• Structural Engineering and Mechanics
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• 제68권4호
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• pp.443-457
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• 2018

In this article, a comparative study has been made to investigate the scattering behaviour of three layered structure model on torsional surface wave. For such model intermediate layer is taken as fiber reinforced composite, resting over a dry sandy Gibson substratum and underlying by different anelastic media. We consider two distinct mediums for topmost layer. In the first case, topmost layer has been taken as fluid saturated homogeneous porous layer, while in the second case the fluid saturated porous layer has been replaced by a transversely isotropic layer. Simple form expression for the secular equation of torsional surface wave has been worked out in both the cases by executing specific boundary conditions, which comprises Whittaker's function and its derivative, for imminent result that have been elaborated asymptotically. Some special cases have been constituted which are in excellent compliance with recorded literatures. For the sake of comparative study, numerical estimation and graphical illustration have been accomplished to identify the effects of the width ratio of the layers, Biot's gravity parameter, sandy parameter, porosity parameter and other heterogeneity parameters corresponding to the layers and half spaces, horizontal compressive and tensile initial stress on the phase velocity of torsional surface wave.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1991년도 추계학술발표회 논문집 지반공학에서의 컴퓨터 활용 COMPUTER UTILIZATION IN GEOTECHNICAL ENGINEERING
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• pp.235-254
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• 1991

In the analysis of seepage behavior through the porous media, unsaturated domain should be included for obtaining more accurate results. The seepage programs considering its domain have been developed and practically used widely. The programs are reviewed and two case studies are presented in this paper. The case studies are performed using PC-SEEP and obtained good results for the cases of saturated-unsaturated transient flow.

• Steel and Composite Structures
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• 제33권1호
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• pp.93-109
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• 2019

In the present study, vibration analysis of double bonded micro sandwich cylindrical shells with saturated porous core and carbon/boron nitride nanotubes (CNT/BNNT) reinforced composite face sheets under multi-physical loadings based on Cooper-Naghdi theory is investigated. The material properties of the micro structure are assumed to be temperature dependent, and each of the micro-tubes is placed on the Pasternak elastic foundations, and mechanical, moisture, thermal, electrical, and magnetic forces are effective on the structural behavior. The distributions of porous materials in three distributions such as non-linear non-symmetric, nonlinear-symmetric, and uniform are considered. The relationship including electro-magneto-hydro-thermo-mechanical loadings based on modified couple stress theory is obtained and moreover the governing equations of motion using the energy method and the Hamilton's principle are derived. Also, Navier's type solution is also used to solve the governing equations of motion. The effects of various parameters such as material length scale parameter, temperature change, various distributions of nanotube, volume fraction of nanotubes, porosity and Skempton coefficients, and geometric parameters on the natural frequency of double bonded micro sandwich cylindrical shells are investigated. Increasing the porosity and the Skempton coefficients of the core in micro sandwich cylindrical shell lead to increase the natural frequency of the structure. Cylindrical shells and porous materials in the industry of filters and separators, heat exchangers and coolers are widely used and are generally accepted today.

• 설비공학논문집
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• 제1권2호
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• pp.128-137
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• 1989

Numerical solutions for two-dimensional, steady, free convection are presented for a cylinder filled with saturated porous media. An annulus is bounded by inner wall with constant heat flux and two adiabatic horizontal walls with outer wall isothermally cooled. Governing equations are numerically solved for the range of Aspect Ratio 1 to 20, Radius Ratio, 1 to 20, and Rayleigh number, 50 to $10^4$ by Finite Difference method utilizing upwind scheme. Results are presented in terms of stream lines and isotherms, temperature distributions and local Nusselt numbers at the heated wall. Average Nusselt numbers are also presented for the comparisons.

• 한국전산구조공학회논문집
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• 제20권2호
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• pp.191-206
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• 2007

본 연구의 I부에서 유도된 포화된 다공성매체의 파동 전파속도와 감쇠에 대한 이론해를 전산코드화 하였다. 본 논문에서는 작성된 전산코드를 사용하여 파동의 전파속도와 감쇠에 미치는 외력 주파수의 영향과 재료특성치의 변화의 영향을 파악하기 위한 파라미터연구를 수행하였다. 첫 번째 형태의 파동에 대한 압축성 파동 속도는 주파수-투수성 곱이 증가함에 따라 파동속도가 하한치로부터 상한치로 변이하는 영역에서는 주파수-투수성 곱의 함수로써 변화함을 보여주었다. 또한 파동의 전파속도 변화율이 가장 클 때 감쇠값이 최대가 됨을 알 수 있었다 두 번째 형태의 파동에서 파동의 전파속도는 주파수-투수성 곱이 작은 값을 가질 때 거의 0값을 나타내며, 주파수-투수성 곱이 큰 값을 가질 때 상한값을 나타냄을 알 수 있었다.

• 한국전산구조공학회논문집
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• 제23권4호
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• pp.369-378
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• 2010

포화된 다공질매체의 수치해석에서는 일반적으로 고체영역과 유체영역을 동시에 고려한 혼합유한요소해석(Mixed Finite Element Analysis)이 쓰인다. 여기서 고체영역과 유체영역에서의 변수를 계산하기 위해서는 직접법(Direct Method) 또는 반복법(Iterative method)을 사용할 수 있으나, 각 구성물질의 상이한 물리적 특성 때문에 수치안정성을 확보하기 위해서는 대부분 스태거드 방법(Staggered method)이 제안된다. 본 논문에서는 수치안정성을 높인 스태거드 방법에서 영역 분할기법 중 하나인 FETI(Finite Element Tearing and Interconnecting)기법을 고체영역에 접목시켜 수치효율성을 증대시키는 방법이 제안되었다. 고체영역에서 라그랑지 승수와 Conjugated Gradient Method를 이용해 영역 분할이 진행되고 MPI(Message Passing Interface) 라이브러리를 사용하여 수치 효율성을 검증하였다.

