Journal Articles
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Item Numerical analysis of the effect of turbulence transition on the hemodynamic parameters in human coronary arteries(AME Publishing Company info@amepc.org, 2016) Mahalingam, A.; Gawandalkar, U.U.; Kini, G.; Buradi, A.; Araki, T.; Ikeda, N.; Nicolaïdes, A.; Laird, J.R.; Saba, L.; Suri, J.S.Background: Local hemodynamics plays an important role in atherogenesis and the progression of coronary atherosclerosis disease (CAD). The primary biological effect due to blood turbulence is the change in wall shear stress (WSS) on the endothelial cell membrane, while the local oscillatory nature of the blood flow affects the physiological changes in the coronary artery. In coronary arteries, the blood flow Reynolds number ranges from few tens to several hundreds and hence it is generally assumed to be laminar while calculating the WSS calculations. However, the pulsatile blood flow through coronary arteries under stenotic condition could result in transition from laminar to turbulent flow condition. Methods: In the present work, the onset of turbulent transition during pulsatile flow through coronary arteries for varying degree of stenosis (i.e., 0%, 30%, 50% and 70%) is quantitatively analyzed by calculating the turbulent parameters distal to the stenosis. Also, the effect of turbulence transition on hemodynamic parameters such as WSS and oscillatory shear index (OSI) for varying degree of stenosis is quantified. The validated transitional shear stress transport (SST) k-? model used in the present investigation is the best suited Reynolds averaged Navier-Stokes turbulence model to capture the turbulent transition. The arterial wall is assumed to be rigid and the dynamic curvature effect due to myocardial contraction on the blood flow has been neglected. Results: Our observations shows that for stenosis 50% and above, the WSSavg, WSSmax and OSI calculated using turbulence model deviates from laminar by more than 10% and the flow disturbances seems to significantly increase only after 70% stenosis. Our model shows reliability and completely validated. Conclusions: Blood flow through stenosed coronary arteries seems to be turbulent in nature for area stenosis above 70% and the transition to turbulent flow begins from 50% stenosis. © Cardiovascular Diagnosis and Therapy. All rights reserved.Item Developing a clients’ charter and construction project KPIs to direct and drive industry improvements(Emerald Group Publishing Ltd. Howard House Wagon Lane, Bingley BD16 1WA, 2017) Kumaraswamy, M.; Mahesh, G.; Mahalingam, A.; Loganathan, S.; Kalidindi, S.N.Purpose: The purpose of this paper is to present a case, with live examples from a construction industry development initiative in India, for developing a proactive construction clients charter; and a core set of key performance indicators (KPIs), as basic tools for facilitating the expectations of this special issue in “securing clients’ organisational objectives and project aspirations throughout construction project lifecycles” apart from empowering construction industry improvements in general. Design/methodology/approach: Having identified 19 critical issues in the Indian construction industry at two construction clients-academia roundtables, two of the “action teams” formed to address specific issue sets, separately developed a relevant construction clients charter and useful KPIs, respectively, through a combination of literature reviews and brainstorming conference calls, along with iterative drafts of, and feedback on interim outputs. Validation of “working papers” presented at a “Consolidation Roundtable” of construction clients and their consultants, elicited further suggestions for fine tuning of final outputs. Findings: The charter was formulated in structured steps, including identifying “priorities” under four categories: overall, expectations from supply chains, by supply chains and by end users. The six sub-heads of the charter are on procurement, design, innovation and technology, project execution, human resource development and worker welfare, and quality, safety and sustainability. The “suggested KPIs” for building clients in India enable organisations to choose: from three different groups (i.e. design phase, construction phase, or business outcomes), and at three different levels (i.e. project/organisation level, benchmarking club level, or industry level). Originality/value: There is no known overarching Construction Clients’ Charter at present. Some project KPI sets are available elsewhere. However, those developed in India, while focusing on project performance, also connect to organisational performance and business outcomes. Furthermore, KPIs are provided to separately probe client, consultant and contractor performance. Significantly, the charter and KPIs are outcomes from an industry-led self-improvement initiative launched with building construction