• 한국측량학회:학술대회논문집
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• 한국측량학회 2010년 춘계학술발표회 논문집
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• pp.183-185
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• 2010

There are many error sources in GPS signal propagation because the signals do not propagate in vacuum. The GPS observations should be preprocessed before they are used for positioning. The cycle slip and outlier detection algorithms are tested in this study in RINEX level using various linear combinations of the observables. The elbourne-Wubbena (M-W) linear combination has an advantage of long wavelength with low noise, and the geometry-free and ionosphere-free linear combinations are used as well to clean the measurements.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 추계학술대회논문집
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• pp.561-562
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• 2008

The numerical analysis of sound radiation by vibrating structure is a well known and mature technology used in many industries. Accurate methods based on the boundary or finite element method have been successfully developed over the last two decades and are now available in standard CAE tools. These methods are however known to require significant computational resources which, furthermore, very quickly increase with the frequency of interest. The low speed of most current methods is a main obstacle for a systematic use of acoustic CAE in industrial design processes. In this paper we are going to present a set of innovative techniques that significantly speed-up the calculation of acoustic radiation indicators (acoustic pressure, velocity, intensity and power; contribution vectors). The modeling is based on the well known combination of finite elements and infinite elements but also combines the following ingredients to obtain a very high performance: o a multi-frontal massively parallel sparse direct solver; o a multi-frequency solver based on the Krylov method; o the use of pellicular acoustic modes as a vector basis for representing acoustic excitations; o the numerical evaluation of Green functions related to the specific geometry of the problem under investigation. All these ingredients are embedded in the ACTRAN/AR CAE tool which provides unprecedented performance for acoustic radiation analysis. The method will be demonstrated on several applications taken from various industries.

• Journal of Positioning, Navigation, and Timing
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• 제12권4호
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• pp.359-367
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• 2023

In order to ensure the high-integrity of reference stations of satellite navigation system, cycle slip should be precisely monitored and compensated. In this paper, we proposed a cycle slip algorithm for the integrity monitoring of the reference stations. Unlike the legacy method using the Melbourne-Wübbena (MW) combination and ionosphere combination, the proposed algorithm is based on ionosphere combination only, which uses high precision carrier phase observations without pseudorange observations. Two independent and complementary ionosphere combinations, Ionospheric Negative (IN) and Ionospheric Positive (IP), were adopted to avoid insensitive cycle slip pairs. In addition, a second-order time difference was applied to the IN and IP combinations to minimize the influence of ionospheric and tropospheric delay even under severe atmosphere conditions. Then, the cycle slip was detected by the thresholds determined based on error propagation rules, and the cycle slip was identified through weighted least square method. The performance of the proposed cycle slip algorithm was validated with the 1 Hz dual-frequency carrier phase data collected under the difference levels of ionospheric activities. For this experiment, 15 insensitive cycle slip pairs were intentionally inserted into the raw carrier phase observations, which is difficult to be detected with the traditional cycle slip approach. The results indicate that the proposed approach can successfully detect and compensate all of the inserted cycle slip pairs regardless of ionospheric activity. As a consequence, the proposed cycle slip algorithm is confirmed to be suitable for the reference station where real time high-integrity monitoring is crucial.

• 한국정밀공학회지
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• 제20권8호
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• pp.185-193
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• 2003

The modular self-wiping co-rotating twin screw extruder (SWCOR) has become the most important of twin screw machines. Screw design is one of the most important factors in determining performance of screw extruder. The screw flight and screw channel geometry of SWCOR is determined by the screw diameter, centerline distance, helix angle, and flights number. The maximum allowable throughput rate on a twin screw extruder is determined by a combination of free volume and available specific torque. In this paper we designed geometrical parameters of extruder screw and presented optimal specific torque value in K=1.55, and then developed screw design program for the screw cutting by the use of JAVA API in the twin screw extruder.

• 한국산업정보학회논문지
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• 제12권1호
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• pp.46-53
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• 2007

3축 CNC 공작기계상에서 자유형상의 벽을 가진 자유곡면을 가공할 때 최종 NC (Numerical Control) 코드를 만들기 위한 공구 경로는 효율적으로 결정 되어져야 한다. 단일화된 황삭과 정삭 알고리즘 및 공구경로가 이미 그래픽으로 Part 1에서 시뮬레이션 되었다. 본 연구에서는 Part 1에서 보여진 시뮬레이션 결과를 3축 CNC 공작기계를 이용하여 자유곡면 바닥을 가진 일반적인 파켓 밀링을 위한 직선 보간 및 직선+아크를 혼합한 보간을 위한 NC 공구경로 데이터로 만들어서 3D 격자 항행 알고리즘을 실험하였고 그 효용성을 증명하였다.

