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.

ObjectiveAn optimal design scheme for the inertial stage structure of the diesel engine intake filter is proposed, in order to meet the requirements of high separation efficiency and low resistance loss at the same time.MethodsFirst, taking the inertial stage of a diesel engine intake filter as the research object, a fusion blade structure was established by the natural fusion of groove and blade. Then, numerical simulation was used to calculate the droplet separation efficiency and resistance loss characteristics, and compare them with commonly used blade structure schemes at present. Finally, the inertial stage performance test of the intake filter was carried out, and the numerical simulation results were verified by the test results.ResultsThe simulation results and test results show that the fusion-type airfoil structure keeps the uniform and continuous distribution of the airflow velocity field and pressure field as much as possible while making full use of inertia to separate droplets, taking into account the requirements of separation performance and resistance performance. The overall performance of the design scheme is optimal. Under standard conditions, the droplet separation efficiency is close to 99.9%, and the resistance loss is about 42 Pa.ConclusionThe design scheme of the blade structure can provide a technical reference for the design of the inertial stage of the filter that takes into consideration the droplet separation efficiency and resistance loss performance.

ObjectiveThis study proposes a design scheme for an underwater magnetic sensor calibration device. The device is composed of an electromagnetic coil and integrated navigation equipment which can be carried on a mobile platform to sail on the water surface, and realize the high-precision calibration of the position and attitude of the underwater magnetic sensor.MethodsAccording to information on the coil's attitude, orientation and trajectory, and the measured values of the magnetic field generated by the coil at the magnetic sensor, the position and attitude of the underwater magnetic sensor can be calculated using a nonlinear optimization algorithm. The mathematical model of the whole system is established and numerical verification tests are carried out, considering the effects of the measuring accuracy of the coil's position and attitude, the magnetic sensor's noise and measuring error, and geomagnetic interference.ResultsWhen the device is used and the magnetic sensor is at a depth of 30 m underwater, the mean value of position error is not more than 0.06 m, and the mean value of attitude error is not more than 0.20°; the accuracy of the magnetic sensor itself is the main factor affecting the calibration accuracy. ConclusionsThe proposed calibration device can achieve the high-precision calibration of the position and attitude of an underwater magnetic sensor at the same time, giving it great application value. It can be widely used in underwater magnetic target detection, resource exploration, medicine and other fields, especially scenarios involving the attitude deviation of underwater magnetic sensors.

ObjectivesIn order to make the energy in the degaussing coil feed back to the degaussing power supply and improve the energy utilization rate, a degaussing power supply control strategy is proposed with a hybrid supercapacitor and lithium battery power supply.MethodsAfter studying the electrical characteristics of the degaussing coil under strong coupling conditions, the hybrid power supply system is introduced. The change of the degaussing coil current is divided into three stages: rising, holding and falling (energy feedback). In different stages of degaussing coil current change, the opening and closing of the corresponding switches are controlled. The simulation is carried out using Matlab/Simulink, and the simulation results are analyzed to verify the feasibility of the energy feedback control strategy based on the hybrid power supply system.ResultsThe analysis and simulation results show that the total current flowing through each degaussing coil can quickly rise to and stabilize near the standard value, the overshoot is small and the energy supplied to the degaussing coil can also be fed back into the supercapacitor.ConclusionThe proposed degaussing system with a hybrid power supply can feed back the energy in the degaussing coil to the supercapacitor, thereby reducing the energy loss of the whole degaussing system.

ObjectiveAccording to the characteristics of the complex waterways of inland rivers, a DC grid solution based on a multi-energy parallel hybrid green intelligent bulk carrier is proposed. MethodsThe advantages of a DC grid for hybrid power are analyzed and the DC grid propulsion efficiencies of each typical working condition for hybrid power are obtained through power chain calculation. The design characteristics of the DC grid are researched according to the specific requirements for the additional signs of green intelligent ships. The DC power system design schemes focused on protection and safety for real ships are then analyzed.ResultsThe results show that the comprehensive performance of the DC grid propulsion system for multi-energy parallel diesel-electric/gas-electric hybrid ships is superior to that of main engine propulsion systems and full electric propulsion systems. The multi-equipment protection mode and blackout recovery solution can ensure the safe application of the DC grid.ConclusionsThe DC grid can build a flexible energy platform for the highest level of green inland river ships, and provide comprehensive support for the intelligent engine room, intelligent energy efficiency and intelligent integrated platform technology and its applications. The results of this study can provide valuable references for other green intelligent hybrid 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.

