Yazar "Dal, Abdurrahim" seçeneğine göre listele

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    A thermohydrodynamic performance analysis of a fluid film bearing considering with geometrical parameters
    (Yildiz Technical Univ, 2023) Dal, Abdurrahim; Sahin, Mahir; Kılıç, Mustafa
    Bearing performance characteristics such as stiffness, and load capacity, are related to the lubrication fluid circulating through the gap. In the fluid film bearings, the characteristic of the lubrication film also depends on the journal geometry and the viscosity. This study aimed to research the bearing geometry influences on the thermohydrodynamic performance of a circular journal bearing. The temperature distribution is modeled using a 3-dimensional energy equation. The velocity components are obtained on the pressure distribution governed by Dowson's equation. Moreover, the heat transfer between the journal and oil is modeled with Fourier heat conduction equation, and the viscosity equation is derived for SAE10W30 commercial oil as a function of the temperature. An algorithm based on the finite difference method is developed, and a serial simulation is performed for different geometrical parameters such as bearing clearance, and bearing length-to-diameter ratio (L/D). When the radial clearance decreases from 150 i.tm to 100 i.tm, the maximum pressure grows up by 53%, and the maximum temperature decreases by 21%. On the other hand, when the L/D ratio rises from 0.8 to 1, the maximum pressure grows up by 22%, but the temperature distribution does not significantly change. The load capacity, and the stiffness are higher for low radial clearance. The load capacity, and the stiffness increase when the L/D ratio grows up.
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    Design and performance evaluation of a 3D printed aerostatic bearing concept with high number of micro-orifices
    (Sage Publications Ltd, 2024) Agoren, Gorkem; Dal, Abdurrahim; Karacay, Tuncay
    This study suggests a 3D printed aerostatic bearing concept. The design has a high number of orifices distributed around the bearing to obtain smoother pressure distribution for performance. Inner channels are formed to connect and feed air to each orifice using the advantage of additive manufacturing. The concept is investigated numerically to determine the performance gain of the high number of orifices by calculating bearing stiffness and load carrying capacity. In order to validate the simulation and performance gain an experimental study is conducted by testing Stereolithography (SLA) type 3D printed bearings with various orifice numbers. The bearing stiffnesses and mass flow rates of the specimens are measured, and results are discussed in terms of performance by comparing numerical results. The 3D printed bearings concept has shown promising results in terms of performance while keeping air consumption limited compared to conventional air bearings.
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    Design and performance evaluation of a 3D printed aerostatic bearing concept with high number of micro-orifices
    (Sage Publications Ltd, 2024) Agoren, Gorkem; Dal, Abdurrahim; Karacay, Tuncay
    This study suggests a 3D printed aerostatic bearing concept. The design has a high number of orifices distributed around the bearing to obtain smoother pressure distribution for performance. Inner channels are formed to connect and feed air to each orifice using the advantage of additive manufacturing. The concept is investigated numerically to determine the performance gain of the high number of orifices by calculating bearing stiffness and load carrying capacity. In order to validate the simulation and performance gain an experimental study is conducted by testing Stereolithography (SLA) type 3D printed bearings with various orifice numbers. The bearing stiffnesses and mass flow rates of the specimens are measured, and results are discussed in terms of performance by comparing numerical results. The 3D printed bearings concept has shown promising results in terms of performance while keeping air consumption limited compared to conventional air bearings.
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    Dynamics of a rotor-aerostatic journal bearings system with asymmetric air feeding
    (Springer Heidelberg, 2022) Dal, Abdurrahim; Karacay, Tuncay
    In this study, the effect of the symmetric and asymmetric air feeding on the dynamics of a shaft-aerostatic journal bearing system is theoretically investigated. In this scope, the pressure distribution of the air in the clearance is modeled with Reynold's equation and the lubrication forces are calculated using this distribution. Then, equations of motion derived in four degrees of freedom are solved for different rotational speeds under symmetric and asymmetric air feeding conditions. To validate the simulation results, an experimental test rig comprised of a rotor, air bearings, and measurement equipment is set up and run for different rotational speeds. The nonlinear dynamic behavior of the imbalance responses of the bearing-shaft system is analyzed using bifurcation diagrams, Poincare map, waterfall, and orbit plots. The results of the presented study brought to light that the system has a nonlinear dynamic motion due to a pneumatic hammer. However, the pneumatic hammer frequency of an aerostatic bearing with asymmetric supply pressure condition is lower than an aerostatic bearing with the symmetric condition. And the results also showed that the bearing performance will be improved by asymmetric supply pressure conditions.
