• The Journal of Engineering Geology
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• v.31 no.4
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• pp.603-620
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• 2021

A land nodal seismic system was employed to acquire seismic reflection data using stand-alone cable-free receivers in a land-river area. Acquiring reliable data using this technology is very cost effective, as it avoids topographic problems in the deployment and collection of receivers. The land nodal airgun system deployed on the mouth of the Hyungsan River (in Pohang, Gyeongsangbuk Province) used airgun sources in the river and receivers on the riverbank, with subparallel source and receiver lines, approximately 120 m-spaced. Seismic data collected on the riverbank are characterized by a low signal-to-noise (S/N) and inconsistent reflection events. Most of the events are represented by hyperbola in the field records, including direct waves, guided waves, air waves, and Scholte surface waves, in contrast to the straight lines in the data collected conventionally where source and receiver lines are coincident. The processing strategy included enhancing the signal behind the low-frequency large-amplitude noise with a cascaded application of bandpass and f-k filters for the attenuation of air waves. Static time delays caused by the cross-offset distance between sources and receivers are corrected, with a focus on mapping the shallow reflections obscured by guided wave and air wave noise. A new time-distance equation and curve for direct and air waves are suggested for the correction of the static time delay caused by the cross-offset between source and receiver. Investigation of the minimum cross-offset gathers shows well-aligned shallow reflections around 200 ms after time-shift correction. This time-delay static correction based on the direct wave is found essential to improving the data from parallel source and receiver lines. Data acquisition and processing strategies developed in this study for land nodal airgun seismic systems will be readily applicable to seismic data from land-sea areas when high-resolution signal data becomes available in the future for investigation of shallow gas reservoirs, faults, and engineering designs for the development of coastal areas.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.33 no.1
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• pp.46-58
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• 1997

The energy saving is one of the most important factors for profit in marine transportation. In order to reduce the fuel oil consumtion the ship's propulsion efficiency must be increased as possible. The propulsion efficiency depends upon a combination of an engine and a propeller. The propeller has better efficiency as lower rotational speed. This situation led the engine manufacturers to design the engine that has low speed, long stroke and a small number of cylinders. Consequently, the variation of rotational torque became larger than before because of the longer delay-time in fuel oil injection process and an increased output per cylinder. As this new trends the conventional mechanical-hydrualic governors for engine speed control have been replaced by digital speed controllers which adopted the PID control or the optimal control algorithm. But these control algorithms have not enough robustness to suppress the variation of the delay-time and the parameter perturbation. In this paper we consider the delay-time and the perturbation of engine parameters as the modeling uncetainties. Next we design the robust servo controller which has zero offset in steady state engine speed, based on H sub($\infty$) control theory. The validity of the controller was investigated through the response simulation. We used a personal computer and an analog computer as the digital controller and the engine (plant) part respectively. And, we could certify that the designed controller maintains its robust servo performance even though the engine parameters may vary.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.2
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• pp.115-125
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• 2007

Minimizing the cylinder wear and the consumption rate of cylinder oil in a large two-stroke marine diesel engine is of great economic importance. In Korea, a motor-driven cylinder lubricator for a large two-stroke marine diesel engine manufactured by $W{\ddot{a}}rtsil{\ddot{a}}$ Switzerland Co., Ltd. was first developed by authors through the joint research of industry-university in 2002. The characteristic of the developed product is that can control automatically the oil feed rate to a load fluctuation by the motor drive and the offset cam. The performance of the product is not also inferior to the conventional one. For manufacturing the reliable and useful products, however, it is necessary to investigate further characteristics and improve the performance of a cylinder lubricator. In this study, the effect of quill with and without accumulator on maximum discharge pressure, delivery delay duration and oil feed rate relative to motor revolution speed using plunger stroke as a parameter is experimentally investigated by using the developed cylinder lubricator. It is found that the maximum discharge pressure with accumulator is higher than that of no accumulator as plunger stroke and motor revolution speed are elevated, and the delivery delay duration with accumulator is shorter than that of no accumulator as plunger stroke and motor revolution speed are increased. Also, oil feed rate with accumulator is less than that of no accumulator except for a plunger stroke of 2 mm as plunger stroke and motor revolution speed are raised.

• Journal of Advanced Marine Engineering and Technology
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• v.19 no.1
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• pp.60-70
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• 1995

In the field of marine transportation the energy saving is one of the most important factors for profit. In order to reduce the fuel oil consumption the ship's propulsion efficiency must be increased as much as possible. The propulsion efficiency depends upon a combination of an engine and a propeller. The propeller has better efficiency as lower rotational speed. This situation led the engine manufacturers to design the engine that has lower speed, longer stroke and a small number of cylinders. Consequently the variation of rotational torque became larger than before because of the longer delay-time in the fuel oil injection process and an increased output per cylinder. As this new trends the conventional mechanical-hydrualic governors for engine speed control have been replaced by digital speed controllers which adopted the PID control or the optimal control algorithm. But these control algorithms have not enough robustness to suppress the variation of the delay-time and the parameter pertubation. In this paper we consider the delay-time and the perturbation of engine parameters as the modeling uncetainties. Next we design the controller which has zero offset in steady state engine speed, based on the two-degree-of-freedom control theory and $\mu$-synthesis. Thd validity of the controller is investigated through the response simulation. We use a personal computer and an analog computer as the digital controller and the engine (plant) part respectively. And, we certify that the designed controller maintains its performance even though the engine parameters may vary.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.9
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• pp.746-756
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• 2017