clients at the forefront, rather than a top-down imposition from government. Furthermore, while prioritising client aspirations, they also address common supply chain and end-user concerns, which may also be interpreted as a longer-term win-win-win client’s aspiration. © 2017, © Emerald Publishing Limited.Item Evaluation of optimal parameters of MR fluids for damper application using particle swarm and response surface optimisation(Springer Verlag service@springer.de, 2017) Gurubasavaraju, T.M.; Kumar, H.; Mahalingam, A.The controllable rheological properties of MR fluid exhibit viscoelastic properties within pre-yield, which are essential for the characterization of MR dampers for the isolation of vibration. In the present work, using particle swarm optimisation (PSO), it is identified that the proportion of MR fluid constituents, fluid gap and current are the parameters which influence majorly on the rheological properties and damping effect of MR damper. Initially, rheological properties of the prepared MR fluid samples are determined using rotational plate–plate type rheometer with the magnetorheological device cell attachment by keeping three levels of gap between the parallel plates. Three different proportions of MR fluid are prepared based on the volume fraction of carbonyl iron particle, i.e., 25, 30 and 35% in the silicone carrier fluid along with 1% of lithium-based grease as stabiliser. The objective function of this optimisation problem is to maximise the shear stress and damping force of the MR damper. The design of experiment (DOE) is employed to obtain the various combinations of parameters and their respective responses. The interaction of the regression model obtained from the DOE is used in PSO to evaluate the optimal parameters. The results indicated that the MR fluid with the particle concentration of 31% is the optimal proportion for MR damper application. © 2017, The Brazilian Society of Mechanical Sciences and Engineering.Item Effect of stenosis severity on wall shear stress based hemodynamic descriptors using multiphase mixture theory(Isfahan University of Technology secretary@jafmonline.net, 2018) Buradi, A.; Mahalingam, A.A variety of wall shear stress (WSS) based hemodynamic descriptors have been defined over the years to study hemodynamic flow instabilities as potential indicators or prognosticators of endothelial wall dysfunction. Generally, these hemodynamic indicators have been calculated numerically using 'single phase' approach. In single phase models, the flow-dependent cell interactions and their transport are usually neglected by treating blood as a single phase non- Newtonian fluid. In the present investigation, a multiphase mixture-theory model is used to define the motion of red blood cells (RBCs) in blood plasma and interactions between these two-components. The multiphase mixture theory model exhibited good agreement with the experimental results and performed better than non-Newtonian single phase model. The mixture-theory model is then applied to simulate pulsatile blood flow through four idealized coronary artery models having different degrees of stenosis (DOS) severities viz., 30, 50, 70 and 85% diameter reduction stenosis. The maximum WSS is seen at the stenosis throat in all the cases and maximum oscillatory shear index (OSI) is seen in downstream region of the stenosis. Our findings suggest that for degree of coronary stenosis more than 50%, a more disturbed fluid dynamics is observed downstream of stenosis. This could lead to further progression of stenosis and may promote a higher risk of atherogenesis and plaque buildup in the flow-disturbed area. The potential atherosclerotic lesion sites were identified based on clinically relevant values of WSS, timeaveraged WSS gradient (TAWSSG), time-averaged WSS (TAWSS), and OSI. Finally, the change in potential atherosclerotic lesion sites with respect to DOS has been quantified. © 2018, Isfahan University of Technology.Item An approach for characterizing twin-tube shear-mode magnetorheological damper through coupled FE and CFD analysis(Springer Verlag service@springer.de, 2018) Gurubasavaraju, T.M.; Kumar, H.; Mahalingam, A.The most promising technology in the field of semi-active suspension systems is the use of magnetorheological property of MR fluid, whose material behavior can be controlled through external magnetic field. Devices developed based on this principle are adaptive and controllable as desired for a specific application. It is important to understand the damping characteristics of these devices before employing them, using experimental or computational approaches. In the present work, both experimental and computational methods have been adopted for characterizing a twin-tube MR damper with an intention to develop a computational approach as an alternative to experimental test in the preliminary design stage. Initially, experimental characterization of MR damper was carried