Cyclic Shear Behaviors of Geosynthetic-soil Interface considering Chemical Effects

Kwak, Changwon 한국방재학회 2015 한국방재학회 학술발표대회논문집 Vol.14 No.-

Geosynthetics have been widely applied in waste landfill site for reinforcement, filtration, drainage, protection, and separation. Geosynthetics inevitably contact soil particle directly, composing a geosynthetic-soil interface corresponding to external conditions. In this study, particularly, the effects of chemical aggressors on the geosynthetic-soil interface were investigated under cyclic shear loading, based on the experimental approach. The Multi-purpose Interface Apparatus (M-PIA) was newly manufactured and modified for better performance. The Disturbed State Concept (DSC) and disturbance function were introduced and employed to estimate shear stress degradation based on the experimental study, quantitatively. New disturbance functions and parameters were mathematically evaluated. Microscopic observation by Focused Ion Beam (FIB) was utilized to clarify the reason of the variation of interface damage subjected to the chemical conditions. As a result, the variation of the cyclic shear behavior at the geosynthetic-soil interface was due to the different damage patterns of the soil particle surface. Furthermore, the numerical back-prediction based on the DSC parametric study of the cyclic shear stress-strain behavior was performed and verified the accuracy and applicability of the DSC parameters. Consequently, a general methodology to estimate the cyclic shear stress degradation of geosynthetic-soil interface considering chemical effects has been established and verified.

주행차량의 수평하중을 고려한 층 경계면의 인장변형률 영향계수 개발

서주원(Seo Joo Won),최준성(Choi Jun Seong),김수일(Kim Soo Il) 대한토목학회 2006 대한토목학회논문집 D Vol.26 No.6D

본 연구에서는 실제 주행차량의 수평하중이 다양한 층 경계면 마찰계수 상태의 포장구조체에 미치는 영향을 고찰하기 위해 수평하중을 고려한 포장구조해석 모델링을 구축하였다. 기존 해석프로그램의 경계층 평가분석을 고찰하기 위하여 기존 다층탄성해석프로그램인 KENLAYER와 구축된 모델링을 이용한 상용 유한요소해석프로그램 ABAQUS 로부터 연직하중과 수평하중이 적용하는 경우 및 하중조합의 경우 포장체 거동을 비교분석하였다. 또한 각각의 하중상태하에서 경계층 상태에 따른 포장구조체의 공용성을 평가한 후, 연직하중과 수평하중이 동시에 가해지는 포장구조체의 경계면 상태에 따른 영향계수의 데이터베이스를 구축하였다. 기존의 주행차량의 연직하중만을 고려한 경우와 실제 주행차량의 수평하중과 연직 하중을 고려한 경우 포장구조체에 미치는 영향을 분석한 결과, 수평하중의 작용으로 인해 공용수명이 약 1/300로 감소하므로, 포장구조해석시 주행차량의 수평하중을 고려한 층 경계면 영향계수 개발이 필요함을 알 수 있었다. 또한 국내 고속도로의 대표단면을 이용하여 수치해석을 실시한 결과, 아스팔트층의 두께가 얇을수록, 또한 아스팔트층의 탄성계수가 작을수록 경계면 상태에 큰 영향을 받음을 알 수 있었다. 포장구조해석시 주행차량의 수평하중을 고려하기 위하여 포장구조체 공용수명에 영향을 미치는 아스팔트층의 두께, 탄성계수, 그리고 경계면 조건으로부터 아스팔트층 하부의 인장변형률을 결정하는 인장변형률 예측식을 제안하였고, 공용중인 포장구조체의 두께와 탄성계수를 이용하여 인장변형률 예측식을 해석적으로 검증하였다. 또한 제안된 예측식을 이용하여 아스팔트층과 보조기층 사이의 접합여부에 따른 인장변형률 영향계수를 개발하였다. Structural pavement analysis considering lateral loads of moving vehicle was carried out in order to simulate passing vehicle loads Linder various interface conditions. To verify of existing multi-layer elastic analysis of layer interface effect parameters, this study compared outputs by using ABAQUS, a three dimensional finite element program and KENLAYER, multi-layer elastic analysis as vertical load was applied to the surface of asphalt pavements. Pavement performance depending on interface conditions was quantitatively evaluated and fundamental study of layer interface effect parameters was performed in this study. As results of the study, if only vertical loads of moving vehicle is applied, subdivision of either fully bonded or fully un bonded is enough to indicate interface effect parameters. On the other hand, when lateral loads are applied with vertical loads, pavement behavior and performance are greatly changed with respect to layer interface conditions. The thinner thickness of the asphalt layer is and the smaller elastic moduli of the asphalt layer is, the more pavement behavior is influenced by interface conditions. In addition, regression analysis equation analytically computing tensile strain which was considered thicknesses and elastic moduli of the asphalt layer and layer interface effect parameters at the bottom of the asphalt layer was presented using database from numerical analyses on national pavement model sections.

