Combined with features of flexible multi-body drilling string system and top-drive drilling system,the characteristic equation for lateral,twisting and longitudinal coupled vibration of flexible multi-body drilling string system is developed based on elastic vibration theory and finite element method,and the lateral vibration constraints is restored.Within 1700m vertical borehole,the relationship between the intrinsic frequency of flexible multi-body drilling string system and axial load,static drilling pressure,mud,length of drill collars,length of drill pipes are gained by analyzing the lateral vibration,twisting vibration and longitudinal fluid-structure vibration of flexible multi-body drilling string system by using software ANSYS.One to five step intrinsic frequencies of flexible multi-body drilling string system are gained.The research is about the theoretical basis for Well bore control theory of top drive drilling.
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