• 소음진동
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• 제4권2호
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• pp.163-175
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• 1994

An analytical method for nautral frequencies of a partially liquid- filled circular cylindrical shell with various boundary conditions is developed by means of the Stokes's transformation and Fourier series expansion on the basis of Sanders' shell equation. The liquid-shell coupled system is divided into two regions for convenient formulation. One is the empty shell region in which the Sanders' shell equations are formulated without the lipuid effect, the other is wetted shell region in which the shell equations are formulated with consideration of the liquid dynamic effect. The shell equations for each regions are combined by the geometry and the force continuities at the junction of the two regions. For the vibration relevant to the liquid motion, the velocity potential of liquid is assumed as a sum of linear combination of suitable harmonic functions in axial direction. The unknown parameters are selected to satisfy the boundary condition along the wetted shell surface. The natural frequencies of the liquid filled cylindraical shells with the clamped- free and the clamped-clamped boundary conditions examined in the previous works, are obtained by this analytical method. The results are compared with the previous works, and excllent agreement is found for the natural frequencies of the shells.

• 한국항행학회논문지
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• 제22권6호
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• pp.616-622
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• 2018

규모가 큰 지진에 의해 발생한 에너지는 전리층까지 도달하여 교란을 발생시킨다. GNSS (global navigation satellite system) 위성의 신호의 전리층 지연을 분석하면 해당 교란을 검출할 수 있다. 지진에 의한 교란 검출에는 주로 band-pass filter가 사용되는데, 교란의 주파수에 맞는 주파수 대역 설정이 중요하다. 따라서 본 논문에선 GNSS 신호를 통해 지진에 의한 전리층 교란의 주파수를 분석하였다. 전리층 교란의 주파수 분석은 반송파의 geometry free combination으로 산출한 전리층 지연을 1 mHz high-pass filter로 처리한 후, fast Fourier transform을 통해 수행했다. 교란의 주파수 분석결과 초기 교란의 주파수는 4.5 mHz~11 mHz의 범위를 가지며, 5.7 mHz가 대표 주파수이다. 후속 교란의 경우 6 mHz~10 mHz의 주파수 대역을 가지며, 7.3 mHz가 대표 주파수로 관찰되었다.

• 센서학회지
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• 제17권4호
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• pp.308-316
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• 2008

For the measurement of liquid level in ship's cargo tank, ballast tank, fuel oil tank and fresh water tank, several types of gauge meter are used such as tubular type, magnetic float type, reflex type transparent type and welding pad type. Among them, magnetic float type gauge meter is environmental friendly device because it is free of power source and maintenance. The main obstacle of the device is relatively large error bound. In this paper, finite element method is used to design and analysis of the magnetic float type gauge meter. The operation of reed switch according to the magnetic field has been successfully described and agreed well with experimental measurement. The optimum geometry with combination of permanent magnet and reed switches are designed to achieve 98 % accuracy of fluid level.

• Nuclear Engineering and Technology
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• 제32권6호
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• pp.618-635
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• 2000

A total of 17 experimental data for the onset of slugging, which is assumed to be the precursor of the condensation-induced waterhammer (CIWH), have been obtained for various How rates of water Incorporating the most recent correlations of interfacial heat transfer and friction factor developed for a circular geometry and using an improved criterion of transition from stratified to a slug flow, two existing analytical models to predict lower and upper bounds for CIWH have been upgraded. Applicability of the present as well as existing CIWH models has been tested by comparison with two sets of CIWH data. The result of this comparison shows that the applicability of the present as well as existing models is reasonably good. Based on the present models for CIWH, a computer code entitled as“KAIST-CIWH”has been developed and sample guide charts to find CIWH free regions for a given combination of major flow parameters in a long horizontal pipe have been presented along with the results of parametric studies of major parameters (D, P, $T_{f,in}$, and L/D) on the critical inlet water flow rate（$W_{f,in}_crit$ for both lower and upper bounds. In addition, two simple formulas for lower and upper bounds that can be used in an emergency for quick results have been presented.

• 한국산업정보학회논문지
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• 제9권1호
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• pp.7-16
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• 2004

효율적인 최종 NC코드를 만들어내기 위해서 공구경로는 효과적인 방법으로 결정되어 져야한다. 이는 3축 CNC 공작기계상에서 자유형상의 벽을 가진 자유곡면을 가공할 때 특히 중요하다. 많은 CAD/CAM 시스템들은 자유곡면가공을 위한 NC코드 생성 시 직선 보간을 이용한다. 그러나 이 방법은 가공된 바닥 표면의 매끄러움과 가공시간, 그리고 CL파일 사이즈를 줄이기 위해서 보정되어야 한다. 곡선 가공이 이러한 문제들을 줄이기 위한 해결책이 될 수 있다. 단일화된 황삭과 정삭 알고리즘과 공구경로가 그래픽으로 시뮬레이션 되었다. 본 연구에서는 자유곡면 바닥을 가진 파켓을 3축 CNC 공작기계를 이용하여 일반적인 파켓 밀링을 위한 직선 보간과 직선+아크를 혼합한 보간을 위한 NC 공구경로 데이터를 만들기 위한 3D 격자 항행 알고리즘을 개발하였다.