Search

ObjectivesIn the context of global carbon reduction, in order to meet the environmental require-ments of the design and construction of polar ships, this paper studies the impact of brash ice on the optimal design of polar expedition cruise ships when navigating across oceans and designs the most optimal energy-saving hull lines. MethodsIn view of the transoceanic characteristics of polar expedition cruise ships, the navigation region-based weighting method is used to quantify the evaluation and analyze the impact of brash ice on resistance and propulsion efficiency. An analysis is carried out of the performance of the propeller in broken ice channel through the coupling calculation of the computational fluid dynamics-discrete element method (CFD-DEM), an optimization model with the goal of combined self-propulsion power is established, and optimization calculations are performed for the parametric model of the whole ship at the designed speed.ResultsThe calculation results show that the optimized ship hull meets the requirements of displacement and effectively reduces navigation power in open water and broken ice channel with a combined self-propulsion power reduction of 9.71%.ConclusionsThe results of this study verify the feasibility and rationality of optimization based on the weighting method, and can provide references for the optimization design of hull form and thrusters of polar expedition cruise ships.

ObjectivesIt is difficult to control the drum water level of a supercharged boiler due to the strong load disturbance in the sailing process. In order to ensure the stability of the drum water level, it is necessary to study drum water level control methods under strong load disturbance. To this end, this paper proposes a sliding mode controller with an improved adaptive genetic algorithm (AGA). MethodsThe velocity and accelerated speed of the drum water level error is combined with an S-function to design a sliding mode controller. Its stability is then proven using the Lyapunov stability theorem. On this basis, the sliding mode controller parameters are optimized with the improved AGA. ResultsThe control performance of the sliding mode controller with improved AGA is compared with that of a PID controller. In response to ramp disturbance signals and step disturbance signals, the sliding mode controller with improved AGA can track the input signal without error. Its stability time is 5 s shorter than that of the PID and its overshoot is lower than that of the PID. ConclusionsThe simulation results show that the sliding mode controller with improved AGA is superior to the PID controller.

ObjectivesThis paper investigates the influence of the span-wise stiffness of a flapping pectoral fin on its generated thrust. MethodsA scheme to fabricate a flexible pectoral fin with uniform span-wise stiffness is introduced. A series of experiments is then conducted to investigate the generated thrust and lateral force of the fabricated pectoral fin with different degrees of span-wise stiffness in the frequency range of 0.3−1.0 Hz. Combined with collected shots by a high speed camera, the impact of span-wise stiffness on generated force is analyzed. Results The experimental results show that the average propulsion force and the average lateral force generated by the flexible bionic pectoral fins are related to the size and distribution of the radial stiffness of the fin in the range of the tested flap frequency. By optimizing the spreadal stiffness of the flexible bionic pectoral fin of the robotic fish prototype (XJmanta), the maximum swimming speed can be increased by about 45%.ConclusionsThe results of this study can be used to guide the design of flapping flexible bionic pectoral fins and optimize the hydrodynamic performance of ray-like underwater robots.

ObjectiveThe artificial bee colony (ABC) algorithm has such characteristics as few control parameters, strong local optimization ability and fast convergence speed. However, when solving path optimization problems, it can easily fall into local optimal solutions. In order to solve the problem of pipeline routing in a ship pipeline system, an improved artificial bee colony (IABC) algorithm is proposed. MethodBased on the traditional artificial bee colony algorithm, the crossover operation of genetic operators is introduced into the update mechanism of following bees, and an adaptive strategy is adopted for the crossover probability of the crossover operator. The crossover operation on the population is used to find new solutions in the global range. The way scout bees search for new paths is improved from updating the points that the path passes to updating the "road sections" in the path. This paper proposes an artificial bee colony co-evolution algorithm for solving the optimization of branch pipeline paths. ResultsCompared with the standard artificial bee colony algorithm, the improved algorithm can improve the path layout effect by 32.3%–37.4% and the convergence speed by 17.7%–29.9%. ConclusionThe improved artificial bee colony algorithm proposed herein has higher solution quality, faster convergence speed and better stability than the traditional artificial bee colony algorithm for a single pipe or branch pipe.

ObjectivesAiming at the challenge of accurate diving modeling of a smart float, an anti-saturation and noise least squares (ASNLS) algorithm is proposed in this paper to achieve diving multi-parameter identification and depth prediction. MethodsFirstly, the nonlinear motion characteristics of the smart float actuator were included in the gray box-based diving model to better fit the actual model, and the continuous diving motion equation was transformed into a discrete form to match the real-world discrete data sampling. Subsequently, the aforementioned discrete diving model was constructed into a correlation form to attenuate the influence of data noise. Finally, by adjusting the values of the covariance matrix, the designed diving parameter identification algorithm achieved resistance to data saturation. ResultsBased on the data of the South China Sea deep diving experiment of the smart float in 2021, diving model parameter identification and depth prediction are carried out. The results demonstrate that the ASNLS algorithm has faster convergence speed (31.8% higher than the least squares algorithm) and smaller depth prediction error (average absolute percentage errors less than 9% at different depths) than both the traditional least squares algorithm and supports the vector machine algorithm.ConclusionsConsequently, the ASNLS algorithm can provide effective support for the depth control and prediction of the smart float.

Objective In systematic operations, ship formation navigation faces such challenges as equipment damage, electromagnetic interference and complex operational environments. To solve these problems, this paper proposes a distributed network-based integrated navigation system and method for surface warship formations that can improve the robustness and flexibility of ship navigation in complex environments.Methods The formation cooperative navigation system is divided into the equipment level, subsystem level and system level. At the equipment level, the original navigation data of GNSS/INS is output. At the subsystem level, the node navigation data is output. At the system level, the formation cooperative navigation data is generated by fusion. In order to realize the data fusion of formation cooperative navigation at the system level, a distributed formation cooperative navigation network is constructed using the Floyd algorithm based on the principle of shortest baseline transmission path, and the node cooperative navigation data is generated through dynamic baseline transfer on the basis of the node navigation data. The formation cooperative navigation data is then output by fusing the cooperative navigation data of multiple nodes through the weighted least square method. Results The simulation results show that the proposed method successfully constructs a distributed cooperative navigation network which can ensure the uninterrupted navigation of damaged nodes through navigation support and improve the navigation accuracy of disturbed nodes through precision support.Conclusion The distributed cooperative navigation method has such advantages as anti-damage, anti-jamming and improved accuracy, enabling it to effectively deal with complex combat environments.

