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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
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Publication Metadata only Measurement and characteristic analysis of ris-assisted wireless communication channels in sub-6 ghz outdoor scenarios(IEEE, 2023) Lan, Jifeng; Sang, Jian; Zhou, Mingyong; Gao, Boning; Meng, Shengguo; Li, Xiao; Tang, Wankai; Jin, Shi; Cheng, Qiang; Cuit, Tie Jun; Department of Electrical and Electronics Engineering; Başar, Ertuğrul; Department of Electrical and Electronics Engineering; College of EngineeringReconfigurable intelligent surface (RIS)-empowered communication has recently drawn significant attention due to its superior capability in manipulating the wireless propagation environment. However, the channel modeling and measurement of RIS-assisted wireless communication systems in real environment has not been adequately studied. In this paper, we construct a channel measurement system using vector network analyzer (VNA) is used to investigate RIS-assisted wireless communication channel in outdoor scenarios at 2.6 GHz. New path loss (PL) models including angle domain information are proposed by refining the traditional close-in (CI) and floating-intercept (FI) models. In the proposed models, both influences of the distance from transmitter (TX) to RIS and the distance from receiver (RX) to RIS on the PL, are taken into account. In addition, the value of root mean square (RMS) delay spread of RIS-assisted wireless communication is found to be much smaller than that of the traditional non line-of-sight (NLOS) case, implying that RIS provides a virtual line-of-sight (LOS) link.Publication Metadata only Measurement-based characterization of physical layer security for ris-assisted wireless systems(IEEE, 2023) Kesir, Samed; Wikelek, Ibrahim; Pusane, Ali Emre; Gorcin, Ali; Department of Electrical and Electronics Engineering; Kayraklık, Sefa; Başar, Ertuğrul; Department of Electrical and Electronics Engineering; CoreLab; Graduate School of Sciences and Engineering; College of EngineeringThere have been recently many studies demonstrating that the performance of wireless communication systems can be significantly improved by a reconfigurable intelligent surface (RIS), which is an attractive technology due to its low power requirement and low complexity. This paper presents a measurement-based characterization of RISs for providing physical layer security, where the transmitter (Alice), the intended user (Bob), and the eavesdropper (Eve) are deployed in an indoor environment. Each user is equipped with a software-defined radio connected to a horn antenna. The phase shifts of reflecting elements are software controlled to collaboratively determine the amount of received signal power at the locations of Bob and Eve in such a way that the secrecy capacity is aimed to be maximized. An iterative method is utilized to configure a Greenerwave RIS prototype consisting of 76 passive reflecting elements. Computer simulation and measurement results demonstrate that an RIS can be an effective tool to significantly increase the secrecy capacity between Bob and Eve.Publication Metadata only Dimensional stability of 51CrV4 steel during bainitic phase transformation under tensile and compressive stresses(Elsevier, 2010) Lambers H.-G.; Maier H.J.; Department of Mechanical Engineering; Canadinç, Demircan; Faculty Member; Department of Mechanical Engineering; College of Engineering; 23433The effect of the prior austenitization treatment on the stress-strain response of a low alloy 51CrV4 steel in its supercooled austenitic state and its effect on the evolution of transformation plasticity strain during a subsequent isothermal bainitic transformation was investigated. One of the key findings is that the prior austenitization treatment strongly affects the evolution of transformation plasticity strains during the subsequent isothermal bainitic transformation under stress, such that higher transformation plasticity strains are present when the austenite grain size is increased. In addition, higher 0.2% offset yield strengths of the supercooled austenite are present following an incomplete austenitization treatment due to the existence of residual carbides. Overall, the current results clearly lay out the effect of the prior austenitization treatment on the stress-strain response of the supercooled austenite and the evolution of transformation plasticity during bainitic transformation.Publication Metadata only On the cyclic stability and fatigue performance of ultrafine-grained interstitial-free steel under mean stress(Trans Tech Publications Ltd, 2008) Niendorf, Thomas; Maier, Hans J.; Karaman, Ibrahim; Department of Mechanical Engineering; Canadinç, Demircan; Faculty Member; Department of Mechanical Engineering; College of Engineering; 23433This paper reports on the fatigue performance of an ultrafine-grained (UFG) interstitial-free (IF) steel deformed at various mean stress levels. The UFG microstructure was achieved using equal channel angular extrusion processing at room temperature (RT) and along an "efficient" route, giving way to the formation of high angle grain boundaries (HAGBs) with a high volume fraction. The current study not only confirms the previous finding that a high volume fraction of HAGBs promotes cyclic stability, but also inquires into the role of mean stress level on the cyclic stability. It is shown that the UFG IF steel exhibits a stable cyclic deformation response in the lowcycle fatigue regime within the medium applied mean stress range of -75 to 75 MPa. The corresponding fatigue lives can still be predicted with the Smith-Watson-Topper approach within this range. Furthermore, the present study demonstrates that the evolution of mean strains with cyclic deformation can be linked to the evolution of mean stresses in strain-controlled loading.Publication Metadata only Flow simulation and optimization of a left