2018 Medical Technologies National Congress (TIPTEKNO), 2018
Blood flow dynamics in arteries with stenosis is a critical issue. In this study, the effect of b... more Blood flow dynamics in arteries with stenosis is a critical issue. In this study, the effect of blood viscosity on the pressure and wall shear stress that form on the walls of an artery with a 70% reduced cross-sectional area was investigated using computational fluid dynamics. It was observed that the increase in blood viscosity caused an increase in the pressure and shear stress on the walls of normal arteries and those with stenosis. It has been shown that these parameters increase linearly with increasing blood viscosity in a normal artery and behave nonlinearly along the different regions of an artery with stenosis.
Journal of Manufacturing Science and Engineering, 2020
During electrochemical machining (ECM) of metals, the electrolyte gets polluted by heavy metal io... more During electrochemical machining (ECM) of metals, the electrolyte gets polluted by heavy metal ions and compounds. This creates crucial process control problems due to variation in electrical conductivity and is an environmental threat if the solution is discharged without treatment. In this study, an economical, simple multistep treatment system based on ion-exchange was developed to remove metal ions from the polluted electrolyte. We specifically looked at the electrolytic discharge from ECM of copper pieces, which is widely used in biomedical and electronic applications. Three different ion-exchange media were used: (1) a natural zeolite, (2) a special type of adsorbent quantitative filter paper, and (3) a polymer-based synthetic cation-holder resin (Lewatit TP 207) that works well with copper ions. Optimization studies for pH and contact time showed the following: (1) by using zeolite alone, and after 2 h of mixing, 43.2% of Cu2+ could be removed; (2) by using the filter paper a...
Among the factors that are important in successful bone tissue regeneration through scaffolds are... more Among the factors that are important in successful bone tissue regeneration through scaffolds are permeability and fluid flow-induced wall shear stress (WSS) because of the direct contribution of these factors to cell bioactivities. The permeability of scaffolds is usually measured using fluids such as water, which are characterized as Newtonian materials with constant viscosity. However, using the fluid properties of blood as bases in measuring permeability can lead to more realistic results given that scaffolds are implanted in the body, where the only flowing fluid (i.e., blood) is a non-Newtonian fluid. Moreover, the linear relationship of WSS with fluid viscosity challenges the use of Newtonian fluids in determining WSS magnitude. With consideration for these issues, we investigated permeability and WSS through computational fluid dynamics (CFD) analyses of lattice-based and gyroid scaffold architectures with Newtonian and non-Newtonian blood flow properties. With reference to geometrical parameters and the pressure drops derived from the CFD analyses, the permeability levels of the Newtonian and non-Newtonian models were calculated by exploiting the classic and modified Darcy's equations, respectively. Results showed that both scaffold architectures were several times more permeable in the Newtonian blood flow models than in their non-Newtonian counterparts. Within the scaffolds, the non-Newtonian flow of blood caused almost twice the magnitude of WSS originating from Newtonian blood flow. These striking discrepancies in permeability and WSS between the two blood models were due to differences in their viscosity behaviors.
Abstract Adopting of a simple, but dependable analytic thermodynamic solution model in the simula... more Abstract Adopting of a simple, but dependable analytic thermodynamic solution model in the simulation of phase transformation kinetics reduces the complexity of computation and the need for extensive thermodynamic data and hence is desired in the practical application of kinetic theories in materials processing. A simple subregular solution model with linear temperature dependency, which can calculate G curves with limited information extracted from an equilibrium phase diagram, is presented and applied to the calculation of (1) the binary Ag-Cu phase diagram with metastable phase boundaries and (2) the kinetics of free dendritic growth in supercooled Ag-Cu melts. The simple T- dependent subregular solution model can duplicate the published Ag-Cu phase diagram with the predicted metastable extensions to the same accuracy as that of calculations with highly structured models that require more computation and wider range of thermodynamic data. Its integration with a free dendritic growth model permits the calculation of correct values of the driving force at non-Henrian interfacial solute concentrations that occur in rapid solidification. The use of the simple T -dependent subregular solution model to calculate the interfacial driving force greatly improves the mathematical stability in the transition stage from mass transfer-limited growth to heat transfer-limited crystal growth.
