• 한국전산구조공학회논문집
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• 제33권5호
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• pp.287-296
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• 2020

본 연구에서는 2D 조파수조를 통해 수행된 모형시험결과를 기반으로 원형실린더에 분포하는 파랑충격압력을 시간에 따라 계측하고 이를 CFD해석 결과와 비교하였다. 전산유체역학 해석을 통해 파랑충격력에 직접평가법에 관한 효용성을 확인할 수 있었고, 실험으로부터 구한 파랑충격 시계열 데이터를 그대로 원형단면을 갖는 실제 해양구조물의 부재에 적용하였다. 실린더에 분포하는 변위 및 응력의 특성과 특이점이 바뀌는 것을 확인하였고 실제 시계열을 적용하는 것이 해양구조물의 강도평가를 보다 정확하게 평가할 수 있음을 확인할 수 있었다. 또한, 선수부에 요구되는 외판의 최소선급규정에 따른 두께 경험식들을 분석하여 적용하고자 하였다. 동일한 재료 물성치를 갖는 강재에 관해 선수외판에 요구되는 구조물의 최소두께와 원형단면 부재에 요구되는 최소두께를 비교·분석하였고 이를 통해 NORSOK standard에 제시되어 있는 구조물의 손상기준을 활용하여 허용 두께치를 추정하고자 하였다. 특히 해양구조물의 갑판충격력(wave in deck)의 경우 이와 관련된 경험식이나 최소두께 요구사항들이 정립되어 있지 않기 때문에 본 연구를 통해 파랑충격력에 따라 요구되는 판재의 최소두께를 제안하고자 하였다.

• 대한토목학회논문집
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• 제26권3B호
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• pp.311-319
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• 2006

저면경계층에서 부유사와 소류사 flux를 포함하는 실제적인 표사이동에 기초한 지형변화모델(SED-FLUX)이 개발되었다. SED-FLUX는 파랑모듈, 동수역학 모듈 및 부유사농도, 순부상 flux($Q_s$)와 소류사 flux를 계산하는 표사수송 및 확산모듈을 포함하며, 소류사 flux는 파-흐름 공존장에서 검증된 van Rijn의 TRANSPOR 프로그램에 의해 평가되어진다. 저면에서 순부상 flux $Q_s$는 표사확산모듈에서 source/sink 항으로서 평가되어지며, 수심변화모듈은 수심변화량을 계산하고 시간에 따른 bed level의 변화를 계산한다. 모델의 검증을 위하여 소류사이동의 이동한계수심은 방사성 동위원소 추적자를 사용한 현장 실험자료와 파와 흐름에 의한 표사이동한계수심에 대한 몇몇 경험식과 비교되었다. 본 모델을 파에 의한 해빈 단면변화에 적용한 결과 입사파의 특성에 따른 명확한 침식과 퇴적분포를 나타내었다. 끝으로, 이안제 배후에서 파와 해빈류에 의한 수심변화를 계산한 결과 이안제의 배후에서 초기 tombolo의 형성을 보여주었다.

• International Journal of Ocean Engineering and Technology Speciallssue:Selected Papers
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• 제6권1호
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• pp.30-37
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• 2003

This paper describes vibration control of a suspended system using wave absorption method. A moving multiple-pendulum system and a moving wire-and-load system are treated. The wire-and-load system is extended to a model crane system that has a motor system to roll up and down the suspended mass like a real crane. The same program with different parameter values controls these three systems. Both numerical simulation and experiment have been conducted, and the present control method has shown to be quite effective.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.723-732
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• 2020

A theoretical calculation model for ship stern bearings with large hull deformation is established and validated theoretically and experimentally. A hull simulation model is established to calculate hull deformations corresponding to the reaction force of stern bearings under multi-factor and multi-operating conditions. The results show that in the condition of wave load, hull deformation shows randomness; the aft stern tube bearing load obeys the Gaussian distribution and its value increases significantly compared with the load under static, and the probability of aft stern tube bearing load greater than 1 is 65.7%. The influence laws and levels between hull deformation and bearing reaction force are revealed, and suggestions for ship stern bearing specifications are proffered accordingly.

