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.

Water-jet pumps are widely used in power fields such as ships, and the internal cavitation flow characteristics have an important impact on propulsion performance. In order to quantitatively evaluate the energy loss in cavitation flow field, the cavitation characteristics of an axial water-jet pump were studied based on entropy production theory. As the tip clearance vortex cavitation is typical in axial-flow propulsion pumps, the local vortical flow features were considered in the present numerical method. The SST-CC turbulence model with rotation correction and a modified cavitation model based on vortex identification were adopted. The numerical calculation method was verified according to the referenced experiment of a model pump. The results show that, under different cavitation conditions, with the deterioration of cavitation, the increase of entropy production value reflects the increase of energy loss of water-jet pump, which is corresponding to the decrease of efficiency curve, and the change law of total entropy production in pump is basically consistent with its power characteristics. Analysis of the energy loss in each geometrical region of the water-jet pump shows that the entropy production in the impeller section is the highest, especially the turbulent dissipation and wall dissipation, which are closely related to the vortex and cavitation flow field in the tip clearance of the impeller. On the different cavitation conditions, study on the flow characteristics at the tip of the impeller shows that the tip leakage vortex region causes cavitation, but significant energy dissipation occurs at the outer edge of leakage vortex and on the nearby wall area, while the cavitating vortex attached on the blade surface is the main source of turbulent dissipation.

Propeller open water tests, hull resistance tests and self-propulsion tests were carried out on two ship models propelled by submerged waterjet and conventional propeller respectively. Detailed analysis was done on the variations of propulsive performances of the submerged waterjet, propeller as well as corresponding hull-propulsor systems. Results show that: (1) the propulsive efficiency of submerged waterjet in open water is equivalent to that of the propeller in model scale, with the maximum efficiency around 0.72, while the high-efficiency operation range of submerged waterjet is wider than that of propeller in open water; (2) compared with propeller ship, the simpler stern-appendage arrangement of submerged waterjet ship can effectively reduce additional hull resistance caused by stern appendages; (3) at Fr = 0.20 and Fr = 0.26, the overall propulsive efficiency of submerged waterjet ship model in self-propulsion is 64.7% and 66.1%, which is 1.2% and 5.3% higher than that of propeller ship respectively. The corresponding absorbed power of the submerged waterjet is 9.41% and 15.4% lower than that of the propeller at two speeds respectively. Generally, the submerged waterjet propelled ship shows a better performance of propulsion and energy saving. This study provides a meaningful reference for the integrated design and optimization of submerged waterjet and its corresponding hull geometry.

For the coupled analysis of tank motion and liquid sloshing, a coupled iteration algorithm was established by involving the Hilber-Hughes-Taylor implicit method for tank motion and the VOF method for liquid sloshing. By application into the experiment designed for a liquid tank of rolling system, the algorithm was validated by comparison of the numerical calculation and experiment results. An effective method was finally presented for analysis of tank motion coupled with liquid sloshing.

In the course of ship structural strength experiment, it is difficult to obtain the full field deformation data of a structure by the traditional discrete point deformation measuring technique. Therefore, the progressive destruction process of a structure cannot be effectively revealed on the base of the method. In this paper, the deformation field measuring technique of a ship grillage structure was established based on the principle of digital image correlation and 3D laser scanning. The displacement shape function and correlation criterion of subset were proposed for deformation measurement of the ship grillage structure. Moreover, a digital speckle making tool was developed in order to obtain a quantitative and controllable digital speckle field. Based on a portable 3D laser scanning system, a method for measuring the geometry of ship grillage structure was presented. An experiment was carried out to verify the deformation field measuring technique of ship grillage structure. The structural deformation field of the model under longitudinal compression load was obtained by the experiment, and the failure evolution behavior was found before and after the critical state of the model structure. Through the above experiment, the space-time evolution law of deformation field for the ship grillage structure was revealed. A basic measuring technique for failure mode recognition of real ship structures was provided in this paper.

