When the force can not contact drill string with one side of the borehole wall, the stiffness of drill string can influence the contact force.

当外力不足以使钻柱紧贴于井壁的一侧时，钻柱的刚度对钻柱与井壁之间的接触力有影响。

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The tangency point of Bottom Hole Assembly is located at where the drill string just touches the wall of the borehole, and the contact force is zero here.

在计算底部钻具组合的受力和变形时，以前一般都是按弯矩为零的条件来确定其上切点的位置。

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