| dc.description.abstract | In the event of 2015 Nepal earthquake, a worldwide broadcasting video clip showed a violent water spilling in a hotel swimming pool. Motivated by the curiosity to investigate the dynamics of fluid field and the wave motion of violent sloshing during an earthquake, we studied forced sloshing in a rectangular tank with internal structure, excited by nonlinear external excitation.
In this thesis, the computational fluid dynamical model, Splash3D, was adopted for studying the sloshing problem accurately. Splash3D solved the 3D Navier-Stokes Equations directly with Large-Eddy Simulation (LES) turbulent closure. The Volume-of-fluid (VOF) method with piecewise linear interface calculation (PLIC) was used to track the complex breaking water surface. The time series of external acceleration was used to excite the water. A series model validations were conducted by comparing numerical results with 3D experimental measurements and previous studies’ results. Good comparisons were observed.
After validations, we performed the simulations for considering a seismic excited sloshing case in a rectangular water tank with a dimension of 12 m long, 8 m wide and 18 m deep, which contained water with 7 m in depth and the bottom structure simplified to porous medium. The seismic movement was imported by considering time-series acceleration in three dimensions, which were about 0.5 g to 1.2 g in the horizontal directions, and 0.3 g to 1 g in the vertical direction, respectively. We focused on describing the kinematics of the wave height, water surface, velocity vector field, pressure field, and most importantly, the vertical kinetic energy distribution in three dimensional view. Sensitivity tests about seismic magnitude, porosity of bottom structure were also conducted. From the simulations, higher averaged wave height can be found at the corner rather than at the middle of each side wall. The maximum wave height can be 6 m occurring at corners in case of water is well prescribed by side walls. If side walls were not high enough, water would jump cross it causing volume-loss, and the maximum wave height would be lower. Three-dimensional wave motion such as diagonal wave and swirling wave can be detected by both coupled wave height analysis and snapshots of free surface distribution.
We found that, the significant fluid dynamics (80% of kinetic energy) occurs at the top 30% of the water body, which can be called a 30-80 hypothesis. 30-80 phenomenon were also found in sensitivity testing cases. When comparing the significant wave heights (SWH) under different magnitude of earthquake events, we found the order anomaly of SWHs and conjectured the reason partly to resonance with natural frequency of the tank of water, furthermore, to wave modulation and nonlinear wave interactions. Discussions about how internal structure properties, rods’ height for example, influence the natural frequency of water body were performed by free sloshing analysis and FFT analysis. | en_US |