• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 2022.06a
• /
• pp.412-414
• /
• 2022

Global Navigation Satellite Systems (GNSSs)을 이용한 위치정보 서비스가 다양해짐에 따라, 전파 교란 및 기만에 대한 GNSSs의 취약성에 대한 우려도 점점 커지고 있다. 이에 미국, 러시아, 유럽 등 자체적으로 GNSS를 보유하고 운영하고 있는 국가조차도 GNSS의 취약성을 보완할 수 있는 부가적인 항법시스템을 개발하고 있다. 그 중 현재 운영 중인 Medium Frequency (MF) 주파수 대역의 신호를 이용하여 Differential GNSS (DGNSS) 정보를 전달하는 인프라를 활용하여 항법 신호를 송출하는 Ranging Mode (R-Mode) 시스템이 유럽과 한국을 중심으로 개발 중에 있다. 하지만 MF 주파수 대역의 신호는 일몰 이후에 전리층 일부가 소멸되면서 상위 전리층에서 신호가 반사되어 지표면에서 강한 세기로 수신되는 특성을 갖고 있다. 이런 특성은 지표를 통해 전파하는 원 신호를 수신하는 과정에 큰 오차요소로 작용할 수 있다. 본 논문에서는 현재 송출되고 있는 R-Mode 신호의 야간 특성을 분석하고자 한다. 현재 충주, 어청도 DGNSS 기준국에서 송출하고 있는 R-Mode 신호를 다양한 안테나 종류로 수신해보고, 항법 시스템의 정밀도 성능에 악영향을 줄 수 있는 특성에 대한 보완방법을 모색하였다.

• Journal of Astronomy and Space Sciences
• /
• v.16 no.2
• /
• pp.241-254
• /
• 1999

Differential time-series observations of BL Camelopardalis classified as a double mode SX Phoenicis type variable were secured with a charge coupled device. The observed photometric data was reduced using the IRAF Package and the differential magnitudes were obtained through aperture photometry. The periods of BL Cam were analyzed with the Generalized Least-Square Method by Vanicek (1971) and the Fourier Decomposition Method. It was found that the first and second period of BL Cam were 0.0391 day respectively which lead the period ratio of P1/P0=0.81. This period ratio is much different from 0.78 determined by other investigators and also much more larger than that of other double-mode SX Phe type variables. In addition, this period ratio is much different from the value expected from the relation between the metallicity and period ratio. From these results, it can be confirmed that BL Cam is the most extreme case among all double-mode SX Phe type variables.

• The Journal of the Korea Contents Association
• /
• v.6 no.3
• /
• pp.38-45
• /
• 2006

A dual-level low voltage differential signalling (DLVDS) circuit is proposed aiming at reducing transmission lines for a LCD driver IC. We apply two data to the proposed DLVDS circuit as inputs. Then, the transmitter converts two inputs to two kinds of fully differential signals. In this circuit, two transmission lines are sufficient to transfer two inputs while keeping the LVDS feature. However, the circuit has a common mode bias fluctuation due to difference of the input bias and the reference bias. We compensate the common mode bias fluctuation using a feedback circuit of the current source bias. The receiver recovers the original input data through a level decoding circuit. We fabricated the proposed circuit using $0.25{\mu}m$ CMOS technology. The simulation results of proposed circuit shows 1-Gbps/2-line data rate and 35mW power consumption at 2.5V supply voltage, respectively.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.25 no.3
• /
• pp.185-194
• /
• 2012

This paper deals with free vibrations of the tapered Timoshenko beam in which both the rotatory inertia and shear deformation are included. The cross section of the tapered beam is chosen as the rectangular cross section whose depth is constant but breadth is varied with the parabolic function. The fourth order ordinary differential equation with respect the vertical deflection governing free vibrations of such beam is derived based on the Timoshenko beam theory. This governing equation is solved for determining the natural frequencies corresponding with their mode shapes. In the numerical examples, three end constraints of the hinged-hinged, hinged-clamped and clamped-clamped ends are considered. The effects of various beam parameters on natural frequencies are extensively discussed. The mode shapes of both the deflections and stress resultants are presented, in which the composing rates due to bending rotation and shear deformation are determined.

