In order to improve the overall positive design ability of ship power engineering, the digital design method of ship power systems engineering is studied. The model-based systems engineering (MBSE) method theory was integrated with the system engineering method, using the independently developed V-Dats software platform and the graphical SysML language, modeling is carried out from four dimensions: requirements, behavior, structure and parameters of the auxiliary system of the generator set. The process analysis of system requirements-function-logic-physics was completed. The system requirement architecture, functional architecture and physical architecture model were obtained, then closed-loop verification and validation were carried out at the system level. By summarizing the top-level framework of the overall design process of ship power systems, an overall forward design method based on MBSE was proposed. The research results can effectively support the overall demonstration and design of ship power engineering.

ObjectiveDigital twin technology and Internet of Things (IoT) technology have been widely used in structural health monitoring, but their application in special equipment is still in its infancy. MethodsIn view of the safety monitoring requirements for the whole life cycle of pressure containers, this paper realizes the temperature data acquisition of the structure through IoT and uses the VUE + Flask framework to write a software monitoring system. The container model is established via the Three.js library to realize the real-time driving of the temperature data of the digital twin model. Additionally, in order to test the feasibility of the twin system, relevant temperature experiments are carried out based on ANSYS simulation. ResultsThe experiment proves that the key digital twin technology based on the pressure container structure can realize functions such as intelligent monitoring, scene perception, digital mining and information feedback. ConclusionThe system architecture proposed herein has good reference value, and the deep integration of IoT technology and digital twin technology can contribute to the development of China’s strategic high-end products and major key equipment.

ObjectivesIn order to solve the problems of the traditional interactive ship engine room simulation system such as its single simulation form and poor immersivity and realism, a new immersive interactive ship engine room simulation system is designed and implemented, divided into the hardware-in-the-loop （HIL）simulation system and 3D virtual reality (VR) system.MethodsReal-time simulation technology is adopted to realize the real-time connection between the VR system and HIL simulation system through a high-speed network. At the same time, an immersive stereo projection system and multi-station VR system are combined and integrated with the data.ResultsThis design realizes the real-time interaction and cooperative operation of the whole system, and the real-time synchronization of the system state between the HIL and VR systems. The internal synchronization characteristics of the VR system are given, and the real-time synchronization of 3D images is realized. Meanwhile, a collaborative interactive operation function of the multi-station VR system is added.ConclusionsThe new immersive interactive ship engine room simulation system proposed herein has guiding significance for ship operation and maintenance management and personnel operation training.

Objective Aiming at the problem that the assembly quality of interference fit components is difficult to control, a method for monitoring the assembly quality of such components based on digital twin technology is proposed.Methods Combined with digital twin technology, the framework of an assembly quality monitoring system for interference fit components is constructed; the actual assembly process is comprehensively analyzed and a real-time monitoring process of the assembly process based on the press-fitting force is designed; and a state prediction model of the press-fitting force based on the Markov model is established, and a comprehensive judgment of the assembly quality of the interference fit components is realized by the comprehensive comparison of theoretical press-fitting force, actual press-fitting force and press-fitting force prediction state.Results The interference fit between the output shaft and sun gear of a typical marine planetary reducer is used as an example for verification. The results show that this method can realize the real-time collection and monitoring of the press-fitting force at key points in the assembly process and predict the future quality characteristics of the point. At the same time, the experimental results of the physical assembly platform are compared with the model prediction results, and it is found that the two are consistent, which proves that the proposed method of monitoring the assembly quality of interference fit components based on digital twin technology is effective and feasible.ConclusionThe results of this study have important reference significance for the realization of quality monitoring in the process of the intelligent assembly of mechanical products.

