• 한국자동차공학회논문집
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• 제9권4호
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• pp.139-147
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• 2001

2 DOF half-car model with 6 semi-active suspension units is utilized to evaluate the tracked vehicle dynamic performance simulated by several suspension control algorithms. The target of this research is to improve the ride comfort to maintain operator's handling capability when the tracked vehicle travels fast on the rough road. The control algorithms for suspension systems, such as full state feedback active, full state feedback semi-active, sky-hook active, sky-hook semi-active, and on-off systems, are evaluated and analyzed in view point of ride comfort. The dynamic performances of vehicle are expressed and evaluated by vibratory characteristic evaluation curves, performance indices and frequency characteristic curves. The simulation results show that the performances of sky-hook algorithms for ride comfort nearly follow those of full state feedback algorithms and on-off algorithm is recommendatory when the vehicle runs relatively fast.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2005년도 추계종합학술대회
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• pp.485-488
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• 2005

본 논문에서는 광대역전력증폭기에 사용가능한 전치증폭기를 설계하였다. 설계된 전치증폭기는 주파수 특성과 잡음특성이 우수한 WJ사의 AM1을 사용하였다. 부궤환을 이용하여 100MHz ${\sim}$ 3GHz 대역에 걸쳐서 우수한 VSWR 특성과 주파수 특성을 갖도록 설계하였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 II
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• pp.1394-1399
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• 2001

The purpose of this paper is that investigates the dynamic behavior characteristic of W.T.S(Wind Turbine System) and carries out the evaluation analysis during operating W.T.S. To investigate the dynamic behavior characteristic of W.T.S. the experiments to measure vibration of the blade from the attached accelerometer on the flap and edge section of the blade that is one of the most important elements of dynamic characteristic of W.T.S are performed. Natural frequency and mode shape are calculated with commercial program (STAR MODAL) using the measured vibration acceleration that receives the signal with F.F.T Analyzer from the accelerometer. For validation of these experiments. the finite element analysis is performed with commercial F.E.M Program (ANSYS) on the basis of the natural frequency and mode shape. The results indicate that experimental values have good agreements with the finite element analysis.

• 대한전자공학회논문지SP
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• 제37권6호
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• pp.9-16
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• 2000

최근 컴퓨터의 급속한 보급에 따라 고밀도 CRT(cathode ray tube)가 요망되고 있다. 이를 위하여 신호 대역과 주사 속도의 증가에 따른 주사선 수를 증가 시켜야 하고 플리커(flicker)도 줄여야 한다. 플리커 현상은 PC작업을 장시간 하는 경우 더욱 심하게 느껴지므로 플리커 현상을 줄이는 연구가 필요하다. 본 논문에서는 플리커가 덜 느껴지도록 하는 디스플레이 시스템의 설계를 위한 기초 연구로서 CRY에 사용된 인광체의 잔광 특성 및 화면의 밝기에 따른 플리커와 프레임 주파수와의 관계를 정량적으로 해석하였으며, 또한 디스플레이 전화면에 대해서 시각을 고려하여 플리커를 덜 느끼도록 하는 프레임 주파수를 제시하였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.721-724
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• 2001

In this paper, we present the effect the length the MSL(Microstrip Line) on the oscillation characteristic of the fabricated VCOs(Voltage Controlled Oscillator) designed and analyzed by RF circuit simulator Serenade(ANSOFT Co.) and fabricated by screen printing method on the alumina substrate. We have fabricated VCOs with 3 different MSL length and each MSL length of the VCO is 140mi1, 280mil and 560mi1. The oscillation frequency of each sample(VCO) was tuned to UHF band(750MHz∼900MHz) varying the capacitance. The experimental result shows the phase noise -82∼-97[dBc/Hz] at a 50 [kHz] offset frequency, the pushing figure 94∼318[kHz] at 3${\pm}$0.15[V] and the harmonics 13∼21 [dBc] between MSL length 140mi1s and 560mi1. The frequency and output variation width are 779∼898[MHz], -36∼-33[dBm] at MSL length 140mi1; 818∼836[MHz], -27.19∼-27.06[dBm] at 280mi1;751.54∼751.198[MHz],-33.44∼ -33.31[dBm] at 560mi1. we examined 3 VCOs oscillation characteristic difference through comparison with phase noise, oscillation power and frequency by control voltage change, harmonics and pushing figure for each sample.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제50권11호
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• pp.568-574
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• 2001

This paper describes a current fed high frequency resonant inverter can be used as the power supply for wax-sealing. This circuit configuration is composed of conventional two unit inverter of single ended current find type in parallel. The proposed inverter can realize ZVS operation by using resonant capacitor to ZVS capacitor and has merits not only reduction of switch current distribution but also extension of load range in comparison with the conventional single-ended current fed high frequency resonant inverter. This analysis of proposed circuit uses normalized parameter and characteristic estimation which is needed in each step before design is generally described according to normalized frequency($\mu$), normalized resistance(λ) and parameters. On the basis of characteristic values, a method of the circuit design is presented. Also, the theoretical analysis is proved through experiment and this proposed circuit shows that it can be practically used as the power supply system for wax-sealing and DC-DC converter.

