• Title/Summary/Keyword: Distinct-element method

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NUMERICAL MODELLING OF SHEET-FLOW TRANSPORT UNDER WAVE AND CURRENT

  • Bakhtiary, Abbas-Yeganeh;Hotoshi Gotoh;Tetsuo Sakai
    • Water Engineering Research
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    • v.3 no.2
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    • pp.75-84
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    • 2002
  • An Euler-Lagrange two-phase flow model is presented fur simulation sheet-flow transport under wave and current. The flow is computed by solving the Reynolds Averaged Navier-Stokes equation in conjunction with the k-$\varepsilon$ turbulence model for turbulence closure. The sediment transport is introduced as a motion of granular media under the action of unsteady flow from the Lagragian point of view. In other word, motion of every single particle is numerically traced with Movable Bed Simulator (MBS) code based on the Distinct Element Method (DEM), in which the frequent interparticle collision of the moving particles during the sheet-flow transport is sophisticatedly taken into account. The particle diameter effect on time-dependent developing process of sheet-flow transport is investigated, by using three different diameter sizes of sediment. The influence of an imposed current on oscillatory sheet-flow transport is also investigated. It is concluded that the sediment transport rate increases due to the relaxation process related to the time-lag between flow velocity and sediment motion.

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Formation of Rolling and Recrystallization Textures in IF Steel Cold-rolled by Cross-Roll Rolling Mill (교차롤로 냉간 압연한 IF 강에서 압연 집합조직과 재결정 집합조직의 형성)

  • Lee, Kye-Man;Kim, Sang-Hyun;Huh, Moo-Young
    • Korean Journal of Metals and Materials
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    • v.48 no.7
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    • pp.644-650
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    • 2010
  • Interstitial free (IF) steel sheets were cold rolled by the cross-roll rolling mill in which the roll axes are tilted by ${\pm}7.5^{\circ}$ away from the transverse direction of the rolled sample. After cross-roll rolling of IF steel sheets, the cold rolling and the recrystallization textures were distinguished from those observed after rolling in a normal rolling mill. The three-dimensional finite element method (FEM) simulation revealed that the operation of a large shear strain ${\varepsilon}_{23}$ during cross-roll rolling leads to the formation of a distinct cold rolling texture. During recrystallization annealing, a pronounced change in texture components was not observed, which is attributed to the lack of either selective growth or oriented nucleation during the recrystallization process. Cold cross-roll rolling led to the formation of finer recrystallized grains in IF steel sheets.

An analytical investigation of soil disturbance due to sampling penetration

  • Diao, Hongguo;Wu, Yuedong;Liu, Jian;Luo, Ruping
    • Geomechanics and Engineering
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    • v.9 no.6
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    • pp.743-755
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    • 2015
  • It is well known that the quality of sample significantly determines the accuracy of soil parameters for laboratory testing. Although sampling disturbance has been studied over the last few decades, the theoretical investigation of soil disturbance due to sampling penetration has been rarely reported. In this paper, an analytical solution for estimating the soil disturbance due to sampling penetration was presented using cavity expansion method. Analytical results in several cases reveal that the soil at different location along the sample centerline experiences distinct phases of strain during the process of sampling penetration. The magnitude of induced strain is dependent on the position of the soil element within the sampler and the sampler geometry expressed as diameter-thickness ratio D/t and length-diameter ratio L/D. Effects of sampler features on soil disturbance were also studied. It is found that the induced maximum strain decreases exponentially with increasing diameter-thickness ratio, indicating that the sampling disturbance will reduce with increasing diameter or decreasing wall thickness of sampler. It is also found that a large length-diameter ratio does not necessarily reduce the disturbance. An optimal length-diameter ratio is suggested for the further design of improved sampler in this study.

