• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 춘계학술대회 논문집
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• pp.79-82
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• 2003

An aquaculture system for feeding the caged fishes in the open water is suggested for ocean application. Survival and operation conditions are defined at the conceptual design. Wave and current drag forces are discussed to determine the proper dimension of the aquaculture system and the related mooring system. Second order wave drift force at the survival condition is the dominant force, which be reduced by minimizing the superstructure open to the surface. Automation in feeding, sorting, cleaning is introduced to use the ongoing technology for quality product. The suggested system has advantage compared to onshore culturing, but not to shallow water culturing system. There is room for real application in future by the countries, such as Korea and Japan, which are in short of fish supply and have willingness to venture towards the ocean aquaculture.

• 비파괴검사학회지
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• 제12권4호
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• pp.26-31
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• 1993

In this paper, the axial force of high tension bolt is measured by using ultrasonic wave. In the case of the different materials the conclusion obtained are as follows : (1) The relation of the material quality of each high tension bolt and form(diameter or section area), and yield axial force can be observed. (2) As 0.1 is devided by the apparent elongation the measurement accuracy of high tension bolt can be achived. Also, it is founded that the Joint axial force of high tension bolt is determined by the yield force.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.1026-1029
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• 2003

There are always some errors in force sensing of multi-axis force sensors that aggravate sensor performance. Error sources may be classified mainly in two groups. One is structural error due to inaccuracy of sensor body, and the other is error due to noise signals existing in the sensed information. This paper presents a brief review about the principle of multi-axis force sensors, and then a method that can reduce the effect of noise signals. The method is to read digital signals in computer instead of analog voltage signals. We can eliminate the bad effect of electromagnetic waves emitted from computer and of 60 Hz noise emitted from AC source by the proposed method. The proposed method is investigated through experimental demonstration. The experimental results show the proposed method improves the sensor performance significantly.

• 한국해안·해양공학회논문집
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• 제27권5호
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• pp.315-323
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• 2015

이상 기후현상으로 인해 폭풍의 강도가 커지고, 지속시간 또한 길어지고 있어 연안 피해가 점차 대규모화 되고 있다. 이러한 변화에 대응하기 위하여 기존 방파제에 대한 평가기준과 신설 방파제의 설계기준이 강화되고 있다. 최근 케이슨식 방파제의 구조적 안정성을 향상시키기 위하여 개별 케이슨이 독립적으로 파에 저항하도록 하였던 방파제 케이슨을 서로 인터로킹시키는 방안이 관심을 받고 있다. 이는 각각의 케이슨에 작용하는 힘을 분산시켜 이상파랑이 발생할 경우에도 최대파력이 저감되어 방파제의 안정성을 확보할 수 있도록 한 것이다. 본 연구에서는 케이블을 이용하여 케이슨 상부를 방파제 기준선방향으로 인터로킹시켰을 때의 파력의 분산특성에 대해서 분석하였다. 수치계산의 효율을 위해 지반과 연결 케이블은 선형 스프링으로 모형화하고 케이슨은 강체로 가정한 정적 선형모델을 개발하였다. 수치해석 결과, 입사각이 커질수록 케이블을 통하여 전달되는 파력비가 높아지고, 인터로킹 케이블의 강성이 클수록 전달 파력비가 증대되어 파력분산 효과가 높아지는 특성을 확인할 수 있었다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제5권4호
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• pp.513-528
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• 2013

A floating Oscillating Water Column (OWC) wave energy converter, a Backward Bent Duct Buoy (BBDB), was simulated using a state-of-the-art, two-dimensional, fully-nonlinear Numerical Wave Tank (NWT) technique. The hydrodynamic performance of the floating OWC device was evaluated in the time domain. The acceleration potential method, with a full-updated kernel matrix calculation associated with a mode decomposition scheme, was implemented to obtain accurate estimates of the hydrodynamic force and displacement of a freely floating BBDB. The developed NWT was based on the potential theory and the boundary element method with constant panels on the boundaries. The mixed Eulerian-Lagrangian (MEL) approach was employed to capture the nonlinear free surfaces inside the chamber that interacted with a pneumatic pressure, induced by the time-varying airflow velocity at the air duct. A special viscous damping was applied to the chamber free surface to represent the viscous energy loss due to the BBDB's shape and motions. The viscous damping coefficient was properly selected using a comparison of the experimental data. The calculated surface elevation, inside and outside the chamber, with a tuned viscous damping correlated reasonably well with the experimental data for various incident wave conditions. The conservation of the total wave energy in the computational domain was confirmed over the entire range of wave frequencies.