ObjectivesA crankshaft is a key component of marine diesel engines. In order to monitor crankshaft stress and ensure the safe and reliable operation of ships, a crankshaft stress monitoring method based on digital twin technology is proposed.MethodsBased on the digital twin concept, a framework for the intelligent operation and maintenance of marine diesel engines is put forward. Taking a certain type of in-line 6-cylinder marine medium-speed diesel engine as the research object, a digital crankshaft health condition assessment system is developed on the basis of available data from real engines. First, based on an RBF neural network, the cylinder head vibration acceleration signal is used to identify in-cylinder pressure, then the load of the crank pin is calculated. Based on the finite element method, the key positions which affect the lifecycle of the crankshaft are obtained after analyzing its stress and fatigue. A BP neural network is used to evaluate the stress of the crankshaft after a reduced-order model of forces and stresses is used to determine real-time performance. A BP neural network is then used to evaluate the stress of the crankshaft.ResultsThe prediction errors of the cylinder pressure and crankshaft stress of the proposed model are both less than 5%, and the stress prediction time is shortened to the second level, realizing the real-time/quasi-real-time update of the twin model.ConclusionsThe results of this study show that it can be used as a new reference for the real-time monitoring and intelligent operation and maintenance of diesel engine components.

ObjectivesHigh fidelity finite element models and effective load identification technology are very important for ship structure health monitoring and evaluation. Therefore, a model updating and load identification method based on improved particle swarm optimization (PSO) is proposed.MethodsThe Rastrigin function is used to compare the improved PSO algorithm with the classical PSO algorithm. An I-beam structure is adopted with pressure applied at the middle of the beam. A limited number of strain sensors are pasted on the surface and divided into two sets: the measured set for model correction and load identification, and the monitoring set for verification. The elastic modulus of the block division of the I-beam is modified and verified, and the load identification based on the modified numerical high fidelity model is verified.Results In the test of the improved PSO algorithm by Rastrigin function, it shows better global optimal solution searching ability under different particle numbers. In the I-beam experiment, the elastic modulus of the two parts of the partition converges to the optimal solution after 23 iterations. By comparing the strain data of the test monitoring points with the data of the numerical calculation results after model correction, the relative error of the strain is within 2%, which verifies the correctness of the model updating method. In addition, the external load pressure of the structure is identified by the load identification method, and the error between the identified calculated value and the load applied in the test is within 2%. The maximum error between the strain value of the monitoring points calculated by the combination of the identified load and modified model and test data is 3.74%, which verifies the effectiveness of the load identification.ConclusionsThe proposed method has a good precision performance in the inversion of the global state of the structure, and can provide technical support for hull structure health monitoring, residual life prediction and predictive maintenance.

The fixed magnetic field of a ship is mainly degaussed by the pulse current output from the degaussing main power supply, and its degaussing effect will directly affect the magnetic stealth level of the ship. By sorting out the composition and structure of different types of energy storage degaussing main power supply systems, their working principles, advantages and disadvantages were reviewed, and the technical development trend of large ship energy storage degaussing main power supply systems was prospected. Topology structures for lithium battery energy storage degaussing main power supply system and high-speed motor energy storage degaussing main power supply system were proposed, and key technical issues were summarized such as the decoupling compensation and degaussing current synchronization control technology of multiple degaussing main power supplies. The research results can provide reference for the design of energy storage degaussing main power supply systems for large ships.

ObjectivesTo improve the stability and efficiency of hybrid propulsion systems for ships, a power distribution strategy based on the particle swarm optimization (PSO) threshold for multi-stack fuel cell systems is proposed. MethodsFor the hybrid power source system composed of multiple fuel cell stacks and batteries, a fuzzy logic energy management strategy based on the PSO algorithm was designed. By flexibly adjusting the number of fuel cell stacks and their individual output power based on the propulsion system load power and the battery state of charge (SOC), the control threshold of the system was optimized using PSO. ResultsMatlab/Simulink simulation results show that this energy management strategy can quickly meet complex and changing load power requirements, and improve the system efficiency of the hybrid power source. Compared with traditional energy management strategies, the hydrogen consumption of the fuzzy logic-based and PSO threshold-based energy management strategies decreased by 18.96% and 31.48%, respectively. ConclusionsThis intelligent energy management strategy is applicable to multi-stack fuel cell systems in hybrid propulsion ships, and can effectively improve the system efficiency of hybrid power sources and reduce hydrogen consumption.

