Mechanical Engineering / Makina Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4129
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Conference Object A Comparative Study of Attention-Augmented YOLO Architectures for Defect Detection in Fused Deposition Modelling(Institute of Electrical and Electronics Engineers Inc., 2025) Cezayirli, H.; Tetik, H.; Dede, M.I.C.; Phone, W.L.; Alkan, B.Additive manufacturing (AM), particularly fused deposition modelling (FDM), facilitates the fabrication of complex geometries with increasing flexibility and efficiency. Ensuring consistent print quality in FDM processes necessitates the development of accurate defect detection mechanisms. Attention-augmented YOLO (You Only Look Once) models have emerged as a promising solution for addressing this challenge. In this study, we systematically benchmark and evaluate the performance of YOLO architectures enhanced with attention mechanisms within the context of FDM 3D printing applications. The models were trained and evaluated using representative defect datasets. The attention-augmented models demonstrate improved detection performance. © 2025 IEEE.Conference Object Redundancy resolution options for the twin-it-romans robotic hybrid manufacturing system(Springer Science and Business Media B.V., 2025) Gündüz, G.M.; Dede, Mehmet İsmet Can; Kiper, Gökhan; Schmitz, M.; Corves, B.The Twinnig Iztech in Robotics Manufacturing System (TWIN-IT-ROMANS) project funded by EU Horizon -Widera-2023-Access-02-01 aims to develop a hybrid manufacturing system that can perform additive and subtractive manufacturing processes and inline quality control using a robotic system. The system will incorporate a 6-degree-of-freedom robot arm and a positioner with 2-degree-of-freedom, which will operate synchronously. This manipulation system is to be designed for performing different manufacturing operations with different degrees-of-freedom requirements. In order to reveal alternative trajectory planning scenarios for this system, this paper presents an initial review of redundancy resolution approaches for kinematically redundant robotic manipulators. First, the four main approaches for redundancy resolution techniques are introduced. Then main studies on energy minimization and stiffness maximization for kinematically redundant robotic manipulators are reviewed. Similar or new approaches are planned to be generated and implemented for the redundant system for hybrid manufacturing. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2025.Conference Object Kinematic Design of a Novel Finger Exoskeleton Mechanism for Rehabilitation Exercises(Springer international Publishing Ag, 2024) Kiper, Gokhan; Inanc, EmirhanThe paper presents the kinematic design of a novel low-cost two degree-of-freedom finger exoskeleton mechanism to be used for rehabilitation exercises for post-stroke or injured patients. The first degree-of freedom is for the flexion/extension of metacarpophalangeal joint and is achieved via a planar 4-bar loop. The second degree-of-freedom is for the simultaneous flexion/extension of distal/proximal interphalangeal joints and is achieved via an over-constrained double-spherical 6-bar linkage, where 3 of the links are the phalanges of the finger and 2 of the joints are finger joints themselves. So, the number of extra links are less compared to other designs in the literature. The motion of an index finger is recorded via image processing. The four-bar mechanism part is designed for optimum transmission angle characteristics. The formulation and application of the kinematic synthesis of the 6-bar linkage is presented. The design is verified via a prototype.Conference Object Citation - Scopus: 3A Continuously Variable Transmission System Designed for Human–robot Interfaces(Springer, 2021) Mobedi, Emir; Dede, Mehmet İsmet CanWithin a predefined limit, continuously variable transmission (CVT) systems can continuously vary the power transmission ratio. The transmission in CVTs is achieved via friction, belt or gear systems. If CVT designs can incorporate backdrivability, independent output position and impedance variation, shock absorbtion, and low mass and inertia, they can be employed in human–robot interfaces. Among various types of CVT designs, the two-cone drive CVT designs have a major drawback since the output torque and position cannot be changed independent of each other. The friction wheel used in this design does not have a holonomic motion capability and causes this inconvenience. In order to overcome this problem, a sphere is used in this work for the CVT design as the transmission element. In addition, it is stated in the literature that common CVT drive systems do not have the capability to be used in cyclic bidirectional motion. In the presented CVT design, a second sphere is added to the system with two springs from the lower part of the cones for pretension in order to solve the bidirectional transmission