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436 results on '"Wang Shizhao"'

14. Bayesian optimization for the spanwise oscillation of a gliding flat-plate

Author

Wang, Chunyu, Xu, Zhaoyue, Zhang, Xinlei, and Wang, Shizhao

Subjects
Physics - Fluid Dynamics
Abstract

The kinematics of a gliding flat-plate with spanwise oscillation has been optimized to enhance the power efficiency by using Bayesian optimization method, in which the portfolio allocation framework consists of a Gaussian process probabilistic surrogate and a hybrid acquisition strategy. We tune three types of acquisition function in the optimization framework and assign three different balance parameters to each acquisition function. The design variables are set as the dimensionless oscillating amplitude and reduced frequency of the spanwise oscillation. The object function is to maximize the power factor to support a unit weight. The optimization results in a maximal power factor of 1.65 when the dimensionless oscillating amplitude and reduced frequency vary from 0 to 1. The features of the probabilistic response surface are also examined. There exists an optimal reduced frequency for the power efficiency at the oscillating amplitudes above 0.40. In addition, the higher power efficiency may be obtained by increasing the amplitude beyond 1.00.

Published
2021

19. Far-field approximations to the derivatives and integrals of the Green's function for the Ffowcs Williams and Hawkings equation

Author

Zhou, Zhiteng and Wang, Shizhao

Subjects
Physics - Fluid Dynamics, 76Q05, J.2
Abstract

We report far-field approximations to the derivatives and integrals of the Green's function for the Ffowcs Williams and Hawkings equation in the frequency domain. The approximations are based on the far-field asymptotic of the Green's function. The details of the derivations of the proposed formulations are provided., Comment: 7 pages

Published
2021

24. The motion of respiratory droplets produced by coughing

Author

Wang, Hongping, Li, Zhaobin, Zhang, Xinlei, Zhu, Lixing, Liu, Yi, and Wang, Shizhao

Subjects
Physics - Fluid Dynamics, Physics - Medical Physics
Abstract

Coronavirus disease 2019 (COVID-19) has become a global pandemic infectious respiratory disease with high mortality and infectiousness. This paper investigates respiratory droplet transmission, which is critical to understanding, modeling and controlling epidemics. In the present work, we implemented flow visualization, particle image velocimetry (PIV) and particle shadow tracking velocimetry (PSTV) to measure the velocity of the airflow and droplets involved in coughing and then constructed a physical model considering the evaporation effect to predict the motion of droplets under different weather conditions. The experimental results indicate that the convection velocity of cough airflow presents the relationship $t^{-0.7}$ with time; hence, the distance from the cougher increases by $t^{0.3}$ in the range of our measurement domain. Substituting these experimental results into the physical model reveals that the small droplets (initial diameter $D \leq$ 100 $\mu$m) evaporate to droplet nuclei and that the large droplets with $D \geq$ 500 $\mu$m and initial velocity $u_0 \geq$ 5 m/s travel more than 2 m. Winter conditions of low temperature and high relative humidity can cause more droplets to settle to the ground, which may be a possible driver of a second pandemic wave in the autumn and winter seasons., Comment: 27 pages, 15 figures, COVID-19, article

Published
2020
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40. Spray Formation during the Impact of a Flat Plate on a Water Surface

Author

Wang, An, Wang, Shizhao, Balaras, Elias, Conroy, Devin, O'Shea, Thomas T., and Duncan, James H.

Subjects
Physics - Fluid Dynamics
Abstract

In naval hydrodynamics most the reseach on the impact of the hull of a vesel to the water surface has focused primarily on mapping the forces on the hull and much less to the formation of the spray. The latter is the topic of the present work, where the spray generated by the impact of a flat plate on a quiescent water surface is studied by experiments and simulations at different impact Froude numbers. Overall two types of sprays are formed: Type I, which is a cloud of droplets and ligaments generated at the impact of the plate's leading edge with the water surface, and Type II, which is formed after the trailing edge of the plate enters the local water surface. Detailed analysis of the experimental data for the Type II spray revealed that the spray envelopes and root point trajectories are independent of Froude number close to the trailing edge, while further away reach higher vertical positions for larger Froude numbers. The numerical simulation captures the general behavior of the Type II spray and agrees favorably with the experimental results. A series of computations with a flexible plate is also reported, where it is shown that increased flexibility reduces the height of the spray and suppresses the formation of droplets., Comment: Proceedings of the 31st Symposium on Naval Hydrodynamics, Monterey, California, USA, September 2016

Published
2018

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