2. Thesis and Dissertations
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Item Studies on Caisson Type Breakwater – A Physical and Numerical Approach(National Institute Of Technology Karnataka Surathkal, 2023) V., Kumaran; ., Manu; Rao, SubbaThe design and construction of coastal structures such as breakwaters, at greater water depths is rapidly increasing as a result of the increasing draught of large vessels and off-shore land reclamations. Vertical caisson-type 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 fulfil the functional utility and impact of the structure on the sea environment, it is necessary to study the hydraulic performance of such breakwaters. In the present project, the hydrodynamic performance of caisson breakwater with various geometric configurations are studied in detail. In the first phase, a physical model approach is carried out extensively to study the stability of toe protection for vertical caisson breakwater. The determination of the size of the toe armour units and their cross-section for the stable design are investigated. The applicability of the Brebner and Donnelly (Coast Eng Proc 1: 24, 1962) design curve for depth-limited conditions is validated for a certain fixed relative foundation depth (d1/d). In the second phase, an investigation of the non-perforated caisson type breakwater is performed considering different wave conditions. The variation of dynamic wave pressure, wave force, wave run-up, and wave reflection are determined for this structure. The maximum wave force on the caisson breakwater is calculated from measured pressure values and is compared with the wave forces calculated by Goda’s and Sainflou wave theories. The comparison of results illustrate that the Goda’s formula provides a good estimation of wave force distribution compared with the experimental findings. In the third phase, a numerical model of caisson breakwater is developed to study its performance using the computational fluid dynamics (CFD) approach using Ansys- Fluent and validated the same using experimental data. In the fourth phase, the experimental investigations are carried out on non-perforated vertical wall breakwater with the presence of a vertical and horizontal slotted barrier. In the fifth phase, the perforations (i.e 8 %, 10%, 13%, 15%, 20%) are introduced in the front face of the caisson breakwater to analyse the hydraulic performance to arrive at better perforations in reducing the wave forces, wave reflection and wave runup.Item Computational Investigation of Hydrodynamics, Mixing and Crystallization in a Batch Stirred Vessel(National Institute of Technology Karnataka, Surathkal, 2021) Falleiro, Lister Herington.; Ali, B Ashraf.In this work, the hydrodynamics, mixing and suspension quality of solids are numerically investigated using computational fluid dynamics (CFD). The transient CFD simulations are performed to obtain the flow field. Here multiple reference frame and sliding mesh approach are used to predict the flow field along with the standard k-ε turbulence model. The velocity field is analyzed spatially and temporally, and liquid circulation is calculated at various impeller speeds to find an optimum impeller speed. To improve the flow field in a batch stirred vessel, various draft tube baffle configurations are introduced. The optimum baffle system (DTB-IV) is identified that supports liquid circulation, mixing and suspension of solids in the batch stirred vessel. It is found that suspension quality is strongly dependent on the prevailing hydrodynamics in the stirred vessel. Further, the optimised baffled stirred vessel (DTB-IV) is used to carry out the cooling crystallisation process. The primary difficulty in the design and scale-up of the crystallization process is the lack of understanding of the flow field, growth and nucleation at different scales. Here, the performance of an unbaffled stirred vessel is compared with a baffled stirred vessel system. To predict crystal size distribution (CSD) in batch stirred vessel system, the population balance equation (PBE) is used. The PBE is solved using the quadrature method of moments. The PBE accounts for both the size and the number of the particles, and it is coupled with the CFD model. This coupled algorithm integrates solubility data, nucleation and growth kinetics. To examine the crystallization process in a batch stirred vessel, potassium dihydrogen phosphate – water system is chosen. This is analyzed for unbaffled and baffled batch stirred vessel to quantify the growth and nucleation rates of the crystals. Further, the effect of seed mass, its size and temperature on the crystallization process is investigated. The results showed that baffled stirred vessel is more advantageous and supports the crystallization process.Item Computational Modelling of Fluid Flow and Heat Transfer through Metal Foam and Wire Mesh(National Institute of Technology Karnataka, Surathkal, 2019) Kotresha, Banjara.; Gnanasekaran, N.The present research work expounds the numerical investigation of fluid flow and heat transfer through high porosity metallic porous mediums such as metal foam and wire mesh filled in a vertical channel. In the present study the metallic porous mediums are placed on either sides of the heater-plate assembly to enhance the heat transfer. Two different heater assemblies are considered