Makine Mühendisliği Bölümü Yayın Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/263

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Citation - WoS: 43
Citation - Scopus: 54
A normally closed electrostatic parylene microvalve for micro total analysis systems
(Elsevier Science Sa, 2012) Yildirim, Ender; Yıldırım, Ender; Arikan, M. A. Sahir; Kulah, Haluk; 120121; Makine Mühendisliği
This paper presents an electrostatically actuated, normally closed microvalve for parylene microfluidics. The proposed valve structure isolates the fluid from the electric field, and hence results in relatively low actuation potentials (<60 V) irrespective of the working fluid. Hereby, the microvalve solves electrolysis or electrode shielding problems observed in electrostatic actuation in micro total analysis systems. To investigate leakage properties, microvalves were tested under pressurized flow with de-ionized (DI) water. No detectable leakage ratio was observed up to 20 kPa inlet pressure, due to the unique semicircular valve seat design. It was shown that the valve seat could be reconfigured to enable sealing at various pressure levels for different applications. (C) 2012 Elsevier B.V. All rights reserved.
Citation - WoS: 3
Citation - Scopus: 4
Comprehensive elastic analysis of functionally graded variable thickness pressurized disk
(Wiley-v C H verlag Gmbh, 2023) Farukoglu, oemer Can; Korkut, Ihsan; Motameni, Ali
This study analytically examines internally pressurized power-law functionally graded variable thickness disk. The power-law consideration is applied to the Young's modulus and the Poisson's ratio of the graded material as well as the radial thickness profile variation of the disk. Under this scheme, the solution yields to different Bessel functions including the first, second, and modified types. Stress and displacement fields are investigated at the elastic limits by operating with these functions. The limits are calculated with the well-known von Mises criteria. Following the analytical modeling, numerical examples are built. Therein the examples, some noteworthy nuances have been achieved. It has been observed that unlike the usual prediction in the literature, constant Poisson's ratio, the effect of variable Poisson's ratio on stresses and displacements is still evident, although not as much as variable Young's modulus and disk geometry. We suggest assigning it as a variable in similar applications to be more precise. Additionally, according to the von Mises criterion, yielding may begin at the inner radius, the outer radius, or both at the same time. Parameters in the simultaneous flow initiation state are critical. These parameters allow the disk to reach the highest elastic limit pressure.
Citation - Scopus: 9
Effect of constitutive material model on the finite element simulation of shear localization onset
(Elsevier B.V., 2020) Yılmaz, O.D.; Nadimi Bavil Oliaei, S.
One of the most challenging problems in the field of machining is to determine the onset of shear localization. The consequences of the emergence of shear localized chips are fluctuations in the machining forces, tool wear, deterioration of the surface quality and out-of-tolerance machined components. Several constitutive material models are developed for the simulation of shear localization during machining, especially for Ti6Al4V. However, the accuracy and capability of the proposed models for the prediction of shear localization onset have not been investigated yet. In this study, the effect of different constitutive material models in the prediction of shear localization onset has been investigated. Different material models are studied including the Johnson-Cook (J-C) material model with Cockcroft-Latham damage model, J-C material model with a J-C damage model, models based on modified J-C material models (MJ-C) with strain softening terms, and material model with power-law type strain hardening and strain rate sensitivity, with polynomial thermal softening and polynomial temperature-dependent damage. The results of the finite element models are verified using orthogonal cutting experiments in terms of chip morphology and machining forces. Metallography techniques are used along with SEM observations to elucidate the distinction between continuous and shear localized chips. The results of this study indicate that three models are capable of predicting shear localization onset. However, when compared to the experiments, where a critical cutting speed of 2.8 m/min is obtained for shear localization onset, the results revealed that the model proposed by Sima and Ozel (2016) which is a model based on MJ-C model with temperature-dependent overarching modifier and temperature-dependent material model parameters is more accurate for the prediction of shear localization onset during machining Ti6Al4V. This model is shown to reveal a good prediction for the machining forces as well. © 2020 Elsevier B.V.
