The warship's power system is crucial for navigation. This study applies a method coupling damage tree analysis (DTA) and spatial dynamic event tree (SDET) analysis to quantify and predict the probability and status of damage to the power system. The DTA model establishes the damage logic relationship between the basic, intermediate, and top events. The innovative SDET model simultaneously considers the impacts of both spatial and temporal factors on the dynamic evolution of events. The coupled of these two methods encompasses all potential logical damage pathways.Coupled acoustic-structural analysis is used to simulate deformations at equipment installation positions under underwater explosion scenarios, in order to acquire the precise basic event probabilities of the DTA model. The computational results indicate that the coupled DTA-SDET method can effectivelypredict the damage position, and evaluate the overall damage status of the power system. The results discussed herein provide valuableguidance for warship navigations.

Under high-magnitude vibration and shock environments, the vibration isolation system of shipboard equipment exhibits pronounced nonlinear characteristics and complex dynamic behaviors. In this paper, the nonlinear dynamics of a piecewise nonsmooth vibration isolation system are studied by combining theoretical analysis and experimental verification. Firstly, considering the cubic nonlinearity of the vibration isolation system with a limiter, a strongly nonlinear piecewise nonsmooth model is established, and analytical solutions are derived using the averaging method. The amplitude-frequency response and backbone curve are analytically expressed. The model and analytical approach are validated through forward and reverse frequency-sweep experiments. Additionally, the influence of key isolation parameters on the primary resonance response is analyzed. Secondly, based on the Routh-Hurwitz stability criterion, the unstable region is derived, and parametric studies are carried out to illustrate the effects of nonlinear parameters on its stability. Subsequently, a design criterion for avoiding jump phenomena induced by saddle-node bifurcation is further proposed. Finally, the absolute displacement transmissibility is adopted as a performance index to evaluate vibration transmission. This research provides theoretical foundations for the design and parametric optimization of shipboard vibration isolation systems under strong nonlinear conditions.

Clinching is a cold-forming joining technology that requires no rivets or pre-drilled holes. Owing to its advantages of high joining efficiency, excellent joint performance, absence of heat-affected zones, and the ability to join dissimilar materials, it has been widely applied in engineering fields. However, under fatigue service conditions, clinched joints are prone to fretting wear, which significantly degrades the structural mechanical properties and shortens service life. To address this issue, this paper analyzes the fretting wear mechanism of clinched joints, and proposes two optimization processes—laser pretreatment and foam metal interlayer—based on the essential conditions for the occurrence of fretting wear, so as to mitigate the adverse effects of fretting wear on the performance of clinched joints. The research results show that the fretting wear regions are concentrated in the overlap area between upper and lower sheets and the circumferential region of the joint neck. The wear marks exhibit non-uniform distribution, accompanied by the generation of black granular aluminum oxide wear debris. Both optimization processes can effectively reduce the degree of fretting wear. Specifically, the laser pretreatment process can increase the static strength of the joint by 44.01

Clinching, as a core joining method for lightweight structures, offers the technical advantages of high efficiency, low cost, and environmental friendliness. Given the practical limitations of clinched joints in static load-bearing capacity, laser micro-texturing can effectively improve loadbearing performance by regulating the interfacial morphology between the two sheets. However, the tighter interfacial interlocking of the sheets leads to more complex fatigue wear accumulation and failure crack propagation. Further research is needed to characterize the evolution law of frequency-domain signals of micro-textured clinched joints under fatigue conditions using nondestructive testing techniques. In this paper, aluminum alloy clinched joints (AC) and lasertextured aluminum alloy clinched joints (LAC) were used as research objects to compare the influence of laser texturing on mechanical and fatigue properties. By designing and conducting an alternating test of dynamic response and strength degradation under constant-amplitude fatigue conditions, the intrinsic correlation between the frequency-domain signals variation law and the strength degradation mechanism was revealed. A residual strength prediction model for clinched joints was established by fitting based on the evolution law of frequency-domain parameters. The results show that laser micro-texturing can increase the interfacial friction of joints and disperse stress concentrations, thereby improving the static strength, average peak load displacement, and energy absorption of clinched joints, with increases of 123.21%, 111.88%, and 170.37%, respectively. Both the static and fatigue failure modes of AC and LAC joints are neck fractures. Due to uneven laser energy distribution, tearing along the texture boundaries occurs in the lap zone of LAC joints, and their fracture surfaces exhibit fatigue fracture characteristics. Under a fatigue load level of 1.400 kN, the natural frequency and residual strength of the LAC joint decrease synchronously. Based on the coupling mechanism of "crack propagation - stiffness degradation - natural frequency attenuation - residual strength decrease", a nonlinear residual strength prediction model based on the change of natural frequency under constant-amplitude loading is established. Laboratory validation demonstrates that the model exhibits high predictive accuracy.

