Flexural waves in drill‐string tubulars with variable loads     

Flavio Poletto  José M. Carcione  Giorgia Pinna 《Geophysical Prospecting》2013,61(5):955-972

We revisit the equations governing the bending motions in thin rods and analyse the filtration of flexural waves in vertical drill strings pre‐stressed by gravity. The aim is to study transverse drill‐string vibrations at seismic frequencies for acoustic communication purposes and provide an algorithm for processing reflected and transmitted bending motions generated by downhole lateral vibrations. We obtain the dispersion equation, including attenuation due to a gravity pre‐stress gradient and frequency‐dependent reflection and transmission coefficients at the interface between subsequent tube intervals. We then develop a propagation‐matrix algorithm to simulate flexural waves in a drill string consisting in an assembly of multiple tube sections of different dimensions. The deflection vibrations are obtained at any arbitrary recording point in the drill string. The modelling is cross‐checked with a full‐wave grid algorithm. The analysis shows that the waves produced by a concentrated force are partitioned in standing and propagating modes, which are calculated by using the flexural impedance of the drill string. Moreover, the reflection coefficients weakly depend on the pre‐stress conditions and pre‐stress has important effects for far‐field signal transmission with variable weight on bit (WOB). We discuss the approximations and limits of the method with respect to realistic drilling conditions.  相似文献   

横向各向同性地层斜井中正交偶极子激发声场的数值模拟   总被引：2，自引：2，他引：0       下载免费PDF全文

阎守国  宋若龙  吕伟国  马俊  王克协 《地球物理学报》2011,54(9):2412-2418

本文采用三维应力-速度有限差分(SV-FD)方法,数值模拟了横向各向同性(TI)地层对称主轴与井轴斜交情况下正交偶极子声源激发的井孔声场.主要解决了与倾斜角有关的三维空间弹性模量矩阵的推导,柱坐标系下应力-速度有限差分方程组的建立,井轴上场点奇异性与内边界处理等几个关键问题,提高了计算精度.在横向各向同性地层对称主轴与井轴平行的情况下,与实轴积分法所得结果进行了对比,验证了本文方法的正确性.计算了不同倾角情况下xx和yy两分量的弯曲波,并用频域加权相似法提取了弯曲波频散曲线,结果显示了横向各向同性介质中不同方向偏振的弯曲波传播的分裂现象,其频散曲线在低频段分裂,随频率增大而逐渐重合.弯曲波低频截止频率处速度与理论公式得到的横波速度基本符合.  相似文献   

Stress state analysis of a collapsed overhanging rock slab: A case study     

Paolo Paronuzzi  Walter Serafini 《Engineering Geology》2009,108(1-2):65-75

This paper describes the geomechanical back-analysis of the flexural failure of an overhanging limestone slab (volume = 68 m³) that collapsed on 26/01/1999 on the abandoned Cellina Valley state road SS 251 (western Friuli, NE Italy). The survey carried out on site examining the contact surfaces between the block and the slope has ascertained that the rock slab was connected to the stable rock mass by means of a single great rock bridge. The detailed reconstruction of the slab geometry and of the actual restraint conditions acting before the rockfall permitted an estimation of the stress state by using a 3D finite element code (Strand7). The finite element numerical model, referred to the restrained cross-section measured on site (A_res = 2.82 m²), gives a maximum value of σ_t = 5.19 MPa for the tensile stress, which is in good agreement with the estimated value for the characteristic strength mobilized at rupture by the intact rock material (T₀ = 3.5–5.5 MPa). Considerably lower maximum tensile stress (σ_t = 2.25 MPa), smaller than one half, is obtained if the whole contact surface is assumed as resisting surface (A_res = 10.50 m²) and the rock bridge is neglected.  相似文献   

刚性下卧层对上部土层变形的影响   总被引：1，自引：0，他引：1  

孔垂烛  邓安福 《岩土工程技术》2005,19(6):303-306

通过自编二维面向对象有限元程序计算,对土岩组合地基中刚性下卧层埋藏深浅及刚度大小对上部土层变形的影响规律进行了分析,得出了一些结论,可为相关工程应用提供适当的参考。  相似文献   

