Korea Aerospace University Research Articles

Heat transfer measurements on a flat plate and cylinders at high velocity conditions: Comparison of calculation models with infrared thermography

In this study, various heat transfer measurement models using infrared (IR) thermography were applied to a flat plate and cylinders to examine the accuracy and suitability of the measurements in a transonic blow-down test facility recently developed at Korea Aerospace University. Experiments were performed under three inlet velocity conditions for the flat plate, and for the cylinders, two diameters, two turbulence intensity levels, and five inlet velocity conditions. The surface temperature distribution during the experiment was acquired using an IR camera, and the surface heat transfer coefficient (HTC) was calculated using four HTC calculation models based on the one-dimensional semi-infinite (1D SI) solid assumption: step change (STEP), Duhamel's superposition (DUH), 1D finite volumetric model (1D FVM), and linear regression model (LRM). The LRM showed minimum deviation with reference correlation for the flat plate heat transfer measurements, while STEP, DUH, and 1D FVM showed increased deviations at higher mainstream velocity conditions. The measurements by LRM at the cylinder stagnation location showed the most comparable value with the reference correlation, whereas STEP and FVM showed about 10% deviation from the reference. It is concluded that the LRM is the most suitable heat transfer calculation model for high velocity tests because the model excludes the ramping data during the transient tests, and it can also obtain the local adiabatic wall temperature experimentally.

Bearing Fault Diagnosis usingEnhanced Envelope Analysis

Early fault detection and diagnosis of bearing is of paramount importance in wind turbines as it contributes to around 70% of gearbox and 21%-70% of generator failure. This paper presents an enhanced envelope analysis technique for bearing fault identification using vibration measurements. The raw vibration signal measured from the outer casing of the WT gearbox with faulty bearing has not only fault frequency component but also resonant frequency, discrete frequency (gear and shaft) and high frequency background noise. The present work diagnose bearing faults through a three-step process: i) using Auto- Regressive(AR) time series model to remove discrete frequency components of gear and shaft ii) fault-sensitive frequency and demodulation band selection using spectral kurtosis. The spectral kurtosis is expected to higher around the region of resonance frequencies when fault occurs otherwise the fault signal is modulated. iii) envelope analysis to obtain spectrum by Hilbert Transform (HT) and retrieval of fault information. The order of the AR model is chosen such that the residual signal exhibits maximum kurtosis and spectral kurtosis is computed through short time Fourier Transform (STFT). The enhanced envelope analysis technique for bearing fault diagnosis is verified and validated using numerical simulations and Korea Aerospace University bearing damage benchmark datasets.

Effect of Mainstream Velocity on the Heat Transfer Coefficient of Gas Turbine Blade Tips

This study experimentally investigated the effects of cascade inlet velocity on the distribution and the level of the heat transfer coefficient on a gas turbine blade tip. The tests were conducted in a transient turbine test facility at Korea Aerospace University, and three cascade inlet velocities—30, 60, and 90 m/s—were considered. The heat transfer coefficient was measured using the transient IR camera technique with a linear regression method, and both the squealer and plane tips were investigated. The results showed that the overall averaged heat transfer coefficient was generally proportional to the inlet velocity. As the inlet velocity is increased from 30 m/s to 60 m/s and 90 m/s, the heat transfer coefficient increased by 11.4% and 25.0% for plane tip, and 26.6% and 64.1% for squealer tip, respectively. However, the heat transfer coefficient near the leading edge of the squealer tip and the reattachment region of the plane tip was greatly affected by the cascade inlet velocity. Therefore, heat transfer experiments for a gas turbine blade tip should be performed under engine simulating conditions.

Satellite disturbance detection and rejection with control moment gyros

Uncertain external disturbances either secular or oscillating make the satellite attitude be deviated or oscillating from the mission attitude. These disturbances should be detected in short and rejected with proper counter torques of actuators. Nonlinear second order sliding mode observer is one of the good algorithms that can be used for the detection of disturbances’ magnitude and frequencies. With a control law of the integration and dipole rejection filters based on the identified disturbance information, the actuator torques can compensate the disturbances. The spacecraft attitude is then stabilized at the mission attitude within a tolerable error. In this paper, the performances of detection and rejection algorithms are checked respectively in computer simulations. The applicability is proved on a satellite ground simulator recently developed in Korea Aerospace University. The results show that the algorithms work properly with small error, which is due to the low grade of sensors and actuators.

