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.

Abrupt annular shear flows induced by internal solitary waves will cause submersibles to produce a large depth drop and pitch motion, threatening the safety and operation performance of submersibles. Based on the velocity inlet wave generation method and overset grid technique of CFD, the motion response prediction method of submersibles in internal solitary wave was established. With the prediction results compared with the experimental results, it is proved that the method can accurately simulate the large amplitude motion of submersibles in internal solitary waves. Through the simulation analysis of motion process of unpowered floating submersibles at the stratified interface under the action of internal solitary waves, the mechanism of depth drop and pitch motion of submersibles in internal solitary waves was revealed, and the effects of stratified thickness ratio, wave amplitude and depth of navigation on the longitudinal motion of unpowered floating submersibles were investigated. The results show that the amplitude of depth drop and pitch of the submersibles in internal solitary waves were determined by the wave amplitude and the maximum slope of wave surface; The factors such as amplitude, stratified thickness ratio and depth of navigation have great influence on the longitudinal motion property of submersibles.

The floating cylindrical structures, such as the floating frame of the fish farming and the floating bodies of wave energy convertor and so on, are generally semi-submerged. However, the investigation on the hydrodynamics on such floating cylinders are few. This status makes the design and analysis of the relevant new structures face the essential problems of the force input uncertainty. The hydrodynamic forces on a semi-submerged cylinder were experimentally investigated under the combined influence of steady and oscillatory flow. To simulate the equivalent combined flow, the cylinder towed by the carriage was forced to oscillate with different amplitudes and periods. A significant mean downward lift force was observed for the semi-submerged cylinders, which was obviously larger than that of the mean drag force. Moreover, the relationship between the hydrodynamic coefficients and multi-sensitive parameters was revealed. It is confirmed that the KC number has a weak influence on the coefficients. The Froude number is seen to be the most important parameter affecting the hydrodynamic coefficients. The empirical models for predicting hydrodynamic coefficients in combined flow are initially developed. This work can provide useful references for the design of the related marine structures and serve as the valuable guideline for future research.

Ships are susceptible to wind and waves causing the declines of installation accuracy and maintenance safety of offshore wind turbines. The most seriously affected case is the non-stationary ship roll motion under long-peaked random wave spectrum. To ensure the stability of offshore operations under complex sea conditions, it is necessary to improve the generalization of the prediction model. In this paper, a preferential feature federation method was proposed. Firstly, the non-stationary ship roll motion was decomposed into multi-component stationary sequences by using the variable modal decomposition method. Then, the long and short-term memory neural network with attention mechanism was used to build a local multi-dimensional multi-step prediction model with error correction. Finally, in order to improve the prediction effect of new type ship motions in complex sea conditions, a federation method was used to combine some ship motion data holders for best model parameters, which were selected with the maximum mean discrepancy method with high similarity for preferential feature federated training. The experimental results show that the federated model has higher prediction accuracy and better generalization ability, which can help the stability control of wave compensation during offshore wind turbines installation.

With the continuous development of large-scale offshore floating structures, the rain load of large-scale offshore floating structures in extreme environment has become one of the focus issues of designers. Based on the discrete particle model, the motion prediction of wind driven rain field was made and the distribution law of spatial characteristic parameters of rain field was quantified. The calculation formula of structural rain load was deduced, and the rain load prediction of offshore platform under different wind speed and rainfall intensity combination conditions was completed. The research results show that the rain load of offshore platforms under the action of DNV wind profile and Davenport wind spectrum follows Gamma distribution. Compared to the average wind load, when the rainfall intensity R is 800 mm/h, the significant value of rain load accounts for 5.07%, and the maximum value accounts for 8.87%; when the rainfall intensity R is 20 mm/h, the significant value of rain load accounts for 0.36%, and the maximum value accounts for 0.6%. The research results of this paper can provide guidance for the design of offshore structures and their mooring systems.

