Analytical and experimental research on impact load during rapid engagement of gas turbine

CHEN Hao;ZHOU Ruiping;FAN Hong;LEI Junsong;ZHOU Shaowei

Chinese Journal of Ship Research,2022,No. 02

[Objectives] This paper proposes a theoretical calculation method for obtaining the impact load and dynamic response of shafting during the rapid engagement of a combined gas turbine and gas turbine (COGAG) power plant. [Methods] According to the mechanical relationships between various components in the meshing process of a synchro-self-shifting (SSS) clutch, a dynamic analysis model of the clutch is established, and the dynamic simulation and bench test during the rapid engagement of COGAG are carried out. [Results] The simulation results show that when the damping dashpot functions, an obvious torque impact appears in the helical spline of the clutch, which can result in a strong dynamic response on the shafting. It is also found that the relative position of the ratchet and pawl is random, which can make the peak of the torque impact and the dynamic response of the shafting fluctuate within a certain range. Through a bench test, the accuracy of the impact load calculation method is verified, and in comparison with the theoretical result, the deviation of its maximum and minimum torque response amplitudes from the theoretically calculated values is 3.56% and 8.86%, respectively. [Conclusions] This paper studies torque impact during the rapid engagement of gas turbines, and the result can provide a reference for the safety evaluation of COGAG power plants.

Study on acoustic vibration similarity law of complex stiffened cone-cylinder shell

PENG Caigeng;ZHANG Shiyang;ZHANG Guanjun

Chinese Journal of Ship Research,2022,No. 02

Objective] Due to the difficulty of accurately converting the experimental results of acoustic vibration from scale models of complex stiffened combined shells into that of prototypes, the acoustic vibration similarity law of the shell is studied, so as to provide a basis for experimental research on the scale model based acoustic vibration test of such underwater structures. [Methods] First, a complex stiffened cone-cylinder shell model and its scale model are constructed by using shell elements for reinforcement simulation. Next, on the basis of the finite element method–boundary element method (FEM-BEM), the acoustic vibration response of the combined shell model is calculated. Based on the model experiment, this paper verifies the accuracy of the calculated vibration response of the combined shell by the FEM-BEM. Finally, the acoustic vibration similarity law of the complex stiffened cone-cylinder shell is studied systematically. [Results] The modal frequency of the combined shell is inversely proportional to the scale ratio under the same material parameters, boundary conditions, and exciting force, while the vibration modal in the corresponding frequency is the same. Under the same exciting force, the vibration response of the combined shell is also inversely proportional to the scale ratio, and the acoustic pressure is inversely proportional to the product of the scale ratio and field point distance of the shell. In addition, the acoustic radiation efficiency and acoustic pressure directivity of the underwater scale model and prototype are the same. [Conclusions] The stiffened cone-cylinder shell represents good acoustic vibration similarity laws under similar conditions, and the requirements of studying the acoustic vibration characteristics of the prototype of the combined shell by scale model experiment under similar conditions are met.

Countermeasures for range false target jamming based on quasi Karhunen–Loève translate basis dictionary learning method

YU Lexin;ZHANG Hui;GONG Linshu;JIANG Tao

Chinese Journal of Ship Research,2022,No. 02

[Objectives] Waveform diversity technology is an effective anti-jamming measure against range false target jamming. However, in an environment of strong energy jamming, the high sidelobe caused by the jamming signal mismatch will still affect the detection performance of the radar. To this end, a dictionary learning method is proposed in order to better suppress and eliminate high-power jamming. [Methods] First, initialization dictionaries corresponding to the target and jamming signals are established. Second, the initialization dictionaries and selected atoms are used to generate autocorrelation matrix templates, and the matching coefficients are obtained using the non-homogeneous linear mean square estimation. Next, approximate quasi-Karhunen-Loève transform (Q-KLT) bases corresponding to the target and jamming signals are constructed with templates and matching coefficients respectively. Finally, a convex optimization algorithm is used to separate and recover the target and jamming signals. [Results] The simulation results show that the proposed method can effectively counter the jamming of one or multiple range false targets at a 30 dB jamming-to-signal ratio. [Conclusions] Compared with the traditional waveform diversity technology, the proposed method still maintains good anti-jamming performance in high jamming-to-signal ratio environments, and can be used by shipboard radar to counter range false target jamming.

Multi-state luxury cruise ship seakeeping based on overlapping grids

ZHANG Mu;WANG Jianhua;WAN Decheng

Chinese Journal of Ship Research,2022,No. 02