ObjectiveThis paper investigates the coupling effect of ship nonlinear wave load and transient high-amplitude slamming load in view of the whipping response of ships under extreme sea conditions. MethodsA two-way computational fluid dynamics-finite element method (CFD-FEM) fluid-structure interaction method is used to carry out the numerical simulation of an S175 container ship, and the results are compared with the test results and 2D linear strip theory. The testing of a segmented ship model with a variable cross-section elastic backbone is carried out, and the analysis of the bow's slamming load and high-frequency nonlinear whipping characteristics is undertaken based on the two-way CFD-FEM fluid-structure interaction method. The results are then verified through comparison with the model test. ResultsThe influence of wave slamming load on the whipping response of the bow cannot be ignored. The second order high-frequency component induced by whipping accounts for 59.86% of the low-frequency wave bending moment in sea state 6. ConclusionsThe proposed two-way CFD-FEM fluid-structure interaction method can calculate the whipping response accurately. The nonlinear wave-induced load and dynamic structural response of the ship under extreme sea conditions are affected by the transient slamming load of the bow. In conclusion, the high-frequency whipping response should be taken into consideration in the safety design and assessment stages of ship structures.

ObjectiveIn view of the failure of type-I steel sandwich plate interfaces, this paper analyzes their interface fatigue debonding characteristics. MethodsBased on the cohesive force model and considering the time history, damage evolution equations and convergence criteria of 3D structural nodes with multiple degrees of freedom, an interface fatigue debonding simulation program suitable for 3D complex structures is developed. The accuracy of the developed program is verified through a comparison with the experimental results of welding joint debonding, and the interface fatigue debonding behavior of type-I steel sandwich plates is simulated numerically. ResultsThe results show that the maximum simulation error between the 3D interface fatigue debonding test and debonding experimentis only 14.05%. When an type-I sandwich plate is subjected to out-of-plane load, the debonding failure at the interface mainly manifests as surface crack propagation in the direction of the extended weld. When the crack propagation reaches about 70% of the length of the plate, the crack begins to penetrate through the web to form a penetrating crack.ConclusionThe interface fatigue debonding program developed herein can effectively evaluate the interface fatigue debonding life of type-I steel sandwich plates, giving it certain guiding significance for practical engineering applications.

ObjectiveThis paper aims to study the wind-induced noise of typical rods in the open areas of cruise ships. MethodsThe numerical simulation of aerodynamic noise and wind-induced vibration noise is carried out using computational fluid dynamics (CFD) combined with the acoustic analogy method and vibro-acoustic coupling method in order to explore the generation mechanisms and characteristics of the two kinds of noise. Results Under different wind speeds, the maximum frequency of aerodynamic noise is dominated by the vortex shedding frequency, while the maximum frequency of wind-induced vibration noise is dominated by the natural frequency of the structure. The aerodynamic noise of three different cross-section rods is generally greater than that of wind-induced vibration noise, and the aerodynamic noise of square rods is the greatest. Under large flexibility, when the fluctuating pressure frequency of the rod is close to the natural frequency, the wind-induced vibration noise will be close to or even exceed the aerodynamic noise. ConclusionsIn the design of typical rods to be applied in the open areas of cruise ships, in order to reduce wind-induced noise, circular rods should be selected, square rods should be avoided, reasonable rod sizes should be selected and the vortex shedding frequency of the rods should not be close to the natural frequency.

This paper reviews the research status of intelligent ship berthing technology at home and abroad in recent years. The hotspots and applications of berthing technology are summarized in the three aspects of berthing mode, mathematical model and control algorithm. The remaining problems in this field are analyzed in terms of autonomy, modeling accuracy, path planning, control algorithm, energy-saving effect and system test. Based on actual navigation needs, it is proposed that the next step is to make breakthroughs in core theories and key technical problems such as information fusion, online modeling, intelligent decision-making, optimization algorithms, green energy conservation and testing technology. The autonomy, robustness, rapidity and "toughness" of berthing technology should be improved so as to realize safe, green and efficient intelligent shipping.

The advantages of fish such as high propulsion efficiency, strong maneuverability and low environmental disturbance have sparked extensive research on bionic robotic fish by both domestic and international scholars. The basic-level gait control method and closed-loop motion control method are currently two hot topics in research on robotic fish control. According to the propulsion mode classification method, this paper summarizes the prototype development and performance of various robotic fish, introduces the research progress of the propulsion mechanisms and hydrodynamics of robotic fish, focuses on two basic gait control ideas, namely the trajectory approximation method and central pattern generator （CPG）, and summarizes the typical closed-loop motion control method. The CPG method has stronger flexibility, stability and operability, and it is easy to introduce feedback items and achieve closed-loop control, for which it plays a leading role in the basic gait control of robotic fish; while the improved learning-based control method and hybrid control method combining multiple methods based on the significant characteristics of robotic fish have broader development prospects, which is in line with the development direction of intelligent biomimetic robotic fish. Establishing a reasonable gait control system and an accurate and efficient closed-loop motion control system based on working conditions and motion requirements is the key to improving the overall performance of robotic fish.

ObjectiveAiming at the problem of the autonomous berthing control of tugboats, this study focuses on the application of a target tracking control strategy based on virtual leadership. MethodsFirst, the autonomous berthing process of the tugboat is transformed into the target tracking control process of the virtual tugboat and actual tugboat. A kinematics model of the berthing system is then designed. Considering special environmental interference in the berthing scenario, the backstepping method and sliding mode control method are used to design an autonomous berthing controller for an azimuth stern drive tugboat. Three different sliding mode surfaces are provided and the stability is verified by the Lyapunov function. Finally, a simulation test is used to verify the control effect through the berthing trajectory, speed error and distance error. ResultsThe simulation results show that the designed tugboat autonomous berthing control strategy and controller have a good effect in the tugboat autonomous berthing scenario and good performance in the face of uncertain disturbances of the system. ConclusionsThe control strategy and berthing controller designed in this paper have good applicability and robustness. The autonomous berthing control of tugboats is realized from a new angle, providing a new direction for subsequent research on the berthing control of tugboats.