빔 조향을 위한 W-대역 카세그레인 안테나 설계

Abstract In this paper, for the mechanical beam steering of the Cassegrain antenna, the steering performances of the main reflector tilting method are characterized, and the Cassegrain antenna for the antenna rotating method is designed and its performances are measured. In the Cassegrain antenna operating at W-band, the changes of characteristics due to changes in the sizes of the main/sub-reflectors and other structural changes are analyzed to obtain the structural variables satisfying the performance goal. The manufactured antenna in W-band shows the measured gain of 42.08 dBi, 3 dB beamwidth of 1.32°, 1.14° and the return loss(  ) of 23.58 dB at the center frequency of 94 GHz.Key words: Cassegrain Antenna, Main Reflector Tilting, Antenna Steering, W-BandWKX=BY Z[\X=]!'C?^'(_.` abc6debc,f3gcd;(School of Electronics and Information Engineering, Korea Aerospace University) *BY Z(Hanwha Thales)Manuscript received , 2016 ; Revised , 2016 ; Accepted , 2016. (ID No. 2016h)Corresponding Author: Taek-Kyung Lee (e-mail: tklee@kau.ac.kr)

선형편파를 갖는 S-대역 SDR용 SIW 안테나 설계

Abstract In this paper, the SIW(Substrate Integrated Waveguide)-based feeding antenna for the application of SDR(Software Defined Radar) is designed and manufactured. It is usually well-known that SIWs are easily integrated on PCB and have low transmission loss toward high powered input signal. Also, it is recommended that SIWs are strongly immunized to Electromagnetic Interferences(EMI). In parti-cular, the manufactured antennas are loaded on the USRP(Universal Software Radio Peripheral) platform and employed to detect target RCS as an experiment in this paper. The operating frequency of the proposed antenna is in ISM(Industrial, Scientific and Medical) band(2.4Y2.48 GHz) and the measured gain is over 8 dBi at 2.44 GHz. Key words: Substrate Integrated Waveguide, Software Defined Radar, Slot Antenna, S-Band^_`ab .cdef]g5'h_U ijk)f]g5l9_m nop[14911-01004, qr2,s$jSDR KLM'hmn]) tu vVw.x Byz{7c|z{2Cf]{c.(Department of Electronics and Information Engineering, Korea Aerospace University) Manuscript received October 2, 2015 ; Revised December 11, 2015 ; Accepted February 2, 2016. (ID No. 20151002-22S)Corresponding Author: Jae-Wook Lee (e-mail: jwlee1@kau.ac.kr)

Long-distance anaphora and the blocking effect

Sohng, Hong-Ki. 2015. Long-distance anaphora and the blocking effect. Linguistic Research 32(3), 719-747. This paper aims at giving a principled account of long-distance anaphora including the blocking effect under the LF movement analysis of LD reflexives in the Minimalist Inquiries framework. I have shown that the absence of the blocking effect for Korean LD anaphora does not follow from the Feature Percolation Principles put forward by Cole, Hermon & Huang (2006). Thus I put forth the Feature Percolation Principle to properly handle the blocking effect for Chinese LD anaphora and the absence of the blocking effect for LD anaphora in Italian, Icelandic, and Korean. The Chinese LD reflexive with no inherent φ-features gets and checks its φ-features in terms of the Feature Percolation Principle at LF. Overall, it is shown that the blocking effect exhibited by the Chinese LD anaphor follows from its lack of inherent φ-featuress and the Feature Percolation Principle, and that the absence of the blocking effect for the LD reflexives in Korean, Italian, and Icelandic is due to the fact that they have inherent φ-features. (Korea Aerospace University)

