Dynamic performance of transmission pole structures under blasting induced ground vibration

Structural integrity of electric transmission poles is crucial for the reliability of power delivery. In some areas where blasting is used for mining or construction, these structures are endangered if they are located close to blasting sites. Through field study, numerical simulation and theoretical analysis, this research investigates blast induced ground vibration and its effects on structural performance of the transmission poles. It mainly involves: (1) Blast induced ground motion characterization; (2) Determination of modal behavior of transmission poles; (3) Investigation of dynamic responses of transmission poles under blast induced ground excitations; (4) Establishment of a reasonable blast limit for pole structures; and (5) Development of heath monitoring strategies for the electric transmission structures. The main technical contributions of this research include: (1) developed site specific spectra of blast induced ground vibration based on field measurement data; (2) studied modal behavior of pole structures systematically; (3) proposed simplified but relatively accurate finite element (FE) models that consider the structure-cable coupling; (4) obtained dynamic responses of transmission pole structures under blast caused ground vibration both by spectrum and time-history analysis; (5) established 2 in/s PPV blast limit for transmission pole structures; (6) developed two NDT techniques for quality control of direct embedment foundations; and (7) described an idea of vibration-based health monitoring strategy for electric transmission structures schematically

Principles and approaches for the machining simulation of ceramic matrix composites at microscale: a review and outlook

Ceramic Matrix Composites (CMC) are advanced materials composed of ceramic fibers embedded in a ceramic matrix, resulting in a highly durable and lightweight composite structure offering exceptional high-temperature performance, excellent mechanical properties, and superior resistance to wear and corrosion. CMC find applications in industries such as aerospace, automotive, energy, and defense, where high strength and thermal stability are crucial. Despite their numerous advantages, machining CMC presents unique challenges. The hardness and brittleness of ceramics make them difficult to machine using conventional methods. The abrasive nature of ceramic particles can rapidly wear down cutting tools, leading to decreased tool life and increased costs. Numeric simulations for the machining of CMC are therefore particularly interesting due to their ability to provide insights into tool-material interactions and optimize machining parameters without the need for expensive and time-consuming physical trials. This paper discusses existing methods and approaches from different materials like Carbon Fiber Reinforced Plastics (CFRP) and monolithic ceramics and puts forward an outlook for the numerical simulation of the machining process of CMC

Numerical Modeling in Civil and Mining Geotechnical Engineering

This Special Issue (SI) collects fourteen articles published by leading scholars of numerical modeling in civil and mining geotechnical engineering. There is a good balance in the number of published articles, with seven in civil engineering and seven in mining engineering. The software used in the numerical modeling of these article varies from numerical codes based on continuum mechanics to those based on distinct element methods or mesh-free methods. The studied materials vary from rock, soil, and backfill to tailings. The investigations vary from mechanical behavior to hydraulic and thermal responses of infrastructures varying from pile foundations to tailings dams and underground openings. The SI thus collected a diversity of articles, reflecting the state-of-the-art of numerical modeling applied in civil and mining geotechnical engineering

Master of Science

thesisAn ever-present challenge at most active mining operations is controlling blastinduced damage beyond design limits. Implementing more effective wall control during blasting activities requires (1) understanding the damage mechanisms involved and (2) reasonably predicting the extent of blast-induced damage. While a common consensus on blast damage mechanisms in rock exists within the scientific community, there is much work to be done in the area of predicting overbreak. A new method was developed for observing near-field fracturing with a borescope. A field test was conducted in which a confined explosive charge was detonated in a body of competent rhyolite rock. Three instrumented monitoring holes filled with quick-setting cement were positioned in close proximity to the blasthole. Vibration transducers were secured downhole and on the surface to measure near-field vibrations. Clear acrylic tubing was positioned downhole and a borescope was lowered through it to view fractures in the grout. Thin, two-conductor, twisted wires were placed downhole and analyzed using a time-domain reflectometer (TDR) to assess rock displacement. Fracturing in the grout was easily observed with the borescope up to 3.78 m (12.4 ft) from the blasthole, with moderate fracturing visible up to 2.10 m (6.9 ft). Measured peak particle velocities (PPV) at these distances were 310 mm/s (12.2 in./s) and 1,490 mm/s (58.5 in./s), respectively, although no fracturing was observed near the depth of the vibration transducers located 3.78 m (12.4 ft) from the blasthole. TDR readings were difficult to interpret but indicated rock displacement in two of the monitoring holes. Three methods were used to predict the radial extent of tensile damage around the blasthole: a modified Holmberg-Persson (HP) model, a shockwave transfer (SWT) model, and a dynamic finite element simulation using ANSYS AutodynTM. The extent of damage predicted by the HP and SWT models is similar to field measurements when using static material properties of the rock, but is underestimated using dynamic material properties. The Autodyn™ model significantly overpredicted the region of damage but realistically simulated the zones of crushing and radial cracking. Calibration of material parameters for the AutodynTM model would be needed to yield more accurate results

