• Geomechanics and Engineering
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• 제21권2호
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• pp.165-170
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• 2020

The groundwater during tunnel excavation not only affects the stability of the tunnel and constructability but also causes the subsidence of the upper ground due to the lowering of groundwater. Generally, the cutoff grouting is applied as a countermeasure to reduce the groundwater inflow during tunnel excavation, and the cutoff grouting is often applied in the range of plastic zone around the tunnel. However, grouting in the plastic zone is only appropriate for ground reinforcement purposes, and guidelines for the application range of cutoff grouting and the targeted permeability coefficient of the grouting zone are required. In this study, the relationship between groundwater inflow into tunnel and application range of cutoff grouting and permeability coefficient is proposed and compared with numerical analysis results. It was found that grouting with tunnel radius thickness is appropriate to reduce the groundwater inflows effectively. More than 90% reduction in groundwater inflow can be achieved when the annular area of the tunnel radius thickness is grouted with a permeability reduction ratio of 1/50~1/200.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2984-2988
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• 2008

Numerical analyses are carried out in order to understand complex thermal characteristics of a gas turbine combustor liner such as combustion gas temperatures, wall temperatures and heat transfer distributions. As results, The maximum internal and external heat transfer is $2218W/m^2K$ and $2358W/m^2K$, respectively. The combustion gas temperatures range is 673K to 1760K. A range of temperature on TBC is 676K to 1382K. Lastly, temperature range on outer surface of combustion liner cooled by compressed air is 676K to 1188K.

• ETRI Journal
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• 제40권6호
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• pp.794-801
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• 2018

This paper proposes a novel graphene-based optical microelectromechanical systems MEMS accelerometer that is dependent on the intensity modulation and optical properties of graphene. The designed sensing system includes a multilayer graphene finger, a laser diode (LD) light source, a photodiode, and integrated optical waveguides. The proposed accelerometer provides several advantages, such as negligible cross-axis sensitivity, appropriate linearity behavior in the operation range, a relatively broad measurement range, and a significantly wider bandwidth when compared with other important contributions in the literature. Furthermore, the functional characteristics of the proposed device are designed analytically, and are then confirmed using numerical methods. Based on the simulation results, the functional characteristics are as follows: a mechanical sensitivity of 1,019 nm/g, an optical sensitivity of 145.7 %/g, a resonance frequency of 15,553 Hz, a bandwidth of 7 kHz, and a measurement range of ${\pm}10g$. Owing to the obtained functional characteristics, the proposed device is suitable for several applications in which high sensitivity and wide bandwidth are required simultaneously.

• 한국해안·해양공학회논문집
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• 제21권1호
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• pp.45-53
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• 2009

RNG $k-{\varepsilon}$ 난류모형이 포함된 3차원 동수역학 수치모형(FLOW-$3D^{(R)}$)을 사용하여 수조 수치실험을 통한 항력계수 산정 가능성을 검토하였다. 물리적 실험으로 항력계수가 알려져 있는 말뚝구조물에 대하여, 사각형 말뚝구조물의 수치해에 의한 항력계수값이 $1.34{\sim}1.52$로 물리적 실험값인 $1.3{\sim}1.5$의 범위와 매우 유사한 결과를 보였다. 원형 말뚝구조물은 0.5$0.75{\sim}0.78$ 정도로서 물리적 실험치와 비교적 잘 일치하였다. 그리고 항력계수값이 알려지지 않은 열을 이룬 말뚝구조물의 경우 항력계수값은 구조물 간의 간섭으로 단일 구조물에 비해 항력계수가 크게 나타났으며, 각 구조물간의 거리비가 작아짐에 따라 구조물이 받는 항력계수값은 증가하는 양상을 보였다.

• 수산해양교육연구
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• 제25권1호
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• pp.1-11
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• 2013

The aim of this study was estimated the characteristics of the wave propagation by the water level conditions using a numerical modeling method at the Wando sea area. For three cases numerical simulation on the condition of incident and incoming of the deepwater design wave and the season normal wave, the spatial distribution of the incident wave at study area were investigated. And the calculated numerical modeling results were compared with measured field wave data. According to on-site wave data measured for 18 days, the range of the significant wave height and period were 0.10~1.14 m, 4.35~8.74 sec, respectively, and the maximum wave height were 0.15~1.66 m. From the results of numerical model for offshore design wave incident, the wave height attacked from Southern-East direction at this study area were over maximum 10.5 m because of rapidly change of water depth. Numerical modeling by three water level conditions of Approxmate Lowest Low Water Level(Approx. L.L.W), Mean Sea Level(M.S.L) and Approximate Highest High Water Level(Approx. H.H.W) were practiced. From the results for the case of Approx. H.W.L, variations of wave height at the back area of islands were about 1.6 m at maximum value for the case of deepwater design wave incoming. The significant wave heights of winter season were bigger than summer under normal wave condition, the incident wave height over 5.5 m decreased by shielding effect of islands. The change of maximum wave height at summer season were distinct than winter and was about 1.2 m and 0.8 m, respectively.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2021년도 학술발표회
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• pp.60-60
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• 2021

