Browsing by Author "Shirlal, K.G."

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A laboratory investigation on a single row of suspended porous pipes is conducted in a two-dimensional wave flume to study their hydraulic performance under regular wave attack. The wave energy losses are computed and the effects of porosity, water depth, incident wave steepness and relative wave height on loss coefficient are studied. It is found that loss coefficient increases with an increase in incident wave steepness. Water depth has insignificant effect on K1 when wave steepness is varied. It is also observed that as porosity increases K1 decreases. For the range of variables studied, as the relative wave height increases, K1 decreases.
(Energy dissipation in suspended porous pipe breakwaters in laboratory) Rao, S.; Rao, N.B.S.; Shirlal, K.G.
2003
A laboratory investigation on a single row of suspended porous pipes was conducted in a two-dimensional regular wave flume to study their hydraulic performance. The wave energy losses at the structure were computed and the effects of depth of submergence, incident wave steepness, water depth, pipe diameter, percentage of perforations, size of perforations and relative wave height on loss coefficient were studied. It was found that as incident wave steepness increases, loss coefficient K 1 increases. Water depth has insignificant effect on K 1. It is also observed that as percentage of perforations increases, K 1 increases. For the range of variables studied, as the relative wave height increases, K 1 decreases.
(Energy dissipation at single row of suspended perforated pipe breakwaters) Rao, S.; Rao, N.B.S.; Shirlal, K.G.; Guddeti, G.R.
2003
A laboratory investigation on perforated hollow piles in two rows was conducted in a two dimensional regular wave flume to study the wave transmission and reflection characteristics. The influence of incident wave steepness, relative clear spacing between the piles and rows of piles on transmission co-efficient and reflection co-efficient have been investigated. The effect of staggering of piles in the rows on both transmission and reflection co-efficients was also studied. The present study has revealed that for perforated pile groups incident wave steepness, relative clear spacing between the piles, relative clear spacing between the rows of piles influence both transmission and reflection co-efficients. Staggering of piles reduces reflection from the perforated piles. Perforated piles have smaller transmission and reflection co-efficient values compared to that of non-perforated piles at lower wave steepness.
(Wave transmission and reflection for two rows of perforated hollow piles) Rao, S.; Shirlal, K.G.; Rao, N.B.S.
2002
Coastal Protection Using Geosynthetic Containment Systemsâ€”An Indian Timeline
(Springer Science and Business Media Deutschland GmbH, 2021) Elias, T.; Shirlal, K.G.
Maritime countries like India face serious coastal erosion issues. Over 1200Â km of Indian coastline is identified as eroding. Unavailability and high cost of natural rocks remain as a major hindrance for construction of conventional hard options like breakwaters, seawalls and groynes. This has forced coastal engineers to find nature friendly and economical alternatives. Experiences from Australia, Germany and United States prove the efficacy of geotextile containment systems in coastal protection. This chapter aims at reviewing Indian examples of protection works using geosynthetic and geotextile containment systems from early 1980s. Geosynthetic protection structures include groynes, submerged reefs, seawalls and breakwaters. Benefits and difficulties in implementation of protection works are identified by reviewing prominent works conducted in the east and west coast of India. Experiences at Hamla, Dahanu and Pentha helped in replacing conventional structures with geotubes. Equilibrium beach profile is attained using near-shore geotube reef system at Hamla and Dahanu, Maharashtra, whereas reef constructed using geotextiles at Candolim, Goa suffered serious damage due to vandalism and toe scour. Geosynthetic systems along with gabions and rock armours improve the stability, wave dissipation and reflection characteristics as seen in Pentha, Odisha and Uppada, Andhra Pradesh. Lack of proper design criteria and deliberate destruction by vandals remains as the major threat. Countering these challenges, geosynthetic containment systems offer a cost-effective alternative to conventional coastal protection methods in India. Â© 2021, Springer Nature Singapore Pte Ltd.
Comprehensive physical model study on wave transmission at plate structure
(CAFET INNOVA Technical Society 1-2-18/103, Mohini Mansion, Gagan Mahal Road, Domalguda, Hyderabad 500029, 2011) Shirlal, K.G.; Rao, S.; Varghese, R.V.
