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Publication Metadata only A deformation-based approach to tuning of magnetic micromechanical resonators(2018) Yalçınkaya, Arda D.; Department of Mechanical Engineering; N/A; Department of Mechanical Engineering; Biçer, Mahmut; Esfahani, Mohammad Nasr; Alaca, Burhanettin Erdem; Researcher; PhD Student; Faculty Member; Department of Mechanical Engineering; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 115108Resonance frequency tuning in magnetic micromechanical resonators remains a primary field of study for frequency reference applications. The use of magnetic micromechanical resonators for innovative timing, oscillator and sensing applications necessitates a platform for the precise control of the resonance frequency. The present work addresses a deformation based technique for tuning the resonance frequency of nickel micromechanical resonators. Frequency response is measured through magnetic actuation and optical readout. The tuning approach is based on a combination of flexural deformation and uniaxial strain. The bending deformation is achieved by using a DC current through the microbeam. This magnetomotive mechanism reduces the resonance frequency by about 13% for a maximum DC current of 80 mA. A substrate bending method is used for applying uniaxial strain to increase the resonance frequency by about 8%. A bidirectional frequency modulation is thus demonstrated by utilizing both deformation techniques. The interpretation of results is carried out by finite element analysis and electromechanical analogy in an equivalent circuit. Using deformation techniques, this study provides a rigorous approach to control the resonance frequency of magnetic micromechanical resonators.Publication Metadata only A novel approach for monitoring plastic flow localization during in-situ sem testing of small-scale samples(Springer, 2018) Niendorf, Thomas; Weidner, Anja; N/A; Department of Mechanical Engineering; Mirzajanzadeh, Morad; Canadinç, Demircan; PhD Student; Faculty Member; Department of Mechanical Engineering; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; College of Engineering; N/A; 23433A novel method is proposed for monitoring the plastic flow localization during in-situ scanning electron microscopy (SEM) testing of small-scale AISI 316 L stainless steel. Stress-strain behavior of the material was obtained using a hybrid numerical-experimental (HNE) approach. By repeatedly illustrating each pair of sequentially taken SEM surface images throughout the deformation history in alternating order in form of a video, location of the material points which are not moving during the deformation can be detected. At the initial stages of deformation these points are located on the geometrical symmetry line of the test sample, however; when uniform straining limit of the material is reached, the locations of the stationary material points reveal the plastic localization regions. The current results clearly prove the feasibility of the presented method in monitoring primary plastic localization events through in-situ SEM tensile testing.Publication Open Access A novel haptic feature set for the classification of interactive motor behaviors in collaborative object transfer(Institute of Electrical and Electronics Engineers (IEEE), 2021) Küçükyılmaz, Ayşe; Department of Mechanical Engineering; Başdoğan, Çağatay; Şirintuna, Doğanay; Al-Saadi, Zaid Rassim Mohammed; Faculty Member; Department of Mechanical Engineering; College of Engineering; Graduate School of Sciences and Engineering; 125489; N/A; N/AHaptics provides a natural and intuitive channel of communication during the interaction of two humans in complex physical tasks, such as joint object transportation. However, despite the utmost importance of touch in physical interactions, the use of haptics is under-represented when developing intelligent systems. This article explores the prominence of haptic data to extract information about underlying interaction patterns within physical human-human interaction (pHHI). We work on a joint object transportation scenario involving two human partners, and show that haptic features, based on force/torque information, suffice to identify human interactive behavior patterns. We categorize the interaction into four discrete behavior classes. These classes describe whether the partners work in harmony or face conflicts while jointly transporting an object through translational or rotational movements. In an experimental study, we collect data from 12 human dyads and verify the salience of haptic features by achieving a correct classification rate over 91% using a Random Forest classifier.Publication Metadata only A novel method for hemodynamic analysis of penile erection(Springernature, 2022) Yıldırım, Canberk; Ertürk, Hakan; Şerefoğlu, Ege Can; Department of Mechanical Engineering; N/A; Pekkan, Kerem; Deniz, Sinan; Faculty Member; Doctor; Department of Mechanical Engineering; College of Engineering; N/A; N/A; Koc University Hospital; 161845; N/AMeasurement of blood flow velocity through the cavernosal arteries via penile color Doppler ultrasound (PDUS) is the most common objective method for the assessment of erectile function. However, in some clinical cases, this method needs to be augmented via the invasive intracavernosal