3차원 유한요소해석을 통한 연성포장의 층간접촉특성이 피로균열에 미치는 영향 평가

조명환,김낙석,Jo,Myoung-Hwan,Kim,Nak-Seok 한국방재학회 2007 한국방재학회 학술발표대회논문집 Vol.2007 No.1

To determine design or remaining life of flexible pavement, tensile strain at the bottom of asphalt concrete course and vertical strain on top of subgrade should be estimated. Various computer programs can be used for determining the strain at the critical position in pavement. However, these are conducted under the assumptions of full bonded or unbound state of layer interface conditions. This study compares the output of finite element analysis and multi-layer elastic analysis as vertical load was applied to the surface of flexible pavement. It is noted that the pavement performance is significantly affected depending upon the interface conditions.

The interface and its role in carrier transfer/recombination dynamics for the planar perovskite solar cells prepared under fully open air conditions

Fei Wang,Yiqing Chen,Guotao Han,Qianlong Zhang,Qilin Ma 한국물리학회 2016 Current Applied Physics Vol.16 No.10

The planar heterojunction perovskite solar cells, where the perovskite film is deposited directly onto a flat hole blocking layer, have recently attracted a great deal of attention owing to their high performance and ease of processing. However, the interface and its underlying role in carrier transport/recombination kinetics for such perovskite devices prepared under ambient air is still obscure. Herein, we addressed this issue by a dynamic intensity modulated photovoltage spectroscopy (IMVS) model using a continuity equation. The interface and its role in charge-carrier transport/recombination kinetics have been explored and discussed as an approach to understand the origin of the photovoltaic properties for the devices prepared under ambient air. The experimental IMVS responses were measured and satisfactorily fitted to the analytical results. Compared to the typical IMVS model based on dye-sensitized solar cells (DSSCs), the better IMVS fitting results presented in this study indicated that there was a discrepancy between the planar perovskite devices and those of DSSCs in electron transport/recombination properties, because carrier transfer across the TiO2/liquid electrolyte interface in DSSCs has been modified. That is, the Schottky interface in DSSCs needs to be replaced by the semiconductor heterojunction interface in perovskite solar cells (PSCs). Besides, the interface exhibits a more significant role in determining the carrier transport/recombination process by influencing the boundary conditions in a continuity equation. Furthermore, the intensity modulated photocurrent/photovoltage spectroscopy responses demonstrated that the carrier recombination characteristic is ultimately related with the surface and defect density in the interface. Interfacial modification, such as air-annealing, resulting in crystallographic changes, oxygen passivation, and variation in grain domain size, could suppress carrier recombination and prolong charge lifetime, which can yield more photo-generated electrons to be collected by anode, subsequently resulting in strikingly improving photovoltaic performance of the devices. In short, the dynamic IMVS model would help in elucidating the role of interface and the importance of interfacial modification or even interface design in order to obtain a highly efficient solar cell. The study can not only pave the way to construct the currentvoltage curve using a continuity equation model, but also provide new insights into the performance-improving steps for the PSCs prepared under fully open air conditions, which is of great importance for their future commercialization.

A discontinuous Galerkin method for elliptic interface problems with application to electroporation

Guyomarc'h, Gré,gory,Lee, Chang-Ock,Jeon, Kiwan John Wiley Sons, Ltd. 2009 Communications in numerical methods in engineering Vol.25 No.10

<P>We solve elliptic interface problems using a discontinuous Galerkin (DG) method, for which discontinuities in the solution and in its normal derivatives are prescribed on an interface inside the domain. Standard ways to solve interface problems with finite element methods consist in enforcing the prescribed discontinuity of the solution in the finite element space. Here, we show that the DG method provides a natural framework to enforce both discontinuities weakly in the DG formulation, provided the triangulation of the domain is fitted to the interface. The resulting discretization leads to a symmetric system that can be efficiently solved with standard algorithms. The method is shown to be optimally convergent in the L<SUP>2</SUP>-norm. We apply our method to the numerical study of electroporation, a widely used medical technique with applications to gene therapy and cancer treatment. Mathematical models of electroporation involve elliptic problems with dynamic interface conditions. We discretize such problems into a sequence of elliptic interface problems that can be solved by our method. We obtain numerical results that agree with known exact solutions. Copyright © 2008 John Wiley & Sons, Ltd.</P>