in the present investigation which involves a uniform aluminium plate-heater assembly and a discrete aluminium plate-heater assembly. The present problem is considered as conjugate heat transfer as it involves both solid aluminium plate and fluid flow in the channel. A two dimensional computational domain is selected for the numerical investigation as the vertical channel is symmetrical about the vertical axis. The metal foam/wire mesh region is considered as a homogeneous porous medium with the Darcy Extended Forchheimer model to evaluate the characteristics of fluid flow while the local thermal non-equilibrium heat transfer model is considered for the analysis of heat transfer. The objectives of the present research work are to quantify the effect of pore density, porosity, partially filling thickness, thickness and thermal conductivity of same pore density metal foam, finding out the isothermal condition in discrete heat source system and to determine the interfacial heat transfer coefficient for the wire mesh porous medium in mixed convection and forced convection regimes. Three different filling rates of 40%, 70% and 100% by volume in the vertical channel are also considered for the investigation for the partial filled metallic porous mediums in the vertical channel. The results in terms of Nusselt number, Colburn j factor and overall performance factor are presented and discussed for the cases studied in this research work. This work serves as the current relevance in electronic cooling so as to open up more parametric and optimization studies to develop new class of materials for the enhancement of heat transfer.Item Heat Transfer Distribution of Impinging Methane-Air Premixed Flame Jets(National Institute of Technology Karnataka, Surathkal, 2019) Ramkishanrao, Kadam Anil.; Kumar, G. N.Flame jets find importance in industrial and household applications like metal and glass melting/forming and cook stoves respectively. Heat transfer distribution of impinging flame jet was compared with that of the impinging air jet based on the experimental data reported in literature for methane-air flame jet and air jet impingement for Reynolds number, Re = 600 to 1400 and the non-dimensional nozzle tip to impingement plate distance, Z/d = 2 to 6. The comparative data based on mapping experimental data reported in literature suggested that there is a good agreement between the Nusselt numbers for higher Z/d near stagnation region. However, away from the stagnation region, the Nusselt number for flame jet is higher than that of air jet for similar operating conditions of Re and Z/d. A CFD simulation for impinging air jet and impinging flame jet was carried out using FLUENT software to explain the physics and reason for the deviations observed in experimental data. A scale analysis was carried out to identify the dominant forces and their influence on the heat transfer distribution on the impingement plate. Heat transfer from impinging flame jets to a flat plate has been assumed to be onedimensional in most of the investigations and without radiation loss treatment. In the present work, the exact nature of diffusion of heat in the plate is investigated via solution to multidimensional heat conduction problem. Two procedures have been employed – Duhamel theorem and three dimensional transient analytical inverse heat conduction problem (IHCP). The Duhamel theorem which is analytical model for transient one dimensional heat conduction was applied and its application failed the check of linearity requirement of the convection rate equation. From the solution by analytical IHCP for transient three dimensional heat conduction, the distribution of wall heat flux and the wall temperature was perfectly linear. This check confirmed that three dimensional approach has to be used. Experimental data is then analyzed by the three dimensional analytical IHCP for short and larger time intervals. It was found that for short time data, heat transfer coefficient and the reference temperature have oscillatory distribution along the radial direction on the impingement plate and for larger time data the oscillations die out. However, at larger time, radiation loss from the impingement plate becomes significant. The effect of variation in thermal conductivity of the impingement plate with the temperature on heat transfer coefficient and reference temperature is discussed. Anovel method was developed to correct the heat transfer coefficient and reference temperature to incorporate radiation losses. The deviation in heat transfer coefficient and reference temperature estimated without considering variable thermal conductivity and radiation loss for large time interval was upto 50%. The scope of the present technique is examined through its application to impinging jets with various configurations. The present study covers the applications of hot jet, cold jet and multiple jets with distinct Reynolds numbers and the nozzle-to-plate spacing and results confirms the validity of technique to impinging jets as well. Effect of plate thickness on the accuracy of the present technique is also studied. Upto 5 mm thick plates can be used in impinging jet applications without compromising much on accuracy. Use of present technique significantly reduces the experimental cost and time since it works on transient data of just few seconds