Research Outputs
Permanent URI for this communityhttps://hdl.handle.net/20.500.14288/2
Browse
8 results
Search Results
Publication Metadata only A LES/PDF simulator on block-structured meshes(Taylor & Francis Ltd, 2019) Pope, Stephen B.; N/A; Department of Mechanical Engineering; Türkeri, Hasret; Muradoğlu, Metin; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 46561A block-structured mesh large-eddy simulation (LES)/probability density function (PDF) simulator is developed within the OpenFOAM framework for computational modelling of complex turbulent reacting flows. The LES/PDF solver is a hybrid solution methodology consisting of (i) a finite-volume (FV) method for solving the filtered mass and momentum equations (LES solver), and (ii) a Lagrangian particle-based Monte Carlo algorithm (PDF solver) for solving the modelled transport equation of the filtered joint PDF of compositions. Both the LES and the PDF methods are developed and combined to form a hybrid LES/PDF simulator entirely within the OpenFOAM framework. The in situ adaptive tabulation method [S.B. Pope, Computationally efficient implementation of combustion chemistry using in situ adaptive tabulation, Combust. Theory Model. 1 (1997), pp. 41-63; L. Lu, S.R. Lantz, Z. Ren, and B.S. Pope, Computationally efficient implementation of combustion chemistry in parallel PDF calculations, J. Comput. Phys. 228 (2009), pp. 5490-5525] is incorporated into the new LES/PDF solver for efficient computations of combustion chemistry with detailed reaction kinetics. The method is designed to utilise a block-structured mesh and can readily be extended to unstructured grids. The three-stage velocity interpolation method of Zhang and Haworth [A general mass consistency algorithm for hybrid particle/finite-volume PDF methods, J. Comput. Phys. 194 (2004), pp. 156-193] is adapted to interpolate the LES velocity field onto particle locations accurately and to enforce the consistency between LES and PDF fields at the numerical solution level. The hybrid algorithm is fully parallelised using the conventional domain decomposition approach. A detailed examination of the effects of each stage and the overall performance of the velocity interpolation algorithm is performed. Accurate coupling of the LES and PDF solvers is demonstrated using the one-way coupling methodology. Then the fully two-way coupled LES/PDF solver is successfully applied to simulate the Sandia Flame-D, and a turbulent non-swirling premixed flame and a turbulent swirling stratified flame from the Cambridge turbulent stratified flame series [M.S. Sweeney, S. Hochgreb, M.J. Dunn, and R.S. Barlow, The structure of turbulent stratified and premixed methane/air flames I: Non-swirling flows, Combust. Flame 159 (2012), pp. 2896-2911; M.S. Sweeney, S. Hochgreb, M.J. Dunn, and R.S. Barlow, The structure of turbulent stratified and premixed methane/air flames II: Swirling flows, Combust. Flame 159 (2012), pp. 2912-2929]. It is found that the LES/PDF method is very robust and the results are in good agreement with the experimental data for both flames.Publication Metadata only Anisotropy of ultrafine-grained alloys under impact loading: the case of biomedical niobium-zirconium(Pergamon-Elsevier Science Ltd, 2012) Rubitschek, F.; Niendorf, T.; Maier, H. J.; N/A; Department of Mechanical Engineering; Toker, Sıdıka Mine; Canadinç, Demircan; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; 255504; 23433The anisotropy-impact response relationship of a biocompatible niobium zirconium (NbZr) alloy with an ultrafine-grained microstructure was investigated. The current findings not only shed light on the micromechanisms dictating the impact response in the microstructures studied, but are also encouraging with respect to the use of NbZr in orthopedic and dental implants.Publication Metadata only Determination of composition of ethanol-CO2 mixtures at high pressures using frequency response of microcantilevers(Elsevier Science Bv, 2018) Jonas, Alexandr; Department of Physics; Department of Mechanical Engineering; Department of Chemical and Biological Engineering; N/A; Kiraz, Alper; Alaca, Burhanettin Erdem; Erkey, Can; Baloch, Shadi Khan; Faculty Member; Faculty Member; Faculty Member; PhD Student; Department of Physics; Department of Mechanical Engineering; Department of Chemical and Biological Engineering; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Sciences; College of Engineering; College of Engineering; Graduate School of Sciences and Engineering; 22542; 115108; 29633; N/AThe