• 한국항공우주학회지
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• 제35권5호
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• pp.397-403
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• 2007

자연에 존재하는 곤충과 새들은 날개짓을 통하여 이동에 필요한 유체력을 발생시킨다. 실현 가능한 플랩핑 MAV를 개발하기 위해서는 날개짓과 추력발생사이의 관계에 관한 기초연구가 필요하다. 본 연구에서는 격자볼츠만법을 사용하여 히빙진동 운동을 하는 평판날개에서 추력 발생이 시작되는 조건을 파악하고자 하였다. 히빙진폭을 0.5C로 고정시키고 환원주파수가 추력발생에 미치는 영향을 파악하였다. 다양한 경우의 히빙진폭에 대하여 환원주파수와 추력 사이의 관계를 파악하고, 추력발생에 더 중요한 파라메터가 Strouhal수임을 보였다. Reynolds수 변화에 따른 추력특성을 파악하였다. 본 연구결과 추력발생이 시작되는 임계 Strouhal 수는 약 0.12이며 추력은 Strouhal 수에 대하여 지수함수의 관계를 갖는다.

• 한국생산제조학회지
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• 제20권5호
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• pp.605-611
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• 2011

In this study, based on previous studies, the thrust generated by using flapping tandem wings is examined. We studied on the relationship between the parameters for characterizing oscillatory tandem wings (namely, the Strouhal number and Reynolds number) for thrust generation in micro flow regime. At each Reynolds number, Strouhal number, heaving amplitude, distance between tandem wings, and phase difference are varied and the flapping motions of tandem mode are calculated to find the optimum conditions for generating thrust. As a result, comparing with a single flapping mode, we found that the minimum Strouhal number for generating thrust is shifted down up to approximately 25% when the tandem flapping mode is applied.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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• pp.291-293
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• 2003

This paper deals with a thrust generation of flapping-airfoil by dynamic stall. From many other previous research results, phase angle $ between pitching and plunging mode of flapping motion must be 90 deg. to satisfy maximum propulsive efficiency. In this case, leading edge vortex is relatively small. This phenomenon is related dynamic stall. So preventing leading edge vortex induced by dynamic stall guarantees maximum propulsive efficiency. But, in this paper we insist the leading edge vortex yields quite a positive influence on thrust generation and propulsive efficiency. In order to certify our opinion, pitching and plunging motions were calculated with the parameter of amplitude and frequency by using the unsteady, incompressible Navier-Stokes flow solver with a two-equation turbulence model. For more efficient computation, it is parallelized by MPI programming method.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2002년도 추계 학술대회논문집
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• pp.35-40
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• 2002

This paper deals with a thrust generation on flapping-airfoil by dynamic stall. Dynamic stall refers to a series of complicated aerodynamic phenomena accompanied by a stall delay in unsteady motion. In most cases, once it occurs, the dynamic stall may lead to an abrupt fluctuation of aerodynamic forces. An inverse $k\acute{a}rm\acute{a}n$ vortex has been considered as a main reason for a thrust generation. In this paper, however, we have found out that a thrust is closely related to reduced frequency and leading edge vortex in addition to inverse Karman vortex. In order to certify our opinion, picking and plunging motions were calculated with the parameter of amplitude and frequency by using the unsteady, incompressible Navier-Stokes flow solver with a two-equation turbulence model. For more efficient computation, it is parallelized by MPI programming method.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2006년도 PARALLEL CFD 2006
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• pp.263-267
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• 2006

The path of a flapping airfoil during upstroke and down-stroke is optimized for maximum thrust and propulsive efficiency. The periodic flapping motion in combined pitch and plunge is described using Non-Uniform B-Splines(NURBS). A gradient based algorithm is employed for optimization of the NURBS parameters. Unsteady, low speed laminar flows are computed using a Navier-Stokes solver in a parallel computing environment based on domain decomposition. It is shown that the thrust generation is significantly improved in comparison to the sinusoidal flapping motion. For a high thrust generation, the airfoil stays at a high effective angle of attack for short durations.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2006년 제4회 한국유체공학학술대회 논문집
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• pp.209-212
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• 2006

Insect and birds in nature flap their wings to generate fluid dynamic forces that are required for the locomotion. Most of the previous published papers discussed mainly on the effect of flapping parameters such as flapping frequency and amplitude on the thrust at a fixed Reynolds number. However, it is not much known on the values of the flapping parameters that the flapping wing requires to generate the thrust at the low Reynolds number flow. In this paper, the onset of the thrust generation is investigated using the lattice Boltzmann method. The wake patterns and velocity profiles behind a flat plate in heaving oscillation are investigated for the heaving amplitude of 0.5C. The time-averaged thrust coefficient value is investigated by changing the reduced frequency from 0.125 to 3.0 for three values of heaving amplitude (h/C=0.25, 0.325, 0.50). It is also found that the critical Strouhal number over which the flat plate starts to produce the thrust is around 0.1 and the thrust is an exponential function of the Strouhal number.