For semi-submersible platforms equipped with dynamic positioning (DP) system, which has a small water-plane area and low metacentric height, vertical motion (roll, pitch, heave) will be affected by the normal control force of the thrusters. In light of this, this paper proposes a novel thrust allocation method based on thruster biasing, which aims to suppress the vertical motion and ensure the positioning accuracy of the horizontal motion. Model scale tests are conducted for the dynamic positioning of a semi-submersible platform in the ocean wave basin, to analyze and compare the six-degree-of-freedom motion responses under different environmental loads and thruster biasing configurations. The results show that the thruster biasing strategy can ensure the ability of station-keeping and significantly reduce the response amplitude near the natural frequency of the vertical motion of the platform, the reduction of the power spectrum peak is up to 54.7% under the given test cases, while the vertical motion in the wave-frequency is unaffected. The research results give a novel idea for the control of semi-submersible platform vertical motion.

If the fluid-structure interaction problem in frequency domain is solved by boundary element method, irregular frequencies will appear at the resonant frequencies of virtual interior fluid domain and exhibit large fluctuation. In order to investigate the underwater acoustic radiation properties of a full-scale submarine, a shaft-hull coupled system was established based on Suboff model. The FE/BE method was adopted to calculate the vibroacoustic radiation of the system in low- and medium-frequency. The closed virtual impedance surface (CVIS) method was respectively used and not used to study the influence of irregular frequencies. It is shown that: (1) for slender submarine hull with complicated shape, irregular frequencies are not only negligible, but even exhibit in continuous irregular bands; (2) enormous errors will occur if irregular frequencies are not eliminated, and convergence zones in far field of deep ocean environment are also“contaminated”; (3) for submarine whose the main body is constructed as slender cylindrical shell, the 1^st irregular frequency can be obtained according to the analytical expression of the irregular frequencies of slender cylindrical shell, and the non-dimensional 1^st irregular frequency is about ka=2.4.

Sail-assisted navigation is one of the effective ways to reduce carbon dioxide emissions in ship industry. In this study, a sail array consisting of six hard sails with a cross section of NACA0018 airfoil was designed. The lift and resistance of each sail were analyzed by numerical simulation under three conditions: upwind, crosswind and downwind. By comparing with the single sail case, the law of inter-sail interference on sail propulsion performance was explored. The confidence level of several independent geometric parameters on the propulsion performance of the sail array was evaluated by combining the experimental design method with ANOVA. The results show that the significance level of the independent parameters is highly dependent on the apparent wind direction. By changing sail layout and using non-uniform angle of attack, the propulsion performance can be better than that of single attack angle. This study is helpful to find the main parameters affecting the thrust performance of a multi-sail propulsion system and support for its global manipulation.

Under the welding process specifications that meet the structural strength requirements, welding energy input and welding sequence result in different welding residual stress and deformation, which significantly impact the typical bidirectional stiffened plate structure’s vibration and acoustic radiation. In order to explore the influence of welding process parameters on the vibro-acoustic characteristics of typical bidirectional stiffened plate structures, the accuracy of the welded structure test method was verified by combining numerical simulation and experiment, several tests of stiffened plate structures were carried out regarding the modal, underwater vibration, and acoustic radiation under different welding energy inputs. The results show that under the same welding sequence, different welding energy inputs have a large effect on the natural frequency of thin plates and a relatively small effect on the natural frequency of thick plates. For stiffened thick plate structures, under the same welding sequence, with the increase in welding energy input, the impact on the natural frequency shows a trend of first decreasing and then increasing, and the overall vibration acceleration level and radiated sound pressure level in the same frequency band decrease first and then increase. Under the symmetrical welding sequence, the optimal welding parameters cover a welding current of 200 A, a welding voltage of 25 V, a welding speed of 3.02-3.06 mm/s, and a welding energy input of 167 J/cm. This study can provide guidance for the design of low-noise processes for acoustic stealth of ships and marine structures.

The accurate measurement of wave evolution is fundamental for the hydrodynamic studies of marine structures. An image-based method was proposed to measure waves in the laboratory based on binocular stereo vision. The light foam particles were used as trackers to mark wave surface for obtaining the wave images with sufficient textures. The images were rectified based on epipolar constraint, and threshold segmentation was used to avoid the interference of uneven light and bottom reflection. A stereo matching algorithm with GPU acceleration was used to achieve the real-time matching of wave images, obtaining the point cloud and mesh of the wave surface. Through the reconstruction of the image sequences, the wave time series, wave heights and periods were extracted. They were then compared with the measurements by wave probes, showing great agreements. The results indicate that the proposed method can accurately measure the 3D wave field in the laboratory, capturing the instantaneous evolution of wave and providing real-time monitoring.