斜直井中考虑摩擦时钻柱的正弦屈曲分析

提出了在斜直井中钻柱正弦屈曲分析时对摩擦阻力的处理方法,给出了考虑摩擦阻力时的屈曲平衡方程,建立了相应的微分求积法列式,用微分求积法对平衡方程直接求解.在力学模型中考虑了摩擦因数、重力线密度、钻柱长度和井斜角对临界载荷的影响,并将数值计算结果与实验数据进行了比较.分析表明,提出的在钻柱正弦屈曲分析时对摩擦阻力的处理方法是正确有效的,能够为实验结果提供理论分析基础;在同等条件下,钻柱正弦屈曲临界载荷随摩擦因数的增加而增大;钻柱越长,摩擦阻力对临界载荷的影响越大,在一定程度上,摩擦可以增加钻柱的稳定性.     

斜直井中考虑摩擦时钻柱的正弦屈曲分析

提出了在斜直井中钻柱正弦屈曲分析时对摩擦阻力的处理方法,给出了考虑摩擦阻力时的屈曲平衡方程,建立了相应的微分求积法列式,用微分求积法时平衡方程直接求解。在力学模型中考虑了摩擦因数、重力线密度、钻柱长度和井斜角对临界载荷的影响,并将数值计算结果与实验数据进行了比较。分析表明,提出的在钻柱正弦屈曲分析时对摩擦阻力的处理方法是正确有效的,能够为实验结果提供理论分析基础;在同等条件下,钻柱正弦屈曲临界载荷随摩擦因数的增加而增大;钻柱越长,摩擦阻力对临界载荷的影响越大,在一定程度上,摩擦可以增加钻柱的稳定性。     

139.7mm加重钻杆外螺纹接头断裂原因分析

为查明某井139.7 mm加重钻杆外螺纹接头的断裂原因,对断口进行了宏观和微观分析,对材料进行了化学成分分析、力学性能试验和金相分析,并进行了有限元分析等。结果表明:加重钻杆断裂属于腐蚀疲劳断裂;断裂主要原因是加重钻杆接头内径大于标准规定值,降低了加重钻杆外螺纹接头断裂扭矩和抗拉载荷,在疲劳载荷与腐蚀介质作用下,腐蚀疲劳裂纹首先在加重钻杆外螺纹接头危险截面部位螺纹牙底萌生,随后在载荷作用下裂纹不断扩展,进一步降低了接头的强度,最终发生了断裂事故。     

工程用钻杆螺纹断裂失效研究

工程用坑道钻机钻杆在孔内受各种载荷作用,包括弯曲、扭转、振动及拉压等,钻进时经常出现钻杆断裂现象,严重影响正常生产.从钻杆接头连接螺纹失效类型分析入手,考虑实际工作载荷对钻杆联结螺纹进行力学分析.基于有限单元法,建立了钻杆连接螺纹接触有限元模型,针对Φ42钻杆进行了强度分析,并对钻杆材质进行了断口的形貌、化学成分测量、硬度测量、金相分析,得出钻杆接头螺纹应力偏高,热处理工艺不稳定为钻杆断裂失效的主要原因,研究为进一步优化钻杆结构提供了重要依据,具有重要的理论意义及工程应用价值.     

飞机结构强度试验局部约束装置设计

采用加载夹具对中央翼接头加载过程中,由于中央翼发生航向变形,垂向和侧向载荷在航向产生载荷分量,容易对接头造成损伤。因此设计一种局部约束装置,通过卡板把该装置安装在中央翼上,限制夹具与接头之间的相对变形,使航向载荷分量通过约束装置传递至中央翼盒段,以保证接头的安全。     

斜直井中钻柱非线性屈曲分析的有限元增量加权迭代法

建立了直井中有重钻柱非线性屈曲平衡方程及相应的泛函表达式，构造了一种能避免发散并加速收敛的有限元增量加权迭代法求解斜直井中钻柱屈曲问题，首次采用直接求解非线性特征值的方法来分析钻柱屈曲问题。计算结果表明，井斜角和屈曲位移幅值中任意一项增大，钻柱的非线性屈曲临界载荷也随之增大，且呈非线性；重力线密度对屈曲载荷的影响与屈曲状态有关；井壁约束力和特征向量的幅值随屈曲位移幅值增大而增大；扭矩对屈曲的影响很小，可以略去。研究结果为实际钻井作业中屈曲载荷的确定提供了参考。     

