检索结果-内蒙古大学图书馆

Hydro-mechanical modeling of borehole breakout in naturally fractured rocks using distinct element method

GEOMECHANICS FOR ENERGY AND THE ENVIRONMENT 2022年 31卷

作者： Wei, Yaoran Feng, Yongcun Deng, Jingen Li, Xiaorong China Univ Petr Coll Petr Engn Beijing Peoples R China China Univ Petr Coll Safety & Ocean Engn Beijing Peoples R China

Borehole breakout incidents in naturally fractured formations have plagued the petroleum drilling industry for decades. Borehole breakout is a progressive failure process controlled by multiple factors. Identifying the main factors that control borehole breakout is critical for successful drilling. This paper proposes a coupled geomechanics and fluid flow model for evaluating borehole breakout in fractured rocks, using a distinct element method. The model considers anisotropic drilling fluid invasion within natural fractures. The effect of in-situ stress, fracture density, fracture orientation, fluid dynamic viscosity, and joint strength on borehole breakout was investigated. The simulation results show that the fracture density dominates the yielded area around the borehole, while the direction of the fractures controls the shape of the breakout. With the increase of open-hole time and decrease in dynamic viscosity, the magnitude of borehole breakout increases due to increasing fluid invasion from the wellbore to the surrounding formation. The impacts of the above factors are demonstrated using numerical examples. Finally, some implications such as plugging fracture and using low permeability mudcake for preventing borehole breakout while drilling in naturally fractured formations are proposed based on the findings of this study. (C) 2021 Published by Elsevier Ltd.

关键词： Borehole breakout Naturally fractured formation distinct element method Numerical simulation

来源：评论

学校读者我要写书评

暂无评论

Rocking of offshore lighthouses under extreme wave impacts: Limit analysis, analytic formulations and distinct element method

引用

ENGINEERING STRUCTURES 2021年 228卷 111534-111534页

作者： Pappas, Athanasios D'Ayala, Dina Dassanayake, Darshana T. Antonini, Alessandro Raby, Alison UCL Civil Environm & Geomat Engn Gower St London WC1E 6BT England Univ Plymouth Sch Engn Comp & Math Plymouth PL4 8AA Devon England Delft Univ Technol Fac Civil Engn & Geosci Stevinweg 1 NL-2628 CN Delft Netherlands Univ Sri Jayewardenepura Fac Technol Dept Civil & Environm Technol Pitipana Sri Lanka

This study describes the structural response of historic lighthouses to extreme wave impacts. Located offshore on exposed rocks, 19th Century lighthouses were built with large interlocked granite blocks and have survived weathering for nearly two centuries. Under extreme wave impacts, lighthouses of this structural typology may uplift and rock, whereas sliding is prevented by the vertical interlocking. The uplift and sliding thresholds calculated with the limit analysis method reveal why this structural system is capable of bearing extreme wave impacts without failure. The ingenious vertical keying is proven to be a major characteristic that contributes to the resilience of these lighthouses. The structural response is explained with the use of analytic formulations of the rocking motion. Detailed analysis of the response to wave impact is conducted with reference to Wolf Rock lighthouse. The impact wave corresponding to a 250-year effective return period is identified using non stationary Bayesian extreme analysis. Moreover, wave flume tests on a scaled cylindrical structure were performed to identify the wave impact force time-history shapes. Based on two waves: a theoretical time-history based on existing models in the literature and the measured time-histories from small-scale experiments, a series of synthetic force time-history sequences are generated for the purposes of a parametric analysis. This parametric analysis, with the distinct element method, using the commercial software 3DEC, reveals the influence of the duration and shape of the force time-history function. For impacts with the same impulse values, shorter time impacts produce the most intense opening of joints, despite causing smaller horizontal displacements. Furthermore, variability in the structural response is revealed even for impacts of the same impulse, duration and maximum force but different shape of the force time-history.

