• Journal of the Korean Society of Propulsion Engineers
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• v.12 no.5
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• pp.9-17
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• 2008

Pseudo-3D spatial distribution of spray droplets is investigated by using Dual-mode Phase Doppler Anemometry (DPDA) in order to examine the disintegration and spreading behavior of spray exiting from liquid-propellant thruster injector. Spray injected from nozzle orifice with length-to-diameter ratio ($L/d_o$) of 1.67 and under the injection pressure of 27.6 bar is aligned to the vertical. Vertical and horizontal mean velocities of droplets, Sauter Mean Diameter (SMD), and volumetric flux decrease as droplets travel from center/upstream toward outer region/downstream of spray. Although the distribution of spray characteristic parameters is symmetric against the geometric axis of nozzle orifice, their absolute values are asymmetric.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.5
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• pp.460-470
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• 2009

In this paper, we described the implementation of the X-Band continuous-wave doppler radar for muzzle velocity measurement. The radar is consisted of microwave transceiver, signal processor, power board, and the measuring program was developed for the operating and field test. The operating frequency of doppler radar is able to set ${\pm}3\;MHz$ with 5 channel from the center frequency, and the output power is 25 dBm. The minimum receiving power is -117 dBm. The radar would obtain the doppler frequency from the artillery, and calculate accurate velocity point and then estimate muzzle velocity. The performance test for this radar was done with 155 mm at barrel and tripod mounted, and also compared the performance with the reference radar. As a result, the performance of the our new radar is equal with the reference one.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.6 no.4
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• pp.519-526
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• 2002

In this paper, a microstrip patch array antenna for a Doppler radar at 10.525GHz is desinged and fabricated. To be used for mobile radar system, the antenna is fabricated on a single layer laminate to resist a fire impact and is covered with the Teflon foam. To obtain the desired characteristics, the array antenna is designed 4$\times$8 array using a corporate 3-dB amplitude taper. Also, using square patch elements, the antenna can be converted to a circular polarized antenna later. The designed and fabricated array antenna has the reflection coefficient$({S_11})$ -53.498dB, the horizontal beam width of $10^{\circ}$, the vertical beam width of $18.8^{\circ}$, the gain of 21dBi, the bandwidth of 220MHz for VSWR<1.5 and a side lobe level of less than -17.5dB.

• Proceedings of the Korean Society of Computer Information Conference
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• 2018.01a
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• pp.47-50
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• 2018

본 논문에서는 초음파 영상에서 환자 정보를 제거하여 ROI 영역을 추출하고, 추출된 ROI 영역에서 최대 명암도를 임계치로 설정한 이진화 기법을 적용하여 ROI 영역을 이진화 한다. 이진화된 ROI 영역에서 4 방향 윤곽선 추적 기법을 적용하여 상완동맥 혈류 영역이 존재하는 사다리꼴 형태의 영역을 추출한다. 추출된 사다리꼴 형태의 영역에서 상완동맥 혈류영역을 정확히 추출하기 위하여 제안된 무게 중심법을 이용하여 추출된 후보 영역을 양자화 한다. 무게 중심법은 추출된 사다리꼴 영역에서 FCM 기반 무게중심법과 PCM 기반 무게중심법을 각각 계산한 후, 두 중심 간의 차이가 존재 할 경우에는 두 중심의 평균값을 새로운 무게 중심으로 설정하여 각 픽셀들을 클러스터링하여 상완 동맥 영역을 추출한다. 추출된 상완 동맥 영역에는 고혈압 영역인 빨강색 영역과 저혈압이나 혈류가 역류하는 영역인 파란색 영역이 존재한다. 추출된 상완 동맥 영역에서 고혈압 영역만을 추출하기 위해 빨강색 영역을 제외한 그 외의 영역은 제거한다. 전문의가 제공한 상완동맥 혈류 초음파 영상을 대상으로 TPR(True Positive Rate) 검사을 분석한 결과, 제안된 방법이 기존의 방법 보다 TPR 값이 높게 나타나는 것을 확인하였다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.113-116
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• 2008

Pseudo-3D Spatial distribution of spray droplets is investigated by using Dual-mode Phase Doppler Anemometry (DPDA) in order to examine the disintegration and spreading behavior of spray exiting from liquid-thruster injector. Spray injected from nozzle orifice with length-to-diameter ratio $(L/d_o)$ of 1.67 and at the injection pressure of 27.6 bar is aligned to the vertical. Vertical and horizontal mean velocities of droplets, Arithmetic Mean Diameter (AMD), Sauter Mean Diameter (SMD), and volumetric flux decrease as droplets travel from center/upstream toward outer region/downstream of spray.

