Abstract
Depth-averaged models such as non-linear shallow water (NLSW) and Boussinesq based codes usually use the quadratic friction law with Manning’s coefficient to describe the surface roughness of the bottom. Large roughness elements such as buildings and tree vegetation, which are too small to be resolved by the grid of the bottom topography, are mainly considered by using purely empirical Manning coefficients. This approach, however, is not physically sound and may thus result in very large uncertainties in inundation modeling. A more physically-based approach is to determine prediction formulae for the hydraulic resistance of large roughness elements, considering for example different shapes, sizes and arrangements which can then be directly implemented in such models. Such prediction formulae can be determined on the basis of systematic simulations using a validated 3D numerical model. To better understand complex flow phenomena involved in tsunami inundation, three vertical emerged cylinders have been arranged in four different configurations with four different distances between each other and subject to a solitary wave and to a bore. A validated three-dimensional two-phase Reynolds-averaged Navier-Stokes (RANS) model and the Volume of Fluid (VOF) method (OpenFOAM) has been used to assess flow velocities and water levels near the cylinders and the inline forces acting on the cylinders. The effects of side-by-side, tandem and two staggered arrangements as well as the effect of the distances between them on the flow induced by a solitary wave and a bore are discussed. The study led to an improved understanding in the near field of cylinders, which forms the basis for further studies related to larger groups of cylinders and other shapes.
Highlights
Propagating tsunamis are influenced by wave characteristics such as wave period and wave direction, the seabed topography and morphologies, such as shoals and reefs, underwater canyons and man-made structures can cause large changes in wave height and direction of travel
When the normalized maximum forces are related to the distance between the cylinders, differences among them are more pronounced under solitary wave conditions, except in the side-by-side arrangement with a distance of 0.5 DB
When the normalized maximum forces are related to the arrangement, the opposite behavior can be noted
Summary
Propagating tsunamis are influenced by wave characteristics such as wave period and wave direction, the seabed topography and morphologies, such as shoals and reefs, underwater canyons and man-made structures can cause large changes in wave height and direction of travel. For example in tsunami risk assessment, large-scale tsunami models are mainly depth-averaged models such as Non-linear shallow water (NLSW) models or Boussinesq models can be applied Due to their size, their resolution is often limited so that the grid of the bottom topography cannot represent adequately smaller morphologies such as buildings and tree vegetation. Models use mainly the concept of the boundary surface roughness They apply for example modified Manning coefficients to account for the interactions of the broken or unbroken wave with the bottom and smaller morphologies A framework has been outlined in which empirical relations for a more physically sound representation of large roughness elements will be developed (Leschka & Oumeraci 2011) As part of this framework, basic parameter tests involving three cylinders subject to a solitary wave and a bore have been performed to better understand the interaction between roughness elements. The numerical domain characteristics of the solitary wave and bore cases are summarized in table 1 and presented in figure 1.e) and f), respectively
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
