• 자연, 터널 그리고 지하공간
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• 제21권2호
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• pp.117-129
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• 2019

Tunnelling in urban environments is very common nowadays as large cities are expanding and transportation demands require the use of the underground space for creating extra capacity. Inevitably, any such new construction may have significant effects on existing nearby infrastructure and therefore relevant assessment of structural integrity and soil-structure interaction is required. Foundation piles can be rather sensitive to nearby tunnel construction and therefore their response needs to be evaluated carefully. Although detailed three-dimensional continuum finite element analysis can provide a wealth of information about this behaviour of piles, such analyses are generally very computationally demanding and may require a number of material and other model parameters to be properly calibrated. Therefore, relevant simplified approaches are used to provide a practical way for such an assessment. This paper presents a simple method where the pile is modelled with beam finite elements, pile-soil interaction is modelled with soil springs and tunnelling-induced displacements are introduced as an input boundary condition at the end of the soil springs. The performance of this approach is assessed through some examples of applications.

• Geomechanics and Engineering
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• 제19권3호
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• pp.229-240
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• 2019

The physical models are useful to understand the soil behaviour. Hence, these tools allow validating analytical theories and numerical data. This paper addresses the design, construction and implementation of a physical model able to simulate the soil liquefaction under different cyclic actions. The model was instrumented with a piezoelectric actuator and a set of transducers to measure the porewater pressures, displacements and accelerations of the system. The soil liquefaction was assessed in three different grain size particles of a natural sand by applying a sinusoidal signal, which incorporated three amplitudes and the fundamental frequencies of three different earthquakes occurred in Colombia. In addition, such frequencies were scaled in a micro shaking table device for 1, 50 and 80 g. Tests allowed identifying the liquefaction susceptibility at various frequency and displacement amplitude combinations. Experimental evidence validated that the liquefaction susceptibility is higher in the fine-grained sands than coarse-grained sands, and showed that the acceleration of the actuator controls the phenomena trigging in the model instead of the displacement amplitude.

• Wind and Structures
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• 제28권6호
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• pp.369-380
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• 2019

Statistical distributions are very useful in describing wind speed characteristics and in predicting wind power potential of a specified region. Although the Weibull distribution is the most popular one in wind energy literature, it does not seem to be able to perfectly fit all the investigated wind speed data in nature. Thus, many studies are still being conducted to find flexible distribution for modelling wind speed data. In this study, we propose a new Odd-Burr Rayleigh distribution for wind speed characterization. The Odd-Burr Rayleigh distribution with two shape parameters is flexible enough to model different shapes of wind speed data and thus it can be an alternative wind speed distribution for the assessment of wind energy potential. Therefore, suitability of the Odd-Burr Rayleigh distribution is investigated on real wind speed data taken from different regions in the South Africa. Numerical results of the conducted analysis confirm that the new Odd-Burr Rayleigh distribution is suitable for modelling most of the considered real wind speed cases and it also can be used for predicting wind power.

• Korean Chemical Engineering Research
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• 제60권1호
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• pp.51-61
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• 2022

Gas separation via hollow fibre membrane modules (HFMM) is deemed to be a promising technology for natural gas sweetening, particularly for lowering the level of carbon dioxide (CO₂) in natural gas, which can cause various problems during transportation and process operation. Separation performance via HFMM is affected by membrane properties, module specifications and operating conditions. In this study, a mathematical model for HFMM is developed, which can be used to assess the effects of the aforementioned variables on separation performance. Appropriate boundary conditions are imposed to resolve steady-state values of permeate variables and incorporated in the model equations via an iterative numerical procedure. The developed model is proven to be reliable via model validation against experimental data in the literature. Also, the model is capable of capturing axial variations of process variables as well as predicting key performance indicators. It can be extended to simulate a large-scale plant and identify an optimal process design and operating conditions for improved separation efficiency and reduced cost.

• Nuclear Engineering and Technology
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• 제52권12호
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• pp.2803-2811
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• 2020

With the aging of nuclear reactors, embrittlement of the reactor pressure vessel (RPV) steel, as a consequence of routine operations, is highly probable. To ensure operational integrity and safety, prediction and mitigation of compromising damage, brought on by pressurized thermal shock (PTS) following an emergency procedure, is of utmost importance. Computational fluid dynamics (CFD) codes can be employed to predict these events and have therefore been an acceptable method for such assessments. In this paper, CFD simulations of a density driven ECC state in the ROCOM facility are analyzed. Obtained numerical results are validated with the experimental measurements. Considerable attention is attributed to the boundary conditions and their influence, specifically outlet definitions, in order to determine and adequately replicate the non-active pumps in the facility. Consequent analyses focused on initial conditions as well as on the temporal discretization and inner iterations. Disparities due to different turbulent modelling approaches are investigated for standard RANS models. Based on observed trends for different cases, a definitive simulation setup has been established, results of which have been ultimately compared to the measurements.

• Geomechanics and Engineering
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• 제32권1호
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• pp.21-34
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• 2023

In order to analyze the effect of the cyclic lateral loading on the response of a pile-soil system, a full-scale single steel pile was subjected to one-way cyclic loading. The test pile was driven into a bi-layered soil consisting of a normally consolidated saturated clay overlying a silty sandy layer, the site being submerged by water up to one meter above the mudline in order to reproduce the conditions of an offshore pile foundation. The aim of this paper is to present the main results of interpretation of the cyclic lateral tests in terms of pile deflections, bending moment, and cyclic P-Y curves. From these latter an absolute secant reaction modulus E_AS,N was derived and a simple calculation model of the test single pile is proposed based on this modulus. Two applications of the proposed model are carried out, one with a 2D finite element modelling, and the second with a load transfer curves-based method.

