• Aerospace Engineering and Technology
• /
• v.13 no.1
• /
• pp.27-36
• /
• 2014

Generally, satellites continuously monitor that its major functions are working properly and their hardware are in a good status using several SOH data. In case a fault that is not recognized as a temporal problem or a failure that can be considered to propagate its damage to the other parts are detected, fault management logic is performed automatically without any contact of ground station. In this paper, attitude error detection using sun sensors on a rotating solar array is proposed. Attitude error can be detected by comparing the offset angle between the actual data computed from the sun sensor and the data predicted from the orbit and ephemeris information for the two types of solar array operation method. During the eclipse, the output of attitude error detection method becomes zero because the sun sensor output cannot be provided. Finally, the proposed method is analyzed through the data processing using on-orbit data.

• Journal of Advanced Navigation Technology
• /
• v.15 no.1
• /
• pp.83-90
• /
• 2011

The technique of localization is the core technology for information exchange or environment monitering to measure the position of an object or person. Today, the techniques of localization have been studied extensively and it can be applied to logistics, medical, robotics, etc. But, a lot of money to apply technique of localization is needed. Hence in this paper, we proposed AoA localization system based on Zigbee at low cost. The System measured the RSSI value by rotating the directional antenna using a step motor and Zigbee module. When the measured RSSI is the largest, the receiver measures the angles from beacons which are located at the corners with the rotating angle of a stepping motor and the position of the receiver will be calculated by appling AoA localization method. The measured results show an error about 35~36 cm.

• Aerospace Engineering and Technology
• /
• v.11 no.2
• /
• pp.65-72
• /
• 2012

Numerical simulations were performed to study the stall characteristics of turboprop aircraft. Stall characteristics were qualitatively investigated using the computational results of various configurations based on the combinations of propeller and high lift device. For the analysis of stall characteristics, three-dimensional Navier-Stokes solver with Spalart-Allmaras turbulence model was used and the relative motion between propeller and wing was simulated using sliding mesh technique. For the cruise configurations, major flow separation was occurred at the fuselage/wing fairing and the separation was reduced under propeller slipstream condition. For the high lift device configuration without propeller, major flow separation was occurred at the outboard side of nacelle. With rotating propeller, early stall onset due to low relative velocity and high effective angle of attack was observed on the outboard wing section. Regarding rotating direction of propeller, inboard-down direction was preferred due to the stall delay effect of propeller slipstream.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.29 no.6 s.237
• /
• pp.737-746
• /
• 2005

The present study investigates heat/mass transfer and flow characteristics in a ribbed rotating passage with turning region. The duct has an aspect ratio (W/H) of 0.5 and a hydraulic diameter ($D_h$) of 26.67 mm. Rib turbulators are attached in the cross arrangement on the leading and trailing surfaces of the passage. The ribs have a rectangular cross section of $2\;mm\;(e){\times}\;mm\;(w)$ and an attack angle of $70^{\circ}$. The pitch-to-rib height ratio (p/e) is 7.5, and the rib height-to-hydraulic diameter ratio ($e/D_h$) is 0.075. The rotation number ranges from 0.0 to 0.20 while the Reynolds number is constant at 10,000. To verify the heat/mass transfer augmentation, internal flow structures are calculated for the same conditions using a commercial code FLUENT 6.1. The heat transfer data of the smooth duct for various Ro numbers agree well with not only the McAdams correlation but also the previous studies. The cross-rib turbulators significantly enhance heat/mass transfer in the passage by disturbing the main flow near the surfaces and generating one asymmetric cell of secondary flow skewing along the ribs. Because the secondary flow is induced in the first-pass and turning region, heat/mass transfer discrepancy is observed in the second-pass even for the stationary case. When the passage rotates, heat/mass transfer and flow phenomena change. Especially, the effect of rotation is more dominant than the effect of the ribs at the higher rotation number in the upstream of the second-pass.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.29 no.8 s.239
• /
• pp.911-920
• /
• 2005

The present study investigates heat/mass transfer and flow characteristics in a ribbed rotating passage with turning region. The duct has an aspect ratio (W/H) of 0.5 and a hydraulic diameter ($D_h$) of 26.67 mm. Rib turbulators are attached in the parallel arrangement on the leading and trailing surfaces of the passage. The ribs have a rectangular cross section of 2 m (e) $\times$ 3 m (w) and an attack angle of $70^{\circ}$. The pitch-to-rib height ratio (p/e) is 7.5, and the rib height-to-hydraulic diameter ratio (e/$D_h$) is 0.075. The rotation number ranges from 0.0 to 0.20 while the Reynolds number is constant at 10,000. To verify the heat/mass transfer augmentation, internal flow structures are calculated for the same conditions using a commercial code FLUENT 6.1. The results show that a pair of vortex cells are generated due to the symmetric geometry of the rib arrangement, and heat/mass transfer is augmented up to $Sh/Sh_0=2.9$ averagely, which is higher than that of the cross-ribbed case presented in the previous study for the stationary case. With the passage rotation, the main flow in the first-pass deflects toward the trailing surface and the heat transfer is enhanced on the trailing surface. In the second-pass, the flow enlarges the vortex cell close to the leading surface, and the small vortex cell on the trailing surface side contracts to disappear as the passage rotates faster. At the highest rotation number ($R_O=0.20$), the turn-induced single vortex cell becomes identical regardless of the rib configuration so that similar local heat/mass transfer distributions are observed in the fuming region for the cross- and parallel-ribbed case.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.11 no.1
• /
• pp.1-7
• /
• 1974

