Mechanical Engineering / Makina Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4129
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Article Citation - WoS: 8Citation - Scopus: 14Partial Gravity Compensation of a Surgical Robot(SAGE Publications Inc., 2021) Maaroof, Omar Waleed Najm; Saeed, Saad Zaghlul; Dede, Mehmet İsmet CanSurgical robots are safety-critical devices that require multiple domains of safety features. This article focuses on the passive gravity compensation design optimization of a surgical robot. The limits of this optimization are related with the safety features including minimization of the total moving mass/inertia and compactness of the design. The particle swarm optimization method is used as a novel approach for the optimization of a parallel remote-center-of-motion mechanism. A compact design is achieved by partially balancing the mechanism, which also decreases the torque requirements from the actuators. © The Author(s) 2021.Article Citation - WoS: 13Citation - Scopus: 17Design of Dimensionally Stable Composites Using Efficient Global Optimization Method(SAGE Publications Inc., 2019) Aydın, Levent; Aydın, Olgun; Artem, Hatice Seçil; Mert, AliDimensionally stable material design is an important issue for space structures such as space laser communication systems, telescopes, and satellites. Suitably designed composite materials for this purpose can meet the functional and structural requirements. In this paper, it is aimed to design the dimensionally stable laminated composites by using efficient global optimization method. For this purpose, the composite plate optimization problems have been solved for high stiffness and low coefficients of thermal and moisture expansion. Some of the results based on efficient global optimization solution have been verified by genetic algorithm, simulated annealing, and generalized pattern search solutions from the previous studies. The proposed optimization algorithm is also validated experimentally. After completing the design and optimization process, failure analysis of the optimized composites has been performed based on Tsai-Hill, Tsai-Wu, Hoffman, and Hashin-Rotem criteria.Article Citation - WoS: 2Mr-Guided Focused Ultrasound Application for Moving Target Tumor Ablation in Abdominal Area: Coil Selection(SAGE Publications Inc., 2021) Mihçin, Şenay; Gagliardo, Cesare; Toia, Patrizia; Dennison, Andrew; Strehlow, Jan; Melzer, AndreasBackground Magnetic Resonance Imaging (MRI)-guided Focused Ultrasound Surgery (MRgFUS) is a non-invasive thermal ablation method utilizing high-intensity focused ultrasound (HI-FU) energy for tissue ablation under MRI with real-time thermal mapping. Ablating to a dynamic target as in the liver is very challenging, requiring approval. A novel quality-assured liver tumor ablation system has been proposed for clinics. The paper reports the evaluation of conventional and new MR-receiving coils. Purpose To evaluate the suitability of MR coils as part of the MRgFUS treatment system for liver, while simulating breathing motion in pre-clinical settings. Material and Methods The novel software communicates with the MR scanner and the transducer. To monitor the temperature via proton resonance frequency (PRF) methodology echo planar imaging (EPI) sequence was used while the algorithms of static, static and dynamic tracking were tested with sonications of 100 W for 30 s on tissue-mimicking phantoms. Different coil sets were used to assess the performance of the system for fitness for dynamic thermometry. Finally, in vivo experiments were performed over a porcine model. Results Single-loop four-channel Duoflex and Gem coils provided adequate signal-to-noise ratio and contrast with consistent thermal readings. Body array coils showed severe loss of signal in dynamic cases since the integration of tracking algorithm causes low efficiency. Conclusion Body array coils are unsuitable for MRgFUS of the liver due to signal loss. The dedicated coil set with a single loop around the FUS transducer combined with four-channel arrays might be the best option for liver treatment using dynamic MRgFUS applications.Article Citation - WoS: 23Citation - Scopus: 26Experimental and Statistical Analysis of Carbon Fiber/Epoxy Composites Interleaved With Nylon 6,6 Nonwoven Fabric Interlayers(SAGE Publications Inc., 2020) Beylergil, Bertan; Tanoğlu, Metin; Aktaş, EnginThermoplastic interleaving is a promising technique to improve delamination resistance of laminated composites. In this study, plain-weave carbon fiber/epoxy composites were interleaved with nylon 6,6 nonwoven fabrics with an areal weight density of 17 gsm. The carbon fiber/epoxy composite laminates with/without nylon 6,6 nonwoven fabric interlayers were manufactured by VARTM technique. Double cantilever beam fracture toughness