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A well-constructed tsunami evacuation facility can be crucial in a disaster. Understanding a tsunami's force and the flow structure variation across various building configurations are essential to engineering designs. Hence, this study assessed the steady-state flow structure at building models (BM) incorporating outer frame openings, including piloti-type designs with a different width-to-spacing ratio of piloti-type columns following an embankment model (EM) with a vegetation model (VM). The experiments also demonstrated the outer frame opening percentage's impact and orientation toward the overtopping tsunami flow at the BM. The results show that the arrangement of an opening on the outer frame and the piloti-type columns are critical in reducing the tsunami force concerning the experimental setup. Moreover, allowing a free surface flow beneath the BM implies that the correct piloti-pillar arrangement is crucial for resilient structure design. In addition, the three-dimensional numerical simulation was utilized to explain the turbulence intensity of the overtopping flow around the critical BM type. The derived resistance coefficient ( C R ) defined the drag and the hydrostatic characteristics at the BM due to the overtopping tsunami flow. Furthermore, for the impervious BM, the value C R was consistent with the previous studies, while the C R value for the BMs with an outer frame opening was directly coincident with the percentage of porosity. [ABSTRACT FROM AUTHOR]

The basic purpose of the present research is to numerically elucidate the flow around a single dike in four different geometric configurations (CN: no cylinders, C5: 5 cylinders, C10: 10 cylinders, C15: 15 cylinders), under conditions of a constant flow rate and subcritical flow. This involved substituting the impermeable dike with varying numbers of piles to validate the observed experimental flow patterns, particularly the conditions leading to reverse flow formation. OpenFOAM, an open-source algorithm, was utilized for the simulation, incorporating the volume of fluid (VOF) method. Accurately depicting the reverse flow formation with minimal numerical diffusion, a strategy involving multizone meshing and the application of mesh refinement zones was utilized. These refinements were particularly focused on the section between 1.8 m and 2.2 m within the numerical domain. The water surface profile in front section of the dike and the averaged velocity at five different locations, which were then compared with the numerical results. The numerically predicted streamwise velocity showed a percentage error ranging between 0.5% and 4.5%. The numerical results from this study are pivotal in dike design, aiming to mitigate accelerated wear during flood events and to protect both the dike head and the adjacent bank from high energy flow failures. [ABSTRACT FROM AUTHOR]

Levee failure due to nappe flow and subsequent erosion presents a significant challenge to flood protection infrastructure. This study evaluates the effectiveness of horizontal drainage layers, a common seepage control method, in mitigating these risks. While many traditional solutions to mitigate overtopping are costly and complex, horizontal drainage layers offer a promising and cost-effective alternative. These layers not only address seepage control but also manage nappe flow-induced erosion, potentially reducing construction and maintenance costs. Despite extensive research on their role in seepage control, a gap remains in understanding their effectiveness against overtopping-induced erosion, particularly in managing reverse flow. Existing studies often address seepage control or nappe flow erosion separately, overlooking the integrated impact of these layers. This study aims to address this gap by evaluating the performance of horizontal drainage layers under simulated overtopping conditions. The research involves two series of experiments, Series I: Focuses on newly built levees equipped with full (HD15L50 and HD25L50, where the thicknesses are 15 and 25 cm, respectively, with a horizontal drainage layer length of 50 cm and a crest length of 40 cm), partial length (HD15L40 and HD25L40), and short/reduced length (HD15L30 and HD25L30). The results showed that full-length layers reduce erosion inside the levee body and foundation by almost 100% and enhance levee stability due to their superior ability to dissipate hydraulic energy. Series II: Investigates practical solutions for retrofitting existing levees using shorter drainage layers with extended crests and gauzed sheets (HD15L15L30C60GH and HD25L30C60GH, where the thicknesses are 15 and 25 cm, the drainage length is 30 cm, and the crest is extended to 60 cm with gauzed sheets). Although shorter layers were less effective than full-length ones, extending the levee crest significantly improved their performance, achieving protection levels comparable to full-length layers, providing a valuable solution for upgrading existing levees. Overall, this study offers valuable insights by systematically evaluating and optimizing seepage control techniques. These findings can be directly applied to guide levee design, maintenance, and risk reduction strategies. This research contributes significantly to improving the resilience of levee systems against water pressure and ensuring their long-term stability. [ABSTRACT FROM AUTHOR]