节点刚度对2008奥运羽毛球热身馆单层网壳稳定性影响研究     

张传成  张宝勤  张爱林 《世界地震工程》2007,23(3):32-40

利用Matrix27单元，对节点半刚性问题进行了APDL二次开发。利用调整节点刚度程序，研究了节点刚度与特征值之间的曲线关系，并重点研究了节点刚度对单层网壳稳定性的影响。通过单层网壳中节点刚度的研究，得到了几点有益的结论，为该类结构的设计提供数据资料和依据。  相似文献   

Flexural response of piles under liquefied soil conditions   总被引：1，自引：1，他引：1  

R. S. Meera  K. Shanker  P. K. Basudhar 《Geotechnical and Geological Engineering》2007,25(4):409-422

The paper pertains to the development of a generalized procedure to analyze and predict the flexural behavior of axially and laterally loaded pile foundations under liquefied soil conditions. Pseudo-static analysis has been carried out taking into consideration the combined effect of axial load and lateral load. Based on the available literature effect of degradation on the modulus of subgrade reaction due to soil liquefaction has been incorporated in the analysis. The developed program was calibrated and validated by comparing the predicted behavior of the pile with theoretical and experimental results reported in literature. The predicted behavior has been found to be in excellent to very good agreement with the theoretical and observed values in the field, respectively. The present study highlights the importance of considering the axial load from the superstructure along with the inertia forces from the superstructure and the kinematic forces from the liquefied soil in the design of pile foundations in liquefiable areas. The significance of densification of the soil in the liquefiable areas and presence of an adequate top non-liquefied soil cover causing appreciable reduction in deflection and bending moment experienced by the piles has been highlighted.  相似文献   

Neutron monitor latitude surveys at aircraft altitudes     

P. H. Stoker  H. Moraal 《Astrophysics and Space Science》1995,230(1-2):365-373

The Space Research Unit operates four stationary neutron monitors and it has conducted several latitude surveys with mobile neutron monitors. Our sea-level surveys have resulted in a clear identification of drift effects in the modulation. We have also conducted several latitude surveys at aircraft altitudes, the data of which have primarily been used to study the barometric attenuation coefficient of a neutron monitor, as well as cutoff rigidities in the Cape Town Magnetic Anomaly. In this contribution we present differential response functions of these aircraft surveys, and conclude that the drift effect is not detectable in them.  相似文献   

3-D finite-element modelling of deformation and stress associated with faulting: effect of inhomogeneous crustal structures   总被引：2，自引：0，他引：2  

S. Zhao  R. D. Müller  Y. Takahashi  Y. Kaneda 《Geophysical Journal International》2004,157(2):629-644

  相似文献   

Deformation of a layered half-space due to a very long tensile fault     

Sarva Jit Singh  Mahabir Singh 《Journal of Earth System Science》2004,113(2):235-246

The problem of the coseismic deformation of an earth model consisting of an elastic layer of uniform thickness overlying an elastic half-space due to a very long tensile fault in the layer is solved analytically. Integral expressions for the surface displacements are obtained for a vertical tensile fault and a horizontal tensile fault. The integrals involved are evaluated approximately by using Sneddon’s method of replacing the integrand by a finite sum of exponential terms. Detailed numerical results showing the variation of the displacements with epicentral distance for various source locations in the layer are presented graphically. The displacement field in the layered half-space is compared with the corresponding field in a uniform half-space to demonstrate the effect of the internal boundary. Relaxed rigidity method is used for computing the postseismic deformation of an earth model consisting of an elastic layer of uniform thickness overlying a viscoelastic half-space.  相似文献   

不同材料桩型时的桩基三维有限元分析     

黄斌  杨敏  熊巨华 《岩土工程技术》2004,18(2):78-82

近年来 ,以控制差异沉降为目标的桩基础变刚度调平方法在我国岩土工程界受到越来越多的重视和应用。用三维有限元方法研究在同一基础下采用不同桩型情况时各桩沉降和刚度的关系 ,探讨通过改变桩型来调整刚度 ,最后控制差异沉降的方法 ,并通过工程实例阐述运用不同桩型进行设计的概念和方法 ,达到减小差异沉降。  相似文献