As a type of periodic porous material, composite lattice sandwich structures exhibit excellent loadbearing capacity and functional characteristics, showing promising application prospects in marine engineering. However, the micro-structures within the lattice substantially increase the computational cost of model prediction, which hinders efficient simulation and analysis. To address this issue, this paper proposes a solid- fluid integrated homogenization model. By simultaneously homogenizing the solid and fluid within the lattice unit cell, the equivalent elastic coefficients and damping loss factors are solved, reducing mesh complexity and computational cost. . The calculation results show that modal analysis based on the solid-fluid integrated homogenization approach significantly reduces the required memory storage and computation time. Moreover, the prediction errors for modal natural frequencies remain within 1. 7%, while those for modal damping loss factors are within 4. 2%, confirming the consistency of the predicted modal frequencies and damping characteristics. Experimental results show that the proposed homogenization-based modal analysis achieves errors within 12% for modal natural frequencies and within 17% for modal damping loss factors compared with test data, which meets the requirements for engineering applications. The proposed method enables efficient and accurate analysis for composite lattice sandwich structures immersed in water, thus facilitating further application in the prediction of underwater modal responses and performance optimization.