ObjectiveThis paper develops a multi-stage path planning algorithm for the auto docking operation of an underactuated surface vehicle (USV). As one of the most difficult tasks, docking requires advanced maneuvering skills. Therefore, it is necessary to generate a smooth trajectory in the berthing environment while maintaining control accuracy. MethodThe proposed method introduces a hybrid A* search algorithm in the pre-docking stage in which the well-known A* search algorithm is combined with the kinematic state space of the USV using the Reeds–Shepp curves, enabling it to produce sub-optimal paths that guarantee kinematic feasibility and low collision risk. For the docking stage, a cubic Bezier curve is introduced to represent the target path. The generated trajectories are then tested in numerical simulations wherein a mathematical model of a ship with two fixed propellers is established and verified. ResultsThe simulation and experimental results show that the path planning and tracking performance of the method are satisfactory.ConclusionThe proposed path planning method can contribute to automatic ship docking and the development of smart ships.

ObjectiveAiming at the problem of ship hull number recognition, this paper proposes a real-time ship's hull number recognition method for unmanned surface vehicles (USVs). MethodsBased on a one-stage object detection model (e.g. YOLO), the attention mechanism is introduced to make the network more sensitive to the target area by the spatial information interaction module and divided attention method. Considering the effect of prior knowledge on accuracy, the adaptive anchor method and positive sample assignment strategy are utilized to improve the accuracy of regression. Aiming to resolve the problem of slow convergence at the beginning, the loss function is redesigned to speed up the convergence and enhance the stability of the network in the training phase. Finally, the proposed method is deployed in a USV to validate the availability of the recognition performance. ResultsThe results shows that the proposed method can achieve the recognition of ships and hull numbers simultaneously under Sea State 3 conditions, and has a 14% improvement in mean average precision (mAP) compared with the original model, with the ability to perform recognition in real time. ConclusionThe results of this study indicate that the proposed method can be applied to USVs to perform hull number recognition, even under complex ocean conditions.

ObjectiveThis paper aims to investigate the complex influence of environmental disturbances on unmanned surface vehicles (USVs) under real ocean conditions, and control USVs to overcome disturbances and realize path following. MethodsAn improved active disturbance rejection controller (ADRC) based on the model-free adaptive control (MFAC) law (ADRC−MFAC) is proposed to establish the non-linear relationship between the input data (rudder angle) and output data (heading angle, angular velocity), and identify the unknown disturbances of the system. In this way, stable heading control can be achieved. Combined with the adaptive line-of-sight (LOS) guidance law, it achieves accurate tracking control through dynamic heading control.ResultsThe simulation results show that the controller can control USVs to approach the preset path quickly and achieve a desirable tracking control effect under complex disturbances. ConclusionThe research results do not depend on the specific model of USV and can provide valuable references for ship tracking control.

ObjectiveThe independent cabling operation of an autonomous underwater vehicle (AUV) in complex submarine terrain should balance cabling quality with self-safety, which means that the AUV should maintain a stable height relative to the seabed. To this end, this paper designs an optimal obstacle avoidance design for a cable-laying AUV based on model prediction control (MPC).Method First, the method establishes a path-following control model based on MPC. It then classifies different obstacles into topographic bulges or depressions, and establishes a simplified mathematical model of the obstacles. Second, the method designs multiple objective optimization functions for different topographic environments according to the feature points, allowing the AUV to choose the shortest path with the minimum variation in cable-laying height. ResultsThe results show that this method achieves the most minimal changes in cable-laying height while also choosing the most optimal path to avoid obstacles. ConclusionThe proposed method not only ensures the safety of AUVs in complex submarine terrain, but also greatly improves the laying quality of submarine cables.

ObjectiveAiming at the area coverage problem of multiple autonomous surface vehicles (ASVs), this paper investigates a coverage path planning (CPP) strategy based on an electronic chart display and information system (ECDIS). MethodFirst, according to the information of sea, land and water depth from ECDIS, an environmental model for the area coverage of ASVs is established based on the grid method. Second, an area division method based on the roulette wheel selection method is proposed to solve the problem of irregular area division in divided areas based on the robots' initial position method, and achieve the reasonable area division of ASVs in the grid map. Finally, a template-based area coverage path planning method is proposed to solve the problem of generating too many turns in paths generated by the spanning tree coverage agorithm.ResultsA human-machine interactive simulation platform for ASVs based on ECDIS is established to verify the effectiveness of the proposed area coverage path planning method based on the roulette wheel method and template method in optimizing the number of turns in the planning path. ConclusionThe proposed area coverage path planning method for ASVs based on ECDIS can be used to achieve coverage path planning in target mission areas at sea.

ObjectiveThis paper puts forward the “virtual wall method” as a novel formation approach intended to address such problems as the high communication volume, slow formation speed and inconvenient expansion of large-scale ship formation. MethodThe proposed method uses local communication, sets virtual force according to the rules of nature to drive the ships to the target positions, and adjusts the formation to completion through the virtual wall. ResultsThe results show that the ship formations can be completed quickly according to the proximity principle using the proposed algorithm, and the communication volume is low without changing with the formation size. The effectiveness of this algorithm is verified by static, dynamic, rotation, scaling and obstacle avoidance simulations of ship formations. ConclusionThe virtual wall method features low communication volume, fast formation speed and convenient expansion, giving it significant advantages in the large-scale formation of ships.

ObjectiveThis paper proposes a null-space-based active disturbance rejection control （ADRC）allocation method to analyze the influence of multi-source disturbances encountered during the autonomous berthing of ships, such as environmental loads, bank effects, model uncertainties and control allocation errors.Methods First, a ship berthing motion model, multi-source disturbance model and control allocation model are established, and a neural network extended state observer (NNESO) is designed to estimate ship states and multi-source disturbances in real time. Second, null-space technology is introduced to design the control allocation algorithm. Based on this method, a scheme for stabilization control outside the berth and parallel berthing is realized. Finally, it is proven that all error signals of the autonomous berthing system under the proposed method remain uniformly ultimately bounded, ensuring the safety of the autonomous berthing process.ResultsThe comparative simulation results show that the proposed method has a trajectory tracking effect similar to that of the quadratic programming (QP) method, with a solution time of about 1.3% and a yaw maximum allocation error of 36.51% of the pseudo inverse (PI) method. ConclusionThe proposed method not only ensures the accuracy of berthing motion control, but also significantly reduces the solution time and maximum allocation error, thereby ensuring real-time control allocation with high accuracy.

