To overcome the limitations of conventional wave-absorbing structures, a novel broadband, low-profile multilayer composite absorber was designed.

The proposed design integrates square loop resistive film units to significantly broaden the operational bandwidth and incorporates miniaturized conductor units based on lumped inductance loading. Structural parameters were further optimized to achieve broadband, low-profile wave-absorption, effectively lowering the minimum operational frequency.

Simulation results show that the developed composite absorber achieves over 90% electromagnetic wave absorption across the frequency range of 3.22 to 14.63 GHz, with a relative bandwidth of 127.8% and a low profile height of just 0.068λ_L.

The operational mechanism of the absorber is analyzed using an equivalent circuit model, and potential improvements are discussed. This design offers valuable insights and a solid reference for the development of broadband, low-profile absorbers. Future work will focus on replacing lumped inductors with metal meander-line structures to reduce processing complexity and costs.

To accurately evaluate the impact of blanking on pulse interception, this study examines the loss probabilities of pulses caused by the blanking.

The influence of blanking on pulse sorting was analyzed. Based on the pulse sorting method used by reconnaissance equipment, the criteria for identifying the loss pulses were established. The output waveform of a pulse erased by the blanking gate was then examined under various time-sequence relationships between the pulse and the blanking gate, allowing the varying law of the residual pulse to be obtained. The expressions were derived for the average loss probabilities of the pulses and the loss probabilities of the periodic pulses both caused by the periodic blanking gates, as well as for the average loss probabilities of the pulses under blanking gates with time-varying duty cycles. Finally, each pulse loss probability was validated by comparing the calculation results with numerical simulation. The maximum absolute deviation between the two was approximately 5.8×10⁻⁴, which is negligible.

The mathematical models for the pulse loss probabilities and the average loss probabilities are obtained, and their accuracy has been verified.

The research provides a quantitative evaluation of the influence of the blanking on the loss of the intercepted pulse. It provides the input for accurately analyzing the missed alarm probability in pulse interception with the blanking gate and supports decision-making regarding the use of blanking measures.

To address the defect that the empirical formula of sea-spray flux depends on observation data from specific ships, this study proposes a correction method for the empirical formula of sea-spray flux on polar ship decks.

By analyzing the parameter characteristics of the empirical formula, it is proposed to modify the empirical formula of sea spray flux using numerical solutions of sea-spray flux for different ship types and corresponding environmental conditions as inputs. The reliability of the numerical method is verified through numerical wave profile and MFV fishing vessel spray flux calculations. Based on the proposed method, the empirical formulas of sea spray flux for four different ship types, such as bulbous bow, ice-resistant bow, clipper bow and raked bow, are modified.

The theoretical and numerical solutions of the empirical formula for fishing vessel spray flux are in good agreement. The spray duration coefficients for the other four ship types are similar to each other, and the liquid water content coefficient is similar to the coefficient in the existing empirical formula.

The results show that the proposed method has the ability to correct the empirical formula of sea-spray flux for different ship types.

To explore the effect of structural elasticity on the ice-structure interaction process, model tests on the interaction between frozen ice and elastic plates were conducted in a low-temperature laboratory. This study aims to provide a theoretical basis for understanding the ice-structure interaction mechanism and predicting ice loads on ships operating in ice-covered areas.

In the experiments, the stiffness of the elastic plates was adjusted by varying their thickness. Two loading rates within the strain-rate range associated with brittle ice failure were selected. A universal testing machine was used to record load-time history data, and a CCD camera was employed to capture the ice failure modes under different test conditions.

The interaction process consists of two typical phases: the loose contact phase and the tight contact phase. Loose contact results from the uneven contact between the plate and the top of the ice specimen, with maximum displacements generally ranging from 0 to 1.5 mm. In the tight contact phase, about 43.3% of the load-displacement curves show a saw-tooth shape, representing multi-stage failure modes. Stiffer plates are more likely to cause single-stage ice failure, while more flexible plates tend to result in multi-stage failures. Multi-stage failures are associated with ice flaking at a 45° angle due to shear failure. During multi-stage failure, the slope of the load-displacement curve remains nearly constant, suggesting constant stiffness of the ice-elastic plate coupling system in the tight contact phase.

Although the structure in this study is simplified as a plate, the experimental results provide valuable insights for designers of ice-going ships into the complex interaction mechanics between ice and ship structures. This research also provides a foundation for further studies on more complex structures and accurate ice load predictions.

As global warming accelerates the melting of sea ice, the Arctic region witnesses an increase in ship navigation. The brash ice area, composed of brash ice of various sizes and shapes, is a common operational scenario for polar ships. Understanding the ice load characteristics of polar ships during oblique navigation in brash ice regions is crucial. This can enhance ship navigation safety in the complex polar marine environment, provide a reference for polar navigation route planning, and fill the gap in the current research that mainly focuses on straight-sailing conditions.