Experiments were carried out on ribbed plates with three different geometrical shaped rib elements i.e. circular, rectangular and triangular. In addition, numerical simulations were performed to study flow field on and around ribs. During the experiments, Reynolds numbers varied from 600 to 1800 and burner tip to target plate distance from 2 to 4. Heat transfer coefficients were found lower whereas reference temperatures were observed higher on ribbed surfaces than smooth surfaces. Obstruction to the flow, flow separation and decrease in momentum are the reasons attributed for lower heat transfer rate to the ribbed surfaces.Item Suitability of Biofuels and Plastic Oil Blended With Diesel in CRDI Engine(National Institute of Technology Karnataka, Surathkal, 2017) Lamani, Venkatesh T.; Yadav, Ajay Kumar; Kumar, G. N.Nitrogen oxides and smoke are the substantial emissions for the diesel engines. Fuels comprising high-level oxygen content can have low smoke emission and higher efficiency due to better combustion. The objective of this research is to assess the potential to employ oxygenated fuels such as dimethyl ether, ethanol and butanol, and waste plastic oil in direct injection engine as alternative fuels for diesel. To reduce NOX, exhaust gas recirculation technology for various fuels is studied. Computational fluid dynamics (CFD) studies on combustion and emission characteristics of common rail direct injection (CRDI) engines using oxygenated fuel-diesel blends are less developed and still under intense study. In view of that detailed CFD simulation is carried out in present study and also validated with experimental results. Ethers are favourable alternative for diesel engine due to their chemical structure. Presence of more oxygen, absence of carbon-carbon (C-C) bond in chemical structure, and high cetane number of dimethyl ether (DME), cause less pollution in DME operated engine compared to diesel engine. Study emphasizes the effect of various EGR rates (0-20%) and DME-diesel blends (0-20%) on combustion characteristics and exhaust emissions of CRDI engine using CFD simulation. Results show that, due to better combustion characteristics of DME, indicated thermal efficiency (ITE) increases with the increase in DME- diesel blends. Ethanol is an attractive alternative fuel because it is oxygenated, renewable and bio-based resource; thereby it has potential to reduce smoke emissions in compression-ignition engines. CFD simulation is carried out to study the effect of EGR and injection timing on the performance, combustion and exhaust emission characteristics of CRDI engine fuelled with bioethanol-diesel blends. The results indicate that the mean CO formation and ignition delay increase whereas mean NOX formation and in-cylinder temperature decrease with increase in the EGR rate. Further, CFD simulation is carried out to find optimum injection timing for bioethanol-diesel blends (0-30% ethanol). Optimum injection timing is obtained for maximum ITE. Obtained CFD results are validated with experimental data available in literature and found good agreements.Several second generation biofuels (e.g., n-butanol) are also promising alternative to diesel fuel. The experimental and CFD simulation is carried out to estimate the performance, combustion and exhaust emission characteristics of n-butanol-diesel blends (0 to 30%) for various injection timings and various EGR rates using modern twin-cylinder, four-stroke, CRDI engine. Experimental results reveal the increase in brake thermal efficiency (BTE) for n-butanol-diesel blends. Attention is also focused to counter plastic waste disposal problem and to find alternate fuel to diesel by waste to energy retrieval. Present range of investigation evaluates the prospective use of waste plastic oil (WPO) as an alternative fuel for diesel engine. Experiments are conducted for various injection timings and for different EGR rates. Combustion, performance and tail pipe emissions of CRDI engine are studied. The NOx, CO and soot emissions for waste plastic oil-diesel blends are found more than neat diesel. To reduce NOx, EGR is employed which results in reduction of NOx considerably. Brake thermal efficiency (BTE) of blends is found to be higher compared to diesel. The higher NOx emitted by engine operated with WPO-Diesel blends are treated by multiple injection strategies. Experiments are carried out for various pilot injection timings and different main injection timings. The remarkable reduction in nitrogen oxide is observed by retarding main injection timing and injecting more fuel in pilot injection compared to single injection.Item Characterization of Magneto-Rheological Fluid and Monotube Damper through Experimental and Computational Analysis(National Institute of Technology Karnataka, Surathkal, 2018) T. M, Gurubasavaraju; Kumar, Hemantha; M, ArunMagnetorheological fluid belongs to a class of smart materials which exhibit change in their rheological properties, when exposed to an external magnetic field and these properties are completely reversible. By utilizing these special characteristics, the damping force of the MR damper can be controlled and varied in real time applications. The main objective of this research work is to investigate the characteristics of MR fluid and MR damper through experimental as well as computational methods and to