out at 1.5 and 2 Hz frequencies for damper stroke length of ± 5 mm under different DC currents ranging from 0.1 to 0.4 A. Later, coupled finite-element and computational fluid dynamic analysis has been carried out to estimate the damping force under same conditions as used in the experiment. The results of computation are in good agreement with experimental ones. Furthermore, using this computational approach, the damping force at different frequencies of 1.5, 2, 3, and 4 Hz has been estimated and its time histories are also plotted. The influence of fluid flow gap on the damping force has been determined and results revealed that damping force behaves inversely with fluid flow gap. © 2018, The Brazilian Society of Mechanical Sciences and Engineering.Item Performance analysis of a semi-active suspension system using coupled CFD-FEA based non-parametric modeling of low capacity shear mode monotube MR damper(SAGE Publications Ltd, 2019) Gurubasavaraju, G.; Kumar, H.; Mahalingam, A.In this work, an approach for formulation of a non-parametric-based polynomial representative model of magnetorheological damper through coupled computational fluid dynamics and finite element analysis is presented. Using this, the performance of a quarter car suspension subjected to random road excitation is estimated. Initially, prepared MR fluid is characterized to obtain a relationship between the field-dependent shear stress and magnetic flux density. The amount of magnetic flux induced in the shear gap of magnetorheological damper is computed using finite element analysis. The computed magnetic field is used in the computational fluid dynamic analysis to calculate the maximum force induced under specified frequency, displacement and applied current using ANSYS CFX software. Experiments have been conducted to verify the credibility of the results obtained from computational analysis, and a comparative study has been made. From the comparison, it was found that a good agreement exists between experimental and computed results. Furthermore, the influence of fluid flow gap length and frequency on the induced force of the damper is investigated using the computational methods (finite element analysis and computational fluid dynamic) for various values. This proposed approach would serve in the preliminary design for estimation of magnetorheological damper dynamic performance in semi-active suspensions computationally prior to experimental analysis. © IMechE 2018.Item EFFECT of STENOSIS SEVERITY on SHEAR-INDUCED DIFFUSION of RED BLOOD CELLS in CORONARY ARTERIES(World Scientific Publishing Co. Pte Ltd wspc@wspc.com.sg, 2019) Buradi, A.; Morab, S.; Mahalingam, A.In large blood vessels, migration of red blood cells (RBCs) affects the concentration of platelets and the transport of oxygen to the arterial endothelial cells. In this work, we investigate the locations where hydrodynamic diffusion of RBCs occurs and the effects of stenosis severity on shear-induced diffusion (SID) of RBCs, concentration distribution and wall shear stress (WSS). For the first time, multiphase mixture theory approach with Phillips shear-induced diffusive flux model coupled with Quemada non-Newtonian viscosity model has been applied to numerically simulate the RBCs macroscopic behavior in four different degrees of stenosis (DOS) geometries, viz., 30%, 50%, 70% and 85%. Considering SID of RBCs, the calculated average WSS increased by 77.70% which emphasises the importance of SID in predicting hemodynamic parameters. At the stenosis throat, it was observed that 85% DOS model had the lowest concentration of RBCs near the wall and highest concentration at the center. For the stenosis models with 70% and 85% DOS, the RBC lumen wall concentration at the distal section of stenosis becomes inhomogeneous with the maximum fluctuation of 1.568%. Finally, the wall regions with low WSS and low RBC concentrations correlate well with the atherosclerosis sites observed clinically. © 2019 World Scientific Publishing Company.Item 3D coupled conduction-convection problem using in-house heat transfer experiments in conjunction with hybrid inverse approach(Emerald Group Holdings Ltd., 2019) Vishweshwara, P.S.; Kumar, M.K.; Gnanasekaran, N.; Mahalingam, A.Purpose: Many a times, the information about the boundary heat flux is obtained only through inverse approach by locating the thermocouple or temperature sensor in accessible boundary. Most of the work reported in literature for the estimation of unknown parameters is based on heat conduction model. Inverse approach using conjugate heat transfer is found inadequate in literature. Therefore, the purpose of the paper is to develop a 3D conjugate heat transfer model without model reduction for the estimation of heat flux and heat transfer coefficient from the measured temperatures. Design/methodology/approach: A 3 D conjugate fin heat transfer model is solved using commercial software for the known