• Smart Structures and Systems
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• v.21 no.5
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• pp.623-635
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• 2018

In order to study the mechanical behavior of shield tunnel segments during assembly stage, the in-situ tests and FDM numerical simulation were conducted based on the Foguan Shiziyang Tunnel with large cross-section. Analysis for the load state of the assembling segments in different assembly steps as well as the investigation for the changing of inner forces and longitudinal stress of segments with assembling steps were carried out in this paper. By comparing the tested results with the simulated results, the conclusions and suggestions could be drawn as follows: (1) It is the most significant for the effects on axial force and bending moment caused by the assembly of adjacent segment, followed by the insertion of key segment while the effects in the other assembly steps are relative smaller. With the increasing value of axial force, the negative bending moment turns into positive and remains increasing in most monitored sections, while the bending moment of segment B1and B6 are negative and keeping increasing; (2) The closer the monitored section to the adjacent segments or the key segment, the more significant the internal forces response, and the monitored effects of key segment insertion are more obvious than that of calculation; (3) The axial forces are all in compression during assembling and the monitored values are about 1.5~1.75 times larger than the calculated values, and the monitored values of bending moment are about 2 times the numerical calculation. The bending moment is more sensitive to the segments assembly process compared with axial force, and it will result in the large bending moment of segments during assembling when the construction parameters are not suitable or the assembly error is too large. However, the internal forces in assembly stage are less than those in normal service stage; (4) The distribution of longitudinal stress has strong influence on the changing of the internal forces. The segment side surface and intrados in the middle of two adjacent jacks are the crack-sensitive positions in the early assembly stage, and subsequently segment corners far away from the jacks become the crack-sensitive parts either.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.2
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• pp.299-305
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• 2008

This present study has dealt with the natural convection of water in a rectangular vessel which has cooling point at the center of itself with numerically. The finite difference method (FDM) is presented for the two-dimensional computer simulation of water controlled by natural convection and heat conduction. According to this study, It is cleared that the overturn of density is clearly existed at the temperature of $4[^{\circ}C]$ and that was compared with experimental result. Also the change of natural convection is known from the streamlines and isotherms. Most of all. It is cleared that the overturn of natural convection is changed with time caused by the fact that the temperature and density relationship of water.

• 제어로봇시스템학회:학술대회논문집
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• 1988.10a
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• pp.370-373
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• 1988

Althouah there have been many attempts to control weld quality in resistance spot welding processes, design method for an on-line feedback controller based upon process dynamics has not been suggested. This is due to the fact that the resistance spot welding is a highly complicated process, whice involves the interaction of electrical, thermal, mechanical and metallurgical phenomena. In this paper, an optimal control method based on FDM model with shunt effect is presented, which can regulate the nugget size, at the same time minimizing the control heat input. Optimal PI gain of the controller were determined by numerical optimization. Simulation results show that, as a result of the proposed optimal control, the weld nugget can be made to approach a desired nugget size with less control heat input than that required for the conventional spot welding process in the face of the shunt effect.

• Journal of computational fluids engineering
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• v.2 no.1
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• pp.21-28
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• 1997

This paper presents a two-dimensional horizontal implicit model to general circulation in estuaries and coastal seas. The model is developed in non-orthogonal curvilinear coordinates system, using the Interpolating Matrix Method (IMM), in combination with a technique of multi-domain. In the propose model, the Saint-Venant equations are solved by a splitting-up technique, in the successive steps; convection, diffusion and wave propagation. The ability of the proposed model to deal with full scale nature is illustrated by the interpretation of a dye-tracing experiment in the Gironde estuary.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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• pp.153-160
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• 2001

피에조콘관입시험(PCPT)의 소산시험은 in-situ 상태의 압밀계수(c/sub v/)를 추정하는 방법으로 널리 이용되어왔다. 본 연구에서는 spherical cavity expansion theory 및 axisymmetric uncoupled linear consolidation equation(Gupta & Davidson, 1986)을 이용하여 과압밀점토에서의 초기과잉간극수압의 분포 및 과잉간극수압의 시간에 대한 소산현상을 해석하는 수치해석방법을 제안하여 현장시험결과 및 실내시험결과와 비교 분석하였다. ADIS (alternating direction implicit scheme)를 이용한 FDM 해석을 실시한 결과와 현장시험의 소산곡선은 잘 부합되는 것으로 나타났으며 압밀계수도 실내실험 또는 피에조콘관입 시험에 대한 추정방법으로 산출된 값과 비교적 일치하는 것으로 나타났다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.5
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• pp.1338-1346
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• 1994

The objective of this study is to investigate the effect of various parameters, such as temperature, mean current density and voltage on the performance of phosphoric acid fuel cell (PAFC) by numerical analysis. Two types of flow passages, which are Z-parallel type and Z-counter type, are evaluated to obtain the best current density and temperature distribution. Parametric studies and sensitivity analysis of the PAFC system's operation in single cell are accomplished. A steady state simulation of the entire system is developed using nonlinear ordinary differential equations. The finite difference method and trial and error procedures are used to obtain a solution.

