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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
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Publication Metadata only Effect of preservation period on the viscoelastic material properties of soft tissues with implications for liver transplantation(Asme, 2010) N/A; N/A; N/A; Department of Mechanical Engineering; Department of Mechanical Engineering; Öcal, Sina; Özcan, Mustafa Umut; Başdoğan, İpek; Başdoğan, Çağatay; Master Student; Master Student; Faculty Member; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; N/A; N/A; 179940; 125489The liver harvested from a donor must be preserved and transported to a suitable recipient immediately for a successful liver transplantation. In this process, the preservation period is the most critical, since it is the longest and most tissue damage occurs during this period due to the reduced blood supply to the harvested liver and the change in its temperature. We investigate the effect of preservation period on the dynamic material properties of bovine liver using a viscoelastic model derived from both impact and ramp and hold experiments. First, we measure the storage and loss moduli of bovine liver as a function of excitation frequency using an impact hammer. Second, its time-dependent relaxation modulus is measured separately through ramp and hold experiments performed by a compression device. Third, a Maxwell solid model that successfully imitates the frequency- and time-dependent dynamic responses of bovine liver is developed to estimate the optimum viscoelastic material coefficients by minimizing the error between the experimental data and the corresponding values generated by the model. Finally, the variation in the viscoelastic material coefficients of bovine liver are investigated as a function of preservation period for the liver samples tested 1 h, 2 h, 4 h, 8 h, 12 h, 24 h, 36 h, and 48 h after harvesting. The results of our experiments performed with three animals show that the liver tissue becomes stiffer and more viscous as it spends more time in the preservation cycle.Publication Metadata only Development of a finite element model of the human cervical spine(Turkish Neurosurgery Society, 2014) N/A; N/A; Department of Mechanical Engineering; N/A; Zafarparandeh, Iman; Erbulut, Deniz Ufuk; Lazoğlu, İsmail; Özer, Ali Fahir; PhD Student; Researcher; Faculty Member; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; School of Medicine; College of Engineering; School of Medicine; N/A; 37661; 179391; 1022The finite element model has been used as an effective tool in human spine biomechanics. Biomechanical finite element models have provided basic insights into the workings of the cervical spine system. Advancements in numerical methods during the last decade have enabled researchers to propose more accurate models of the cervical spine. The new finite element model of the cervical spine considers the accurate representation of each tissue regarding the geometry and material. The aim of this paper is to address the new advancements in the finite element model of the human cervical spine. The procedures for creating a finite element model are introduced, including geometric construction, material-property assignment, boundary conditions and validation. The most recent and published finite element models of the cervical spine are reviewed. / Sonlu eleman yöntemi efektif bir araç olarak omurga biyomekaniğinde yaygın kullanılmaktadır. Servikal omurga içerisinde meydana gelebilecek biyomekanik değişimlerin incelenmesine fırsat verebilmektedir. Geçtiğimiz on yıl içerisinde, geliştirilmiş olan nümerik metodlar sayesinde, daha gerçekçi omurga modellerinin çıkarılması sağlanmıştır. Günümüzde, servikal omurga modellerinde kullanılan geometri ve malzeme özellikleri olabildiğince gerçeğe yakın oluşturulabilmektedir. Bu makalenin amacı, sonlu eleman yöntemi kullanılarak insan servikal modellinin oluşturulmasını örneklerle açıklamaktır. Servikal omurga modelinin sonlu eleman yöntemi ile oluşturulmasının her bir adımı detaylı ele alınmıştır. Literatürde en son yayınlanan servikal omurga sonlu eleman modelleri incelenmiş ve karşılaştırılmıştır.Publication Metadata only Noninvasive in vivo determination of residual strains and stresses(ASME, 2015) N/A; Department of Molecular Biology and Genetics; Department of Mechanical Engineering; Donmazov, Samir; Pişkin, Şenol; Pekkan, Kerem; PhD Student; Researcher; Faculty Member; Department of Molecular Biology and Genetics; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; N/A; 148702; 161845Vascular growth and remodeling during embryonic development are associated with blood flow and pressure induced stress distribution, in which residual strains and stresses play a central role. Residual strains are typically measured by performing in vitro tests on the excised vascular tissue. In this paper, we investigated the possibility of estimating residual strains and stresses using physiological pressure-radius data obtained through in vivo noninvasive measurement techniques, such as optical