Numerical modelling of additive manufacturing process for stainless steel tension testing samples

Nowadays additive manufacturing (AM) technologies including 3D printing grow rapidly and they are expected to replace conventional subtractive manufacturing technologies to some extents. During a selective laser melting (SLM) process as one of popular AM technologies for metals, large amount of heats is required to melt metal powders, and this leads to distortions and/or shrinkages of additively manufactured parts. It is useful to predict the 3D printed parts to control unwanted distortions and shrinkages before their 3D printing. This study develops a two-phase numerical modelling and simulation process of AM process for 17-4PH stainless steel and it considers the importance of post-processing and the need for calibration to achieve a high-quality printing at the end. By using this proposed AM modelling and simulation process, optimal process parameters, material properties, and topology can be obtained to ensure a part 3D printed successfully

Numerical modeling of thermal fracture development in unconventional reservoirs

Rapid depletion of hydrocarbons in conventional reservoirs and the availability of abundant oil and gas resources in unconventional forms demand new technology to economically produce these energy resources. From exploration to consumption of hydrocarbons, a great number of complex physical, chemical, mechanical, electrical, and thermal phenomena occurs in reservoir from reservoir rock to surface facilities. In addition to good rock samples and cores which could represent the reservoir rock for laboratory experiments, numerical tools should always be used to provide predictive capability of reservoir rock and fluid behavior. A great number of numerical methods have been developed and used over the past decades for rock mechanics problems. In this research the main focus is on thermal fracturing, heat transfer in rock, flow in porous media and stress-deformation analysis. We use three numerical methods for thermal fracturing of reservoir rock and investigate their capabilities in providing a solution for fracture propagation in rock. We finally propose the best numerical method among the ones we used in this work. We finally show two applications of thermal rock fracturing for improvement of hydrocarbon recovery in tight formations.Petroleum and Geosystems Engineerin

Micromechanical Study of Rock Fracture and Fragmentation under Dynamic Loads using Discrete Element Method

The study presented in this thesis aims to numerically explore the micro-mechanisms underlying rock fracture and fragmentation under dynamic loading. The approach adopted is based on the Discrete Element Method (DEM) coupled to the Cohesive Process Zone (CPZ) theory. It assumes rock material as assemblage of irregular-sized deformable fragments joining together at their cohesive boundaries. The simulation, which is referred to as Cohesive Fragment Model (CFM), takes advantage of DEM particle/contact logic to handle the fragments and boundaries in between. In this idealization, mechanical properties of particle and more dominantly those of contact control macroscopic response of the particle assemblage. A rate-dependent orthotropic cohesive law is developed for DEM contacts to capture rock material specific features, e.g. brittleness, anisotropy and rate-dependency. Rock experimental behavior is then modeled in order to assess individually the sensitivity of results to grain size, confining pressure, micromechanical parameters, stored strain energy, loading rate etc. The thesis is organized to approach the problem systematically. First, CFM application for static analysis is examined. It is shown that CFM quantitatively and qualitatively predicts compressive and tensile failure of hard and soft rocks as well as shear strength, dilatancy and degradation of rough rock joints. CFM micro-parameters, i.e., stiffness of particle and strength, stiffness, and friction of contact are calibrated using a combination of statistical disciplines and original closed-form expressions. The calibration process provides useful physical interpretation for each micro-parameter in terms of standard rock mechanical properties. These interpretations enable to understand how macroscopic behavior of rock material originates from its mineral microstructure. Energy needed to fully open a contact, the contact energy numerically represents material fracture energy in CFM. Experimental investigations suggest that fracture energy is independent of loading rate in quasi-static circumstances. Thus, contact energy is simply assumed as constant in static analysis. However, simulation on fast fracturing by CFM warns that this assumption causes serious deviations in fracture dynamic analysis. Laboratory observations reveal that fast-moving fracture consumes more energy than slow-moving one does. This inspires to consider contact energy as variable and rate-dependent to provide the model with the appropriate prediction of the fracture energy release process. Applying this new approach, fracture behavior of PMMA plates is investigated under different levels of stored strain energy. As the final stage, dynamic fracture toughness of rock samples, measured by the split-Hopkinson pressure bar test, is simulated and promising results are obtained. They demonstrate how numerical modeling can practically aid experimental methods in terms of measurement verification, error estimation, and performing appropriate corrections. The studies suggest that DEM is an effective and convenient tool to investigate fracture and fragmentation problems. While predictions by continuum models are restricted only to crack initiation, simulation by DEM made it possible to track both the initiation and progression of fracture over time by following consecutive damage of contacts. Moreover, the research specifically demonstrates that the proposed contact model properly predicts the experimental behavior of rock fracture under static and dynamic loading. This result verifies the model validity and adequacy for rock fracture analysis

