The commonly used finite element software does not provide a three-dimensional (3D) fluid-saturated element available for dynamic analysis of two-phase media, which extremely limits their advantages in solving complicated engineering problems. This paper develops a user element for 3D dynamic analysis of fluid-saturated porous media in ABAQUS based on the u-U formed equations. The dynamic governing formulations are firstly revisited, and an implicit time integration algorithm is adopted to solve the dynamic equations. Then, the major development steps, the structure of the subroutine file, and the keywords directly related to the user element in the input file are carefully presented for the application of the user element. Moreover, the equivalent linear approach is introduced with a detailed realization procedure to consider the soil nonlinearity. Finally, the effectiveness and accuracy of the developed user element are validated by comparing the results with those from four different analytical and numerical solutions. The proposed numerical method with user element has a great potential in modeling practical engineering problems due to the prominent advantages of ABAQUS in simulating complicated materials and irregular geometrics.

常用的有限元软件没有提供可用于两相介质动态分析的三维（3D）流体饱和单元，这极大地限制了其在解决复杂工程问题方面的优势。本文开发了一个用户元素，用于在 ABAQUS 中基于u - U形成的方程。首先重新审视动态控制公式，采用隐式时间积分算法求解动态方程。然后，对主要的开发步骤、子程序文件的结构以及输入文件中与用户元素直接相关的关键词，都精心呈现出来，供用户元素的应用使用。此外，引入等效线性方法和详细的实现程序来考虑土壤非线性。最后，通过将结果与来自四种不同解析和数值解的结果进行比较，验证了开发的用户元素的有效性和准确性。