problem. In this paper, the working principle and conceptual design details of the novel two-cone CVT drive are presented. Experimental results showed that the novel CVT has the capacity to transmit bidirectional power with some accuracy. © 2021, Springer Nature Singapore Pte Ltd.Conference Object Determination of Interfacial Heat Transfer Coefficient for a Mixed Convection Heat Transfer in a Vertical Channel Filled With Uniformly Heated Blocks(Begell House Inc., 2015) Çelik, Hasan; Mobedi, Moghtada; Manca,O.; Buonomo,B.The interfacial convective heat transfer coefficient of a periodic porous medium under mixed convection heat transfer is determined computationally by using volume averaging method. The porous medium consists of square blocks in inline arrangement. The continuity, momentum and energy equations are solved in dimensionless form for a representative elementary volume of porous medium and the velocity and temperature fields for different values of Richardson and Reynolds numbers are obtained. Based on the obtained results, the interfacial convective heat transfer coefficient is calculated by using volume average method. The temperature of the solid phase is considered uniform and different than the inlet temperature. A detailed discussion on the effect of the governing dimensionless parameters (i.e. Reynolds, Richardson numbers, and porosity) on the local and average interfacial Nusselt number is done. It is concluded that the local interfacial convective heat transfer coefficient increases with Reynolds number, however the rate of increase depends on Richardson number and porosity. The study is performed for two values of porosity of 0.51 and 0.94. © 2021, Begell House Inc. All rights reserved.Conference Object A Numerical Study on the Determination of the Effects of Pore To Throat Size Ratio on the Thermal Dispersion in Porous Media(Begell House, 2014) Özgümüş, Türküler; Mobedi, Moghtada; Özkol, ÜnverDirect pore-level numerical simulations are widely used to estimate macroscopic properties of fluid flow and heat transfer in porous media. Thermal dispersion is one of the most important macroscopic transport parameters for analyzing convective heat transfer in a porous medium. It should be known in order to predict the macroscopic temperature distribution. In the present study, a microscopic scale analysis is performed for a porous medium with periodic structure. A representative elementary volume is chosen from an infinite medium consists of rectangular rods in inline arrangement. The continuity and momentum equations are solved to obtain flow field and the energy equations for fluid and solid phases are solved to obtain microscopic temperature distributions in two phases. There are velocity and temperature deviations between macroscopic and microscopic local values. Volume averaging method is applied to the computed deviations and thermal dispersion conductivity of porous media is determined. The aim of this study is to analyze the effects of pore to throat size ratio on the longitudinal and transverse thermal dispersion in porous media. The study is performed for representative elementary volumes with different pore to throat size ratios and Reynolds numbers from 1 to 100. The study is performed for high porosity porous media (ε = 0.7 and 0.91). It is shown that the porosity and pore to throat size ratio have more influence on the transverse rather than longitudinal thermal dispersion. © 2014, Begell House Inc. All rights reserved.Book Part Citation - WoS: 1Citation - Scopus: 1A Historical Review of Polyhedral Linkages(Springer, 2024) Kiper, GökhanPolyhedral linkages are linkages that resemble polyhedral shapes at different configurations. This paper summarizes the necessary geometrical fundamentals of polyhedral geometry and presents a historical and critical review of the polyhedral linkage designs available in the literature. Basic definitions of polyhedral geometry and operations are needed to comprehend and design polyhedral linkages. First, early works on polyhedral linkages are presented, where flexible polyhedra with rigid faces and flexible edges are issued. The final part is reserved to conformal polyhedral linkages, which go through shape transformations while plane, dihedral and solid angles are preserved. Conformal polyhedral linkages are examined in four categories: 1) Jitterbug-like linkages with screwing polygonal links connected to each other with dihedral angle preserving links, 2) polyhedral linkages with planar kinematic chains in radial motion planes, 3) polyhedral linkages with planar kinematic chains on faces, that are connected to each other with dihedral angle preserving links, and 4) other conformal polyhedral linkages. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024.Article Citation - WoS: 2Citation - Scopus: 3Design and Manufacturing of a Hip Joint Motion Simulator With a Novel Modular Design Approach(Springer, 2024) Torabnia, S.; Mihçin, D.