For floating structures deployed in waters near the coast or island lagoons, the shallow water depth makes the impact of seabed topography changes on the mooring system non-negligible, and the seabed can no longer be simplified as flat when exploring the characteristics of the mooring system. To study the static characteristics of the anchor chain under the condition of uneven seabed terrain, an anchor chain model was established based on the lumped mass method, and effects of the seabed inclination angle and the arrangement of the anchor chain on the tension and the tension angle at the top of the anchor chain, and the length of the catenary were discussed through numerical simulation, in an attempt to guide the design and safety performance evaluation of floating mooring system in shallow waters.

To solve the path tracking problem of ROV deep-sea mining equipment, where a Mining Robot (MRT) is towed by a Remote Operated Vehicle (ROV), the motion model of a simplified ROV deep-sea mining equipment was established first. Then, a path tracking algorithm based on Linear Model Predictive Control (LMPC) and Nonlinear Model Predictive Control (NMPC) was proposed. Different from the traditional Model Predictive Control (MPC), the proposed Double Model Predictive Control (DMPC) algorithm consists of two parts: (1) the LMPC controller of MRT for calculation of the speed control law of MRT, which is used to quickly converge the tracking error of MRT; (2) the NMPC controller of the ROV for calculation of the control input of the ROV, which is used to follow the speed control law of the MRT. In the design of DMPC, constraints of state quantity and control quantity were considered effectively. In order to ensure the smoothness of ROV control input, the incremental control quantity constraint of ROV was introduced. Finally, simulation experiments were designed to verify the path tracking performance of MRT. Numerical simulation results demonstrate the effectiveness of the proposed algorithm.

In this paper, the open-source computational fluid dynamics software OpenFOAM was used to simulate the effect of plunging breaker waves and non-breaking waves on the typical column of an offshore platform in the extreme ocean environment. The purpose was to compare and analyze the variation of wave loads and structural stress in the column under the above two wave types. The motion of the fluids was simulated based on the Reynolds-averaged Navier-Stokes equations combined with k-ω SST turbulence model. The numerical results show that the breaking wave load on the column is much higher than the non-breaking wave load under the same design wave parameter input. The maximum stress values for each structure of the column under non-breaking wave loads are less than the yield limit of material. However, under the plunging breaker load, the maximum stress of some structures exceeds the yield limit of materials and cannot meet the requirements of structural safety. Therefore, the impact of breaking wave load on structural strength should be considered in the safety design of marine structures to ensure that the structure has sufficient safety margins.

Aiming at the difficulty in modelling the diving process of spherical shells, a data-driven algorithm for diving process modelling and anomaly detection of deep-sea pressurized spherical shells was proposed in this paper. Firstly, the spherical shell structures and historical diving data of manned capsules were analyzed. Then, the diving process modelling algorithm was established based on the long short-term memory network (LSTM), taking the diving depth as the input and the key hot spot strain as the output. The deduction results were analyzed and compared with the DNN model and BP model, the derivation error was reduced by 35.89% and 63.80%, respectively. Finally, based on the LSTM model, a data anomaly detection algorithm was proposed. The proposed algorithm can diagnose and correct abnormal data when a sensor fails.

Aluminum alloys have been widely used in the ship industry for their low density, high specific strength and specific stiffness. However, compared with steel, the strength of aluminum alloy is low. To improve its strength, JDA1b aluminum alloy, which is often used in die casting and outfitting parts of ships, was taken as the research object. Pre-strain tensile, pre-bend tests and dynamic tensile tests were carried out to investigate the effects of pre-strain and pre-bend on the mechanical performance of JDA1b alloy, and the effects of strain rate on the flow behaviors of the alloy were also investigated. The results show that increasing the strain rate can increase the flow stress and tensile strength of the material; the yield stress and tensile strength of this material increase with the increase of pre-strain, and the elongation decreases, and that the increase of pre-bend is favorable to improve the bending yield load, bending stiffness and damage displacement of the material. A new dynamic constitutive model considering ultimate stress and critical strain was proposed, which allows the flow stress to be predicted more precisely at various strain rates over a wide range of 1~800/s, and the fitting goodness-of-fit value reached 0.999. This study provides methods to improve the strength of aluminum alloys, and the proposed constitutive model is conducive to the improvement of the accuracy of the simulation of mechanical performance of parts.