coherence tomography or ultrasound modalities. This analytical approach first tested with in vitro results using experimental data sets for three different arteries such as rabbit carotid artery, rabbit thoracic artery, and human carotid artery based on Fung's pseudostrain energy function and Delfino's exponential strain energy function (SEF). We also examined residual strains and stresses in the human swine iliac artery using the in vivo experimental ultrasound data sets corresponding to the systolic-to-diastolic region only. This allowed computation of the in vivo residual stress information for loading and unloading states separately. Residual strain parameters as well as the material parameters were successfully computed with high accuracy, where the relative errors are introduced in the range of 0-7.5%. Corresponding residual stress distributions demonstrated global errors all in acceptable ranges. A slight discrepancy was observed in the computed reduced axial force. Results of computations performed based on in vivo experimental data obtained from loading and unloading states of the artery exhibited alterations in material properties and residual strain parameters as well. Emerging noninvasive measurement techniques combined with the present analytical approach can be used to estimate residual strains and stresses in vascular tissues as a precursor for growth estimates. This approach is also validated with a finite element model of a general two-layered artery, where the material remodeling states and residual strain generation are investigated.Publication Metadata only In silico analysis of elastomer-coated cerclage for reducing sternal cut-through in high-risk patients(The American Society of Mechanical Engineers (ASME), 2021) Erdoğan, Mustafa Bilge; N/A; N/A; N/A; Department of Mechanical Engineering; Department of Mechanical Engineering; Subaşı, Ömer; Oral, Atacan; Torabnia, Shams; Erdoğan, Deniz; Lazoğlu, İsmail; PhD Student; PhD Student; PhD Student; Undergraduate Student; Faculty Member; Department of Mechanical Engineering; Manufacturing and Automation Research Center (MARC); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; N/A; N/A; N/A; N/A; 179391Background: AISI 316 L stainless steel wire cerclage routinely used in sternotomy closure causes lateral cut-through damage and fracture, especially in cases of high-risk patients, which leads to postoperative complications. A biocompatible elastomer (Pellethane(R)) coating on the standard wire is proposed to mitigate the cut-through effect. Methods: Simplified peri-sternal and transsternal, sternum-cerclage contact models are created and statically analyzed in a finite element (FE) software to characterize the stress-reduction effect of the polymer coating for thicknesses between 0.5 and 1.125 mm. The performance of the polymer-coated cerclage in alleviating the detrimental cortical stresses is also compared to the standard steel cerclage in a full sternal closure FE model for the extreme cough loading scenario. Results: It was observed via the simplified contact simulations that the cortical stresses can be substantially decreased by increasing the coating thickness. The full closure coughing simulation on the human sternum further corroborated the simplified contact results. The stress reduction effect was found to be more prominent in the transsternal contacts in comparison to peri-sternal contacts. Conclusions: Bearing in mind the promising numerical simulation results, it is put forth that a standard steel wire coated with Pellethane will majorly address the cut-through complication.Publication Metadata only Finite element modeling of a vibrating touch screen actuated by piezo patches for haptic feedback(Springer, 2012) N/A; N/A; Department of Mechanical Engineering; Baylan, Buket; Arıdoğan, Mustafa Uğur; Başdoğan, Çağatay; Master Student; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 125489The aim of our work is to design a touch screen for displaying vibrotactile haptic feedback to the user via piezo patches attached to its surface. One of the challenges in the design is the selection of appropriate boundary conditions and the piezo configurations (location and orientation) on the screen for achieving optimum performance within the limits of human haptic perception. To investigate the trade-offs in our design, we developed a finite element model of the screen and four piezo actuators attached to its surface in ABAQUS. The model utilizes the well-known Hooke's law between stress and strain extended by piezoelectric coupling. After selecting the appropriate boundary condition for the screen based on the range of vibration frequencies detectable by a human finger, the optimum configuration for the piezo patches is determined by maximizing the vibration amplitude of the screen for a unit micro Coulomb charge applied to each piezo patch. The results of our study suggest that the piezo patches should be placed close to the clamped sides of the screen where the boundary conditions are applied. © 2012 Springer-Verlag.Publication Metadata only Evolution of