Faculty Publications

Now showing 1 - 5 of 5

Stability of breakwater defenced by a seaward submerged reef
(2006) Shirlal, K.G.; Rao, S.; Ganesh, V.; Rao, M.
The stability of a uniformly sloped conventional rubble mound breakwater defenced by a seaward submerged reef is investigated using physical model studies. Regular waves of wide ranging heights and periods are used. Tests are carried out for different spacings between two rubble mound structures (X/d=2.5-13.33) and for different relative heights (h/d=0.625-0.833) and relative widths (B/d=0.25-1.33) of the reef. It is observed that a reef of width (B/d) of 0.6-0.75 constructed at a seaward distance (X/d) of 6.25-8.33 breaks all the incoming waves and dissipates energy and protects the breakwater optimally. © 2005 Elsevier Ltd. All rights reserved.
Ocean wave transmission by submerged reef-A physical model study
(2007) Shirlal, K.G.; Rao, S.; Rao, M.
Ocean waves can be destructive as steeper waves due to their high energy eroding the sandy beaches. During storm surge or high tide, the water level rises and if large waves occur, they will break closer to the beach, releasing enormous amount of energy resulting in strong currents. This causes heavy loss of beach material due to large-scale erosion. If these waves are made to break prematurely and away from the beach, they can be attenuated so as to reduce beach erosion. The reef, which is a homogeneous pile of armour units without a core, breaks the steeper ocean waves, dissipates a major portion of their energy and transmits attenuated waves. This paper experimentally investigates the armour stone stability of the submerged reef and the influence of its varying distance from shore and crest width on ocean wave transmission. © 2007 Elsevier Ltd. All rights reserved.
Physical model studies on wave transmission of a submerged inclined plate breakwater
(2009) Rao, S.; Shirlal, K.G.; Varghese, R.V.; Govindaraja, K.R.
This paper examines the results of physical model studies conducted in a monochromatic wave flume, to evaluate the wave transmission characteristics of a submerged plate breakwater consisting of a fixed plate of 0.50 m length and 0.003 m thickness. The model was oriented at varying inclinations and submergence. The influence of wave steepness, relative depth, relative submergence and angle of inclination on wave transmission was analysed. It was found that the horizontal plate is effective for short waves with steepness parameter higher than 5×10-3 in relative depth grater than 0.21. The plate oriented at an angle of inclination of 60° is found to be effective for the entire ranges of wave parameters considered for the study and it reduces the wave height by about 40%. © 2009 Elsevier Ltd. All rights reserved.
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.
Laboratory investigation on hydraulic performance of enlarged pile head breakwater
(Elsevier Ltd, 2020) Suvarna, P.S.; Hunasanahally Sathyanarayana, A.H.; Umesh, P.; Shirlal, K.G.
Coastal erosion of beaches has been a common problem around the world. One of the eco-friendly control measures for coastal erosion is to dissipate the energy of waves impinging on the shores by constructing offshore breakwater. Pile breakwater is one such type of offshore breakwater that consists of a number of closely spaced piles. Construction of piles at closer spacing is highly challenging and expensive. This problem can be addressed by reducing the number of piles and modifying the pile with an enlarged head in the vicinity of the water surface, where wave energy is concentrated. In the present study, an experimental investigation on the hydraulic performance of enlarged pile head breakwater is conducted in a wave flume. The concept breakwater is subjected to monochromatic waves of varying wave heights, wave periods and water depth. The experimental results show that the least value of transmission coefficient is 0.62 and reflection coefficient is 0.123 with the highest value of dissipation coefficient of 0.77 for the structural configuration of b/D ratio of 0.2, D/Hmax of 0.6 and Y/Hmax of 1.0 at a water depth of 0.3 m. Observed results are encouraging and are in line with the similar type of pile breakwaters in a single row. The present experimental data is also validated with the available theoretical solutions. Since the results from the compared theoretical solution are not in good agreement, a hybrid theoretical model is reconstructed based on experimental results of pile head breakwater. The proposed modified version of the hybrid equation predicts encouragingly better transmission, reflection and dissipation coefficient than the existing solutions. Moreover, the results predicted by the proposed hybrid equation are in good agreement with that of other similar pile breakwater models. © 2020 Elsevier Ltd

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