measurement of the composition of ethanol-CO2 mixtures at high pressures is important in many applications involving supercritical fluids such as drying of alcogels or release of MEMs. Resonant frequency and quality factor (Q-factor) of microcantilevers immersed in ethanol-CO2 mixtures were measured at a temperature of 308 K and pressure range from 8 MPa to 22 MPa. The measurements were carried out for different mixture compositions ranging from 0.91 to 6.16 wt% of ethanol in CO2. At a given pressure and temperature, the resonant frequencies were found to decrease linearly with the increasing ethanol weight percent in the mixture. The sensitivity of the resonant frequency to changes in composition was found to increase with decreasing pressure. The experimental results show that ethanol-CO2 mixture composition can be determined with good accuracy using mainly the measured resonant frequency of microcantilevers.Publication Metadata only Determination of viscosity and density of fluids using frequency response of microcantilevers(Elsevier Science Bv, 2015) Jonas, Alexandr; Department of Chemical and Biological Engineering; Department of Mechanical Engineering; Department of Physics; Department of Chemical and Biological Engineering; Eris, Gamze; Alaca, Burhanettin Erdem; Kiraz, Alper; Erkey, Can; Researcher; Faculty Member; Faculty Member; Faculty Member; Department of Mechanical Engineering; Department of Physics; Department of Chemical and Biological Engineering; College of Engineering; College of Engineering; College of Sciences; College of Engineering; N/A; 115108; 22542; 29633We report on the simultaneous measurement of density and viscosity of nitrogen in gas and supercritical phases at 308.15 K and pressures up to 24 MPa. The density and viscosity were extracted from the measured frequency responses of an oscillated microcantilever immersed in N-2. To this end, a model of oscillatory motion of immersed cantilevers incorporating the effects of hydrodynamic forces was employed. Using argon as a reference fluid of known density and viscosity, cantilever calibration parameters were obtained from nonlinear regression of cantilever resonant frequencies and quality factors recorded in argon. Subsequently, these calibration parameters were used in the model equations to determine the density and viscosity of nitrogen at the given experimental pressure and temperature. In the studied pressure range, the root-mean-square deviations of the measured density and viscosity of nitrogen from the reference values obtained from NIST database were 2.5% and 5.2%, respectively. (C) 2015 Elsevier B.V. All rights reserved.Publication Metadata only Frequency response of microcantilevers immersed in gaseous, liquid, and supercritical carbon dioxide(Elsevier, 2013) N/A; Department of Chemical and Biological Engineering; Department of Physics; N/A; Department of Physics; Department of Mechanical Engineering; Department of Physics; Department of Electrical and Electronics Engineering; Department of Chemical and Biological Engineering; Uzunlar, Erdal; Beykal, Burcu; Ehrlich, Katjana; Şanlı, Deniz; Jonas, Alexandr; Alaca, Burhanettin Erdem; Kiraz, Alper; Ürey, Hakan; Erkey, Can; Master Student; Undergraduate Student; N/A; Researcher; Other; Faculty Member; Faculty Member; Faculty Member; Faculty Member; Department of Mechanical Engineering; Department of Physics; Department of Electrical and Electronics Engineering; Department of Chemical and Biological Engineering; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; N/A; College of Engineering; College of Engineering; College of Engineering; College of Engineering; College of Engineering; N/A; N/A; N/A; N/A; N/A; 115108; 22542; 8579; 29633The frequency response of ferromagnetic nickel microcantilevers with lengths ranging between 200 mu m and 400 mu m immersed in gaseous, liquid and supercritical carbon dioxide (CO2) was investigated. the resonant frequency and the quality factor of the cantilever oscillations in CO2 were measured for each cantilever length in the temperature range between 298 K and 323 K and the pressure range between 0.1 MPa and 20.7 MPa. at a constant temperature, both the resonant frequency and the quality factor were found to decrease with increasing pressure as a result of the increasing CO2 density and viscosity. very good agreement was found between the measured cantilever resonant frequencies and predictions of a model based on simplified hydrodynamic function of a cantilever oscillating harmonically in a viscous fluid