• 한국전자파학회논문지
• /
• 제24권12호
• /
• pp.1167-1172
• /
• 2013

본 논문에서는 하나의 트랜지스터로 발진과 주파수 혼합이 동시에 이루어지는 self-oscillating-mixer(SOM) 방식을 적용하여 높은 변환 이득을 갖는 X-band 도플러 레이더를 설계하였다. SOM의 위상 잡음 특성을 향상시키기 위하여 ${\lambda}/2$ slotted square patch resonator(SSPR) 공진기를 제안하였으며, 동일 주파수에서 기존 공진기에 비해 50 %의 면적 감소와 175.4의 높은 Q값을 이루었다. 제작된 SOM은 저 전력 시스템을 구현하기 위해 1.7 V의 낮은 바이어스 전압을 인가해 주었으며, 높은 변환 이득을 위하여 트랜지스터의 pinch-off voltage 근처를 동작점으로 설정하였고, 변환 이득이 최대가 되도록 최적화 하였다. 제안된 SOM의 출력 파워는 10.65 GHz에서 -3.16 dBm으로 측정되었으며, DC Power consumption은 7.65 mW로 상대적으로 작은 전력을 소모한다. 또한, 9.48 dB의 높은 변환 이득 특성과 100 kHz offset에서 -90.91 dBc/Hz의 위상 잡음 특성을 나타내며, 이때 성능지수(FOM)는 -181.8 dBc/Hz 으로 다른 SOM에 비해 7 dB 이상 개선되었다.

• 한국산학기술학회논문지
• /
• 제21권11호
• /
• pp.672-682
• /
• 2020

최근 다양한 산업/제조 현장에서 운영 효율화를 위한 디지털 트윈(digital twin) 기술 연구가 활발하게 수행 중이고, 화석 연료의 점진적 고갈과 환경오염 문제는 파력발전소와 같은 신재생/친환경 발전방식을 요구한다. 하지만, 파도의 에너지에 의해서 전기를 생산하는 파력발전에서 변동성이 높은 파도에너지에 의해서 발전량과 고장 등의 운영효율화 요소가 밀접하게 관련되어 있어 이들 사이의 관계를 이해하고 예측하는 것이 매우 중요하다. 따라서 첫 번째로 파고 데이터, 진동수주(OWC: Oscillating Water Column, 이하 OWC) 챔버의 센서 데이터 등과 같은 변동성이 높은 데이터 간에 의미 있는 상관관계 도출이 필요하다. 두 번째로 도출된 상관관계를 기반으로 추출된 데이터로 예측 상황을 학습함으로써 원하는 정보를 예측할 수 있는 방법론 연구가 이루어져야 한다. 본 연구에서는 파력발전 시스템의 디지털 트윈으로 스마트 운용 및 유지보수가 가능하도록 실제 파력발전소의 IoT 센서 데이터를 이용하여 OWC의 압력 예측을 위해 머신러닝 프레임워크를 활용한 워크플로우 기반의 학습모델을 설계하고, 검증 및 평가 데이터셋을 통한 압력 예측분석의 유효성을 확인한다.

• 한국해양공학회:학술대회논문집
• /
• 한국해양공학회 2004년도 학술대회지
• /
• pp.268-273
• /
• 2004

A study on experimental method of the model test for the impulse turbine is carried out. the wave simulator is used to reproduce the real wave condition. It controls two parameter correspond to wave height and wave frequency. The optimum design which is reported by T. Setoguchi is manufactured and tested for the validation of our test facilities. The comparison of model test show that our facilities produce little bit higher efficiency at maximum efficiency point. To increase the efficiency of turbine, the new rotor with negative tip clearance is designed and being tested.

• Interaction and multiscale mechanics
• /
• 제5권1호
• /
• pp.27-40
• /
• 2012

The two-dimensional incompressible flow of a linear viscoelastic fluid we considered in this research has rapidly oscillating initial conditions which contain both the large scale and small scale information. In order to grasp this double-scale phenomenon of the complex flow, a multiscale analysis method is developed based on the mathematical homogenization theory. For the incompressible flow of a linear viscoelastic Maxwell fluid, a well-posed multiscale system, including averaged equations and cell problems, is derived by employing the appropriate multiple scale asymptotic expansions to approximate the velocity, pressure and stress fields. And then, this multiscale system is solved numerically using the pseudospectral algorithm based on a time-splitting semi-implicit influence matrix method. The comparisons between the multiscale solutions and the direct numerical simulations demonstrate that the multiscale model not only captures large scale features accurately, but also reflects kinetic interactions between the large and small scale of the incompressible flow of a linear viscoelastic fluid.