Numerical analysis of offshore monopile during repetitive lateral loading

  • Chong, Song-Hun;Shin, Ho-Sung;Cho, Gye-Chun
    • Geomechanics and Engineering
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    • v.19 no.1
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    • pp.79-91
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    • 2019
  • Renewed interest in the long-term pile foundations has been driven by the increase in offshore wind turbine installation to generate renewable energy. A monopile subjected to repetitive loads experiences an evolution of displacements, pile rotation, and stress redistribution along the embedded portion of the pile. However, it is not fully understood how the embedded pile interacts with the surrounding soil elements based on different pile geometries. This study investigates the long-term soil response around offshore monopiles using finite element method. The semi-empirical numerical approach is adopted to account for the fundamental features of volumetric strain (terminal void ratio) and shear strain (shakedown and ratcheting), the strain accumulation rate, and stress obliquity. The model is tested with different strain boundary conditions and stress obliquity by relaxing four model parameters. The parametric study includes pile diameter, embedded length, and moment arm distance from the surface. Numerical results indicate that different pile geometries produce a distinct evolution of lateral displacement and stress. In particular, the repetitive lateral load increases the global lateral load resistance. Further analysis provides insight into the propagation of the shear localization from the pile tip to the ground surface.

Advanced Approach for Performance Improvement of Deep Learningbased BIM Elements Classification Model Using Ensemble Model (딥러닝 기반 BIM 부재 자동분류 학습모델의 성능 향상을 위한 Ensemble 모델 구축에 관한 연구)

  • Kim, Si-Hyun;Lee, Won-Bok;Yu, Young-Su;Koo, Bon-Sang
    • Journal of KIBIM
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    • v.12 no.2
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    • pp.12-25
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    • 2022
  • To increase the usability of Building Information Modeling (BIM) in construction projects, it is critical to ensure the interoperability of data between heterogeneous BIM software. The Industry Foundation Classes (IFC), an international ISO format, has been established for this purpose, but due to its structural complexity, geometric information and properties are not always transmitted correctly. Recently, deep learning approaches have been used to learn the shapes of the BIM elements and thereby verify the mapping between BIM elements and IFC entities. These models performed well for elements with distinct shapes but were limited when their shapes were highly similar. This study proposed a method to improve the performance of the element type classification by using an Ensemble model that leverages not only shapes characteristics but also the relational information between individual BIM elements. The accuracy of the Ensemble model, which merges MVCNN and MLP, was improved 0.03 compared to the existing deep learning model that only learned shape information.

Numerical analysis on the general requirement of permanently unsupported tunnels (영구 무지보 터널의 일반적인 조건에 관한 수치해석적 연구)

  • Yoon, Ji-Sun;Ryu, Ju-Yeol
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.5 no.2
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    • pp.209-216
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    • 2003
  • The present with in this country, rock bolt installation, shotcrete, and concrete lining in construction order has become accepted as a general tunnelling method in NATM. On the other hand Unlined tunnelling method, which was developed by many countries near Scandinavian Peninsula with hard rocks comparatively, has recently been introduced all over the world, and numerous studies about that have been being devoted to domestic tunnels. Unlined tunnelling method has been developed on the basis of the permanently unsupported openings, and general 7 requirements for them were suggested by Nick Barton. There are no case record about these conditions for Q-system in this country. Therefore, input parameters for Q-system under these conditions were applied to general road tunnel cross-section and numerical analyses for each condition were executed with UDEC-BB, Distinct Element Method.

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Comparison Analysis of Factor of Safety on Rock Slope in Boeun Region Using Distinct Element Method and Limit Equilibrium Method (개별요소법과 한계평형법을 이용한 보은지역 암반사면 안전율 비교해석)

  • 이지수;유광호;박혁진;민경덕
    • Journal of the Korean Geotechnical Society
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    • v.19 no.4
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    • pp.33-41
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    • 2003
  • The large planar failure has occurred in a rock cut slope of highway construction site in Boeun. This area is considered to be unstable since the discontinuity, whose orientation is similar to the orientation of the failure plane, is observed in many areas. Therefore, several analysis techniques such as SMR, stereographic analysis, limit equilibrium, numerical analysis, which are commonly used in rock slope stability analysis, are adopted in this area. In order to analyze the stress redistribution and nonlinear displacement caused by cut, which are not able to be obtained in limit equilibrium method, DEM and shear strength reduction technique were used in this study. Then the factors of safety evaluated by shear strength reduction technique and limit equilibrium were compared. In addition, the factor of safety under fully saturated slope condition was calculated and subsequently, the effect of the reinforcement was evaluated.