tests were carried out on the prepared composite test specimens in accordance with ASTM 5528 standard. The experimental test data were statistically analyzed by two-parameter Weibull distribution. The results showed that the initiation and propagation fracture toughness Mode-I fracture toughness of carbon fiber/epoxy composites could be improved by about 34 and 156% (corresponding to a reliability level of 0.50) with the incorporation of nylon 6,6 interlayers in the interlaminar region, respectively. The results also revealed that the percent increase in the propagation fracture toughness value was 67 and 41% at reliability levels of 0.90 and 0.95, respectively.Article Citation - WoS: 6Citation - Scopus: 7Aerodynamic Optimization of Through-Flow Design Model of a High By-Pass Transonic Aero-Engine Fan Using Genetic Algorithm(SAGE Publications Inc., 2018) Kor, Orçun; Acarer, Sercan; Özkol, ÜnverThis study deals with aerodynamic optimization of a high by-pass transonic aero-engine fan module in a through-flow inverse design model at cruise condition. To the authors’ best knowledge, although the literature contains through-flow optimization of the simplified cases of compressors and turbines, an optimization study targeting the more elaborate case of combined transonic fan and splitter through-flow model is not considered in the literature. Such a through-flow optimization of a transonic fan, combined with bypass and core streams separated by an aerodynamically shaped flow splitter, possesses significant challenges to any optimizer, due to highly non-linear nature of the problem and the high number of constraints, including the fulfillment of the targeted bypass ratio. It is the aim of this study to consider this previously untouched area in detail and therefore present a more sophisticated and accurate optimization environment for actual bypass fan systems. An in-house optimization code using genetic algorithm is coupled with a previously developed in-house through-flow solver which is using a streamline curvature technique and a set of in-house calibrated empirical models for incidence, deviation, loss and blockage. As the through-flow models are the backbone of turbomachinery design, and great majority of design decisions are taken in this phase, such a study is assessed to result in significant guidelines to the gas turbine community.Article Citation - WoS: 9Citation - Scopus: 10Experimental Studies of Autoignition and Soot Formation of Diesel Surrogate Fuels(SAGE Publications Inc., 2013) Diez, Alvaro; Crookes, Roy J.; Lovas, TereseComputational simulation has undergone vast development for internal-combustion engine research as a time- and costsaving tool. Yet combustion simulation for conventional hydrocarbon petroleum fuels faces difficult challenges since such fuels have very complex compositions, consisting of many different molecular species, for which data are sparse. The use of surrogate fuels for combustion simulation could provide a solution to this problem. In this investigation, n-heptane and mixtures of n-heptane and toluene were studied within a broad range of potential surrogate diesel fuels, and the ignition delay and soot formation trends were compared with those of diesel fuel. Ignition delays show good agreement with those for diesel fuel and it was also possible to replicate partially the soot formation behaviour for certain engine conditions. Further investigation is needed to find a surrogate fuel that closely matches over the range of operating conditions of a diesel engine.Article Citation - WoS: 7Citation - Scopus: 8An Extension of the Streamline Curvature Through-Flow Design Method for Bypass Fans of Turbofan Engines(SAGE Publications Inc., 2017) Acarer, Sercan; Özkol, ÜnverThe two-dimensional through-flow modeling of turbomachinery is still one of the most powerful tools available to the turbomachinery industry for aerodynamic design, analysis, and post-processing of test data due to its robustness and speed. Although variety of aspects of such a modeling approach are discussed in the publicly available literature for compressors and turbines, not much emphasis is placed on combined modeling of the fan and the downstream splitter of turbofan engines. The current article addresses this void by presenting a streamline curvature through-flow methodology that is suitable for inverse design for such a problem. A new split-flow method for the streamline solver, alternative to the publicly available analysis-oriented method, is implemented and initially compared with two-dimensional axisymmetric computational fluid dynamics on two representative geometries for high and low bypass ratios. The empirical models for incidence, deviation, loss, and end-wall blockage are compiled from the literature and calibrated against two test