This study selects a specific type of polar ship as the research object and utilizes the discrete element method (DEM) to predict the ice loads on the ship during oblique navigation through brash ice regions. First, a numerical model of the target ship is established. The model parameters include a ship model with a scale ratio of 60, a total length of 2.04 m, a beam of 0.37 m, and a design draft of 0.13 m. The ice particles have a density of 917.0 kg/m³, a Poisson's ratio of 0.3, and other specific properties. The accuracy of the model is verified by comparing it with the experimental results from the literature under the straight-sailing condition. Then, different oblique-sailing angles (0° −15°), speeds (0.6, 0.7 m/s), and ice thicknesses (0.011 67, 0.014 97 m) are set. The ice-load calculation is carried out based on the momentum conservation equation, angular momentum conservation equation, and the linear spring contact force model in the DEM.

The results show that as the drift angle increases, the ice-breaking resistance and lateral force on the ship increase non-linearly. For example, at a speed of 0.6 m/s, an ice concentration of 70%, and an ice thickness of 0.014 97 m, when the drift angle is 15°, the ice-breaking resistance and lateral force increase by 4.25 times and 6.04 times respectively, compared to the straight-sailing condition. In terms of speed, when the drift angle is between 0° and 10°, the ice-breaking resistance increases slowly, but when it exceeds 10°, it increases significantly. The lateral force also increases non-linearly, and the influence of speed on the lateral force is more significant than whether the ship is on the ice-facing side. Regarding the influence of ice thickness, when the drift angle is greater than 10°, the ice-breaking resistance and lateral force increase significantly as the ice thickness increases.

In conclusion, this research provides reliable data support for the safety assessment of ships during oblique navigation in polar brash ice regions. It offers a valuable reference for predicting and studying ice loads on polar ships under such conditions. Ship operators should be cautious when increasing speed or entering thicker ice areas, especially when the drift angle is greater than 10°. This is to avoid potential risks caused by sudden changes in ice-breaking resistance and lateral force, ensuring the safe and stable navigation of polar ships in complex ice-covered waters.

To address the challenge of low fault diagnosis accuracy in traditional neural networks with few labeled samples, a method based on contrastive learning and convolution transformer network is proposed.

First, raw monitoring data are transformed into similar sample pairs by data augmentation. These similar sample pairs are then mapped to a deep feature space by a feature extractor. A transformer network is utilized to design cross-prediction tasks for both local and global comparisons, facilitating the clustering of data with the same fault type by comparing the intrinsic similarity between the same batches of data. Finally, the downstream classification network is trained with few labeled samples to improve the diagnostic performance of the proposed model.

The effectiveness of the proposed method is validated using a self-built reducer test rig. The results show that accuracy of the proposed method reaches 98.38% with few labeled samples, showing significant advantages over existing methods.

The research results can provide the key technology for fault diagnosis of industrial equipment with few labeled samples, contributing to the advancement of intelligent manufacturing.

This paper addresses the path tracking control problem for underactuated unmanned surface vehicles (USVs) under the conditions of lumped disturbances, input saturation, and limited onboard energy. These factors complicate the path tracking process and reduce the effectiveness of traditional control methods. The aim of this study is to propose an event-triggered fixed-time path tracking control strategy that improves robustness, energy efficiency, and tracking precision in complex environments.

The proposed control strategy integrates several key components to address the challenges mentioned. First, a longitudinal speed guidance law and a fixed-time line-of-sight (SGFTLOS) guidance law are designed to provide the desired longitudinal speed and heading angle for the USV, ensuring it follows the trajectory with optimal speed and heading. Next, to handle model uncertainties and external disturbances (such as wind and current), a Fixed-Time Extended State Observer (FESO) is introduced. The FESO estimates and compensates for lumped disturbances, improving the system's robustness in uncertain environments. To address input saturation, an auxiliary dynamic system is designed to smooth inputs and maintain stable path tracking, even when saturation occurs. Finally, to overcome onboard energy limitations, a periodic event-triggered mechanism based on relative threshold is proposed. This mechanism adjusts control signal update frequency based on system states, minimizing unnecessary actuator activity and energy consumption.

The stability of the system is proven to be fixed-time stable using Lyapunov's fixed-time stability theory, which also eliminates Zeno behavior (infinite triggering in finite time) that could otherwise cause instability. SimuNPS simulation results demonstrate that the tracking error converges within a fixed time, verifying the effectiveness of the proposed method. Compared to existing methods, the proposed strategy exhibits faster transient response, smaller steady-state errors, and superior robustness in the presence of lumped disturbances. Furthermore, the introduction of the FESO provides accurate real-time disturbance estimation, allowing the controller to compensate for disturbances and maintain precise path tracking. Additionally, the event-triggered mechanism significantly reduces the number of control signal updates and actuator actions, improving the system's energy efficiency.

The proposed event-triggered fixed-time path tracking control strategy effectively addresses the challenges of lumped disturbances, input saturation, and limited onboard energy in underactuated USVs. By integrating event-triggered mechanisms, innovative guidance laws, and robust disturbance compensation, the strategy provides a reliable solution for path tracking in complex and uncertain environments. The fixed-time convergence property ensures that the USV achieves desired performance within a fixed time, making the strategy suitable for real-time applications requiring stability, precision, and energy efficiency. This method offers a robust, efficient, and reliable solution for USV path tracking control under difficult operational conditions.