The directional dimensional analysis method is commonly used in the design of similar scale-down models of hull structures. However, the traditional dimensional analysis method based on elastic theory cannot reflect the nonlinear response process of a structure, which limits its application in the scale down model test of hull structures. In this paper, based on the finite similarity method, the scale-down factors of the geometric dimension, material density and time of a structure were obtained by matching the transport equations in the physical space and the trial space. The nonlinear similarity relationship between the scaled down model of the stiffened plate structure and the prototype was derived, and the influence of the material parameters on the nonlinear similarity process was analyzed. By calculating the ultimate strength of the stiffened plates subjected to plain compression, the effectiveness of the scaling criterion based on the finite similarity method was verified. The result shows that the present method can well reflect the nonlinear characteristics of materials, and achieve a good prediction on the ultimate strength of the original model through the results of the scale down model.

The complexity of the stern appendage of a four-screw ship and the differences in the spatial layout of the internal and external propellers will lead to the unbalanced load distribution of the internal and external propellers. Based on the CFD method, numerical prediction simulation for the viscous wake field of a ship with four propellers was carried out. According to wake field distribution and turbulence characteristics, the difference in wake fields between the inner and outer propellers was compared and analyzed, and also the results was contrasted with the test values. The study results show that the inner propeller in the turbulence zone is affected by the hull boundary layer, which makes the axial velocity at the inner propeller disk less than that at the outer propeller disk, resulting in uneven load distribution between the inner and outer propellers. The flow at the outer propeller is a mixed one of the hull boundary layer and the turbulent wake, which makes the wake at the outer propeller disk more uneven. The research can provide basis and support for four-screw ship design and stern layout optimization.

Hazardous noise of flight deck due to jet blast deflector impingement causes a serious damage to the health of crew members. An experiment of jet impinging on a blast deflector was carried out in a full anechoic chamber to study the acoustic characteristics. With a diameter (D) of 56.4 mm, a convergent nozzle was used to investigate a Mach number of 1.01 jet impingement. Flow visualization and far-field microphones were employed to observe the flow field and measure the far-field noise, respectively. The test was performed on a 600 mm×600 mm deflector and with three inclined angles (β) of 45°, 55°and 65°. The results show that the impact angle has a significant influence on the wall jet structure and overall sound pressure level (OASPL). With the increase of impact angle, the OASPL of upstream and downstream rise and fall respectively. It is found that the OASPL increases by 15 dB in the upstream direction and decreases by 7 dB in the downstream direction for β=65°. Flow visualization and spectra analysis indicate that downstream directions are radiated by low frequency noise originated from trailing edge of the deflector due to separation of the large scale vortex. Specifically, it can be illustrated by correlation analysis that the directivity of the trailing separation noise becomes more significant when the impact angle reduces. Upstream directions are dominated by impingement noise. Although impingement noise is significantly affected by impact angle, the radiation structure of impingement acoustic wave under different impact angles is similar to each other according to the correlation analysis. In addition, the deflector forms a low-pass filtering effect on the impingement noise, and the sideline spectra have steep peaks. The OASPL and spectra of sideline directions are less affected by the impact angle. The research results are expected to be helpful for noise pollution control on carrier deck.

MFC actuators, widely used in intelligent sensing/actuation, energy harvesting, underwater bionic robots and other fields, have increasingly attracted attention due to their good flexibility, large actuation force and excellent waterproof performance. In this paper, the vibration characteristics and dynamic response of underwater flexible structure driven by MFC actuators were studied. The driving force of the MFC actuators were calculated, and the additional inertia force and additional damping force of the fluid were derived according to Morrison's semi-empirical formula. Based on the Euler-Bernoulli beam theory, the assumed mode method and the second kind of Lagrange equation, a coupled nonlinear dynamic model of MFC-actuated underwater flexible structures was established. The harmonic balance method was used to convert the nonlinear damping into linear. The numerical simulation and experimental results show that the local stiffness of the flexible beam structure with the MFC actuator is increased, and the measured modal shape is basically consistent with the simulated one. Affected by the hydrodynamic force of the surrounding fluid, the first two orders resonance frequency and dynamic response of the MFC-actuated cantilever beam underwater decrease significantly. The amplitude-frequency response curve predicted by the model is in good agreement with the measured curve, which confirms the validity of the coupling dynamic model. This study provides a reference for underwater bionic propulsion devices based on smart materials.