A study on the Risk Analysis of the Anchor Impact Scenario of the Buried Structures in the Seabed and the Design Criteria of Rock-berm for the Additional Protection

본 연구는 해저에 설치되는 구조물들에 대해 주요 위해요소인 선박용 앵커를 이용하여 투묘 및 주묘에 의한 위험성 분석을 실시하였다. 먼저 투묘에 의한 충돌 시나리오는 투하된 앵커가 수직낙하하여 해저에 설치된 파이프에 충돌하는 조건을 선택했다. 종단속도를 산정하기 위해 전산유체해석 프로그램인 FLUENT의 MDM(Moving Deforming Mesh)기법을 사용하였고, ABAQUS/CAE 프로그램을 이용하여 해저지반 성질 및 파이프라인의 매설깊이에 따른 충돌해석을 실시하여 투묘에 의한 위험성 분석이 수행되었다. 다음으로, 주묘에 의한 충돌 시나리오는 보수적인 설정으로 앵커 끌림 해석을 실시하기 위해 초기 앵커 침투깊이와 앵커 끌림 속도 및 각도, 그리고 앵커와 락범의 이격거리를 결정하기 위한 선행 시뮬레이션을 수행하였다. 선행 시뮬레이션 결과를 바탕으로, ABAQUS/CAE 프로그램의 CEL(Coupled Eulerian Lagrangian)기법을 이용하여 해저지반 성질에 따른 앵커 침투깊이를 산정하여 주묘에 의한 위험성을 분석하였다. 마지막으로 앵커 투묘 및 주묘에 의한 위험성 분석을 기반으로 추가 보호를 위한 락범을 설계하였고, 락범 검증을 위한 투묘 및 주묘의 추가 해석을 실시하였다. 추가 해석 결과를 바탕으로 해저지반 성질 및 파이프라인의 매설깊이에 따른 락범 설계 기준을 정리하여 제시하였다.|In this study risk analysis of subsea pipeline was carried out by dropping and dragging of ship anchors, which are major risk factors for structures installed on the seabed. Firstly, impact scenario of a ship anchor dropped vertically and impacted an installed subsea pipeline was considered to calculate the impact force through terminal velocity. For that a computational fluid dynamic program, FLUENT, and MDM (Moving Deforming Mesh) technique were applied. Then, impact analysis of subsea pipeline was carried out using the dynamic finite element program, ABAQUS/CAE, considering seabed soil properties and pipeline buried depths in the seabed. Then, preliminary simulations were performed to determine the initial anchor penetration depth, anchor drag velocity, drag angle, and the distance between the anchor and the rock-berm before simulating dragging of anchor. Based on the preceding simulation results, risk analysis of dragging anchor was carried out to calculate the anchor dragging penetration depth according to the seabed soil properties using CEL(Coupled Eulerian Lagrangian) technique of the ABAQUS/CAE program. Lastly, based on the risk analysis of subsea pipeline, Rock-Berm was designed for additional protection, and risk analysis were carried out through the dropping and dragging of anchor for verification of safety. Based on the results of the additional simulation, the design criteria of Rock-Berm considering the seabed soil properties and pipeline burial depths in the seabed was suggested.목 차 List of Figures iii List of Tables vi Abstract vii 제 1 장 서 론 1 1.1 연구 배경 1 1.2 연구 동향 및 목적 3 제 2 장 앵커 투묘에 의한 위험성 분석 4 2.1 앵커 투묘 시나리오 4 2.2 종단속도 산정을 위한 수치해석 6 2.3 앵커 투묘에 의한 충돌 해석 13 2.3.1 앵커 모델링 14 2.3.2 파이프라인 모델링 15 2.3.3 해저지반 모델링 16 2.4 해석 결과 및 위험성 분석 18 제 3 장 앵커 주묘에 의한 위험성 분석 23 3.1 앵커 주묘 시나리오 23 3.2 앵커 주묘 시나리오 설정을 위한 선행해석 24 3.2.1 앵커 주묘 시나리오 설정을 위한 선행해석 개념 24 3.2.2 선행해석을 위한 유한요소해석 기법 26 3.2.3 선행해석을 위한 3차원 유한요소 모델링 27 3.2.4 선행해석 결과 분석 및 시나리오 결정 31 3.3 앵커 주묘에 의한 충돌 해석 35 3.4 해석 결과 및 위험성 분석 36 제 4장 추가 보호를 위한 락범 설계 40 4.1 추가 보호공법 방안 40 4.2 추가 보호를 위한 락범 단면 설계 41 제 5장 설계된 락범 단면에 대한 검증 42 5.1 앵커 투묘에 의한 설계된 락범 단면 검증 42 5.1.1 설계된 락범의 유한요소 모델링 42 5.1.2 락범을 적용한 앵커 투묘 해석 결과 및 위험성 분석 45 5.2 앵커 주묘에 의한 설계된 락범 단면 검증 54 5.2.1 설계된 락범의 유한요소 모델링 54 5.2.2 락범을 적용한 앵커 주묘 해석 결과 및 위험성 분석 56 5.3 앵커 투묘 및 주묘에 의한 락범 설계 기준 63 제 6장 결 론 65 참고문헌 69Maste