• Structural Engineering and Mechanics
• /
• v.62 no.1
• /
• pp.65-77
• /
• 2017

The free vibration analysis of fluid conveying Timoshenko pipeline with different boundary conditions using Differential Transform Method (DTM) and Adomian Decomposition Method (ADM) has not been investigated by any of the studies in open literature so far. Natural frequencies, modes and critical fluid velocity of the pipelines on different supports are analyzed based on Timoshenko model by using DTM and ADM in this study. At first, the governing differential equations of motion of fluid conveying Timoshenko pipeline in free vibration are derived. Parameter for the nondimensionalized multiplication factor for the fluid velocity is incorporated into the equations of motion in order to investigate its effects on the natural frequencies. For solution, the terms are found directly from the analytical solution of the differential equation that describes the deformations of the cross-section according to Timoshenko beam theory. After the analytical solution, the efficient and easy mathematical techniques called DTM and ADM are used to solve the governing differential equations of the motion, respectively. The calculated natural frequencies of fluid conveying Timoshenko pipelines with various combinations of boundary conditions using DTM and ADM are tabulated in several tables and figures and are compared with the results of Analytical Method (ANM) where a very good agreement is observed. Finally, the critical fluid velocities are calculated for different boundary conditions and the first five mode shapes are presented in graphs.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.31 no.3 s.258
• /
• pp.331-337
• /
• 2007

Rotating cantilever beams can be found in several practical engineering applications such as turbine blades and helicopter rotor blades. For reliable and economic design, it is necessary to estimate the dynamic characteristics of those structures accurately and efficiently since significant variation of dynamic characteristics resulted from rotational motion of the structures. Recently, Differential Transformation Method(DTM) was proposed by Zhou. This method has been applied to fluid dynamics and vibration problems, and has shown accuracy, efficiency and convenience in solving differential equations. The purpose of this study, the free vibration analysis of a rotating cantilever beam, is to seek for the reliable property of DTM and confidence in the results obtained by this method by comparing the results with that of finite element method applied to linear partial differential equations. In particular, this study is worked by supposing optional T-function values because the equations governing chordwise motion are based on two differential equations coupled with each other. This study also shows mode shapes of rotating cantilever beams for various rotating speeds.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.21 no.8
• /
• pp.96-101
• /
• 2007

Gas Discharge Tubes (GDTs) are widely used as surge protectors for communication applications due to their small internal capacitance. In these days, however, they are mostly used in combined configurations, because the sparkover voltage required to initiate the discharge process in the GDTs and the time taken for arc formation process can be large enough to damage to sensitive circuits. For GDTs with a considerably high initial residual voltage, we should limit the peak voltage using a TVS or filter. We made a hybrid SPD circuits of common-mode type and differential-mode type with the filter using common-mode choke. Also, we applied lightning impulse voltage and ring wave voltage which frequency bandwidth are different each other and verified the characteristics of hybrid SPD circuits according to waveshapes. We describe how the applied SPDs operate in protection process steps with the actual data obtained from the residual voltage measurement at each step. The experiment results show that the surge voltage reduction with the choke coil is more effective in differential-mode circuit than in common-mode circuit.

• Proceedings of the KIEE Conference
• /
• 2001.11a
• /
• pp.53-55
• /
• 2001

A dual probe laser Doppler vibrometer (LDV) that has one laser source and provides two independent object beams has been developed for the first time. An electronic circuit that converts light signal to electronic signal has been also developed using phase locked loop(PLL). It was found that this types of dual probe LDV can be used in differential mode and self-vibration compensation mode.

• Proceedings of the KIEE Conference
• /
• 2001.07c
• /
• pp.1838-1840
• /
• 2001

A dual probe laser Doppler vibrometer (LDV) that has one laser source and provides two independent object beams has been developed for the first time. An electronic circuit that converts light signal to electronic signal has been also developed using digital phase locked loop(DPLL). It was found that this types of dual probe LDV can be used in differential mode and self-vibration compensation mode.

• Proceedings of the KSME Conference
• /
• 2000.11a
• /
• pp.612-617
• /
• 2000

The vibrational characteristics of Langevin-type piezoelectric torsional transducers have been studied theoretically and experimentally in this paper. The differential equations of piezoelectric torsional motion have been derived in terms of the circumferential displacement and the electric potential. Solutions of the boundary-value problem have yielded the natural frequencies and mode shapes of the transducers. The theoretical solutions have been verified by comparing the numerical results with experimental ones.