With the implementation of new carbon reduction rules for international shipping, as well as the domestic "peak carbon and carbon neutrality" strategy, the innovative air lubrication drag reduction technology for ship energy-saving and carbon reduction has recently attracted increasing attention in the shipping and shipbuilding industries. At present, according to the drag reduction mechanism and two-phase interfacial morphology, air lubrication can be divided into continuous air layer drag reduction and dispersed bubble drag reduction. We introduce the application status of continuous air layer drag reduction and dispersed bubble drag reduction both at home and abroad. An overview of the layout, form, drag reduction and net energy-saving of ship air lubrication is provided. The energy-saving and carbon reduction benefits of ship air lubrication are then discussed based on the reported data. Finally, brief predictions are made for the technical challenges and directions worthy of further research in the application of air lubrication.

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.

ObjectivesThe unsteady force of the rotor is the main excitation source of pump-jet shafting vibration, and rotor-stator interaction has an important impact on the characteristics of the unsteady force. Therefore, the suppression method of pump-jet unsteady force should be studied. MethodsOscillating flaps are introduced onto the trailing edge of the stator. The secondary flow generated by the flaps is used to affect the rotor inflow conditions so as to suppress the unsteady force of the rotor. A numerical model is established on the basis of the unsteady Reynolds-averaged Navier–Stokes equation (URANS) method of the shear stress transport (SST k–ω) turbulence model, and a SUBOFF with full appendages and a pump-jet with stator trailing edge flaps is taken as the research object. Aiming at suppressing the unsteady force amplitude at the rotor blade passing frequency, the oscillating law of the stator flaps is given. ResultsThe results show that under the optimal control of the flaps, the hydrodynamic performance of the pump-jet varies by less than 1%, the axial unsteady force of the rotor decreases by 83.35% at the rotor blade pass frequency (BPF) and that of a single rotor blade decreases by 81.8% at the rotor BPF. Further analysis shows that the oscillating flaps can manipulate the stator wake and velocity on the rotor inlet plane. ConclusionsThe results show that stator trailing edge flaps can significantly suppress the characteristic line spectrum of rotor unsteady force while maintaining hydrodynamic performance, which will shed some light on controlling the BPF line spectra of pump-jets.

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 $k - \varepsilon $ model or Realizable $k - \varepsilon $ 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 $k - \varepsilon $ turbulence model, the cavitation region obtained with the Realizable $k - \varepsilon $ 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 $k - \varepsilon $ model is higher than that of the standard $k - \varepsilon $ model.

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.

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.

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.

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.

ObjectiveFocusing on the problem of underactuated surface vehicle (USV) swarm trajectory tracking control with unmodeled dynamics in the context of external environment disturbance and reference signals unknown, this study explores the USV swarm motion decision-making strategy and proposes a finite-time trajectory tracking control scheme. MethodsFirst, using the Lyapunov function and artificial potential function, combined with the position information of the swarm virtual reference vehicle (SVRV), a swarm motion decision-making strategy with velocity guidance is constructed. Second, a finite-time lumped uncertainty observer (FLUO) is designed to compensate for the unknown information contained in the velocity error equation. Furthermore, a non-singular terminal sliding mode (NTSM) swarm trajectory tracking control method based on FLUO is adopted to design the control law. Result Based on the theoretical analysis and simulation experiments, it is proven that the system is stable. ConclusionBased on the proposed swarm motion decision-making strategy and FLUO-NTSM tracking control scheme, USVs can maintain their swarm and achieve accurate path tracking.

Objective As one of the key technologies for the safe navigation of ships, intelligent collision avoidance decision-making is of great significance for the development of intelligent ships. Aiming at the intelligent collision avoidance decision-making problem under multi-vessel encounters, an improved chaos sparrow search optimization algorithm (CSSOA) based on Gaussian variation and Tent chaos is proposed. Methods The algorithm uses Tent chaotic mapping to initialize the original sparrow population and improve its diversity, chaotic mapping is applied to sparrows with poor adaptability and stagnant search ability, and Gaussian mutation is used to improve the local search ability and robustness. The improved scheme optimizes the problems of heuristic algorithms such as slow convergence speed and tendency to fall into the local optimum. A collision risk model is established using the fuzzy membership function with the comprehensive consideration of the ship-to-ship speed ratio, minimum encounter distance, relative distance, minimum encounter time and relative orientation. ResultsIn a typical encounter scenario involving multiple ships, the experimental results demonstrate that the average number of iterations for the improved algorithm is reduced by 77.97% and 53.57% compared to particle swarm optimization and the original sparrow algorithm respectively. ConclusionThe improved CSSOA can achieve a safer and more efficient collision avoidance path at a superior convergence speed, providing valuable guidance for ship navigators in making collision avoidance decisions.

