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.

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.

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.

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 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.

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.

Mobile floating offshore wind turbines (MFOWTs) can store the generated wind energy onboard, and navigate to preset working areas due to their mobility. Compared to fixed and moored floating offshore wind turbines, MFOWT can not only harness the abundant far-offshore wind resource but also supply power to offshore energy consumers, because of its superior working ability in deep sea. In this paper, key technical problems in the development of MFOWT are summarized and discussed in several aspects based on a literature review and our research: (1) floating substructure selection; (2) conceptual design and approval; (3) dynamic response analysis for the integrated system; (4) operational strategy decision; (5) safety assessment; (6) model test in ocean wave basin; (7) construction and installation.

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.

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.