Nanoscale multilayers of binary metallic systems, such as nickel/aluminum, exhibit selfpropagatin... more Nanoscale multilayers of binary metallic systems, such as nickel/aluminum, exhibit selfpropagating exothermic reactions due to the high formation enthalpy of the intermetallic compounds. Most of the previous modeling approaches on the reactions of this system rely on the use of mass diffusion with a phenomenological derived diffusion coefficient representing single-phase (NiAl) growth, coupled with heat transport. We show that the reaction kinetics, temperatures and thermal front width can be reproduced more satisfactorily with the sequential growth of Ni 2 Al 3 followed by NiAl, utilizing independently obtained interdiffusivities. The computational domain consisted of a dynamically generated bi-modal grid consisting of fine and coarse zones corresponding to rapid and slower reacting regions to improve computational efficiency. The PDEPE function in MATLAB was used as a basis for an alternating direction scheme. A modified parabolic growth law was used to model intermetallic growth in the thickness direction. A multiphase enthalpy function was used to solve for temperatures after discrete phase growth and transformations at each time step. The results show that the Ni 2 Al 3 formation yields a preheating zone to facilitate the slower growth of NiAl. At bilayer thicknesses lower than 12 nm, the intermixing layer induces oscillating thermal fronts, sharply reducing the average velocities.
Gazi Üniversitesi Mühendislik-Mimarlık Fakültesi Dergisi, 2014
Yeni bir elektrokimyasal işleme tezgahında bakır iş parçalarının işlenmesi sonrası ağır metal iyo... more Yeni bir elektrokimyasal işleme tezgahında bakır iş parçalarının işlenmesi sonrası ağır metal iyonları ile kirlenen elektrolitin sisteme yeniden beslenmeye hazır hale getirilmesi amacı ile tezgah çevre birimleri dahilinde arıtım yöntemleri incelenmiştir. Elektrokimyasal işleme (EKİ), metal bir parçanın yüzeyinin iyonlaştırma yöntemi ile işlenmesine ve metal iyonlarının elektrolit ile işleme bölgesinden uzaklaştırılmasına dayanmaktadır. Endüstriyel sularda bulunan ağır metal iyonlarının giderilmesi ve suların yeniden kullanıma hazır hale getirilmesi sistem verimliliğinin arttırılması ve çevre sağlığının korunması açısından önem taşımaktadır. Bu çalışmada, EKİ sonucu bakır iyonları ile kirlenen elektrolitin arıtılması için iyon değiştirme yöntemi tercih edilerek üç-aşamalı bir uygulama önerilmiştir. İyon değiştirici olarak birinci aşamada kağıt filtre, ikinci aşamada Türkiye'de yaygın rezervleri bulunan doğal bir zeolit ve son aşamada polimer bazlı katyon tutucu Lewatit TP 207 reçinesi kullanılmıştır. Bakır iyonları ile kirlenen elektrolitte zeolit ile iki saat etkileşim sonucu % 40, kağıt filtre ile üç kez filtreleme sonucu % 90, Lewatit TP 207 reçine kolonu ile işlem sonrası ise % 100 oranında arıtma sağlanmıştır.
Gazi Üniversitesi Mühendislik-Mimarlık Fakültesi Dergisi, 2014
Bu çalışmada ülkemizde henüz uygulama imkanı bulamayan ileri bir metal işleme yöntemi olan elektr... more Bu çalışmada ülkemizde henüz uygulama imkanı bulamayan ileri bir metal işleme yöntemi olan elektrokimyasal işleme (EKİ) yöntemi incelenmiştir. Yeni bir EKİ tezgâhı, üç-eksenli bilgisayarlı sayısal denetimli (CNC) bir tezgâhın elektrokimyasal işlemeye uygun şekilde geliştirilerek darbeli doğru akım güç kaynağı, dikey yönde elektrot aralığı kontrolünü sağlayan servo kontrol sistemi, elektrolit vakumlama, arıtma ve geri-çevrim sistemi ile bütünleştirilmesi ile elde edilmiştir. EKİ sisteminin istenilen sınırlarda kontrollü çalışması katot ucu tasarımının doğru yapılması, katot ile anot arasındaki mesafenin hassas ayarlanması, akım ve gerilim değerlerinin kontrol altında tutulması ve elektrot yüzeylerinin maskelenmesi ile sağlanmıştır. Sistemin kararlı çalışabilmesi için elektrolit derişiminin sabit tutulması gerektiği tespit edilmiştir.