ObjectiveAn adaptive finite-time filtered backstepping sliding mode controller is designed to solve the rudder roll stabilization control problem of underactuated ships in unknown wave disturbance conditions. MethodFirst, in order to avoid differential operation for the virtual control law, a first-order filter is introduced to address the problem of differential explosion that affects the backstepping approach. By combining the filtered backstepping technique with adaptive sliding mode control, finite-time convergent control laws for rudder roll stabilization are designed on the basis of the finite-time control theory. Finally, the stability of the heading control subsystem and roll damping subsystem is proven by the Lyapunov stability theory. ResultsThe simulation results indicate that the designed controller can realize course tracking and roll damping simultaneously in finite time under different wave disturbance conditions. Compared with backstepping sliding mode control, the designed controller can improve the course-keeping control performance, and the roll reduction rate is increased by 5%. ConclusionThe proposed method can provide useful references for the rudder roll stabilization control problem of underactuated ships.

ObjectivesAiming at the bottleneck of the insufficient electric endurance of unattended vehicles, the configuration design, motion performance and energy capture efficiency analysis of a manta ray bionic unmanned underwater vehicle (UUV) are carried out. MethodsThe configuration of a multi-module bionic long-endurance manta ray UUV is proposed, and its motion and energy capture mechanism are deduced and obtained under the principle of wave energy capture by a floating hydraulic cylinder. Next, based on the multi-module floating body theory and three-dimensional potential theory, hydrodynamic calculation and analysis are carried out, and the motion response and wave energy capture law of the multi-module manta ray UUV are revealed under different wave directions and different connected stiffness and damping of the UUV. ResultsFinally, the wave energy capture efficiency of the multi-module manta ray UUV in waves is studied in combination with the optimal stiffness and damping of the hydraulic cylinder.ConclusionsIt is concluded that the wave energy capture characteristics of a multi-module manta ray UUV can be analyzed by its motion equations and energy capture formula.

ObjectiveWhen a fire occurs in the multi-storey dwelling section of a ship, the temperature distribution pattern during the spread of smoke along corridors and ladder openings is significantly different from that of a building fire. Therefore, it is necessary to fully understand the characteristics of fire smoke in crew cabins. MethodsAn experimental study on the temperature distribution characteristics of fire smoke in single and multi-storey corridors is carried out in a 1︰5 scaled down ship model by changing the size of the heptane oil pool and the states of ladder openings. ResultsIn the case of a single-storey spread of fire smoke, the vertical temperature distribution in the corridor shows an obvious thermal stratification phenomenon with a height of over 0.4 m. In the case of a multi-storey spread, the vertical temperature gradient in the corridors is lowered and the thermal stratification height is reduced to 0.2 m or less; the vertical thermal stratification height within the corridors is reduced at corners and turnouts; the smoke temperature continues to decrease during horizontal spreading; and the temperature distribution satisfies the exponential decay law. ConclusionsThe thermal stratification height in a multi-storey corridor is significantly reduced compared with a single-storey spread of fire smoke, and the temperature attenuation coefficient k in the horizontal spread process increases as the size of the fire source increases. The results of this study can provide theoretical support for the fire risk assessment and fire protection design of ships.

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.