ventricular assist device(American Society of Mechanical Engineers (ASME), 2007) Sorguven, Esra; Ciblak, Namik; Okyar, A. Fethi; Akgun, Mehmet A.; Egrican, A. Nilufer; Safak, K. Koray; Ahn, Hojin; Kucukaksu, Suha; Department of Mechanical Engineering; Lazoğlu, İsmail; Faculty Member; Department of Mechanical Engineering; College of Engineering; 179391Artificial assist devices offer a promising treatment option for patients with congestive heart failure, especially when the patient is not eligible for heart transplantation. In order to develop a left ventricular assist device an interdisciplinary research, involving engineering and medical research teams, is conducted. The left ventricular assist device investigated in this study is the MicroMed DeBakey VAD [1], an axial blood pump that provides flow from the left ventricle to the aorta. The geometry of this baseline design is generated via parametric modeling. An optimization surface around the baseline design is formed by using the design of experiments method. Accordingly, eighty parameter sets and the corresponding CAD models are created. Flow through these pumps is simulated at the operation point. Flow data are evaluated to predict the pump performance, blood damage and bearing friction. An axial pump, closer to the optimum, is found that provides 8635 Pa pressure increase at a flow rate of 6 l/min and a rotational speed of 10000 rpm. Pressure head of the selected pump is 18% higher and blood damage is 4% less than the baseline design.Publication Metadata only Analog velocity feedback controller for vibration suppression and sound attenuation(American Society of Mechanical Engineers, 2011) Department of Mechanical Engineering; Başdoğan, İpek; Arıdoğan, Mustafa Uğur; Boz, Utku; Külah, Serkan; Faculty Member; PhD Student; PhD Student; Master Student; Department of Mechanical Engineering; College of Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; 179940; N/A; N/A; N/AIn this paper, an analog velocity feedback controller is considered for active vibration suppression of a thin plate for attenuation of sound levels in the frequency range of 0-100 Hz. The active control methods can be applied to interior cavity noise reduction, as encountered for instance in automotive applications. For that purpose, a simplified experimental vibro-acoustic cabin model was built in our laboratory and developed methodologies are demonstrated on the set-up. The set-up includes a rectangular box (1 × 1 × 2 m) which is separated with a flexible thin plate (1 × 1 × 0.001 m) to obtain two enclosed cavities: the passenger compartment (PC) and the engine compartment (EC). The vibration control is applied only on the flexible plate since the walls enclosing the cavities are made of more rigid material (wood filled concrete). By employing piezoelectric patch as actuator and laser doppler vibrometer as vibration sensor, an analog proportional velocity feedback controller is designed and built experimentally for suppressing the low-frequency modes of the flexible plate. In order to attenuate only lower-frequency structural modes of the thin panel, pre-filters are also included in analog circuit. The vibration of thin plate and sound in the passenger compartment is measured for controller-inactive and active cases while disturbing the thin plate via shaker. By measuring vibration and sound response, closed and open loop experimental frequency responses are obtained and presented. The aim of this experimental study is to investigate performance of active vibration control applications on acoustic attenuation as the first step towards robust structural acoustic control. © 2011 by ASME.Publication Metadata only Future mars mission demonstrationwith gamification and socioeconomictraits: nextgenerationworkforce development and self-knowledge management(American Institute of Aeronautics and Astronautics Inc, AIAA, 2015) N/A; N/A; Kara, Ozan; PhD Student; Graduate School of Sciences and Engineering; N/AThis research enhance proper gamification scenerios for future Mars missions. Scenarios include mars atmosphere and surface design, cubesat Mars orbiter, micro flying robot demonstration, in-situ research support, human health risk reduction, digital 3D printing and hands-on rover experiments. The scheduled Mars mission concepts consisting of gamification allow the first uncrewed orbital return with Orion around 2024. The forecasted crewed mission can be realized in early 2030. The next generation workforce development for Mars exploration is presented from 2014 IPMC Young Professional workshop “entering and growing into the space sector” group findings, 2014 OECD Space report and NASA APPEL studies. The workshop findings compare young professional development in academia, industry and government. In addition, findings are classified under student, K12 education, boss relations, sociological conditions and global workforce demand data. OECD report show total space economy is $256B US dollars in 2013. NASA APPEL and CKO has new knowledge map for NASA to unite people and systems in sustainable and effective way. The groundwork of the young professional development and impacts of gamification are comprehended by self-knowledge management and decision making. Finally, reflections of space missions such as Orion, Rosetta and New Horizons inspire public society and have different impacts in countries.Publication Metadata only Process modeling in composites manufacturing, second edition(CRC Press, 2010) Advani, Suresh G.; Department of Mechanical Engineering; Sözer, Murat; Faculty Member; Department of Mechanical Engineering; College of Engineering; 110357There is a wealth of literature on modeling and simulation of polymer composite manufacturing processes. However, existing books neglect to provide a systematic explanation of how to formulate and apply science-based models in polymer composite manufacturing processes. Process Modeling in Composites Manufacturing, Second Edition