ASME 2010 10th Biennial Conference on Engineering Systems Design and Analysis, ESDA2010, 2010
In this study, the Shannon entropies of six different roadprofiles ranging from "very good asphal... more In this study, the Shannon entropies of six different roadprofiles ranging from "very good asphalt road" to "dirt road (terrain)" were calculated. Results indicate that each type of road has a well defined entropy value and that the entropies of roads ranging from "very good asphalt" to "dirt road (terrain)" lie on a nearly linear locus. A second approach presented in this paper consists in measuring the sprung mass vertical acceleration of a vehicle running over segments of roads of different qualities and calculating the entropies of the acceleration signals. This procedure has been applied to assess the influence of nonlinear damping and vehicle speed. It has been seen that it is possible to identify the type of the road surface through the calculation of entropy if the vehicle operating parameters are known. Finally, it is observed that the locus of entropy values is concave on the plot of acceleration entropy versus root mean square (RMS) acceleration.
The formulations of existing free dendritic growth models were compared, and an extended model wa... more The formulations of existing free dendritic growth models were compared, and an extended model was proposed that employs a subregular solution model to compute the driving force for dendritic growth without Henrian restrictions. These models were also applied to a Ag-15 mass pct Cu alloy to numerically compare their predictions. Models that address only the thermal, solutal, and curvature supercoolings do not properly account for the interface kinetics, even with modifications with the kinetic partition coefficient and liquidus slope. It is only in models that account for the interfacial driving force,-DG * , that the kinetic supercooling is properly addressed. All of the models in comparison yield numerically similar predictions for the solutal growth regime, but models that employ the kinetic partition coefficient and liquidus slope, but do not address the interfacial driving force, fail to correctly describe the thermal control regime. The solutal-to-thermal transition is characterized by a rapid increase of interfacial driving force, which causes the tip temperature T * to increase with increasing growth rate V. The criterion for the transition stage is given as d lnðÀDG à Þ=d ln V>1.
2018 Medical Technologies National Congress (TIPTEKNO), 2018
Blood flow dynamics in arteries with stenosis is a critical issue. In this study, the effect of b... more Blood flow dynamics in arteries with stenosis is a critical issue. In this study, the effect of blood viscosity on the pressure and wall shear stress that form on the walls of an artery with a 70% reduced cross-sectional area was investigated using computational fluid dynamics. It was observed that the increase in blood viscosity caused an increase in the pressure and shear stress on the walls of normal arteries and those with stenosis. It has been shown that these parameters increase linearly with increasing blood viscosity in a normal artery and behave nonlinearly along the different regions of an artery with stenosis.
Journal of Manufacturing Science and Engineering, 2020
During electrochemical machining (ECM) of metals, the electrolyte gets polluted by heavy metal io... more During electrochemical machining (ECM) of metals, the electrolyte gets polluted by heavy metal ions and compounds. This creates crucial process control problems due to variation in electrical conductivity and is an environmental threat if the solution is discharged without treatment. In this study, an economical, simple multistep treatment system based on ion-exchange was developed to remove metal ions from the polluted electrolyte. We specifically looked at the electrolytic discharge from ECM of copper pieces, which is widely used in biomedical and electronic applications. Three different ion-exchange media were used: (1) a natural zeolite, (2) a special type of adsorbent quantitative filter paper, and (3) a polymer-based synthetic cation-holder resin (Lewatit TP 207) that works well with copper ions. Optimization studies for pH and contact time showed the following: (1) by using zeolite alone, and after 2 h of mixing, 43.2% of Cu2+ could be removed; (2) by using the filter paper a...