• The Journal of the Acoustical Society of Korea
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• v.28 no.4
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• pp.336-342
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• 2009

A conventional Closest Point of Approach (CPA) analysis allows a non-maneuvering moving source that is radiating a constant frequency tone to be located using doppler shifted frequency measurements obtained by a stationary receiver. The original frequency, relative speed of the target, time at the CPA, and range from the CPA to the sensor are estimated by the conventional CPA. However, this paper proposes a new CPA analysis that allows the motion parameters of a target to be estimated using the bearing and frequency measurements obtained by a moving receiver that has a constant velocity. The validity of the proposed estimation scheme is confirmed through a performance analysis and simulation study.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.7
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• pp.648-656
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• 2015

Active SAR satellite's main maneuver is roll axis maneuver to change SAR antenna direction. In addition, yaw steering is required to minimize the doppler centroid variation. Thus, it is resonable to assign the torque/momentum capacity mostly to roll axis and then yaw axis. In this case, the pitch axis shows low agility performance. However, due to orbit maintenance, large angle maneuver about pitch axis is sometimes required. In this paper, we study the pitch axis maneuver time reduction through sequential rotation about roll and yaw axis. Since these two axes have high agility performance than pitch axis, maneuver time reduction is possible when large angle rotation about pitch axis is required.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.9
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• pp.799-804
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• 2007

The behavior of spray emanating from an injector to be employed in a liquid-propellant thrust chamber is investigated by optical measurement techniques. The injector has eight holes, each of which has 30 cant angle from the center-axis with the diameter of 0.406 mm. In order to examine an atomization process according to the spray-generation conditions and the evolution along spray downstream, variational features in the velocity and size of droplets obtained through Dual-mode Phase Doppler An 799emometry (DPDA) are delineated and discussed together with instantaneous plane images captured by using Nd:Yag laser sheet beam. A categorization of spray-flow regime representing the atomization and turbulent nature is made through evaluating the non-dimensional parameters, i.e., Reynolds number and Weber number based upon the theoretical injection velocity. These qualitative and quantitative data of spray breakup will be a firm basis for the design of brand-new thruster

• Korean Journal of Optics and Photonics
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• v.11 no.5
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• pp.306-311
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• 2000

This paper deals with the development of Laser Doppler Vibrometer (LDV) that can mea~ure the tlequency and amphlude of the ultrasonic vibralion. Hc-Ne laser (632.8 om) is used as a light source, and Michelson interferometer in winch frequency of the objective beam is shIfted by Bragg cell IS adopted The frequency modulated signal centered at 40 MHz flom the PIN diode IS amplified. down-col1vel1ed to 2.5 MHz, filtered and digiLized. The voltage output that is proportional to the velocity of the vibratwg surface is obtawed using digItal PLL. A microprocessor is used to extract the frequcncy aud amplitude of the vibratIOn from the voltage output. It is found that the developed LDV can measure up to 300 kHz vibratIOn and the mlillmUITI measurable amplitude is I nm at 300 kHz. We believe thatlhis LDV can be used to measure the vibratIOn of the heavy electric maclllnery and micro-size structures. tures.

• Korean Journal of Remote Sensing
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• v.30 no.2
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• pp.185-205
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• 2014

SAR ground moving target indicator (GMTI) has long been an important issue for SAR advanced applications. As spatial resolution of space-borne SAR system has been significantly improved recently, the GMTI becomes a very useful tool. Various GMTI techniques have been developed particularly using multi-channel SAR systems. It is, however, still problematic to detect ground moving targets within single channel SAR images while it is not practical to access high resolution multi-channel space-borne SAR systems. Once a ground moving target is detected, it is possible to retrieve twodimensional velocities of the target from single channel space-borne SAR with an accuracy of about 5 % if moving faster than 3 m/s. This paper presents a quick-and-dirty method for detecting ground moving targets from single channel SAR single-look complex (SLC) images by differentiation. Since the signal powers of derivatives present Doppler centroid and rate, it is very efficient and effective for detection of non-stationary targets. The derivatives correlate well with velocities retrieved by a precise method with a correlation coefficient $R^2$ of 0.62, which is well enough to detect the ground moving targets. While the approach is theoretically straightforward, it is necessary to remove the effects of residual Doppler rate before finalizing the ground moving target candidates. The confidence level of results largely depends on the efficiency and effectiveness of the residual Doppler rate removal method. Application results using TerraSAR-X and truck-mounted corner reflectors validated the efficiency of the method. While the derivatives of moving targets remain easily detectable, the signal energy of stationary corner reflectors was suppressed by about 18.5 dB. It results in an easy detection of ground targets moving faster than 8.8 km/h. The proposed method is applicable to any high resolution single channel SAR systems including KOMPSAT-5.