泥浆返回管线是深水无隔水管钻井系统的关键装备，其内部充满高流速的泥浆，泥浆对管线的激振力学特性尚不清晰。全面考虑内流惯性力、摩擦力、离心力和科氏力作用，采用微元法建立内外流综合作用下的泥浆返回管线力学模型，融合有限单元法和Newmark-β法建立数值模型，对内流作用力的单独效果和综合效果进行分析，并研究泥浆流速、泥浆密度等因素对内流力学特性的影响。结果表明：惯性力会增大返回管线振动幅值，摩擦力会减小返回管线侧向位移，离心力和科氏力均会增大返回管线侧向位移；内流作用力对返回管线影响较大，其中摩擦力影响最大，惯性力、科氏力和离心力影响很小，在进行工程实际分析时需要考虑内部泥浆对返回管线的影响。

The mud return line is the key equipment of deepwater riserless drilling system. It is filled with high flow velocity mud， and the mechanical characteristics of mud on the line are not clear. The mechanical model of the mud return line under the combined action of internal and external flow was established by using the microelement method， considering the internal flow inertia force， friction force， centrifugal force and Coriolis force. The numerical model was established by using the finite element method， and the solver developed by Newmark-β method and MATLAB. The single effect and the combined effect of the internal flow force are analyzed， and the influence of mud flow rate， mud density and other factors on the internal flow mechanical characteristics is also studied. The result shows that the inertia force increases the vibration amplitude of the return line， riction decreases the lateral displacement of the return line， centrifugal force and Coriolis force increase the lateral displacement of the return line. The internal flow force has great influence on the return line， and the friction force has the greatest influence on the mud return line. The effects of inertia force， Coriolis force and centrifugal force are small. The effect of internal mud on the return line should be considered in the actual engineering analysis.