boundary conditions. Navier–Stokes equation is solved to obtain the necessary temperature distribution of the fin. Later, the complete model is replaced with neural network to expedite the computations of the forward problem. For the inverse approach, genetic algorithm (GA) and particle swarm optimization (PSO) are applied to estimate the unknown parameters. Eventually, a hybrid algorithm is proposed by combining PSO with Broyden–Fletcher–Goldfarb–Shanno (BFGS) method that outperforms GA and PSO. Findings: The authors demonstrate that the evolutionary algorithms can be used to obtain accurate results from simulated measurements. Efficacy of the hybrid algorithm is established using real time measurements. The hybrid algorithm (PSO-BFGS) is more efficient in the estimation of unknown parameters for experimentally measured temperature data compared to GA and PSO algorithms. Originality/value: Surrogate model using ANN based on computational fluid dynamics simulations and in-house steady state fin experiments to estimate the heat flux and heat transfer coefficient separately using GA, PSO and PSO-BFGS. © 2019, Emerald Publishing Limited.Item Impact of coronary tortuosity on the artery hemodynamics(Elsevier Sp. z o.o., 2020) Buradi, A.; Mahalingam, A.The presence of tortuosity in coronary artery (CA) affects the local wall shear stress (WSS) which is an influencing hemodynamic descriptor (HD) for the development of atherosclerotic sites. To conduct a morphological parametric study in coronary arteries (CAs), several idealized tortuous artery models were obtained by varying three morphological indices namely, curvature radius (CR), distance between two bends (DBB) and the angle of bend (AoB). Computational fluid dynamics methodology with multiphase mixture theory is used to explore the effect of coronary tortuosity on various WSS based hemodynamic descriptors (HDs) namely, time-averaged WSS, oscillatory shear index, time-averaged WSS gradient, endothelial cell activation potential and the relative residence time that are used to determine the vulnerable locations for the onset of thrombosis and atherosclerosis. Our findings suggest that all the tortuosity morphological indices, CR, DBB and AoB have significant influence on the distributions of various HDs and hemodynamics. It is also observed that atherosclerosis prone sites were witnessed at the inner artery wall at downstream regions of the bend section 1 and bend section 2 in all the tortuous artery models studied and found to increase as the CR and DBB were reduced however, found to increase as the AoB is increased. Hence, severe coronary tortuosity in CAs with small CR, small DBB and higher AoB may have lower WSS zones at inner bend sections which promote atherosclerosis plaque progression. The analysis obtained from this multiphase blood flow study can be employed potentially in the clinical assessment on the severity of atherosclerosis lesions as well as in understanding the underlying mechanisms of localization and formation of atherosclerotic plaques. © 2019 Nalecz Institute of Biocybernetics and Biomedical Engineering of the Polish Academy of SciencesItem Comparative computational appraisal of supercritical CO2-based natural circulation loop: effect of heat-exchanger and isothermal wall(Springer Science and Business Media B.V., 2020) Thimmaiah, S.; Wahidi, T.; Yadav, A.; Mahalingam, A.Natural circulation loop (NCL) is a geometrically simple heat transfer device in which fluid flow occurs due to density gradient of loop fluid, induced by the temperature difference between the source and the sink. NCL has an inherent problem of instability caused by the combined effect of buoyancy, friction and inertia forces at varying operating conditions, and hence it requires an elegant solution of instability. The primary objective of the present work is to do a comparative study on the dynamic performance between two different configurations of NCL based on supercritical CO2, i.e. (i) NCL with isothermal heater and a cold heat-exchanger (ISO-CHX), and (ii) NCL with hot and cold heat-exchangers (HHX-CHX). To explore these NCLs, two-dimensional transient computational fluid dynamics studies have been carried out on the stability of supercritical CO2-based natural circulation loop. Results are obtained for different operating pressures and temperatures in the form of mass flow rate and velocity variation with respect to time. Results show the higher instabilities in both side heat-exchanger loop than an isothermal heater with heat-exchanger loop. At a lower rate of heat input at source in the HHX-CHX loop, the mass flow is bidirectional, whereas it is unidirectional in the ISO-CHX loop at all level of heat input. It is also observed that as pressure increases, flow instability also increases. Obtained results are validated with the published experimental and numerical data and found in good agreement. © 2020, Akadémiai Kiadó, Budapest, Hungary.