Among the factors that are important in successful bone tissue regeneration through scaffolds are... more Among the factors that are important in successful bone tissue regeneration through scaffolds are permeability and fluid flow-induced wall shear stress (WSS) because of the direct contribution of these factors to cell bioactivities. The permeability of scaffolds is usually measured using fluids such as water, which are characterized as Newtonian materials with constant viscosity. However, using the fluid properties of blood as bases in measuring permeability can lead to more realistic results given that scaffolds are implanted in the body, where the only flowing fluid (i.e., blood) is a non-Newtonian fluid. Moreover, the linear relationship of WSS with fluid viscosity challenges the use of Newtonian fluids in determining WSS magnitude. With consideration for these issues, we investigated permeability and WSS through computational fluid dynamics (CFD) analyses of lattice-based and gyroid scaffold architectures with Newtonian and non-Newtonian blood flow properties. With reference to geometrical parameters and the pressure drops derived from the CFD analyses, the permeability levels of the Newtonian and non-Newtonian models were calculated by exploiting the classic and modified Darcy's equations, respectively. Results showed that both scaffold architectures were several times more permeable in the Newtonian blood flow models than in their non-Newtonian counterparts. Within the scaffolds, the non-Newtonian flow of blood caused almost twice the magnitude of WSS originating from Newtonian blood flow. These striking discrepancies in permeability and WSS between the two blood models were due to differences in their viscosity behaviors.
Abstract Adopting of a simple, but dependable analytic thermodynamic solution model in the simula... more Abstract Adopting of a simple, but dependable analytic thermodynamic solution model in the simulation of phase transformation kinetics reduces the complexity of computation and the need for extensive thermodynamic data and hence is desired in the practical application of kinetic theories in materials processing. A simple subregular solution model with linear temperature dependency, which can calculate G curves with limited information extracted from an equilibrium phase diagram, is presented and applied to the calculation of (1) the binary Ag-Cu phase diagram with metastable phase boundaries and (2) the kinetics of free dendritic growth in supercooled Ag-Cu melts. The simple T- dependent subregular solution model can duplicate the published Ag-Cu phase diagram with the predicted metastable extensions to the same accuracy as that of calculations with highly structured models that require more computation and wider range of thermodynamic data. Its integration with a free dendritic growth model permits the calculation of correct values of the driving force at non-Henrian interfacial solute concentrations that occur in rapid solidification. The use of the simple T -dependent subregular solution model to calculate the interfacial driving force greatly improves the mathematical stability in the transition stage from mass transfer-limited growth to heat transfer-limited crystal growth.
Nanoscale multilayers of binary metallic systems, such as nickel/aluminum, exhibit selfpropagatin... more Nanoscale multilayers of binary metallic systems, such as nickel/aluminum, exhibit selfpropagating exothermic reactions due to the high formation enthalpy of the intermetallic compounds. Most of the previous modeling approaches on the reactions of this system rely on the use of mass diffusion with a phenomenological derived diffusion coefficient representing single-phase (NiAl) growth, coupled with heat transport. We show that the reaction kinetics, temperatures and thermal front width can be reproduced more satisfactorily with the sequential growth of Ni 2 Al 3 followed by NiAl, utilizing independently obtained interdiffusivities. The computational domain consisted of a dynamically generated bi-modal grid consisting of fine and coarse zones corresponding to rapid and slower reacting regions to improve computational efficiency. The PDEPE function in MATLAB was used as a basis for an alternating direction scheme. A modified parabolic growth law was used to model intermetallic growth in the thickness direction. A multiphase enthalpy function was used to solve for temperatures after discrete phase growth and transformations at each time step. The results show that the Ni 2 Al 3 formation yields a preheating zone to facilitate the slower growth of NiAl. At bilayer thicknesses lower than 12 nm, the intermixing layer induces oscillating thermal fronts, sharply reducing the average velocities.
