Ship motions induced by waves have a significant impact on the efficiency and safety of offshore operations. Real-time prediction of ship motions in the next few seconds plays a crucial role in performing sensitive activities. However, the obvious memory effect of ship motion time series brings certain difficulty to rapid and accurate prediction. Therefore, a real-time framework based on the Long-Short Term Memory (LSTM) neural network model is proposed to predict ship motions in regular and irregular head waves. A 15000 TEU container ship model is employed to illustrate the proposed framework. The numerical implementation and the real-time ship motion prediction in irregular head waves corresponding to the different time scales are carried out based on the container ship model. The related experimental data were employed to verify the numerical simulation results. The results show that the proposed method is more robust than the classical extreme short-term prediction method based on potential flow theory in the prediction of nonlinear ship motions.

In order to understand the influence of bow shape on ice resistance and provide guidelines for hull line design in the early design stage, an investigation of the impact of bow shape on ice resistance for the Arctic LNG carriers is carried out based on semi-empirical methods. Firstly, some typical semi-empirical formulas developed for ice resistance estimation of cargo carriers in different ice conditions are summarized. Then, formulas appropriate for ice resistance estimation of Arctic LNG carriers under different ice conditions are verified according to the result comparison between semi-empirical formulas and experimental tests. The comparison result indicates that the Lindqvist formula is appropriate for ice resistance estimation in level ice conditions, Zuev and Dobrodeev formula for ice resistance estimation in broken ice conditions, and Dobrodeev formula for ice resistance estimation in brash ice conditions. After that, the parameters considered in the selected formulas are summarized, and the influence of critical parameters on ice resistance is analyzed. Some parameters describing the ship's bow shape characteristic like ship breadth, waterline angle and stem angle greatly influence the ice resistance. Ice resistance increases with both the growth of ship breadth under all ice conditions and the growth of stem angle in level ice and broken ice conditions while ice resistance decreases with the development of waterline angle under all ice conditions. Finally, the optimization of the bow shape is discussed, and an optimized bow shape with both a large waterline angle and low stem angle is proposed. The optimized bow shape can decrease ice resistance by 9.9% in the level ice condition and reduce ice resistance by 11.3% in the brash ice condition.

Sloshing experiment is crucial to determine the reaction performance of regeneration columns on an offshore floating platform. A novel type of column motion simulating device and a Marine Predator Algorithm-based Sliding Mode Controller (MPA-SMC) are proposed for such sloshing experiments. The simulator consists of a Stewart platform and a steel framework. The Stewart platform is located at the column's center of gravity (CoG) and supported by the steel framework. The platform's hydraulic servo system is controlled by a sliding mode controller with parameters optimized by MPA to improve robustness and precision. A numerical sloshing experiment is conducted using the proposed device and controller. The results show that the novel motion simulator has lower torque during the column sloshes, and the proposed controller performs better than a well-tuned PID controller in terms of target tracking precision and anti-interference capability.

In polar regions, floating ice exhibits distinct characteristics across a range of spatial scales. It is well recognized that the irregular geometry of these ice formations markedly influences their dynamic behavior. This study introduces a polyhedral Discrete Element Method (DEM) tailored for polar ice, incorporating the Gilbert-Johnson-Keerthi (GJK) and Expanding Polytope Algorithm (EPA) for contact detection. This approach facilitates the simulation of the drift and collision processes of floating ice, effectively capturing its freezing and fragmentation. Subsequently, the stability and reliability of this model are validated by uniaxial compression on level ice fields, focusing specifically on the influence of compression strength on deformation resistance. Additionally, clusters of ice floes navigating through narrow channels are simulated. These studies have qualitatively assessed the effects of Floe Size Distribution (FSD), initial concentration, and circularity on their flow dynamics. The higher power-law exponent values in the FSD, increased circularity, and decreased concentration are each associated with accelerated flow in ice floe fields. The simulation results distinctly demonstrate the considerable impact of sea ice geometry on the movement of clusters, offering valuable insights into the complexities of polar ice dynamics.

A tunneled planing hull has unique hybrid hydrodynamic and aerodynamic characteristics due to the presence of a tunnel. In this paper, experimental and numerical investigations on hydrodynamic analysis of a tunneled planing hull are carried out. The resistance tests of models with three different masses (127.4 kg, 159.5 kg, 202.9 kg) are conducted for the Froude number in the range of 0.761≤Fn≤1.925. The results of resistance measured by towing tank imply that the tunneled planing hull with a larger displacement has a superior resistance performance. The numerical simulation of Reynolds Average Navier Stokes (RANS) equations based on the finite volume method is performed to analyze the hull characteristics in calm water (M=159.5 kg) with two degrees of freedom (sinkage and trim). The numerical results are compared with the experimental data, which shows good agreement. Pressure distribution, wave profiles and lift forces obtained by SST k-ω and Realizable k-ε turbulence models are compared and discussed. Finally, the local fluid flow of streamline around the hull can be divided into four regions due to the presence of a tunnel, which is different from the behaviors of the conventional planing monohull with prismatic form.

For the ultimate strength model test evaluation of large ship structures, the distortion model with non-uniform ratio between the main size and the plate thickness size is usually adopted. It is the key to carry out scale model test to establish a distortion model similar to the real ship structure under combined load. A similarity criterion for ship distortion model under the combined action of bending moment and surface pressure was proposed, and the scale effect for the criterion was verified by a series of numerical analysis and model tests. The results show that the similarity criterion for ship distortion model under combined loads has a certain scale effect. For the model tests of ship cabin structures, it is suggested that the scale range between the plate thickness scale and the main dimension scale should be controlled within 2:1, which can be used as a reference for distortion model design and ultimate strength test of large-scale ship structures.