Citation - WoS: 43
Exploring the relationship between software process adaptive capability and organizational performance
(Ieee Computer Soc, 2015) Clarke, Paul; Yılmaz, Murat; O'Connor, Rory V.; Leavy, Brian; Yilmaz, Murat; Yazılım Mühendisliği
Software development is a complex socio-technical activity, with the result that software development organisations need to establish and maintain robust software development processes. While much debate exists regarding the effectiveness of various software development approaches, no single approach is perfectly suited to all settings and no setting is unchanging. The capability to adapt the software process is therefore essential to sustaining an optimal software process. We designed an exploratory study to concurrently examine software process adaptive capability and organisational performance in 15 software development organisations, finding that companies with greater software process adaptive capability are shown to also experience greater business success. While our exploratory study of the complex relationship between these phenomena is limited in some respects, the findings indicate that software process adaptive capability may be worthy of further integration into software process engineering techniques. Software process adaptive capability may be an important organisational strength when deriving competitive advantage, and those responsible for the creation and evolution of software process models and methodologies may want to focus some of their future efforts in this area.
Citation - WoS: 6
Citation - Scopus: 10
Implementation and characterization of an absorption filter for on-chip fluorescent imaging
(Elsevier Science Sa, 2017) Yildirim, Ender; Yıldırım, Ender; Arpali, Caglar; Arpali, Serap Altay; 31835; 20809; 51304; Makine Mühendisliği
Here we present fabrication and characterization of an absorption filter with superior roll-on properties and precisely tunable cut-off wavelengths for fluorescent imaging applications in lab-on-a-chip systems. The filters were fabricated by spinning dye doped photopolymer (Orasol Yellow in Norland Optical Adhesive 60) on glass substrates. The fabrication technique allowed us to precisely tune the cut-off wavelength of the filters. We showed that filters with different cut-off in the range of 386 nm-504 nm could be obtained simply by controlling the settling time before spinning. The filters exhibited a steep roll-on from stopband to passband at the cut-off. Transmission in the stopband was observed to be maximum 3% while it was almost constant at 100% in the passband within the range of 220 nm-620 nm. On-chip use of the filters was also demonstrated for imaging particular fluorescent beads. (C) 2016 Elsevier B.V. All rights reserved.
Citation - WoS: 16
Citation - Scopus: 19
Investigation of surface integrity in laser-assisted turning of AISI 4340 hardened steel: Finite element simulation with experimental verification
(Elsevier Sci Ltd, 2022) Khatir, Farzad Ahmadi; Akar, Samet; Sadeghi, Mohammad Hossein; Akar, Samet; 315516; Makine Mühendisliği
This study investigates the laser-assisted turning (LAT) of AISI 4340 hardened steel (similar to 52 HRC). Despite the various advantages of this process for machining hard materials, the issues related to the machined surface integrity remain the most important challenge. The laser heating used in this process substantially affects the surface integrity characteristics of the workpiece and its mechanical properties. Therefore, it is important to understand, predict, and optimize the workpiece's heat effects at various regions. Due to the complexity of the process, experimental investigations alone cannot reveal thorough information of various phenomena involved. Therefore, a reliable finite element model has been developed to predict the effect of various process input parameters on the metallurgical changes of the machined workpieces. Since general-purpose finite element codes cannot predict the phenomena of interest, three user-defined subroutines have been developed to capture surface integrity parameters such as heat-affected zone, hardness variations of the machined surface, and white layer formation. The developed FE model consists of three parts: mechanical model, thermal model, and coupled thermo-mechanical model. The results of the FE models are verified with experimental data, and a good agreement has been observed. The effect of various process parameters on the surface integrity characteristics of the workpiece has been studied in detail. It has been observed that the laser scanning speed, laser power, and undeformed chip thickness have the most significant influence on the metallurgical effects on the workpiece, respectively.