关键词： Limit analysis distinct element method Historic lighthouse Rocking Wave impact

来源：评论

学校读者我要写书评

暂无评论

A numerical investigation on the mechanical properties of hydrate-bearing sand using distinct element method

引用

JOURNAL OF NATURAL GAS SCIENCE AND ENGINEERING 2021年 96卷 104328-104328页

作者： You, Zeshao Li, Yanghui Jiang, Mingjing Wu, Peng Liu, Yu Song, Yongchen Dalian Univ Technol Minist Educ Key Lab Ocean Energy Utilizat & Energy Conservat Dalian 116024 Peoples R China Tianjin Univ Dept Civil Engn Tianjin 300072 Peoples R China

Natural gas hydrates (NGH) are cage-like crystalline solids that are widely found in marine and permafrost sediments. The microstructure of NGH affects the mechanical properties of hydrate-bearing sediments (HBS). However, the underlying mechanisms are often difficult to detect. In this paper, distinct element method (DEM) is used to simulate the microstructure of hydrate observed in CT slices. Biaxial compression tests are conducted to investigate the mechanical properties of HBS and the relevant strengthening and volumetric dilation mechanisms. The simulation results show that the hydrate and sand particles jointly share the loading and many hydrate-related micro force-chains are created. Hydrate enhances the cohesive strength and frictional strength components of HBS. Compared with hydrate free sediment, the internal friction angle of the sediment at 45% hydrate saturation increases by 2.38 degrees, but hardly increases for the sediments at 5% and 20% hydrate saturations. Large local porosity changes and intensive hydrate cementation failure occur in the regions where the shear bands develop. Particle-scale observation shows the deformation characteristics of hydrate and the effects of hydrate on the structure and strength evolution of HBS.

关键词： Mechanical properties Hydrate cementation Strengthening mechanism Volumetric dilation distinct element method

来源：评论

学校读者我要写书评

暂无评论

Study of reinforcement support mechanisms for wide-span horse-shoe-shaped openings in horizontally layered jointed rock using the distinct element method

引用

ROCK MECHANICS AND ROCK ENGINEERING 2019年第4期52卷 1179-1191页

作者： Boon, C. W. Gamuda Engn Sdn Bhd Petaling Jaya 47820 Selangor Malaysia

Wide-span openings in horizontally layered jointed rock were analysed using the distinct element method (DEM) to provide additional insight into rock bolt support mechanisms and forces. The rock bolt forces in the DEM calculations exhibited distinct mechanisms, identified here as reinforced rock unit, beam building or suspension mechanisms. Each of these mechanisms was found to be associated with certain characteristics in the jointed rock structure. In jointed rock with thick horizontal beddings, the rock bolt forces at the roof tapered off with distance leading to a reinforced rock unit where each layer exhibited a self-support mechanism akin to a voussoir beam. In jointed rock with thinner horizontal beddings not capable of self-supporting, a beam building mechanism took place. When the rock bolts were extended into a rigid layer above the thinner layers, a suspension mechanism took place. Potential inaccuracies of thrust line predictions and the benefits of rock bolt tensioning were investigated, and their effects were found to be sensitive to the bedding thickness. A case history of the cavern roof of the underground car park for the Sydney Opera House was modelled. The calculated deflections of the cavern roof compared well with field measurements reported in the literature. The findings in this paper highlight the importance to ensure that the reinforcement support for wide-span underground excavations in horizontally layered jointed rock are tailored to the geological conditions being encountered.

关键词： Rock bolt Ground support design distinct element method Jointed rock Horizontally bedded rock

来源：评论

学校读者我要写书评

暂无评论

Investigating Earth Reaction to Pull-Out Process of Frictional Rock Bolts Using distinct element method

引用

Open Journal of Geology 2020年第8期10卷 851-862页

作者： Mohammad Sadegh Ayyoobi Arash Refahi Mining Department Faculty of Engineering University of Zanjan Zanjan Iran

The reaction of earth to pull-out process of frictional rock bolts was here modeled by the distinct element method (DEM). Ten frictional bolts were prepared;the expanding shells of five bolts included convex edges and the others had the shells with concave bits. The strength of bolts was measured by applying a standard pull-out test;the results confirmed that the strength of shells with convex edges was remarkably more than the strength of other shells. Furthermore, a two-dimensional DEM model of the test was developed by a particle flow code;the obtained results showed that the reaction of rock particles to the contacts occurring between the convex edges and earth was considerably more than those of the concave bits. In the other words, the convex edges transferred the pull-out force into a large area of the surrounded rock, causing these bolts to have the highest resistance against earth movements.