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    Effects of geometrical parameters on thermohydrodynamic performance of a bearing operating with nanoparticle additive oil
    (Emerald Group Publishing Ltd, 2023) Dal, Abdurrahim; Sahin, Mahir; Kılıç, Mustafa
    PurposeBearing performance characteristics, such as stiffness and load capacity, are related to the viscosity of the fluid circulating through the gap. Nanoparticle additives in lubricant are one way to enhance of the viscosity. This study aims to investigate the effect of nanoparticle additives on the thermohydrodynamic performance of journal bearing with different bearing parameters. Design/methodology/approachThe temperature distribution is modeled using a three-dimensional energy equation. The velocity components are calculated on the pressure distribution governed by Dowson's equation. Moreover, the heat transfer between the journal and lubricant is modeled with Fourier heat conduction equation. On the other hand, the viscosity equation is derived for Al2O3 nanoparticles as a function of the volume ratio and the temperature. An algorithm based on the finite difference method is developed, and a serial simulation is performed for different parameters and different volume ratio of nanoparticle. FindingsWith the increase in the nanoparticle volume ratio, the maximum temperature decreases for the lower clearance values, but the addition of the nanoparticle influence on the maximum temperature reverses when the clearance grows up. The nanoparticle additives increase further the maximum temperature for higher values of L/D ratios. Moreover, the effects of the nanoparticle additives on the pressure are stronger at high eccentricity ratios for all bearing parameters. Originality/valueThis paper provides valuable design parameters for journal bearing with lubricant containing the nanoparticle additives.
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    Effects of lubricant fluid with nanoparticle additive on the load capacity of a hydrostatic journal bearing
    (TUBITAK, 2020) Dal, Abdurrahim; Kiliç, Mustafa; Akyüz, Ali Özhan; Tuncer, Azim Doğuş; Gungor, Afsin
    Hydrostatic journal bearings are recommended for supporting shafts operating at high speeds and under heavy loads in the industry. In the journal bearings, lubricant viscosity decreases with increasing temperature at high rotation speeds and hence, the fluid between the surfaces should be circulated using a pump to cool the lubricant. However, the lubricant supplying between the surfaces at the high flow rate causes the whirl instability and vibrations problems in the bearing-shaft system. These instability problems give rise to significant damage on the system during operating at the high speeds and under heavy loads. As a solution to this problem, it could be suggested to control the variation of the lubricant viscosity concerning the temperature by adding nanoparticle. In the present work, the effects of the lubricant with nanoparticle additives on the load carrying capacity of a hydrostatic journal bearing are theoretically investigated. The fluid film flow between the bearing and rotor surfaces are modelled with Reynolds equation and the viscosity term in Reynold’s equation is defined as a function which depends on the nanoparticle properties. Then, the pressure distribution is obtained with solving the film flow equation and the load capacity is calculated for different nanoparticle parameters using this pressure distribution. The results show that the usage of the lubricant with nanoparticle increases the load performance of the hydrostatic journal bearing and the influences of the nanoparticle size on the load performance is more dominant for high volumetric ratio. © 2020, TUBITAK. All rights reserved.
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    Effects of the Shaft Speed on Stiffness and Damping Coefficients of Hydrodynamic Bearing-Shaft System under Variable Viscosity
    (Gazi Univ, 2024) Dal, Abdurrahim
    The rotating shaft-hydrodynamic bearings systems operated with high speed and/or heavy load conditions expose serious rotordynamics instability problems due to characteristics of the supporting bearings. The stability and the dynamics of these systems, directly relate to the lubricant properties that are directly affect by the heat generation. The main purpose of this study is investigation of the dynamic characteristics and the stability of a shaft supported by hydrodynamic journal bearing under variable viscosity. Th e equations of lubricant flow were derived by Dowson's model under variable viscosity, and the dynamic characteristics were modelled with the perturbation model in direct and cross directions. The heat transfers between oil and the journal surface was modelled in a 3-dimensional energy and the heat conduction equation. An algorithm based on finite difference and successive-over-relaxation method was developed to solve the theoretical models, simultaneously, and a serial simulation was performed to investigate the variations of the dynamic coefficients of the bearing-shaft system concerning the shaft speed for different radial clearance values. It was determined that the high speed increases the lubricant temperature, and so the static and dynamic performance characteristics decrease, moreover, this effect is more dominant for the smaller radial clearance.
