Makine Mühendisliği Bölümü

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Citation - WoS: 8
Citation - Scopus: 7
Experimental Investigation Into the Effect of Magnetorheological Fluid Damper on Vibration and Chatter in Straight Turning Process
(Elsevier Sci Ltd, 2023) Nasab, Vahid Hasan; Akar, Samet; Batako, Andre; Emami, Mohsen
Magneto-Rheological (MR) dampers have received a great deal of attention in recent years due to the potential of offering semi-active control. MR dampers have been successfully applied in the vibration control of several machining processes. However, the effect of the material of the damper's fluid chamber on its magnetic prop-erties has not been studied much. In this study, an MR damper has been designed to control the chatter vibration of the straight turning operation. The magnetic properties of the MR damper are simulated in the FEM software COMSOL Multiphysics with two types of steel AISI 410 and AISI 1018, and the material with the best perfor-mance for constructing the fluid chamber is determined. Then, the MR damper with an assembly to hold the cutting tool was fabricated and experimentally tested during straight turning operation and its effect on the tool vibration, and work surface roughness was analyzed. From the result, it was observed that the MR damper reduced tool vibration and chatter effectively. The results obtained in this research confirm that the application of the MR damper in the straight-turning process can either suppress the chatter or greatly reduce the frequency amplitude of the chatter. The reduction of the tool's acceleration amplitude with the MR damper was more intense in the condition of chatter suppression and reached up to 89.42 %. Moreover, the MR damper reduced the roughness of the machining surface. This reduction was higher in cases where the chatter was suppressed and it was observed up to 29 %.
Citation - WoS: 18
Citation - Scopus: 23
Investigation of Surface Integrity in Laser-Assisted Turning of Aisi 4340 Hardened Steel: Finite Element Simulation With Experimental Verification
(Elsevier Sci Ltd, 2022) Sadeghi, Mohammad Hossein; Akar, Samet; Khatir, Farzad Ahmadi
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: 25
Citation - Scopus: 29
Investigation of Surface Integrity in the Laser-Assisted Turning of Aisi 4340 Hardened Steel
(Elsevier Sci Ltd, 2021) Sadeghi, Mohammad Hossein; Akar, Samet; Khatir, Farzad Ahmadi
The use of laser-assisted turning (LAT) can improve different aspects of the machinability of high hardness/strength materials. The heat applied in this process reduces the strength of the material and upon a proper selection of laser heat source and machining process parameters, a significant improvement in the machining process can be achieved. This research studies the effect of machining and laser heat source parameters on the surface integrity of the LAT process of AISI 4340 hardened steel with a hardness of 560 HV using Response Surface Methodology (RSM). The effect of machining process parameters (feed rate, depth of cut and cutting speed) and laser power on the surface integrity characteristics of the machined surfaces (white layer thickness, microhardness, surface roughness, and surface chemical composition) are investigated. A detailed finite element simulation of the process has been performed to better understand the physics of the process and to interpret the experimental results. Laser power and feed rate are shown to be the most significant parameters affecting the surface integrity of the machined surfaces. It has been shown that a proper selection of machining and laser heat source parameters makes it possible to minimize the adverse effect of laser heating in the LAT process. This can pave the way for the widespread application of the LAT process by eliminating one of the most important obstacles of this process by controlling the laser heat diffusion into the workpiece.
Citation - WoS: 11
Citation - Scopus: 11
A Novel Cfd-Ann Approach for Plunger Valve Optimization: Cost-Effective Performance Enhancement
(Elsevier Sci Ltd, 2024) Kaak, Abdul Rahman Sabra; Celebiog, Kutay; Bozkus, Zafer; Ulucak, Oguzhan; Ayli, Ece
This paper introduces a novel computational fluid dynamics-artificial neural network (CFD-ANN) approach that has been devised to enhance the efficiency of plunger valves. The primary emphasis of this research is to achieve an optimal equilibrium between hydraulic flow and geometric configuration. This study is a novel contribution to the field as it explores the flow dynamics of plunger valves using Computational Fluid Dynamics (CFD) and proposes a unique methodology by incorporating Machine Learning (ML) for performance forecasting. An artificial neural network (ANN) architecture was developed using a thorough comprehension of flow physics and the impact of geometric parameters acquired through computational fluid dynamics (CFD). Using optimization, the primary aspects of the Artificial Neural Network (ANN), including the learning algorithm and the number of hidden layers, have been modified. This refinement has resulted in the development of an architecture exhibiting a remarkably high R2 value of 0.987. This architectural design was employed to optimize the plunger valve. By utilizing Artificial Neural Networks (ANN), a comprehensive analysis comprising 1000 distinct configurations was effectively performed, resulting in a significant reduction in time expenditure compared to relying on Computational Fluid Dynamics (CFD). The result was a refined arrangement that achieved maximum head loss, subsequently verified using computational fluid dynamics (CFD) simulations, resulting in a minimal discrepancy of 2.66%. The efficacy of artificial neural networks (ANN) becomes apparent due to their notable cost-efficiency, along with their capacity to produce outcomes that are arduous and expensive to get through conventional optimization research utilizing computational fluid dynamics (CFD).
Citation - WoS: 49
Citation - Scopus: 54
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
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: 11
Citation - Scopus: 14
Numerical Study on Effects of Computational Domain Length on Flow Field in Standing Wave Thermoacoustic Couple
(Elsevier Sci Ltd, 2019) Turkoglu, Hasmet; Mergen, Suhan; Yildirim, Ender
For the analysis of thermoacoustic (TA) devices, computational methods are commonly used. In the computational studies found in the literature, the flow domain has been modelled differently by different researchers. A common approach in modelling the flow domain is to truncate the computational domain around the stack, instead of modelling the whole resonator to save computational time. However, where to truncate the domain is not clear. In this study, we have investigated how the simulation results are affected by the computational domain length (I-d) when the truncated domain approach is used. For this purpose, a standing wave TA couple which undergoes a refrigeration cycle was considered. The stack plate thickness was assumed to be zero and the simulations were performed for six different dimensionless domain length (I-d/lambda) varying between 0.029 and 0.180. Frequency and Mach number were taken as 100 Hz and 0.01, respectively, and kept constant for all the cases considered. The mean pressure and the pressure amplitude were taken as 10 kPa and 170 Pa, respectively (Drive ratio of 1.7%). Helium was considered as the working fluid. To assess the accuracy of the simulation results, the pressure distributions across the domain were compared with that of the standing wave. In addition to the pressure variation, the effects of the domain length on the phase delay of the pressure and velocity waves along the stack plate were also investigated. The results showed that with the increasing I-d/lambda. ratio, the simulated pressure distribution compares better with the standing wave pressure distribution. With the lowest I-d/lambda ratio (0.029) considered, the difference between the amplitudes of the computed pressure distribution and theoretical standing wave pressure distribution was approximately 50 Pa. However, as I-d/lambda value increases, the simulation results approach to the theoretical standing wave pressure distribution better. The computational results obtained with Id/lambda = 0.132 and 0.180, were almost identical with standing wave acoustic field. Hence, it was concluded that the domain length has a significant effect on the accuracy of the computational results when the truncated domain approach is used. It was also observed that for a given TA device and operating parameters, there is a minimum I-d/lambda value for obtaining reliable results.

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