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.

ObjectiveIn order to solve the problem that noise detection inside a cabin is difficult due to the complexity and narrow space, a local space planning method of a manipulator based on the goal-oriented rapidly-exploring random tree (RRT) algorithm is proposed. MethodA six-degrees-of-freedom (6-DOF) manipulator is used as the carrier, and a fixture is installed at the end of the manipulator. The four fixed points inside the cabin are used as the reference points to study the mechanical arm in the local space. The trajectory planning is traversed and the reference point-1 is taken as an example to measure the noise of its 6 measurement surfaces and 147 measurement points. The noise signal and the position and attitude information of the space to be measured are matched and analyzed, and the environmental noise of the current measurement point is fed back to form a sound pressure cloud map. ResultsThe experimental results show that the robotic arm can realize trajectory planning and noise measurement for all measurement points corresponding to the four reference points without collision. ConclusionThe proposed method has practical value in being able to realize intelligent planning and internal noise detection in narrow cabin areas.

ObjectivesIn order to solve the problems of the complexity of the existing robot arm pose prediction algorithm model and its over-reliance on the parameters of the camera and robot, a new robot arm pose prediction method based on RGB image gradient vector mapping is proposed. MethodsFirst, a series of robot arm image texture gradient features is calculated based on the Histogram of Oriented Gradient (HOG) algorithm. The mapping relationship between the image features and joint angles of the robot arm is then established by training Deep Neural Networks (DNNs). Finally, the pre-trained vector mapping model is used to quickly predict the pose of the robot arm in a motion frame image. The training and test datasets of the model are generated by synthetic data techniques. ResultsThe results show that the average error of the angle prediction of the three joints of the target robot arm is 2.92°, and the pose prediction time of a single image is about 0.08 s. ConclusionsThe results show that the proposed pose prediction method has better prediction speed and accuracy, and only uses RGB image information to achieve end-to-end pose prediction.

ObjectivesDomain adaptive technology is widely used in the bearing fault diagnosis of variable operating conditions. However, most domain adaptive technology only focuses on the global domain distribution and ignores the subdomain distribution, and the domain-invariant feature quality is easily affected by noise, leading to a significant decrease in diagnostic accuracy under varying operation conditions. Therefore, a fault diagnosis method based on a self-attention subdomain adaptive adversarial network (SASAAN) is proposed.MethodsFirst, a convolutional block attention module (CBAM) is utilized to extract the fault-related domain-invariant features in the vibration signals of the source and target domains. The adversarial network and subdomain adaptive module are then combined to reduce differences in the global and local domain edge distributions of different operating condition data, thereby improving the transferability of the data. The loss function is optimized by back propagation using the Adam optimizer to improve the diagnostic performance of the model, and the hyperparameter tuning of the model is also performed. Finally, the diagnostic results on the target domain test set are output by the failure classifier, and the Ottawa bearing data set is used to validate the effectiveness of the proposed method. ,ResultsThe results show that the fault diagnosis accuracy of the proposed method is higher than 96% under the condition of strong noise and varying operation conditions, which is obviously better than other methods.ConclusionThe results of this study can provide valuable references for the fault diagnosis of rolling bearings under varying operation conditions.