ObjectiveTo solve the problem of the autonomous and safe landing of multi-rotor unmanned aerial vehicles (UAVs) in the application of unmanned platforms at sea, this paper studies multi-rotor UAV landing devices and their safety boundary assessment methods.MethodBased on the idea of the "Harpoon-Grid" rapid securing system, a new type of "V-foot–net" landing device is designed for multi-rotor UAVs. Multi-rigid body dynamic models of the UAV and deck are established, and simulations of the landing process are carried out using ADAMS under different rolling amplitudes and period conditions to obtain the attitude change process, landing critical period and attitude stabilization time of the UAV. ResultsThe simulation results show that the proposed "V-foot–net" device has higher docking redundancy under a smaller rolling period and larger rolling amplitude, and achieves attitude stability faster than ordinary landing devices.ConclusionThe results show that this device has superior safety compared to ordinary devices, and its safety boundary obtained through simulation can provide valuable references for improving the reliability of the autonomous landing of UAVs on offshore platforms.

ObjectiveThis paper presents a tracking control method based on dynamic programming guidance to address the challenges presented by the autonomous recovery of underactuated unmanned surface vehicles (USVs). MethodsAt the kinematic level, constant bearing approach (CB) guidance is combined with a dynamic window algorithm (DWA) to guide the USV in achieving target tracking and dynamic obstacle avoidance. At the dynamic level, considering the uncertainties in the model parameters and recovery environment, a radial basis function neural network (RBFNN) is employed to design a dynamic sliding mode controller for the tracking control of the guidance output. Finally, the stability of the system is analyzed using Lyapunov theory. ResultsThe simulation results demonstrate that the proposed method enables the USV to exhibit stable tracking performance, effectively avoid dynamic obstacles during the recovery process and adapt to uncertain factors in the estimation model and unknown environmental disturbances. ConclusionThe proposed method exhibits strong robustness and flexibility, providing valuable references for the guidance and target tracking of USVs during recovery in dynamic environments.

ObjectiveThis paper develops a heading tracking design strategy for unmanned ships with state quantization and input quantization in order to address the problem of limited communication at sea for unmanned ships on the water surface.Methods First, a control law is designed on the basis of backstepping and combined with dynamic surface control to reduce the computational complexity of the virtual control law. An extended state observer is also designed to estimate uncertainties and unknown disturbances. Second, all state variables and control variables in the control system are assumed to be quantized by the uniform quantizer, and the quantized state feedback information is only available for the tracking control design. A controller of unmanned ships based on the extended state observer and using quantized states is recursively designed to ensure the tracking of the desired heading. The boundedness of the quantization errors between quantized variables and non-quantized variables in the closed-loop system is analyzed by presenting several theoretical lemmas.ResultsBased on the Lyapunov stability theory, the stability of the designed unmanned ship heading tracking control system with state quantization and input quantization is demonstrated, and the simulation results verify the effectiveness of the resulting tracking scheme. Conclusion The results of this study can provide references for the heading tracking of unmanned ships.

Objective This paper aims to investigate the effect of the strut geometry on the open water performance of the azimuth thruster with contra-rotating propellers （CRPs ）. Methods The RANS method and k-ω turbulence model are applied to predict the hydrodynamic performance of an azimuth thruster with CRPs and different strut design schemes at model scale and real scale in open water. Meanwhile, the flow field characteristics and wake fraction of the rear propeller are explored, and analysis on the flow separation at the stern of the strut after and before optimization is carried out. Results The results show that the optimization scheme of the struts moving forward and the leading edge thinning increases the propeller open water efficiency by 1.01%. The optimization scheme of the struts adopting a twist design and the strut section introducing cambers increases that value by 1.15%. In addition, the flow separation at the model scale is more serious than that at the real scale. Conclusions It is found that the optimized struts can reduce the flow separation at the stern, improve the rear propeller absorption of the wake vortex energy of the front propeller and increase the inflow of the rear propeller, which has practical engineering significance for improving the propulsion performance of an azimuth thruster with CRPs.

ObjectivesThis study focuses on the multi-agent cooperative getting-to-the-firing-position decision-making algorithm design of underwater battlefields based on the MoZi platform, and explores the combat application of underwater unmanned platforms. MethodsA design idea based on the MoZi platform is proposed. For action decision-making under deterministic rules, the design of knowledge graph modules is discussed. The Neo4J database is used to build a global knowledge database, and a data exchange interface is designed to provide the auxiliary decision information input of deterministic rules for the intelligent algorithm module. For action decision-making under uncertain and incomplete information, the design of a cooperative space occupying a decision-making algorithm based on MADDPG is discussed under the set scenario, and the design concept of a state space, action space, reward function and interaction with the knowledge graph module is put forward. ResultsThe overall design of the algorithm framework is completed on the basis of the abovementioned ideas. The integration of the knowledge graph and intelligent algorithm is realized on the MoZi platform, and the effectiveness of the integration of behavior constraints under deterministic rules and the intelligent algorithm for processing uncertain situation information is further verified through the visualization provided by the platform.ConclusionsThis paper can provide valuable references for the design of multi-agent underwater getting-to-the-firing-position cooperative algorithms.

ObjectivesAs the core system of an unmanned surface vehicle, the autonomous control system (ACS) is responsible for coordinating other systems to achieve combat missions, which is the key to unmanned surface ship technology. MethodsFirst, based on the physiological structure and cognitive mechanism of the nervous system, this paper proposes six bionic revelations for the ACS. Furthermore, based on such revelations, a system architecture and its typical ACS case are proposed as the biomimetic of the central and peripheral nervous system. Finally, a design scheme for the ACS architecture that composed of eight functional modules with service-oriented architecture is obtained which draws upon the information processing of the human brain. ResultsThe bionic physical architecture and functional architecture is achieved. ConclusionsThis study can provide useful references for the overall construction, system design and equipment development of the ACS for medium to large unmanned surface ships.

