This study takes a typical pressure hull segment of an unmanned underwater vehicle (UUV) as the object and explores its load bearing capacity law based on lightweight design technology.

First, several typical materials are analyzed using the mechanical properties of the pressure hull, load law and optimal critical load design value (stress strength failure and stability failure occur concurrently). The bearing properties of a typical pressure hull with varying depths are then discussed further in terms of the specific engineering requirements.

The failure mode of the shell gradually transitions from stability failure to strength failure as the depth increases, and the optimal critical load design value is proportional to the qualities of the material. Taking bearing efficiency and other factors into consideration, aluminum alloy shells should be selected within the 300 m depth range, titanium alloy and glass fiber composite shells within the 300−600 m depth range, and titanium alloy and carbon fiber composite shells within the 600−1 000 m depth range. In the 1 000−3 000 m depth range, a carbon fiber and boron fiber composite shell is the ideal solution.

The findings of this study can be used to guide the design of pressure hulls for UUVs made of various materials.

In order to explore the feasibility of replacing steel trusses with composite reinforcements, this study proposes a composite reinforcement design for the near-field acoustic scattering characteristics of stiffened plates, and conducts the requisite experiments.

First, based on the hydroacoustic material testing standards, a test protocol for the sound transmission performance of stiffened plates is established; second, the feasibility of the test environment and conditions is verified through the free field calibration of an anechoic pool and comparisons between the sound transmission performance of flat steel and steel trusses; finally, the sound transmission performance law of stiffened plates under the conditions of positive and oblique incidence is analyzed through experiments.

The results show that the sound transmission performance of stiffened plates under the conditions of positive and oblique incidence is basically the same, and in the order of bare plate > steel truss > composite stiffened plate. The sound transmission performance of composite stiffened plates is influenced by the cross-sectional area of the incident surface, and the smaller the cross-sectional area, the better the performance.

Combined with experimental analysis to explore the future development direction of high sound transmission composite stiffened plates and ensure equal bending stiffness, the design of composite reinforcements should try to use a hollow structural form and reduce the cross-sectional area of the incident surface as far as possible; in addition, the types of material used should be minimized so as to reduce the number of different material interfaces in reinforcements.

In order to investigate the influence of joints in composite laminate plates on the vibration transfer characteristics of structures, this study uses power flow based on the finite element method (FEM) and a related visualization technique.

First, a method that describes plate vibration by power flow in solid elements is proven to be feasible, then power flow transmission efficiency is introduced and a method of calculating it in a finite element model is proposed and verified by the admittance power flow method. Finally, two joint simulations of embedded joints and screw joints are obtained, as well as the power flow transmission efficiency curve and typical power flow vector diagram.

The results show significant differences in vibration transmission and power flow transmission efficiency between the two models.

Power flow based on FEM can directly reflect the vibration energy transmission path of a connected structure, which can provide useful references for the design of composite structures.

To tackle the problem of the longitudinal strength of composite superstructures, the finite element analysis method is used to study their longitudinal bending characteristics and design requirements.

First, an analysis is made of the longitudinal strain distribution along the height direction of a simplified hull model with different lengths and the equivalent elastic moduli of superstructure materials, and the quadratic function is used to perform nonlinear fitting. Second, the design requirements of composite superstructures are proposed based on the fitting results and explained in terms of both structural size and material properties. Finally, based on the concept of bending moment effectiveness and national military standards, a superstructure method with different elastic moduli and lengths is proposed that fully participates in longitudinal bending determination.

The results show that glass fiber and carbon fiber reinforced plastic reach the longitudinal strength requirements of superstructures, and composite superstructures longer than 0.3 times the length of the hull should be included in section stiffness checks.

The results of this study can provide references for the future design of naval ships with composite materials.