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Publication Metadata only “O/F shift” in hybrid rockets(American Institute of Aeronautics and Astronautics, 2014) Toson, Elena; Evans, Brian; Department of Mechanical Engineering; Karabeyoğlu, Mustafa Arif; Faculty Member; Department of Mechanical Engineering; College of Engineering; 114595For most hybrid rocket systems, oxidizer to fuel ratio (O/F) changes over time due to 1) natural growth of the fuel port diameter and 2) oxidizer flow rate variations, if throttling is employed. This phenomenon, which is referred to as “O/F shift”, leads to a reduction in motor performance. Note that liquid or solid rocket motors are not subject to temporal O/F variations, which is wrongfully considered as one of the most critical disadvantages of hybrid rockets. In this paper, the effect of “O/F shift” is quantified for hybrid rocket motors. Analytical formulas for the temporal O/F variation and the overall c* efficiency drop associated with the variation has been derived for single circular port motors. It has been shown that for a typical motor, c* efficiency drop due to O/F variation is well below 0.2%, a value which is too small to be measured in an actual motor test. It is also shown that for a wagon wheel type multiport configuration (with triangular ports), efficiency drop is significantly worse than the single circular port case. Even for the multiport systems, the shift does not have a controlling effect on the overall efficiency of the motor. A number of strategies have been outlined to control the adverse effects of O/F variation in a hybrid rocket. For a single circular port design with limited throttling, no mitigation is required. For systems with deep throttling requirements, aft oxidizer injection seems like a viable strategy to retain a high level of overall efficiency.Publication Metadata only 3D bioprinted glioma models(Iop Publishing Ltd, 2022) N/A; N/A; N/A; N/A; N/A; N/A; N/A; Department of Mechanical Engineering; Yığcı, Defne; Sarabi, Misagh Rezapour; Üstün, Merve; Atçeken, Nazente; Sokullu, Emel; Önder, Tuğba Bağcı; Taşoğlu, Savaş; Undergraduate Student; PhD Student; PhD Student; Researcher; Faculty Member; Faculty Member; Faculty Member; Department of Mechanical Engineering; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); School of Medicine; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; N/A; School of Medicine; School of Medicine; College of Engineering; N/A; N/A; N/A; N/A; 163024; 184359; 291971Glioma is one of the most malignant types of cancer and most gliomas remain incurable. One of the hallmarks of glioma is its invasiveness. Furthermore, glioma cells tend to readily detach from the primary tumor and travel through the brain tissue, making complete tumor resection impossible in many cases. To expand the knowledge regarding the invasive behavior of glioma, evaluate drug resistance, and recapitulate the tumor microenvironment, various modeling strategies were proposed in the last decade, including three-dimensional (3D) biomimetic scaffold-free cultures, organ-on-chip microfluidics chips, and 3D bioprinting platforms, which allow for the investigation on patient-specific treatments. The emerging method of 3D bioprinting technology has introduced a time- and cost-efficient approach to create in vitro models that possess the structural and functional characteristics of human organs and tissues by spatially positioning cells and bioink. Here, we review emerging 3D bioprinted models developed for recapitulating the brain environment and glioma tumors, with the purpose of probing glioma cell invasion and gliomagenesis and discuss the potential use of 4D printing and machine learning applications in glioma modelling.Publication Metadata only 3D surface topography analysis in 5-axis ball-end milling(Elsevier, 2017) N/A; Department of Mechanical Engineering; Khavidaki, Sayed Ehsan Layegh; Lazoğlu, İsmail; PHD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 179391This article presents a new analytical model to predict the topography and roughness of the machined surface in 5-axis ball-end milling operation for the first time. The model is able to predict the surface topography and profile roughness parameters such as 3D average roughness (Sa) and 3D root mean square roughness (Sq) by considering the process parameters such as the feedrate, number of flutes, step over and depth of cut as well as the effects of eccentricity and tool runout in 5-axis ball-end milling. This model allows to simulate the effects of the lead and tilt angles on the machined surface quality in the virtual environment prior to the costly 5-axis machining operations. The effectiveness of the introduced surface topography prediction model is validated experimentally by conducting 5-axis ball-end milling tests in various cutting conditions. (C) 2017 Published by Elsevier Ltd on behalf of CIRP.Publication Metadata only 3D-printed micrometer-scale wireless magnetic cilia with metachronal programmability(American Association for the Advancement of Science, 2023) Zhang, Shuaizhong; Hu, Xinghao; Li, Meng; Bozüyük, Uğur; Zhang, Rongjing; Suadiye, Eylül; Han, Jie; Wang, Fan; Onck, Patrick; Department of Mechanical Engineering; Sitti, Metin; Faculty Member; Department of Mechanical Engineering; College of Engineering; 297104Biological