ObjectiveThis paper puts forward a hybrid digital twin monitoring system for structural health to realize the whole-life health monitoring of ships. MethodThe proposed model collects and feeds back the deformation of key cabin structures in real time in order to improve the information and safety management capabilities of shipping. The singular value decomposition method is used to compress and reduce the dimensions of the physical field information formed by multiple groups of loads to obtain the specific standard orthogonal basis, create the response surface model of the relationship between the basis vector and the load, and output a finite element reduced order model based on the real-time input load. The Kriging interpolation algorithm based on geostatistics is used to arrange points according to the specific topological structure, and the real-time sensor data and supplementary point data output by the reduced model are fused and corrected through the Kalman filter algorithm to jointly calculate the deformation of the monitored object. Finally, through the construction of a deformation monitoring software and hardware system, the whole process of physical characteristic collection and visualization is realized. ResultsUnder the preset load, the hardware acquisition system can stably collect data while the supporting application program can visualize the acquisition process in real time according to the expected requirements. ConclusionThe proposed structural health hybrid digital twin monitoring system meets the needs of ship health monitoring and has certain reference significance for the future development of highly integrated and intelligent ships.

ObjectiveThis paper focuses on using reinforcement learning-based automatic generation technology to generate loading and unloading schemes for the liquid cargo tanks of oil tankers. MethodsUsing the cargo capacity of an actual operating oil tanker as the input and the loading rates of the cargo tank and ballast water tank as the targets, an intelligent agent and environment are built based on Unity ML-Agents. The agent is trained using the PyTorch framework, and a reward function calculation method that comprehensively considers the loading time and changes in the trim amplitude is proposed. Finally, example analysis is carried out to validate the feasibility of the proposed method. ResultsThe results show that the trained agent can learn effective strategies for achieving the autonomous generation of liquid cargo tank loading schemes. ConclusionsThis study proves that it is reasonable and feasible to apply reinforcement learning to solve the problem of the autonomous generation of liquid cargo tank loading schemes under multi-objective conditions.

[Objectives] To achieve lightweight design of double-arm propeller shaft brackets.[Methods] By comparing and analyzing the requirements of the current domestic rules and the main classification societies in the world for the dimension of propeller shaft brackets,this paper interprets the differences between the rules,and searches for ways to reduce the weight of the double-arm shaft brackets from such differences. According to the differences between the rules,DNV-GL rules with significant differences from the CCS rules in the relevant aspects are selected. Based on the same propeller parameters, double-arm propeller shaft brackets are designed according to the minimum sizes requirements specified in the two rules. Subsequently,the strength and vibration performance of the double-arm propeller shaft brackets are verified by the relevant regulations of the national military standard.[Results] The results show that the strength and vibration performance of the propeller shaft brackets designed according to the two rules meet the requirements. The total weight of the propeller shaft brackets designed according to the minimum sizes requirements of DNV-GL rules is reduced by about 16.8%.[Conclusions] If the double-arm propeller shaft brackets are designed with the DNV-GL rules,the weight thereof can be reduced to some extent. This paper provides an idea for the lightweight design of the double-arm propeller shaft brackets in practical engineering.

[Objectives] In the passive shock isolator,stiffness and damping are important factors to reduce the transient shock and reduce the vibration transmission. Therefore,it is the key to select the appropriate damping form and consider the appropriate stiffness.[Methods]In this paper,on the basis of established Coulomb damping shock isolation model, the isolation system of Coulomb damping combined with linear spring and switch spring is studied. The system model is expressed by the motion differential equation with the exponential law characteristics to explore the characteristics of Coulomb damping in the shock isolation system and study the stiffness and the law of function on the system response.[Results] The study results show that the Coulomb damping can significantly improve the shock isolation efficiency of the system and reduce the relative displacement amplitude. In the same shock environment,the system composed of Coulomb damping and the switch spring is superior to the linear system in suppressing the peak value and reducing the residual response.[Conclusions]The results of this paper have some guiding significance for the application of Coulomb damping in shock isolation.

[Objectives]This study aims to solve the problem of the track control for submarine in the horizontal plane.[Methods]Firstly,the paper builds dynamics and kinematics model of the submarine in the horizontal plane,then builds the error model of the track control for submarine by Line-of-Sight (LOS)in order to transform the problem of track control in the horizontal plane to the problem of following dynamic expected heading angle. Then the paper designs a model prediction control algorithm based on the state space accordingly.[Results]Simulation results show that the trace control method which combines LOS and the prediction control algorithm can effectively solve the track control problem for submarine,and the model predictive control algorithm can solve the constraint problem of rudder angle and the rudder speed of submarine.[Conclusions]The designed trace control algorithm for submarine can be referential for the subsequent development of track control system.

[Objectives] As an important component of the connecting circuit,the reed contact switch has been widely used in the electrical system of the naval ship. The switch is very sensitive to underwater non-contact explosion impact,and thus once damaged,it may lead to the failure of the electrical system. This paper studies the impact resistance of the reed contact switch in order to determine its critical working conditions.[Methods] To this end,this paper employs the finite element method to simulate the impact process,and analyzes the response characteristics of different frequency bands based on the critical acceleration amplitude of the corresponding band derived from the triangular wave impact load of certain band applied to the switch model.[Results] The results show that the switch contact will be separated once the shock spectrum of the excitation force at a fixed point exceeds the allowable value. Thus,the preload should be increased to improve the impact resistance of the switch.[Conclusions] This study provides the basis for the research on the damage modes and the protection of the electrical switches of naval ships.

[Objectives] This paper studies the development of a microstrip antenna with both traditional radiation characteristic and good out-of-band rejection characteristic.[Methods] Through the filter integrated design method,the microstrip antenna with filtering characteristic,composed of a microstrip antenna,a coupled line,and two resonators is designed. In addition to the capability of meeting the traditional antenna design requirements,the microstrip antenna shall have the external quality factor that is equal to the external quality factor of the last resonator of the band-pass filter,thus enabling it to still function as a filter after being used as a substitute of the last resonator of the filter;in the filter design,the coupled line acts as an admittance converter to realize the energy coupling between the filter resonator and the microstrip antenna.[Results] The simulation results show that as the impedance bandwidth is 2.37-2.53 GHz,the gain variation within the impedance bandwidth is gentle,the maximum in-band gain deviation is about 0.5 dB,the maximum gain is 7.5 dB,and the gain at 100 MHz outside the passband is rapidly reduced to -10 dBi, the microstrip antenna has good out-of-band rejection characteristic.[Conclusions] The microstrip antenna with filtering characteristic designed in the paper reduces the overall size of filter and antenna and the transmission loss between the filter and the antenna,and can be used in modern communication systems.

