【作者】 杨晓亮；

【导师】 刘海笑；

【作者基本信息】 天津大学 ， 港口、海岸及近海工程， 2006， 硕士

【摘要】 随着深海石油,天然气等资源的开发,大型浮式采油,储存,装卸设备(FPSO)等海上大型结构物使用的增多,高承载力锚式系泊系统的研究和开发成为需要。对于这些大都建造在深海上的大型结构物而言,如果采用传统的悬链式系泊系统(Catenary Systems),它的经济成本是可想而知的,而且施工和设计都面临着许多新的问题,近几年发展起来的绷紧索系泊系统(Taut-wire Mooring Systems),克服了前者在深海中的许多缺点,成为深海系泊的一种主要的系泊方式。法向承力锚(Vertically Loaded Anchor)是适用于绷紧索系泊系统的一种新型的系泊基础,具有很高的抗拔承载力。法向承力锚的安装过程和传统的拖曳锚是没有本质区别的,但它从安装状态到工作状态的转变可以使其自身的承载力大幅度地提高。法向承力锚在理想工作状态是法向受力的,即系泊力的合力的作用方向垂直于锚板平面,这时的法向承力锚类似于一块埋入土中的板式结构。本文旨在通过建立考虑锚板埋深、锚板埋置角度和系泊力角度等参数影响的VLA的极限抗拔力计算方法,对法向承力锚的极限抗拔特性有深层次的理解和认识。本文基于塑性上限理论和极限平衡法,采用Tresca屈服准则,建立了一种计算VLA极限抗拔力的理论计算方法。在VLA的数值计算工作中,本文采用了大型通用有限元软件MARC。针对工作在饱和软粘土中的VLA在MARC中建立数值计算模型,采用MRAC中内嵌的VON MISES屈服准则,建立土的弹性-理想塑性模型,并采用施加位移约束条件求反力的方法确定VLA的UPC,在统一的工况下,对数值计算的结果、塑性上限理论计算结果以及工程经验公式的结果进行比较,并对几种计算方法各自的特点进行分析和总结。更多还原

【Abstract】 With the exploration for oil and gas reaching deeper waters, the use of floating production, storage and offloading (FPSO) facilities has increased, identifying a need for high-capacity anchoring systems. Conventional catenary systems have become too costly, and this led to the introduction of taut-wire mooring systems, where anchors are subjected to significant vertical loads. While large drag embedment anchors can have very high holding capacities and offer an economical and simple means of anchoring for a catenary system, their suitability for taut wire systems remains in question. As a result, drag-in plate anchors, or vertically loaded anchors (VLAs), were introduced by anchor manufacturers. VLAs are installed like conventional fluke anchors by pulling up to a target installation load. The loading direction is then changed such that it becomes normal to the fluke, leading to a significant increase in anchor resistance. In this normal loading mode, the anchor acts as an embedded plate.The purpose of this article is to present calculations of ultimate pullout capacity for VLA foundations, accounting for embedment, embedment angle, rate of increase of strength with depth, and width of the foundation. The soil is assumed to be elestic-perfect plastic, with yield determined by the Tresca condition with an undrained strength su. The method of upper bound and limit equilibrium calculations based on assumed mechanisms is used for the ultimate pullout capacity calculation. Finite element analysis of the fluke-soil interaction behaviour of VLA drag anchors in undrained soft clay has allowed calculation of plastic yield loci for characterisation of anchor failure states. The VLA fluke-soil interaction are introduced into the MSC.MARC software .The soil is assumed to be elestic-perfect plastic, with yield determined by the Von Mises condition.The plastic limit formulation is evaluated through comparisons with finite element simulations and the methed using conventional bearing capacity theory.更多还原