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Experimental investigations on perforated hollow piles in two rows were conducted in a two dimensional wave flume. The influence of water depth, incident wave steepness, clear spacing between the piles and the spacing of pile rows on transmission coefficient have been studied. The effect of staggering of piles in rows is investigated. The results are also compared with the results of experiments on piles without perforations. The investigations have revealed that perforated piles attenuate more wave energy than non-perforated piles. The transmission coefficient K(t) decreases as the wave steepness increases for both non-perforated and perforated piles. For non-perforated piles as relative clear spacing between the piles (b/D) decreases, for waves of higher steepness, K(t) decreases while for perforated piles as b/D decreases, K(t) is decreasing for all the steepness considered. As the relative clear spacing between the pile rows (B/D) increases K(t) initially decreases till B/D is around one and later it starts increasing for both non-perforated and perforated piles. Staggering of piles has little effect on K(t). It is also found that water depth has insignificant influence on transmission coefficient at higher steepness for both perforated and non-perforated piles. Wave period alone does not directly influence transmission coefficient K(t).; Experimental investigations on perforated hollow piles in two rows were conducted in a two dimensional wave flume. The influence of water depth, incident wave steepness, clear spacing between the piles and the spacing of pile rows on transmission coefficient have been studied. The effect of staggering of piles in rows is investigated. The results are also compared with the results of experiments on piles without perforations. The investigations have revealed that perforated piles attenuate more wave energy than non-perforated piles. The transmission coefficient Kt decreases as the wave steepness increases for both non-perforated and perforated piles. For non-perforated piles as relative clear spacing between the piles (b/D) decreases, for waves of higher steepness, Kt decreases while for perforated piles as b/D decreases, Kt is decreasing for all the steepness considered. As the relative clear spacing between the pile rows (B/D) increases Kt initially decreases till B/D is around one and later it starts increasing for both non-perforated and perforated piles. Staggering of piles has little effect on Kt. It is also found that water depth has insignificant influence on transmission coefficient at higher steepness for both perforated and non-perforated piles. Wave period alone does not directly influence transmission coefficient Kt.
(Elsevier Sci Ltd, Laboratory investigation on wave transmission through two rows of perforated hollow piles) Rao, S.; Rao, N.B.S.; Sathyanarayana, V.S.
1999
The basic principle involved in the design of S-shaped breakwater is the provision of a wide berm at or around the water level with smaller size armor stones than that used in conventional design, which are allowed to reshape till an equilibrium slope is achieved. An attempt is made to assess the influence of wave height, wave period, and berm width on the stability of S-shaped breakwater with reduced (30% reduction in armor stone weight) armor unit weight. From the investigation, it is found that the berm breakwater with 30% reduced armor weight would be stable for the design wave height if the berm width is 60 cm and wave period 1.2 s. For higher wave periods studied, zero damage wave height reduces by 20-40% of the design wave height. Wave period has large influence on the stability of berm breakwaters. The runup increases with decrease in weight up to Wo/W=0.9. © 2004 Elsevier Ltd. All rights reserved.
(Stability of berm breakwater with reduced armor stone weight) Rao, S.; Pramod, Ch.; Balakrishna Rao, K.B.
2004
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.
Stability aspects of nonreshaped berm breakwaters with reduced armor weight
(2008) Rao, S.; Subrahmanya, K.; Balakrishna Rao, B.K.; Chandramohan, V.R.
The present work involves the investigation of the influence of wave height, wave period, water depth, and sea-ward slope on the stability, wave runup, and wave rundown of statically stable rubble-mound berm breakwater. The weight of armor stones used in the present study is 20% lighter than the weight that is required for a conventional breakwater, designed using Hudson formula for a wave height of 0.1 m in the model. In the present work models with a berm width of 0.6 m, at constant depth of 0.32 m from the seabed were tested. The damage to the breakwater model with the berm was compared with the results on a model without the berm using different armor weights. The variation of relative runup and rundown was found for different values of wave steepness and water depths in front of the structure. The damage to the breakwater, wave runup, and rundown for the structure with seaward slope 1:2 and 1:1.5 were compared. The investigation was carried out in the Marine Structures Laboratory, Department of Applied Mechanics and Hydraulics, National Institute of Technology Karnataka, Surathkal. © 2008 ASCE.
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.
On numerical modelling of waves, currents and sediment movement around Gurupur-Netravathi river mouth
(2010) Radheshyam, B.; Rao, S.; Shirlal, K.G.