Accurately detecting the axial stress of bolts is of significant importance for the safety and reliability of the entire equipment or structure. In response to the problems of low accuracy in measuring bolt stress using conventional stress detection methods and difficulty in experimental calibration using ultrasonic stress detection methods, this paper proposes an ultrasonic detection method of bolt axial stress based on simulation calibration. Firstly, a mathematical model of the relationship between axial stress and the time-of-flight (TOF) of ultrasonic waves inside the bolt is derived based on the acoustic elastic theory and Hooke’s law, and the calculation method for TOF is provided. Then, a finite element model is used to investigate the propagation characteristics of ultrasonic waves inside the bolt and perform stress calibration simulations to establish the functional relationship between stress and TOF. Finally, a hardware and software platform for bolt axial stress detection is built using self-developed equipment. The TOF of ultrasonic waves in bolts under different stress states is measured, and the calculated axial stress of the bolt is obtained by incorporating the TOF difference into the established functional relationship. When the bolt axial stress exceeds 100 MPa, the relative error between the stress indirectly measured by the ultrasonic detection method of bolt axial stress based on simulation calibration and the stress directly measured using strain gauges is as low as 4.25

Accurate assessment of a warship's damage state is crucial in naval warfare. However, most methods take the binary state of components as input, neglecting the impact of time-varying repair actions on the status of ship systems. To address this issue, this paper proposes a time-varying state assessment method for ship systems considering repair behaviour. Firstly, according to the redundancy of high reliability systems in ships, the SPARE gate is introduced. Secondly, the repair distribution function of the spare components in the dynamic repair tree (DRT) with time as a variable is derived based on the component repair order rule and the personnel absence factor in the SPARE gate. Finally, a case study indicates that the quantitative results are consistent with the distribution pattern of the repair time of the corresponding components, which proves the accuracy of the assessment method.

To address the high computational cost in global sensitivity analysis of large shipborne equipment, a CNN-BiLSTM-Attention model optimized by a Genetic Algorithm-Particle Swarm Optimization with adaptive weight updating (AGPSO) is proposed. This model is combined with Sobol’ global sensitivity analysis for efficient multi-input multi-output (MIMO) sensitivity evaluation of complex structural systems. Firstly, an AGPSO-CNN-BiLSTM-Attention model is developed to automatically optimize three key hyperparameters: learning rate, batch size, and L2 regularization, thereby obtaining the optimal network. Comparative results demonstrate that it achieves training accuracies of 99.49% for relative displacement and 99.12% for absolute acceleration, significantly improving prediction performance and computational efficiency. Secondly, integrated with the Sobol’ method, a MIMO sensitivity framework is established to quantify parameter influence. Finally, applied to a gas turbine isolation system, the approach identifies critical isolator and limiter parameters affecting shock response. The method significantly improves efficiency and generalization, offering practical value for structural design and optimization of marine equipment.

With the increasing demand for faster, more intelligent and digitalized material processing, material joining technology has garnered growing attention, among these technologies, laser and its composite joining techniques stand out as key areas of interest. Currently, laser joining technology has become a key enabler for transforming traditional techniques and achieving high-end product manufacturing, it has also become a focal point of research for academic institutions and industries worldwide. This paper provides a comprehensive overview of the current research status and advancements in laser processing technology for thin sheet material joining in recent years. It explores laser technology as both a direct and auxiliary joining method, presents the research on process parameter selection and optimization algorithms for laser-based material joining, and concludes by summarizing laser joining technology and discussing its future development trends.

The TA1 titanium alloy single-lap clinched joint was investigated focusing on fatigue damage prediction. A model was developed to calculate fatigue damage and remaining life by analyzing changes in natural frequency under fatigue conditions, combined with existing damage models. Based on the law of strength degradation and the existing strength degradation model, a strength degradation index model is established to predict the residual strength. Additionally, the cycle ratio was used to link natural frequency changes with strength degradation. Experimental data showed similar trends between natural frequency changes and strength degradation during fatigue. A predictive model for residual strength and remaining life was established by integrating these findings with classical models, and a predictive model for residual strength and remaining life was established. Validation demonstrated that the two-group data model, which incorporates both strength degradation and natural frequency change, offers more accurate predictions than the single-group data model.

The contact fatigue of carbon steel gear tooth surfaces under different lubrication conditions has been investigated and a model of the effect of lubrication conditions on contact fatigue has been established. Micro damage less than Hertzian contact is more likely to expand into macro pitting. The pressure around the micro damage increases when the micro damage partially coincides with the contact width, so the tooth surface around the pit is more likely to produce new pits, and then forms the superposition and aggregation. The larger the lubricating oil supply, the larger the contact width, and the larger the width of the micro damage that can be activated, the improvement of lubrication can promote the propagation of micro damage.