• 한국압력기기공학회 논문집
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• 제13권1호
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• pp.54-60
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• 2017

When a sudden rupture occurs in high energy lines, ejection of inner fluid with high temperature and pressure causes blast wave as well as thrust forces on the ruptured pipe itself. The present study is to examine pipe whip behaviors and blast wave phenomena under postulated pipe break conditions. In this context, typical numerical models were generated by taking a MSL (Main Steam Line) piping, a steam generator and containment building. Subsequently, numerical analyses were carried out by changing break locations; one is pipe whip analyses to assess displacements and stresses of the broken pipe due to the thrust force. The other is blast wave analyses to evaluate the broken pipe due to the blast wave by considering the pipe whip. As a result, the stress value of the steam generator increased by about 7~21% and von Mises stress of steam generator outlet nozzle exceeded the yield strength of the material. In the displacement results, rapid movement of pipe occurred at 0.1 sec due to the blast wave, and the maximum displacement increased by about 2~9%.

• Smart Structures and Systems
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• 제18권2호
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• pp.335-354
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• 2016

This contribution presents an extended one-dimensional theory for piezoelectric beam-type structures with non-ideal electrodes. For these types of electrodes the equipotential area condition is not satisfied. The main motivation of our research is originated from passive vibration control: when an elastic structure is covered by several piezoelectric patches that are linked via resistances and inductances, vibrational energy is efficiently dissipated if the electric network is properly designed. Assuming infinitely small piezoelectric patches that are connected by an infinite number of electrical, in particular resistive and inductive elements, one obtains the Telegrapher's equation for the voltage across the piezoelectric transducer. Embedding this outcome into the framework of Bernoulli-Euler, the final equations are coupled to the wave equations for the longitudinal motion of a bar and to the partial differential equations for the lateral motion of the beam. We present results for the wave propagation of a longitudinal bar for several types of electrode properties. The frequency spectra are computed (phase angle, wave number, wave speed), which point out the effect of resistive and inductive electrodes on wave characteristics. Our results show that electrical damping due to the resistivity of the electrodes is different from internal (=strain velocity dependent) or external (=velocity dependent) mechanical damping. Finally, results are presented, when the structure is excited by a harmonic single force, yielding that resistive-inductive electrodes are suitable candidates for passive vibration control that might be of great interest for practical applications in the future.

• 대한기계학회논문집
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• 제13권4호
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• pp.708-716
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• 1989

본 연구의 목적은 고속도 카메라로 촬영된 순간사진들로부터 액주면의 파장, 진폭, 파의 진행속도 및 교란의 성장속도 등을 측정하여 액주의 분열에 미치는 기류 및 액량의 효과를 구하였고, 또 이것을 선행 연구자들의 이론 및 실험과 비교분석하여 액주의 분열 기구를 밝히는 데 있다.

• 한국해안·해양공학회논문집
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• 제22권1호
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• pp.10-17
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• 2010

투과성 이중 반원통 구조물과 경사 입사파간의 상호작용문제를 선형포텐셜 이론을 사용하여 살펴보았다. 투과성 이중 반원통 구조물은 바닥에 고정된 동심원상으로 배열된 2개의 원통 구조물로 이루어지며 각 원통 구조물의 전면은 일정한 공극율을 갖는 투과벽으로 후면은 투명한 벽으로 구성된다. 전면 투과벽의 공극율과 간격 그리고 파랑특성(주파수, 입사각)을 변화시키면서 파랑하중과 처올림 파형 그리고 파 차단성능을 살펴보았다. 파 차단 성능의 척도로서 차단영역내의 평균제곱 변위의 제곱근(R.M.S.)을 사용하였다. 투과성 반원통 구조물은 불투과성 구조물과 비교하여 차단영역내의 파도응답을 감소시키며 구조물에 작용하는 파랑하중을 크게 줄여준다. 특히 이중 구조물은 고주파주 영역에서 단일 구조물보다 파를 차단하는데 효과적이다.

• 대한기계학회논문집A
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• 제35권1호
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• pp.115-120
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• 2011

본 논문에서는 해양 풍력발전기를 해상 크레인으로 리프팅하기 위해 두 개의 탄성 붐을 가진 해상 크레인을 모델링 하고 동적 거동을 시뮬레이션 하였다. 운동 방정식은 강체와 탄성체가 포함된 다물체계 동역학을 기반으로 구성하였다. 외력으로는 유체정역학 힘, 규칙파에 의한 유체동역학 힘, 와이어로프의 장력, 계류력, 그리고 중력이 고려되었다. 두 개의 탄성 붐을 사용한 시뮬레이션 결과는 탄성 붐 한 개를 사용한 경우와 비교하여 모델의 타당성을 검증하였다. 5-MW(megawatt)급 해양 풍력 발전기를 해상 크레인이 리프팅하는 경우에 대해 동적 거동을 시뮬레이션하고 그 결과를 분석하였다.