Objectives Aiming at the problems that the traditional marine main engine fault diagnosis model is difficult to update with real-time data, and the marine main engine has many monitoring points but few fault samples, a fault diagnosis method which can handle unbalanced data and update the model online is proposed. MethodsFirst, principal component analysis (PCA) is used to reduce and extract the features of the monitoring samples to reduce the complexity of the training model, and the SMOTETomek technique is used to construct fault samples to balance the training set. Next, to solve the problem that the diagnosis model is difficult to update in real time, the online sequential extreme learning machine with regularization (OSRELM) model which combines regularization method and can update online is introduced. Finally, the feasibility of the OSRELM model is verified by taking the main engine fuel system as an example, and the effectiveness of the overall model is verified by ablation experiments with unbalanced marine main engine data. ResultsThe results show that the proposed method can improve the diagnostic accuracy by 29.73% on the basis of the original model. ConclusionsThe proposed method has higher diagnostic accuracy, a smaller fluctuation range and better stability than other similar algorithms. In the case of unbalanced data, it still has a strong ability to identify fault samples, providing valuable references for research on marine main engine fault diagnosis.

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 study aims to carry out systematic research on the hydrodynamic performance of a small unmanned catamaran. MethodsBased on STAR-CCM+ numerical simulation software, the hydrodynamic performance of a small unmanned catamaran in a hydrostatic state and self-propelled state under different Froude (Fr) numbers is numerically simulated. The unsteady RANSE model is selected and the Dynamic Fluid Body Interaction (DFBI) model and overset grid function are used to simulate the trim and heave of the catamaran. A body-force propeller is used to replace the propeller effect. The empirical formula of the friction resistance coefficient is used to verify the simulation results of the hydrostatic state. The self-propelled experimental results are then compared to the simulation results of the self-propelled state to verify the accuracy of the simulation results. ResultsWhen the propeller speed is 3 000 r/min, the difference in total resistance between the self-propelled and hydrostatic states of the small unmanned catamaran is 21.099%. Under different propeller rotation speeds, the relative errors of the thrust between the simulation and experimental results of the self-propelled catamaran is less than 10%. ConclusionsThe comparison between the simulation results and experimental results verifies the reliability of the simulation. The hydrodynamic performance of the self-propelled ship hull studied by the volume method is quite different from that under hydrostatic conditions. The numerical method can provide valuable references for further predicting the hydrodynamic performance of small unmanned catamarans.

ObjectiveIn order to further improve the speed and accuracy of calculating the acoustic scattering fields of underwater concave targets, the acoustic scattering characteristics of underwater corner reflector complexes are studied. MethodBy applying the Kirchhoff approximation and ray tracing methods, and considering the multiple effects of scattering and occlusion by corner reflectors, a simplified acoustic scattering prediction model of an underwater corner reflector complex is established and a rapid prediction method （i.e. modified planar element method, PEM）of acoustic scattering fields is proposed. The acoustic scattering field of a corner reflector complex is calculated by this method and verified via finite element simulation; on this basis, an analysis is made of the characteristics of octahedral corner reflectors, combined polyhedral corner reflectors and cluster-based and space-based strong scattering targets. ResultsThe results show that the modified PEM allows the rapid and accurate calculation of the acoustic fields scattered by diagonal reflectors. The acoustic scattering fields of octahedral corner reflectors and combined polyhedral corner reflectors varies with the incident wave frequency, angle and reflector complex distance. ConclusionThe results of this study can provide important technical support for the design of underwater passive interferer models.

ObjectivesTo improve the efficiency of naval aircraft support, the optimization design of aviation support resource performance indexes under pit-stop support mode is carried out.MethodA naval aircraft deck operation scheduling model is established with the objective of minimizing the support time, the carrier surface aviation support resource performance index is regarded as the independent variable satisfying the interval constraint, and a two-layer optimization model is constructed.ResultsThe optimal resource allocation scheme and support operation scheduling scheme under different sortie modes are obtained through the simulation of various typical mission scenarios, and the effectiveness of the solution algorithm is verified.ConclusionThe proposed method can effectively solve the joint optimization problem of pit-stop support resource performance index and support operation scheduling, providing theoretical support for the optimization of pit-stop support resource configuration.