Ş.; Lazoglu, I.The study is aimed to develop a hip joint wear simulator using a modular design approach to help experimentally monitor and control critical wear parameters to validate in-silico wear models. The proper control and application of wear parameters such as the range of motion, and the applied force values while estimating the lost material due to wear are essential for thorough analysis of wear phenomena for artificial joints. The simulator's dynamics were first modeled, then dynamic loading data was used to calculate the forces, which were further used for topology optimization to reduce the forces acting on each joint. The reduction of the link weights, connected to the actuators, intends to improve the quality of motion transferred to the femoral head. The modular design approach enables topology-optimized geometry, associated gravitational and dynamic forces, resulting in a cost-effective, energy-efficient product. Moreover, this design allows integration of the subject specific data by allowing different boundary conditions following the requirements of industry 5.0. Overall, the in-vitro motion stimulations of the hip-joint prosthesis and the modular design approach used in the study might help improve the accuracy and the effectiveness of wear simulations, which could lead into the development of better and longer-lasting joint prostheses for all. The subject-specific and society-based daily life data implemented as boundary conditions enable inclusion of the personalized effects. Next, with the results of the simulator, CEN Workshop Agreement (CWA) application is intended to cover the personalized effects for previously excluded populations, providing solution to inclusive design for all. © 2023, The Author(s), under exclusive licence to Springer-Verlag France SAS, part of Springer Nature.Article Citation - WoS: 9Citation - Scopus: 11Experimental Investigation of Spray Characteristics of Ethyl Esters in a Constant Volume Chamber(Springer, 2024) Ulu, A.; Yildiz, G.; Özkol, Ü.; Rodriguez, A.D.Abstract: Biodiesels are mainly produced via the utilization of methanol in transesterification, which is the widespread biodiesel production process. The majority of this methanol is currently obtained from fossil resources, i.e. coal and natural gas. However, in contrast with methanol, biomass-based ethanol can also be used to produce biodiesels; this could allow the production line to become fully renewable. This study aimed to investigate the spray characteristics of various ethyl ester type biodiesels derived from sunflower and corn oils in comparison to methyl esters based on the same feedstocks and reference petroleum-based diesel. Spray penetration length (SPL) and spray cone angle (SCA) were experimentally evaluated in a constant volume chamber allowing optical access, under chamber pressures of 0, 5, 10 and 15 bar and injection pressures of 600 and 800 bar. Sauter mean diameter (SMD) values were estimated by using an analytical correlation. Consequently, ethyl esters performed longer SPL (2.8–20%) and narrower SCA (5.1–19%) than diesel under ambient pressures of 5 and 10 bar. Although the SMD values of ethyl esters were 48% higher than diesel on average, their macroscopic spray characteristics were very similar to those of diesel under 15 bar chamber pressure. Moreover, ethyl esters were found to be very similar to methyl esters in terms of spray characteristics. The differences in SPL, SCA and SMD values for both types of biodiesels were lower than 4%. When considering the uncertainty (± 0.84%) and repeatability (±5%) ratios, the difference between the spray characteristics of methyl and ethyl esters was not major. Graphical abstract: [Figure not available: see fulltext.] © 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.Conference Object Energy and Exergy Analysis of a Roof-Mounted Photovoltaic System in Gebze-Turkey(Springer, 2024) Khalejan, Seyed Hamed Pour Rahmati; Cankurt, Tolga; Dede, Mehmet İsmet CanThis study investigates the electrical and thermal exergy, power conversion efficiency and exergy efficiency of a roof-mounted photovoltaic (PV) system considering environmental parameters such as solar irradiation, ambient temperature and wind speed over a year. The values of solar exergy and solar potential are obtained by taking into account the solar insolation. Experimental and theoretical results indicate that wind speed and surface temperature have significant effects on the thermal exergy and exergy efficiency of solar PV systems. The mean solar potential in the region was found to be 93%. In addition, the electrical exergy was varied from 9145 W to 40460 W and the thermal exergy of PV systems was varied from 1639 W to 6193 W. While the range of PV power conversion efficiency varies from 6.15% to 11.56% over a year, the range of exergy efficiency varies from 5.31% to 9.78%. © 2024, The Author(s), under exclusive license to Springer Nature Switzerland AG.