In modern naval warfare, advancements in weaponry have significantly increased the vulnerability of ships to explosion impacts. Precision-guided weapons, in particular, pose a significant threat, as internal explosions within ship cabins can cause extensive damage to thin-walled structures. This damage not only compromises the ship's structural integrity but also affects its overall functionality and safety. To accurately assess a ship's ability to withstand such damage and make informed battlefield decisions, it is crucial to evaluate the residual load-bearing capacity of damaged structures under complex sea conditions. This analysis is essential for evaluating the ship's damage tolerance and determining its ability to safely return to port.

This study focuses on the behavior of hull plates damaged by in-cabin explosions. A series of meticulously designed model tests were conducted, aiming to analyze the residual load-bearing capacity of thin plates exhibiting dent damage under biaxial compression. The use of biaxial compression is highly relevant, as it replicates the complex stress states experienced by ship hulls in actual sea conditions. To measure the detailed mechanical behavior of the damaged plates, the digital image correlation (DIC) method was employed. This advanced technique enabled the creation of a three-dimensional full-field strain measurement system, which recorded the out-of-plane deformation of the plates with high precision. By analyzing this data, the study explored the failure modes of dent-damaged thin plates under biaxial compression, illuminating the mechanisms through which such damage progresses and ultimately leads to structural failure.

The experimental results provided significant insights into the behavior of damaged thin plates under biaxial compression. A key finding was that, regardless of the applied loading ratio, the presence of dent damage led to a substantial reduction in the residual load-bearing capacity of the thin plates. In some cases, this reduction reached up to 19.96%, demonstrating the severe impact of even minor damage on the structural performance of the plates. Furthermore, all tested plates ultimately failed due to significant plastic deformation at the intersection of the loading edges, which underscores the localized nature of the damage and its catastrophic consequences for structural integrity. Another key finding was that an increase in the load at one end of the biaxial compression resulted in a notable decline in the ultimate bearing capacity at the other end.

This study provides valuable insights into assessing the damage survivability of ships under complex stress conditions. The findings help naval personnel better understand the structural state of damaged ships, enabling them to make informed decisions regarding mission continuation or safe return to port. Additionally, the research provides a basis for future research focused on optimizing ship structural design and enhancing damage-tolerance capabilities. Overall, this study plays a vital role in ensuring the safety and operational effectiveness of ships in combat and their safe return to port.

This study aims to develop a concept design for an unmanned aerial-aquatic cross-medium vehicle that can fly in the air and navigate underwater, and features repeatable medium transitions and superior hydrodynamic performance.

After analyzing the shape of manta ray that evolved good fluid dynamics performance through natural selection, 3D scanning and mathematical fitting methods are employed to conduct a configuration study of the unmanned vehicle. To achieve covert propulsion underwater, numerical analysis methods are used to determine the propulsion amplitude and frequency by fitting the swimming gaits of manta ray. To protect the rotor blades and enhance airborne efficiency, an innovative soft hybrid cross-medium approach is developed that uses ducted rotor devices as flight propulsion units. The numerical simulation method is then employed to study the unmanned vehicle's rapid underwater movement, aerial performance, and cross-medium capabilities.

The results show that during underwater navigation, with a biomimetic fish fin swinging cycle of 2 seconds and a maximum swing angle of 15°, the unmanned vehicle achieves a speed of over 3 knots. During aerial flight, with an attack angle of 7° for the hybrid vehicle and rotor speed set at 3 000 r/min, the aerial speed exceeds 100 km/h. During the transition from air to water, the average load is 0.17 MPa, with the maximum load occurring at abrupt structural edges, reaching up to 0.46 MPa stress. Structural strength calculations are performed for applying 0.17 MPa load at the center bottom and 0.46 MPa load at the bottom edge of the vehicle. The maximum stress occurs at the center bottom, measuring 47.94 MPa, with maximum deformation of 0.02 mm.

The designed cross-medium unmanned aerial-aquatic vehicle satisfies the proposed requirements for both aerial and underwater operation. Furthermore, the fluid loads and structural safety during the air-water transition scheme are assessed, ensuring the vehicle's ability to safelyand repeatedly shift between aerial and aquatic environments.

In order to improve the safety of ship navigation, this study focuses on virtually aided ship navigation strategies.

Two different inland river routes are chosen for the simulation of virtually aided ship navigation models based on the fluid-structure interaction mechanism, while taking the navigation rules and flow details of the rivers into consideration. The simulation of the ship sailing process on a typical inland river route under specific current conditions provides the corresponding virtually aided navigation plan in which the ship's velocity, location and course are obtained in a timely manner.

It is found that the simulation method established on the basis of Fluent can be used to solve the problems of multi-degree-of-freedom motion and fluid-structure interaction. When sailing through bends or branches, steering with a small rudder angle over long distances ensures safe navigation and prevents speed reduction and significant lateral displacement.

The proposed method can be effectively combined with the flow field information of digital channels to simulate the ship sailing process, thereby providing data support for the decision-making of intelligent navigation on inland river routes.

At present, the oil companies international marine forum (OCIMF) rules are frequently used to calculate wind load for large tankers and the American petroleum institute (API) rules for offshore platforms. However, due to the complexity of floating production storage and offloading (FPSO) superstructures, whether these two sets of rules can be applied to the wind load calculation of FPSO requires further study.

This paper establishes a numerical model of a 300000-ton class FPSO with a universal superstructure. The wind load on the FPSO under severe sea conditions and different wind angles is calculated and compared to the results of the rules. The shielding effect and heeling angle of the FPSO are analyzed.

The maximum heeling moment and wind load under an upright floating attitude appear at a 270° wind angle. The heeling moment and wind load under a heeling floating attitude are greater than those under an upright floating attitude, and the maximum heeling moment appears at a 10.5° heeling angle and a 280° wind angle. The results of the API and OCIMF rules show big differences compared with CFD: the differences between their results at a 270° wind angle and CFD are 13.6% and 24.5% respectively.

The flow field details obtained by numerical simulation are conducive to analyzing the shielding effect between superstructures and enhancing the accuracy of ship wind load prediction, thereby providing valuable references for the stability design of FPSO.