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Item Effect of emerged coastal vegetation on wave attenuation using open source CFD tool: REEF3D(Springer, 2019) Hunasanahally Sathyanarayana, H.S.; Suvarna, P.; Abhijith, P.A.; Prabhu, A.S.; Umesh, U.; Kamath, A.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 2m 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. © Springer Nature Singapore Pte Ltd. 2019.Item Laboratory investigations on the effect of fragmentation and heterogeneity of coastal vegetation in wave height attenuation(Springer, 2019) Shirlal, K.G.; John, B.M.; Rao, S.It has long been known that “bio-shields” do function as a sustainable solution for preserving our coasts. The presence of gaps in the “bio-shield”, that is, the forest cover, referred to as patchiness, is a common phenomenon in natural habitats. Various anthropogenic and natural causes can result in such gaps in coastal forests. This paper presents the results of a physical model investigation carried out with a fragmented heterogeneous vegetation model in a wave flume 50 m long, 0.71 m wide and 1.1 m deep. The heterogeneous meadow is modelled as a combined body of artificial submerged seagrass, rigid vegetation and emergent vegetation. To study the effect of fragmentation in vegetation, transverse gaps of varying widths are introduced in the heterogeneous model. The material used for modelling is polyethylene and nylon. The test runs were carried out with monochromatic waves of heights ranging from 0.08 to 0.16 m in water depths of 0.40 and 0.45 m, and wave periods 1.8 and 2 s. The wave height measurements at different locations within the vegetated meadow exhibit an exponential decay of wave heights. The presence of gaps in vegetation does not have a significant effect on wave height reduction. However, the experimental study revealed that heterogeneous vegetation showed a great promise leading to considerable wave attenuation, thus offering a good level of protection to life and property on the leeside. © Springer Nature Singapore Pte Ltd. 2019.Item Effect of artificial vegetation on wave attenuation - An experimental investigation(Elsevier Ltd, 2015) John, B.M.; Shirlal, K.G.; Rao, S.In the wake of threats posed by rising sea levels and increasing severity of storms, the use of soft measures in coastal protection is acquiring an ever increasing importance. Coastal vegetation acts as a complex interface ecosystem between human communities and the sea and provides important ecosystem services by protecting these communities from coastal hazards, providing critical habitat for fishes and marine invertebrates and primary food source for animals like sea turtles. This paper tries to bring out the effect of simulated vegetation on wave attenuation through an experimental study. The tests were carried out with submerged artificial seagrass and artificial rigid vegetation in a 50 m long wave flume. For wave heights ranging from 0.08 m to 0.16 m at an interval of 0.02 m and wave periods 1.8 s and 2 s in water depths of 0.40 m and 0.45 m, measurements of wave heights at locations along the vegetation were observed. © 2015 The Authors. Published by Elsevier Ltd.Item Item Laboratory investigation on horizontal and vertical plate breakwaters(2010) Rao, S.; Shirlal, K.G.; Prashanth, S.; Varghese, R.V.Submerged breakwaters are commonly used for coastal protection on many eroding coasts. Plates are proved to induce wave breaking and dissipate wave energy. These have the advantages of low interference with current and sediment transport while saving substantial quantity of material. They permit exchange of surface and subsurface water and living organisms and hence, suitable for ecologically sensitive region. This paper explains the physical model studies to evaluate the transmission coefficients of a rigid submerged horizontal and vertical plate. It is found that the horizontal plate with ds/Hi < 1.0 is effective to bring the values of Kt below 0.6 when d/L > 0.22. Vertical plate is effective for the entire range of d/L for ds/Hi = 0. © 2010 Taylor & Francis Group, LLC.Item Wave steepness and relative width: Influence on transmission coefficient of horizontal interlaced, multilayered, moored floating pipe breakwater with five layers(2011) Rajappa, S.; Hegde, A.V.; Rao, S.; Channegowda, V.This paper presents the results of a series of physical model scale experiments conducted to determine the transmission characteristics of a horizontal interlaced, multilayered, moored floating pipe breakwater. The studies are conducted on physical breakwater models having five layers of PVC pipes. The wave steepness (H i/gT 2, where H i is incident wave height, g is acceleration due to gravity, and T is time period) was varied between 0.063 and 0.849, relative width (W/L, where W is width of breakwater and L is the wavelength) was varied between 0.4 and 2.65, and relative spacing (S/D, where S is horizontal centre to centre spacing of pipes and D is the diameter of pipes) was set equal to 2. The transmitted wave height is measured, and the gathered data are analyzed by plotting nondimensional graphs depicting the variation of K t (transmission coefficient) with Hi/gT 2 for values of d/W (d is depth of water) and of K t with W/L for values of H i /d. It is observed that K t decreases as H i /gT 2 increases for the range of d/W between 0.082 and 0.139. It is also observed that K t decreases with an increase in W/L values for the range of H i /d from 0.06 to 0.40. The maximum wave attenuation achieved with the present breakwater configuration is 78%.Item Study on performance of Savonius rotor type wave energy converter used in conjunction conventional rubble mound breakwater(Elsevier Ltd, 2014) Bikas, G.S.; Ramesh, H.; Hindasageri, V.In the present study the performance characteristics of a wave energy converter used in conjunction with conventional rubble mound breakwater is investigated using physical model studies. Savonius rotor type converter is used in the present study. The rotor is placed in front of the breakwater towards seaward side can cause substantial wave attenuation and thereby reduce the impact on the breakwaters apart from generating electricity. Regular waves of wide ranging heights and periods are considered in the present study. Tests are carried out for different spacing between the breakwater and the wave energy converter (X/d=10 to 40) and for two depth cases viz. shaft of the rotor at SWL (z=0) and rotor fully submerged case (z=-55 mm). The dead weight loading (shaft power) capacity for the rotor is also optimised in the present study. From the experimental study, it is observed that at a distance of X/d=22.5 to 30 and for submerged case (z=-55 mm) the rotor is found to be most efficient. It results in a wave height attenuation of 15-33%. © 2014 Elsevier Ltd.Item Laboratory investigations of wave attenuation by simulated vegetation of varying densities(Taylor and Francis Ltd. michael.wagreich@univie.ac.at, 2019) John, B.M.; Shirlal, K.G.; Rao, S.Coastal communities across the world are facing the need to adapt to rising sea levels, an increase in the frequency of natural hazards like storm surges, cyclones, tsunamis, and an increase in beach erosion. This present-day scenario calls for a sustainable, environment-friendly, and cost efficient solution for coastal protection. Under these circumstances, the role of vegetation in providing ecosystem services to coastal populations is becoming increasingly prominent. This work presents the results of an experimental study carried out with simulated rigid submerged and emergent vegetation meadows of varying plant densities in a wave flume 50 m long, 0.71 m wide and 1.1 m deep. The material used for modeling the vegetation is nylon. The tests are carried out with regular waves for water depths of 0.40 and 0.45 m, and wave periods 1.4–2 s at an interval of 0.2 s. Five different wave heights ranging from 0.08 to 0.16 m at an interval of 0.02 m are generated. Measurements of wave heights at different locations indicate an exponential decay in wave height along the vegetation meadow which leads to wave attenuation and confirms that vegetation can be a viable option for coastal protection. © 2017, © 2017 Indian Society for Hydraulics.