ObjectiveThe structural response and dynamic structural collapse mode of a container ship in waves are studied by fully considering the effects of load nonlinearity and surface nonlinearity.MethodsFirst, a hydrodynamic model of a container ship is established based on the CFD platform, and the overset grid method is used to realize matching between the dynamic boundary grid of the hull hydrodynamic model and the Euler grid in the far-field fluid domain. The volume of fluid method is used to simulate the nonlinearity of the free surface in the whole fluid domain, and the N–S equations in three directions are solved in the whole flow field domain so as to solve the nonlinear wave load of the ship in real time. A nonlinear finite element model of the ship that can simulate its collapse behavior is then established, and the time-domain collapse response of the ship including plasticity and buckling is calculated based on the explicit dynamic nonlinear finite element method (FEM). Finally, the transmission of fluid pressure and node displacement between the hydrodynamic model and structural finite element model on the wet surface are realized, and two-way iterative coupling between the CFD solver and nonlinear finite element solver is carried out to calculate the nonlinear wave load and structural collapse response during the structural collapse of a 4600 TEU container ship in real time. ResultsUnder extreme waves, the upper to middle structures of the container ship are widely plastic, the main deck, side plate, deck longitudinal, side longitudinal and other components have typical yield instability under the action of wave loads, the deck longitudinal, side longitudinal and other structural members have serious lateral instability, and the hull structure loses its bearing capacity.ConclusionThe proposed CFD nonlinear FEM can accurately solve the structural response and dynamic collapse mode, making it viable as a new approach to studying the collapse response of ship structures.

ObjectiveIn order to determine the strength of the special deck structure of a cruise ship, this study investigates the ultimate bearing capacity of an unconventional stepped deck used in the layout of the cruise theater.MethodsBased on the quasi-static ABAQUS method, the ultimate bearing capacity of a stepped deck is calculated and the weak positions of the structure are determined and compared with conventional deck failure modes. Meanwhile, the influence of the deck, longitudinal frame, girder web and girder panel thickness on the ultimate bearing capacity of the structure are investigated, and two structural optimization ideas are proposed: pillar reinforcement and longitudinal reinforcement.Results The results show that the failure of the stepped deck mainly occurs at the boundary of the layer with the largest height difference; the ultimate bearing capacity of the stepped deck decreases significantly compared with that of a conventional deck; and the corresponding compression displacement and collapse depth increase obviously. The ultimate bearing capacity increases with the thickness of the deck, longitudinal frame, girder web and girder panels, and the improvement effect of girder web thickness is the most significant. The ultimate bearing capacity of the structure can be effectively improved by adding struts or increasing the height of the web in the weak position of the structure.ConclusionThis study has great significance for the design and optimization of special decks for modern cruise ships.

ObjectiveWhen using the circumference crack method to calculate the ice load, the size of the circumference crack is usually determined by an empirical formula, but this can introduce many uncertainties to the selection of input parameters.MethodsTo accurately determine the size of circumference cracks, we propose a method of recognizing ice circumference crack size based on YOLACT, which can identify ice in images taken with ships. We then detect the edge of the mask and obtain the shape of the ice cracks, and the ice breaking radius and angle can be estimated by fitting the cracks.Results The results show that the accuracy of the ice breaking radius and angle estimated by the proposed method can reach up to 96.12% and 96.58% respectively.ConclusionThis method can accurately determine the size of circumference cracks and assist in the initial design of marine structures in cold regions.

ObjectiveAs polar exploration develops, hull structure designs for ice routes are no longer limited to the traditional empirical formula method as more attention is paid to the actual ice load and structural response acting on the structure. The study of structural response calculation under ice load is crucial for the structural design of polar ships. MethodsFirst, the finite element method is used to numerically simulate the ice load cases of a polar navigation ship, such as crushed ice, floating ice and layered ice. Considering the influence of the material strain rate, the dynamic response of the structure under ice load is calculated. Second, based on the structural response equivalence, the static transformation of the dynamic response is completed, and the concept of the dynamic static transformation coefficient is proposed. Finally, the range of the dynamic static conversion coefficient under different ice load cases is obtained.ResultThe results show that the conversion coefficient of the dynamic-static equivalent conversion of the bow structure under different ice load cases is between 1.0 and 1.4.ConclusionThe quasi-static equivalent method of the ice-induced dynamic response of a bow structure is verified as reasonable and feasible.