Citation - WoS: 44
Citation - Scopus: 51
Numerical investigation on the performance of a small scale solar chimney power plant for different geometrical parameters
(Elsevier Sci Ltd, 2020) Yapici, Ekin Ozgirgin; Ayli, Ece; Nsaif, Osama; 31329; 265836
In recent decades, demand for energy has been significantly increased, and considering environmental impacts and the degrading nature of fossil fuels, clean and emission-free renewable energy production has attracted a great deal of attention. One of the most promising renewable energy sources is solar energy due to low cost and low harmful emissions, and from the 1980s, one of the most beneficial applications of solar energy is the utilization of solar chimney power plants (SCPP). A SCPP is a simple and reliable system that consists of three main components; a solar collector, a chimney (tower) and a turbine to utilize electrical energy. Recently, by the advancement in computer technology, the use of CFD methodology for studying SCPP has become an extensive, robust and powerful technique. In light of the above, in this study, numerical simulations of a SCPP through three-dimensional axisymmetric modeling is performed. A numerical model is created using CFD software, and the results are verified with an experimental study from the literature. After ensuring good agreement with the experiments, chimney's and collector's geometric parameters effects and different configurations effects on SCPP performance, simultaneously and additively is investigated. The study introduces an insight to the performance enhancement methods and finding the best configuration of a SCPP model, which will be the basis of a detailed prototyping process. Based on the numerical results, the best configuration of the SCPP has been found as the diverging chimney which enhances the generated power. The results of the study showed that the chimney height and collector radius increase has a positive effect on the power output and efficiency of the system, but when construction and material costs are also considered, each has an optimal value. The maximum impact on the performance is found to be by the chimney tower radius and the collector height and inclination are found to have optimum values considering performance. According to the obtained results, the best performance for the SCPP was obtained with 3.5 m chimney height, 30 cm tower diameter, 400 cm of collector diameter with 6 cm height and zero inclination angle. By the correct selection of the dominant performance parameter which can be done by correctly interpreting the results of this study, "the best" design of a SCPP real scale prototype considering maximum power requirement can be done. (C) 2020 Elsevier Ltd. All rights reserved.
Citation - WoS: 22
Citation - Scopus: 21
Phaseguide assisted liquid lamination for magnetic particle-based assays
(Royal Soc Chemistry, 2014) Phurimsak, Chayakom; Yıldırım, Ender; Yildirim, Ender; Tarn, Mark D.; Trietsch, Sebastiaan J.; Hankemeier, Thomas; Pamme, Nicole; Vulto, Paul; 31835; Makine Mühendisliği
We have developed a magnetic particle-based assay platform in which functionalised magnetic particles are transferred sequentially through laminated volumes of reagents and washing buffers. Lamination of aqueous liquids is achieved via the use of phaseguide technology; microstructures that control the advancing air-liquid interface of solutions as they enter a microfluidic chamber. This allows manual filling of the device, eliminating the need for external pumping systems, and preparation of the system requires only a few minutes. Here, we apply the platform to two on-chip strategies: (i) a one-step streptavidin-biotin binding assay, and (ii) a two-step C-reactive protein immunoassay. With these, we demonstrate how condensing multiple reaction and washing processes into a single step significantly reduces procedural times, with both assay procedures requiring less than 8 seconds.
Citation - WoS: 26
Citation - Scopus: 30
Phaseguides as tunable passive microvalves for liquid routing in complex microfluidic networks
(Royal Soc Chemistry, 2014) Yildirim, Ender; Yıldırım, Ender; Trietsch, Sebastiaan J.; Joore, Jos; van den Berg, Albert; Hankemeier, Thomas; Vulto, Paul; 31835; Makine Mühendisliği
A microfluidic passive valving platform is introduced that has full control over the stability of each valve. The concept is based on phaseguides, which are small ridges at the bottom of a channel acting as pinning barriers. It is shown that the angle between the phaseguide and the channel sidewall is a measure of the stability of the phaseguide. The relationship between the phaseguide-wall angle and the stability is characterized numerically, analytically and experimentally. Liquid routing is enabled by using multiple phaseguide with different stability values. This is demonstrated by filling complex chamber matrices. As an ultimate demonstration of control, a 400-chamber network is used as a pixel array. It is the first time that differential stability is demonstrated in the realm of passive valving. It ultimately enables microfluidic devices for massive data generation in a low-cost disposable format.

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