An easier and more efficient method is proposed for evaluating the ultimate strength of ship structures under fire conditions. Based on the Ideal Structural Unit Method (ISUM) and experiments from reference literature, a stress and strain equation for stiffened plates under fire conditions, as well as Fire ISUM, are proposed. To verify the effectiveness of the Fire ISUM method, 48 sets of FEA simulations incorporating the Fire ISUM were used to calculate the ultimate strength of different cabin fire positions and temperatures. The results showed that both the simulation and Fire ISUM were able to evaluate the high temperature ultimate strength. However, the Fire ISUM method does not account for initial imperfections due to the use of ideal high-temperature stress-strain curves. As a result, simulation results are lower than those obtained with the Fire ISUM, with a maximum error of 5.24%. To study the influence mechanism of ultimate strength of ship under high temperature conditions, the ultimate strength attenuation factor “IUR” was defined. Simulation results show that the ultimate strength attenuation of different cabins is not only related to the high-temperature width but also to the distance between the deck and the neutral axis. In actual fire rescue processes, when a deck of the same area is subjected to high temperatures, the further the deck is from the neutral axis, the more important its protection.

This paper investigates the impact of wall slip on the screw extrusion of cementitious materials. A wall slip extrusion model is developed based on the theory of infinite parallel plates. Then, the extrusion characteristics under different slip conditions of the screw and the cylinder wall are discussed. Finally, the Finite Element Method is used to verify the conclusions drawn from theoretical model analysis. The results show that when −1≤ a ←1/3 (where a is the ratio of pressure flow to the sum of drag flow and slip flow), slippage on either the screw wall or the cylinder wall can reduce the extrusion flow rate, and the number of flow recirculation planes is one. When −1/3≤ a ≤1, the number of flow recirculation planes increases to two, and screw wall slip is conducive to expanding the extrusion flow rate. Conversely, cylinder wall slip may reduce the extrusion flow rate. Moreover, the simulation results are consistent with those of the theoretical model, further verifying the rationality of the model.

Clinching has emerged as a key research area in lightweight automotive design. A single-lap clinched joint of 5182 aluminum alloy was selected as the subject of this study. A dynamic response test platform was developed to conduct fatigue-dynamic response tests on clinched joints. The rate of change in the natural frequency characterizes the stages of fatigue failure, and a life cycle prediction model for clinched joints was established. The results indicate significant changes in the 14th-order natural frequency under high and medium loads, whereas the ninth-order frequency changes significantly at low loads. The crack propagation rate was the highest at the medium load level, and the natural frequency change remained stable for the first 66% of its lifespan, with significant changes following crack initiation. The proposed prediction model quantitatively identifies the real-time service state of a clinched joint and predicts its fatigue life.

The current clinical application of ultrasonic osteotomes is mainly aimed at use by surgeons, with a lightweight design and small amplitude that limit the ability to fully utilize the advantages of surgical robots, such as load capacity, repetitive accuracy, and overall functionality. The cutting efficiency of traditional small-amplitude ultrasonic osteotomes is relatively low, making them mainly suitable for localized cutting of bone tissue with a thickness of less than 3 mm. To improve the clinical efficacy of ultrasonic osteotomes, this paper introduces a large-amplitude ultrasonic osteotome designed for surgical robots and establishes a corresponding dynamic model. Utilizing the boundary conditions of freedom at both ends and the continuity conditions of displacement and elastic force at each connection, we derive the longitudinal vibration frequency equation and an analysis formula for vibration modes. The dynamic model of the ultrasonic osteotome proposed in this paper serves as the foundation for optimization design and provides a mathematical modeling method that quantitatively describes the resonant frequency and vibration displacement characteristics of the ultrasonic osteotome without the need for complex and time-consuming numerical calculations, such as finite element analysis. A multi-objective optimization model for the ultrasonic osteotome was subsequently developed based on the dynamic model, and the optimal solution was derived using the three-stage method outlined in this paper. The feasibility of this dynamic modeling and optimization method for ultrasonic osteotomes in surgical robotic applications was verified by comparing the vibration characteristics and cutting performance of the ultrasonic osteotome before and after optimization through simulation analysis, performance testing, and cutting experiments. The results of this research provide novel design ideas and performance optimization methods for the application of ultrasonic osteotomes in the field of surgical robots, with the potential to establish a comprehensive design system for ultrasonic orthopedic surgical instruments.

