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.
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.
Bistable nonlinear energy sinks and piezoelectric energy harvesters have attracted extensive attention in recent years due to their advantages in broadband vibration suppression and energy harvesting. To bridge the gap in understanding the synergistic mechanism of vibration suppression and energy harvesting for engine crankshaft torsional vibration, this paper proposes a rotational self-powered dynamic absorber (RSPDA) capable of switching freely among linear, nonlinear, monostable, and bistable states. A closed-loop coupled crankshaft‑RSPDA model is established and validated. A two‑stage particle swarm multi‑objective optimization framework is then developed, incorporating 15 RSPDA design variables and engine operating conditions. Parameter sensitivity analysis, stability analysis, and numerical simulation are conducted using the improved Newmark‑β method. The results indicate that the designed RSPDAs suppress both the primary resonance and superharmonic resonances at 1/3 ωn and 1/2 ωn. Further investigation shows that the linear RSPDA (L‑RSPDA) achieves the best vibration suppression at all resonance points but the weakest energy harvesting, whereas a wider potential well in the bistable RSPDA (B‑RSPDA) yields a broader vibration reduction bandwidth and enhanced power output.
Droplet impact on walls is a widespread phenomenon in nuclear engineering, yet studies on the dynamics of double droplets impacting curved surfaces remain insufficient. In this paper, the CLSVOF method is employed to investigate the behavior of double droplets simultaneously impacting a cylindrical wall. The effects of the curvature ratio on pressure distribution, central sheet characteristics, and secondary droplet generation under two impact modes (along the generatrix direction and along the directrix direction) are analyzed. The results show that for impacts along the generatrix direction, the pressure at the central sheet decreases with increasing curvature ratio, and both the width and height of the central sheet decrease. For impacts along the directrix direction, the pressure at the impact center decreases as the curvature ratio increases, and the pressure at the upper neck decreases significantly; the variations in the central sheet characteristics and the pressure at the central sheet follow the same trends as those for the generatrix direction. Under both impact modes, the number of secondary droplets decreases with increasing curvature ratio, with even fewer droplets generated in the directrix direction. The curvature ratio has a more pronounced effect on the directrix impact mode.
Continuous high-speed visualization of key intermediate species in turbulent flames is highly desirable yet remains challenging, with such diagnostics historically limited to a few species like OH and CH, primarily in hydrocarbon flames. With society's transition toward a zero-carbon energy future, combustion of carbon-free fuels such as am monia (NH3) and hydrogen (H2) has garnered significant attention. However, robust diagnostic tools for resolving the structures and dynamics of turbulent NH3/H2 flames have been lacking. This work explores the potential for kHz-rate planar laser-induced fluorescence (PLIF) imaging of the NH radical. We present an excitation-detection scheme within the strong NH A3 Pi-X3 Sigma-(0, 0) band near 334 nm, realizing 10 kHz NH imaging, for the first time, with an excellent signal-to-noise ratio (SNR). Furthermore, this approach proves resilient to interferences from elastic Rayleigh and Mie scattering, facilitating measurements in particle-laden environments or enabling simul taneous measurements with particle image velocimetry (PIV)-a crucial combination to explore the fundamentals of NH3/H2 flame dynamics.