The failure of ice sheets caused by various forces applied vertically is an important scenario in the polar exploration and utilization engineering. The characteristics of ice strength has a direct impact on the design and evaluation of the structural strength and safety manipulation of platform structures active in this area. In this paper, relying on the Small Ice Model Basin of China Ship Scientific Research Center (CSSRC SIMB), the columnar saline model ice was made to carry out circular plate center loading tests. During the test, the center of the ice specimen on the evenly-distributed circumferential support was loaded vertically, the force curve of the ice specimen from the initial loading to the flexural failure was recorded by a force measurement system, and the flexure strength was obtained according to the peak force. At the same time, the failure details of the ice specimen were documented by a high-speed video camera, and then the process and mode of ice destruction were analyzed. On this basis, a series of experimental tests were carried out to analyze the influence on the flexural strength of the model ice by varying the loading speed and the ice temperature. The work of this paper provides a feasible method for measuring and analyzing the strength characteristics of the model ice for CSSRC SIMB and establishes a preliminary foundation for the further research of the mechanism of ice loading under the vertical interaction between the structure and the ice sheet.

Active control can directly control the low-frequency vibration and noise of a structure by applying control force on the structural system, so it plays an important role in vibration and noise control. In this paper, a method of left eigenvector assignment based on structural receptances was proposed, and the active control of structural vibration was realized by using the relationship between left eigenvector and excitation of vibration system. Firstly, the assignment of eigenvalues and left eigenvectors was derived based on the structural receptances, so there is no need to establish the system model of the structure and know the M, C and K matrices. Secondly, using the redundant space of the left eigenvector assignment, the left eigenvector of the closed-loop system was assigned in the form of orthogonality with the excitation force vector, and the active control of structural vibration was realized. Finally, the numerical examples were given to verify the effectiveness of the method.

The icing problem seriously threatens the safety of ship navigation in the polar environment. The droplet collection coefficient is to determine how effectively a body collects water droplets and is the key parameter for prediction of ice accretion. In this paper, the Euler method was used to numerically simulate the two-phase flow around a circular cylinder. Analysis of the influence on the trajectory of the droplet by studying the droplet Stokes number (St) and droplet Reynolds number (Re_w). Research shows that St has a significant effect on the trajectory of droplets. When St is large (St>1), the collection coefficient depends entirely on the St, Re_w influence is weaker, the total collection coefficient and local collection coefficient slowly decrease with the increase of Re_w. When St is small (0.26<St<1), as Re_w increases, the local and total collection coefficients significantly decrease. Because the fluid forms a vortex downstream of the cylinder, it has a greater flow-following feature at St<0.26, driving droplet coiling to be sucked into the near-wall area at the end of the cylinder, even colliding with the back wall of the cylinder, such that the local and total collection coefficients become larger with the increase of Re_w.

Ship collision is the main risk for the large-scale floating offshore wind turbine's (FOWT) safety, especially in the deep water zones. The ship collisions for the monopile and jacket offshore wind turbines have been studied abundantly, and this paper focuses on the issue of the operation and maintenance vessel collision with FOWT. The coupled mathematical dynamic model of the vessel and FOWT was built based on the multi-body hydrodynamics in MATLAB/Simulink, and the impact force was simulated using the physical numerical modeling method. The collision process was modeled in the time domain assuming the dynamic positioning system was broken. And then, the effects of the relative impact velocity and the impact locations on the floaters’ response were analyzed. The results show that the magnitude of the impact force is proportional to the relative impact velocity. The dynamic response of roll and yaw degree of freedom of the ship is intense due to its small added mass.The impact location determines the kinetic energy redistribution and the magnitude of the impact force.

The current Level 2 vulnerability criteria assessment method for the surf-riding/broaching stability failure mode of the IMO Second Generation Intact Stability Criteria only applies to ships using conventional propellers. However, waterjet propelled ships are also prone to this stability failure mode. Therefore, it is necessary to establish a regulatory assessment method for such a ship type as well. This study established a mechanical model for waterjet propulsion systems through the analogy to the model for propellers. The Level 2 vulnerability assessment method applicable to waterjet propelled ships was proposed and validated based on the actual pump data and sample ship calculations. A specific assessment method for waterjet propelled ships was proposed to overcome the limitation on propulsion type, which not only makes the regulation more complete, but also provides technical support for the stability safety assessment of waterjet propelled ships.

In order to select and optimize the skin friction reduction scheme for high-speed underwater vehicles, a better technical scheme of skin friction reduction test, the expression method of characteristic parameters and the technical way to improve the measurement accuracy were put forward in this paper. The feasibility of the above scheme and approach was demonstrated by the actual skin friction reduction test of PEO. The results can provide support for the selection and optimization of the skin friction reduction scheme for high-speed underwater vehicles.