In this study, 5182 aluminium alloy clinched joints and hybrid clinched joints containing Cu foam were prepared. The effect of the copper-foam sandwich on the static strength of aluminium alloy clinched joints was analysed through a static tensile-shear test. Modal analysis was conducted using the finite element simulation software, and the variation in the inherent frequency of the two joints under fatigue service was investigated through alternating fatigue-dynamic response tests. The law of asymptotic failure under fatigue service and the effect of a copper-foam sandwich on the fatigue performance of clinched joints were explored. It was concluded from the analysis that the tensile-shear strength of the clinched joints was increased by 9.14% due to the addition of the copper-foam sandwich. With fatigue accumulation in the joints, the inherent frequency curves were observed to gradually shift to the left. The tendency of inherent frequency reduction was mitigated by the copper-foam sandwich, and the ratio of inherent frequency decline was reduced. Furthermore, micromotion wear between the upper and lower sheets was effectively isolated by the copper-foam sandwich, abrasive debris between the sheets was reduced, and the process of microcrack formation and expansion was inhibited, resulting in an improved fatigue performance of the clinched joints. The variation law of inherent frequency with fatigue accumulation, as analysed in this study, provides a valuable reference for the prediction of fatigue life.

The safe berthing of ships requires a stable wharf structure. With the increasing significance of marine safety issues, the caisson wharf is faced with the potential threat of underwater explosions. This study aimed to investigate the displacement damage effect of caisson wharves subjected to underwater explosions in shallow water. The overall displacement damage mode of the caisson wharf was proposed. The movement process of the caisson wharf was analysed, and the displacement damage mechanism of the caisson wharf was revealed. Firstly, three underwater explosion tests were conducted to obtain damage data of caisson wharves under different TNT charges and explosion distances, including underwater explosion pressure, wave height, overall displacement of the wharf, and acceleration response. Then, the acoustic-solid coupling method was used to establish the finite element model of the underwater explosion of the caisson wharf, and the reliability of the finite element model and analysis approach was validated by comparing with the test results. Finally, the influences of explosion depth and TNT charge on the overall displacement of the caisson wharf were numerically examined. The results show that the overall displacement of the caisson wharf under underwater explosion loads is a reciprocating motion. This movement causes the caisson wharf to move out of initial position and lose stability, ultimately coming to rest in a direction close to the explosion. When the TNT charge is constant, the increase in explosion depth causes the overall displacement of the caisson wharf to increase. As the TNT charge increases, the movement process of the caisson wharf becomes more complex, and the exacerbation of surface damage on the rubble base also increases the risk of the caisson wharf overturning. The present work could provide beneficial references for enhancing the stability of caisson wharves.

To evaluate the residual strength of the ship after explosion, the Explosion Smith Method (ESM) is proposed. The innovation of the ESM lies in two aspects: firstly, based on the Baker shock wave and quasi-static pressure model, Jones critical velocity model, propose a method for assessing the range of explosion damage of cabin and validated through referenced experiments. Secondly, proposes the strain-stress relationship of the deformation element. To verify the feasibility of the ESM and study the influence of TNT location and mass,16 simulations and EMS calculations were conducted. The results showed that the residual strength is most impacted when the TNT in top deck. For side cabin, the explosion products discharged and impact reduced. The trend of the ESM and simulation were consistent, but the result of ESM was more severe. The reason that strain-stress relationship of the deformation element more stringent, resulting in the ESM smaller than the simulation. However, as the TNT increases the error decreases. In the future, more research can be conducted on the deformed structures to enhance the accuracy of the ESM.

Fast setting and hardening cement has the advantages of short setting time and high early strength. However, when using screw extrusion for 3D printing, there is often a serious blockage problem, which limits the application. In this study, we presented a novel approach to address this issue. Firstly, the blockage reasons in the printing process were obtained through simulations and experimental tests, then a superhydrophobic coating was applied to reduce the slip coefficient of the screw and the inner surface of the nozzle, the printing performance was improved finally. The results indicated that the pressure gradient in the cylinder decreased by 75.07% compared to the uncoated printhead. The shear rate and the flow velocity at the outlet were homogeneously distributed, and no plug flow was formed in the channel. Even after 60 min of continuous printing, the paste only adhered to the pushing flight flank, and no significant blockage occurred.

This paper proposes a model prediction method for tracking wear trajectories under lubricated conditions, based on the Archard wear model and the theory of elastohydrodynamic lubrication. Tracking wear in such a system was challenging due to the random nature of the tooth surface condition and the unstable force. The Archard wear model usually ignored the change in wear depth at the pitch point as it was inherently dedicated to the relationship between relative sliding distance and normal force. To overcome these problems, the proposed approach embedded the force analysis model of the micro convex body with time-varying reference into the constrained optimization process of the Archard model. The model was therefore called the Archard wear optimization model. By embedding the time-varying characteristics of the micro convex into the wear model, the wear depth at the pitch point was calculated and the model was optimized. In addition to inheriting the advantages of the Archard wear model, the proposed model ensures accurate tracking of key points, and is experimentally evaluated. Meanwhile, lubricating oil supply coefficient have been introduced to study tooth surface wear under different lubrication conditions.