• International Journal of Aeronautical and Space Sciences
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• 제2권2호
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• pp.65-72
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• 2001

This paper demonstrates an explicit-implicit, finite element analysis for linear as well as nonlinear hygrothermal stress problems. Additional features, such as moisture diffusion equation, crack element and virtual crack extension(VCE) method for evaluating J-integral are implemented in this program. The Linear Elastic Fracture Mechanics(LEFM) Theory is employed to estimate the crack driving force under the transient condition for an existing crack. Pores in materials are assumed to be saturated with moisture in the liquid form at the room temperature, which may vaporize as the temperature increases. The vaporization effects on the crack driving force are also studied. The ideal gas equation is employed to estimate the thermodynamic pressure due to vaporization at each time step after solving basic nodal values. A set of field equations governing the time dependent response of porous media are derived from balance laws based on the mixture theory. Darcy's law is assumed for the fluid flow through the porous media. Perzyna's viscoplastic model incorporating the Von-Mises yield criterion are implemented. The Green-Naghdi stress rate is used for the invariant of stress tensor under superposed rigid body motion. Isotropic elements are used for the spatial discretization and an iterative scheme based on the full Newton-Raphson method is used for solving the nonlinear governing equations.

• 지질공학
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• 제15권1호
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• pp.29-39
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• 2005

지반오염을 조사하기 위해서는 시추작업을 통하여 시료를 채취하는 방법이 일반적이지만, 실시간으로 원위치에서 다양한 오염물질들의 오염 도 변화를 체계적으로 모니터링 하는 것은 대단히 어렵다. 본 연구에서는 frequency Domain Reflectometry (FDR) 장비를 고안하여 지반의 유류오염을 파악하기 위한 유전율 측정법의 실험적 접근을 시도하였다. 구체적으로 포화 및 불포화 매질에 대한 유류 오염도 측정 및 체적함수비 (θ/sub w/)와 체적 유류비 ( θ/sub al/)의 관계에서 유전율 상수 반응에 따른 매질의 유류 오염도 등의 측정 가능성을 실내 시험을 통해 검토하였다. 뿐만 아니라 실내 칼럼 시험을 수행하여 포화 매질 내에서 유류 거동 특성을 각기 설치된 FDR 측정 센서를 이용해 모니터링하여 포화 매질의 유효공극률과 유류 잔류비를 측정하였다. 그 결과 초기 공극률 0.40으로 제작된 포화 매질의 유효공극률은 약 0.35로 공극률 대비 약 87.5% 범위내에 존재함을 알 수 있었으며, 유류 잔류비는 약 62.5% 정도로 매우 높게 나타났다.

• 한국조경학회지
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• 제28권2호
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• pp.28-38
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• 2000

The aim of this study is evaluate artificial soils which are used alone or in a blend with field soil for the greening of artificial ground. To achieve these, determination of physicochemical properties was made in four artificial media[Perlite small grain(PSG), perlite large grain(PLG), crushed porous glass+bark(AS), crushed porous glass(CPG)] used alone and/or in a blend with field soil, then evaluation of their effect on th plant growth of Ligustrum obtusifolium and Syringa vulgaris were conducted. In bulk density of root media at field capacity and the saturated hydraulic conductivity, LG and AS showed good performance. But, PLG was though to be unsuitable as artificial soil when used alone because of poor plant growth. PLG, AS, and CPG were thought to be good when it is used in a blend with field soil. But, PSG was thought to be unsuitable. In the result, PSG is recommended as artificial soil which is used alone for greening of artificial ground. PLG is recommended as artificial soil which is used in a blend with field soil. AS is recommended as artificial soil which is used alone and in a blend with field soil. Thought CPG+field soil(v/v, 1:1) might be undesirable in consideration of the chemical properties in six months after planting, it was thought to be superior to th other treatments in the plant growth. CPG can be used as artificial soil which is used in a blend with field soil. Follow-up studies are being conducted to investigate their effects on the plant growth of the other plants and the practical use of them in artificial grounds.

• 한국방재안전학회논문집
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• 제10권1호
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• pp.19-27
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• 2017

최근 도심지에서 상하수도 등의 지중매설관 노후 및 접합 불량에 따른 누수에 의해 일어나거나, 터널굴착 및 지하구조물 시공 시 부실시공 또는 관리 부실로 인한 지하수의 유입으로 지중공동이 발생하고 이로 인하여 지반침하가 빈번하게 발생하고 있다. 이에 본 연구에서는 포화-불포화 다공성 매질에 대한 지하수 변동을 예측할 수 있는 수치모델(SEEFLOW3D)을 개발하였으며 개착식 및 비개착식 굴착 시나리오를 구성하여 지반굴착에 따른 영향을 모사하였다. 또한, 개발모델의 검증을 위해 범용수치해석 프로그램(Visual MODFLOW)과 비교 분석을 수행하였다. 그 결과 평균 오차는 -3.95~5.72%이며 정규화 된 RMSE는 0.56~4.62%로 나타났다. 향후 본 연구의 개발모델은 지반굴착 공사 시 지하수 유출량을 예측하고 이에 따른 차수벽의 최적 설계 등을 위한 해석툴로 활용 가능할 것으로 기대된다.