• 지질학회지
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• 제54권6호
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• pp.615-630
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• 2018

분지 해석은 퇴적분지의 형성과 진화를 이해하기 위한 연구 분야로서 여러 종류의 지구과학 자료들을 종합적으로 분석해야 하며, 분지의 시공간적 발달을 입체적으로 구현하기 위해서는 모델링 기술이 적용된다. 분지해석과 모델링 연구를 위해 2016년 MATLAB 기반의 프로그램 BasinVis 1.0이 공개되었으며 최근에는 새로운 기능과 수정된 사용자 인터페이스를 포함한 BasinVis 2.0이 개발되었다. 이 연구에서는 BasinVis 2.0을 이용한 분지 모델링을 소개하기 위해 비엔나 분지의 남부에서 사례 연구를 수행하였다. 이 연구는 BasinVis 1.0을 이용한 비엔나 분지 중북부의 모델링 연구와 함께 앞으로 수행될 비엔나 분지 전지역의 모델링을 위한 예비 연구로서, 연구 지역의 마이오세 퇴적층과 침강 발달을 시공간적으로 구현하였다. 마이오세 초기의 후반 동안 퇴적과 침강은 북동-남서 방향의 주향이동 단층과 안행성 점완 정단층들을 따라 빠르게 나타난다. 하지만 마이오세 중기부터 후기까지 침강은 급격히 감소한다. 이는 인리형 시스템의 발달에 연관하며, 주향이동 분지의 단기간의 빠른 지구조 침강 패턴과 일치한다. 마이오세 중기의 침강은 주로 주향이동 단층을 따라서 나타나는 반면, 마이오세 중기 후반부터는 북-남 방향의 점완 정단층을 따라 저지대로 퇴적 중심지가 이동되었다. 이는 광역적 고응력장이 북동-남서 방향의 횡인장에서 동-서 방향의 인장으로 변화하는 것과 일치한다. 이 연구에서는 다양한 기능과 기법들이 사례 연구에 적용되었으며, 모델링 결과는 BasinVis 2.0이 분지 모델링 연구에 효과적으로 적용 가능함을 보여준다.

• Structural Engineering and Mechanics
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• 제65권5호
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• pp.573-585
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• 2018

This article presents strain gradient elasticity-based procedures for static bending, free vibration and buckling analyses of functionally graded rectangular micro-plates. The developed method allows consideration of smooth spatial variations of length scale parameters of strain gradient elasticity. Governing partial differential equations and boundary conditions are derived by following the variational approach and applying Hamilton's principle. Displacement field is expressed in a unified way to produce numerical results in accordance with Kirchhoff, Mindlin, and third order shear deformation theories. All material properties, including the length scale parameters, are assumed to be functions of the plate thickness coordinate in the derivations. Developed equations are solved numerically by means of differential quadrature method. Proposed procedures are verified through comparisons made to the results available in the literature for certain limiting cases. Further numerical results are provided to illustrate the effects of material and geometric parameters on bending, free vibrations, and buckling. The results generated by Kirchhoff and third order shear deformation theories are in very good agreement, whereas Mindlin plate theory slightly overestimates static deflection and underestimates natural frequency. A rise in the length scale parameter ratio, which identifies the degree of spatial variations, leads to a drop in dimensionless maximum deflection, and increases in dimensionless vibration frequency and buckling load. Size effect is shown to play a more significant role as the plate thickness becomes smaller compared to the length scale parameter. Numerical results indicate that consideration of length scale parameter variation is required for accurate modelling of graded rectangular micro-plates.

• 터널과지하공간
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• 제18권1호
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• pp.58-68
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• 2008

임하댐 비상여수로 터널 공사가 단층파쇄대가 포함된 화강암지역에 굴착되고 있는데 본 터널이 3련 터널임을 감안하여 터널이격거리, 터널막장간 이격거리를 검토하였으며 단층파쇄대가 여수로 터널의 안정성에 미치는 영향을 검토하였다. 이를 위해 여러 가지 지구물리학적 조사와 암반공학적 현장 실험을 실시하였다. 터널 막장간 이격거리는 최소 25 m 이상을 유지하면서 2터널의 선행 굴착이 적합하리라 판단되며 단층대의 영향을 받는 터널 만곡부의 3차원 수치해석결과 2터널의 천단변위 및 내공변위는 미미하며 숏크리트 최대 휨압 축응력, 숏크리트 최대전단응력, 록볼트 최대축력 등을 살펴보면 만곡부 굴착에 따른 응력집중은 미미하여 여수로 터널의 안정성에는 문제가 없는 것으로 판단되었다.

• Structural Engineering and Mechanics
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• 제32권2호
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• pp.283-300
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• 2009

The characteristic response of a structure to blast load may be divided into two distinctive phases, namely the direct blast response during which the shock wave effect and localized damage take place, and the post-blast phase whereby progressive collapse may occur. A reliable post-blast analysis depends on a sound understanding of the direct blast effect. Because of the complex loading environment and the stress wave effects, the analysis on the direct effect often necessitates a high fidelity numerical model with coupled fluid (air) and solid subdomains. In such a modelling framework, an appropriate representation of the blast load and the high nonlinearity of the material response is a key to a reliable outcome. This paper presents a series of calibration study on these two important modelling considerations in a coupled Eulerian-Lagrangian framework using a hydrocode. The calibration of the simulated blast load is carried out for both free air and internal explosions. The simulation of the extreme dynamic response of concrete components is achieved using an advanced concrete damage model in conjunction with an element erosion scheme. Validation simulations are conducted for two representative scenarios; one involves a concrete slab under internal blast, and the other with a RC column under air blast, with a particular focus on the simulation sensitivity to the mesh size and the erosion criterion.