valid for Reynolds numbers in the range of [1;1000] (average deviation of 2.40%). at high pressures of CO2, the experimental Q-factors agreed well with the predicted ones. at low CO2 pressures, Additional internal mechanisms of the cantilever oscillation damping caused lowering of the measured Q-factor with respect to the hydrodynamic model predictions.Publication Metadata only Modeling adsorption, conformation, and orientation of the Fis1 tail anchor at the mitochondrial outer membrane(MDPI, 2022) Dunn, Cory D.; N/A; Department of Mechanical Engineering; Özgür, Beytullah; Sayar, Mehmet; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 109820Proteins can be targeted to organellar membranes by using a tail anchor (TA), a stretch of hydrophobic amino acids found at the polypeptide carboxyl-terminus. The Fis1 protein (Fis1p), which promotes mitochondrial and peroxisomal division in the yeast Saccharomyces cerevisiae, is targeted to those organelles by its TA. Substantial evidence suggests that Fis1p insertion into the mitochondrial outer membrane can occur without the need for a translocation machinery. However, recent findings raise the possibility that Fis1p insertion into mitochondria might be promoted by a proteinaceous complex. Here, we have performed atomistic and coarse-grained molecular dynamics simulations to analyze the adsorption, conformation, and orientation of the Fis1(TA). Our results support stable insertion at the mitochondrial outer membrane in a monotopic, rather than a bitopic (transmembrane), configuration. Once inserted in the monotopic orientation, unassisted transition to the bitopic orientation is expected to be blocked by the highly charged nature of the TA carboxyl-terminus and by the Fis1p cytosolic domain. Our results are consistent with a model in which Fis1p does not require a translocation machinery for insertion at mitochondria.Publication Metadata only On the role of slip-twin interactions on the impact behavior of high-manganese austenitic steels(Elsevier Science Sa, 2014) Taube, Alexander; Gerstein, Gregory; Maier, Hans Jürgen; N/A; Department of Mechanical Engineering; Toker, Sıdıka Mine; Canadinç, Demircan; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; 255504; 23433The temperature-dependent relative contributions of slip, twinning, and slip-twin interactions to the deformation response of a high-manganese austenitic steel were investigated under impact loading. Thorough transmission electron microscopy and scanning electron microscopy showed that either twinning or slip dictates the deformation response under impact loading, as opposed to the slip-twin interactions typically observed in high-manganese austenitic steels under tensile or compressive loading. Specifically, slip dominates at elevated temperatures, whereas slip activity is restricted by enhanced twinning at low temperatures, and the parameters, such as twin volume fraction, twin thickness and length, or glide dislocation density, show a strong temperature-dependence. The enhanced activity of only one mechanism rather than the slip-twin interaction is associated with the high-strain rate deformation taking place under impact loading, which does not allow for significant interaction of the two mechanisms.Publication Metadata only Polymeric hollow fiber membrane oxygenators as artificial lungs: a review(Elsevier, 2022) Teber, Oğuz Orhun; Altınay, Ayşegül Derya; Mehrabani, Seyed Ali Naziri; Taşdemir, Reyhan Şengür; Zeytinci, Bihter; Genceli, Esra Ateş; Dilekgürgen, Ebru; Koyuncu, İsmail; Department of Mechanical Engineering; Pekkan, Kerem; Faculty Member; Department of Mechanical Engineering; College of Engineering; 161845The oxygenator is one of the most important components of respiratory support devices, which began as a heartlung machine for the treatment of heart diseases. Hollow fiber membranes have been widely used in oxygenators due to their outstanding performance in oxygen and carbon dioxide exchange with the blood. In this review, general information on the oxygenator historical evolutions is summarized. Then, the advantages and usage of hollow fiber membranes as oxygenators are explained. Modification strategies to prevent platelet adhesion, plasma leakage have been summarized. There has been some information given on design parameters for hollow fiber membrane oxygenators. In recent years, the rapid development of microchannel structures in oxygenators has been summarized. It is thought that this review will help the reader to find recent studies on the subject.