Researcher:
Subaşı, Ömer

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Ömer

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Subaşı

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Subaşı, Ömer

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2010 - 201932020 - 20238

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    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; 179391
    Background: 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.
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    In silico analysis of modular bone plates
    (Elsevier, 2021) N/A; N/A; Department of Mechanical Engineering; N/A; Department of Mechanical Engineering; Subaşı, Ömer; Oral, Atacan; Noyan, Sinan; Tunçözgür, Orçun; Lazoğlu, İsmail; PhD Student; PhD Student; Undergraduate Student; Master 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; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; N/A; N/A; 179391
    Background: Inventory management or immediate availability of fracture plates can be problematic since for each surgical intervention a specific plate of varying size and functionality must be ordered. Modularization of the standard monolithic plate is proposed to address this issue. Methods: The effects of four different unit module design parameters (type, degree of modularization, connector screw diameter, sandwich ratio) on the plate bending stiffness and failure are investigated in a finite element four-point-bending analysis. A chosen, best-performing modular plate is then tested in silico for a simple diaphyseal tibial fracture scenario under anatomical compressional, torsional, and bending loads . Results: A modularization strategy is proposed to match the monolithic plate bending properties as closely as possible. With the best combination of design parameters, a fully modularized equivalent length plate with a 42.3% decrease in stiffness and 46.2% decrease in strength could be assembled. The chosen modular plate also displayed sufficient mechanical performance under the fracture fixation scenarios for a potentially successful osteosynthesis. Conclusions: Via computational methods, the viability of the modularization strategy as an alternate to the traditional monolithic plate is demonstrated. As a further realized advantage, the modular plates can alleviate stress shielding thanks to the reduced stiffness.
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    A novel lower bound for tip-apex distance
    (Springer Heidelberg, 2022) N/A; N/A; N/A; N/A; Department of Mechanical Engineering; Subaşı, Ömer; Aslan, Lercan; Demirhan, Mehmet; Seyahi, Aksel; Lazoğlu, İsmail; PhD Student; Faculty Member; Faculty Member; Faculty Member; Faculty Member; Department of Mechanical Engineering; Manufacturing and Automation Research Center (MARC); Graduate School of Sciences and Engineering; School of Medicine; School of Medicine; School of Medicine; College of Engineering; Koç University Hospital; N/A; 145301; 9882; 52082; 179391
    Purpose: The cut-out of the cephalomedullary nail is among the most common post-surgery complications for intertrochanteric fractures. As a risk predictor, a tip-apex distance (TAD) below 25 mm, observed from orthogonal fluoroscopic views, is recommended in the literature. This study aims to demonstrate that TAD < 25 mm is a mathematically insufficient risk definition and to complement the TAD upper bound with an appropriate lower bound, with the introduction of a novel distance parameter, TADX, based on the orthogonal projection of the nail tip on the central femoral midline. Method: Through a mathematical simulation software, all the possible points that lie inside the AP and lateral views of the proximal femoral hemisphere are utilized to create a 3D grid that is sorted into geometrically safe and risk-bearing regions. Extending this methodology, TAD < 25 mm, 10 mm < TAD < 25 mm, and the ideal tip position volumes are simulated. Finally, intersection volumes are created by a combination of different candidate lower TADX bounds and TAD < 25 mm upper bound to determine satisfactory TADX limits. Results: Simulation of TAD-bound zones exposed that TAD is only a mathematically suitable parameter for defining the upper boundary but not the lower boundary for the optimal region. However, using a TADX lower limit creates a 3D volume that is much closer to the optimal tip region volumetrically and can still be as quickly calculated from 2D AP and lateral views. Conclusions: According to the mathematical simulations, the use of a TADX lower bound of 9 mm for small, 7.5 mm for medium, and 7 mm for large femoral heads in conjunction with a TAD upper bound of 25 mm is suggested.
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    A novel approach to tube design via von Mises probability distribution
    (Taylor & Francis Ltd) Subay, Şehmuz Ali; N/A; N/A; N/A; Department of Mechanical Engineering; Oral, Atacan; Subaşı, Ömer; Öztürk, Çağlar; Lazoğlu, İsmail; PhD Student; Researcher; PhD student; Faculty Member; Department of Mechanical Engineering; Manufacturing and Automation Research Center (MARC); Graduate School of Sciences and Engineering; N/A; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; N/A; 179391
    Discharge tube is a critical component in a reciprocating compressor that carries the refrigerant. It also transmits vibrations from compressor body to housing, making the design of tube a complex engineering problem combining static, modal and flow behaviour. This study proposes a novel design algorithm for discharge tube, to decrease the dependency on the trial-and-error approach commonly used by manufacturers. The computational approach creates a tube that connects the inlet and outlet using von Mises probability distribution. The created geometries are checked for static and dynamic properties using FEA. The algorithm continues until a candidate design passes the imposed thresholds. The candidate designs perform similarly to benchmark in evaluated aspects, demonstrating promising results. The presented algorithm is successful in generating alternative tube designs from scratch and can accommodate varying requirements. The main novelty of this study is the development of a comprehensive decision algorithm that considers multiple engineering parameters simultaneously.