[Objectives] Emergency surfacing is an important aspect of submarine vitality which is closely related to submarine safety. In order to master the motion laws of submarine during emergency surfacing performance,[Methods] this paper establishes a structure model of submarine with non-watertight zone and drain-holes in the superstructure,solves the RANS equation to obtain the hydrodynamic force through discretizing the fluid field with an overset grid method,and combines solid motion equations to obtain the submarine's attitude.[Results] The simulation successfully calculates variables in terms of roll angle, pitch angle and oscillation period,and predicts the attitude of the submarine when it is underwater,out of water and oscillating on the surface.[Conclusions] The results of this paper can be applied to the simulation of submarine emergency surfacing operation,thereby providing technical support for the overall design of submarines.

[Objectives] In order to guarantee the navigation safety of high speed Autonomous Underwater Vehicles(AUV),a new type of practical and reliable emergency system is developed.[Methods] First, this paper introduces the composition of the emergency self-rescue system and analyses and designs the reliability of the system. Secondly,it mainly focuses on the emergency mechanism and strategies,which include the multi-channel data collection mechanism,active emergency switch mechanism and automatic fault priority setting mechanism,as well as the contents of the emergency action methods. Next,an expert emergency decision-making model is designed to output action decisions to handle the faults. Discrete steering rules are introduced to raise the AUV in emergency conditions. Finally,based on the VxWorks real-time operating system,the emergency system control software is coded and hardware in the loop simulation carried out.[Results] The results show the feasibility of the emergency self-rescue mechanism and strategies.[Conclusions] As such,the emergency system and mechanism introduced in this paper can make up for shortages in traditional emergency means,which has important reference value for the self-rescue methods of submarine-shaped AUVs.

[Objectives] Cooperative operation of Manned/Unmanned Aerial Vehicle(MAV/UAV)hybrid formation in antisubmarine warfare can give full play to both MAV and UAV to improve the operational efficiency significantly,being one of the typical air operation modes in the future under the network condition.[Methods] This paper analyzes the operational advantages and technical challenges of cooperative operation of MAV/UAV in antisubmarine warfare,and introduces the theoretical research status and equipment development of this operation at home and abroad. On this basis,this paper focuses on five typical operation modes in antisubmarine warfare,and based on the antisubmarine mission requirements,puts forward the cooperative operation planning, cooperative data chain, capacity requirement for antisubmarine warfare aircraft and UAV platform and the key technologies to be solved to achieve cooperative antisubmarine warfare.[Results] It is shown that cooperation of MAV/UAV has great potential in antisubmarine warfare,[Conclusions] and the findings provide guidance for future UAV equipment development and MAV/UAV cooperative antisubmarine warfare training.

[Objectives] 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. [Methods] 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. [Results] 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. [Conclusions] The conclusions of this paper can provide design reference data for the subsequent anti-shock design of equipment.

[Objectives] Compared with other types of air compressor, reciprocating compressors can obtain compressed air with a higher pressure, exerting more stress on the crank connecting rod mechanism. [Methods] This paper analyzes the inertia force and torque characteristics of the three structural forms of the star-type reciprocating air compressor. It then concludes that the air compressor has a good self-balance ability of inertial force while also reducing inertial torque to a certain extent at the same time. A virtual prototype of a crank connecting rod mechanism is built. The derivation of the force on the piston is acquired in order to construct a SPLINE curve, which is loaded on the centroid of the piston. With a flexible crankshaft, the contact force model of the IMPACT function is added between the crank pin and connecting rod. [Results] The dynamic simulation results show that the air compressor can self-balance second-order inertial force. Clearance will decrease the vibration of the air compressor to a certain extent, but will greatly broaden the excitation frequency band. [Conclusions] The findings of this paper can provide valuable references for the design of air compressors.

ObjectivesThis paper aims to study the influencing factors and mechanisms of ship model resistance prediction uncertainty, as well as proposing corresponding suppression methods. MethodsResistance tests and local flow measurements on the flow around KCS models of 1.725 m and 3.450 m are carried out in a circulating water channel. The effects of the model scale on the resistance predictions are obtained by comparing the results of the two tests. Numerical simulations of the flow around the 3.450 m model in an unbounded water area and circulating water channel are achieved. The results under the two conditions are compared to analyze the blockage effect and validate the simplified Tamura correction formula. Numerical simulations of the flow around the 3.450 m model under different turbulence intensities in a circulating water channel are then carried out to analyze the effects of turbulence intensities on resistance predictions. ResultsThe results show that the resistance prediction uncertainty of small ship models due to statistics collections and inflow uniformity can be amplified if the inflow velocity is too low. This demonstrates that the blockage effect of the large model could increase hull sinkage, pressure gradients on the hull and wave amplitudes, leading to an increase in ship resistance. The average difference between the resistances predicted in the unbounded water area and circulating water channel is 4.56% without correcting for the blockage effect. The difference is reduced to 2.25% with the correction of the simplified Tamura formula. The total resistance increases by an average of 3.75% as the turbulence intensity increases from 1% to 2%. It is observed that the decay of turbulence intensity along the flow direction is linear from the entrance to the bow. ConclusionsThis study shows that reasonably large models should be used wherever possible and the turbulence intensity should be strictly controlled to reduce the uncertainty of ship resistance tests in circulating water channels. In addition, the simplified Tamura formula should be used to correct the blockage effect, and the appropriate inflow turbulence intensity should be used in numerical prediction according to the dissipation of the turbulence intensity.