evaluate the semi-active suspension with MR dampers performance in terms of ride comfort and road holding of vehicles, when subjected to random road conditions. The rheological characterization of the MR fluid samples under different magnetic fields and fluid gap has been evaluated through experimentation. The measured fluid properties were used for computing the damping force of MR damper. Using single and multi-objective particle swarm optimization techniques, the optimal proportion of iron particles for MR damper application was determined to maximize the shear stress and damping force. The dynamic characterization of MR damper through experimental approach using dynamic test facility at 1.5 Hz and 2 Hz frequencies has been carried out. Also, the influence of material properties of MR damper components on the induced magnetic flux density and geometrical parameters on the damping force was investigated through finite element analysis as well as analytical methods. Multi-objective genetic algorithm and screening optimization techniques were employed to maximize the magnetic flux density and to identify the optimal values of the design variables. Using the analytical method, damping force of the damper was computed for the obtained optimal values of the design variables. It was observed that the damping force of the MR damper whose cylinder is made up of magnetic material was 2.79 times greater than that of MR damper whose cylinder is made up of non-magnetic material. Further, a coupled finite element analysis (FEA) and computational fluid dynamics (CFD) analysis was used for estimating the magnetic flux density and damping force for different input currents. The credibility of the shear mode monotube MR damperanalysis results were validated with experimental results. To overcome certain limitations of shear mode damper, an attempt has been made to realize the mixed mode damper by combining the flow and shear mode operations. The variations in the damping characteristics of flow and mixed mode MR damper under different input were compared with shear mode MR damper. Results showed that combination of two modes of operation could enhance the damping force to a significant level. The damping force of mixed mode MR damper was found to be 3 times greater than that of shear mode MR damper at 2 Hz frequency and 0.4 A current. Based on results obtained from computational analyses, a non-parametric representative model exhibiting the hysteretic behavior of MR damper was developed. The developed nonparametric model was implemented in a quarter car semi-active suspension to determine the dynamic response of the vehicle subjected to random road excitations. Further, this model was implemented in three-wheeler vehicle semi-active suspension system to evaluate its dynamic performance. The outcome showed that the vehicle with non-parametric based MR suspension system provided good vibration isolation for semi-active suspension than passive suspension system in terms of rice comfort and road holding.Item Inverse Techniques for the Estimation of Multiple Parameters Using Steady State Heat Transfer Experiments(National Institute of Technology Karnataka, Surathkal, 2018) M. K, Harsha Kumar; N, GnanasekaranThe aim of the present research work is to estimate the unknown parameters by using the information obtained from in-house steady state heat transfer experiments and to employ stochastic inverse techniques. With the advent of latest technologies in the field of advance computing, conjugate heat transfer problems that are highly complex can easily be solved to obtain temperature distributions. In the present work, suitable mathematical models are proposed as forward models for a class of conjugate heat transfer problem. The first problem solved was a conjugate heat transfer from a mild steel fin. The numerical model is developed using ANSYS FLUENT with an extended model which facilitates natural convection heat transfer. Based on the experimental temperatures and with accompanying mathematical model, heat flux is estimated using Genetic Algorithm as inverse method. To accelerate the inverse estimation, Genetic algorithm is assisted with the Levenberg- Marquardt method for the estimation of the heat flux, thus making the whole process as hybrid estimation. In the second problem, 3-D conjugate fin model is proposed for the estimation of heat flux and heat transfer coefficient using Artificial Neural Network (ANN) method. The novelty of the work is to inject the experimental temperature methodologically in to the forward model which is trained by Neural network thereby the forward model is driven by experimental data and to accomplish the task of parameter estimation, ANN is used as inverse method that leads to a non-iterative solution. The concept of a priori information is then introduced for the simultaneous estimation of heat flux and heat transfer coefficient using experimental data. This was accomplished using Bayesian framework along with Markov Chain Monte Carlo (MCMC) method to condition the posterior probability density function. A powerful Metropolis-Hastings algorithm is exploited in order to attain stable Markov chains during the process of inverse estimation. Finally, this was followed by estimation of heat generation and heat transfer coefficient from a Teflon cylinder within the Bayesian framework.