This paper presents a numerical analysis of the nonlinear interaction between water waves and the movable superstructure of a coastal bridge. An improved mesh update method is used to dynamically configure the computational meshes solving the Navier-Stokes equations for viscous and incompressible free surface flows with the volume of fluid (VOF) method. To maintain the mesh quality as the bridge deck is displaced, the computational domain is separated into several parts corresponding to a specific type of body motion. The numerical model results have been compared with the laboratory experiments conducted at Oregon State University with good agreement. This hydrodynamic model is then used to simulate the failure process of the prototype U.S. Highway 90 (US 90) Bridge during Hurricane Katrina (2005). It is found that the bridge deck is most vulnerable to be displaced by the waves when the bridge is partially submerged because of the combined effects of the vertical and horizontal wave forces. Numer...

Reducing vessel resistance by using ventilated cavities has been a highly researched topic in the marine industry. There is limited literature on ventilated supercavities near the free surface, which indicates that their dynamic behavior is more complex than conventional ventilated cavities due to the effect of the free surface. This paper employs numerical simulations to study the dynamic behavior of the ventilated supercavity, taking into account the effect of the free surface. Numerical simulations can predict gas leakage behaviors, cavity geometry, and internal flow structures. The influence of the free surface shortens the length of the ventilated cavity and increases the diameter. The presence of the free surface mainly changes the vertical velocity distribution between the free surface and the cavity. The results show that there are two typical gas leakage mechanisms under different immersion depths: twin-vortex tube leakage mode and re-entrant jet leakage mode. The internal flow field of ventilated supercavity is classified into three regions: the internal boundary layer, the ventilation influence region, and the reverse flow region. As the distance between the free surface and the ventilated supercavity decreases, the ventilated supercavity is affected by both the free surface effect and the gravity effect.

Film cooling using coolant jets is effective for increasing the cooling effectiveness of turbines. In the present study, large eddy simulation was employed for predicting small-scale vortices in the film-cooling process with different blowing ratios (BRs). The counter-rotating vortex pair (CRVP) was compared with the hairpin vortex, and results indicated the CRVP was the cross section of hairpin vortex. The results of a spectral analysis indicated a high correlation between the shedding period of the CRVP and the film-cooling effectiveness, and the dominant frequencies of the temperature and vorticity spectra were both identical to the shedding frequency of the CRVP when BR is less than 0.75. Furthermore, a higher shedding frequency of CRVP will suck the hot cross-flow into the core region more frequently, which will lead to a worse film-cooling effectiveness.

Knowledge of the distributions of various properties within a proton exchange membrane (PEM) fuel cell is a prerequisite for the improvement of cell performance, stability, and durability. In this paper, statistical tools are employed to investigate the variations of the current density, membrane water content, and local temperature in six flow-field configurations of PEM fuel cells, utilizing a three-dimensional two-phase multicomponent model. Under the same operating conditions, although the polarizations of the cells are similar, the results show that the extent of the uniformity of different physical properties varies in different flow-field configurations. Due to the proper distributions of reactants, the current density, membrane water content, and temperature in channel-perpendicular flow-fields are distributed more uniformly than in channel-overlapping ones. Furthermore, for all flow-field configurations, the three physical properties showed better uniformity in cases with fewer cathodic serpentine channels than in cases with more channels. These results reveal that a uniformity analysis using statistical tools is useful for a comparison of the merits of different configurations of PEM fuel cells.