• Steel and Composite Structures
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• 제31권4호
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• pp.341-359
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• 2019

Non-monolithic concrete structural connections are commonly used both in new constructions and retrofitted structures where anchors are used for connections. Often, flaws are present in anchor system due to poor workmanship and deterioration; and methods available to check the quality of the composite system afterward are very limited. In case of presence of flaw, load transfer mechanism inside the anchor system is severely disturbed, and the load carrying capacity drops drastically. This raises the question of safety of the entire structural system. The present study proposes a wave propagation technique to assess the integrity of the anchor system. A chemical anchor (embedded in concrete) composite system comprising of three materials viz., steel (anchor), polymer (adhesive) and concrete (base) is considered for carrying out the wave propagation studies. Piezoelectric transducers (PZTs) affixed to the anchor head is used for actuation and the PZTs affixed to the surrounding concrete surface of the concrete-anchor system are used for sensing the propagated wave through the anchor interface to concrete. Experimentally validated finite element model is used to investigate three types of composite chemical anchor systems. Studies on the influence of geometry, material properties of the medium and their distribution, and the flaw types on the wave signals are carried out. Temporal energy of through time domain differentiation is found as a promising technique for identifying the flaws in the multi-layered composite system. The present study shows a unique procedure for monitoring of inaccessible but crucial locations of structures by using wave signals without baseline information.

• 지구물리와물리탐사
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• 제14권4호
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• pp.305-315
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• 2011

암석시료에 대한 음파 속도측정의 정확성을 검증하고 정밀한 측정을 위한 기초적인 실험의 일환으로 아크릴과 스테인리스강 재질의 시료에 대하여 길이와 축하중을 달리하여 각각에 대해 3회씩 측정한 총 864 경우에 대하여, 시험편을 통과한 초동 주시를 측정하고 분석하였다. 축하중이 가해진 상태에서의 S-파 측정은 P-파에 비해 측정에 어려움이 있었으며 이에 따라 반복측정, 길이, 축하중에 의한 편차도 S-파가 훨씬 크게 나타났다. 또한, 재질에 따라서는 스테인레스강 시편보다는 아크릴 시편의 초동주시 편차가 약 2배 정도 양호하게 나타났으며 이는 아크릴 시험편의 경우가 트랜스 듀서와 시험편 간의 접촉 coupling이 안정적이며 또한 동일한 시간 분해능이나 유사한 전기적 잡음에 비하여 초동 주시가 길기 때문으로 판단된다. 실험결과, 아크릴 시험편과 스테인리스강 시험편의 탄성파 속도를 측정할 때는 60 ~ 90 mm 정도의 길이를 갖는 시험편을 20 kg (27.7 $N/cm^2$) ~ 30 kg (41.6 $N/cm^2$) 내외의 축하중 하에서 측정하는 것이 가장 좋으며, 스테인리스강 시험편의 S-파 속도는 길이 50 mm 이하의 시험편을 사용하여 측정해야 한다. 이러한 실험 결과는 암석 코어의 속도 측정시 시스템 지연의 측정 및 보정에 활용될 수 있을 것이다.

• Ocean Systems Engineering
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• 제6권1호
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• pp.61-97
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• 2016