An algorithm is developed to generate measurement data of deep space network for Korea Pathfinder Lunar Orbiter (KPLO) mission. The algorithm can provide corrected measurement data for the Orbit Determination (OD) module in deep space. This study describes how to generate the computed data such as range, Doppler, azimuth angle and elevation angle. The geometric data were obtained by General Mission Analysis Tool (GMAT) simulation and the corrected data were calculated with measurement models. Therefore, the result of total delay includes effects of tropospheric delay, ionospheric delay, charged particle delay, antenna offset delay, and tropospheric refraction delay. The computed measurement data were validated by comparison with the results from Orbit Determination ToolBoX (ODTBX).

• Proceedings of the IEEK Conference
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• 1998.10a
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• pp.691-694
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• 1998

This paper describes a 6-b 400 MSPS CMOS folding and interpolating(F&I) ADC. To overcome the delay difference of an MSB part and an LSB part in a typical F&I ADC the ADC is composed of only one LSB part and to alleviate the offset voltage of comparators in the LSB part preamplifiers are used in front of the comparators. This paper analyzes a folder and presents a design procedure of the folder. The ADC has the DNL of 0.3 LSB and the INL of 0.6 LSB and consumes the power of 120mW $$ 3 V. The ADC is designed in a 0.6 $\mu\textrm{m}$ CMOS process.

• Bulletin of the Korean Space Science Society
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• 1993.04a
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• pp.7.1-7
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• 1993

위성의 정밀 거리 결정을 위해 1993년 9월 5일부터 IS일간 중국의 상해 천문대 Sheshan관측소와 장춘 인공위성 관측소에서 LAGEOS 11 (Laser Geodynamics Satellite II)에 대한 SLR (Satellite Laser Ranging) 관측을 수행하였다. SLR 관측에서는 지상의 관측소에서 발사한 LASER 펄스 (pulse)가 반사경들(retroflectors)로 둘러싸인 인공위성에 반사되어 돌아오는 RTT (Round Trip Time)를 측정하여 위성까지의 거리를 결정하는데, 관측된 시간과 거리 자료는 많은 잡음(noise)를 포함하고 있기 때문에 정확한 자료를 얻기 위해서는 많은 보정이 필요하다. 관측된 시간, 거리 자료를 지상 목표물 조준(ground target ranging )에 의한 system보정, 원자시계와 GPS에서 수신된 시간과의 시간 비교, 측정된 온도, 기압, 상대 습도에 따른 대기 영향의 보정 등을 통해 오차를 줄이고 다시 LASERF beam의 대기 굴절에 따른 거리 변화 보정, 위성의 질량 중심 거리(offset) 보정, 조석력에 의한 변화값 보정, 전자기적 지연(electromagnetic delay)에 의한 상대론적 보정등을 통해서 정밀한 거리 자료를 얻었다.

• Proceedings of the KIEE Conference
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• 2006.10c
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• pp.479-481
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• 2006

This paper describes a 2.5V, 320MHz low-noise and low-power Phase Locked Loop(PLL) using a noise-rejected Voltage Controlled ring Oscillator(VCO) fabricated in a TSMC 0.25um CMOS technology. In order to improve the power consumption and oscillation frequency of the PLL, The VCO consist of three-stage fully differential delay cells that can obtain the characteristic of high speed, low power and low phase noise. The VCO operates at 7MHz -670MHz. The oscillator consumes l.58mA from a 320MHz frequency and 2.5V supply. When the PLL with fully-differential ring VCO is locked 320MHz, the jitter and phase noise measured 26ps (rms), 157ps (p-p) and -97.09dB at 100kHz offset. We introduce and analysis the conditions in which ring VCO can oscillate for low-power operation.

• Journal of Korean Society of Transportation
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• v.1 no.1
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• pp.10-27
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• 1983

In order to improve the traffic enviroments in the urban streets of Seoul, the computer controlled traffic signal system was installed on 45 intersections at 1980. Afterward, yearly expansion was done to the numbers of 132 intersections and 232 loop detectors. The problems of timing plans were discussed, mainly pedestrian crossing timing as well as the generations of split and offset. The broad urban streets more than 30m require long phasing time of pedestrians, even though the equivalent or correspondent traffic volume is rare. The configuration of computer system for traffic control was disscussed in terms of control strategy. An overview also given. The improvements were measured at every quater. The travel speed improved to 42%, delay time reduced to 41% and number of stops to 43% respectively.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1937-1938
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• 2008

본 논문에서는 868/915MHz 대역 IEEE 802.15.4b LR-WPAN(Low-Rate Wireless Personal Area Network; ZigBee)시스템의 수신기를 위한 주파수 옵셋 영향을 감소시키는 알고리즘을 제안한다. 저가 구현을 지향하는 LR-WPAN 시스템의 특성에 맞추어 반송파 중심주파수의 $\pm$80ppm에 해당하는 주파수 옵셋 환경에서 안정된 수신을 보장할 수 있는 알고리즘으로 868/915MHz수신기 Correlator에 multiple delay differential filter를 적용함으로써 주파수 옵셋에 대한 강인성 및 수신 성능의 안정성을 증대시켰다.