Faculty Publications
Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736
Publications by NITK Faculty
Browse
8 results
Search Results
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 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.Item Investigation on innovative pile head breakwater for coastal protection(SAGE Publications Ltd, 2024) Hunasanahally Sathyanarayana, A.H.; Suvarna, P.S.; Umesh, P.; Shirlal, K.G.Coastal erosion is a global concern that has been augmenting due to the natural evolution of beaches, human activities and sea-level rise. One of the eco-friendly shore protection methods is to dissipate the wave energy by constructing offshore breakwaters. Conical pile head breakwater (CPHB) is one of the eco-friendly innovative offshore structures consisting of closely spaced piles with an enlarged cross-sectional area (conical pile head) in the vicinity of the free surface. In the present study, perforations are incorporated over the conical pile head to achieve higher efficiency by promoting energy dissipation. The influence of the perforations on the performance characteristics, namely wave transmission (Kt), wave reflection (Kr) and energy dissipation (Kd) of the perforated CPHB is comprehensively investigated through physical model studies. The effect of perforations and their distribution around the pile head (Pa), percentage of perforation (P) and size of perforations (S/D) on the wave attenuation characteristics are evaluated to arrive at an optimum configuration. The study is carried out under monochromatic waves of varying wave height (0.06–0.16 m) and wave period (1.4–2 s) at different depths of water (0.35, 0.40 and 0.45 m). A minimum Kt of 0.58 associated with Kr of 0.26 and Kd of 0.78 is obtained with an optimum configuration of Pa = 50%, P = 19.2% and S/D = 0.25. The Kt of the proposed CPHB is about 19 to 35% lesser than that of the perforated hollow pile breakwater under matching test conditions. Overall, providing the perforations is found to be effective in enhancing the wave attenuation capability by up to 12.4%. Further, empirical equations are formulated and validated with the experimental data. The empirical equations estimate the Kt and Kr values accurately with a high coefficient of determination (R2≥ 0.90). © IMechE 2023.Item Investigating the wave attenuation capabilities of rectangular pile head breakwater: A physical modelling approach(Elsevier Ltd, 2024) Hunasanahally Sathyanarayana, A.H.; Suvarna, P.S.; Banagani, V.K.Y.; Umesh, P.; Shirlal, K.G.The study provides a comprehensive examination of single row Rectangular Pile Head Breakwaters (RPHB), encompassing both non-perforated and perforated variations. In the non-perforated RPHB category, the investigation delves into the effects of pile head height and width, and wave climate. For perforated RPHB structures, the study analyses the influence of percentage of perforations, perforation size, and depth of water. Further, the research includes a comparative assessment between non-perforated and perforated RPHB structures. Additionally, the research conducts a comparative analysis with similar structures. In the case of non-perforated RPHB, the configuration with relative pile head diameter (D/d) of 2.4 and relative pile head height (Y/Hmax) of 1.5 stood out as the most effective model. Similarly, the perforated RPHB demonstrated its maximum wave attenuation potential with percentage of perforations (P) of 24% with relative size of perforations (S/D) of 0.25. This optimal configuration achieved a minimal wave transmission coefficient (Kt) of 0.53, reflection coefficient (Kr) of 0.33, and energy dissipation coefficient (Kd) of 0.79 at a relative water depth (h/H) 0.865. Notably, the introduction of perforations on the RPHB structure led to an improvement in wave attenuation performance by 4–8%, resulting in lower reflection and higher energy dissipation. Comparatively, the RPHB structure outperformed the Enlarged (cylindrical) Pile Head Breakwater (EPHB) and Conical Pile Head Breakwater (CPHB) structures in terms of wave attenuation, exhibiting higher reflection and superior energy dissipation characteristics. The consistent outcome of these investigations reveals that the RPHB exhibits superior hydrodynamic performance characteristics and design suitability, making it a promising choice for breakwater applications. © 2024 Elsevier Ltd