pressure (ICP) measurement, which is arguably a more direct index for erectile function. The aim of this study is to develop a lumped parameter model (LPM) of the penile circulation mechanism integrated to a pulsatile, patient-specific, bi-ventricular circulation system to estimate ICP values non-invasively. PDUS data obtained from four random patients with erectile dysfunction are used to develop patient-specific LPMs. Cardiac output is estimated from the body surface area. Systemic pressure is obtained by a sphygmomanometer. Through the appropriate parameter set determined by optimization, patient-specific ICP values are predicted with only using PDUS data and validated by pre- and post-papaverine injection cavernosometry measurements. The developed model predicts the ICP with an average error value of 3 mmHg for both phases. Penile size change during erection is predicted with a similar to 15% error, according to the clinical size measurements. The developed mathematical model has the potential to be used as an effective non-invasive tool in erectile function evaluation, expanding the existing clinical decision parameters significantly.Publication Metadata only A review of active vibration and noise suppression of plate-like structures with piezoelectric transducers(Sage Publications Ltd, 2015) N/A; Department of Mechanical Engineering; Arıdoğan, Mustafa Uğur; Başdoğan, İpek; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 179940Structural vibrations are the major causes of noise problems, passenger discomforts, and mechanical failures in aerospace, Automotive, and marine systems, which are mainly composed of lightweight and flexible plate-like structures. in order to reduce structural vibrations and noise radiations of lightweight structures, passive and active treatments have been used and investigated over the last three decades. Our aim of this article is to review current state-of-the-art of active vibration and noise suppression systems for plate and plate-like structures with various kinds of boundary conditions. the reviewed articles use numerical methods and experimental tools to study different aspects of controller architectures. in particular, the focus is placed on the active vibration and noise control systems utilizing piezoelectric patches as sensors and actuators since their popularity in vibration-based applications has increased significantly during the last two decades. We first classify the controllers according to their architectures, then compare their performance in vibration and noise attenuation, and finally provide suggestions for further progress. the categorization of the information regarding the controller strategies and sensor/actuator configurations for different host structures can be used by the controller designers as a starting point for their specific configuration.Publication Metadata only A review of surface haptics: enabling tactile effects on touch surfaces(Institute of Electrical and Electronics Engineers (IEEE) Computer Society, 2020) Giraud, Frederic; Levesque, Vincent; Choi, Seungmoon; Department of Mechanical Engineering; Başdoğan, Çağatay; Faculty Member; Department of Mechanical Engineering; College of Engineering; 125489In this article, we review the current technology underlying surface haptics that converts passive touch surfaces to active ones (machine haptics), our perception of tactile stimuli displayed through active touch surfaces (human haptics), their potential applications (human-machine interaction), and finally, the challenges ahead of us in making them available through commercial systems. This article primarily covers the tactile interactions of human fingers or hands with surface-haptics displays by focusing on the three most popular actuation methods: vibrotactile, electrostatic, and ultrasonic.Publication Metadata only Adaptive human force scaling via admittance control for physical human-robot interaction(IEEE Computer Soc, 2021) Aydın, Yusuf; N/A; Department of Mechanical Engineering; Al Qaysi, Yahya Mohey Hamad; Başdoğan, Çağatay; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 125489The goal of this article is to design an admittance controller for a robot to adaptively change its contribution to a collaborative manipulation task executed with a human partner to improve the task performance. This has been achieved by adaptive scaling of human force based on her/his movement intention while paying attention to the requirements of different task phases. In our approach, movement intentions of human are estimated from measured human force and velocity of manipulated object, and converted to a quantitative value using a fuzzy logic scheme. This value is then utilized as a variable gain in an admittance controller to adaptively adjust the contribution of robot to the task without changing the admittance time constant. We demonstrate the benefits of the proposed approach by a pHRI experiment utilizing Fitts' reaching movement task. The results of the experiment show that there is a) an optimum admittance time constant maximizing the human force amplification and b) a desirable admittance gain profile which leads to a more effective co-manipulation in terms of overall task performance.Publication Metadata only Adsorption, folding, and packing of an amphiphilic peptide at the