ObjectiveThis study seeks to explore the effects of a protective bulkhead structure on the load and damage characteristics of a typical cabin under warhead internal blast, and guide protective bulkhead design for important ship cabins. MethodA typical double cabin structure model is designed in which the large cabin is used to simulate the explosion cabin, while the small cabin is used to simulate the important cabin. A comparative study is then carried out on the load and damage characteristics of the original bulkhead model and multi-layer liquid-containing protective bulkhead model under an internal explosion of thr shell warhead with 6.12 kg TNT, and an analysis is made of the load characteristics of fragments, shockwaves, structural crevasses, deformation damage characteristics. ResultsThe fragment flying angle produced by the front end of the warhead is basically the same, and there are fewer fragments at the front end than in the circumferential direction. The presence or absence of a protective bulkhead has little effect on the fragment load characteristics. The explosion shockwave has obvious corner convergence characteristics. The shockwave energy changes with the strength of the structure, and it is easier for the overall energy to pour into the weak parts of the structure. Under the combined damage of shockwave and fragments, the center of the conventional steel transverse bulkhead suffers a large break, while the multi-layer liquid-containing protective bulkhead only suffers large plastic deformation on the projectile-facing surface and perforation by a small number of fragments, with the structure of the projectile backing surface remaining complete. Multi-layer liquid-containing protective bulkheads can effectively prevent the transmission of explosive energy to the adjacent cabin, but they will aggravate the structural damage of the explosion cabin. ConclusionThe "evacuating and blocking" protection design method has important practical application value for the protection of important ship cabins.

ObjectivesDuring the anti-explosion process, the deformation and damage of blast wall connectors can lead to anti-explosion failure. Therefore, it is necessary to study the structural response characteristics of blast wall connectors under explosive loading. MethodsSpecifically, four load forms, namely triangular load, gradually applied load, linearly decaying load and rectangular load, are set in LS-DYNA in order to simulate the dynamic response of blast wall connectors under the condition that the energy of each applied load is equal. ResultsThe results show that for cases with linearly decaying and rectangular pulses, blast wall connectors are more likely to deform and suffer higher stress values. Blast wall connectors are more sensitive to gradually applied load and rectangular load, and the corresponding maximum deformation and maximum stress value can be 202.6% and 93.8% higher respectively than cases with the other two types of loads. Additionally, reverse loading conditions can lead to significant deformation, and the increment of peak pressure can induce plastic deformation under reverse pulse loads. ConclusionsThis study can provide useful references for the design of blast wall connectors.

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.

ObjectivesThe springback is the main factor affecting the forming quality of hull plates in the cold forming process. To improve the forming quality, it is necessary to investigate springback prediction, obtain the appropriate springback control method and further guide the die design.MethodsA fully convolutional network (FCN) is used to perform pixel-level calculations and regression calculation on the springback image so as to achieve springback prediction for each forming position on the sheet. In this study, a finite element (FE) model is established using ABAQUS 2019, and the numerical results are validated by the experimental results. The verified model is then applied to obtain the training sample set. The workpiece geometric information is used as the input of the neural network to retain all the information of the image, and the TensorFlow Core V2.2.0 platform is used to build the FCN based on different convolutional neural network models. Finally, the pros and cons of different neural networks are compared, and the optimal network is applied to the die design.ResultsThe results show that the maximum error of the predicted springback is 8.49%, where the constructed FCN32 has the highest accuracy. The proposed model can also realize one-time mould design with a calculation time of only 0.5 seconds and a maximum error of only 1.00%, significantly improving calculation efficiency.ConclusionsThe FCN-based algorithm proposed herein provides a springback prediction method for strips with high accuracy and efficiency, as well as offering a new approach to quick mould design.

ObjectiveThis study investigates complex welding residual stress and its effect on the vibration characteristics of a ring-stiffened cylindrical shell.MethodsFusion welding with carbon dioxide as the shield gas is employed to finish the welding of a ring-stiffened cylindrical shell. The non-destructive X-ray diffraction (XRD) approach is used to measure the longitudinal residual stress of critical regions after welding and annealing heat treatment. Effective thermal elastic-plastic finite element (FE) computation is then used to examine the temperature and welding residual stress during welding, as well as considering the influence of the moving body heat source and fixed heat source on welding computation. Under the state of freedom, the vibration characteristics of the examined ring-stiffened cylindrical shell after welding and annealing heat treatment are measured, and the vibration modes and corresponding natural frequency are both predicted with FE analysis.ResultsBased on experimental measurement, thermal elastic-plastic FE computation measurement during welding and structural vibration is carried out, and the residual stress and vibration characteristics of the ring-stiffened cylindrical shell after welding and annealing heat treatment are obtained.ConclusionsA fixed heat source can effectively predict the thermal and mechanical response during the welding of a ring-stiffened cylindrical shell, and the predicted welding residual stress shows good agreement with the measurements. Annealing heat treatment can significantly reduce welding residual stress and lower its influence on the vibration characteristics of a ring-stiffened cylindrical shell.

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.