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19 results on '"Feng, Yikun"'

6. Numerical study of a self-propelled biomimetic robotic fish driven by pectoral fins in labriform mode.

Author

Feng, Yikun and Su, Yumin

Subjects
*PECTORAL fins, *VORTEX shedding, *SURFACE pressure, *REYNOLDS number, *SURFACE dynamics
Abstract

In contrast to other swimming modes, the motions of fins in the labriform mode can be categorized into the drag-based mode and the lift-based mode, which differ in terms of the thrust generation mechanisms. This variance in thrust generation mechanisms gives the labriform mode unique advantages in underwater propulsion. The term labriform indicates that propulsion occurs due to oscillatory movements of pectoral fins. Herein, to identify the key features of labriform locomotion, numerical simulations of a self-propelled biomimetic robotic fish with a Reynolds number (Re) of up to 3 000 000 in the labriform mode are performed. This study includes a detailed analysis of swimming performance and hydrodynamic mechanisms and their connection to three-dimensional vortex dynamics. Compared with the drag-based mode, the fish is observed to cruise faster and swim more smoothly in the lift-based mode. This study also finds that the pectoral fin can produce continuous thrust during one cycle in lift-based mode but can only generate thrust during the power stroke in the drag-based mode. By connecting vortex dynamics and surface pressure, the results show that the leading-edge vortices generated by pectoral fins are associated with most of the thrust production in both motion modes. The analysis of the vortex structure shows that the pectoral fins shed one vortex ring in one cycle of the drag-based mode and two vortex rings in one cycle of the lift-based mode. Our results provide new insights regarding the self-propelled swimming mechanism of biomimetic robotic fish with different labriform propulsion modes. [ABSTRACT FROM AUTHOR]

Published
2024
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10. Influence of a walking mechanism on the hydrodynamic performance of a high-speed wheeled amphibious vehicle

Author

Xu, Haijun, Xu, Liyang, Feng, Yikun, Xu, Xiaojun, Jiang, Yue, and Gao, Xue

Abstract

In order to reduce the resistance and increase speed for a high-speed wheeled amphibious vehicle, a wheel-retracting mechanism was applied to a walking mechanism and the influence was researched. Firstly, to obtain a reliable numerical method, a realizable shear stress transport (SST) k-ω turbulence model and computational fluid dynamic (CFD) model built by an overset mesh technique was used and compared with the corresponding model tests. Secondly, the effect of the wheels' flip angle on resistance, heave and pitch was investigated. Then, the wheel well was optimized by numerical simulation. Finally, the results showed that the influence of the wheels on resistance was more significant, and the larger the wheels' flip angle was, the more significant the resistance reduction would be. An optimized wheel well was beneficial to resistance reduction. Furthermore, the running attitude became steadier, thereby decreasing the heave and pitch.

Published
2023

12. Drag reduction design and research of high-speed amphibious vehicle's deformable track wheels.

Author

Liu, Bolong, Xu, Xiaojun, Pan, Dibo, Feng, Yikun, and Lu, Shengyang

Subjects
DRAG reduction, VEHICLE models, EXPERIMENTAL design, WHEELS, NUMERICAL calculations
Abstract

In this study, the resistance characteristics of the amphibious vehicle in the transitional stage are studied. A deformable track wheel is designed and its effect on the amphibious vehicle's resistance is studied. The numerical calculation method based on the RANS solver and the towing test method is used to analyse the hydrodynamic performance of the amphibious vehicle. Based on the comparison of the vehicle model with no wheel, the influence of wheels on additional resistance at the groove fault is studied. The inclination angles of the front and rear deformation wheels are studied respectively. The influence and principle of the track wheel configuration on drag are analysed and expounded in terms of pressure distribution, water climbing and spray on the wheel grooves, and the hull attitude. Finally, an adjustment strategy of the deformable configuration wheel in the transition stage is proposed. [ABSTRACT FROM AUTHOR]

Published
2023
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14. The effects of caudal fin deformation on the hydrodynamics of thunniform swimming under self-propulsion

Author

Su Yuanyuan, Liu Huanxing, Yumin Su, and Feng Yikun

Subjects
Physics, Mechanical Engineering, Fish fin, 020101 civil engineering, Angular velocity, Thrust, 02 engineering and technology, Kinematics, Mechanics, Deformation (meteorology), Condensed Matter Physics, 01 natural sciences, 010305 fluids & plasmas, 0201 civil engineering, Vortex, Acceleration, Mechanics of Materials, Modeling and Simulation, Self propulsion, 0103 physical sciences, human activities
Abstract