air/water interface(amer Chemical Soc, 2012) 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; 109820Peptide oligomers play an essential role as model compounds for identifying key motifs in protein structure formation and protein aggregation. Here, we present our results, based on extensive molecular dynamics simulations, on adsorption, folding, and packing within a surface monolayer of an amphiphilic peptide at the air/water interface. Experimental results suggest that these molecules spontaneously form ordered monolayers at the interface, Adopting a beta-hairpin-like structure within the surface layer. Our results reveal that the beta-hairpin structure can be observed both in bulk and at the air/water interface. However, the presence of an interface leads to ideal partitioning of the hydrophobic and hydrophilic residues, and therefore reduces the conformational space for the molecule and increases the stability of the hairpin structure. We obtained the adsorption free energy of a single beta-hairpin at the air/water interface, and analyzed the enthalpic and entropic contributions. the adsorption process is favored by two main factors: (1) Free-energy reduction due to desolvation of the hydrophobic side chains of the peptide and release of the water molecules which form a cage around these hydrophobic groups in bulk water. (2) Reduction of the total air/water contact area at the interface upon adsorption of the peptide amphiphile. By performing mutations on the original molecule, we demonstrated the relative role of key design features of the peptide. Finally, by analyzing the potential of mean force among two peptides at the interface, we investigated possible packing mechanisms for these molecules within the surface monolayer.Publication Metadata only An investigation of the electromechanical coupling and broadband shunt damping in composite plates with integrated piezo-patches(Sage Publications Ltd, 2019) N/A; N/A; Department of Mechanical Engineering; Gözüm, Mehmet Murat; Aghakhani, Amirreza; Başdoğan, İpek; PhD Student; PhD Student; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 179940The popularity of laminated composite plate-like structures is increasing in various engineering applications. Piezoelectric patches with electrical circuit elements can be integrated into these structures for shunt damping applications. for analyzing the shunt damping performance of these systems, precise modeling tools are required, which consider the two-way electromechanical coupling between the piezo-patches and the host plate. This study aims to identify the system parameters which affect the electromechanical coupling coefficient, A metric for measuring the effectiveness of mechanical-to-electrical energy conversion. for that purpose, A thorough investigation is performed to determine the critical system parameters and their combined effects on the electromechanical coupling coefficient of laminated composite plates with surface-bonded piezo-patches. First, the first four natural frequencies of the electromechanical system are obtained using the Rayleigh-Ritz method for various patch sizes. then, the electromechanical coupling coefficient variations for a different set of system parameters are presented. Later, to demonstrate the applicability of the developed methodology for a broader frequency range, four independently shunted piezo-pairs are attached to the plate. the contours of electromechanical coupling coefficient values with respect to ply angle and patch-pair size are presented for the first four modes. Finally, the vibration amplitudes are successfully reduced for these modes using the optimal system parameters.Publication Open Access An optoelectromechanical tactile sensor for detection of breast lumps(Institute of Electrical and Electronics Engineers (IEEE), 2013) Yıldız, Mustafa Zahid; Güçlü, Burak; Department of Mechanical Engineering; Başdoğan, Çağatay; Ayyıldız, Mehmet; Faculty Member; Master Student; Department of Mechanical Engineering; College of Engineering; 125489; N/AWe developed a compact tactile imaging (TI) system to guide the clinician or the self-user for noninvasive detection of breast tumors. Our system measures the force distribution based on the difference in stiffness between a palpated object and an abnormality within. The average force resolution, force range, and the spatial resolution of the device are 0.02 N, 0-4 N, and 2.8 mm, respectively. To evaluate the performance of the proposed TI system, compression experiments were performed to measure the sensitivity and specificity of the system in detecting tumor-like inclusions embedded in tissue-like cylindrical silicon samples. Based on the experiments performed with 11 inclusions, having two different sizes and two different stiffnesses located at three different depths, our TI system showed an average sensitivity of 90.8 +/- 8.1 percent and an average specificity of 89.8 +/- 12.7 percent. Finally, manual palpation experiments were performed with 12 human subjects on the same silicon samples and the results were compared to that of the TI system. The performance of the TI system was significantly better than that of the human subjects in detecting deep inclusions while the human subjects performed slightly better in detecting shallow inclusions close to the contact surface.