• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1999년도 추계학술대회 논문집 - 한국공작기계학회
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• pp.405-410
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• 1999

Hydraulic pipeline between servo valve and actuator affect the dynamic characteristics of electrohydraulic servo systems in serveral ways. This paper deal with the speed control of oil hydraulic gear motor using electrohydraulic servo valve. The frequency and transient response of electrohydraulic servo valve coupled to a gear motor is anlayzed. In particular, the effect of short and long hydraulic pipelines between servo valve and gear motor is investigated. The dynamic characteristics of the speed control systems of gear motor with short pipeline is first described via frequency response experiments with small signal linearized analysis. Loner pipeline is applied distributed parameter pipeline model with consideration of frequency dependent viscous friction.

• 로봇학회논문지
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• 제14권4호
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• pp.348-356
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• 2019

The backdrivable servovalve is a desirable component for force and interaction control of hydraulic actuation systems because it provides direct force generation mechanical impedance reduction by its own inherent backdrivability. However, high parametric uncertainty and friction effects inside the hydraulic actuation system significantly degrade its advantage. To solve this problem, this letter presents a disturbance-adaptive robust internal-loop compensator (DA-RIC) to generate ideal interactive control performance from the backdrivable-servovalve-based system. The proposed control combines a robust internal-loop compensator structure (RIC) with an explicit disturbance estimator designed for asymptotic disturbance tracking, such that the controlled system provide stable and ideal dynamic behavior for impedance control, while completely compensating the disturbance effects. With the aid of a backdrivable servovalve, we show that the proposed control structure can be implemented based on a simplified nominal model, and the controller enables implementation without accurate knowledge of the target system parameters and disturbances. The performance and properties of the proposed controller are verified by simulation and experiments.

• Structural Engineering and Mechanics
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• 제46권5호
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• pp.595-613
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• 2013

A new effective model for calculation of the equivalent uniform blast load for non-uniform blast load such as close-in explosion of a one-way square and rectangle reinforced concrete slab is proposed in this paper. The model is then validated using single degree of freedom (SDOF) system with the experiments and blast tests for square slabs and rectangle slabs. Test results showed that the model is accurate in predicting the damage level on the tested RC slabs under the given explosive charge weight and stand-off distance especially for close-in blast load. The results are also compared with those obtained by conventional SDOF analysis and finite element (FE) analysis using solid elements. It is shown that the new model is more accurate than the conventional SDOF analysis and is running faster than the FE analysis.

• 해양환경안전학회지
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• 제21권1호
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• pp.72-82
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• 2015

본 논문에서는 기존의 POM(Princeton Ocean Model) WAD(Wetting and Drying) 모형을 연안역에서 조석조류의 계산에 적합하도록 개경계에서 조석조화상수를 입력하여 사용할 수 있도록 하였고, CTS(Computing Time Saving) 기법을 도입하여 계산시간을 단축할 수 있도록 개선하였다. 이와 같이 수정된 모형은 장방형 내만에 하나의 절점을 갖는 정상파에 대한 해석해 실험과 유속 및 열확산에 대한 수리모형 실험결과와 비교하여 좋은 결과를 얻었다. 그리고 간석지가 발달한 광양만의 현지해역에 이 CTS 기법을 적용하여 계산시간이 39.4% 단축되는 결과를 얻었다.

• 한국해안해양공학회지
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• 제4권4호
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• pp.261-270
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• 1992

서해안에 위치한 태안근해에서 대조기 때 유동특성 및 물질확산을 연구하기 위해서 조류, 염료운 및 온배수의 확산에 대한 현장관측, 수리실험 및 수치실험을 실시하였다. 현장관측, 수리 및 수치실험에 의한 유황은 상호간에 대체로 잘 일치하였다. 현장에서 조류는 해안선을 따라 낙조류시에는 남서방향으로, 창조류시에는 북동방향으로 탁월하게 흐르고, 대상영역내 최대유속은 WSW 방향으로 2.13㎧로 관측되었다. 현장에서 유속관측치로부터 구한 Eulerian 확산계수는 7.82$\times$$10^{5}$ $ extrm{cm}^2$/s이다. 수리모형에서 염료운의 면적으로부터 구한 확산계수는 0.18 $r^{(4}$3)/이며, 그 크기는 $10^{5}$ ~$10^{6}$$\textrm{cm}^2$/s로서 현장에서 Eulerian 확산계수와 비슷하게 나타났다. 모형실험에 의한 당 해역의 확산계수는 남해안에 위치한 진해만에서 구한 확산계수보다는 2~3 order, 동해안에 위치한 온산만에서 구한 확산계수보다는 1~2 order 크게 나타났다. 화전(1975)의 2차원 수치모델을 적용한 결과 얻어진 온배수의 확산양상은 수리실험에 의한 염료운의 확산양상과 유사하게 나타났다. 수리실험 및 수치실험 결과에 의하면, 태안해역의 물질확산은 창조류 때보다 낙조류 때 탁월하게 일어났다.다.

