• International Journal of Naval Architecture and Ocean Engineering
• /
• 제13권1호
• /
• pp.86-101
• /
• 2021

This study examined the effects of buoy shape and Nonlinear Froude-Krylov force (NFK) on a heaving-buoy-type Wave Energy Converter (WEC). Based on the Maclaurin expansion, the theoretical solutions of the NFK were derived for three different buoy shapes; hemispheric buoy, circular vertical cylinder, and truncated conical cylinder. A hydraulic power take-off system was adopted, and the latching control strategy was applied to maximize the extracted power from the WEC. The nonlinear effects of the Froude-Krylov force and restoring force on the heaving point absorber were investigated by comparing the heave Response Amplitude Operator (RAO) and time-averaged power extraction. The results showed that the conventional linear analyses were overestimated by up to 50% under the high amplitude wave condition. The latching control strategy was the most effective when peak wave period of regular or irregular wave was 0.4-0.45 times the heave natural period of the buoy.

• 한국지반공학회논문집
• /
• 제33권3호
• /
• pp.49-62
• /
• 2017

지반의 동결-융해 과정에 의한 지반구조물의 거동 특성을 이해하기 위해서는 지반내 간극수의 상변화와 지반과 구조물의 상호작용에 대한 이해가 필요하다. 본 연구에서는 모듈러 도로시스템의 동결융해의 영향에 대한 수치해석적 연구를 수행하였다. Neumann의 동결-융해 이론식을 이용하여 기본 지반 물성치와 지중과 지표면의 온도조건에 대한 동결심도와 히빙량을 예측할 수 있으나, 지반의 완전포화 및 완전동결의 제한된 경우에만 적용할 수 있다. 동결지수에 따른 모듈러 도로시스템의 수치해석은 다양한 지반조건과 지하수위에 대하여 수행되었다. 동결 히빙량은 화강풍화토이나 모래지반에 비하여 실트질 지반에서 매우 크게 발생하였으며, 지하수위의 저하는 동결 히빙량을 감소시켰다. 실트질 지반에 설치된 도로시스템의 온도이력에 대한 수치해석은 지표면의 동결-융해 과정을 거치면서 지표면에 잔류히빙을 예측하였다. 이는 지반의 강성과 지지력을 급격하게 감소시켜 모듈화 도로시스템의 안정성과 사용성을 저해할 수 있다. 다만, 화강풍화토와 모래지반의 경우는 잔류 히빙량은 미비한 것으로 나타났다. 모듈러 도로시스템은 기존 도로포장 시스템과 달리 지지구조 상부에 설치된 포장 구조물이므로, 포장 구조물의 균등 연직변위와 부등 변형에 대한 엄격한 기준이 적용되어야 할 것으로 사료된다.

• 한국도로학회논문집
• /
• 제12권2호
• /
• pp.71-79
• /
• 2010

겨울에는 시베리아기단의 영향으로 한랭 건조한 대륙성 고기압의 영향을 받아 춥고 건조하여 1월 평균기온이 $-6{\sim}-7^{\circ}C$의 영하의 온도로 낮아져 지반동결시 수분이동으로 동상현상이 발생하여 도로의 불균형 동결팽창을 초래하며, 결국 포장체를 파손시킨다. 동상발생시 토립자는 모관력에 의해 지하수를 흡수하여 아이스렌즈를 형성하며, 이 모관 흡수력은 토립자의 크기에 영향을 받는다. 도로는 다양한 재료와 단면으로 구성된 구조물이기 때문에 환경성과 재료 물성뿐만 아니라 포장체 각 층의 구조적 적정성 또는 지지력을 파악하는 것이 무엇보다 중요하다. 현재 기존 동상방지층 설계법에 따르면, 동상방지층은 포장체의 구조적 적정성과는 무관하게 온도 조건에 따른 동결깊이에 따라 일률적으로 결정되고 있다. 이러한 동결깊이를 포장구조설계에 적용함으로써 포장의 과다설계 우려가 있다. 따라서 본 논문에서는 도로 동상방지층의 효용성 검증 및 설치기준 확립을 위해 실내동결시스템을 활용하여 도로 노상토의 동상 특성에 대한 민감성을 판별, 도로건설 현장 노상토에 대한 역학적 특성과 실내 동결 시험을 수행하였으며, 외부 동결온도의 지속 조건에 대한 시료의 온도변화, 동상팽창압, 동상팽창량, 부동수분 등의 결과값을 통하여 동결 과정에 따른 지반공학적 특성을 평가하였다.