• Geomechanics and Engineering
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• v.13 no.5
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• pp.881-892
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• 2017

Design and management of concrete slabs in concrete-faced rock-fill dams are crucial issues for stability and overall dam safety since cracks in the concrete face induced by stress, shrinkage, and deterioration can cause severe leakage from the reservoir into the dam. Especially, the increase of dam height to a certain level to enhance the storage capacity and to improve hydraulic stability can lead to undesirable deformation behavior and stress distribution in the existing dam body and in the concrete slabs. In such conditions, simulation of a concrete slab with a numerical method should involve the use of an interface element because the behavior of the concrete slab does not follow the behavior of the dam body when the dam body settles due to the increase of dam height. However, the interfacial properties between the dam body and the concrete slab have yet to be clearly defined. In this study, construction sequence of a 125 m high CFRD in South Korea is simulated with commercial FDM software. The proper interfacial properties of the concrete slab are estimated based on a comparison to monitored vertical displacement history obtained from the concrete slab. Possibility of shear strength failure under the critical condition is investigated based on the simplified model. Results present the significance of the interfacial properties of the concrete slab.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.06a
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• pp.1149-1154
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• 2005

The finite difference lattice Boltzmann method(FDLBM) is a quite recent approach for simulating fluid flow, which has been proven as a valid and efficient tool in a variety of complex flow problems. It is considered an attractive alternative to conventional FDM and FVM, because it recovers the Navier-Stokes equations and is computationally more stable, and easily parallelizable to simulate for various laminar flows and a direct simulation of aerodynamics sounds. However, the research of a numerical simulation of turbulent flow by FDLBM, which is important to analyze the structure of turbulent flow in engineering fields, is not carried out. In this research, the FDLBM built in the turbulent model is applied, and a flowfield around 2-dimensional square to validate the applied model with 2D9V is simulated. Besides, 2D computation of the cavity noise generated by flow over a cavity at a Mach number of 0.1 and a Reynolds number based on cavity depth of 5000 is calculated. The computation result is well presented a understanding of the physical phenomenon of tonal noise occurred primarily by well-jet shear layer and vortex shedding and an aeroacoustic feedback loop.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.4
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• pp.309-313
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• 2011

In this study, we proposed a novel electrode structure for the fringe field switching (FFS) mode LCD and performed a three-dimensional computer simulation to calculate the optical transmittance for the new structure. In the simulation Erickson-leslie equation and Berreman $4{\times}4$ matrix were used for obtaining the director distribution profiles of liquid crystal molecules and the electro-optical characteristics, respectively. Considering the complexity of the motional equation of the liquid crystal molecules, FDM (finite difference method) was used as a numerical method. From the results, We revealed that the light transmission of the newly designed pixel structure is expended to the edge of the pixel electrode. We also confirmed that the light transmittance increased more than 13% compared to that of the conventional electrode structure.

• Geophysics and Geophysical Exploration
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• v.12 no.2
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• pp.183-191
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• 2009

Finite difference method using not general SSG (standard staggered grid) but RSG (rotated staggered grid) was applied to simulation of elastic wave propagation. Special free surface boundary condition such as imaging method is needed in finite difference method using SSG in elastic wave propagation. But free surface boundary condition in finite difference method using RSG is easily solved with adding air layer or vacuum layer. Recently PML (Perfectly Matched layer) is widely used to eliminate artificial reflection waves from finite boundary because of its' greate efficiency. Absorbing ability of CPML (convolutional Perfectly Matched Layer) that is more efficient than that of PML and CPML that don't use splitting of wave equation that should be adapted to PML was applied to FDM using RSG in this study. Frequency absorbing characteristic and energy absorbing ability in CPML layer were investigated and CPML eliminated artificial boundary waves very effectively in FDM using RSG in being compared with that of Cerjan's absorbing method. CPML method also diminished amplitude of waves in boundary layer of solid-liquid model very well.