cases: experimental data of NASA two-stage fan and three-dimensional computational fluid dynamics of a custom-designed transonic fan stage. Finally, experimental validation against GE-NASA bypass fan case is accomplished to validate the complete methodology. The proposed method is a simple extension of streamline curvature method and can be applied to existing compressor methodologies with minimum numerical effortArticle Citation - WoS: 8Citation - Scopus: 9The Increased Compression Strength of an Epoxy Resin With the Addition of Heat-Treated Natural Nano-Structured Diatom Frustules(SAGE Publications Inc., 2017) Zeren, Doğuş; Güden, MustafaNatural diatom frustules composing nanometer size silica particles were heat-treated at temperatures between 600 and 1200℃ for 2 h and used as filler/reinforcing agent (15 wt%) in an epoxy resin. The opal structure of as-received natural diatom frustules was transformed into cristobalite after the heat-treatment above 900℃. The epoxy resin test samples reinforced with heat-treated and as-received frustules and neat epoxy test samples were compression tested at the quasi-static strain rate of 7 × 10−3 s−1. The results showed that the inclusion of the frustules heat-treated at 1000℃ increased the compressive yield strength of the resin by 50%, while the addition of the diatom frustules heat-treated above and below 1000℃ and the as-received frustules increased the strength by ∼25% and 16%, respectively. The heat treatment above 1000℃ decreased the surface area of the frustules from 8.23 m2 g−1 to 3.46 m2 g−1. The cristobalite grains of the frustules heat-treated at 1000℃ was smaller than 100 nm, while the grain size increased to ∼500 nm at 1200℃. The increased compressive stresses of the resin at the specific heat treatment temperature (1000℃) were ascribed to nano size crystalline cristobalite grains. The relatively lower compressive stresses of the epoxy resin filled with frustules heat-treated above 1000℃ were attributed to the micro-cracking of the frustules that might be resulted from higher density of the cristobalite than that of the opal and accompanying reduction of the surface area and the surface pore sizes that might impair the resin-frustule interlocking and intrusion.Article Citation - WoS: 14Citation - Scopus: 16Microstructure and Mechanical Properties of A357/Sic Nanocomposites Fabricated by Ultrasonic Cavitation-Based Dispersion of Ball-Milled Nanoparticles(SAGE Publications Inc., 2017) Kandemir, SinanIn this work, A357/0.5 wt.% SiC nanocomposites were fabricated with a combination of ultrasonic processing and a nanoparticle feeding mechanism that involves the introduction of a closed end aluminium tube filled with the ball-milled SiC nanoparticles (20-30 nm) and aluminium powders (<75 μm) into the melt for complete deagglomeration and uniform dispersion of nanoparticles through the matrix. The microstructural and mechanical properties of the fabricated nanocomposites were investigated. The microstructural studies conducted with optical and advanced electron microscopes indicate that relatively effective deagglomeration and uniform dispersion of SiC nanoparticles into the molten alloy were achieved. The hardness and tensile properties of the nanocomposites were notably improved compared to those of the ultrasonically processed A357 alloy without reinforcement, showing the strengthening potency of nanoparticles and the good bonding obtained at the particle-reinforcement interface.Article Citation - WoS: 6Citation - Scopus: 7Experimental and Numerical Investigation of the Effect of Interlayer on the Damage Formation in a Ceramic/Composite Armor at a Low Projectile Velocity(SAGE Publications Inc., 2017) Taşdemirci, Alper; Tunusoğlu, GözdeThe damage formation in a multilayered armor system without and with an interlayer (rubber, Teflon, and aluminum foam) between the front face ceramic layer and the composite backing plate were investigated experimentally and numerically. The projectile impact tests were performed in a low-velocity projectile impact test system and the numerical studies were implemented using the nonlinear finite element code LS-DYNA. The results of numerical simulations showed that the stress wave transmission to the composite backing plate decreased significantly in Teflon and foam interlayer armor configurations. Similar to without interlayer configuration, the rubber interlayer configuration led to the passage of relatively high stress waves to the composite backing plate. This was mainly attributed to the increased rubber interlayer impedance during the impact event. The numerical results of reduced stress wave transmission to the backing plate and the increased damage formation in the ceramic front face layer with the use of Teflon and foam interlayer was further confirmed experimentally.