Faculty Publications
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Item Performance investigation of regenerative evaporative cooled air-to-air heat recovery ventilator under different humidity conditions(Elsevier Ltd, 2019) Arun, B.S.; Mariappan, V.; Anish, R.; Nimisha, P.To enhance the energy efficiency of an air-conditioning system air-to-air plate heat recovery ventilator can be installed to utilise the exhaust air for sensibly cooling of the ambient air. This pre-cooled intake air under low moisture content can be further cooled with a regenerative evaporative cooler. Therefore, an experimental investigation was conducted by fabricating a combined air-to-air heat exchanger and regenerative evaporative cooler test rig. The performances under low and high humidity were evaluated. Under low humidity, air-to-air heat exchanger works as sensible heat recovery ventilator, and under high humidity, it works as a dehumidifier for the regenerative evaporative cooler. The dynamic performance during the transition in humidity conditions and steady performance were studied. The results showed that the temperature below the wet-bulb temperature of intake air is achieved under low humidity. Under high humidity, condensation takes places for the intake air, increasing the latent cooling and decreasing the sensible cooling. Minimum temperature and humidity ratio of 19.9 °C and 17.05 g/kg were obtained respectively. © 2019 Elsevier Ltd.Item A Study on Effect of Fluid on the Modal Characteristics of Ground Supported Water Tanks(IOP Publishing Ltd custserv@iop.org, 2020) Anagha, B.V.; Nimisha, P.; Jayalekshmi, B.R.Liquid storage tanks are one of the essential lifeline structures which should function even after natural disasters. Water tanks in particular are essential for proper supply of water in the affected areas and for fire-fighting purposes. Sloshing is an important phenomenon occurring in partially filled tank with free surface. It can cause violent liquid motions that can cause instability in carrier-vessel and structural damage in the tank walls. To maintain the structural integrity of the carrier vessels, modal characteristics should be known as the impact of sloshing will increase when the excitation frequency matches with the natural frequency of container and result in resonant condition. This study investigates the modal characteristics such as natural frequency, mode shapes of square tank by 3-D finite element method using ANSYS 2019 R1software. The effect of impulsive and convective frequency of tanks with different fill levels and different boundary conditions are considered. © Published under licence by IOP Publishing Ltd.Item Study of Dynamic Characteristics of Circular Liquid Storage Tanks Using Acoustic Principles(Springer Science and Business Media Deutschland GmbH, 2021) Nimisha, P.; Jayalekshmi, B.R.; Venkataramana, K.Liquid storage tanks are lifeline structures, which should be designed with utmost care. Any damage to a tank, which is used to store hazardous liquid is catastrophic. The estimation of fundamental natural frequencies of liquid storage tanks situated in seismic regions is important for a seismic design. The present study deals with the estimation of natural frequencies of circular steel liquid storage tanks with reference to codal provisions and numerical analysis by using acoustic principles with the aid of FEM software. The study has been carried out for circular tank of diameter 6 m and height 8 m with different liquid depths, viz. 1/3rd, 2/3rd and full tank conditions and stiffness conditions, incorporating the sloshing effect. The natural frequencies obtained by finite element analysis of tanks are compared with those values obtained as per various International codes, viz., IS 1893(part2):2014, API 650 and Eurocode 8. The results show that the convective mode frequencies are matching well whereas, there is slight variation in impulsive mode frequency values obtained as per IS 1893. © 2021, Springer Nature Singapore Pte Ltd.Item Influence of Geometric Parameters in Self-damping Efficiency of Rectangular Liquid Storage Tanks(Springer Science and Business Media Deutschland GmbH, 2023) Nimisha, P.; Jayalekshmi, B.R.; Venkataramana, K.Turbulent fluctuation of the liquid medium under lateral excitation is a major area of concern due to the potential severities it may cause if the contained structure is damaged.Therefore, this study focuses on variation in the self-damping efficiency of the liquid mass in a liquid tank under lateral excitation.For this, a parametric study has been carried out by changing the aspect ratio of the tank with respect to the horizontal and vertical dimensions.Pressure-based transient analysis has been carried out considering harmonic excitation as well as seismic ground motions.The transient response of the liquid medium is observed in terms of free surface elevation and hydrodynamic pressure.The study reveals that an accurate geometric design of the tank structure improves the self-damping of the sloshing liquid.An aspect ratio of less than ‘1’ results in the improved self-damping efficiency of the contained liquid mass.The effect of the vertical dimension of the tank on slosh damping is less significant compared with that of the horizontal dimension. © 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.Item Parametric Study on Frequency Characteristics of Cylindrical Liquid Tanks(Springer, 2022) Nimisha, P.; Jayalekshmi, B.R.; Venkataramana, K.The response of liquid-storage tanks under seismic loading is a key research area. The study of free vibration characteristics is a prerequisite for understanding the dynamic behaviour of liquid tanks under seismic loading. Hence, the present study focuses on the analysis of different parameters that may influence the frequency characteristics of cylindrical liquid tanks. For this, a database