ABSTRACT
This study explores the mitigation of cavitation damage in hydraulic engineering through air entrainment. The primary aim is to experimentally analyze the shock wave characteristics emitted by cavitation bubbles adjacent to air bubbles affixed to a tube nozzle. The schlieren optical system is utilized to visualize the shock wave, while a hydrophone measures its pressure. Experiments are conducted on cavitation bubbles induced by the spark-generated method in the vicinity of air bubbles, varying the dimensionless distances and sizes of the air bubbles. The results indicate that (1) The introduction of an air bubble noticeably changes the morphology, kinematic behavior, and shock wave features of the cavitation bubble. (2) Four distinct shock wave patterns are identified based on the quantity and shape of the shock wave, with variations in the cavitation bubble's collapsing behavior and shock wave characteristics across different patterns. (3) The dimensionless distance γ and size δ exert significant influence on the shock wave's quantity, pressure peak, shape, and energy. With γ decreases or δ increases, the shock wave quantity increases while the shock wave intensity decreases. This investigation of the interaction between cavitation bubbles and air bubbles is essential for elucidating the mechanism through which air entrainment mitigates cavitation damage.
ABSTRACT
The analytical formula for characteristic parameters of optical wave (wave structure function, spatial coherence radius, and Fried parameter) in the slant path of ocean turbulence are derived and analyzed. Under the Rytov approximation, the wave structure function derived by the oceanic power spectrum of the refractive index of optical turbulent fluctuations in the slant path still complies with the five-thirds power law of the Kolmogorov spectrum in the inertial subregion, and the relationship between spatial coherence radius and Fried parameters satisfies 2.1 times. The correctness of analytical formulation of the wave structure function is demonstrated by comparing the numerical results of the original integral formula with the analytical formula of the derived in this paper.
ABSTRACT
A mathematical model considering the effects of amplitude and phase random fluctuations on the signal-to-noise ratio (SNR) of heterodyne detection was established, and the effects of irradiance and phase fluctuations on the performance of heterodyne detection were investigated. The results show that the inner scale of turbulence significantly affects the SNR. The first 20 Zernike modes have a greater effect on the SNR of the heterodyne detection system. The SNR is affected more significantly by phase fluctuations than by irradiance fluctuations. The SNR decreases by four orders of magnitude because of amplitude and phase fluctuations.
ABSTRACT
Maksutov-Cassegrain (MC) systems are widely used in long-range free-space optical (FSO) communication. In this study, analytical expressions for the diffraction field of a Laguerre-Gaussian (LG) beam passing through an MC system have been derived. The numerical results reveal that, in the long-range FSO system, the replacement of a Gaussian beam by the LG beam enhances the emission efficiency of the MC. Furthermore, the MC has a shaping effect on the LG beam, and the orbital angular momentum of the LG beam is not dispersed when the beam is diffracted by the MC.
ABSTRACT
A mathematical model of the effect of random pointing errors on the mixing efficiency of heterodyne detection is established, and the effect of angle-of-arrival fluctuation on the mixing efficiency of heterodyne detection is investigated. The results show that the average mixing efficiency is significantly affected by the angle-of-arrival fluctuation in the outer scale. The larger the obscuration ratio and receiving aperture of the optical system, the lower the average mixing efficiency is. The closer the value of D/r0 is to 0.79, the closer the bit error rate of heterodyne detection is to 1×10-9 under weak turbulence.
