Objectives This paper integrates the finite element method (FEM) with the discrete-module-beam (DMB) method and improves the derivation of the lumped-mass stiffness matrix in order to efficiently apply the DMB method to complex and compound very large floating structures (VLFS).

Methods First, 3D potential flow theory is introduced to the DMB method to establish the hydroelastic equation. FEM theory is then introduced to discretize each macro-submodule into micro beam elements, and the lumped-mass matrix is then derived on the basis of the sub-structure approach and matrix manipulation. In dealing with complex boundary conditions, the cross-zeros-set-one approach or adding an additional constraint into the total stiffness matrix is adopted. In dealing with complex interconnections, the node numbering is first altered and then an additional constraint stiffness matrix is added to the total stiffness matrix.

Results When the FEM+DMB method is applied to VLFS with fixed/spring-damped boundary conditions and hinged/rigid/spring-damped interconnections, good agreement is shown with the results from the direct method.

Conclusions The proposed FEM+DMB method can analyze the hydroelasticity of VLFS in complex engineering scenarios with enhanced speed and accuracy.