DLC 코팅에 의한 사판식 피스톤 펌프의 저속 영역 동력 손실 개선

This paper details application of a DLC(Diamond Like Carbon)-coating to the swash plate and the ball joint of pistons that make sliding contact with the piston shoes of an axial piston pump. This process, aimed to reduce the frictional and leakage power losses of the hydrostatic piston shoe bearings at the low speed range. At lower speeds than 100rpm, the positive effects of the DLC-coating on the power loss reduction of the hydrostatic piston shoe bearings could be confirmed. These effects resulted in little improvement in volumetric efficiency of the test pump, but the mechanical efficiency could be raised by up to 5% at 100rpm; here, the DLC-coated swash plate played a more dominant role than the DLC-coated ball joint. * Corresponding author: yshong@kau.ac.kr 1 Aerospace & Mechanical Engineering, Korea Aerospace University, Goyang-si, Gyeonggi-do 412-791, Korea 2 Aerospace & Mechanical Engineering, Graduate School, Korea Aerospace University, Goyang-si, Gyeonggi-do 412-791, Korea Copyright C 2014, KSFC This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License(http:// creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 기호 설명  : Balance ratio  : Inclination angle of swash plate,∘  : Piston diameter, mm  : Recess diameter, mm  : Piston shoe diameter, mm  : Friction force on piston, N  : Lift force on piston shoe, N  : Normal load on piston shoe, N  : Cylinder pressure, bar  : Recess pressure, bar  : Recess ratio()

가변 용적형 사판식 피스톤 펌프의 회전 속도 조절에 의한 정압 제어 소비 동력 절감

This paper proposes a control scheme to reduce the power consumption of a variable displacement swash-plate type piston pump supplying oil to a valve-controlled hydraulic cylinder at constant pressure. Whenever flow rate demand was absent, the swash plate angle and the pump speed were changed to the minimum values required to compensate for the internal leakage flow. In response to command signals, the pump speed was changed in proportion to the absolute mean value of the speed component for position commands. At the same time, a pressure regulator was activated to maintain constant system pressure by precisely adjusting the pump speed with the swash plate angle fixed at the maximum. The conventional system consisting of a pressure-compensated variable displacement type pump is driven at a constant speed of 1,800rpm. By comparison, computer simulation and experimental results showed that idling power at stand-by status could be reduced by up to 70% by reducing the pump speed from 1,800rpm to 300rpm and the swash plate angle to the minimum. * Corresponding author: yshong@kau.ac.kr 1 Aerospace & Mechanical Engineering, Graduate School, Korea Aerospace University, Goyang-si, Gyeonggi-do 412-791, Korea 2 Aerospace & Mechanical Engineering, Korea Aerospace University, Goyang-si, Gyeonggi-do 412-791, Korea Copyright C 2014, KSFC This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License(http:// creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 기호 설명  : Position Command Signal, mm  : Reference System Pressure, bar  : Accumulator Pressure, bar  : Pump Flow Rate, l/min  : Cylinder Flow Rate, l/min  : Accumulator Flow Rate, l/min  : Gas Pre-charge Pressure, bar  : Effective Gas Volume, m 3  : Oil Volume in the Accumulator, m 3  : Volumetric Displacement, cc/rev  : Cross Sectional Area of Cylinder, mm 2  : Pitch Circle Diameter of Barrel, mm  : Piston Diameter, mm  : Number of Pistons  : Swash Plate Angle, deg  : Bulk Modulus of Oil, MPa

위성 SAR 센서용 전개형 경량화 안테나 설계

Abstract We present a design of the deployable lightweight antenna to be used in the satellite satisfying the required performance of the onboard sensor. The analysis is performed on the SAR antenna requirements, deploying techniques including material selection, and the characterization of deployable antenna with central disk. The performance of the solid deployable antennas and the mesh antennas are simulated, and the CFRP(Carbon Fiber Reinforced Plastics) samples are manufactured and tested. It is confirmed that the deployable antennas with central disk can meet the required performance by using deploying panels or mesh.Key words: Spaceborne Antenna, Deployable Antenna, Lightweight Antenna, SAR, CFRP  I3JK#LMN&,JOP7QRSTU7K#-VJWXYU7JZF.[ K \]^V_\] `.abcd]Ve(School of Electronics, Telecommunication and Computer Engineering, Korea Aerospace University) fManuscript received October 10, 2014 ; Revised October 31, 2014 ; Accepted November 4, 2014. (ID No. 20141010-03I)fCorresponding Author: Taek-Kyung Lee (e-mail: tklee@kau.ac.kr)