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    Effect of starting position of crankshaft on transient body vibrations of reciprocating compressor
    (Elsevier, 2023) Sahin C.; Haque U.U.; N/A; N/A; Department of Mechanical Engineering; Oral, Atacan; Subaşı, Ömer; 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; 179391
    The maximum reciprocating compressor vibrations occur during the startup and shutdown operations and understanding the factors that influence the transient vibrations can help in developing solutions to reduce the excessive displacements. In this study, the effect of crankshaft starting position on the vibration phenomenon is investigated and the optimal starting position to deliver a smooth start is proposed. The structural forces are analytically modeled to estimate the body displacements by considering the system resonance frequencies and modal vectors. An experimental setup is also constructed to validate the prediction model results, with the integration of an encoder to track the crankshaft angular position and transducers to measure the discharge and suction pressures. The transient responses of three different crankshaft start positions are then compared using the experimental setup and the analytical model. The results indicate that if the crankshaft starts to rotate from positions close to the bottom dead center, a higher amount of startup vibrations is observed, revealing the optimal starting position zone. The magnetization effect can potentially be addressed by the sensorless starting strategy developed by Lee et al. (2008) that implements a phase current controller for a smoother startup. While out of scope for this study, shutdown strategies can also be devised to have the piston consistently land at the favorable SAP range. By separately investigating the instances when the ‘stop’ command is provided to the steady-state operating compressor, solutions that attempt to replicate the conditions that lead to the favorable stop position can be developed; a limiting factor in mass production will be implementing the encoder for continuous position tracking and an accompanying undesirable cost increase in manufacturing. Nevertheless, the investigation of passive and active strategies is ripe for research in literature. 2022 Elsevier Ltd and IIR
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    The safety and accuracy of the fluoroscopic imaging during proximal femoral fixation: a computerized 3D reappraisal of the joint penetration risk
    (Elsevier Sci Ltd, 2021) N/A; N/A; N/A; N/A; Department of Mechanical Engineering; Aslan, Lercan; Subaşı, Ömer; Demirhan, Mehmet; Seyahi, Aksel; Lazoğlu, İsmail; Faculty Member; PhD Student; Faculty Member; Faculty Member; Faculty Member; Department of Mechanical Engineering; School of Medicine; Graduate School of Sciences and Engineering; School of Medicine; School of Medicine; College of Engineering; 145301; N/A; 9882; 52082; 179391
    Background: To assess the success of proximal cephalomedullary nailing operations for treating trochanteric fractures, surgeons utilize 2D fluoroscopy to observe the relative positions of the femoral head and the implant. One distance-based risk parameter, observed from the AP and Lateral projections, is the Tip-Surface Distance(TSD) that dictates how close to the outer cortex should the implant tip be residing to avoid post-surgical complications such as cut-out or joint penetration. In this study, the safety and the accuracy of the orthogonal fluoroscopic imaging were evaluated. Methods: A femoral head model was created and the risk zone was defined as a hemispherical shell of 5 mm thickness beneath the subchondral cortex, which should not be violated during screw insertion. The remaining hemisphere beneath the risk zone was designated as the safe zone. To assess the effect of head size, each simulation was conducted for 34, 47, and 60 mm diameter(Dfemur) femoral heads. The rate of safe zone violation was calculated for all possible screw endpoints with a TSD of at least 5 mm on fluoroscopic orthogonal views (TSDAP and TSDLat). Results: The minimum risk of joint penetration was achieved when the TSDAP/TSDLat ratio was 1. For Dfemur of 34 mm there was a risk of 91.7% of the safe zone violation when each TSDAP and TSDLat were 5 mm and 0% for 9 mm. For Dfemur of 47 mm, the risk was 92.2% for 5 mm and 0% for 11 mm. For Dfemur of 60 mm, the risk was 92.3% for 5 mm and 0% for 13 mm. Safety maps were constructed for all possible TSD combinations for 34, 47, and 60 mm femoral heads. Conclusions: Depending solely on the orthogonal fluoroscopic images is not a safe and accurate technique for assessing joint penetration risk during proximal femoral fixation due to the spherical geometry of the femoral head. The screw tip can lie completely outside of the femoral head even when it appears inside, in both orthogonal fluoroscopic views. Evidently, when using TSD, more stringent distance limits should be chosen, contrary to the recommended 5 mm limit. Our safety maps for TSD combinations may be used to check the security of the implantation. (C) 2020 Elsevier Ltd. All rights reserved.
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    In silico analysis of superelastic nitinol staples for trans-sternal closure
    (Elsevier, 2020) N/A; N/A; Department of Mechanical Engineering; Subaşı, Ömer; Torabnia, Shams; 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; 179391