provides tangible methods to optimize this process - and it remains a proven, powerful introduction to the basic principles of fluid mechanics and heat transfer. Includes tools to develop an experience base to aid in modeling a composite manufacturing process Building on past developments, this new book updates the previous edition’s coverage of process physics and the state of modeling in the field. Exploring research derived from experience, intuition, and trial and error, the authors illustrate a state-of-the-art understanding of mass, momentum, and energy transfer during composites processing. They introduce computer-based solutions using MATLAB® code and flow simulation-based analysis, which complement closed-form solutions discussed in the book, to help readers understand the role of different material, geometric, and process parameters. This self-contained primer provides an introduction to modeling of composite manufacturing processes for anyone working in material science and engineering, industrial, mechanical, and chemical engineering. It introduces a scientific basis for manufacturing, using solved example problems which employ calculations provided in the book. End-of-chapter questions and problems and fill in the blanks sections reinforce the content in order to develop the experience base of the manufacturing, materials, and design engineer or scientists, as well as seniors and first-year graduate students.Publication Metadata only Small satellite architecture optimization: electric propulsion moon imaging mission(American Institute of Aeronautics and Astronautics Inc, AIAA, 2015) N/A; Department of Mechanical Engineering; Karabeyoğlu, Mustafa Arif; Kara, Ozan; Faculty Member; Master Student; Department of Mechanical Engineering; College of Engineering; Graduate School of Sciences and Engineering; 114595; N/AThis study underlies small satellite architecture optimization by using existing electric propulsion systems for the Moon missions. The estimated objective is panoramic imaging of the Moon accompanied with future in-situ applications. Edelbaum’s low thrust trajectory transfer with optimal control theory is used to calculate the required ΔV. During the journey, 1.5h eclipse duration effects the solar array design. The optimized xenon propellant density and pressure are 1350 kgm3 and 8.3 MPa within 300K. Two types of optimization process revealed based on hexagonal SC architecture. The iterative method with LEO departured ion thruster has 23 mN with minimum 213 kg total mass. Corresponding SC volume is 0.70 m3, propellant mass is 64 kg. This scenario cost $108.5M and takes 980 days. Same thruster level for GEO departure case takes 880 days with 58 kg xenon gas. The total cost reduces $2.5M. For HALL engine design, LEO departure case needs 0.8 m3, 247 kg SC including 82 kg xenon. 77 mN thrust operates 208 days towards the Moon that ends up with $121M total cost. If the SC to be launched from GEO, flight time reduces 45 days by consuming 65 kg propellant. Total SC mass, volume and power values are 230 kg, 0.71 m3 and 1351W which cost $115M. Results are compared with previous Moon or electric propulsion missions such as SMART-1, LADEE, Clementine and Hayabusa. For future applications of small satellites, innovative concepts are envisioned for in-space, Earth-independent exploration and space education. 2015, American Institute of Aeronautics and Astronautics Inc, AIAA. .Publication Metadata only Equivalent circuit modeling and experimental validation of a piezoelectric energy harvester attached on a thin plate with AC-DC conversion(International Conference on Adaptive Structures and Technologies, 2015) Erturk, Alper; Department of Mechanical Engineering; Başdoğan, İpek; Aghakhani, Amirreza; Faculty Member; PhD Student; Department of Mechanical Engineering; College of Engineering; 179940; N/APlate-like structures are widely used in numerous automotive, marine and aerospace applications. Power output investigations of patch-based piezoelectric energy harvesters integrated to these structures require accurate models for energy harvesting performance evaluation and optimization. The equivalent circuit modeling of the cantilever-based vibration energy harvesters for estimation of electrical response has been proposed in the recent years for predicting the electrical outputs of the harvesters. However, equivalent circuit modeling of piezoelectric patch harvesters integrated to plate-like structures including nonlinear circuits has not been studied in the existing literature. Considering these needs, a multi-mode equivalent circuit model of a piezoelectric energy harvester integrated to a thin plate is developed and verified experimentally in the present study. Equivalent circuit parameters are obtained from analytical distributed-parameter model of the plate and harvester which governs the electromechanical coupling behavior of piezoelectric patch and vibration of the host plate. The multi-mode circuit representation of the harvester is built via electronic circuit simulation software SPICE. Using the SPICE software, electrical outputs of the piezoelectric energy harvester are computed for the standard AC input-AC output and AC input-DC output problems. In the AC-AC case, only a resistive load is connected to the harvester, whereas for the AC-DC case, a full-wave rectifier and a smoothing capacitor are connected to the circuit before the resistive load to convert the AC voltage to stable DC voltage. In the AC-AC problem, voltage FRFs are calculated for various resistive loads and validated by the published analytical closed-form solution. In the AC-DC problem, simulation results of the DC voltage and power outputs are computed for a wide range of load resistance values and validated with comparisons against the analytical single-mode representation of the harvester. Finally, experimental measurements of DC voltage FRFs are conducted for a case study and verified against the numerical model.