http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
오늘 본 자료
장수풍뎅이의 정지 비행시 공력 특성에 관한 수치적-이론적 연구
오세형(Sehyeong Oh),이부건(Boogeon Lee),박형민(Hyungmin Park),최해천(Haecheon Choi),김선태(Sun-Tae Kim) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12
A rhinoceros beetle is one of the heaviest and has the highest wing loading among the flyers that satisfy the requirements of flapping wing micro air vehicles (FWMAVs). In this work, a hovering rhinoceros beetle is investigated through high-speed photogrammetry, numerical simulation and blade element theory (BET). The wing kinematics are directly obtained from experimental measurements using three high speed cameras. The simulations are performed at Re=16,737, based on the maximum velocity at the wing tip and the mean chord length of the hind wing, using an immersed boundary method. The results of numerical simulations indicate that the lift force generated by hind wings alone is sufficient to support the weight, and the elytra generate negligible lift force. In order to understand the mechanisms of lift and drag forces and aerodynamic power generation, we present a BET model based on quasi-steady assumptions. Compared to the existing quasi-steady models, the proposed model uses a nonstationary airfoil theory but does not require any empirical corrections. We show that our current BET model is in excellent agreement with the numerical results.
오세형(Sehyeong Oh),이부건(Boogeon Lee),박형민(Hyungmin Park),최해천(Haecheon Choi) 대한기계학회 2018 대한기계학회 춘추학술대회 Vol.2018 No.12
We investigate the optimal wing geometry and kinematics of a rhinoceros beetle in hovering motion for minimum power consumption. The original wing kinematics of a hovering beetle is measured using high speed cameras. Based on the measured wing kinematics, numerical simulations are conducted using an immersed boundary method. Numerical results indicate that the enhancement of vertical force and reduction of aerodynamic power requirement due to twist of hindwings are less than 3% as compared to their rigid counterparts, and the effect of elytra on the force generation is negligible. Therefore, we consider rigid and flat hindwings for optimization. We develop a predictive aerodynamic model which predicts the force generation and power requirement of the flapping wing. Optimal wing kinematics and geometry are obtained applying this model together with a hybrid of a clustering genetic algorithm and a gradient-based optimizer. We find optimal solutions for the minimizations of aerodynamic and mechanical power consumption, respectively. Optimization results showed that optimal wing kinematics and geometry for mechanical power consumption than for aerodynamic power consumption are closer to those of a rhinoceros beetle.
계류 비행하는 장수 풍뎅이 주위 유동장 가시화 및 분석
이부건(Boogeon Lee),오세형(Sehyeong Oh),박형민(Hyungmin Park),최해천(Haecheon Choi),김선태(Sun-Tae Kim) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12
The aerodynamics of various flying insects has been investigated to understand how they generate large aerodynamic forces, which could not be understood with a traditional aerodynamic theory. Mostly, this problem has been approached with the measurements of flow fields near their wings and body. Compared to other flying insects, the beetle is known to have a very high wing loading but also show a very exceptional flight performance. Morphologically, the beetle has highly flexible inner wings (hindwings) and rigid outer wings (elytra), so it is thought that the specific wing-wing interaction would be one of mechanisms to be used by beetle flight. In the present study, the flow fields around the body and wings of a beetle in a tethered flight are visualized in a wind tunnel, through a high-speed smoke-wire technique while varying the body angle of the beetle. The existence of leading edge vortex (LEV) on each wing is confirmed during the flapping and vortical structures due to the wing-wing interaction are captured, which will be analyzed further.
이부건(Boogeon Lee),오세형(Sehyeong Oh),박형민(Hyungmin Park),최해천(Haecheon Choi) 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11
In the present study, smoke-wire flow visualizations were conducted to investigate the flow structures generated by a tethered flight of a rhinoceros beetle in a wind tunnel. Measurements are done at five planes along the wing span while the varying the body angle (angle between the horizontal and the body axis) and free-stream velocity to relate the advance ratio and Strouhal number which are widely accepted as important parameters on the aerodynamic force generation of flying insects. It is observed that the angle of wake-induced flow, spanwise flow in LEV (leading-edge vortex) and the instant of LEV generation vary depending on the body angles that represent different flight mode such as hovering, forward and take-off flights. On the other hand, it is found that most of aerodynamic forces would be generated by hindwings (flexible inner wings) compared to the elytra (hard outer wings) inferring from the size of the attached leading attached vortex (LEV) on the wings. Furthermore, specific flow patterns from other unsteady aerodynamic mechanisms such as clap-and-fling, wing-wing interaction and wake capture are found as well.
큰 에디 모사 기법을 이용한 회전익 무인비행체 주위 유동해석
김소희(Sohee Kim),오세형(Sehyeong Oh),윤영진(Young-Jin Yoon),최해천(Haecheon Choi) 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11
Large eddy simulation is conducted to analyze the flow structures around a propeller of a multirotor unmanned aerial vehicle (UAV). The propeller consists of two blades, and the angle of attack of blades varies along the spanwise (radial) direction. An immersed boundary method is used to satisfy the no-slip condition on the propeller surface in a noninertial reference frame (Kim and Choi, 2006). A global dynamic subgrid-scale model (Lee et al., 2010) is used for the subgrid-scale stress tensor. The Reynolds number based on the tip velocity and chord length at the 75% span is about 73,000. The lift coefficient from the present numerical simulation is in good agreements with that from experiments. The flow around the propeller is nearly attached on the surfaces, and wingtip vortices are generated near the tip of the propeller during rotation. To predict the performance of the propeller, the sectional lift coefficient is obtained along the spanwise direction and compared with models derived using the thin airfoil theory and actuator disk model, showing good agreements.