• 한국항공우주학회지
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• 제35권1호
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• pp.1-9
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• 2007

검정금파리 날개의 “8자 운동”에 의한 공기역학적 힘의 발생에 관해 수치해석을 수행하였다. 날개운동은 자유류가 있는 tethered flight 실험에서 관찰된 결과에서 인용하였다. 해석결과 양력은 downstroke 중일 때 주로 발생하였고 추력은 upstroke 끝에서 갑작스럽게 발생하였다. 본 연구에서는 양력과 추력 발생의 이러한 특성을 후류에서의 와류구조와 에어포일 주위의 압력장을 통해 물리적으로 이해하고자 하였다. 결과적으로 양력발생은 유효받음각의 증가에 따른 앞전와류와 관계있었으며, 추력발생은 유동장 형태의 측면에서 와류 짝(vortex pairing)현상과 압력장 측면에서 와류정지 현상으로 설명할 수 있었다.

• 제어로봇시스템학회논문지
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• 제18권2호
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• pp.103-109
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• 2012

Fish generates large thrust through an oscillating motion with a compliant joint of caudal fin. The compliance of caudal fin affects the thrust generated by the fish. Due to the flexibility of the fish, the fish can generate a travelling wave motion which is known to increase the efficiency of the fish. However, a detailed research on the relationship between the flexible joint and the thrust generation is needed. In this paper, the compliant joint of a caudal fin is implemented in the driving mechanism of a robotic fish. By varying the driving frequency and stiffness of the compliant joint, the relationship between the thrust generation and the stiffness of the flexible joint is investigated. In general, as the frequency increases, the thrust increases. When higher driving frequency is applied, higher stiffness of the flexible joint is needed to maximize the thrust. The bending angles between the compliant joint and the caudal fin are compared with the changes of the thrust in one cycle. This result can be used to design the robotic fish which can be operated at the maximum thrust condition using the appropriate stiffness of the compliant joint.

• 한국항공우주학회지
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• 제35권1호
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• pp.10-17
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• 2007

Part 1에서 수행된 검정금파리의 “8자 운동”에 대한 해석결과는 와류들이 양력과 추력발생에 중요한 역할을 하는 것으로 나타났다. 곤충날개에서 발생되는 공기역학적 힘은 레이놀즈수와 같은 공기역학적 요소와 더불어 진동수, 운동진폭, 운동성분 등과 같은 운동학적적 요소들 또 날개의 형태 및 개수등과 같은 형태학적 요소들에 따를 것으로 생각된다. 본 연구에서는 레이놀즈수, 진동수 그리고 운동성분에 따른 양력과 추력발생을 고찰함으로써 이들이 공기역학적으로 어떤 영향을 미치는가를 조사하였다. 이로써 part 1의 결과를 물리적으로 좀 더 상세하게 설명할 수 있는 근거를 찾고자 하였다. 해석결과 “8자 운동”을 구성하는 운동성분 중 회전운동이 추력발생에 지배적인 역할을 하고 있었으며, 또한 추력발생은 반시계 방향의 회전순환과 깊은 관련이 있었다.

• 한국산업융합학회 논문집
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• 제23권5호
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• pp.835-842
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• 2020

This paper considers a method of reproducing abnormal and fault operation for smart monitoring of thrust bearing used in wave power generation system. In order to develop smart monitoring technology, abnormal and failure data of actual equipment are required. However, it is impossible to artificially break down the actual equipment in operation due to safety and cost. To tackle this problem, a test bed that can secure data through reproduction of a faulty operating environment should be developed. Therefore, in this study, test bed that can reproduce each situation was developed and the operation result was analysis after identifying the situation to be reproduced through the failure factor analysis of the thrust bearing.