    Background: Superelastic Nitinol staples, utilized routinely in foot surgeries, are proposed to be used for sternal closure application in this study. It is hypothesized that the shape memory induced superelasticity will allow multiple staples placed along the sternum to promote fast and safe recovery by maintaining constant clamping pressure at the sternotomy midline. Methods: Two different Nitinol staples of different alloying compositions, one representing the metal formed wire geometry and, the other, powder metallurgy manufactured rectangular geometry, are chosen from the literature. Austenite finish temperatures of both materials are confirmed to be appropriately below the body temperature for superelastic shape memory activation. The adopted finite element superelasticity model is first validated and, via design optimization of parametrized dimensions, the staple geometries for producing maximal clamping forces are identified. The performances of the optimized staples for full trans-sternal closure (seven staples for each) are then tested under lateral sternal loading in separate computational models. Results: The optimized metal formed staple exerts 70.2 N and the optimized powder metallurgy manufactured staple exerts 245 N clamping force, while keeping the maximum localized stresses under the yield threshold for 90 degrees leg bending. Testing the staple-sternum constructs under lateral sternal loading revealed that the former staple can be utilized for small-chested patients with lower expected physiological loading, while the latter staple can be used for high-risk patients, for which high magnitude valsalva maneuver is expected. Conclusion: Computational results prove that superelastic Nitinol staples are promising candidates as alternatives to routinely performed techniques for sternal closure.
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    A novel sensor using photo-interrupter for measuring static friction coefficient
    (Korean Soc Mechanical Engineers, 2020) N/A; N/A; N/A; Department of Mechanical Engineering; Hussain, Abbas; Subaşı, Ömer; Lazoğlu, İsmail; PhD Student; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; Manufacturing and Automation Research Center (MARC); N/A; N/A; 179391
    A force sensor design utilizing a photo-interrupter is presented for measuring the static coefficient of friction (COF). The measurement of ice friction on polymer surfaces, a process that requires detecting forces in the sub-Newton range, is chosen for the study. The photo-interrupter is coupled with a specially designed sensitive flexure, with structural parameters validated through finite element methods, to detect the small forces. The static properties of the sensor are characterized by calibration techniques. An accompanying rotary table is constructed to measure the COF of ice on polymethylmethacrylate (PMMA) and polyester specimens under refrigeration conditions. The experimental results indicate that the device can be utilized to predict the COF. The designed portable and miniature friction measurement setup can be a compact and cost-efficient alternative to bulky tribo-rheometer equipment.
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    A novel adjustable locking plate (ALP) for segmental bone fracture treatment
    (Elsevier Sci Ltd, 2019) N/A; N/A; Department of Mechanical Engineering; Subaşı, Ömer; Oral, Atacan; 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; 179391
    A novel Ti6Al4V adjustable locking plate (ALP) is designed to provide enhanced bone stability for segmental bone fractures and to allow precise positioning of disconnected segments. The design incorporates an adjustable rack and pinion mechanism to perform compression, distraction and segment transfer during plate fixation surgery. The aim of this study is to introduce the advantages of the added feature and computationally characterize the biomechanical performance of the proposed design. Structural strength of the novel plate is analyzed using numerical methods for 4-point bending and fatigue properties, following ASTM standards. An additional mechanical failure finite element test is also conducted on the rack and pinion to reveal how much torque can be safely applied to the mechanism by the surgeon. Simulation results predict that the new design is sufficiently strong to not fail under regular anatomical loading scenarios with close bending strength and fatigue life properties to clinically used locking compression plates. The novel ALP design is expected to be a good candidate for addressing problems regarding fixation of multi-fragmentary bone fractures.
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    Simplifying linearizability proofs with reduction and abstraction
    (Springer, 2010) Qadeer, Shaz; N/A; N/A; N/A; Department of Computer Engineering; Elmas, Tayfun; Sezgin, Ali; Subaşı, Ömer; Taşıran, Serdar; PhD Student; N/A; PhD Student; Faculty Member; Department of Computer Engineering; Graduate School of Sciences and Engineering; N/A; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; N/A; N/A
    The typical proof of linearizability establishes an abstraction map from the concurrent program to a sequential specification, and identifies the commit points of operations. If the concurrent program uses fine-grained concurrency and complex synchronization, constructing such a proof is difficult. We propose a sound proof system that significantly simplifies the reasoning about linearizability. Linearizability is proved by transforming an implementation into its specification within this proof system. The proof system combines reduction and abstraction, which increase the granularity of atomic actions, with variable introduction and hiding, which syntactically relate the representation of the implementation to that of the specification. We construct the abstraction map incrementally, and eliminate the need to reason about the location of commit points in the implementation. We have implemented our method in the QED verifier and demonstrated its effectiveness and practicality on several highly-concurrent examples from the literature.