Investigators are increasingly concentrating their focus of research on coastal protection which is shifting from the hard measures to eco-friendly solutions with optimal usage of construction materials. A structure located near the water surface is known to be effective in bringing down the wave activity behind it, since; the energy of the waves is concentrated in the region close to the surface. This paper explains the comprehensive experimental study to evaluate the transmission coefficients (Kt) of various configurations of submerged plate structures. Kt for various plate configurations such as single plate, twin plate and combined plate are obtained. It is found that a single plate inclined at 60° to the horizontal is generally effective i. e. Kt ? 0.6 to a large extent. However, the twin and combined plate structures improved the performance. © 2011 CAFET-INNOVA TECHNICAL SOCIETY. All rights reserved.
Concrete cubes as armour unit—an experimental study for berm breakwater
(2011) Shirlal, K.G.; Rao, S.; Madhu, M.
Berm breakwater consists of a wide berm at or around the water level and has an armour layer, whose shape changes in response to wave action yielding a stable profile. In the present study the influence of wave height, wave period and berm width on the stability of the breakwater as well as on the wave runup and wave rundown are studied. Experiments were conducted on berm breakwater model of 1:30 scale using concrete cubes as armour units. For the given experimental conditions the stability number was found to vary from 2.21 to 3.63. Further the model in 0.37m water depth was more stable than the one in 0.40 and 0.43m. The runup values were within the range of 0.52 to 1.08. While, the rundown values had the variation from 0.45 to 0.88. © 2011 Taylor & Francis Group, LLC.
Development of concrete armoured protected breakwater structure
(CAFET INNOVA Technical Society 1-2-18/103, Mohini Mansion, Gagan Mahal Road, Domalguda, Hyderabad 500029, 2011) Rao, M.; Rao, S.; Shirlal, K.G.
The present work involves the physical model study of stability of conventional single breakwater and the reef protected breakwater, constructed with concrete cube as an artificial armour unit. Regular waves of wide ranging heights and periods are used. The tests are carried out for different spacings between the two 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 1.0-1.33 constructed at a seaward distance (X/d) of 6.25-8.33 exhibits a transmission coefficient (Kt) of 0.38-0.708, wave dissipates energy and protect the breakwater optimally. © 2011 CAFET-INNOVA TECHNICAL SOCIETY. All rights reserved.
Effect of armour unit layers and placement mode in the determination of stability of geotextile sand container (GSC) breakwaters
(Elsevier Ltd, 2022) Elias, T.; Geetha, T.; Shirlal, K.G.
Geosynthetic Sand Containers (GSCs) are increasingly harnessed for their coastal protection capabilities. Recent studies point to its efficacy to be used even as armour units of breakwaters. The current investigation aims at understanding the effect of armour unit layers and placement modes in altering the stability of GSC breakwaters. Single-layered and double-layered GSC structures with slope parallel and perpendicular placement are tested for stability against wave conditions of the Mangaluru coast. A 1:30 scaled monochromatic wave flume model study is adopted to detail the damage levels and stability of various GSC breakwaters. It is observed that the stability of structure increased by up to 17% when supplemented with double layers. Structure tends to be stable with increasing armour units size and fill percentage. Larger bags stacked to double layers is found to be the most stable configuration. 80% filled, slope parallel placement exhibited the least stability. The paper dealt with all factors affecting structure stability and deduced stability nomograms helpful for coastal engineers to design GSC breakwaters. © 2022
Effect of artificial vegetation on wave attenuation - An experimental investigation
(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.
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. Â© 2015 The Authors. Published by Elsevier Ltd.
Experimental Investigation of the Hydraulic Performance of Breakwater Structures with Geotextile Armor Units
(American Society of Civil Engineers (ASCE), 2022) Elias, T.; Shirlal, K.G.
Geotextile sand containers (GSCs) gained popularity recently as a modern age coastal protection measure. Its usability as an ecofriendly alternative for traditional breakwaters overcomes issues such as scarcity and quarrying prohibition of natural rocks. The current work involves a 1:30 scaled physical experimentation on the hydraulic performance of an emerged, nonovertopping breakwater model with GSCs. Four configurations of GSC structures are analyzed for their runup, rundown, and reflection characteristics confining to wave parameters of Mangaluru. The study revealed that the reflection coefficient (Kr) for GSC structures could range from 0.26 to 0.69. In addition, reducing GSC fill percentage from 100 to 80 is found to be more effective (up to 64%) in reducing reflection, runup, and rundown rates, than altering GSC size. These results can serve as a practical guideline for designing GSC breakwaters. © 2022 American Society of Civil Engineers.