ObjectivesThis paper aims to research the effects of the temperature and compressibility of liquid water on the super-cavitation phenomenon of an ultra-high-speed underwater vehicle and its motion characteristics. Methods First, based on CFD general software Fluent 19.2, the free motion of transonic and supersonic vehicles is computed using a numerical model that considers both the compressibility and temperature of the water. Qualitative and quantitative comparisons with the experimental results of reference [1] are made, and the effectiveness of the numerical method is verified. The motion characteristics at different initial speeds are then analyzed using the range at the sailing time of 0.008 s as the comparison base. Finally, the influence of the launch depth and environment temperature on the motion characteristics is discussed. Results It is found that when the speed is greater than 2 000 m/s, increasing the initial speed does not significantly increase the effective range; the critical speed is found between 1 450 m/s and 1 475 m/s, where the range variation is less than 3% with or without the influence of the temperature; as the launch depth increases, the resistance of the vehicle becomes greater and the sailing range gradually decreases; and the higher the environment temperature, the shorter the effective range. Conclusions It is shown that the numerical model proposed herein, which considers both the temperature and compressibility of liquid water, can provide valuable references for the motion analysis of ultra high-speed underwater vehicles and corresponding practical applications.

ObjectiveShip maintenance projects have such characteristics as complex implicated tasks, space interference and uncertain task durations. A mathematical model and optimization algorithm are proposed to solve the stochastic duration optimization problem of ship maintenance. MethodsAccording to the scenario concept, this paper designs the expected duration as an objective function and constructs a mathematical model, then proposes an improved firefly algorithm to solve the problem. Finally, a group of benchmark projects and one dock maintenance engineering project are carried out to test the validity of the proposed method. ResultsThe results show that the proposed method has the best performance in solving the problem. The optimized dock maintenance engineering project has 89.6 days of the expected duration and a 95.6% confidence level. Compared with the original method, the expected duration is reduced by 13.4 days and 13.1%. ConclusionThis method can provide a basis for planning the schedules of ship maintenance projects.

ObjectiveWelding is a common method for connecting ship structures, but it obviously affects their acoustic and vibration characteristics. Thus, it is necessary to study the influence of welding process parameters on the acoustic and vibration characteristics of structures. MethodIn this paper, the thermo-elastoplastic finite element method and acoustic-structure coupling finite element method are combined to study the influence of welding parameters on the acoustic and vibration characteristics of typical ship stiffened plate structures. ResultsThe results show that welding residual stress is significantly affected by welding input power and speed. Higher welding input power and lower welding speeds both result in a larger welding residual stress distribution range which causes changes to the natural frequency, vibration response and radiated sound pressure of typical stiffened plate structures. ConclusionWelding residual stress should be analyzed to determine the acoustic and vibration response of low-damping welded structures, thereby providing guidance for the formulation of low-noise welding processes.

ObjectiveThe purpose of this paper is to study the effects of cavitation models on the simulation of full-scale propeller cavitation. MethodsThe minimum rotational speed of the propeller required for cavitation is predicted by the Bernoulli equation, and the propeller's cavitation condition is observed by full-scale experiment. After determining the boundary layer mesh thickness and establishing the hydrodynamic model, meshes are generated. In the numerical simulation, the turbulence model is selected from either the standard \begin{document}$k - \varepsilon $\end{document} model or Realizable \begin{document}$k - \varepsilon $\end{document} model, and the cavitation model is selected from either the Schnerr−Sauer (S−S) model or the Zwart−Gerber−Belamri (ZGB) model. The maximum gas volume fraction on the surface of the propeller is tracked and recorded. In the meantime, the reliability of the numerical simulation is evaluated by observing the gas distribution on the surface of the propeller. And the simulation accuracy of the related models is compared. ResultsThe simulation results show that compared with the standard \begin{document}$k - \varepsilon $\end{document} turbulence model, the cavitation region obtained with the Realizable \begin{document}$k - \varepsilon $\end{document} model is significantly more consistent with the experimental results. By monitoring the maximum gas volume fraction on propeller's surface, it is found that the choice of turbulence model has little effect on the cavitation intensity, and the cavitation intensity obtained by S−S model is significantly higher than that obtained by the ZGB model. ConclusionsThis study shows that the turbulence model has a great influence on the area of the cavitation region, and cavitation models have a great influence on cavitation intensity. In terms of the simulation of propeller cavitation, the accuracy of the Realizable \begin{document}$k - \varepsilon $\end{document} model is higher than that of the standard \begin{document}$k - \varepsilon $\end{document} model.

ObjectivesAs the ship side wet exhaust system is widely equipped on many stealth frigates, it is necessary to study its infrared signature suppression (IRSS) effect.MethodsIn this paper, the IRSS principle of the wet exhaust system is analyzed, a mathematical model of the system based on an exporting vessel is built, the exhaust system outlet temperature is simulated and a real vessel infrared signature test is carried out.Results The simulation results show that the outlet temperature is reduced to 60 ℃. Compared to popular funnel IRSS devices, the infrared signature of the 3–5 μm wave band can be reduced. The real vessel infrared signature test results show that the outlet temperature is reduced to 66.7–70.0 ℃ and the infrared signature intensity is 1.39 W/s.ConclusionsThe results of this study can provide useful references for the application of the ship side wet exhaust system in the naval ship IRSS field.

This paper reviews research on vibration and noise in the open deck spaces of large cruise ships. In the first part, the main functions, features and vibration and noise source characteristics of typical leisure and entertainment areas in open deck spaces are analyzed and categorized. The second part outlines sub-model methods adapted to predict structural vibration caused by wind in open spaces, and the research progress of wind-induced vibration is introduced. An analysis is then made of the advantages and disadvantages of different prediction methods, including discrete methods (FEM/BEM/IEM), statistical energy analysis (SEA) and geometric acoustic method (i.e. ray tracing), in the two dimensions of noise frequency and acoustic field, and a hybrid method is recommended due to its good adaptability for noise prediction in open deck spaces, which provides the basis for the prediction process. Finally, a soundscape comfort-based design concept is proposed through an analysis of traditional noise evaluation and measurement methods, which can be used as a reference for vibration and noise control in the open deck spaces of large cruise ships.

ObjectivesLaser scanning technology used in the intelligent installation of ship shafting has such advantages as non-contact, high-speed scanning and high-precision imaging. The laser point cloud data includes the size, position and direction information of space objects. Point cloud segmentation can greatly reduce the calculation scale of the data and improve the measurement efficiency of the relative pose of the butt flange. MethodsIn this paper, deep learning theory is used to study point cloud segmentation and obtain a point cloud dataset of flange parts. The PointNet model is used for training. Optimization strategies are formulated in three aspects, namely dropout regularization, learning rate attenuation and point cloud data enhancement, then tested on a ship shafting intelligent installation platform. ResultsThe convergence results of the model tend to be stable, with the accuracy of the training set reaching 0.88 and that of the verification set reaching 0.65. The flange point cloud segmentation experiment shows clear contour edges. ConclusionThe results of this study show that the proposed method has good convergence and generalization performance, and can improve the efficiency of ship shafting intelligent installation.