확률론과 위상학적 모델링을 이용한 이중 공진구조 내의 PCB 주파수 응답해석

Abstract In recent, the requirements for the safety to the effects of high power electromagnetic wave have been increased along with the development of electricity and electronic equipments. The small sized electronic devices and the various components have been analyzed by using the full-EM simulation and solving a complete set of Maxwell equation. However, the deterministic approach has a drawback and much limitation in the electromagnetic analysis of an electrically large cavity with a high complexity of the structure. In this paper, statistical theory and topological modeling method are combined to analyze the large cavity with a complex structure. In particular, the PWB(Power Balance) method and BLT(Baum-Liu-Tesche) equation are combined and employed to solve the frequency response to the large-scaled cavity with remarkably reduced time-consumption. For instance, a PCB substrate inside box of box are considered as a large structure with a complexity.Key words: Power Balance Method, Electromagnetic Compatibility, BLT Equation, Topological Analysis, Full Wave Analysis rsiJtsi!puviJ#(Department of Electronics, Telecommunication and Computer Engineering, Korea Aerospace University) *ru vOw(Electronics and Telecommunications Research Institute)Manuscript received July 7, 2014 ; Revised September 5, 2014 ; Accepted September 11, 2014. (ID No. 20140707-09S)Corresponding Author: Jae-Wook Lee (e-mail: jwlee1@kau.ac.kr)

EHA 펌프용 피스톤 슈 정압베어링의 경계 마찰 성능 개선

The pumps of electro-hydrostatic actuators operate most frequently in boundary lubrication speed range, as they compensate for the position control errors as a control element. When conventional swash plate type piston pumps are applied to electro-hydrostatic actuators, the frictional power losses as well as the wear rate of sliding components, such as piston shoes can increase drastically under the boundary friction condition. In this paper, the power losses of the piston shoes were investigated which were engendered by a frictional solid-to-solid contact and leakage flow rate of their hydrostatic bearing. In order to reduce them, DLC-coating was applied to the swash plate and the ball joint of pistons along with its effects were demonstrated. In addition, it was also shown that the wear rate of the piston shoes could be markedly reduced using the DLC-coated swash plate. * Corresponding author: yshong@kau.ac.kr 1 Aerospace & Mechanical Engineering, Korea Aerospace University, Goyang-si, Gyeonggi-do 412-791, Korea 2 Aerospace & Mechanical Engineering, Graduate School, Korea Aerospace University, Goyang-si, Gyeonggi-do 412-791, Korea 3 Yoowon Industries LTD., Busan 604-030, Korea Copyright C 2014, KSFC This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License(http:// creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 기호 설명  : Balance ratio  : Inclination angle of swash plate, deg  : Piston diameter, mm  : Recess diameter, mm  : Piston shoe diameter, mm  : Friction force on piston, N  : Lift force on piston shoe, N  : Normal load on piston shoe, N  : Cylinder pressure, bar  : Recess pressure, bar  : Recess ratio()

레이다 시스템 상호 간 운용을 위한 간섭 보호 기준 분석

Abstract Recently, a mutual interference threat has been increasing among the radar systems due to the rapid growth of the military radar operation. In this paper, the radar interference protection criteria is presented for interoperability in terms of the radar coverage and target detection probability in association with the international recommendation on the interference spectrum by ITU-R. The required criteria for the minimum allowable interference is also presented in terms of INR. In order to ensure the maximum detection probability of the radar under the mutual interference situation, only 5 % of detection range loss is allowed for the case of INR of 6 dB, and required SNR is presented at each INR in terms of the detection range and detection probability. This result will be useful for establishing the interference protection criteria in the combined military radar systems. Key words: Radar, Radar Band, Interference Protection Criteria, INR(Interference-to-Noise Ratio), Interoperabilityh#iO'/j^kiOl/jmT3iOW nop mRgqrstuv.w E/xyDkzxyyk^(Department of Avionics Engineering, Korea Aerospace University) Manuscript received December 5, 2013 ; Revised January 9, 2014 ; Accepted January 21, 2014. (ID No. 20131205-123)Corresponding Author: Young-Kil Kwag (e-mail: ykwag@kau.ac.kr)

하이브리드 로켓 모터의 신뢰성 분석을 위한 FMEA 및 FTA

In this study, the FMEA and FTA for reliability analysis of hybrid rocket motor are performed, that was designed in the Hybrid Rocket Propulsion Laboratory of Korea Aerospace University. In order to carry out these analyses the structure of the hybrid rocket motor is hierarchically divided into 36 parts down to the component level and FMEA is carried out with 72 failure modes. Reliability is assessed based on the FMEA, and the results are used in the FTA to evaluate the overall system reliability. In the FMEA, the relationship between the cause and failure modes, effects and their risk priorities are evaluated qualitatively. 27 failure modes are chosen as those with the critical severity that should be improved with priority. As a result of the FMEA / FTA study, a series of design or material changes are made for the improvement of reliability.

