H. S. Arunakumar

Bio: H. S. Arunakumar is an academic researcher from National Institute of Technology, Karnataka. The author has contributed to research in topics: Attenuation & Vegetation (pathology). The author has an hindex of 1, co-authored 1 publications receiving 2 citations.

Effect of Emerged Coastal Vegetation on Wave Attenuation Using Open Source CFD Tool: REEF3D

Abstract: Coastal vegetation is a soft solution for protecting the coast from the action of waves by attenuating the wave height and reducing the energy of the waves. Effect of wave height attenuation as a result of the presence of emerged coastal vegetation is studied numerically by resolving the Reynolds-averaged Navier–Stokes (RANS) equations. A three-dimensional numerical wave tank model is simulated using an open source computational fluid dynamics (CFD) software REEF3D, and wave attenuation due to emerged coastal vegetation is determined. An artificial, rigid, emerged vegetation for a length of 2 m is developed in a numerical wave tank of REEF3D. The model is tested for regular waves of height 0.08, 0.12, and 0.16 m and wave periods of 1.8 and 2 s in a water depth of 0.40 and 0.45 m. The wave heights are measured at different locations along the vegetation meadow at 0.5 m intervals. The devolved numerical model is corroborated by comparing the obtained numerical results with the experimental results as reported by John et al. (Experimental investigation of wave attenuation through artificial vegetation meadow, ISH—HYDRO, [1]). The numerically obtained results are concurrent with the experimental results.

A Comparison of Different Wave Modelling Techniques in An Open-Source Hydrodynamic Framework

Abstract: Modern design for marine and coastal activities places increasing focus on numerical simulations. Several numerical wave models have been developed in the past few decades with various techniques and assumptions. Those numerical models have their own advantages and disadvantages. The proper choice of the most useful numerical tool depends on the understanding of the validity and limitations of each model. In the past years, REEF3D has been developed into an open-source hydrodynamic numerical toolbox that consists of several modules based on the Navier–Stokes equations, the shallow water equations and the fully nonlinear potential theory. All modules share a common numerical basis which consists of rectilinear grids with an immersed boundary method, high-order finite differences and high-performance computing capabilities. The numerical wave tank of REEF3D utilises a relaxation method to generate waves at the inlet and dissipate them at the numerical beach. In combination with the choice of the numerical grid and discretisation methods, high accuracy and stability can be achieved for the calculation of free surface wave propagation and transformation. The comparison among those models provide an objective overview of the different wave modelling techniques in terms of their numerical performance as well as validity. The performance of the different modules is validated and compared using several benchmark cases. They range from simple propagations of regular waves to three-dimensional wave breaking over a changing bathymetry. The diversity of the test cases help with an educated choice of wave models for different scenarios.

Quantitative delimitation of radiant belt toward lake of lake-terrestrial ecotone

Abstract: Abstract Background Lake-terrestrial ecotone is a transition zone between terrestrial and aquatic ecosystems. Linking land and lake, it is thus highly sensitive and vulnerable to disturbances. It includes three parts, namely, radiant belt toward land, shoreline zone and radiant belt toward lake. Extending from multi-year average low water level line to open water, radiant belt toward lake is a key part of lake-terrestrial ecotone. However, the delimitation method for radiant belt toward is unsolved, which is a big obstacle to protecting lake-terrestrial ecotone effectively. Wave is a major hydrodynamic factor in lakes, especially large shallow lakes. For linking landward and waterward directions, the boundary of radiant belt toward lake may be affected by waves. Hence, exampled as Lake Taihu, this research was carried out from wave perspective. Results In July 2021, a total of 12 species aquatic macrophyte were collected, including 3 species of floating-leaved and 9 submerged macrophyte within radiant belt toward lake of Lake Taihu. Aquatic macrophyte were incorporated into calibrated wave models driven by constant winds via MIKE21 SW. Wave height attenuation was successfully simulated, ranging − 0.19% ~ 8.89% under eastern-wind condition and − 0.08% ~ 23.37% under western-wind condition. In general, wave height gradually attenuates from shore to water. The abrupt change point in relative wave height was used as the boundary of the radiant belt toward lake. A total of 26 sampling lines from bank to water around the whole lake of Lake Taihu were set, ranging 701 ~ 2155 m. Based on the setups of sampling lines, the delimitation range of Lake Taihu is about 1 ~ 2 km. Conclusions A novel approach was developed for quantitative delimitation of radiant belt toward lake. Both wind forcing and aquatic vegetation has slight impact on results of delimitation, indicating the feasibility of this approach. It determines a theoretical boundary of lake-terrestrial ecotone, which is helpful to a more precise protection and restoration of large shallow lakes. Moreover, it could provide a potential method for quantitative delimitation for large shallow lakes with similar conditions.