ObjectivesThis study focuses on how the sampling efficiency of a free-diving sediment trap (FST) is affected by its body posture, and uses quantitative analysis to describe the changes of the center of gravity and attitude angles. MethodsAn FST is designed which consists of a sampling module and a buoyancy control system. A 3D model of the FST is built using SolidWorks. Kinematic analysis is completed using Matlab, and the offset of the center of gravity at each moment in the whole working cycle is obtained by simulation. The principle of moments is used to derive its attitude changes caused by the offset of the center of gravity. The influence of the attitude changes on the effective collection area is then quantitatively analyzed using projective transformation. ResultsThe result shows that the offset of the center of gravity is limited to a circle with the origin of the body-fixed coordinate system as the center and a radius of $ 8 \times {10^{ - 3}}\;{\text{m}} $. It is seen that the domains of x and y are ${x~~{\text{g}}} \in ( - 6 \times {10^{ - 3}}\;{\text{m}},{\text{ }}3 \times {10^{ - 3}}\;{\text{m}})$, ${y~~{\text{g}}} \in ( - 1 \times {10^{ - 3}}\;{\text{m}},{\text{ }}7 \times {10^{ - 3}}\;{\text{m}})$, and the domains of the attitude angles are $ \theta \in ( - 1.5^\circ ,{\text{ }}16.6^\circ ) $ and $\phi \in ( - {2.6^ \circ },{16.8^ \circ })$. When $\theta = 14.7^\circ {\text{ and }}\phi {\text{ = 13}}^\circ$, the effective collection area is reduced to 94.27% of the original value. Compared with the 100% effective collection area, it takes 1.06 times the original collection time to collect the same volume of sinking particles. ConclusionsThe results of this study can provide useful references for FST stability analysis and buoyancy regulation system design.

ObjectivesAiming at the high-precision recovery guidance control requirements of current stern ramp recovery technology, a self-adaptive cascade tracking control method for unmanned surface vessels (USVs) is proposed specifically for stern ramp recovery. MethodsBased on the technical requirements of stern ramp recovery, a motion model of an underactuated USV is established, and the generalized Kalman filter (GKF) algorithm is used to predict the navigation state and recovery position of the mother ship. Introducing the idea of constant bearing guidance combined with the sliding mode variable structure control theory, a stable cascade control system is constructed to solve tracking control problems during the recovery process. ResultsIt is proven that the USV can stably track the target, by analyzing the stability of the system through the Lyapunov theory and cascade theorem. ConclusionsThe simulation results show that the proposed control method gives the USV stable tracking performance and strong robustness against uncertain disturbances.

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.

ObjectivesThe optimization of midship sections is characterized by the large amount of design variables and the complex constraints. Most relevant research applied the intelligent optimization algorithm embedded with the rule-based calculation program (e.g., Mars2000) from classification society to deal with this issue, which has a large computation cost. Therefore, a general fast optimization method based on sensitivity ranking is proposed for the optimization of midship sections. MethodsFirstly, the sensitivity of each constraint about each design variable was evaluated. According to the result of sensitivity, the order of design variables to be modified can be obtained when each constraint is violated. Whether the constraint is only related to local variables or not can be determined as well. During optimization iteration, based on the constraint violation of the current scheme, variable adjustment can be made with the above sensitivity information, and the sensitivity result was updated periodically. Finally, minor adjustment of optimized schemes based on coordinate alternation was employed to further improve the optimization effect. ResultsThe optimization result of an oil tanker midship section shows that the proposed method can achieve a 5.195% reduction of weight. ConclusionsCompared with the intelligent optimization algorithm nesting Mars2000 directly, the optimization effect of the proposed method is satisfactory, and the time cost is only 5.58% of the former. The advantage of the proposed method in time cost is quite obvious.

