Browsing by Author "Raja, S."

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Analysis of piezoelectric composite beams and plates with multiple delaminations
(2006) Raja, S.; Prathima, Adya, H.P.; Viswanath, S.
In the present work, the effect of delamination or debonding on the static and dynamic characteristics of laminated piezoelectric beams and plates is studied. A four-noded quadrilateral shear flexible plate element is developed to model the damages in composite substrate and in piezoelectric layers. The elastic stiffness and electro-elastic stiffness degradations are introduced at the elemental level through coupled constitutive relations. The undamaged structure is modeled as a single laminate while the delaminated region is modeled as sublaminates whose interface contains the desired delamination or debonding. The continuity of displacement is maintained across the delaminated edge by imposing the strain-based multipoint constraints. Numerical studies are conducted on composite specimens with surface bonded active layers. The results are presented to evaluate the performance of these smart structures in the presence of delamination. For actuators, the performance is measured in terms of the achievable deflection control and in sensors as a measurable output voltage. It is observed that actuator and sensor debonding degrade the capabilities of active materials significantly. Therefore, the study concludes that a damage tolerant approach is essential for the design of smart structural systems to account for damage-induced uncertainty in the functional properties of smart actuators and sensors. Copyright 2006 SAGE Publications.
Analysis of piezoelectric composite beams and plates with multiple delaminations
(2006) Raja, S.; Prathima Adya, H.P.; Viswanath, S.
In the present work, the effect of delamination or debonding on the static and dynamic characteristics of laminated piezoelectric beams and plates is studied. A four-noded quadrilateral shear flexible plate element is developed to model the damages in composite substrate and in piezoelectric layers. The elastic stiffness and electro-elastic stiffness degradations are introduced at the elemental level through coupled constitutive relations. The undamaged structure is modeled as a single laminate while the delaminated region is modeled as sublaminates whose interface contains the desired delamination or debonding. The continuity of displacement is maintained across the delaminated edge by imposing the strain-based multipoint constraints. Numerical studies are conducted on composite specimens with surface bonded active layers. The results are presented to evaluate the performance of these smart structures in the presence of delamination. For actuators, the performance is measured in terms of the achievable deflection control and in sensors as a measurable output voltage. It is observed that actuator and sensor debonding degrade the capabilities of active materials significantly. Therefore, the study concludes that a damage tolerant approach is essential for the design of smart structural systems to account for damage-induced uncertainty in the functional properties of smart actuators and sensors. Copyright © 2006 SAGE Publications.
Influence of Structural Discontinuity on Slope Stability using Numerical Modelling and Sirovision
(Books and Journals Private Ltd., 2024) Raja, S.; Murthy, Ch.S.N.
The rock mass consists of heterogeneous and anisotropic materials, with smaller and larger blocks of rock, and the presence of structural discontinuities is a significant concern. Characterising the rock mass is crucial for the success of engineering excavations in such areas. A detailed study of joints, their orientation, and discontinuities in the exposed rock mass is crucial as they greatly influence stability and fragmentation. Existing rock mass classifications like Rock Mass Rating (RMR) and Q-classification require various geological parameters and physico-mechanical properties of the rock. However, determining these parameters conventionally can be time-consuming, requiring careful on-site measurements. The number of opencast coal mines is increasing compared to underground mines due to shorter gestation periods, higher productivity, and quicker returns. However, opencast mining raises environmental concerns such as air and water pollution, solid waste management, land degradation, and socio-economic issues. Additionally, many opencast coal mines, regardless of size, are reaching greater depths, making analysing bench slopes and ultimate pit slope design crucial. Slope failure in these mines leads to production loss, additional costs for recovery and handling of failed material, pit dewatering, sometimes mine abandonment or premature closure, and loss of life. A study was conducted at Prakash Khani Opencast Mine – IV, Manuguru area, M/s The Singereni Company Collieries Limited (SCCL), to investigate the influence of structural discontinuities on slope stability. SIROVISION software was used to assess rock mass characterisation, while PLAXIS-2D software was employed to analyse the influence of structural discontinuities on slope stability. A comparative conclusion was drawn based on the results obtained from SIROVISION and PLAXIS-2D analyses. The study revealed that the RMR of the mine ranged from very poor to fair due to numerous discontinuities. It was also found that discontinuities in the slope decrease the Factor of Safety (FOS), indicating an impact on slope stability. © 2024, Books and Journals Private Ltd.. All rights reserved.
Numerical Investigations on Alternate Droplet Formation in Microfluidic Devices
(Springer Science and Business Media B.V., 2021) Raja, S.; Satyanarayan, M.N.; Umesh, G.; Hegde, G.
We present numerical investigations on generating droplets in both single and double T-junction microfluidic devices using the Volume of Fluid (VOF) method. We validate our 2D simulation results with an experimental data reported in the past. The average pressure in the channel increases by 6% and capillary number by 16% for an increase in the width of side-channel from 50 ?m to 100 ?m in a single T-junction device. Similar increase in average pressure and capillary number is seen, for the increase in the width of one of the side channel in double T-junction device. The temporal variation of pressure in both the side channels shows that the pressure is lesser in the wider side channel. The average pressure in the channel decreases by 75% and capillary number by 15% for an increase in width of the main channel from 50 ?m to 100 ?m in a single T-junction device. Similar decrease in average pressure and capillary number is seen for the increase in the width of the main channel in double T-junction device. A gradual increase in the width of the main channel shows that, droplets generated in alternate regime when the width of the main channel is 1.4 times the width of side channel. In this regime, the temporal variation in pressure show a periodic change in both the side channel. Finally, in double T-junction device, the addition of surfactant has no significant effect on droplet generation in merging regime but it is seen in alternate regime. © 2021, The Author(s), under exclusive licence to Springer Nature B.V.