• 한국해안·해양공학회논문집
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• 제24권1호
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• pp.36-47
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• 2012

본 연구에서는 단주기파랑의 저감을 위해 기설의 직선배치된 방파제와 직사각형항만의 개구부에 기존의 연구에서 제안된 공진장치를 부착하여 3차원수리모형실험과 수치해석으로부터 공진장치의 제어능을 검토하였다. 수치 해석에 있어서는 연직선 Green함수에 기초한 특이점분포법의 선형해석법과 3D-NIT모델에 의한 강비선형해석법을 적용하여 수리실험결과와 수치해석결과의 비교 분석으로부터 본 수치해석법의 타당성을 검증하였다. 또한, 공진장치가 부착되지 않은 경우와 대비 검토하여 단주기파랑의 제어에 대한 공진장치의 제어능을 다각도로 검토하여 그의 유효성을 충분히 확인할 수 있었다.

• Nuclear Engineering and Technology
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• 제47권5호
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• pp.633-645
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• 2015

In order to analyze the mechanical properties of two-way different configurations of prestressed concrete members subjected to axial loading, a finite element model based on the nuclear power plant containments is demonstrated. This model takes into account the influences of different principal stress directions, the uniaxial or biaxial loading, and biaxial loading ratio. The displacement-controlled load is applied to obtain the stress estrain response. The simulated results indicate that the differences of principal stress axes have great effects on the stress-strain response under uniaxial loading. When the specimens are subjected to biaxial loading, the change trend of stress with the increase of loading ratio is obviously different along different layout directions. In addition, correlation experiments and finite element analyses were conducted to verify the validity and reliability of the analysis in this study.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권1호
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• pp.530-541
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• 2019

To improve our current understanding of tsunami-like solitary waves interacting with a row of vertical slotted piles on a sloping beach, a 3D numerical wave tank based on the CFD tool $OpenFOAM^{(R)}$ was developed in this study. The Navier-Stokes equations were employed to solve the two-phase incompressible flow, combining with an improved VOF method to track the free surface and a LES model to resolve the turbulence. The numerical model was firstly validated by our laboratory measurements of wave, flow and dynamic pressure around both a row of piles and a single pile on a slope subjected to solitary waves. Subsequently, a series of numerical experiments were conducted to analyze the breaking wave force in view of varying incident wave heights, offshore water depths, spaces between adjacent piles and beach slopes. Finally, a slamming coefficient was discussed to account for the breaking wave force impacting on the piles.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2005년도 학술발표회(1)
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• pp.590-591
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• 2005

Hydrodynamic pressure fluctuations and their roles on the design of hydraulic structures has been the subject of many investigations. The studies showed that turbulent pressure fluctuations may cause serious damages to hydraulic structures. In case of high velocity flows, separation of flow from the boundary also causes the local pressure to drop and as a result, the resultant pressure fluctuations may trigger cavitation. Sever hydrodynamic pressures are also associated with the vibration of structures. Therefore, in this work, experiments were performed to determine the intensity of pressure fluctuations and their distribution along the bed of a ski-jump flip bucket. Experiments were completed on a physical model at the Institution of Water Research of Iran. The results consist of the statistical characteristics of pressure fluctuations, its maximum, minimum, and r.m.s values along the bed of the bucket. The spectral analysis of pressure fluctuations which is useful for the instability analysis of such structures is also provided. It is hoped that the present results will help the designer of such structures.

• Geomechanics and Engineering
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• 제17권5호
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• pp.485-496
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• 2019

Sealing of leakage in waterfront or water-retaining structures is one of the major issues in geotechnical engineering practices. With demands for biological methods as sustainable ground improvement techniques, bioclogging, defined as the reduction in hydraulic conductivity of soils caused by microbial activities, has been considered as an alternative to the chemical grout techniques for its economic advantages and eco-friendliness of microbial by-products. This study investigated the feasibility of bioaugmentation and biostimulation methods to induce fermentation-based bioclogging effect in coarse sands. In the bioaugmentation experiments, effects of various parameters and conditions, including grain size, pH, and biogenic gas generation, on hydraulic conductivity reduction were examined through a series of column experiments while Leuconostoc mesenteroides, which produce an insoluble biopolymer called dextran, was used as the model bacteria. The column test results demonstrate that the accumulation of bacterial biopolymer can readily reduce the hydraulic conductivity by three-to-four orders of magnitudes or by 99.9-99.99% in well-controlled environments. In the biostimulation experiments, two inoculums of indigenous soil bacteria sampled from waterfront embankments were prepared and their bioclogging efficiency was examined. With one inoculum containing species capable of fermentation and biopolymer production, the hydraulic conductivity reduction by two orders of magnitude was achieved, however, no clogging was found with the other inoculum. This implies that presence of indigenous species capable of biopolymer production and their population, if any, play a key role in causing bioclogging, because of competition with other indigenous bacteria. The presented results provide fundamental insights into the bacterial biopolymer formation mechanism, its effect on soil permeability, and potential of engineering bacterial clogging in subsurface.