Browsing by Author "Ren, Luquan"

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    Dynamics and hydrodynamic efficiency of diving beetle while swimming
    (Elsevier, 2023-03-05) Qi, Debo; Zhang, Chengchun; Wu, Zhengyang; Shen, Chun; Yue, Yongli; Ren, Luquan; Yang, Liang
    Diving beetle, an excellent biological prototype for bionic underwater vehicles, can achieve forward swimming, backward swimming, and flexible cornering by swinging its two powerful hind legs. An in-depth study of the propulsion performance of them will contribute to the micro underwater vehicles. In this paper, the kinematic and dynamic parameters, and the hydrodynamic efficiency of the diving beetle are studied by analysis of swimming videos using Motion Capture Technology, combined with CFD simulations. The results show that the hind legs of diving beetle can achieve high propulsion force and low return resistance during one propulsion cycle at both forward and backward swimming modes. The propulsion efficiencies of forward and backward swimming are 0.47 and 0.30, respectively. Although the efficiency of backward swimming is lower, the diving beetle can reach a higher speed in a short time at this mode, which can help it avoid natural enemies. At backward swimming mode, there is a long period of passive swing of hind legs, larger drag exists at higher speed during the recovery stroke, which reduces the propulsion efficiency to a certain extent. Reasonable planning of the swing speed of the hind legs during the power stroke and the recovery stroke can obtain the highest propulsion efficiency of this propulsion method. This work will be useful for the development of a bionic propulsion system of micro underwater vehicle.
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    Effects of eigen and actual frequencies of soft elastic surfaces on droplet rebound from stationary flexible feather vanes
    (Royal Society of Chemistry, 2020-05-05) Zhang, Chengchun; Wu, Zhengyang; Shen, Chun; Zheng, Yihua; Yang, Liang; Liu, Yan; Ren, Luquan
    The aim of this paper is to investigate the effect of eigenfrequency and the actual frequency of the elastic surface for the droplet rebound. The elastic surface used in this study is the stationary flexible feather vanes. A fluid-structure interaction (FSI) numerical model is proposed to predict the phenomenon, and later is validated by the experimental that the droplets impact the stationary flexible feather vanes. The effect of mass and stiffness of the surface is analysed. First, the suitable combination of mass and stiffness of the surface will enhance the drop rebound. Second, a small mass system with higher eigenfrequency will decrease the minimum contact time. In the last, the actual frequencies of the elastic surface, approximate at 75 Hz, can accelerate the drop rebound for all cases.
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    Water entry of slender segmented projectile connected by spring
    (Elsevier, 2020-09-16) Wu, Zhengyang; Zhang, Chengchun; Wang, Jing; Shen, Chun; Yang, Liang; Ren, Luquan
    An object that enters the water experiences a large impact acceleration at the initial stage of water entry, which can cause structural damage to objects that are dropped or launched into the water. To reduce the peak impact acceleration, a spring-connected segmented projectile with compressible nose was designed. Through inertial measurement unit and high-speed camera, the influence of the nose compressibility on the initial impact acceleration was qualitatively investigated. The experimental results demonstrate that the introduction of a spring between the nose and the main body of the projectile can significantly suppresses the peak acceleration during the early stage of impact (0–50 ms). Furthermore, the maximum impact acceleration experienced by the main body is only related to the maximum compression of the nose without considering the spring stiffness. In addition, using the spring exerts a slight effect on the non-dimensional pinch-off times of the cavity but increases the initial velocity required for the occurrence of cavity pinch-off events on the side of the main body