GPS를 이용한 토호쿠 대지진 이후 한반도 지각변동 속도 분석

Abstract The great Tohoku-oki earthquake which occurred on March 11, 2011, caused crustal movements in both Korea and Japan. This study attempts to analyze velocity changes of crustal movement of Korea Peninsula due to the Tohoku-oki earthquake and to compare the calculation with precious crustal movenents of Korea Peninsula. We found that the crustal movement velocity of South Korea increased 3.9 mm/yr northward and 7.5 mm/yr eastward on average as a result of the Tohoku-oki earthquake; when this figure is compared with the past crustal movement velocities of the Korea Peninsula.Key words : GPS, Crustal Movement Velocity, Tohoku-oki earthquake *  7uvu4TUwxV(Spatial Information Research Institute, Korea Cadastral Survey Corporation) ** uK(Korea Aerospace University) ‧ 1yz(First Author) : >(Ji-Hyun Ha, tel : +82-10-3171-6740, email : hajh@lx.or.kr) ‧ {hz: 20131013‧ |v(hT)z: 20131015(hTz: 20131224) ‧ }?z: 20131230 http://dx.doi.org/10.12673/jkoni.2013.17.6.600 I. 서 론

국제물류시장의 차별화된 Alliance Network에 관한 연구 : 우리나라 중소형 국제물류기업을 중심으로

Ho Seon Hong․Kyu Seon ParkDoctor’s Course, Dept. of Aviation Management. Korea Aerospace University, Gyeonggi-do, 412-791, KoreaThe core of this research studies the strategic alliance of airlines, container shipping liners, and port operators that have shown successful results through the recent differentiated strategic Alliance Network, although a difference of scale exists between these firms and the small and mid-sized International Logistics firms, but because of the worldwide traditional Alliance Network of International Logistics firms, HTFN’s(High Tech Forwarder Network) half hearted attitude and the small scale alliance of the small and mid-sized International Logistics firms organized in 1998 cannot breakthrough the present strenuous situation. And these results, creating an attempt to save our country’s International Logistics Industry which have fallen into depression, suggests an awakening of a new strategy based on specialized nationals innovative IT-which does not exist in the world market-by categorizing our country’s small and mid-sized International Logistics firms which are active worldwide.

Tribological and Corrosion Properties of Cr-Zr-N Coatings

Tribological and Corrosion Properties of Cr-Zr-N Coatings Gwang-Seok Kim, Young-Su Kim, Sung-Min Kim and Sang-Yul Lee Department of Materials Engineering, Korea Aerospace University, Koyang 412-791 Kwang-Ryeol Lee Computational Science Center, Future Convergence Technology Lab., Korea Institute of Science and Technology, Seoul 130-650 (Received 16 June 2008) In this work, ternary Cr-Zr-N coatings with not only much improved mechanical properties but also a very low surface roughness were synthesized by closed eld unbalanced magnetron sputtering with vertical magnetron sources and their tribological properties under the various relative humidity (RH) conditions were investigated. Especially, in the case of the Cr1 xZrxN coating with x = 0.34, its friction coe cient obtained under a 90 % RH environment was compared with that of DLC(diamond like carbon) lms measured under the same conditions. In addition, to evaluate the corrosion behavior of the coatings, we carried out potentiodynamic polarization tests in a deaerated 3.5 wt.% NaCl solution at 40 C and we compared the results with those obtained from CrN lms. The tribological behaviors of the Cr-Zr-N coatings did not seem to be signi cantly a ected by the humidity of the air. Under a 90 % RH environment, the average friction coe cient of the Cr1 xZrxN coating with x = 0.34 against a steel ball was approximately 0.17 and this value was lower than those of the CrN (0.49) and DLC (0.2) lms. In the potentiodynamic polarization test results, we found that the corrosion resistance of the Cr-Zr-N coatings was signi cantly improved in comparison with that of CrN and that their corrosion current density (icorr) and corrosion rate decreased with increasing Zr content (x value). PACS numbers: 62.20.Qp, 68.35.Ct, 68.55.Jk