A Review of Hydraulic Fracturing Simulation

Along with horizontal drilling techniques, multi-stage hydraulic fracturing has improved shale gas production significantly in past decades. In order to understand the mechanism of hydraulic fracturing and improve treatment designs, it is critical to conduct modelling to predict stimulated fractures. In this paper, related physical processes in hydraulic fracturing are firstly discussed and their effects on hydraulic fracturing processes are analysed. Then historical and state of the art numerical models for hydraulic fracturing are reviewed, to highlight the pros and cons of different numerical methods. Next, commercially available software for hydraulic fracturing design are discussed and key features are summarised. Finally, we draw conclusions from the previous discussions in relation to physics, method and applications and provide recommendations for further research

Modelling of biomass milling

Strategies to combat climate change focus on every industry and has led to government policies to reduce electricity generation through coal combustion. Switching to biomass provides an opportunity to use infrastructure constructed for coal combustion with carbon neutral fuels; however, the process of grinding biomass pellets as fuel in pulverised fuel combustion is not well known. 1% of energy generated at a power plant is utilised to achieve the required size for the fuel. Improvements in the understanding of biomass pellet milling could lead to optimisation of operating conditions and minimisation of energy consumption. The process could aid generators determine appropriate fuels and costs for each; this represents a potential opportunity to elongate the life of current power stations, which is more cost effective than construction of new biomass specific plants. This research has developed a population balance equation (PBE) model simulation to predict the output of biomass pellet grinding for Lopulco E1.6 mill and a Retsch PM100 planetary ball mill; this has never been published in literature. It has proven it can predict the output particle size distribution of a Lopulco E1.6 mill, a scale model of an industrial mill, for biomass pellet PSD’s. It has shown that the simulation parameters can be based on axial and flexure deformation testing results, and that it can predict the PSD to within an average 88% accuracy against blind test. A novel technique in evaluating a PSD has been achieved using an overlapping coefficient, a measure better suited to PSD analysis than conventional model validation techniques. The PBE simulation has also shown that back calculating parameters can separate mill and material contributions when utilising a popularly used selection function and a breakage function developed in this research based on the Rosin-Rammler equation. This has been shown for the Lopulco mill and a lab scale planetary ball mill for axial and flexure deformation tests respectively. The research shows that emphasis should be placed on understanding classifier dynamics due to unexpected behaviour in the Lopulco mill experiments. Further conclusions show that energy consumption can be related to axial deformation energy that can be explained by the action of a Lopulco mill’s application of compressive force on and the orientation of pellets against the rollers