尾管悬挂固井中钻杆接头伸长量计算模型建立

尾管悬挂固井作业过程中,钻杆受到多种载荷联合作用产生轴向变形;若注水泥施工步骤前的钻杆上提距离过短,会导致钻杆和尾管悬挂器在后续作业时重新扣合,使得起钻时悬挂器无法顺利脱手造成卡钻。通过对直井尾管固井施工过程中钻杆受载情况的分析,并基于钻杆接头与钻杆本体存在结构差异这一特点,提出了一种综合考虑结构场、温度场、压力场等因素的钻杆接头最大伸长量工程计算模型。运用该模型可以对尾管固井过程中钻杆的伸长量进行更加准确的分析计算,尽量减少卡钻事故。通过分析得知,静止状态下钻杆的轴向伸长量是最大的;对钻杆接头伸长量影响最大的因素是温度场,影响最小的因素是压力场,且温度对钻杆接头的影响要比对同尺寸的管柱的影响略小。     

对薄壁圆筒单道环形焊缝所引起的残余应力和变形计算方法的改进

本文叙述了薄壁圆筒单道环形焊缝所引起的残余应力和变形的新的计算方法。这种方法采用正态分布载荷假设代替均匀分布载荷假设[1],得到了更符合实际测量值的计算结果。特别是环向应力的计算结果消除了由于均布载荷假设所引起的应力值的突变。     

切削热对双台肩螺纹加工精度与连接强度影响研究

双台肩螺纹以其高抗扭能力,在钻井作业过程中得到广泛应用。然而双台肩螺纹加工精度要求高,致使国内很多厂家生产的双台肩钻杆螺纹接头达不到设计要求。切削热是影响双台肩螺纹接头加工精度的主要因素之一。为研究切削热对双台肩螺纹加工精度和连接强度的影响,建立了一种基于CAE协同仿真的方法:通过建立双台肩螺纹车削加工的有限元模型,分析其在加工过程中的温度场分布情况;然后建立双台肩螺纹接头的温度-变形模型,研究温度场对螺纹变形的影响,即加工精度影响;通过建立三维的螺纹接头有限元计算模型,评价切削热所引起的加工误差对双台肩钻杆螺纹接头连接强度的影响。通过研究得出,切削热引起的螺纹牙单侧面轴向变形约0.014 8 mm,该变形量将导致接头抗扭和抗拉性能下降30%,且大幅度降低了压缩载荷或弯曲载荷作用时的使用寿命。因此加工应考虑切削热的影响,提出了相应的改进措施,并计算了多种常用切削用量下的变形量。     

变厚度多孔梯度材料圆板的热后屈曲分析

为分析多孔梯度材料圆板在非均匀温度场中的热后屈曲响应,基于经典板理论和物理中面概念建立了梯度多孔材料圆板在热载荷作用下的控制微分方程,其中假设厚度变化沿半径为二次抛物线型且板在其厚度上具有对称和非对称的非均匀孔隙率分布。采用打靶法数值求解了问题的屈曲和后屈曲响应,给出了均匀升温和热传导下的梯度多孔非线性变厚度圆板后屈曲平衡路径。结果显示：变厚度系数、孔隙率系数、孔隙分布方式以及温度场对板的临界载荷和后屈曲平衡路径均有影响;在不同温度场中孔隙率系数越大,屈曲时的临界载荷越小;孔隙率对称分布下的临界载荷大于非对称情况下的。     

Horizontal cylinder-in-cylinder buckling under compression and torsion: Review and application to composite drill pipe

Available analytical results and experiments on the structural behavior of constrained horizontal cylinders subjected to axial compression, torsion, and gravitational loads are reviewed. Such configurations are of interest to the oil-drilling field and provide static design expressions for steel tubulars. The buckling problem is similar to restrained railroad tracks and submerged/underwater pipelines under thermal expansion. Due to outer cylinder constraint and gravitational loads, analysis has shown that long cylinders initiate buckling at loads significantly higher than classical Euler buckling loads. For these constrained long cylinders, buckling initiates in a sinusoidal mode that snakes along the lower surface of the constraining cylinder. Classic analytical expressions hold that as the axial load increases, the cylinder achieves an overall helically buckled state in which the buckled cylinder forms a helix spiraling around the inner surface of the constraining cylinder. Torsion is shown to have little effect on either buckling load but controls the sense/direction of the helical buckling. Little experimental data exist on constrained cylinder buckling, and it is unclear how the initiating sinusoidal mode transitions to the helical mode. Implications of the buckling progression for composite cylinder applications are described including the finding that composites perform poorly relative to steel on the metric of buckling due to lower density and axial stiffness; composites perform well on the metric of lock-up length when friction is considered. Based on this review and findings for composite cylinders, recommendations are made for further work.     

Parametric studies on buckling loads and critical speeds of microdrill bits

Transverse bending vibrations of the spinning microdrill bit subjected to a compressive axial load are developed based on the Timoshenko beam theory. The system equations of motion are discretized into the form of time-dependent ordinary differential equations by the finite element method. Two types of eigenvalue problems are formulated and utilized to study the effects of the drill helix angle, flute length and diameter on the buckling load and critical speed of microdrill bits with different supported ends. Equivalent formulae similar to those of untwisted Euler beams are established to predict critical buckling loads and critical speeds for microdrills and provide results with sufficient accuracy. The effect of rotational speed on the buckling load, and the influence of thrust force on critical speed are also investigated. A Galef-type equation associated with critical speed, thrust force and buckling load is formulated.     

Buckling of rectangular plates with various boundary conditions loaded by non-uniform inplane loads

In the present paper, buckling loads of rectangular composite plates having nine sets of different boundary conditions and subjected to non-uniform inplane loading are presented considering higher order shear deformation theory (HSDT). As the applied inplane load is non-uniform, the buckling load is evaluated in two steps. In the first step the plane elasticity problem is solved to evaluate the stress distribution within the prebuckling range. Using the above stress distribution the plate buckling equations are derived from the principle of minimum total potential energy. Adopting Galerkin's approximation, the governing partial differential equations are converted into a set of homogeneous linear algebraic equations. The critical buckling load is obtained from the solution of the associated linear eigenvalue problem. The present buckling loads are compared with the published results wherever available. The buckling loads obtained from the present method for plate with various boundary conditions and subjected to non-uniform inplane loading are found to be in excellent agreement with those obtained from commercial software ANSYS. Buckling mode shapes of plate for different boundary conditions with non-uniform inplane loadings are also presented.     

Exact solution for the free vibration of axially-loaded pretwisted rods

For a pretwisted rod, in which torsional and flexural effects are decoupled, both vibration and buckling behaviour may be described by a pair of fourth-order linear ordinary differential equations. By considering the free vibration of axially-loaded pretwisted rods, a superset of the buckling and vibration equations may be obtained, and these equations may be solved analytically. Such solutions indicate that the relationship between the natural frequency and the applied load is effectively independent of the pretwist angle, for compressive loads and moderate tensile loads.     

The analytical solution of the buckling of composite truncated conical shells under combined external pressure and axial compression?

The objective of this research is determining the buckling load of composite truncated conical shells under external loading by theoretical and numerical methods. The boundary conditions are assumed to be clamped. At first, basic equations and stability relations of conical shells were derived. The analysis is carried out using Donnel-type stability equations for thin cross-ply conical shells. By applying Galerkin??s method, these equations are converted to a system of ordinary time dependent differential equations. Ritz method is employed for finding the dynamic stability load. Finally, the critical static and dynamic buckling loads and the corresponding wave numbers have been found analytically. Then comparison of results is considered. Results of analytical calculations are compared with numerical results and with other researchers?? analytical results. The effects of geometric parameters, the cone semi-vertex angle, number of layers and material of fibers on buckling loads are discussed.     

Out of plane stability of circular arches

An elastic buckling theory is developed for thin-walled arches. Using the principle of minimum total potential energy derives the governing differential equations. An explicit and clear approximation of the curvature effect is made in the derivation process. Closed form solutions are obtained for arches subjected to equal and opposite end moments (uniform bending) and to uniformly distributed radial loads (uniform compression). Also, closed form solutions for the torsional buckling moment of braced arches in uniform bending and for the torsional buckling load of braced arches in uniform compression are obtained. The solutions are compared with previous theoretical results.     

纤维增强FGM梁的自由振动和临界屈曲载荷分析

基于经典梁理论（CBT）研究轴向力作用下纤维增强功能梯度材料（FGM）梁的横向自由振动和临界屈曲载荷问题。首先考虑由混合律模型来表征纤维增强FGM梁的材料属性,其次利用Hamilton原理推导轴向力作用下纤维增强FGM梁横向自由振动和临界屈曲载荷的控制微分方程,并应用微分变换法（DTM）对控制微分方程及边界条件进行变换,计算了纤维增强FGM梁在固定-固定（C-C）、固定-简支（C-S）和简支-简支（S-S）3种边界条件下横向自由振动的无量纲固有频率和无量纲临界屈曲载荷。退化为各向同性梁和FGM梁,并与已有文献结果进行对比,验证了本文方法的有效性。最后讨论在不同边界条件下纤维增强FGM梁的刚度比、纤维体积分数和无量纲压载荷对无量纲固有频率的影响以及各参数对无量纲临界屈曲载荷的影响。     

Static, dynamic, and buckling analysis of partial interaction composite members using Timoshenko's beam theory

The static, dynamic, and buckling behavior of partial interaction composite members is investigated in this paper by taking into account for the influences of rotary inertia and shear deformations. The governing differential equations obtained are very comprehensive, covering and extending the current models for the problems that are based on Euler–Bernoulli beam theory. The analytical solutions of the deflection are then found for the beam with uniformly distributing load under common boundary conditions. The free vibration and buckling behavior are also studied and the analytical expressions of the frequencies of the simply supported beam are obtained explicitly, as are the buckling loads. For other boundary conditions, the eigen-equations are transcendental and thus some numerical examples are presented to demonstrate the effects of the shear deformation and rotary inertia on the resonant frequencies and buckling loads.     

热-机荷载作用的P-FGM扁球壳跳跃屈曲分析

基于经典壳体理论和Sanders非线性应变-位移关系,导出了幂律型功能梯度材料(P-FGM)扁球壳在热-机械荷载作用下的几何非线性常微分控制方程。推导过程考虑了沿厚度存在一维热传导温度场和法向均布荷载作用。采用打靶法求解了由控制方程和固定夹紧边界条件构成的两点边值问题。得到了FGM扁球壳的一些典型的屈曲平衡路径和双稳态构形。对热-机械荷载作用的FGM扁球壳的跳跃屈曲行为进行了参数影响分析。结果表明：温度上升时,球壳上临界荷载显著增加、下临界荷载变化不明显。梯度指数增加时,球壳上、下临界荷载均显著减小。组分材料模量增加时,球壳上、下临界荷载均显著增加。当底圆半径和厚度给定时,随壳体中面曲率半径增加,球壳上、下临界荷载均显著增加。当中面曲率半径和厚度给定时,随底圆半径增加,球壳下临界荷载显著减小,上临界荷载几乎不变。     

Dynamic analysis and grinding tracks in the magnetic fluid grinding system: Part I. Effects of load and speed

The differential equations of ball and float motions in the magnetic fluid grinding system are formulated. In this dynamic model, depending on the magnitudes of the contact loads, the ball will either contact or separate from the shaft and/or the float during the grinding process. Using the steady-state solutions as the initial conditions, the differential equations of motion are solved. Numerical results show that in contact cases, the effects of variable shaft speed and variable contact load on the ball-spin angle and the resultant area covered by the grinding tracks are small. However, when the ball separates from the shaft, the ball-spin angle varies with time because the ball has lost the driving force from the shaft, and thus the area covered by the grinding tracks on the ball surface increases. Furthermore, the combined effect of variable shaft speed and variable contact load on the appearance of grinding tracks is different from that of variable contact load alone, and this difference provides the ergodic possibility to grind a ball with high roundness using the magnetic fluid grinding method.