Investigating Backward-Facing Step(BFS) flow is important in that it is a representative case for separation flows in various engineering flow systems. There have been a wide range of experimental, theoretical, and numerical studies to investigate the flow characteristics over BFS, such as flow separation, reattachment length and recirculation zone. However, most of such previous studies were concentrated only on the perpendicular step angle. In this study, several numerical investigations on the flow pattern over BFS with various step angles (10° ~ 90°) and expansion ratios (1.48, 2 and 3.27) under different Reynolds numbers (5000 ~ 64000) were carried out, mainly focused on the reattachment length. The numerical simulations were performed using an open source 3D CFD software, OpenFOAM, in which the velocity profiles and turbulence intensities are calculated by RANS (Reynolds Averaged Navier-Stokes equation) and 3D LES (Large Eddy Simulation) turbulence models. Overall, it shows a good agreement between simulations and the experimental data by Ruck and Makiola (1993). In comparison with the results obtained from RANS and 3D LES, it was shown that 3D LES model can capture much better and more details on the velocity profiles, turbulence intensities, and reattachment length behind the step for relatively low Reynolds number(Re < 11000) cases. However, the simulation results by both of RANS and 3D LES showed very good agreement with the experimental data for the high Reynolds number cases(Re > 11000). For Re > 11000, the reattachment length is no longer dependent on the Reynolds number, and it tends to be nearly constant for the step angles larger than 30°.) Based on the calibrated and validated numerical simulations, several additional numerical simulations were also conducted with higher Reynolds number and another expansion ratio which were not considered in the experiments by Ruck and Makiola (1993).

• Smart Structures and Systems
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• 제14권6호
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• pp.1131-1150
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• 2014

One of the issues in extending the range of applicable problems of real-time hybrid simulation is the computation speed of the simulator when large-scale computational models with a large number of DOF are used. In this study, functionality of real-time dynamic simulation of MDOF systems is achieved by creating a logic circuit that performs the step-by-step numerical time integration of the equations of motion of the system. The designed logic circuit can be implemented to an FPGA-based system; FPGA (Field Programmable Gate Array) allows large-scale parallel computing by implementing a number of arithmetic operators within the device. The operator splitting method is used as the numerical time integration scheme. The logic circuit consists of blocks of circuits that perform numerical arithmetic operations that appear in the integration scheme, including addition and multiplication of floating-point numbers, registers to store the intermediate data, and data busses connecting these elements to transmit various information including the floating-point numerical data among them. Case study on several types of linear and nonlinear MDOF system models shows that use of resource sharing in logic synthesis is crucial for effective application of FPGA to real-time dynamic simulation of structural response with time step interval of 1 ms.

• 수산해양기술연구
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• 제35권3호
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• pp.335-342
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• 1999

The purpose of present research is to develop and efficient numerical method for the calculation of potential flow and predict the wave-making resistance for the application to ship design of tuna purse seiner. Havelock was considered the wave resistance of a post extending vertically downwards through the water from the surface, its section by a horizontal plane being the same at all depths and having its breadth small compared with its length. This enables us to elucidate certain points of interest in ship resistance. However, the ship has not infinite draft. So, the problem which is investigated ind detail in this paper is the wave resistance of a mathematical quadratic model in a uniform stream. The paper deals with the numerical calculation of potential flow around the series 60 with forward velocity by the new slender ship theory. This new slender ship theory is based on the asymptotic expression of the Kelvin-source, distributed over the small matrix at each transverse section so as to satisfy the approximate hull boundary condition due to the assumption of slender body. The numerical results using the panel shift method and finite difference method are compared with the experimental results for wigley mono hull. There are no differences in the wave resistance. However, it costs much time to compute not only wave resistance but also wave pattern over some range of Froude numbers. More improvements are strongly desired in the numerical procedure.

• 대한기계학회논문집B
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• 제24권11호
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• pp.1513-1522
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• 2000

In this study, the burning velocities of LFG and LFG mixed fuels have been numerically determined. C3 reaction mechanism involving 92 species and 621 reactions was adopted in the calculation. The computed burning velocities using C3 mechanism show good agreements with experimental data. Based on numerical results, the maximum burning velocities of LFG and LFG mixed fuels were correlated as a function of CH$_4$ and LFG component percentage at stoichiometric conditions. In addition, the correlations of burning velocities of LFG and LFG mixed fuels were obtained over a wide range of the equivalence ratio. The numerical results are well agreed with the burning velocity correlations. The burning velocity correlations for LFG and LFG mixed fuels suggested in this study can be applied to the practical utilization of LFG.

• 한국환경과학회지
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• 제22권8호
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• pp.1029-1041
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• 2013

In this study, eight episode days of high-concentration $PM_{10}$ occurrences in the Gimhae region between 2006 and 2011 were analyzed. Most of them appeared in winter and the highest concentration was observed around 12 LST. Furthermore, the wind direction, wind velocity, and temperature elements were compared with observed values to verify the WRF numerical simulation results used in this study, and they simulated well in accordance with the trend of the observed values. The wind was generally weak in the high-concentration episode days that were chosen through surface weather chart and the numerical simulation results for wind field, and the air pollutants were congested due to the effects of the resulting local winds, thereby causing a high concentration of air pollutants. Furthermore, the HYSPLIT model was performed with the WRF numerical simulation results as input data. As a result, they originated from China and flowed into Gimhae in all eight days, and the lowest concentration appeared on the days when recirculation occurred.