transformation plasticity during bainitic transformation(Carl Hanser Verlag, 2011) Lambers, Hans Gerd; Tschumak, Sergej; Maier, Hans Juergen; Department of Mechanical Engineering; Canadinç, Demircan; Faculty Member; Department of Mechanical Engineering; College of Engineering; 23433The influences of prior austenitization treatment and the state of applied stresses on the evolution of transformation plasticity strains during isothermal bainitic phase transformation and the resulting microstructures were examined. The key finding is that, upon pre-straining, the amount of transformation plasticity strain under superimposed elastic stresses is dictated by both the prior austenite grain size and the (0.01 % offset) yield strength of the supercooled austenite. Furthermore, the superimposition of internal stresses present due to pre-straining and externally applied stresses results in transformation plasticity strains similar to those obtained when a permanent stress equivalent to the 0.01 % offset yield strength of the supercooled austenite is applied. Another important result is that lower transformation plasticity strains were observed when decreasing the austenite grain size, which is accompanied by an increase in grain boundary area per volume, hindering the growth of preferred variants. Overall, the results clearly lay out the influence of austenite grain size and the particular 0.01 % offset yield strength of the supercooled austenite in limiting the transformation plasticity strains, which has to be incorporated into current models involving bainitic phase transformations.Publication Metadata only Effect of modified blalock-taussig shunt anastomosis angle and pulmonary artery diameter on pulmonary flow(Turkish Society of Cardiology, 2018) Arnaz, Ahmet; Yalçınbas, Yusuf; Sarioglu, Tayyar; Department of Mechanical Engineering; Department of Mechanical Engineering; N/A; Pişkin, Şenol; Pekkan, Kerem; Oğuz, Gökçe Nur; Researcher; Faculty Member; PhD Student; Department of Mechanical Engineering; College of Engineering; College of Engineering; Graduate School of Sciences and Engineering; 148702; 161845; N/AObjective: This study aimed to identify the best graft-to-pulmonary artery (PA) anastomosis angle measuring pulmonary blood flow, wall shear stress (WSS), and shunt flow. Methods: A tetralogy of Fallot with pulmonary atresia computer model was used to study three different modified Blalock-Taussig shunt (mBTS) anastomosis angle configurations with three different PA diameter configurations. Velocity and WSS were analyzed, and the flow rates at the right PA (RPA) and left PA (LPA) were calculated. Results: A 4-mm and 8-mm diameter of RPA and LPA, respectively with vertical shunt angle produces the highest total flow. In the RPA larger diameter than the LPA configutations, the left-leaning shunt produces the lowest total PA flow whereas in the LPA larger diameter than the RPA configuratios, the right-leaning shunt produces the lowest total PA flow. Therefore, the shunt anastomosis should not be leaned through the narrow side of PA to reach best flow. As the flow inside the shunt increased, WSS also increased due to enhanced velocity gradients. Conclusion: The anastomosis angle between the conduit and PA affects the flow to PA. Vertical anastomosis configurations increase the total PA flow; thus, these configurations are preferable than the leaned configurations.Publication Metadata only A short-term in vivo evaluation of the Istanbul heart left ventricular assist device in a pig model(Middle East Society for Organ Transplantation, 2019) Küçükaksu, Deniz Süha; Bakuy, Vedat; Arat, Nurcan; Erkasap, Pelin Çelikbilek; Aksoy, Emin; Department of Mechanical Engineering; N/A; N/A; N/A; N/A; N/A; Lazoğlu, İsmail; Öztürk, Çağlar; Aka, İbrahim Başar; Yalçın, Özlem; Uğurel, Elif; Ruacan, Ahmet Şevket; Faculty Member; PhD Student; PhD Student; Faculty Member; Researcher; Faculty Member; Department of Mechanical Engineering; Manufacturing and Automation Research Center (MARC); College of Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; School of Medicine; School of Medicine; School of Medicine; 179391; N/A; N/A; 218440; N/A; N/AObjectives: a continuous-flow centrifugal blood pump system has been recently developed as an implantable left ventricular assist device for patients with endstage heart failure. The objective of this study was to evaluate the initial in vivo performance of a newly developed left ventricular assist device (iHeart or Istanbul heart; Manufacturing and Automation Research Center, Koc University, Istanbul, Turkey) in an acute setting using a pig model. Materials and Methods: three pigs (77, 83, 92 kg) received implants via a median sternotomy, with animals supported for up to 6 hours. An outflow cannula was anastomosed to the ascending aorta. Anticoagulation was applied by intravenous heparin administration. During the support period, pump performance was evaluated under several flow and operating conditions. All pigs were humanely sacrificied after the experiments, and organs were examined macroscopically and histopathologically. Results: flow rate ranged between 1.5 and 3.6 L/min with pump speeds of 1500 to 2800 revolutions/min and motor current of 0.6 to 1.3 A. Initial findings confirmed thatthe iHeart ventricular assist device had sufficient hydraulic performance to support the circulation. During the experimental period, plasma free hemoglobin levels were found to be within normalranges. Thrombus formation was not observed inside the pump in all experiments. Conclusions: the iHeart ventricular assist device demonstrated encouraging hemodynamic performance and good biocompatibility in the pig model for use as an implantable left ventricular assist device. Further acute in vivo studies will evaluate the short-term pump performance prior to chronic studies for long-term evaluation.Publication Metadata only Hemodynamics of neonatal double lumen cannula malposition(2020) Yıldız, Yahya; Salihoğlu, Ece; Department of Mechanical Engineering; Department of Mechanical Engineering; Department of Mechanical Engineering; Department of Mechanical Engineering; Department of Mechanical Engineering; Jamil, Muhammad; Rezaeimoghaddam, Mohammad; Çakmak, Bilgesu; Rasooli, Reza; Pekkan, Kerem; Researcher; Researcher; Researcher; Researcher; Faculty Member; Department of Mechanical Engineering; College of Engineering; College of Engineering; College of Engineering; College of Engineering; College of Engineering; N/A; N/A; N/A; N/A; 161845Objective: Malposition of dual lumen cannula is a frequent and challenging complication in neonates and plays a significant role in shaping the in vitro device hemodynamics. This study aims to analyze the effect of the dual lumen cannula malposition on right-atrial hemodynamics in neonatal patients using an experimentally validated computational fluid dynamics model. Methods: A computer model was developed for clinically approved dual lumen cannula (13Fr Origen Biomedical, Austin, Texas, USA) oriented inside the atrium of a 3-kg neonate with normal venous return. Atrial hemodynamics and dual lumen cannula malposition were systematically simulated for two rotations (antero-atrial and atrio-septal) and four translations (two intravascular movements along inferior vena cava and two dislodged configurations in the atrium). A multi-domain compartmentalized mesh was prepared to allow the site-specific evaluation of important hemodynamic parameters. Transport of each blood stream, blood damage levels, and recirculation times are quantified and compared to dual lumen cannula in proper position. Results: High recirculation levels (39 ± 4%) in malpositioned cases resulted in poor oxygen saturation where maximum recirculation of up to 42% was observed. Apparently, Origen dual lumen cannula showed poor inferior vena cava bloodcapturing efficiency (48 ± 8%) but high superior vena cava blood–capturing efficiency (86 ± 10%). Dual lumen cannula malposition resulted in corresponding changes in residence time (1.7 ± 0.5 seconds through the tricuspid). No significant differences in blood damage were observed among the simulated cases compared to normal orientation. Compared to the correct dual lumen cannula position, both rotational and translational displacements of the dual lumen cannula resulted in significant hemodynamic differences. Conclusion: Rotational or translational movement of dual lumen cannula is the determining factor for atrial hemodynamics, venous capturing efficiency, blood residence time, and oxygenated blood delivery. Results obtained through computational fluid dynamics methodology can provide valuable foresight in assessing the performance of the dual lumen cannula in patient-specific configurations.Publication Metadata only Electromechanical modeling of a novel moving magnet linear oscillating actuator(Korean Soc Mechanical Engineers, 2018) N/A; N/A; N/A; Department of Mechanical Engineering; Hassan, Adnan; Bijanzad, Armin; Lazoğlu, İsmail; PhD Student; PhD Student; Faculty Member; Department of Mechanical Engineering; Manufacturing and Automation Research Center (MARC); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 179391This article presents a design of a novel moving magnet linear actuator (MMLa) for linear refrigerator compressor. a methodology to estimate the magnetic flux density as well as the magnetic force of MMLa is presented. Considering the simulation time of a 3D FEM software, A combination of 2D FEM with the analytical models makes this technique convenient and expeditious. Using the 2D FEM, the magnetic flux path is segregated into several loops which are divided into finite reluctance zones. the reluctance models for each zone incorporates the effect of armature position to predict the magnetic flux density and linear force incorporating the stator saturation. a 3D FEM simulation is executed to compare the presented models as well as computation times. Furthermore, An analytical approach for evaluating the effect of the excitation frequency and motor constant on the dynamic performance of a linear oscillating actuator is presented and validated experimentally.
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