• 한국해양공학회지
• /
• 제34권2호
• /
• pp.66-76
• /
• 2020

A light buoy is equipped with lighting functions and navigation signs. Its shape and colors indicate the route to vessels sailing nearby in the daytime, with its lights providing this information at night. It also plays a role in notifying the presence of obstacles such as reefs and shallows. When a light buoy operates in the ocean, the visibility and angle of light from the lantern installed on the buoy changes, which may cause them to function improperly. Therefore, it is necessary for the buoy to have stable and minimal motions under given environmental conditions, mainly waves. In this study, motion analyses for a newly developed lightweight light-buoy in waves were performed to predict the motion performance and determine the effect of the developed appendages for improving the motion performance. First, free decay tests, including benchmark cases, were performed using computational fluid dynamics (CFD) to estimate the viscous damping coefficients, which could not be obtained using potential-based simulations. A comparison was made of the results from potential-based simulations with and without considering viscous damping coefficients, which were estimated using CFD. It was confirmed that the pitch and heave motions of the buoy became smaller when the developed appendages were adopted.

• 제어로봇시스템학회논문지
• /
• 제17권6호
• /
• pp.546-551
• /
• 2011

Tilt sensor is required to control the attitude of the biped robot when it walks on an uneven terrain. Vision sensor, which is used for recognizing human or detecting obstacles, can be used as a tilt angle sensor by comparing current image and reference image. However, vision sensor alone has a lot of technological limitations to control biped robot such as low sampling frequency and estimation time delay. In order to verify limitations of vision sensor, experimental setup of an inverted pendulum, which represents pitch motion of the walking or running robot, is used and it is proved that only vision sensor cannot control an inverted pendulum mainly because of the time delay. In this paper, to overcome limitations of vision sensor, Kalman filter for the multi-rate sensor fusion algorithm is applied with low-quality gyro sensor. It solves limitations of the vision sensor as well as eliminates drift of gyro sensor. Through the experiment of an inverted pendulum control, it is found that the tilt estimation performance of fusion sensor is greatly improved enough to control the attitude of an inverted pendulum.

• 한국환경과학회지
• /
• 제22권5호
• /
• pp.543-554
• /
• 2013

Acoustic Doppler Current Profilers (ADCPs) are increasingly popular in the river research and management communities being primarily used for estimation of stream flows. ADCPs capabilities, however, entail additional features that are not fully explored, such as morphological representation of river or reservoir bed based upon multi-beam depth measurements. In addition to flow velocity, ADCP measurements include river bathymetry information through the depth measurements acquired in individual 4 or 5 beams with a given oblique angle. Such sounding capability indicates that multi-beam ADCPs can be utilized as an efficient depth-sounder to be more capable than the conventional single-beam eco-sounders. The paper introduces the post-processing algorithms required to deal with raw ADCP bathymetry measurements including the following aspects: a) correcting the individual beam depths for tilt (pitch and roll); b) filtering outliers using SMART filters; d) transforming the corrected depths into geographical coordinates by UTM conversion; and, e) tag the beam detecting locations with the concurrent GPS information; f) spatial representation in a GIS package. The developed algorithms are applied for the ADCP bathymetric dataset acquired from Han-Cheon in Jeju Island to validate themselves applicability.

• 항공우주기술
• /
• 제11권1호
• /
• pp.185-191
• /
• 2012

본 논문에서는 축소 로터의 성능시험과 축소 헬기 Flight Test Bed 개발이 가능한 헬리콥터 섀시다이나모미터(HCDS)를 개발하여 지상시험을 수행하였다. 축소 헬기는 엔진 출력에 따른 컬렉티브 피치각의 상호 관계로부터 로터의 일정 회전속도에 대한 추력과 동력의 변화를 확인하고, 그 결과로 OGE에서의 정지비행효율(F.M.)이 0.76으로 비행시험 가능성을 점검하였다. 본 헬리콥터 섀시다이나모미터(HCDS) 시험 결과는 축소 헬기 개발과 로터 블레이드의 성능 평가에 활용할 것이다.

• 항공우주기술
• /
• 제12권2호
• /
• pp.193-201
• /
• 2013

프로펠러는 인간동력 항공기 추진시스템의 중요한 구성품이다. 높은 프로펠러 효율을 얻기 위하여 프로펠러는 큰 지름을 가지고 느리게 구동된다. 프로펠러는 인간동력 항공기용 프로펠러 설계 프로그램을 사용하여 설계되었다. 프로펠러의 피치는 지상에서 조정이 가능하다. 본 논문에서는 여러 가지 변수에 대하여 설계에 사용된 동일한 프로그램을 통하여 프로펠러의 성능 해석을 수행하였다. 또한, 파일롯의 체력이나 비행속도의 변화에 따른 탈 설계점 해석도 수행하였다. 설계된 프로펠러는 카본 복합재의 초경량 구조로 제작되어 총 950g의 무게로 제작되었다. 제작된 프로펠러는 아이언 버드에서의 지상 성능 시험을 통하여 속도 및 동력을 측정하고 튜닝을 수행하여 실기에 장착되어 최종적으로 291 m 비행에 성공하였다.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2011년 춘계학술대회논문집
• /
• pp.447-452
• /
• 2011