• 건축사
• /
• 통권607호
• /
• pp.138-155
• /
• 2019

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2000년도 봄 학술발표회 논문집
• /
• pp.548-555
• /
• 2000

It was investigated whether the waste polyethylene chips can be recycled as construction materials in geotechnical engineering field. The standard Proctor test, the hydraulic conductivity test, the large box direct shear test, the thermal conductivity test, the frost heaving test and the time domain reflectometry test were performed on weathered granite soil mixed with variable amount of the waste polyethylene chips. The experimental results showed that the hydraulic conductivity and the shear strength of weathered granite soil increase with increasing the amount of the waste polyethylene chips. On the other hand, the thermal conductivity, the amount of frost heaving and the unfrozen water contents of weathered granite soil decrease with increasing the amount of the waste polyethylene chips.

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 1996년도 가을 학술발표회 논문집
• /
• pp.89-94
• /
• 1996

The use of shield is increasing day by day, because it's method is advantageous tunneling method to soft and collapsible ground. In case of analyzing shield tunnel by FEM, short term behavior of ground by initial heaving and tail void closure and long terms of it because of consolidation by changes of pore pressures in clay must be considered. In this paper, the shield tunneling construction stages was analyzed from 2 dimensional elasto - viscoplastic finite element program used Mohr - Coulomb yield criterion but not considered the changes of pore pressures. The object of investigation was N - 2 Tunnel. Since the good results of analysis compared to the measured behavior of ground for heaving, tail void closure and liner installation, this results can be applied to design and construction of shield tunneling for the subways, sewage lines etc.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 2001년도 ICCAS
• /
• pp.166.3-166
• /
• 2001

This paper presents a modeling and control method of active suspension system with full-car model by using H$\infty$ control theory. The full-car model has seven degree of freedom including heaving, pitching and rolling motions. As the control method, H$\infty$ controller is designed so as to guarantee the robustness of closed loop system under the presence of uncertainties and disturbances. Active system with H$\infty$ controller can reduce the accelerations of the car-body in the heaving, pitching and rolling directions. The effectiveness of the controller is proved through simulation results in both time and frequency domains.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 1995년도 Proceedings of the Korea Automation Control Conference, 10th (KACC); Seoul, Korea; 23-25 Oct. 1995
• /
• pp.162-165
• /
• 1995

For an accurate on-line measurement of the ship's attitude the paper develops an intelligent sensing system which uses one servo-type accelerometer and two servo-type inclinometers appropriately located on the ship. By considering the dynamics of the servo-controlled rigid pendulums of the inclinometers, linear equations for the rolling and pitching of the ship are derived separately from each other. Moreover, one accelerometer is used for extracting the heaving signal. Through the introduction of linear dynamic models and the linear observation equations for the heaving, rolling and pitching, the on-line measurement of the three signals can be reduced to the state estimation of the linear dynamic systems. A bank of Kalman filters is adaptively used to achieve the on-line accurate state estimation and to overcome changes in parameters in the linear dynamic models.

• 한국해양공학회지
• /
• 제31권1호
• /
• pp.1-7
• /
• 2017

There are two wave modes induced by an oscillating body on the free surface of a two-layer fluid: the barotropic and baroclinic modes. To investigate the generated waves composed of two modes, a radiation problem involving a heaving rectangular body was solved in a numerical wave tank. A new artificial damping zone scheme was developed and applied in the frequency-domain analysis. The performance of this damping scheme was compared with given radiation boundary conditions for various conditions. The added mass and radiation damping coefficients for the heaving rectangular body were also calculated for various fluid-density ratios.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2003년도 추계학술대회
• /
• pp.950-955
• /
• 2003

The fluid propulsion mechanism of two oscillating flat plates is studied numerically using a discrete vortex method. Presently, the flat plates are assumed to be rigid. To analyze the closely coupled aerodynamic interference between the flat plates, a core addition scheme and a vortex core model are combined together. A calculated wake pattern for a flat plate in heaving oscillation motion is compared with the flow visualization. The effect of wake shapes on the aerodynamic characteristics of the flat plate in pitching oscillation is investigated. The velocity profiles behind the flat plates in pitching oscillations are plotted to investigate the possible thrust generation mechanism.