• 동력기계공학회지
• /
• 제15권1호
• /
• pp.64-71
• /
• 2011

The Tension Leg Platform(TLP) is restrained from oscillating vertically by tethers(or tendons), which are vertical anchor lines tensioned by the platform buoyancy larger than the platform weight. Thus a TLP is a compliant structure which allows lateral movements of surge, sway, and yaw but restrains heave, pitch, roll. In this paper, the motions of a TLP in current and waves were investigated. Hydrodynamic forces and wave exciting forces acting on the TLP were evaluated using the three dimensional source distribution method. The motion responses and tension variations of the TLP were analyzed in the case of including current or not including one in regular waves and effects of current on the TLP were investigated.

• 동력기계공학회지
• /
• 제20권4호
• /
• pp.26-31
• /
• 2016

The implementation of chirplet transform to locate axially aligned defects in pipes has been investigated. The results are obtained from experiments performed on a carbon steel pipe using magnetostrictive sensors. Chirplet transform is applied to the reflected signal to separate the individual modes from dispersive and multimodal waveform. The separated modes are used to calculate reflection coefficients which would be used to characterize defects. It is found that the reflection from a defect consists of the wave pulses with gradually decaying amplitudes. Also the results show that the reflection coefficient initially increases with the crack length but finally reaches an oscillating regime.

• 한국해양공학회지
• /
• 제25권1호
• /
• pp.1-7
• /
• 2011

The radiation of water waves by a heaving truncated circular cylinder with damping plate is solved in the frame of the three-dimensional linear potential theory. The damping plate has a distinct advantage in reducing the motion response of a floating circular cylinder by increasing the added mass and the damping coefficient. Using the matched eigenfunction expansion method, the characteristics of hydrodynamic added mass and the damping coefficient are investigated with various system parameters, such as the radius and submergence depth of the damping plate. It is found that both added mass and the damping coefficient are significantly increased due to the arranged features of the larger damping plate with shallow submergence, which are positive factors as a motion reduction device of the floating offshore platform. Also the numerical results for an oscillating submerged disk show that the added mass is negative and that the damping coefficient has a peak value at resonant frequency when submergence depth is sufficiently small.

• 펄프종이기술
• /
• 제31권3호
• /
• pp.35-46
• /
• 1999

Mathematical modeling provided a systematic analysis for the dynamic behavior of stock fluid in a paper machine pressurized headbox. Dynamic responses of liquid level, sheet basis weight and hydraulic pressure were predicted from the simulation model which represents the system. A unit step and asinusoidal wave load were considered as the input forcing functions in the headbox. Results are summarized as follows : 1. The dependence of sheet basis weight on liquid level in the pressurized-headbox was non -linear. 2. Liquid level in the head-box showed first-order lag with a unit step forcing to fluid input rate ; 3 . The amplitude of wave response of liquid level was inversely proportional to the time content for the sinusoidal input changes ; 4.Sheet basis weight showed second-order oscillating underamped responses for the step input load of flow rate ; 5. The damping factor in the second-order system was a function of air-pressure in the headbox ; and, 6. Dead-time existed in the measuring process for the headbox slice pressure.

• Journal of Biosystems Engineering
• /
• 제14권2호
• /
• pp.85-93
• /
• 1989

This study was intended to develop the system which controls header height of combine automatically by means of sensing the difference between the header and the ground surface. A micro-computer was used for the controller. The sensing unit designed for the study was composed of potentiometer, oscillating link, and gage wheel. An electric-hydraulic circuit was driven by microcomputer to control header height of combine. Performance of the control system was tested by computer simulation, stationary operation of header, and traveling on the simulated ground.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2001년도 춘계학술대회논문집
• /
• pp.289-294
• /
• 2001

Three kinds of viscoelastic damper model, which has a non-linear spring as an element is studied analytically and numerically. The behavior of the damper model shows non-linear hysteresis curves which is qualitatively similar to those of real viscoelastic materials. The motion is governed by a non-linear constitutive equation and an additional equation of motion. Harmonic balance method is applied to get analytic solutions of the system. The frequency-response curves show that multiple solutions co-exist and that the jump phenomena can occur. In addition, it is shown that separate solution branch exists and that it can merge with the primary response curve. Saddle-node bifurcation sets explain the occurrences of such non-linear phenomena.