During the mission, the ship may be simultaneously subjected to the combined wave load and underwater explosion bubble pulsation load, resulting in the "superposition effect" of hull response and the loss of total strength of the ship. Therefore, it is necessary to explore the dynamic response law of hull girder under the combined action of above-mentioned loads.

First, a simplified hull girder model is established by theoretical analysis, and the bubble pulsation load of underwater explosion and wave load are solved. Then, based on the Hamilton Principle, the differential equations of motion of hull girder at both free ends subjected to the two loads are derived separately and jointly. Finally, based on the solution of the motion differential equation, the hull girder's free vibration response and the simplified model's motion response under the three working conditions of external load combination are analyzed.

The results show that under the combined action of the two loads, the motion response of the hull girder is 15% larger than the linear superposition of the motion response of the two loads alone.

The research done can provide a reference for developing an algorithm to analyze the motion response of ship structures under combined loads.