Ventilation law of supercaviting vehicles plays an important part in cavity shape control. This paper presents the development of an experimental method in high speed water tunnel to study the supercavity stability which describes the relationship between cavity shape and ventilation rate. An empirical formula was established based on test results of cavity shape and ventilation flow rate under different cavitator sizes and angles of attack of the model. By making analysis and comparison of the experiment results with and without tail wings, the influence of tail wing on ventilation law was preliminarily obtained. The results show that ventilation rate needs to be kept in certain range in order to maintain a steady and smooth ventilated supercavity.

Aiming at the actual demand of improving the numerical simulation of unsteady submarine motion in maneuvering condition, the overset mesh was used to directly model six degree of freedom coupling motion of a submarine and the independent motion of each control surface, and the sliding mesh was used to directly simulate the propeller rotation at the stern of a submarine, so as to carry out the research on the numerical simulation of a generic submarine in self-propulsion and free running maneuvering conditions. Through the procedure of numerical simulation in typical working conditions, such as submerged self-propulsion, turning maneuver, zigzag maneuver, crashback, etc., the issues of submarine/propeller/rudder hydrodynamic coupling modeling and PD (proportional-derivative) numerical control realization of autopilot in maneuvering condition were emphatically solved, and the technology of free running submarine model numerical simulation based on overset mesh was established. At the same time, the surrounding flow phenomenon and the time-history change process of kinematics and dynamics parameters of the submarine in maneuvering condition were analyzed. By comparing the numerical simulation results of typical dynamics parameters with the model test results, the practicability of the approach for engineering prediction was verified. The research can provide a guidance for the prediction and evaluation of submarine maneuverability and seaworthiness. It is beneficial for the improvement of free running submarine model tests.

Path planning is one of the key technologies for autonomous navigation of unmanned vehicles. A good path planning method is of great significance to the intelligent development of unmanned vehicles. In the existing path planning research, the maneuvering performance of unmanned vehicles is not considered. In order to make the planned path have shorter voyage time, shorter path length and better path tracking ability, it is necessary to combine the maneuvering performance of unmanned vehicles with the path planning algorithm. In order to accurately predict the ship maneuverability, the channel-type unmanned catamaran was taken as the research object, and simulation tests of three planar motion mechanisms were carried out by CFD technology. Simulation results were fitted with different hydrodynamic models, and corresponding hydrodynamic derivatives were calculated. The MMG model was used to establish a mathematical model of ship maneuvering motion to simulate the turning motion and Z-shape motion of the unmanned catamaran. The influence of different hydrodynamic models on the simulation results was analyzed, and the maneuvering pre-diction of the unmanned catamaran was realized.

With a scale model of tuned liquid multi-column damper (TLMCD) and floating substructure established, experiments were carried out in a flume to study the control effect of TLMCD on the pitch motion response of the floating foundation under regular wave excitation. The numerical model was established and verified by OpenFOAM. The coupling mechanism of TLMCD and floating foundation was analyzed from the aspects of flow field, hydrodynamic loads, floating body motion and damping force. The results show that TLMCD has the best pitch suppression effect under resonant excitation, and that the liquid with a mass ratio of 2% reduces the maximum pitch response of the floating body under resonant excitation by 10.84% to 18.53%, and achieves at least 7.32% damping effect in the range of 0.9<T/T₀<1.1. By numerical method, it was observed that under the condition of resonance, the hydrodynamic force generated by tank sloshing took up 89.52% of the time to do positive work, and that the sloshing of liquid in the liquid columns periodically provided reverse damping moment for the floating body.

In order to evaluate the 3D effects of wave glider spring hydrofoil mechanism in waves on its dynamic performance, a numerical computational model of the wave glider spring hydrofoil mechanism was developed. Based on the overset mesh technology, the dynamic performance between 2D and 3D hydrofoils was analyzed and studied by using CFD FLUENT software. The results show that due to the limited span of the 3D hydrofoil, the tip vortex phenomenon is generated at the wing tip, resulting in reduced hydrofoil dynamic performance, and that the forward propulsion efficiency of the 3D hydrofoil is reduced by 22.1% compared with that of the 2D hydrofoil. Then, the bionic principle was used to design the wave glider bionic hydrofoil. It is found that the bionic hydrofoil reduces the loss of hydrofoil power performance by the tip vortex, while the forward thrust of the bionic hydrofoil is increased by 17.6% and the efficiency by 10.4% compared with the 3D hydrofoil of the same spreading chord ratio. Finally, the experimental comparison shows that the CFD simulation data and the experimental data have the same trend, and the reliability of the CFD simulation model is verified.

The two compulsory conditions for boundary layer separation are fluid viscosity and positive pressure gradient. By designing the shape of a vehicle so that its surface has a negative pressure gradient area as large as possible, the flow transition and separation are delayed so as to achieve the purpose of drag reduction. Based on the theoretical flow non-separation shape design method of slender bodies, the shape of a vehicle with a critical speed of 100 m/s was designed, and numerical simulation was used to analyze its flow characteristics at different speeds and angles of attack. It is found that the simulation results at zero angle of attack are consistent with those of the theoretical calculation, which proves that the surface of the vehicle can be in a state of non-separation of laminar flow through the shape design. A small attack angle will not destroy the fluid adhesion state on the surface of the vehicle, but whirlpools will appear in the flow when the attack angle is greater than 2 degrees.

In order to improve the efficiency of multi-parameter, high dimensional and high nonlinear optimization of ship structure reliability optimization design and make up the lack of uncertainty factors affecting structural safety in traditional deterministic optimization design, a river-sea-going ship was taken as the research object. BP (Back Propagation) neural network agent model technique and SMOTE (Synthetic Minority Oversampling Technique) algorithm were used to increase the number of sample points near the failure surface, in order to obtain a high-precision limit state agent model of ship structure with fewer sample points. Combined with Monte Carlo simulation method, the reliability calculation program of hull structure was developed. Structural reliability optimization analysis was performed adopting the simulated annealing optimization algorithm in order to reduce the structural weight. A set of complete and effective reliability optimization design system based on agent model technology was established to improve the efficiency of reliability optimization design, which has guiding significance to the reliability optimization design of river-sea-going ship structures.

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.