关键词： Frictional Rock Bolt Pull-Out Test distinct element method Particle Flow Code

来源：评论

学校读者我要写书评

暂无评论

Mesoscopic distinct element method for Multiscale Modeling of Carbon Nanotubes

Mesoscopic Distinct Element Method for Multiscale Modeling o...

引用

作者： Xu, Hao University of Minnesota

学位级别：Ph.D.

Super strong lightweight material systems comprising carbon nanotubes (CNTs) are especially suitable for aerospace applications. Assembles of CNTs obtained by mechanically stretching the CNT sheets, represent a promising material platform for developing composite materials with mechanical attributes approaching those of individual CNTs. In this quest, the guidance power of computational materials modelling is critical. Ideally one would like to investigate CNT assembles with all atom simulation methods, but this approach is computationally prohibitive. Due to the inherent spatial and temporal limitations of atomistic modeling and the lack of mesoscale models, mesoscopic simulation methods for CNT systems are missing. My work focuses on deriving ultra-coarse-grained models based on mesoscopic dintinct element method (mDEM). Our mDEM model is informed by atomistic data obtained with molecular dynamics (MD) and density functional theory-based tight-binding (DFTB) objective molecular modeling. Our mDEM model is capable of reproducing the atomistic elastic and frictional properties of CNTs. With the mDEM model, tensile tests of mesoscale CNT network were carried out, showing results in good agreement with experiments. The tensile tests revealed nanofriction was a key factor deciding the load transfer of CNT network. Our mDEM model serves as a powerful tool to expand the understanding and guide the development of CNT materials.

关键词： Carbon Nanotubes distinct element method Molecular Dynamics

来源：评论

学校读者我要写书评

暂无评论

Dynamic analysis of rock slopes using the distinct element method: A case study at the right abutment of the Upper Gotvand Dam, Iran

引用

JOURNAL OF AFRICAN EARTH SCIENCES 2018年 145卷 53-67页

作者： Broojerdi, Mohsen Sharifi Behnia, Mahmoud Aghchai, Mousa Hazrati Mahab Ghodss Consulting Engn Dastgerdi Ave Tehran Iran Isfahan Univ Technol Dept Min Engn Esfahan Iran

This paper reviews the dynamic stability of the right abutment of the Gotvand Dam, the highest earth fill dam located at the southwest of Iran, using the distinct element method. The right abutment comprises a soft clayey layer called the Lower Mudstone Siltstone interlayer (LMST) covered by disturbed conglomerate blocks. According to the results of the dynamic numerical analyses, no collapse will occur at the right abutment area. However, the residual shear displacement of disturbed blocks on the LMST layer will be 20-60 fcm for Maximum Credible Earthquake (MCE) loading. Such a displacement can cause cracking in the cut-off wall, and hence it was considered the main indicator of the right abutment instability. Investigating different solutions, such as buttressing and excavation, showed that these approaches are not effectively preventing abutment shear displacement. Therefore, the designing process was carried out by accepting the risk of cut-off wall cracking in seismic loading conditions. However, some pre-remedial solutions (as discussed thoroughly in the text) have been considered in the construction process to minimize the risk of water seepage from the cut-off wall.

关键词： Upper Gotvand Dam Slope stability Numerical analysis distinct element method

来源：评论

学校读者我要写书评

暂无评论

Calibration of tensile strength to model fracture toughness with distinct element method

引用

INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES 2018年 144卷 180-191页

作者： Dontsov, E., V Zhang, F. Univ Houston Dept Civil & Environm Engn Houston TX 77204 USA Tongji Univ Minist Educ Key Lab Geotech & Underground Engn Shanghai 200092 Peoples R China Tongji Univ Dept Geotech Engn Shanghai 200092 Peoples R China