Propeller shall have high efficiency and improved aerodynamic characteristics to get the thru5t to fly at high speed for the Regional turboprop aircraft. That is way Clark-Y airfoil which is used to conventional turboprop aircraft propeller is selected as a blade airfoil. Adkins method is used for aerodynamic design and performance analysis with respect to the propeller design point. Adkins method is based on the vortex-blade element theory which design the propeller to satisfy the condition for minimum energy loss. propeller geometry is generated by varying chord length and pitch angle at design point of Regional turboprop aircraft. The propeller design results indicate that is evaluated to be properly constructed, through analysis of propeller aerodynamic characteristics using the Meshless method and MRF, SM method.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2008년도 춘계학술대회논문집
• /
• pp.39-42
• /
• 2008

In the case of the general helicopter among rotorcraft, length of the rotor blade for thrust-generation is longer than that of fuselage and tail rotor is required in order to compensate moment of the fuselage. For those reasons, enough space for take-off and landing should be secured and an accessibility for building is low. Also, the accidents caused by tail rotor occur frequently. However, the case of counter-rotating has merits that tail rotor is unnecessary as well as length of the rotor blade can be shortened but has a weakness that the weight of body is increased. In the present study, aerodynamic force measurement on single rotor system equipped with NACA0012 airfoil, which has aspect ratio of 6 and chord length of 35.5 mm, was carried out. And measurement was conducted with blade which has a half size of the former blade by using single motor counter-rotating. Aerodynamic force measurement was acquired by using 6-component balances and coefficients of thrust and power were derived along the pitch angle varying from 0$^{\circ}$ to 90$^{\circ}$ with the increment of 10$^{\circ}$. Those aerodynamic force data will be utilized for the design and production of brand-new counter-rotating rotor blade system which has same thrust with single blade system and provides a good accessibility to building by reducing its blade length.

• 한국전산유체공학회지
• /
• 제18권3호
• /
• pp.60-66
• /
• 2013

Numerical simulation was performed for the rotor blade with fixed tab in hover using an unstructured mesh Navier-Stokes flow solver. The inflow and outflow boundary conditions using 1D momentum and 3D sink theory were applied to reduce computational time. Calculations were performed at several operating conditions of varying collective pitch angle and fixed tab length. The aerodynamic effect of fixed tab length was investigated for hovering efficiency, pitching moment and flapping moment of the rotor blade. The results show that it affects linearly increasing on the pitching moment of the rotor blade but does not affect on the flapping moment. The required power is less than 45kw for ground rotating test in hover. Numerical simulations also show that the vortex generate not only from the tip of the rotor blade but also from the fixed tab on the rotor blade.

• 대한기계학회논문집B
• /
• 제32권4호
• /
• pp.300-306
• /
• 2008

In the present study, the second order response surface method (RSM) is carried out to get optimum thermal design for enhancing heat transfer in a square channel with bleed flow. The RSM is used as an optimization technique. To calculate the heat transfer, RNG k-epsilon model and enhanced wall function are used. To design optimum rib turbulators, two design variables such as attack angle of rib $({\alpha})$ and rib pitch-to-rib height ratio (p/e) are optimized. In these analyses, the channel inlet Reynolds number was fixed at 10,000 in both non-bleeding and bleeding cases. The response surfaces of two design variables are constructed in cases with and without bleed flow. As a result, the optimum (or highest) heat transfer values are almost the same in ranges of two cases with and without bleed flow. However, the friction losses in the case with bleed flow are lower than those without bleed flow.

• Journal of Advanced Marine Engineering and Technology
• /
• 제39권10호
• /
• pp.1023-1030
• /
• 2015

The purpose of this paper is to present the basic mathematical modeling of a hexacopter, which could be used to develop proper methods for stabilization and trajectory control. A hexacopter consists of six rotors with three pairs of counter-rotating fixed-pitch blades. This mechanism is an under-actuated, dynamically unstable, six-degrees-of-freedom system. The whole motion of this object consists of translational and rotational motion in three dimensions, where the translational motion is created by changing the direction and magnitude of the upward propeller thrust. The hexacopter is controlled by adjusting the angular velocities of the rotors, which are spun by electric motors. It is assumed to be a rigid body; thus, the differential equation of the hexacopter dynamics can be derived from the Newton-Euler equation. The Euler-angle parametrization of the three-dimensional rotations contains singular points in the coordinate space that can cause failure of both the dynamical model and control. In order to avoid singularities, the rotations of the hexacopter are parametrized in terms of quaternions. This choice has been made considering the linearity of the quaternion formulation and their stability and efficiency. Further, control simulation of a hexacopter applying cascaded-PID control is also presented in this paper.