Bio-inspired underwater acoustic communication (BUAC) provides a promising solution for long-range covert information transmission in deep-sea environments. However, the large delay spread and severe multipath propagation in deep-sea channels lead to significant inter-symbol interference (ISI), which substantially degrades demodulation performance. Furthermore, the absence of a fixed synchronization header in the new BUAC system renders conventional channel estimation methods inapplicable, making effective ISI mitigation particularly challenging. To address this issue, this paper proposes a DiffWave-inspired receiver for the deep-sea BUAC system. Inspired by the architectural design of DiffWave, the proposed receiver learns a direct mapping from multipath-distorted observations to clean transmitted signals, enabling adaptive signal reconstruction without explicit channel estimation. Simulation and sea-trial results demonstrate that the proposed receiver effectively mitigates multipath-induced ISI and enhances demodulation robustness in deep-sea multipath environments.
The integration of wind energy, wave energy, and aquaculture on a shared floating platform can improve offshore space and infrastructure utilisation. Model-scale regular-wave experiments were conducted on a semi-submersible multi-use platform configured with different combinations of a simplified wind-turbine module, an oscillating water column (OWC) array, and flexible or rigid cage components. A comparative test matrix was used to separate draft effects from module induced and system-level responses. The prescribed steady thrust primarily altered the mean surge offset and mooring load distribution, whereas the changed mass distribution and rotational inertia associated with the wind-turbine module affected the wave-frequency responses. At T = 1.1 s, the maximum tension increase and mean tension variation of the windward line were 85.0% and 100.0% higher, respectively, after the wind turbine module was installed. The rigid perforated cage produced the largest response changes, amplifying the mooring-controlled lowfrequency surge response and windward mooring loads. Compared with the rigid-cage configuration, the fully coupled OWC-integrated configuration exhibited 28.3%-57.1% lower heave responses and 18.7%-56.4% lower pitch responses. At the system level, the observed behaviour reflects the competition between cage-induced low-frequency load amplification and OWCrelated motion mitigation. These findings clarify the coupled hydrodynamics of floating windwave-aquaculture systems and support the coordinated design of the cage, OWC, and mooring subsystems.
In natural environments, the pore fluid of sand often contains a certain amount of gas, either in the form of closed bubbles or dissolved gas. As a result, even sand below the groundwater table may be in an imperfectly saturated state. Existing experimental studies have shown that the sand liquefaction resistance increases under imperfectly saturated conditions. However, numerical models describing the cyclic liquefaction behaviors of imperfectly saturated sand are still lacking. In the present study, a finite element model considering the effects of imperfect saturation was developed, and element-scale simulations were conducted to further investigate how this condition affects the cyclic liquefaction behaviors of sand: (1) First, a fully explicit finite element model was established based on the two-phase Biot’s theory. The pore water containing gas was treated as a homogeneous fluid, in which the effects of free and dissolved gas were described by Boyle’s and Henry’s laws, respectively. An advanced constitutive model was employed to represent the cyclic behaviors of the soil skeleton. (2) Subsequently, the proposed algorithm and self-developed FEM program was validated through comparisons with analytical solutions as well as laboratory monotonic and cyclic undrained tests, confirming that the mechanical responses of fully and imperfectly saturated sands can be reasonably captured. (3) Finally, the developed numerical approach was employed to investigate the distinctive cyclic liquefaction behaviors of imperfectly saturated sands under conventional triaxial conditions. The influences of degree of saturation, dissolved gas content, and cyclic stress path were examined, and the effect of dynamic evolution of saturation due to volumetric strain was also discussed.
The Ti-6Al-4V alloy exhibits exceptional specific strength, excellent corrosion resistance, and high thermal stability but suffers from poor wear resistance. To enhance the service life of titanium alloys under frictional wear, this study examines an improved surface-strengthening method. While traditional nitriding increases surface hardness, the effect of the treatment atmosphere, especially the role of trace oxygen, remains poorly explored. This paper investigates the effects of varying treatment temperatures on the surface properties of titanium alloys when a small amount of oxygen (0.5%) is added to the nitriding gas. Titanium alloy specimens were processed via ion nitriding at 650 degrees C and 850 degrees C, and the resulting layers were analyzed through various experiments. The findings indicate that treatment temperature significantly influences the properties of the enhanced layer. Elevated temperatures yield a thicker and denser composite layer consisting of nitrides, oxides and their compounds. Specimens treated at 850 degrees C exhibit significantly increased surface hardness, and there were signs of improvement in wear resistance. These specimens also exhibit lower and more stable friction coefficients during testing. Electrochemical tests further confirm that the dense composite layer provides effective protection against corrosion, thus substantially improving the corrosion resistance of the alloy.
Abstract When an earthquake occurs, elevators are highly susceptible to damage, leading to people being trapped and posing significant challenges to emergency rescue. This paper proposes a method for assessing the number and distribution of elevator-trapped individuals in urban areas postearthquake. First, an elevator quantity estimation model is established by integrating elevator configuration rules and design principles for different building functions across regions including Europe, the United States, Japan, and China. Second, through an analysis of the correlation and degree of impact of various factors such as building damage and power outages, an elevator failure assessment model was developed using the Bayesian network method. Then, time-varying curves of elevator occupancy in different types of buildings are developed, with full consideration of the impact of regional differences in daily schedules. Finally, a comprehensive assessment model for the number and distribution of trapped individuals is established, and its effectiveness is verified through a case study in Dongchuan District, Kunming City. Comparative analysis with results from other literature methods confirms the model’s reliability. The assessment outcomes provide dual-scale references: macrodistribution levels and building-specific evaluations, enabling accurate prediction of trapped individuals’ locations at both regional and street levels. This offers valuable support for rescue teams in determining rescue sequences and allocating resources, thereby enhancing postearthquake rescue efficiency. From an international perspective, the method demonstrates wide applicability and transferability, serving as a scientific tool for earthquake-prone regions worldwide.