of 560 three-dimensional cylindrical liquid tank models was developed by carrying out modal analysis using ANSYS Mechanical APDL software. The database was analysed with the aid of artificial neural networks and nonlinear regression analysis. Average deviations of 30% and 32% were observed for the impulsive frequency values estimated based on IS1893 (Part2):2014 and Eurocode-8, respectively, compared to the finite element results. Hence, modification coefficients were suggested with aspect ratio as the demarcating parameter and obtained a Pearson correlation coefficient of rXY > 0.9, between the predicted values of frequency and actual values. The predicted formulae reduced the deviations observed between the frequency estimated based on the codal expressions and those obtained from finite element analysis to 13% and 15%, corresponding to IS1893 (Part2):2014 and Eurocode-8, respectively. © 2022, The Institution of Engineers (India).Item Effective configuration of perforated baffle plate for efficient slosh damping in liquid retaining tanks under lateral excitation(Elsevier Ltd, 2022) Nimisha, P.; Jayalekshmi, B.R.; Venkataramana, K.Perforated baffle plates are used as an anti-slosh mechanism in various fields owing to the need for slosh suppression and weight reduction. However, there is an uncertainty in the selection of configuration of perforated baffle plate due to the several influencing parameters for slosh damping efficiency. Therefore, the present study focuses on the development of an efficient slosh damping configuration for the perforated baffle plate. For this, nonlinear dynamic analysis under seismic ground motions with different PGA/PGV ratios has been carried out in the time domain using the concepts of Computational Fluid Dynamics (CFD) in the numerical models of liquid tanks with perforated baffle plates of different configurations. The response of the system under impulsive and convective modes is analysed by observing the free surface elevation, hydrodynamic pressure, turbulence kinetic energy and turbulence eddy dissipation as the response parameters. The study developed an effective baffle configuration for efficient slosh damping, considering the various response parameters. © 2022 Elsevier LtdItem Slosh Damping in Rectangular Liquid Tank with Additional Blockage Effects under Pitch Excitation(American Society of Mechanical Engineers (ASME), 2022) Nimisha, P.; Jayalekshmi, B.R.; Venkataramana, K.The quantification and damping of slosh responses are significant due to the increasing demand for safety of the liquid-based applications under severe external excitation. Recently, the solid or perforated baffle plates have been used to damp the slosh response of the liquid. However, there is uncertainty in the selection of an effective configuration of the baffle plates. In addition, most of the studies reported the slosh response under surge excitation. Therefore, this study focuses on the slosh response of the rectangular tank fitted with perforated baffle plates of different configurations under pitch excitation. For this, the liquid sloshing is simulated using the concepts of computational fluid dynamics (CFD) using pressure-based solver in the time domain. A detailed parametric study is carried out to develop an effective configuration of the perforated baffle plates considering the area of perforations, interperforation distance, size of perforations, distance between the perforated baffle plates, alignment of perforations, and the vertical position of perforated baffle plate as the parameters. The slosh responses are observed in terms of free surface elevation, hydrodynamic pressure, turbulence kinetic energy, velocity streamlines, power spectral density corresponding to the free surface elevation and the free surface deformation. The study developed a "zig-zag blocking alignment"of perforations for effective slosh damping, with the solid area between the perforations being 50%-60% of the area of perforations. In addition, "single-acting range"and "damping range"are identified to pilot the positioning of the multiple baffle plates in a rectangular tank under pitch excitation. © 2022 by ASME.Item Effect of Frequency Content of Seismic Excitation on Slosh Response of Liquid Tank with Baffle Plate(World Scientific, 2023) Nimisha, P.; Jayalekshmi, B.R.; Venkataramana, K.The violent dynamic behavior of liquid under horizontal excitation is a key factor that needs to be addressed in the seismic-resistant design of liquid tanks. Therefore, this study focuses on the slosh response of the liquid medium in a rectangular tank under Imperial Valley 1979, El Centro 1940 and Kobe 1995 ground motions of different frequency ranges. The ground motions records are selected based on the PGA/PGV ratio. For slosh control, a single vertical perforated baffle plate is used as an anti-slosh element with different configurations of perforations. Considering the free surface elevation as the major response parameter, the effect of percentage of perforation of the baffle plate, clear spacing of perforations and offset distance of the perforated plate are investigated by carrying out the pressure-based transient analysis using computational fluid dynamic (CFD). The optimum perforation varies from 10% to 17%, corresponding to the frequency of ground motion in the range of far-resonant to near-resonant conditions. Additionally, "rapid zone"(R-zone) and "moderate zone"(M-zone) are identified to pilot the positioning of the perforated baffle plate in liquid tanks. The perforated baffle plate with an optimum range of moderately spaced perforations positioned at the moderate zone of the tank effectively reduces the free surface elevation. Furthermore, the perforated baffle plate is more advantageous during violent sloshing under near-resonant conditions. © 2023 World Scientific Publishing Company.