VLFS. Corrections are made to the relationship between the forces of two lumped masses and their displacements, obtaining a revised structural stiffness matrix and excitation force matrix, and solving the new hydroelastic equations. Finally, the varying trends of the structural dynamic response of VLFS against different bending stiffness by four methods are explored, and the corresponding reasons for their response differences are analyzed. ResultsThe results show that all four methods are capable of precisely predicting the hydroelastic response of VLFS with complex forms of interconnection. ConclusionThe methods in this paper extend the application of the DMB-based method in predicting the dynamic response of non-continuous VLFS, such as multi-hinged VLFS or VLFS with fracture places.

Objectives This paper aims to clarify the characteristics of the unsteady force spectrum of a pump-jet operating under inflow turbulence. MethodsThe turbulence grid and Fourier synthesis method are employed to produce inflow turbulence with spatial flow structure and temporal fluctuation, combined with large eddy simulation (LES) to obtain the broadband unsteady force spectrum of the pump-jet. ResultsThe results show that the proposed method can obtain the unsteady force broadband spectrum for the duct, stator and rotor. The unsteady force broadband spectrum of the pump-jet is composed of the ''humps'' around the blade passing frequency and its multiples, the characteristic line spectrum at the stator blade passing frequency and the shaft frequency of the adjacent stator multiples. As the number of blades increases, the ''humps'' become more obvious and the characteristic peaks change periodically and reach the minimum when the number of blades is equal to the number of rotors. Due to the use of the stator and duct, the amplitudes of the unsteady force broadband spectrum of the pump-jet are higher than those of the propeller, but the ''humps'' are not as obvious. ConclusionsThe results of this paper can be helpful for clarifying the unsteady force characteristics of a pump-jet induced by inflow turbulence, and provide ideas for the vibration and noise reduction of pump-jets.

ObjectiveThe aim of this paper is to proposes methods for better recognizing and positioning ships sailing in critical and wide-area waterways during monitoring operation.MethodsBased on video surveillance technology, the joint use of the motion and appearance features of ship target is carried out to realize a wide-area multi-dimensional recognition function via the combination of background subtraction based moving object detection algorithm and deep learning based target recognition algorithm. In addition, the improved approaches including water ripple noise reduction, hierarchical moving object detection and window segmentation of waterway monitoring image are put forward to further improve recognition accuracy.ResultsThe field demonstration results show that the improved methods proposed in this paper allow the accurate recognition of a ship of any type or size on the monitoring screen, and the use of conventional cameras can also achieve the recognition and position of a ship navigating a water area within a radius of 3 km. Conclusions The improved methods proposed in this study have a range of advantages including wide-area monitoring, complete coverage of ship types and sizes, automatic target recognition and robust anti-interference ability.

ObjectivesNaval ship systems such as the hull structure, weapons equipment and power equipment will deteriorate during their service life. Thus, a ship maintenance strategy based on the actual deterioration state is essential for ensuring the safety and availability of naval ships. MethodsIn this paper, a multi-state deterioration system model is established on the basis of the Markov decision process. A reinforcement learning mode is then introduced to train the agent that generates the maintenance strategy, and the optimal condition-based maintenance strategy is obtained in the process of adaptive learning. ResultsThe proposed method is applied to a ship structural deterioration system for demonstration, and the results show that it can obtain the optimal maintenance policy for a multi-state deterioration system considering the actual conditions, thereby providing an intelligent supporting tool for decision-makers to formulate optimal ship maintenance strategies. ConclusionsThis paper shows that the reinforcement learning method has great potential in comprehensively improving ship maintenance support.

ObjectivesThe "cost plus 5% profit" pricing method has been adopted for ship equipment scheduled repair for many years, but it does not reflect quality and schedule of repair project, so it is unable to motivate contractors to cost-effectively improve their repair work.MethodsThis paper chooses cost, schedule and quality as the incentive factors, and develops an incentive fee method which distinguishes between the fixed and incentive parts of the cost, with a schedule-based incentive fee to encourage the elimination of delays by Party A and a quality-based incentive fee to encourage the construction of a quality evaluation index based on the features of ship equipment scheduled repair.ResultsThe example analyses show that the contractors can thus earn reasonable profits from contracts adopting this method, Among the examples,projects with better overall performance can break the 5% profit margin limit.Conclusions The method put forward in this paper can effectively motivate contractors to control their costs, improve their quality and accelerate their schedule. This is of great practical significance for perfecting the incentive fee mechanism and promoting effective ship equipment scheduled repair.

ObjectivesThis paper aims to study the fatigue damage problem of large ship prone to springing effect.MethodsThe test result in two generation 400 000 DWT very large ore carrier (VLOC) are compared based on ship model test method, and the relation of sea states and fatigue including hull girder springing are analyzed. According to the recursion method, a classical sea state is selected from a series of model test sea states.ResultsThe results show that the fatigue damage magnification effect has a trend relationship with significant wave height and encounter period. The concept of "dominant sea state" is proposed based on the recurrence method, and the expression of fatigue damage magnification factor is improved. The springing effect varies significantly according to different sea states, and the fatigue damage magnification effect of springing increases very rapidly as significant wave height and encounter period decrease.ConclusionsReplacing multiple model test loading conditions with dominant sea state could allow relatively accurate fatigue damage magnification factor to be ascertained rapidly. As such, this paper can provide references during the initial design period.

