For a naval ship with a long strength superstructure and a lot of hatch, it is difficult to evaluate the hull girder's strength by general beam theory because of the complexity of the hull structure.

Authors suggest a practical method based on dynamic analysis of finite element for modifying natural frequencies of hull grillage beam, and its software is completed.

The method for torsional analysis of ship hull as a stepped thin-walled beam using the restrained torsion theory has been applied widely in the field of naval architecture.