Experimental Study of Pipe Artificial Reef on Wave Attenuation
(Springer Science and Business Media Deutschland GmbH, 2025) Xaviour, S.; Shirlal, K.G.
Submerged artificial reefs are the coastal structures that protect the coast-line in an effective way with minimum damage to the coastal environment and enhance the marine ecology in the region. The artificial reefs (AR) commonly used come in various shapes and sizes, which offer different levels of coastal protection and serve various recreational purposes. This paper discusses a physical model study that provides insight into comparing the performance of circular pipe-shaped submerged artificial reef structures made of two different diameter pipes, tested under different wave conditions in a wave flume. The inference of the study shows that the larger diameter AR shows comparatively less wave transmission compared to the smaller diameter AR. However, the wave transmission reduction is considerably less with the maximum change noted to be under 26%. Â© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2025.
Hydraulic performance of perforated enlarged pile head breakwaters through laboratory investigation
(Elsevier Ltd, 2021) Suvarna, P.S.; Hunasanahally Sathyanarayana, A.H.; Umesh, P.; Shirlal, K.G.
An economical, ecofriendly and efficient breakwater system is vital for coastal protection and harbour tranquility. In this regard, various researchers are working to develop the appropriate solutions to encounter site-specific challenges. With this viewpoint, concept of enlarged pile head breakwater is developed. The study focuses on improving the hydraulic efficiency of pile breakwater by enlarging the structure near the free surface and providing it with perforations. Effect of percentage distribution of perforations, size of perforations and percentage of perforations on wave transmission, reflection and dissipation characteristics of the structure is investigated. The physical experiments are conducted in a two-dimensional wave flume under varying monochromatic wave climates. Results indicate that the pore size highly dominants the wave attenuation than considering the increasing percentage of perforations with the small size of the pore. Perforations effectively reduce the Kt of about 10%–18% to that of non-perforated pile head breakwater. Hydraulic efficiency of enlarged pile head breakwater is optimum when D/Hmax = 0.6, Y/Hmax = 1.0, b/D = 0.2, S = 0.25D, pa = 75% and P = 22.5 at 0.3 m water depth. A hybrid theoretical solution is developed based on the current set of experimental data for the quick estimate of hydraulic coefficients. The proposed hybrid equation for the perforated pile breakwater predicts more desirable values of Kt, Kr and Kd. The proposed concept of breakwater gives a reasonably enhanced hydraulic efficiency than the compared type of breakwaters. © 2021 Elsevier Ltd
Hydraulic performance of tandem breakwater with concrete cubes as armour units
(2009) Rao, M.; Shirlal, K.G.; Rao, S.; Bharadwaj, P.
Tandem breakwater system consists of a conventional breakwater protected by a seaward submerged reef. The paper discusses physical model study on the hydraulic performance of an isolated as well as tandem breakwater system subjected to varying wave climate and water depths, while keeping a constant crest width of submerged reef. The breakwater in both the cases are armoured with concrete cubes and the submerged reef is constructed with natural stones. It is found that the isolated breakwater is damaged for all waves except those of period 2.5 s. While a submerged reef of crest width (B) 0.40m placed at a seaward spacing(X) of 2.5m transmits only 52% to 81% of the incident wave height and thereby reduces the wave force on the main structure which inturn protects the inner main breakwater completely without causing any damage.
In order to study sediment travelling paths across shoreline in different seasons, sediment samples were collected normal to the shoreline along three profiles, separated by 220m from Surathkal beach near Karnataka Regional Engineering College (K.R.E.C.), Karnataka. The sediments were analysed for their grain size characteristics (statistical parameters) and sediment trend matrix was prepared. By using sediment trend matrix, sediment travelling paths were drawn. It has been found that during premonsoon, sediments were moving predominantly towards offshore region, resulting in erosion. Sediments were moving predominantly towards shore and build-up of beach takes place during the post monsoon season.
(Sediment trend matrix analysis along shore normal transects off Surathkal beach, Karnataka) Rao, S.; Shirlal, K.G.; Rao, N.B.S.
2003
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
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.
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.
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
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.