cilia play essential roles in self-propulsion, food capture, and cell transportation by performing coordinated metachronal motions. Experimental studies to emulate the biological cilia metachronal coordination are challenging at the micrometer length scale because of current limitations in fabrication methods and materials. We report on the creation of wirelessly actuated magnetic artificial cilia with biocompatibility and metachronal programmability at the micrometer length scale. Each cilium is fabricated by direct laser printing a silk fibroin hydrogel beam affixed to a hard magnetic FePt Janus microparticle. The 3D-printed cilia show stable actuation performance, high temperature resistance, and high mechanical endurance. Programmable metachronal coordination can be achieved by programming the orientation of the identically magnetized FePt Janus microparticles, which enables the generation of versatile microfluidic patterns. Our platform offers an unprecedented solution to create bioinspired microcilia for programmable microfluidic systems, biomedical engineering, and biocompatible implants.Publication Metadata only 3D-printed micrometer-scale wireless magnetic cilia with metachronal programmability(Amer Assoc Advancement Science, 2023) Zhang, Shuaizhong; Hu, Xinghao; Li, Meng; Bozuyuk, Ugur; Zhang, Rongjing; Suadiye, Eylul; Han, Jie; Wang, Fan; Onck, Patrick; Department of Mechanical Engineering; Sitti, Metin; Department of Mechanical Engineering; College of Engineering; School of MedicineBiological cilia play essential roles in self-propulsion, food capture, and cell transportation by performing coor-dinated metachronal motions. Experimental studies to emulate the biological cilia metachronal coordination are challenging at the micrometer length scale because of current limitations in fabrication methods and ma-terials. We report on the creation of wirelessly actuated magnetic artificial cilia with biocompatibility and meta-chronal programmability at the micrometer length scale. Each cilium is fabricated by direct laser printing a silk fibroin hydrogel beam affixed to a hard magnetic FePt Janus microparticle. The 3D-printed cilia show stable actuation performance, high temperature resistance, and high mechanical endurance. Programmable meta-chronal coordination can be achieved by programming the orientation of the identically magnetized FePt Janus microparticles, which enables the generation of versatile microfluidic patterns. Our platform offers an unprecedented solution to create bioinspired microcilia for programmable microfluidic systems, biomedical en-gineering, and biocompatible implants.Publication Metadata only A bioinspired stretchable membrane-based compliance sensor(Natl Acad Sciences, 2020) Matsuhisa, Naoji; You, Insang; Ruth, Sarah Rachel Arussy; Niu, Simiao; Foudeh, Amir; Tok, Jeffrey B. -H.; Chen, Xiaodong; Bao, Zhenan; Department of Mechanical Engineering; Beker, Levent; Faculty Member; Department of Mechanical Engineering; College of Engineering; 308798Compliance sensation is a unique feature of the human skin that electronic devices could not mimic via compact and thin form-factor devices. Due to the complex nature of the sensing mechanism, up to now, only high-precision or bulky handheld devices have been used to measure compliance of materials. This also prevents the development of electronic skin that is fully capable of mimicking human skin. Here, we developed a thin sensor that consists of a strain sensor coupled to a pressure sensor and is capable of identifying compliance of touched materials. The sensor can be easily integrated into robotic systems due to its small form factor. Results showed that the sensor is capable of classifying compliance of materials with high sensitivity allowing materials with various compliance to be identified. We integrated the sensor to a robotic finger to demonstrate the capability of the sensor for robotics. Further, the arrayed sensor configuration allows a compliance mapping which can enable humanlike sensations to robotic systems when grasping objects composed of multiple materials of varying compliance. These highly tunable sensors enable robotic systems to handle more advanced and complicated tasks such as classifying touched materials.Publication Metadata only A CAM-based path generation method for rapid prototyping applications(Springer London Ltd, 2011) N/A; Department of Mechanical Engineering; Lazoğlu, İsmail; N/A; Faculty Member; Department of Mechanical Engineering; Manufacturing and Automation Research Center (MARC); N/A; College of Engineering; N/A; 179391A wide range of rapid prototyping (RP) methods are available commercially. Even though the hardware and production materials of these RP methods differ, their production techniques are built on the same idea: layer-by-layer material additive manufacturing. Whatever the material is used, it is deposited, vulcanized, or melted by following a pre-determined path, and each layer is stowed on the previous one to create the 3D model which is designed by using a computer-aided design program. The path which is followed while creating the model is very crucial. In this paper, a novel idea for path generation for RP processes is introduced. This new method is based on computer numerical controlled milling operation. Although the RP process and the milling