In order to clarify the influencing factors of the amplitude of local ice pressure and pressure-area curve of the upright wide structures, the calculation method of the local ice pressure in ISO 19906 was firstly analyzed in this paper, and its limitation was found. Secondly, the discrete element method was used to simulate the interaction between different sea ice conditions and multi-scale structures. It is found that the amplitude of local ice pressure increases with the increase of ice thickness and decreases with the increase of structure width. The amplitude and standard deviation of local ice pressure decrease with the increase of width-thickness ratio, showing obvious scale effect. Finally, the influence of ice thickness and width on pressure-area curve parameters was studied by square-averaging method, and one similar working condition was selected to compare with that of ISO specifications. The rationality of the discrete element simulation method in dealing with the local ice pressure-area curve was verified, which provides a certain basis and reference for the ice resistance performance analysis and structural design of the platform.

The existing fatigue S-N curves are no longer applicable to the low-temperature environment in the Arctic regions. In order to evaluate the low-temperature fatigue life of Arctic offshore engineering equipment, it is necessary to establish the low-temperature fatigue S-N curves of metal structures, especially welded structures. In this paper, based on the equivalent structural stress method, the master S-N curve of the girth weld of Q690 high strength steel pipes was calculated, and the method was verified by resonance fatigue test. On this basis, combined with a large number of test results of high-strength steel welded structures, the temperature sensitive factor c was introduced into the derivation of the low-temperature fatigue master S-N curve. The master S-N curve based on low-temperature metal welded structures was established for the first time, and the fatigue S-N test data in the literature and the correction method in ASME were compared and verified. The results show that the equivalent structural stress method can accurately calculate the weld fatigue S-N curve, and the derived low-temperature main S-N curve of metal welded structures is in good agreement with the test curve, which can meet the engineering requirements in low-temperature areas, and provide theoretical guidance for the wide application of high-strength steel welded structures in low-temperature environments in the Arctic regions. This method can save a lot of costs for the low temperature fatigue research of metal welded structures and reduce unnecessary errors caused by non-standard test operations. This research is of great significance to the design, safe operation and fatigue assessment of Arctic offshore engineering equipment.

A dynamic numerical analysis model for hang-off evacuation down-hole riser was established with coupling the longitudinal and transverse deformation. The hard hang-off and soft hang-off boundary conditions were given considering the horizontal evacuation and vertical heave movement of the platform. The down-hole riser model was discretized by the finite element method and solved by the Newmark-β method. An experiment for the hang-off riser was conducted to verify the accuracy of the numerical model. For a deep-water well in the South China Sea, the dynamic characteristics of hard hang-off and soft hang-off risers coupling the longitudinal and transverse deformation were analyzed. The research results show that the lateral deformation of the hang-off evacuation riser presents a wave shape, and the vertical deformation vibrates periodically with the platform heaving. The maximum lateral and longitudinal displacements of the down-hole risers appear at the bottom of the riser under both hard and soft hang-off conditions. The displacement of the down-hole riser under the hard hang-off condition is small near the top, where the bending moment reaches a maximum value. The displacement of the down-hole riser near the top increases sharply under the soft hang-off condition, but the maximum bending moment appears near the water surface. The range of longitudinal displacement envelope of the hang-off evacuation riser increases gradually from top to bottom, while the range of axial tension envelope increases gradually from bottom to top. Besides, the minimum tension of the down-hole riser under hard hang-off conditions is negative near the top, where obvious axial compression with the risk of buckling failure appears.

In order to solve the problem in accurate identification of dynamic load of marine propulsion shafting bearings, this paper proposes a kind of frequency-domain inverse identification method based on inversion of frequency response functions by using full measured data as well as the corresponding data processing and evaluation methods. Then, on the propulsion shafting vibration test platform, radial bearing dynamic load identification tests under three types of external excitation were carried out to verify the proposed method. The test results show that the identification results of bearing dynamic load under unbalanced, random vibration and impulse excitation are consistent with the trends of amplitude-frequency and phase-frequency curves of measured results in the frequency band of 10 Hz-1 kHz, with a high degree of coincidence, and that in the frequency band of 10 Hz-1 kHz, the identification errors of bearing dynamic load are 0.21-3.5 dB under unbalanced excitation, 2.03-2.53 dB under random vibration excitation and 2.16-4.64 dB under pulse excitation, which proves that the inverse identification method is feasible and accurate.

The potential-viscous flow coupling method, which combines the potential flow method with the CFD method, has gradually attracted attention in solving issues of wave evolution and wave structure interaction in marine engineering field. The potential-viscous coupling method can effectively reduce the computational cost of numerical simulation while ensuring the calculation accuracy, making it possible to achieve fine simulation of fluid-structure coupling on a real scale. In this paper, the state of art of the potential-viscous flow coupling method for marine engineering hydrodynamic applications are reviewed. Two types of coupling methods, domain decomposition and functional decomposition, are discussed to analyze advantages and challenges of the coupling method.