Marine structures are frequently subjected to repeated impact loadings, resulting in failure of the structures, even causing serious accidents. The analytical expressions of dimensionless permanent deflection and impact force of a metal beam based on maximal normal yield surface are derived by membrane factor method (MFM), then the results are compared with repeated impact tests. It can be found that the solutions based on MFM are between the upper and lower bounds, and very close to the results of the repeated impact tests, indicating the theoretical model proposed can predict the plastic responses of the metal beam accurately. What’s more, the influences of impact location and boundary condition on the dynamic responses of the beam subjected to repeated impacts are determined. Results show that, as the distance of impact location from the middle span of the beam increases, the permanent deflection decreases, while the impact force increases. Meanwhile, the influences of impact location enhance as the impact number increases. When the permanent deflection is smaller than the thickness, the effect of boundary condition on the plastic responses is significant. However, when the deflection is larger than the thickness, the beam will be like a string and only axial force works, resulting in little influence of boundary condition on the plastic responses of the beam.

Ships navigating in ice-covered regions will inevitably collide with ice ridges. Compared to other ice bodies, ice ridges exhibit more complicated mechanical behaviors due to the scale and structure characteristics. In this paper, nonlinear finite element method is used to investigate the interaction between a polar ship and an ice ridge. The ice ridge is modelled as elastic-plastic material based on Drucker-Prager yield function, with the consideration of the influence of cohesion, friction angle and material hardening. The material model is developed in LS-DYNA and solved using semi-implicit mapping algorithm.The stress distribution of ice ridge and ship, and the ice load history are evaluated through the simulation of multiple collisions. In addition, parametric analysis is performed to investigate the influence of ridge thickness and impact velocity on the ice load and energy absorption.

In this study, the influence of opening parameters on the ultimate strength of perforated plates subjected to extreme cyclic loading in the presence of material kinematic hardening and isotropic hardening was analyzed. It is found that the ultimate strength of the perforated plates decreases rapidly and stabilizes in the first four cycles. Plates with oblong openings have a greater ultimate strength compared to plates with rectangular openings, while the relative strengthening ratio decreases over the duration of the cycle. The location of the openings is also an important parameter that affects the strength of the structure, as the plates with openings close to the edges in the longitudinal direction have higher strengths, while in the transverse direction the strengths are higher when the openings are close to the center. Among the three opening-strengthening methods compared, the Carling stiffener method maintains a better strengthening effect under cyclic loads for many periods.

A hull structure is prone to local deformation and damage due to the pressure load on the surface. How to simulate surface pressure is an important issue in ship structure test. The loading mode of hydraulic actuator combined with high-pressure flexible bladder was proposed, and the numerical model of the loading device based on flexible bladder was established. The design and analysis method of high-pressure flexible bladder based on aramid-fiber reinforced thermoplastic polyurethane was proposed to break through the surface pressure loading technology of ship structures. The surface pressure loading system based on flexible bladder was developed. The ultimate strength verification test of the box girder under the combined action of bending moment and pressure was carried out to systematically verify the feasibility and applicability of the loading system. The results show that the surface pressure loading technology can be used well for applying uniform pressure to ship structures. Compared with the traditional surface loading methods, the improved device can be applied with horizontal constant pressure load, with rapid response and safe process, and the pressure load is always stable with the increase of the bending moment load during the test. The requirement for uniform loading in the comprehensive strength test of large structural models is satisfied and the accuracy of the test results is improved by this system.

To further investigate the forming mechanism and springback characteristics of strips under multi-square punch forming (MSPF) considering partial-unloading effects, a series of concave forming tests of strips are conducted on the MSPF machine. This paper aims to reveal the physical mechanism of the elastic-plastic deformation in the MSPF process considering the effect of the forming approaches, and derive appropriate mathematical interpretations. The theoretical model is firstly established to analyse the concave forming mechanism and springback characteristics of the strip, and its accuracy is then validated by experimental data. The forming history and load evolutions are depicted to explore the required forming capacity through the proposed analytical method. Besides, the parametric studies are carried out to discuss their effects on the springback of the strip. The results suggest that the deformation paths of the strip are influenced by the forming approach, and the springback of the strip in convex forming is larger than that in concave forming.

High-static-low-dynamic stiffness (HSLDS) vibration isolators have been demonstrated to be an effective means of attenuating low-frequency vibrations, and may be utilized for ship shafting applications to mitigate torsional vibration. This paper presents the construction of a highly compact HSLDS torsional vibration isolator by connecting positive and negative stiffness components in parallel. Based on mechanical model analysis, the restoring torque of negative stiffness components is derived from their springs and connecting rods, while that of positive stiffness components is obtained through their circular section flexible rods. The quasi-zero stiffness characteristics of the HSLDS isolator are achieved through a combination of static structural simulation and experimental test. The torsional vibration isolation performance is assessed by means of numerical simulation and theory analysis. Finally, the frequency-sweep vibration test is conducted. The test results indicate that the HSLDS torsional vibration isolator exhibits superior low-frequency isolation performance compared to its linear counterpart, rendering it a promising solution for mitigating low-frequency torsional vibration in ship shafting.