HIGH-EFFICIENCY UNDERWATER BIOMIMETIC FIN PROPULSION IN LOW-SPEED FLOW REGIME

• Main Author: Sukma Jaya, Arie
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/46647
• Institution: Institut Teknologi Bandung

Indonesia as a maritime country could be benefited from the advancement of the underwater science and technology. One of the related field of the underwater technology is the development of the underwater vehicle. In recent years, most of the development of the underwater vehicle involved an unmanned capabilities in a relatively smaller size than manned vehicles. These vehicles perform underwater locomotion by producing thrust in locomotion direction. The common thrust producing device of the vehicles is propeller-based thruster. The propeller has been known for a high thrust generator with a relatively high efficiency at a high speed condition. However, several research argued that the propeller is not an efficient propulsion mechanism for small underwater vehicles at a low speed condition. One of the possible methods to solve the drawback is a biomimetic approach of mimicking a natural propulsion mechanism of the aquatic animals such as fin of the fishes. The basic assumption of the biomimetic approach is that natural propulsion mechanism has been evolved for more than half billion years to effectively and efficiently adapt with the environmental changes. This highly efficient and effective characteristics of the natural propulsion mechanism could be simplified and applied to enhance the efficiency performance of the underwater vehicle. Therefore, the main objective of this research is to identify the main characteristic of the highefficiency underwater biomimetic fin in low-speed flow regime. The present research focused on the experimental activities in the water tunnel facility for the enhancement scheme of the efficiency performance of the underwater biomimetic fin. The developed underwater biomimetic fins consist of the single-joint rigid fins, single-joint flexible fins, and two-joint fin. The experimental activities by using single-joint fins accommodate external factors of the fin amplitude and fin frequency and internal factors of the fin shapes and fin flexibility. The flexibility of the fin is evaluated by using fin with flexible material and cupping fin. The fin performance are evaluated in the terms of the static performances, such as the average net-force and the thrust to power ratio (TPR), and the dynamic performance of the estimated cruising speed. The experimental results show that the flexible fins enhance the efficiency and thrust performance of the rigid fins. There is an optimum flexibility configuration that maximi zes the static and dynamic performances. Deflection of the fin is the key of the performance enhancement of the flexible fin in which it directs more forces in thrust direction, i thus a thrust vectoring mechanism. Combination of the flexibility characteristics of the flexible and cupping fins could optimizes the overall performance of the singlejoint fins. The two-joint fin is the final form of the performance enhancement scheme in the present study. It refers to a lift-based fin in which basically a wing-like fin that is oriented in asymmetry configuration to the flow. The asymmetry creates pressure different at the front and rear surfaces of the fin to generate lift in thrust direction. The fin reduces torque by adopting a narrow caudal peduncle shape of the fish. The performance evaluation of the experimental results show a highly significant enhancement for both static and dynamic performances of the fin. Maximum average net-force of the two-joint fin is approximately seven times higher than the rigid fin and approximately three times higher than the flexible fin. Another static performance of the maximum TPR of the two-joint fin is approximately ten times higher than the rigid fin and approximately three times higher than the flexible fin at the high fin frequency. The dynamic performance of the estimated cruising speed of the two-joint fin is almost two times higher than the rigid fin and about one and a half times higher than the flexible fin. The two-joint fin should be considered to be a promising alternative of the high-efficiency underwater propulsion in lowspeed flow regime. Keywords: