悬挂管柱正弦向螺旋屈曲转变时的临界载荷研究

悬挂管柱正弦向螺旋屈曲转变时的屈曲构型发生跳跃性变化,管柱与井筒存在接触和脱离等非线性力学问题。基于慢动力法,将悬挂管柱静力屈曲问题转换成动力学问题,建立了悬挂管柱上端受拉、下端受压的后屈曲分析有限元模型。研究表明,通过虚拟较大的阻尼比,能够有效地抑制管柱振动,可以计算出稳定的正弦屈曲和螺旋屈曲构型。当无量纲长度取8时,正弦向螺旋屈曲转变的无量纲临界载荷为4. 11,螺旋屈曲构型中存在两个接触点,两接触点之间的螺旋角为77.9°,下接触点距井底的无量纲长度为1.30。摒弃了管柱屈曲挠曲线假设,得出了悬挂管柱螺旋屈曲的最小临界载荷,对扶正器安放位置设计具有实际意义。

Critical load of a suspended tubular string from sinusoidal buckling to helical one

The buckling configuration of a suspended tubular string has a jump change when it transfers from sinusoidal buckling to helical one. Nonlinear mechanical problems,such as,contact and detach between tubular string and wellbore exist. Due to its own weight,the top and the bottom of the tubular string are subjected to tensile force and compressive one,respectively. Here,based on the slow dynamic method,the static buckling problem of the suspended tubular string was converted into a dynamic problem to establish its post-buckling finite element model. The study showed that the vibration of the tubular string can be suppressed with a larger virtual damping ratio to calculate its stable configurations of sinusoidal buckling and helical one;when its dimensionless length is 8,its dimensionless critical load during it transferring from sinusoidal buckling to helical one is 4.11;there are two contact points in helical buckling configuration,the spiral angle between the two contact points is 77.9;the dimensionless length between lower contact point and well bottom is 1.30;the assumption of buckling deflection curve for the tubular string is given up,the minimum critical load for helical buckling of the suspended tubular string is obtained,this is helpful for design of centralizer’s position.