계면경계조건이 매입된 이동최소제곱 차분법을 이용한 계면경계문제 해석

윤영철 한국전산구조공학회 2019 한국전산구조공학회논문집 Vol.32 No.4

복합재료의 열전달 문제는 일반적으로 만족시켜야 하는 보존방정식과 경계조건 외에 추가적으로 만족시켜야 하는 계면경계조건의 존재로 인해 새로운 수치기법의 개발에 어려움이 있다. 계면경계조건이 미분방정식의 해에 불연속성을 유발시키기 때문에 이것을 적절하게 처리할 수 있는 특수한 함수의 도입이 필요하며, 이산화를 통한 계 방정식의 구성도 쉽지 않다. 본 논문에서는 계면경계의 불연속성을 모사하는 특수함수를 포함하면서 계면경계조건을 항상 만족시킬 수 있도록 계면경계식 자체를 매입한 미분근사식을 제안하고, 불연속 재료상수를 갖는 열전달 문제를 무요소 강형식으로 이산화한 이동최소제곱 차분법을 제시한다. 개발된 수치기법은 기존의 수치기법들과 달리 수치적분과 계면경계조건을 만족시키기 위한 별도의 구속 방정식이 필요없으며, 빠르고 정확하게 이종재료 열전달 문제의 수치해를 구해준다. 개발된 수치기법으로 다양한 복합재료 열전달 문제를 해석하고 오차의 수렴률을 조사한 결과, 높은 정확성과 계산 효율성을 갖는다는 것을 확인할 수 있었으며, 특히, 계면경계가 기하학적 특이성을 나타내는 문제에서도 우수한 성능을 발휘하는 것을 보였다. The heat conduction problem with discontinuous material coefficients generally consists of the conservative equation, boundary condition, and interface condition, which should be additionally satisfied in the solution procedure. This feature often makes the development of new numerical schemes difficult as it induces a layered singularity in the solution fields; thus, a special approximation is required to capture the singular behavior. In addition to the approximation, the construction of a total system of equations is challenging. In this study, a wedge function is devised for enriching the approximation, and the interface condition itself is embedded in the moving least squares(MLS) derivative approximation to consistently satisfy the interface condition. The heat conduction problem is then discretized in a strong form using the developed derivative approximation, which is named as the interface immersed MLS difference method. This method is able to efficiently provide a numerical solution for such interface problems avoiding both numerical quadrature as well as extra difference equations related to the interface condition enforcement. Numerical experiments proved that the developed numerical method was highly accurate and computationally efficient at solving the heat conduction problem with interfacial jump as well as the problem with a geometrically induced interfacial singularity.

재하시험과 유한요소해석에 의한 플라스틱 필름 온실의 거동특성 분석

류희룡(Hee Ryong Ryu),이응호(Eung Ho Lee),조명환(Myeong Whan Cho),유인호(In Ho Yu),김영철(Young Chul Kim) (사)한국생물환경조절학회 2012 생물환경조절학회지 Vol.21 No.4

부재 교차 결합부 조건에 따른 초기강성은 고정 조건인 경우와 비교하여 반고정 조건인 경우 33% 작게 나타났으나 부재 교차 결합부 특성에 의하여 재하지점과 3m 떨어진 지점에서는 9% 크게 나타났다. 즉, 고정 조건인 경우 구조물 전체로 하중이 분산되어 재하지점과 떨어진 지점에서는 상대적으로 반고정 조건 구조물의 강성이 높게 나타났다. 기초 조건에 따른 초기 강성은 강관 삽입 기초의 경우에는 고정기초 조건과 비교하여 31% 크게 나타났으며, 휨강성은 20% 높게 나타났다. 인터페이스 요소(beam interface element, BIE) 및 지반요소(3-D solid element)를 사용하여 재하시험 결과를 기반으로 각종 계수를 산정하고 시험조건과 동일하게 수치모델링하여 유한요소해석을 수행한 결과 실험결과와 유사한 구조거동을 나타냈다. 그러나 극한하중 조건에서는 비선형 특성의 발현 등에 의하여 다소 상이한 결과 값을 보였다. 이상의 결과로부터 플라스틱 필름 온실의 설계 및 구조성능 평가에서 절점 및 지점 조건에 대한 임의 또는 과다한 이상화는 구조물의 성능 평가에 적지 않은 영향을 줄 수 있음을 알 수 있었다. 한편 플라스틱 필름 온실은 세장한 부재로 구성된 유연한 철골구조물이므로 구조성능 산정에 있어서 좌굴과 함께 대변형 및 지반의 비선형 특성 등을 충분히 고려해야 할 것으로 판단된다. This study analyzed the effect of semi-rigid rafter-purlin cross-linking connection and driven steel pipe base on the static behavior of plastic greenhouse (PG). To promote the time and cost efficiency of the assembly process, each cross-linking connections of space arch type grid that consists of rafter and purlin is linked with steel-wire buckles, and each end of the rafters was driven directly to the ground to support the PG structure. However, in the design process, cross-linking connections and bases are idealized by being categorized as fully rigid or frictionless pinned, which does not appropriately reflect actual conditions. This study takes a full-scale loading test of PG and analyzes the effect of member cross-linking connections and driven steel pipe base on the behavior of a structure. The analysis provided a basis for determining the rigidity factor of member cross-linking nodes needed for finite element analysis, and the reliability of the result regarding the static behavior of PG.

