Journal Articles
Permanent URI for this collectionhttps://idr.nitk.ac.in/handle/123456789/19884
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Item Influence of combined grain refinement and modification on the microstructure, tensile strength and wear properties of Al-15Si, Al-15Si-4.5Cu alloys(Carl Hanser Verlag Kolbergerstrasse 22 Munchen D-81679, 2015) Channappagoudar, S.; Sannayallappa, N.; Desai, V.; Venkateswarlu, V.Microstructure, tensile strength and dry sliding wear studies of Al-15Si, Al-15Si-4.5Cu alloys with and without grain refinement and modifications are presented. Experimental alloys such as Al-15Si and Al-15Si-4.5Cu were conventionally melted and gravity die cast. For grain refinement, 1 wt.% of Al-1Ti-3B and for modification, 0.17 wt.% of aluminum phosphide (AlP) and 0.4 wt.% of Al-10Sr were added to the alloy melt. The results reveal refined microstructure due to grain refinement, modification, improved hardness, higher tensile strength and better sliding wear. Moreover, Al-15Si-4.5Cu alloy (untreated and treated) showed improved mechanical properties as compared to conventional hypereutectic Al-Si alloy. © Carl Hanser Verlag GmbH & Co. KG.Item Influence of combined grain refinement and modification on the Microstructure, tensile strength and wear properties of Al-15Si, Al-15Si-4.5Cu alloys(Carl Hanser Verlag Kolbergerstrasse 22 Munchen D-81679, 2015) Channappagoudar, S.; Sannayallappa, N.; Desai, V.; Venkateswarlu, V.Microstructure, tensile strength and dry sliding wear studies of Al-15Si, Al-15Si-4.5Cu alloys with and without grain refinement and modifications are presented. Experimental alloys such as Al-15Si and Al-15Si-4.5Cu were conventionally melted and gravity die cast. For grain refinement, 1 wt.% of Al-1Ti-3B and for modification, 0.17 wt.% of aluminum phosphide (AlP) and 0.4 wt.% of Al-10Sr were added to the alloy melt. The results reveal refined microstructure due to grain refinement, modification, improved hardness, higher tensile strength and better sliding wear. Moreover, Al-15Si-4.5Cu alloy (untreated and treated) showed improved mechanical properties as compared to conventional hypereutectic Al-Si alloy. © Carl Hanser Verlag GmbH & Co. KG ISSN 1862-5282.Item Wave scattering by vertical porous block placed over flat and elevated seabed(Springer Science and Business Media Deutschland GmbH, 2019) Venkateswarlu, V.; Karmakar, D.The present study addresses the hydrodynamic characteristics of the incident wave through porous structure for both finite and shallow water depth. The oblique wave transformation due to the porous block over flat and elevated seabed and the submerged rigid block is presented. Analytical direct formulae are proposed to determine the wave reflection and transmission coefficient for the porous structure considering different configurations like porous block, porous block backed by wall, vertical wall away from the porous block and semi-infinite porous block at flat and elevated seabed. The analytical results for wave interaction with porous structure are presented considering the mode-coupling relation and eigenfunction expansion technique. Further, the significance of the semi-infinite porous block placed on the flat and elevated seabed is studied in detail. The analytical results obtained in the present study are validated with the numerical results available in the literature for specific cases. The significance of the critical angle and skin depth for the semi-infinite structure is explored in the wave structure interaction problems. The comparative study between various structural configurations suggests that, if the ratio of wavelength and width of the structure is greater or equal to unity (d/??1), then the structure can be regarded as semi-infinite porous block for flat and elevated seabed. The derived analytical formulae will be helpful in the preliminary design and analysis of the porous blocks. © 2019, Sociedade Brasileira de Engenharia Naval.Item Influence of impermeable elevated bottom on the wave scattering due to multiple porous structures(Isfahan University of Technology secretary@jafmonline.net, 2020) Venkateswarlu, V.; Karmakar, D.The significance of multiple porous structures with finite spacing upon elevated seabed in the presence and absence of the leeward wall is examined under oblique wave impinging. Fluid propagation is assumed over the impermeable elevated bottom, and the fluid realm is separated into open water and porous structure regions. Continuity of the dynamic pressure and mass fluxes at the interfaces of the porous structure and the open water regions are adopted. The resistance and reactance due to the presence of the porous structure are taken into account using the porous structure dispersion relation. The numerical model is developed based on the eigenfunction expansion method along with matched velocity potentials at the interfaces of open water and the porous block regions. The wave reflection and transmission characteristics, energy damping and wave force impact on the leeward wall is analysed. The significance of the porosity, structural width, angle of incidence, width