This paper presents an overview of the investigations that were carried out to understand the coastal process along Bengre and Ullal at the Gurupur-Netravathi River mouth in the west coast of India. This river inlet was facing problems of migration and siltation since several decades and therefore two rubble mound breakwaters were constructed during the year 1994 as an intervention to maintain the inlet mouth. After the construction of these river training jetties, the inlet was stabilized, but severe erosion has been taking place along the Ullal spit on the south side of southern breakwater, since 1996 and heavy accretion on the North of Northern Breakwater along Bengre spit, which is now almost stabilized. This study has been undertaken to understand the hydrodynamics along the beaches adjoining the river mouth. For the present study, various field data was collected for the post monsoon season of 2006. The hydrodynamic (HD), Parabolic mild slope (PMS) and Sediment transport (ST) modules of MIKE-21 software were used to understand the hydrodynamics of the study area. Before the model was made use, it was first validated by using field data to understand the hydrodynamics of the area. Since the field data is of limited duration, data collected from the NMPT wave buoy for an entire year was used for the model simulation. From the studies it was confirmed that current direction and sediment movement follow a similar pattern in monsoon and pre-monsoon and a different pattern during post-monsoon. It is observed that the main cause of erosion is due to direct action of waves on the adjoining beaches of the coast and the beaches in the study area are generally in dynamic equilibrium with a small amount of erosion at Ullal. © 2010 CAFET-INNOVA TECHNICAL SOCIETY. All rights reserved.
Variation of transmission coefficient and mooring forces with wave steepness on horizontal interlaced multilayered moored floating pipe breakwater with three layers
(2011) Rajappa, S.; Pramod, K.; Hegde, A.V.; Rao, S.
The paper presents the results of a series of physical model scale experiments conducted for the study of the transmission characteristics and mooring forces of horizontal interlaced, multi-layer, moored floating pipe breakwater, part of which have been presented in conferences. The studies are conducted on physical breakwater models having three layers of PVC pipes, wave steepness, Hi/L (Hi is incident wave height and L is incident wave length) varying from 0.01384 to 0.0661, relative width, W/L (W is width of breakwater) varying from 0.4 to 2.65 and relative spacing, S/D = 3 (S is horizontal spacing of pipes and D is diameter of pipe). The transmitted wave height is measured and data gathered is analyzed by plotting non-dimensional graphs depicting the variation of Kt (transmission coefficient) with Hi/L for values of d/W (d is depth of water) varying between 0.082 to 0.276 and Kt with W/L for values of d/W varying between 0.082 to 0.221. It is observed that Kt marginally decreases as Hi/L increases for the range of d/W between 0.082 and 0.221, considered in the present study. The maximum wave attenuation achieved with present breakwater configuration is 68%. The variation of measured mooring forces are analyzed by plotting non-dimensional graphs depicting fs/?w2 and fl/?W2 (fs and fl are the forces in the seaside and leeside moorings per unit length of the breakwater, ? is the unit weight of sea water) as a function Hi/L for various values of d/W. The mooring force parameter (fs /?W2) increases with an increase in wave steepness (Hi/L) for a range of d/W values studied. It is observed that for d/W = 0.082, maximum force parameter attained was 2.11E-04, and for d/W = 0.276 maximum force parameter was 6.88E-04. A similar trend is observed for leeside side force parameter. Hence, it clearly indicates the influence of d/W on f/?W2. © 2011 CAFET-INNOVA technical society. All right reserved.
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%.
Reshaping berm breakwaters: A physical model study
(National Institute of Science Communication and Policy Research, 2018) Janardhan, P.; Rao, S.; Shirlal, K.G.
In the present study, the structural stability of statically stable reshaping berm breakwater for different wave parameters and armour weights were verified by physical model study carried out at NITK Surathkal Mangalore. Wave run-up and rundown studies were also carried out. The results show that a safe structure can be evolved with reduction in armour weight by up to 25% for all the relative berm position values. The position of berm greater than or equal to 1.3 was found to be good in reducing recession as well as wave run-up. An empirical new berm recession formula was derived for berm recession based on sea state and structural parameters. © 2018, National Institute of Science Communication and Information Resources (NISCAIR). All rights reserved.
Assessment of dynamic pressure and wave forces on vertical-caisson type breakwater
(Taylor and Francis Ltd., 2022) Kumaran, V.; Rao, M.; Rao, S.
The design and construction of coastal structures such as breakwaters, at great water depths is rapidly increasing as a result of the increasing draught of large vessels and off-shore land reclamations. Vertical caisson breakwaters may be the best alternative compared to ordinary rubble mound breakwaters in larger water depths, in terms of performance, total costs, environmental aspects, construction time and maintenance. To fulfilling the functional utility and impact of the structure on the sea environment, it is necessary to study the hydraulic performance. This can be found by field investigation, numerical simulations and by physical modelling. Scale modelling techniques are used to study various coastal engineering problems. This article presents the results obtained by conducting series of experiments in two-dimensional wave flume to assess the hydrodynamic performance of vertical-caisson breakwater, which is made of concrete, with the protection of toe. The dynamic pressure distribution, wave runup, wave reflection, wave forces and stability parameter on the vertical caisson breakwater are discussed. The maximum wave force on the wall breakwater is calculated from measured pressure values and is compared with the forces calculated by Goda’s and Sainflou wave theories. © 2021 Informa UK Limited, trading as Taylor & Francis Group.

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