• Structural Engineering and Mechanics
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• 제56권6호
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• pp.939-957
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• 2015

In this paper, a new approach based on the continuum model is proposed to estimate the main cable tension force of suspension bridges from measured natural frequencies. This approach considered the vertical vibration of a main cable hinged at both towers and supported by an elastic girder and hangers along its entire length. The equation reflected the relationship between vibration frequency and horizontal tension force of a main cable was derived. To avoid to generate the additional cable tension force by sag-extensibility, the analytical solution of characteristic equation for anti-symmetrical vibration mode of the main cable was calculated. Then, the estimation of main cable tension force was carried out by anti-symmetric characteristic frequency vector. The errors of estimation due to characteristic frequency deviations were investigated through numerical analysis of the main cable of Taizhou Bridge. A field experiment was conducted to verify the proposed approach. Through measuring and analyzing the responses of a main cable of Taizhou Bridge under ambient excitation, the horizontal tension force of the main cable was identified from the first three odd frequencies. It is shown that the estimated results agree well with the designed values. The proposed approach can be used to conduct the long-term health monitoring of suspension bridges.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2004년도 춘계학술대회 논문집
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• pp.55-60
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• 2004

이 논문은 기적음이 선박 선교에 전달되는 음향전달특성의 측정기술에 관한 것이다. 실습선 ‘새누리호’를 대상으로 선교 내부에 전달되는 기적음을 선교문 개폐상태에 따라서 B＆K 2260D으로 측정한 후, B＆K 7830소프트웨어를 이용하여 주파수특성을 축출하였다. 측정한 주파수 특성을 이용하여 주파수 샘플링에 의한 FIR 필터 설계법으로 128차 FIR 필터를 구축하였다. 그리고, 기적원음과 FIR 필터의 콘볼류션 연산으로 실험음을 생성한 후, 6단계 평가지표를 이용하여 측정한 음향전달특성을 평가하였다. 평가결과, 실험음이 실제 선교에서 듣는 음과 '유사함'을 나타내는 A／sub s／=3.3∼4.7로 나타나서 본 연구에서 개발한 기법이 선교의 음향전달특성 측정기술로서 유효함을 확인하였다.

• Smart Structures and Systems
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• 제8권3호
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• pp.321-341
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• 2011

Acoustic emission (AE) monitoring was conducted for mortar specimens under three types of static loading patterns (cubic-splitting, direct-shear and pull-out). Each of the applied loading patterns was expected to produce a particular fracture process. Subsequently, the AEs generated by various fracture or damage processes carried specific information on temporal micro-crack behaviors of concrete for post analysis, which was represented in the form of detected AE signal characteristics. Among various available characteristics of acquired AE signals, frequency content was of great interest. In this study, cement-based piezoelectric sensor (as AE transducer) and home-programmed DEcLIN monitoring system were utilized for AE monitoring on mortar. The cement-based piezoelectric sensor demonstrated enhanced sensitivity and broad frequency domain response range after being embedded into mortar specimens. This broad band characteristic of cement-based piezoelectric sensor in frequency domain response benefited the analysis of frequency content of AE. Various evaluation methods were introduced and employed to clarify the variation characteristics of AE frequency content in each test. It was found that the variation behaviors of AE frequency content exhibited a close relationship with the applied loading processes during the tests.

• 전기학회논문지
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• 제57권4호
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• pp.729-734
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• 2008

Vibroarthrographic(VAG) signals, emitted by human knee joints, are non-stationary and multi-component in nature and time-frequency distributions(TFD) provide powerful means to analyze such signals. The objective of this paper is to classify VAG signals, generated during joint movement, into two groups(normal and patient group) using the characteristic parameters extracted by time-frequency transform, and to evaluate the classification accuracy. Noise within TFD was reduced by singular value decomposition and back-propagation neural network(BPNN) was used for classifying VAG signals. The characteristic parameters consist of the energy parameter, energy spread parameter, frequency parameter, frequency spread parameter by Wigner-Ville distribution and the amplitude of frequency distribution, the mean and the median frequency by fast Fourier transform. Totally 1408 segments(normal 1031, patient 377) were used for training and evaluating BPNN. As a result, the average value of the classification accuracy was 92.3(standard deviation ${\pm}0.9$)%. The proposed method was independent of clinical information, and showed good potential for non-invasive diagnosis and monitoring of joint disorders such as osteoarthritis and chondromalacia patella.