뇌-컴퓨터 인터페이스(BCI)와 인간의 조건에 대한 정치철학적 고찰

정진화(Jinwha Chung) 경희대학교 인류사회재건연구원 2023 OUGHTOPIA Vol.37 No.3

과학기술이 혁신과 초월을 거듭하고 있는 시대에 새롭게 부상하고 있는 ‘뇌-컴퓨터 인터페이스(Brain-Computer Interface: BCI)’는 삶의 형태와 인간의 존재 방식까지 변화시킬 수 있을 것으로 보이며 BCI가 가져올 미래는 인간의 자유와 조건에 대한 궁극적인 질문을 던지고 있다. 이 점에서 BCI에 관한 문제는 과학, 경제, 산업 분야의 긍정적 전망과 윤리적 차원의 부정적 전망을 넘어 정치의 영역으로 이동시켜 논의할 필요가 있다. 이에 본 연구는 Arendt가 사유한 인간의 조건을 이론적 토대로 삼아 BCI에 내포된 특징과 문제들을 탐구하고, 정치적 과제와 역할을 모색해보고자 하였다. 인간의 조건을 활동적 삶과 정신의 삶 두 측면에서 사유한 Arendt의 사상과 이론은 BCI와 같이 신체적 활동뿐 아니라 정신적 활동까지 변화시킬 수 있는 기술을 고찰하는데 중요한 이론적 토대가 될 것이며 Arendt가 강조한 정치의 의미는 향후 정치적 과제와 역할을 모색하는 데에 중요한 실마리를 제공해 줄 수 있을 것이라 생각한다. In an era where science and technology are constantly innovating and transcending, the newly emerging ‘Brain–Computer Interface(BCI)’ is expected to change the form of life and even the way humans exist, and which BCI will bring the future is asking ultimate questions about freedom and conditions of human. In this respect, the issue of BCI needs to be discussed beyond the positive outlook in the fields of science, economy and industry and the negative outlook in the ethical dimension, and moved to the realm of politics. Therefore, this study tried to explore the characteristics and problems contained in BCI, and to seek political tasks and roles, based on the human condition thought by Arendt as a theoretical basis. Arendt’s thoughts and theories, which considered the human condition in terms of both ‘vita action’ and ‘the life of the mind’, will serve as an important theoretical basis for examining technology that can change not only physical activity but also mental activity, such as BCI. And I think that the meaning of politics emphasized by Arendt will be able to provide an important clue to finding political tasks and roles in the future.

스트란드형 유리섬유 강화 복합재료의 특수환경에 대한 내구성 시험

이승렬(SEONG-RYUL LEE),김부안(BU-AN KIM),문창권(CHANG-KWON MOON) 한국해양공학회 2006 韓國海洋工學會誌 Vol.20 No.2

The effect of various environmental conditions on the durability of E-glass fiber/vinylester resin composites has been investigated using the tensile test specimen of strand type. It was found that the durability test method performed by the strand type specimen was more convenient and reliable than other conventional test method. The weight gains increased with the immersion time in both water and alkaline solution, and the weight gains at 80℃. were much bigger than those at 20℃ in both conditions. The tensile strength decreased with the pass of immersion time in all aqueous solution, and the tensile strength at 80℃ in alkaline solution decreased very steeply at beginning of immersion time. The decrement of tensile strength according to the immersion time in various environmental conditions was mainly caused by the degradation of interface and the damage of glass fiber surface.

적층구성이 CFRP 사이드 부재의 충돌안전성에 미치는 영향

황우채 ( Woo Chae Hwang ),양인영 ( In Young Yang ) 한국안전학회(구 한국산업안전학회) 2014 한국안전학회지 Vol.29 No.3

The global demand for reduction in the weight of automobiles has led many countries to focus on the development of hybrid, eco-friendly, and electric cars. Reduction in the weight of materials can both increase fuel efficiency and maximize automobile performance. Therefore, the design of automobile should be inclined towards the safety aspects. but at the same time, it also consider reducing the structural weight of an automobile. In this study, CFRP side members with circular and double hat shaped section was manufactured. The impact collapse tests performed with change of the stacking condition, such as variation of interface number and outerlayer angle. The impact collapse load and absorbed energy were quantitatively analyzed according to the changes in section shapes and stacking condition. This analysis was performed to obtain design data that can be applied in the development of optimum lightweight members for automobiles.