The Phase-velocity Dispersion Characteristics of Love Wave and Rayleigh Wave in the Half Space and Multi-layered System (반무한체와 다층구조 지반에서 러브파 및 레일레이파의 위상속도 분산특성)

  • 이일화;조성호
    • Journal of the Korean Geotechnical Society
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    • v.20 no.1
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    • pp.61-73
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    • 2004
  • Rayleigh wave and Love wave are the major elastic waves belonging to the category of the surface wave. The fact that Love wave is not contaminated by P-wave makes Love wave superior to Rayleish wave and other body waves. Therefore, the information that Love wave carries is more distinct and clearer than the information of Rayleigh wave. In this study, for the purpose of employing Love wave in the SASW method, the dispersion characteristics of the Love wave were extensively investigated by the theoretical, numerical and experimental approaches. The 2-D and 3-D finite element analyses for the half space and two-layer systems were performed to determine the phase velocities from Love wave as well as from both the vertical and the horizontal components of Rayleigh wave. Also, the SASW measurements were performed at the geotechnical sites to verify the results obtained by the numerical analysis. The results of the numerical analysis and the field testing indicated that the dispersion characteristics of Love wave can be an extended information to make better evaluation of the subsurface stiffness structure by SASW method.

Shape-Based Subsequence Retrieval Supporting Multiple Models in Time-Series Databases (시계열 데이터베이스에서 복수의 모델을 지원하는 모양 기반 서브시퀀스 검색)

  • Won, Jung-Im;Yoon, Jee-Hee;Kim, Sang-Wook;Park, Sang-Hyun
    • The KIPS Transactions:PartD
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    • v.10D no.4
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    • pp.577-590
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    • 2003
  • The shape-based retrieval is defined as the operation that searches for the (sub) sequences whose shapes are similar to that of a query sequence regardless of their actual element values. In this paper, we propose a similarity model suitable for shape-based retrieval and present an indexing method for supporting the similarity model. The proposed similarity model enables to retrieve similar shapes accurately by providing the combination of various shape-preserving transformations such as normalization, moving average, and time warping. Our indexing method stores every distinct subsequence concisely into the disk-based suffix tree for efficient and adaptive query processing. We allow the user to dynamically choose a similarity model suitable for a given application. More specifically, we allow the user to determine the parameter p of the distance function $L_p$ when submitting a query. The result of extensive experiments revealed that our approach not only successfully finds the subsequences whose shapes are similar to a query shape but also significantly outperforms the sequence search.

Forensic Analysis of chatting messenger service in KakaoTalk and Comparison Study of KakaoTalk and WhatsApp Artifacts (KakaoTalk의 채팅 메시지 포렌식 분석 연구 및 WhatsApp의 Artifacts 와의 비교 분석)

  • Yoon, JongCheol;Park, Yongsuk
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.20 no.4
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    • pp.777-785
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    • 2016
  • IM(Instant Messenger) chatting service can carry user's various information including life style, geographical position, and psychology & crime history and thus forensic analysis on the IM service is desirable. But, forensic analysis for KakaoTalk's chatting service is not well studied yet. For this reason, we study KakaoTalk's forensic analysis focusing on chatting service. This paper first details a general method of IM forensics investigating the previous articles about IM forensics although there are not many articles. Second, we discuss methodologies for IM forensics wherein we present analysis of table structure and method for reconstruction of chatting message. These result in the basic element of forensic tools of KakaoTalk chatting message. Last, we compare artifacts of KakaoTalk with that of WhatsApp. We conclude that these applications are, at least, different in that table structures and the ways to reconstruct chatting messages are not same and therefore digital evidences or artifacts are not same and somewhat distinct.