between the two structures and water chamber length is studied considering multiple porous blocks with finite spacing under oblique wave impinging in the presence and absence of leeward wall. The numerical results obtained in the present study agrees well with the theoretical and experimental results available in the literature. The present study illustrates that, with the increase in the number of porous blocks and gap between the porous blocks, the resonating trend is observed in the wave transformation and the influence of the elevated step height is revealed for the wave trapping. © Isfahan University of Technology.Item Significance of seabed characteristics on wave transformation in the presence of stratified porous block(Taylor and Francis Ltd. michael.wagreich@univie.ac.at, 2020) Venkateswarlu, V.; Karmakar, D.The wave transformation due to the presence of stratified porous structure lying on flat seabed, elevated seabed, and stepped seabed is analyzed under the oblique wave incidence. The stratified porous structure in the absence and presence of the leeward wall along with the confined region is examined using the matched eigenfunction expansion technique. The direct analytical relations are obtained to examine the wave transformation for the case of long-wave approximations for multilayered porous structure lying on various types of seabed. The wave reflection coefficient, transmission coefficient, energy damping, and wave force on the vertical wall in the presence of stratified porous block are analyzed with variation in the sea-bed characteristics, porosity, friction factor, structural width, and water chamber length. The study shows that the energy damping increases with the increase in the porosity of the seaside porous layer due to the presence of high void spaces. Further, the stratified porous structure shows a considerable impact in decreasing the resonating peaks and troughs for the wave force acting on the seawall. In addition, the stepped seabed is observed to reduce the wave force on the leeward wall as compared with the uniform and elevated seabed in the presence of stratified porous block. © 2019, © 2019 Japan Society of Civil Engineers.Item Wave transformation due to barrier-rock porous structure placed on step-bottom(Taylor and Francis Ltd. michael.wagreich@univie.ac.at, 2020) Venkateswarlu, V.; Karmakar, D.The oblique wave transport through barrier-rock porous structure for different structural configurations are examined considering impermeable uniform/step-bottom topography. The numerical study is performed on using the linearised wave theory and mode-coupling relation at seaward/leeward structural interfaces. The wave reflection, transmission, energy absorption, wave force on the rigid wall, the wave force on seaward and leeward barriers is reported considering various ranges of porosity, friction factor, structural thickness, trapping chamber spacing and angle of impinging. The analytical relations for calculating the wave reflection and transmission coefficients are reported for plane-wave approximation and the effectiveness of present analytical results are verified with the available literatures for specific structural configurations. The fluid resonance plays a vital role in the design of trapping chamber thickness, and resonating troughs in wave scattering suggest an effective structural configuration for better wave damping. © 2019 Informa UK Limited, trading as Taylor & Francis Group.Item Scattering of Gravity Waves by Multiple Submerged Rubble-Mound Breakwaters(Springer Science and Business Media Deutschland GmbH info@springer-sbm.com, 2020) Vijay, K.G.; Venkateswarlu, V.; Karmakar, D.A numerical model based on multi-domain is developed to investigate the scattering of surface gravity waves by an array of submerged rubble-mound breakwaters. The boundary value problem is analysed in two dimensions under the assumption of small-amplitude wave theory in the water of finite depth. Analytical solution based on the eigenfunction expansion method is independently developed to validate the numerical model in addition to available results in the literature. Various configurations such as trapezoidal, triangular, and circular shapes are investigated parametrically. The performance characteristics are discussed by analysing the scattering coefficients (such as reflection, transmission, and damping coefficient) for different physical parameters like relative water depth, relative structural dimensions, relative spacing, and the number of submerged breakwaters. In the case of trapezoidal breakwaters, the crest width plays a major role in dampening the wave energy by a whopping 90%. Moreover, the wave damping performance of triangular breakwaters is very poor. The Bragg resonant reflection is observed to be a trivariate function, which depends on structural porosity, structural thickness, and the number of submerged breakwaters. The free spacing is evident in adjusting the position of Bragg resonant reflection by multiple equi-spaced structures of several shapes. The present study will be useful in the effective design of Bragg breakwaters