Szukana fraza: [Abstract = "The implication of these findings is that neglecting the effect of rotation of the drill string leads to under\-estimation of the deflection and over\-estimation of the natural frequency. Further analysis reveals that for a drilling riser of given dimensions, a drill string rotational speed exists at which the natural frequency of the drilling riser is theoretical equal to zero, and this rotational speed is the threshold rotational speed."]

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