ObjectivesThe atrium structure is an important functional cabin in the superstructure of a large cruise ship. Atriums have a large spatial span and are always subjected to complex loads. A fast and reliable safety assessment simulation method for atrium structures is required to assist in their structural design.MethodsBased on the Guidance for Direct Calculation of Local Structures of Cruise Ships 2021 by the China Classification Society (CCS) and the loading characteristics of atriums, a direct calculation design method is proposed in which loads on structures are equivalent to combined simplified loads in three groups, namely longitudinal bending, vertical shear and local cargo pressure.ResultsThe results of the proposed direct calculation design method of a specific atrium structure are in good agreement with the whole-ship finite element analytical results, verifying its effectiveness.ConclusionsThis study can provide guidance for the design process of atrium structures in large cruise ships.

ObjectivesIn order to improve the accuracy of the ultimate strength evaluation of hull plates, this study carries out a nonlinear finite element numerical simulation of the ultimate strength of ship hull plates under cyclic loading based on the critical state of elastic shakedown. MethodsFinite element software ANSYS is used to primarily investigate the effects of elastic-perfectly plastic and cyclic-plastic Chaboche material models on the release of welding residual stress and ultimate strength of hull plates after reaching the critical state of elastic shakedown. ResultsThe results show that after the first cycle, the welding residual stress is basically released and tends to become stable after reaching the elastic shakedown state under cyclic loading, at which point the ultimate strength of the Chaboche model is greater than that of the elastic-perfectly plastic model. ConclusionsWhen performing the nonlinear finite element numerical simulation of the ultimate strength of ship hull plates under cyclic loading based on the critical state of elastic shakedown, it is necessary to select a material model that takes into account material hardening and the Bauschinger effect. The obtained results have a certain reference value for further research on the ultimate strength of hull structures under cyclic loading.

ObjectivesIn view of the fact that the structural performance assessment method of the internal-pressure-resistant square cabin is not clear and the general specifications for naval ships are not fully applicable, the stress analysis method and strength assessment criteria applicable to the internal-pressure-resistant square cabin are studied. MethodsBased on the theory of elasticity, the two yield criteria Mises and Tresca commonly applied in ASME BPVC were analyzed. According to the principle of safety, Tresca was determined to be the analysis criterion applicable to the internal-pressure-resistant square cabin. By taking the bulkhead grillage as the basic unit, the stress classification of the internal-pressure-resistant square cabin was carried out based on ASME BPVC, and four typical assessment locations were obtained: the center of the plate panel, the midpoint of the short side of the plate panel, the midpoint of the long side of the plate panel, and the corner of the plate panel. In order to reduce the amount of engineering calculation, the theoretical formula and numerical calculation method of stress components for plate element finite element analysis were proposed based on the stress linearization theory, and the solid finite element model of grillage was established for comparing the difference between the structural assessment results of two models. ResultsCompared with the accurate results of the solid element model, the error of plate element stress analysis result is basically about 3%, and the results of plate elements are generally larger. Considering the safety conservative assessment principle of ships and nuclear structures, it can be considered that the strength assessment method of internal-pressure-resistant square cabins based on the plate element finite element model and ASME BPVC meets the engineering requirements. ConclusionsThis study can provide a reference for the stress analysis and strength assessment of the internal-pressure-resistant square cabin, and is of great significance for tackling the technical bottleneck faced by the ships using nuclear power plants.

ObjectivesIn order to study the effects of impact damage on the compressive strength and failure modes of woven carbon fiber reinforced thick composite laminates, in-plane compression tests are carried out. MethodsThe modified Hashin failure criterion and material degradation model are realized with user-defined subroutines to simulate the failure behaviors of laminates using the ABAQUS/Explicit modelling package. The effectiveness of the numerical model is validated through comparison with experiments aimed at the compressive strength and failure modes. ResultsThe results show that the impact damage reduces the compressive strength of the impacted laminates. The compressive failure mode of the non-destructive specimen is concentrated at the ends of the impacted laminates, while truncated failure occurs across the middle region. The compressive strength decreases with the increase in impact energy, but there is no linear relationship between the compressive strength and impact energy. The evolution of the damage behavior of laminated plates is closely related to the history of compression load. The damage failure of laminates hardly develops when the compression load is below the threshold of the failure load. Otherwise, the damage expands rapidly in the width direction, and compression damage eventually occurs across the whole width direction of the laminate. ConclusionsThe results of this study can provide references for evaluating the impact resistance of woven carbon fiber reinforced thick composite laminates.