for establishing a calm wave environment near the harbour regions. © 2020, King Fahd University of Petroleum & Minerals.Item Surface gravity wave scattering by multiple energy absorbing structures of variable horizontal porosity(Taylor and Francis Ltd., 2020) Venkateswarlu, V.; Praveen, P.; Karmakar, D.The oblique wave scattering by fully-extended two-layered, three-layered and submerged two-layered porous structures occupying finite width is reported using an analytical model based on the eigenfunction expansion method. The fully extended two-layered structure is composed of two porosities and friction factors in the surface porous layer and the bottom porous layer. In addition, the three-layered energy-absorbing structure is composed of two-porous layers along with the bottom rigid layer to replace the natural seabed variation. Further, the study is extended for multiple energy-absorbing structures to report the impact of free spacing available between the two subsequent structures on fluid resonance. The two-layered porous structure dispersion relation is derived and solved using step approach and Newton-Raphson method. The derived analytical results are validated with the published results of notable authors. The effect of the surface and bottom layers porosity, friction factor, free spacing, structural width, number of structures, and angle of contact on the wave scattering is reported. Finally, the comparative study between the single and multiple energy absorbing structures of multiple horizontal layers is discussed. Further, the significance of the critical angle of contact and fluid resonance for better wave blocking is presented precisely, which is essential for the coastal engineers to design offshore structures. © 2020 Japan Society of Civil Engineers.Item Wave motion over stratified porous absorber combined with seaward vertical barrier(SAGE Publications Ltd info@sagepub.co.uk, 2020) Venkateswarlu, V.; Karmakar, D.The oblique wave reflection by horizontally stratified porous absorber having two horizontal porous bars of different porosities and friction factors placed on step-type bottom is studied using eigenfunction expansion method based on linearised wave theory. The present study examines several structural configurations such as porous absorber consisting of finite and semi-infinite thickness with/without seaward vertical barrier. The present study derived the direct analytical relations to determine wave reflection by each of the structural configuration for plane-wave assumption using potential flow theory. Initially, the porous absorber considering uniform porosity and friction factor is examined and validated with available numerical results, and the direct analytical relations are also validated with available relations of possible structural configurations. In addition, the present study reported wave reflection performance of submerged single-layer and double-layer porous absorbers with/without seaward vertical barrier. The effect of bottom rigid bar, surface porous bar, middle porous bar depth, multiple porosities, friction factors, incident wave angle and porous effect parameter on wave reflection coefficient is presented in detail for various structural configurations. The significance of seaward vertical barrier on wave reflection and wave trapping is reported. The point of wave trapping, critical angle of impinging, resonating peaks and troughs due to various structural configurations are presented against structural thickness. © IMechE 2020.Item Gravity wave trapping by series of horizontally stratified wave absorbers away from seawall(American Society of Mechanical Engineers (ASME), 2020) Venkateswarlu, V.; Karmakar, D.The fluid oscillation between the rigid wall and stratified wave absorber is analyzed in the context of the linearized water wave theory. The stratified wave absorber is composed of multiple horizontal layers considering higher porosity in the surface layer, moderate porosity in the middle layer, and zero porosity in the bottom layer. The study examined the wave motion through multiple horizontally stratified wave absorbers on solving the multilayer dispersion relation. The eigenfunction expansion method is used to form the system of analytical equations using the property of orthogonal mode-coupling relation with continuity of dynamic pressure and velocity at each of the interfaces. The free spacing available between leeward porous wave absorber and the rigid wall is termed as “trapping chamber.” The effect of the trapping chamber on wave reflection and fluid force experienced by a rigid wall is discussed. The analytical results formulated for the physical problem are validated with the available experimental and numerical results. The wave trapping is examined and compared for three types of seawalls such as vertical wall, permeable wall, and stepped wall. The change in trapping chamber length shows the harmonic peaks and troughs in the trapping coefficients and the harmonic oscillations help in the design and development of the stratified porous wave absorbers for the protection of marine infrastructure. © © 2020 by ASME