This is the second of two papers on the 3D numerical modeling of nearshore hydro- and morphodynamics. In Part I, the focus was on surf and swash zone hydrodynamics in the cross-shore and longshore directions. Here, we consider nearshore processes with an emphasis on the effects of oceanic forcing and beach characteristics on sediment transport in the cross- and longshore directions, as well as on foreshore bathymetry changes. The Delft3D and XBeach models were used with four turbulence closures (viz., ${\kappa}-{\varepsilon}$, ${\kappa}-L$, ATM and H-LES) to solve the 3D Navier-Stokes equations for incompressible flow as well as the beach morphology. The sediment transport module simulates both bed load and suspended load transport of non-cohesive sediments. Twenty sets of numerical experiments combining nine control parameters under a range of bed characteristics and incident wave and tidal conditions were simulated. For each case, the general morphological response in shore-normal and shore-parallel directions was presented. Numerical results showed that the ${\kappa}-{\varepsilon}$ and H-LES closure models yield similar results that are in better agreement with existing morphodynamic observations than the results of the other turbulence models. The simulations showed that wave forcing drives a sediment circulation pattern that results in bar and berm formation. However, together with wave forcing, tides modulate the predicted nearshore sediment dynamics. The combination of tides and wave action has a notable effect on longshore suspended sediment transport fluxes, relative to wave action alone. The model's ability to predict sediment transport under propagation of obliquely incident wave conditions underscores its potential for understanding the evolution of beach morphology at field scale. For example, the results of the model confirmed that the wave characteristics have a considerable effect on the cumulative erosion/deposition, cross-shore distribution of longshore sediment transport and transport rate across and along the beach face. In addition, for the same type of oceanic forcing, the beach morphology exhibits different erosive characteristics depending on grain size (e.g., foreshore profile evolution is erosive or accretive on fine or coarse sand beaches, respectively). Decreasing wave height increases the proportion of onshore to offshore fluxes, almost reaching a neutral net balance. The sediment movement increases with wave height, which is the dominant factor controlling the beach face shape.

• 한국기계가공학회지
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• 제18권11호
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• pp.9-17
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• 2019

Interest in renewable energy is rapidly growing around the world. One of the most popular renewable energy sources is solar power, and photovoltaic (PV) systems are the most representative route for generating solar energy. However, with the growing adoption of solar power systems, the demand for land on which to install these systems has increased, which has caused environmental degradation. Recently, floating PV systems have been designed to utilize idle water surface areas of dams, rivers, and oceans. Because floating PV systems will be exposed to harsh environmental stresses, the safety of such systems should be secured before installation. In this study, the structural robustness of a floating PV system was analyzed by conducting numerical simulation to investigate whether the system can withstand harsh environmental stresses, such as wind and wave loads. Additionally, conventional wind and wave load predictions based on the design method and the simulation results were compared. The comparison revealed that the design method overestimated wind and wave loads. The total drag of the PV system was significantly overestimated by the conventional design criteria, which would increase the cost of the mooring system. The simulation offers additional advantages in terms of identifying the robustness of the floating PV system because it considers real-world environmental factors.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2001년도 전력전자학술대회 논문집
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• pp.479-482
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• 2001

This paper proposes a modified $\alpha$ conduction mode for controlling the output voltage magnitude of three-phase square-wave VSIs with an R-L load. From the viewpoint of both power capacity and switching losses, three-phase square-wave inverters are now used in most high power systems. When the square-wave VSI is driven with $\alpha$ conduction mode to control the magnitude of output voltages, interval over than half period is operated with $180^{\circ}$ conduction mode and the other interval with $120^{\circ}$ conduction mode. In $120^{\circ}$ conduction mode operation, two output terminals are connected to DC supply and the third one remains open. The potential of this open terminal will depend on the load characteristics and is unpredictable except the case of pure resistive loads. To cope this problem, we propose the modified α conduction mode.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2004년도 학술대회지
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• pp.96-101
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• 2004

When the wind blows hard, most waves are breaking in sea. Breaking waves occur, exceeding limitation of wave steepness(wave height/wave length=l/7). Because a wave of single angular frequency couldn't generate the breaking phenomena at two dimensional ocean engineering basin, the breaking wave can be generated by the superposition of waves with various angular frequencies. We research how are the particle kinematics in the breaking wave and the magnitude of the breaking wave exciting force. We compare the force in a regular wave which has same specifications(wave height, period and length) as the breaking wave. Also the experimental results of wave exciting force and particle velocity are investigated by comparison on the analytic results using the potential theory.