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

ObjectivesThe structural parameters of the stiffened plate have an essential influence on its resistance to underwater explosion. It is necessary to analyze the specific influence degree of different parameters such as the stiffeners' height, number, and thickness. MethodsA series of numerical simulations were performed using the CEL method. Then, the influence of stiffened plates' structural parameters on their resistance to underwater explosion was analyzed. Based on the energy absorption law of stiffened plates underwater explosion load, a coefficient was introduced to characterize the influence degree of stiffeners. A calculation method of equivalent thickness was proposed considering stiffener coefficients. ResultsThe height of the stiffener, the panel thickness, and the stiffener's thickness have remarkable effects on the resistance to underwater explosion. In contrast, the thickness of the wing plate has an insignificant impact. Under the condition of the same amount of structural mass change, the influence of the height of the transverse/longitudinal stiffener on the damaged area of the stiffened plate is 2.5 times that of the wing panel thickness. The impact of the panel thickness and the thickness of the transverse/longitudinal stiffener on the damaged area is twice that of the wing panel thickness. With the increase of the stiffeners' height, number, and thickness, the structural strength and resistance to underwater explosion of the stiffened plate are enhanced, and the damage degree of the stiffened plate is reduced. The correlation coefficient of the proposed equivalent thickness calculation method considering the stiffener coefficient is -0.94. The method can adequately reflect the stiffened plate's resistance to underwater explosion. ConclusionsThe research results can be used as the basis for evaluating the ship structure against underwater explosion load and provide a reference for the design of the ship's anti-explosion structure.

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.

ObjectiveThis study analyzes different high-skew propeller blade parameters to obtain the laws of their influence on blade vibration modes. MethodsA certain high-skew propeller is taken as the research object, a series of variable parameter schemes is designed and the finite element calculations for the vibration modes are conducted. The numerical method is validated effectively by adopting model tests. Through an analysis of the calculation results, the influence laws of the different design parameters on the blade natural frequency, attenuation coefficient and mode shapes are obtained. ResultsThe calculation results show that the blade natural frequency increases with its sectional thickness, area ratio and hub ratio, and decreases with its skew angle. Furthermore, the sectional thickness and skew have the greatest influence among the research parameters. The fluid-structure interaction effect has the greatest influence on the first order attenuation coefficient. The increase of the sectional thickness overall or at the outside radius is beneficial for reducing the first order attenuation coefficient. On the contrary, the increase of the area ratio, inward movement of skew balance point and large rake angle design is negative for first order attenuation coefficient reduction. The first order mode shape is almost the same for the series design scheme, which means that changes of the design parameters such as sectional thickness and skew angle mainly influence the blade's high order mode shapes. ConclusionThe results of this study can provide guidance and references for vibration mode optimization control in the design process of high-skew propellers.

A digital twin is a digital model that comprehensively and accurately depicts physical entities in a computer system. Such technology can improve the intelligent management level of waterway transportation. Based on an analysis of the key enabling technologies of a digital twin model for waterway transportation, including big data monitoring and analysis, digital twin model construction, real-time matching and interaction of virtual and real model information, data-driven control of virtual and real models, and dynamic visualization technologies, the research and application status of the intelligent manufacturing of ship systems, operation management of waterway transportation equipment, intelligent life cycle operation and maintenance, virtual scenario construction and virtual experiments based on the digital twin are analyzed in detail. On this basis, digital twin technology for waterway transportation is summarized and predicted, providing valuable references for the development and application of digital twin technology in the field of waterway transportation.