process are completely opposite of each other since one of them is an additive and the other one is a subtractive method, the paths which are followed for these operations are very similar and based on the same idea: The progress goes on layer by layer. In this novel method, cutter location source files are used to create paths for RP processes. Examples of the prototypes produced by using this new method are also presented in the paper.Publication Metadata only A challenge for peptide coarse graining: transferability of fragment-based models(Wiley-V C H Verlag Gmbh, 2011) Villa, Alessandra; Peter, Christine; N/A; Department of Mechanical Engineering; Engin, Özge; Sayar, Mehmet; Master Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 109820Peptides are highly promising building blocks for design and development of novel materials with potential application areas ranging from drug design to biotechnology. The necessity to understand the structural and thermodynamic properties of these complex materials has led to a dramatic increase in the development of computational techniques geared specifically towards peptide-based systems. Both all-atom (AA) and coarse-grained (CG) simulations of such materials have become extremely important, where the latter is an indispensable tool for reaching the time and length scales relevant to the experiments. Here, we review different approaches and discuss the challenges in the development of CG models for peptides. In particular, we concentrate on the transferability of fragment-based CG models. We analyze the transferability of a solvent-free CG model developed to model hydrophobic phenylalanine dipeptides (FF) in water. Here, we employ the same CG strategy-with non-bonded potentials based on peptide fragments-to two other hydrophobic dipeptides, valine-phenylalanine (VF) and isoleucine-phenylalanine (IF). In line with the previously developed model, the dipeptides are described by seven beads and the potentials developed for FF (bonded and non-bonded) are directly applied to describe the phenylalanine and backbone atoms, while new potentials are developed to account for the valine and isoleucine sidechains. By comparing AA and CG intra and intermolecular samplings, we show the ability of the CG model to reproduce the conformational behavior and thermodynamic association properties of the corresponding atomistic systems.Publication Metadata only A comparison of solid model and three-orthogonal dexelfield methods for cutter-workpiece engagement calculations in three- and five-axis virtual milling(Springer London Ltd, 2015) Erdim, H.; N/A; Department of Mechanical Engineering; Boz, Yaman; Lazoğlu, İsmail; Master Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 179391Virtual simulation of three- and five-axis milling processes has started to become more important in recent years in various industries such as aerospace, die-mold, and biomedical industries in order to improve productivity. In order to obtain desired surface quality and productivity, process parameters such as feedrate, spindle speed, and axial and radial depths of cut have to be selected appropriately by using an accurate process model of milling. Accurate process modeling requires instantaneous calculation of cutter-workpiece engagement (CWE) geometry. Cutter-workpiece engagement basically maps the cutting flute entry/exit locations as a function of height, and it is one of the most important requirements for prediction of cutting forces. The CWE calculation is a challenging and hard problem when the geometry of the workpiece is changing arbitrarily in the case of five-axis milling. In this study, two different methods of obtaining CWE maps for three- and five-axis flat and ball-end milling are developed. The first method is a discrete model which uses three-orthogonal dexelfield, and the second method is a solid modeler-based model using Parasolid boundary representation kernel. Both CWE calculation methods are compared in terms of speed, accuracy, and performance for three- and five-axis milling of ball-end and flat-end mill tools. It is shown that the solid modeling-based method is faster and more accurate. The proposed methods are experimentally and computationally verified in simulating milling of complex three-axis and five-axis examples as well as predicting cutting forces.Publication Metadata only A comprehensive evaluation of parameters governing the cyclic stability of ultrafine-grained FCC alloys(Elsevier Science Sa, 2011) Niendorf, T.; Maier, H. J.; Department of Mechanical Engineering; Canadinç, Demircan; Faculty Member; Department of Mechanical Engineering; College of Engineering; 23433The current paper presents results of a thorough experimental program undertaken to shed light onto the mechanisms dictating the cyclic stability in ultrafine-grained (UFG) alloys with a face-centered cubic structure. Cyclic deformation responses of several copper- and aluminum-based UFG alloys were investigated and the corresponding microstructural evolutions were analyzed with various microscopy techniques. The important finding is that a larger volume fraction of high-angle grain boundaries and solid solution hardening significantly improve the fatigue performance of these alloys at elevated temperatures and high strain rates, and under large applied strain amplitudes.