Movement of a revolution body at high speed with an angle of attack induces a large-scale asymmetric cloud cavitation flow attached to the surface of the revolution body. The large pressure induced by the interface instability at the end of the cloud cavitation has an important impact on the performance of the revolution body, which is an important basic theory problem in the development of revolution bodies. This paper combs the relevant research on asymmetric cloud cavitation flow of revolution bodies, introduces the experiment and numerical simulation method research on asymmetric cloud cavitation flow mechanism of flow control, and flow field structure and interface stability of the asymmetric cloud cavitation, analyzes the future development trend, and offers some suggestions of the main research directions in future.

High-resolution flow field data are of great significance to the study of fluid mechanics. Limited by measurement methods and calculation efficiency, it is still difficult to obtain high-resolution flow fields directly in some circumstances. A low-dimensional representation model for flow time history data was poposed, and a deep learning method for reconstruction of unsteady flow time history data was developed. The proposed method extracted the time-history features contained in the samples using one-dimensional convolution directly; then, the mapping from the physical space and the encoding space was built; and finally, the decoder in the representation model was utilized to generate flow time history data at unknown positions. Unsteady laminar flow with Re_D=200 was studied, and the accuracy of the method was verified. The method proposed in this paper, a new flow field data reconstruction method in an unsupervised training manner in the time dimension, can be widely used in point-based sensor data analysis.

Ship roll damping estimation based on roll decay curves is very common in engineering. There are many methods to estimate damping from roll decay curves, which lead to difference in damping estimation results. In order to achieve the purpose of obtaining high-precision damping prediction methods, the principle of estimation of roll damping based on roll decay curves in recent years was analyzed in detail first in this paper and then its scope of application was expanded. The methods were divided into two categories according to the principle, namely, one based on piecewise linear assumption and the other based on parameter identification. The data of standard model (DTC) were used to verify and compare the characteristics of different methods, and the error sources of damping coefficient estimation were analyzed. The results show the accuracy of estimation is strongly related to the used method. The Froude energy method with clear physical meaning, few error sources, and insensitivity to measurement noise and error is recommended as the preliminary estimation method. If a damping model with sufficient accuracy can be found, estimation based on the Prony-SS method, which has an inherent noise suppression mechanism and a unique solution, can be further done to improve the accuracy.

As the application of composite materials can improve the cavitation performance and vibration characteristics of propellers, it has been widely concerned in the field of advanced marine propulsion equipment. In this paper, the flow field of a composite material propeller was calculated based on URANS, the dynamic response of the blade structure was solved by FEM, and the hydrodynamic load and structural deformation were transmitted in real time bi-directionally. The simulation of the evolution of tip cavitation in the high wake region shows that the maximum tip deformation increases with the initiation and development of tip cavitation, reaches the maximum at the stage of tip vortex cavitation formation, and then decreases with the collapse of bubbles. The mechanism of the improvement of propeller propulsive efficiency and the suppression of tip cavitation due to the application of composite materials was revealed, indicating that the composite material propeller produces bending torsion coupling deformation under cavitation hydrodynamic load, and adaptively adjusts the angle of attack to suppress cavitation development. Comparison of the cavitation performance between the composite material propeller and the rigid propeller under typical cavitation condition reveals that the composite material propeller has a mild peak pressure fluctuation and a better adaptability to the non-uniform wake.

Based on the immersed boundary-multiple relaxation-lattice Boltzmann method, a numerical simulation of the flow around three cylinders in equilateral triangle arrangement was conducted at Re=100, the influence of two key parameters, the spacing ratio (K_d) and incoming flow angle (α), on fluid force coefficient and flow field characteristics was analyzed, and several flow mechanisms were revealed. The calculation results show that the wake pattern in different flow fields is divided into single vortex, single vortex to double vortex, irregular double vortex, regular double vortex, double vortex to triple vortex, irregular triple vortex and regular triple vortex pattern, and that the downstream vortex street is more regular and the wake pattern changes faster at α=30°. The time-averaged fluid force coefficient of three cylinders is greatly affected by the gap flow velocity, and the changing trend with the spacing ratio (except for the small spacing ratio) at each incoming flow angle is nearly identical. The transition of the wake pattern will change the root mean square value of three cylinders’ fluid force coefficient significantly. When K_d≥3.5, the root mean square value of upstream cylinder’s fluid force coefficient fluctuates greatly. Except for α=0°, the vortex shedding frequency of the midstream cylinder is less affected by α and K_d when K_d≥2.5, which is relatively stable.