This study investigates the relation between two approaches for modeling fracture propagation. The first one is the classical approach, in which fracture propagates once the stress intensity factor exceeds a critical value, called fracture toughness. In the second approach, the fracture propagates once the tensile stress ahead of the fracture tip exceeds a critical value, called tensile strength. The purpose of this study is to examine the relation between the two approaches and to determine a methodology to make them equivalent. To address the goal, propagation of a radially symmetric fracture is first analyzed. A universal relation between the tensile strength and fracture toughness is obtained, which is then verified via a series of numerical examples. It is found that in order to capture the fracture toughness the tensile strength should be varied with respect to the mesh size and other material parameters. The developments are then applied to a three-dimensional distinct element code, which can be used in various applications involving modeling of a jointed and blocky material. An additional challenge with the distinct element code lies in the fact that the use of uniform value of tensile strength does not lead to a spatially uniform apparent fracture toughness. The latter is caused by mesh distortions and orientation of the elements relative to the fracture front. This problem is successfully addressed by introducing a variation of the tensile strength relative to local geometry of the mesh in the vicinity of the fracture front. The obtained result develop a procedure to accurately model fracture toughness in numerical methods that use tensile strength as a fracture propagation criterion. (C) 2018 Elsevier Ltd. All rights reserved.

关键词： Hydraulic fracturing Numerical modeling Fracture propagation distinct element method

来源：评论

学校读者我要写书评

暂无评论

Evaluation of load-carrying capacity of full-scale falling protection net using distinct element method

引用

INTERNATIONAL JOURNAL OF PROTECTIVE STRUCTURES 2018年第3期9卷 269-288页

作者： Horiguchi, Toshiyuki Takahashi, Toshinobu Takamori, Kiyoshi Katsuki, Satishi Natl Def Acad Dept Civil & Environm Engn Yokosuka Kanagawa 2398686 Japan TOKYO ROPE MFG CO LTD Tokyo Japan

This article presents a simulation of a full-scale falling protection net using three-dimensional distinct element method. First, an application of distinct element method utilized cylinder rigid body element for collision response analysis of a flexible structure that has a long and slender shape similar to wire rope. Second, contact spring normally obtain contact force between the cylindrical element and spherical element in the case of distinct element method. However, connect spring that expresses axial stiffness like tension or compression and bending stiffness of the flexible structure was indicated as a fresh approach of the analysis method. Third, it is suggested to simulate large deformation program using connect spring of three-dimensional distinct element method and examine the application of reproducibility to analyze a full-scale falling protection net. Finally, the analysis result evaluated the performance of falling protection net using distinct element method which utilized connect spring and cylindrical model.

关键词： Falling protection net distinct element method limit design load evaluation real-scale experiment connect spring

来源：评论

学校读者我要写书评

暂无评论

Cyclic performance of adhesively bonded joints using the distinct element method: Damage and parametric analysis

引用

COMPOSITES PART B-ENGINEERING 2019年 178卷 107468-000页

作者： Biscaia, Hugo C. Micaelo, Rui Chastre, Carlos UNIDEMI FSE P-2829516 Caparica Portugal Univ Nova Lisboa Fac Ciencias & Tecnol Dept Civil Engn P-2829516 Caparica Portugal CESUR CERIS P-2829516 Caparica Portugal ICIST CERIS P-2829516 Caparica Portugal

Adhesively bonded joints have been widely used by engineers to solve problems in different industries. Despite recent studies which have helped with the design and application of these joints, there are still several uncertainties that justify empirical implementation in practice. One main aspect is the rigorous understanding of the performance of these joints when subjected to cyclic loading. Although the monotonic performance of adhesively bonded joints is well known, the cyclic behaviour raises several issues. Therefore, a numerical strategy based on the distinct element method (DEM) was implemented in this work to mitigate the lack of knowledge about the cyclic behaviour between two materials adhesively bonded to each other. For that purpose, the single-lap pull-push test was modelled and due to the diversity of the existing cohesive models, four different bond-slip relationships and two unloading paths (with ductile or "cleavage unloading") were considered. The results suggest that if the bond-slip relationship has an elastic stage, then the interfacial bond degradation is delayed. On the other hand, the interfacial damage of the joints with the number of cycles increases rapidly in those cases where the bond-slip relationships have no elastic stage and, at the same time, the slip accumulation is allowed. In addition, the results of two different tests available in the literature were implemented and fairly reproduced by the DEM.

关键词： Bond Cyclic loading Numerical simulations Damage distinct element method

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：