ObjectiveIn order to accurately assess the ice resistance experienced by an icebreaker during continuous icebreaking when sailing in a level ice zone, and understand the characteristics of different prediction methods, this paper uses the empirical formula method, numerical simulation method and ship model test method to evaluate an icebreaker's continuous sailing in smooth ice and predict the ice resistance. MethodIn this paper, the nonlinear finite element software DYNA is used to construct ice numerical simulation models based on the traditional finite element and cohesive element methods respectively, and simulations are performed of the bending fracture and interaction process that occurs when level ice interacts with an icebreaker. At the same time, using the empirical formula method, three different empirical formulas are used to calculate the ice resistance, and a sensitivity analysis of the parameters affecting the prediction results of the empirical formula method is also carried out. ResultsThe study finds that ice resistance shows an upward trend with the increase in speed, ice thickness and bending strength. Among them, ice thickness has the greatest influence on ice resistance. Among the three empirical formulas, the prediction results of the Lindqvist formula are closer to the ship model test results, while those of the Vance and Lewis formulas are more conservative. The traditional finite element and cohesive element methods obtain more accurate ice resistance prediction results when the thickness is small. When the thickness is large, the error is about 25%. In case of small ice thickness and high speed, the ice resistance value predicted by the cohesive element method is more accurate than that of the traditional finite element method, and the accuracy error is within 10% compared with the ship model test results. ConclusionIn the actual ice resistance prediction, the empirical formula method and numerical simulation method can be combined to take into account the accuracy and efficiency of the prediction results.

The physical and mechanical properties of sea ice and the failure modes of ice sheets significantly affect the ice loading of offshore structures. This paper first introduces the physical and mechanical characteristics of sea ice, then describes the physical processes of the interaction of ice sheets with offshore structures. Finally, the progress of research on the ice loading of offshore structures is briefly analyzed, including the three main approaches of formula estimation, experimental testing and numerical simulation. By discussing the applicability of formula estimation, the research focus and difficulties of experimental testing, and the development trends of numerical simulation, we find that the model testing of ice loading is an effective method. This paper covers the research trends and problems faced by ice loading on offshore structures, and it can provide certain guiding references for the related research of scholars in the field.

ObjectivesChinese ship design and approval institutions usually use different 3D design platforms, which can cause the problems of unsmooth model transfer and ineffective data conversion. This paper addresses the data conversion techniques of 3D ship structure models to ascertain whether a converted model can be directly used by classification societies for approval.MethodsBy analyzing the model data of the CAD and CAE systems, the required data for generating an approval-oriented 3D hull structure model is summarized. The storage format of the required data and the interface between the stored data and common 3D software platforms are introduced. Taking a cargo tank section of a ship as an example, the required data of the 3D model of the target section is stored in an XML data file. Based on this data file, the design model and FE analysis model of the target section are reconstructed through CATIA and Patran software, and equipped with a secondary developed interface.ResultsThe reconstructed model has been submitted to Bureau Veritas (BV) for direct approval of the structural design.ConclusionsThe data conversion method proposed in this paper simplifies model transfer among different platforms, and can provide valuable references for realizing the paper-free approval of 3D ship models.

ObjectivesIn order to obtain a simplified mathematical model of ship motion for intelligent control, this paper takes a Mariner-class vessel as the research object and proposes a sensitivity analysis method combining the standard maneuverability test and PID (proportion-integral-differential) heading control test.Methods Compound analysis of the control index, maneuverability index and squared loss of typical motion state variables throughout the entire process is performed to obtain a dataset containing multi-dimensional sensitivity coefficients. A K-means machine learning algorithm is introduced to perform cluster analysis on the dataset. The sensitivity division of hydrodynamic derivatives is completed and the model is simplified.ResultsContrastive simulation tests of heading control and track control are carried out among the simplified model, former simplified model and complete model, and the results show that the sensitivity analysis method proposed in this paper is effective and the model proposed in this paper has higher control prediction accuracy.ConclusionsThe method proposed in this paper has certain significance for guiding ship motion modeling for intelligent control.

With the development of structural protection design concepts, numerous multicellular filled impact resistant protection structures have gradually emerged. As many studies at home and abroad show, great progress has been made in the strength and vibration characteristics of multicellular filled impact resistant protective structures compared with traditional structures. Meanwhile, the overall optimization direction of such structures has also progressed from traditional linear studies to various nonlinear and multi-material design methods. In this paper, the exposition of various multicellular filled impact resistant protective structures is carried out in terms of mechanical properties, failure modes and protection characteristics. By generalizing the theoretical calculation methods and response characteristics of various multicellular filled impact resistant protective structures, this paper puts forward the development prospects of such structures for use as references in the study of structural forms, optimal design and application directions.

ObjectivesThis paper proposes an algorithm for optimizing the layout of carrier aircraft in a hangar. MethodsTo solve the problem of the mixed layout of aircraft in a hangar, based on the basic spatial combination relationship, this paper sets up a combinatorial relationship library, optimizes the solution space and converts the constrained two-dimensional layout problem into a combinatorial optimization problem. A hangar layout model is established with the maximum number of carrier aircraft and maximum number of emergency dispatch aircraft, and a heuristic algorithm is used to solve the model.ResultsUsing the case study of a USS Nimitz-class aircraft carrier, the resulting layout scheme can maximize the total number of carrier aircraft while ensuring the number of emergency dispatch aircraft, and the results satisfy actual business constraints and requirements. Compared with the layout scheme of USS aircraft carrier, the area utilization rate of hangar deck is increased by 16.92%.Conclusions The proposed algorithm can be used to effectively solve the layout problem of carrier aircraft in a hangar.