Gazi Üniversitesi Mühendislik-Mimarlık Fakültesi Dergisi, 2014
Yeni bir elektrokimyasal işleme tezgahında bakır iş parçalarının işlenmesi sonrası ağır metal iyo... more Yeni bir elektrokimyasal işleme tezgahında bakır iş parçalarının işlenmesi sonrası ağır metal iyonları ile kirlenen elektrolitin sisteme yeniden beslenmeye hazır hale getirilmesi amacı ile tezgah çevre birimleri dahilinde arıtım yöntemleri incelenmiştir. Elektrokimyasal işleme (EKİ), metal bir parçanın yüzeyinin iyonlaştırma yöntemi ile işlenmesine ve metal iyonlarının elektrolit ile işleme bölgesinden uzaklaştırılmasına dayanmaktadır. Endüstriyel sularda bulunan ağır metal iyonlarının giderilmesi ve suların yeniden kullanıma hazır hale getirilmesi sistem verimliliğinin arttırılması ve çevre sağlığının korunması açısından önem taşımaktadır. Bu çalışmada, EKİ sonucu bakır iyonları ile kirlenen elektrolitin arıtılması için iyon değiştirme yöntemi tercih edilerek üç-aşamalı bir uygulama önerilmiştir. İyon değiştirici olarak birinci aşamada kağıt filtre, ikinci aşamada Türkiye'de yaygın rezervleri bulunan doğal bir zeolit ve son aşamada polimer bazlı katyon tutucu Lewatit TP 207 reçinesi kullanılmıştır. Bakır iyonları ile kirlenen elektrolitte zeolit ile iki saat etkileşim sonucu % 40, kağıt filtre ile üç kez filtreleme sonucu % 90, Lewatit TP 207 reçine kolonu ile işlem sonrası ise % 100 oranında arıtma sağlanmıştır.
Gazi Üniversitesi Mühendislik-Mimarlık Fakültesi Dergisi, 2014
Bu çalışmada ülkemizde henüz uygulama imkanı bulamayan ileri bir metal işleme yöntemi olan elektr... more Bu çalışmada ülkemizde henüz uygulama imkanı bulamayan ileri bir metal işleme yöntemi olan elektrokimyasal işleme (EKİ) yöntemi incelenmiştir. Yeni bir EKİ tezgâhı, üç-eksenli bilgisayarlı sayısal denetimli (CNC) bir tezgâhın elektrokimyasal işlemeye uygun şekilde geliştirilerek darbeli doğru akım güç kaynağı, dikey yönde elektrot aralığı kontrolünü sağlayan servo kontrol sistemi, elektrolit vakumlama, arıtma ve geri-çevrim sistemi ile bütünleştirilmesi ile elde edilmiştir. EKİ sisteminin istenilen sınırlarda kontrollü çalışması katot ucu tasarımının doğru yapılması, katot ile anot arasındaki mesafenin hassas ayarlanması, akım ve gerilim değerlerinin kontrol altında tutulması ve elektrot yüzeylerinin maskelenmesi ile sağlanmıştır. Sistemin kararlı çalışabilmesi için elektrolit derişiminin sabit tutulması gerektiği tespit edilmiştir.
ASME 2010 10th Biennial Conference on Engineering Systems Design and Analysis, ESDA2010, 2010
In this study, the Shannon entropies of six different roadprofiles ranging from "very good asphal... more In this study, the Shannon entropies of six different roadprofiles ranging from "very good asphalt road" to "dirt road (terrain)" were calculated. Results indicate that each type of road has a well defined entropy value and that the entropies of roads ranging from "very good asphalt" to "dirt road (terrain)" lie on a nearly linear locus. A second approach presented in this paper consists in measuring the sprung mass vertical acceleration of a vehicle running over segments of roads of different qualities and calculating the entropies of the acceleration signals. This procedure has been applied to assess the influence of nonlinear damping and vehicle speed. It has been seen that it is possible to identify the type of the road surface through the calculation of entropy if the vehicle operating parameters are known. Finally, it is observed that the locus of entropy values is concave on the plot of acceleration entropy versus root mean square (RMS) acceleration.
The formulations of existing free dendritic growth models were compared, and an extended model wa... more The formulations of existing free dendritic growth models were compared, and an extended model was proposed that employs a subregular solution model to compute the driving force for dendritic growth without Henrian restrictions. These models were also applied to a Ag-15 mass pct Cu alloy to numerically compare their predictions. Models that address only the thermal, solutal, and curvature supercoolings do not properly account for the interface kinetics, even with modifications with the kinetic partition coefficient and liquidus slope. It is only in models that account for the interfacial driving force,-DG * , that the kinetic supercooling is properly addressed. All of the models in comparison yield numerically similar predictions for the solutal growth regime, but models that employ the kinetic partition coefficient and liquidus slope, but do not address the interfacial driving force, fail to correctly describe the thermal control regime. The solutal-to-thermal transition is characterized by a rapid increase of interfacial driving force, which causes the tip temperature T * to increase with increasing growth rate V. The criterion for the transition stage is given as d lnðÀDG à Þ=d ln V>1.
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