This paper discribes the reflector type ultrasonic concentrator which makes hghintencity of ultrasonic field. This was made by rotating parabolic surface which only using total reflection aria, that makes boundary by the critical angle of reflection of sound. I made two binds of concentrator acording to the type of ultrasonic transduser: one is internal surface reflector type concentrator, which is available for disc type transducer, and the other is external surface reflector type concentrator which is available cylinderical transduser. In the mony aspects the reflector tripe concentrator is supel'ier to the reflection type concentrator as plastics lens; It is more durable in high temperature and high intencity ultrasonicfield then refrector type concentrator because of it is made by glass or metal, and it has higher. efficiency because of it wasts made by only total reflection aria that is without absoption lose. I think this is useful ultrasonic concentrator in mony industrial field, in which high intencitr of ultrasonic energy was used.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.30 no.9 s.252
• /
• pp.921-928
• /
• 2006

Wake-induced boundary-layer transition on a NACA0012 airfoil with zero angle of attack is experimentally investigated in periodically passing wakes under the moderate level of free-stream turbulence. The periodic wakes are generated by rotating circular cylinders clockwise or counterclockwise around the airfoil. The free-stream turbulence is produced by a grid upstream of the rotating cylinder, and its intensities $(Tu_{\infty})$ at the leading edge of the airfoil are 0.5 and 3.5%, respectively. The Reynolds number (Rec) based on chord length (C) of the airfoil is $2.0{\times}10^5$, and Strouhal number (Stc) of the passing wake is about 1.4. Time- and phase-averaged streamwise mean velocities and turbulence fluctuations are measured with a single hot-wire probe, and especially, the corresponding wall skin friction is evaluated using a computational Preston tube method. The patch under the high free-stream turbulence $(Tu_{\infty}=3.5%)$ grows more greatly in laminar-like regions compared with that under the low turbulence $(Tu_{\infty}=0.5%)$ in laminar regions. The former, however, does not greatly change the turbulence level in very near-wall region while the latter does it. At further downstream, the former interacts vigorously with high environmental turbulence inside the pre-existing transitional boundary layer and gradually loses its identification, whereas the latter keeps growing in the laminar boundary layer. The calmed region is more clearly observed under the lower free-stream turbulence level and with the receding wakes.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.20 no.5
• /
• pp.157-162
• /
• 2020

In the existing photovoltaic generation system, the system equipped with the reflecting plate is a method in which solar energy (insolation) is concentrated on the surface of the photovoltaic module. However, the solar energy (insolation) lost by being reflected back through the solar module is not considered. Although a method of increasing the amount of power generated by installing a reflector around the solar modules has been proposed, this affects the power generation degradation caused by the shading of other solar modules. Therefore, in order to improve this problem, in this paper, 1) without affecting the development of photovoltaic module according to the shade, 2) photovoltaic module using a reflector rotating the solar energy (insolation) lost by the solar module Study and suggest how to join again. Therefore, the loss of solar energy (insolation) can be minimized through the method of recycling the solar energy according to the countless reflection angle of the lost solar energy (insolation). As a result, it is possible to increase the amount of power generation of the photovoltaic generation system by maximizing the amount of power generation for the same solar radiation.

• Journal of Aerospace System Engineering
• /
• v.11 no.5
• /
• pp.20-27
• /
• 2017

The present paper describes the flow analysis of the flows around the multicopter for the selection of optimal position of air data sensor. For the flow analysis, the commercial fluid dynamics solver, STAR-CCM+ was used with polygon mesh and k-w SST turbulence modeling options. For the simulation of each rotating 4 propellers, unstructured overset mesh method was used. Hovering, forward flight, ascending and descending flight conditions are selected for the analysis and airspeed and flow angle errors were investigated using the CFD results. Through the flow field analysis, sensor location above one propeller diameter distance from the propeller rotating plane showed airspeed error less than 1m/s within the typical flight conditions of multicopter except descending.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.25 no.7
• /
• pp.896-902
• /
• 2021

Rotated face detection is required in many applications but still remains as a challenging task, due to the large variations of face appearances. In this paper, a polar coordinate transform that is not affected by rotation is proposed. In addition, a method for effectively detecting rotated faces using the transformed image has been proposed. The proposed polar coordinate transform maintains spatial information between facial components such as eyes, mouth, etc., since the positions of facial components are always maintained regardless of rotation angle, thereby eliminating rotation effects. Polar coordinate transformed images are trained using AdaBoost, which is used for frontal face detection, and rotated faces are detected. We validate the detected faces using LBP that trained the non-face images. Experiments on 3600 face images obtained by rotating images in the BioID database show a rotating face detection rate of 96.17%. Furthermore, we accurately detected rotated faces in images with a background containing multiple rotated faces.