ObjectiveThis paper aims to study the coupled dynamic response characteristics of an integrated system of a semi-submersible wind turbine and fish farming cage under wind, wave and current actions.MethodBased on the self-designed semi-submersible wind turbine SJTU-SPIC, an integrated floating wind turbine and fish farming cage concept is proposed and numerically modeled. The dynamic response characteristics of the integrated concept under wind, wave and current actions are then studied using coupled aero-hydro-servo-elastic-mooring analysis.ResultsThe numerical simulations indicate that introducing the fish farming cage can induce slightly a larger surge motion but suppress the pitch, which is beneficial for wind power production.ConclusionThe dynamic behavior of the integrated system of a semi-submersible wind turbine and fish farming cage proposed herein is similar to that of a floating wind turbine, and the system is shown to be feasible.

ObjectivesThe aim of this paper is to obtain test scenarios of autonomous collision avoidance for inland waterway ships by modeling. MethodsStarting with the automatic identification system (AIS) and radar data collection and fusion method, a ship navigation data collection and fusion system is established. Taking the inland waterway between the Three Gorges Dam and Gezhouba Dam as an example, ship scenario elements are collected and analyzed, and a parametric generation method of inland waterway collision avoidance test scenarios is proposed which can automatically generate a ship collision avoidance test scenario by setting a series of parameters. Taking two-ship and multi-ship encounters scenario as examples, a series of test scenarios are generated and simulated. ResultsThe collision avoidance simulation tests results show that the parameterized test scenario generation method proposed herein can effectively test the autonomous ship collision avoidance algorithm. ConclusionsThe research providing a basis for improving the pertinence and practicality of inland river smart ship collision avoidance testing.

ObjectivesThis paper aims to analyze the influence of polar low temperature environment and ballast water capacity on the dynamic change process of the temperature field in polar ship's ballast tank. MethodsThe volume of fluid (VOF) model was used to simulate the two phases of gas and liquid, and the standard k-ε turbulence model was used to simulate the fluid movement. The numerical analysis model of heat transfer in the ballast tank of polar ships was established to analyze the dynamic change process of the temperature field of the ballast tank at low temperature, and reveal the influence mechanism of multiple ambient temperatures and multiple loading heights on the temperature field of the ballast tank. ResultsWith the continuous occurrence of heat transfer, the temperature in the area above the waterline of the side ballast tank decreases rapidly, and the cooling area extends laterally to the cabin and downward along the bulkhead respectively. When there is more ballast water, the temperature field in the cabin is relatively stable due to the large heat capacity of water, but the air heat capacity is low and the temperature field changes greatly, which is prone to cyclones and further affects the temperature field distribution in the calculation domain. Under the condition of the same ballast water capacity, the lower the external ambient temperature, the greater the difference between internal and external temperatures, the more intense the heat exchange, and the faster the temperature of the ballast tank changes. ConclusionsThe VOF two-phase flow model and the standard k-ε turbulence model can better reveal the temporal and spatial evolution characteristics of the temperature field in the ballast tank in polar low temperature environment, and analyze the influence of internal and external thermal boundary conditions on the change of the temperature field in the ballast tank, which can provide necessary technical reference for the cold/freeze protection of polar ships' ballast tanks.

ObjectivesThis paper aims to study the free vibration characteristics of complicated shape plate coupled with fluid under elastic boundary conditions. MethodsTo this end, the rectangular domain enveloping the complicated shape plate domain is selected, and the plate displacement is expressed by the improved Fourier series in the rectangular domain. Combined with the Rayleigh integral, the relationship between the plate displacement and the surface sound pressure is established, and the integral formula is transformed into polar coordinates to avoid singularity. Aiming at the problem that it is difficult to obtain the explicit expression of the boundary curve in the variable limit integral in local polar coordinates, the structural boundary curves are treated by "replacing curve with straight" to simplify the Rayleigh integral. Based on the energy principle, a semi analytical method for analyzing the free vibration characteristics of complicated shape plate contacting with water on one side is established. ResultsThe numerical examples of rectangular plate, circular plate and some complicated shape plates are given. Compared with the finite element method and literature results, the convergence and accuracy of the method are verified, and the influence of elastic boundary conditions on the added virtual mass incremental (AVMI) factor of plate is discussed. The AVMI factor of each mode reaches the maximum near the dimensionless displacement spring stiffness of 103. At this time, the structure is relatively most affected by the fluid. ConclusionsThis method has strong adaptability and high calculation efficiency. It reveals the free vibration law of complicated shape plate coupled with fluid, and has certain engineering guiding significance.

ObjectivesThis paper aims to cope with the possible impact of external condition disturbances on the operating parameters of a supercritical carbon dioxide (S-CO2) Brayton cycle power generation system and ensure its efficient, safe and stable operation. MethodsA dynamic numerical simulation model of a simple S-CO2 Brayton cycle power generation system is built using the Matlab/Simulink platform, and the transient operation characteristics of the system are analyzed. The change laws of the operating parameters of the thermodynamic cycle system under changing cooler parameters are then simulated, and the influence of the temperature fluctuation of the cooling source on the inlet and outlet parameters of the system components, system cycle efficiency and adjustment methods are analyzed. ResultsThe results show that the maximum error between the established system transient simulation model results and the experimental results is 3.658%; a 2 K increase in the cooling water temperature will lead to a 1.4 K increase in the compressor inlet temperature, and the system will need 300 s to restore stability; after adding a PID control system, the compressor inlet temperature change amplitude is reduced by 50% and the system stabilization time is reduced by 62%. ConclusionsThe established model can accurately reflect the operation of the system. Based on the opposition of the influence of cooling water temperature increase and flow increase on the system, the proposed PID control system can ensure that the carbon dioxide working fluid in the system is always above the critical point, thereby ensuring the safe and stable operation of the system.