To investigate the effects of the caudal fin deformation on the hydrodynamic performance of the self-propelled thunniform swimming, we perform fluid-body interaction simulations for a tuna-like swimmer with thunniform kinematics. The 3-D vortices are visualized to reveal the role of the leading-edge vortex (LEV) in the thrust generation. By comparing the swimming velocity of the swimmer with different caudal fin flexure amplitudes fa, it is shown that the acceleration in the starting stage of the swimmer increases with the increase of fa, but its cruising velocity decreases. The results indicate that the caudal fin deformation is beneficial to the fast start but not to the fast cruising of the swimmer. During the entire swimming process, the undulation amplitudes of the lateral velocity and the yawing angular velocity decrease as fa increases. It is found that the formation of an attached LEV on the caudal fin is responsible for generating the low-pressure region on the surface of the caudal fin, which contributes to the thrust. Furthermore, the caudal fin deformation can delay the LEV shedding from the caudal fin, extending the duration of the low pressure on the caudal fin, which will cause the caudal fin to generate a drag-type force over a time period in one swimming cycle and reduce the cruising speed of the swimmer.

Published
2020

17. Numerical study on the hydrodynamics of C-turn maneuvering of a tuna-like fish body under self-propulsion

Author

Yumin Su, Feng Yikun, and H.X. Liu

Subjects
Physics, Heading (navigation), Mechanical Engineering, Flow (psychology), Fish fin, Thrust, 02 engineering and technology, Mechanics, 01 natural sciences, 010305 fluids & plasmas, Vortex ring, Vortex, 020303 mechanical engineering & transports, 0203 mechanical engineering, 0103 physical sciences, Trajectory, Stage (hydrology)
Abstract

In this work, numerical simulations are employed to study the hydrodynamics of a virtual swimmer with a tuna-like body during C-turn maneuvering. During the preparatory stroke (Stage 1), the swimmer bends its flexible posterior body into a C-shape. During the propulsive stroke (Stage 2), the swimmer bends out of the C-shape and accelerates forward. The computational trajectory of the swimmer’s center of mass (COM) shows that the swimmer translates mainly in the lateral direction in Stage 1 and accelerates forward in both Stage 2 and the coasting stage. The evolution of the heading angle shows that the swimmer rotates rapidly in Stage 1 and rotates back gradually in Stage 2 and the coasting stage. The visualization of the vortex structures of the flow field shows that two vortex rings are shed by the caudal fin during the whole turn maneuver: one during Stage 1 and the other during Stage 2. The pressure distribution on the swimmer’s surface shows that the thrust is mainly produced by the caudal fin. The vortex ring generated in Stage 2 is elongated under the backflip of the caudal fin and forms a wide and strong jet flow, which makes the fish slide forward rapidly after the end of the turning maneuver. Furthermore, a comparison of our numerical results with those of published experimental and numerical studies on live fish and virtual swimmers shows that our results sufficiently handle the flow regime of a natural C-turn maneuver.

Published
2020

19. Plexiform fibromyxoma of the stomach: a clinicopathological study of 10 cases.

Author

Hu G, Chen H, Liu Q, Wei J, Feng Y, Fu W, Zhang M, Wu H, Gu B, and Ren J

Abstract

Plexiform fibromyxoma (PF) is a unique mesenchymal tumor of the stomach. The molecular characteristics of these tumors remain unclear. Here, we report 10 cases of PF with clinicopathological features and molecular features in detail. The patients ranged in age from 26 to 72 years (mean, 49 y) and most commonly presented with abdominal pain and distension, black stool, and anemia. Eight tumors were located at the antrum while two in the fundus of stomach. Histologically, tumor cells exhibited a plexiform growth pattern with multiple nodules in the muscularis propria of stomach wall and infiltrative borders. Immunohistochemically, all tumors were strongly positive for vimentin and smooth muscle actin (SMA), some were staining for CD10 (5/10), desmin (5/10), H-caldesmon (6/10) and progesterone receptor (PR, 6/10), however, CD34, S-100, Estrogen Receptor (ER), ALK, CD117 and DOG-1 were all negative in our cases. The glioma-associated oncogene homologue 1 ( GLI1 ) gene translocation was detected in eight cases by FISH with three positive and five negative. Mutation analyses of C-KIT and platelet-derived growth factor receptor alpha ( PDGFRA ) genes were performed on five cases and all of which were wild-type for mutation. Our follow-up indicated that all of the patients made an uneventful recovery at 24 to 95 months after diagnosis. In summary, the distinctively histological features and immunohistochemical positivity of SMA, CD10 and PR can help differentiate PF from other gastrointestinal mesenchymal tumors. GLI1 gene translocation offers an additional molecular instrument for the diagnosis. The expression of PR and the existence of GLI1 gene translocation in PF highlights of our article., Competing Interests: None., (IJCEP Copyright © 2017.)

Published
2017

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