Understanding microcracking near coalesced fracture generation is critically important for hydrocarbon and geothermal reservoir characterization as well as damage evaluation in civil engineering structures. Dense and ...Understanding microcracking near coalesced fracture generation is critically important for hydrocarbon and geothermal reservoir characterization as well as damage evaluation in civil engineering structures. Dense and sometimes random microcracking near coalesced fracture formation alters the mechanical properties of the nearby virgin material. Individual microcrack characterization is also significant in quantifying the material changes near the fracture faces （i.e. damage）. Acoustic emission （AE） monitoring and analysis provide unique information regarding the microcracking process temporally, and infor- mation concerning the source characterization of individual microcracks can be extracted. In this context, laboratory hydraulic fracture tests were carried out while monitoring the AEs from several piezoelectric transducers. In-depth post-processing of the AE event data was performed for the purpose of under- standing the individual source mechanisms. Several source characterization techniques including moment tensor inversion, event parametric analysis, and volumetric deformation analysis were adopted. Post-test fracture characterization through coring, slicing and micro-computed tomographic imaging was performed to determine the coalesced fracture location and structure. Distinct differences in fracture characteristics were found spatially in relation to the openhole injection interval. Individual microcrack AE analysis showed substantial energy reduction emanating spatially from the injection interval. It was quantitatively observed that the recorded AE signals provided sufficient information to generalize the damage radiating spatially away from the injection wellbore.展开更多
盾构姿态控制过程中通过尽量减小各区压大小差异,可降低管片受剪开裂和纵向错台风险。为实现目标区压均衡分配,构建均衡分配几何模型,推导区压均衡约束条件,结合目标总推力和目标力矩条件,推导可实现任意多个区压均衡分配的计算公式。...盾构姿态控制过程中通过尽量减小各区压大小差异,可降低管片受剪开裂和纵向错台风险。为实现目标区压均衡分配,构建均衡分配几何模型,推导区压均衡约束条件,结合目标总推力和目标力矩条件,推导可实现任意多个区压均衡分配的计算公式。对比验证结果表明:1)相对于传统伪逆法和人工分配方法,所提出的均衡法有效提升了区压的均衡性,明显降低了相邻分区压差。2)基于区压均衡原则,提出不同总推力对应的力矩/力心极限边界解算方法,并描述了对应规律,即随着总推力由0 k N增长至分界值,同一方位的极限力矩由0 k N·m线性增至最大值,而极限力心半径为定值;当总推力继续增至最大总推力,极限力矩从最大值线性衰减至0 k N·m,极限力心也从最大值非线性衰减至0 m。3)基于所述极限边界,可避免力矩/力心设定超界引发的控制风险。展开更多
基金financial support for much of the early development of the AE analysis methods was provided by the U.S. Department of Energy (DOE) (Grant No. DE-FE0002760)
文摘Understanding microcracking near coalesced fracture generation is critically important for hydrocarbon and geothermal reservoir characterization as well as damage evaluation in civil engineering structures. Dense and sometimes random microcracking near coalesced fracture formation alters the mechanical properties of the nearby virgin material. Individual microcrack characterization is also significant in quantifying the material changes near the fracture faces （i.e. damage）. Acoustic emission （AE） monitoring and analysis provide unique information regarding the microcracking process temporally, and infor- mation concerning the source characterization of individual microcracks can be extracted. In this context, laboratory hydraulic fracture tests were carried out while monitoring the AEs from several piezoelectric transducers. In-depth post-processing of the AE event data was performed for the purpose of under- standing the individual source mechanisms. Several source characterization techniques including moment tensor inversion, event parametric analysis, and volumetric deformation analysis were adopted. Post-test fracture characterization through coring, slicing and micro-computed tomographic imaging was performed to determine the coalesced fracture location and structure. Distinct differences in fracture characteristics were found spatially in relation to the openhole injection interval. Individual microcrack AE analysis showed substantial energy reduction emanating spatially from the injection interval. It was quantitatively observed that the recorded AE signals provided sufficient information to generalize the damage radiating spatially away from the injection wellbore.
文摘盾构姿态控制过程中通过尽量减小各区压大小差异,可降低管片受剪开裂和纵向错台风险。为实现目标区压均衡分配,构建均衡分配几何模型,推导区压均衡约束条件,结合目标总推力和目标力矩条件,推导可实现任意多个区压均衡分配的计算公式。对比验证结果表明:1)相对于传统伪逆法和人工分配方法,所提出的均衡法有效提升了区压的均衡性,明显降低了相邻分区压差。2)基于区压均衡原则,提出不同总推力对应的力矩/力心极限边界解算方法,并描述了对应规律,即随着总推力由0 k N增长至分界值,同一方位的极限力矩由0 k N·m线性增至最大值,而极限力心半径为定值;当总推力继续增至最大总推力,极限力矩从最大值线性衰减至0 k N·m,极限力心也从最大值非线性衰减至0 m。3)基于所述极限边界,可避免力矩/力心设定超界引发的控制风险。
文摘考虑门架变形、轮胎刚度阻尼以及车体惯性质量等参数的影响,搭建了基于VL motion的纵向动力学模型,结合门架液压系统模型建立基于AMESim与VL motion的联合仿真分析平台,辨识负载高位抖动/晃动工况中惯性力矩的时变特征,根据零力矩点理论(Zero Moment Point,ZMP)分析了叉车纵向堆垛的稳定条件。针对叉车纵向堆垛过程中由于液压系统冲击引起的失稳问题,设计了一种组合式液压缓冲装置。仿真结果表明,由于组合式液压缓冲装置的节流与吸能作用,减轻了负载运动状态变化所引起的液压系统冲击问题,提高了叉车纵向堆垛稳定性。