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    Integrated analytic hierarchy process and multi-criteria decision-making approach: An Application for Unmanned Underwater Vehicle Control Method Selection
    (Pergamon-Elsevier Science Ltd, 2024) Nennioglu, Ahmet Kemal; Abdulvahitoglu, Asli; Dal, Abdurrahim
    Using Multi-Criteria Decision Analysis (MCDA) techniques, it is possible to thoroughly examine all available options and determine the most desirable ones. However, the prevalence of these methods, which employ various computational changes, can result in disparate outcomes. Therefore, the final rankings should be as dependable and consistent as possible. In this study, the consistency of the findings obtained from the TOPSIS, COPRAS, MAUT, and MOOSRA methodologies was investigated in the real-world problem of Unmanned Underwater Vehicle Control Method Selection by forming decision matrices through simulations.
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    Investigation of nanoparticle diameter influences on performance of hydrodynamic journal bearings operating with nanolubricant
    (Sage Publications Ltd, 2024) Dal, Abdurrahim
    The nanolubricant's effectiveness on the bearings' performance depends on the types of nanoparticles, volume ratio, and their size and/or diameter. Although the nanolubricant influences on the characteristics of the journal bearings are well known, cost-effective solutions for using nanolubricants, have continued to need in industrial applications. Because the nanoparticle's diameter plays a key role in the fluid with nanoparticle additives, research on its effect is important for hydrodynamic journal bearing. In this work, the nanoparticle diameter impacts on the characteristics of the hydrodynamic journal bearings are investigated with under thermal effects. At first, four hydrodynamic journal bearings have different parameters such as radial clearance and bearing length-diameter ratio are considered and designed. Then, the lubricant flow through the radial clearance is modeled with Dowson's equation. Besides, the temperature field in the journal and the lubricant are governed by the heat conduction and energy equations, respectively. The physical and thermal properties of the nanolubricant are expressed by considering nanoparticle diameter and the volume ratio. Then, an algorithm is developed to solve the mathematical models based on the finite difference method. Finally, a serial simulation is conducted under different nanoparticle diameters and operational conditions. When the nanoparticle diameter becomes small, the temperature and pressure values of the nanolubricant, load capacity, and stiffness increase.
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    Performance characteristics of an aerostatic journal bearing with partially blocked orifices
    (Sage Publications Ltd, 2021) Dal, Abdurrahim; Karacay, Tuncay
    Aerostatic journal bearing applications mainly focus on high-speed precision machining, so predictable and smooth functioning of the system is crucial. Air is supplied to the bearing through a number of orifices and any unevenness in the size of these orifices will affect the performance of the system. The size difference could be due to manufacturing error and/or blockage of the orifice because of foreign materials in the air system. In this study, the performance of an aerostatic bearing with a partially blocked orifice is numerically investigated. Firstly, the airflow in the bearing clearance was modeled with Reynolds equation and this equation was numerically solved with the finite difference and differential transform hybrid method to obtain the pressure distribution. Then, the force and the stiffness are calculated from the pressure distribution for different blockage cases of the orifice and different blockage ratios. The results show that the partial blockage of the orifice significantly changes the performance of the system in a positive or a negative way according to the feeding hole position, and the blockage ratio also affects performance.
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    Performance characteristics of an aerostatic journal bearing with partially blocked orifices
    (Sage Publications Ltd, 2021) Dal, Abdurrahim; Karacay, Tuncay
    Aerostatic journal bearing applications mainly focus on high-speed precision machining, so predictable and smooth functioning of the system is crucial. Air is supplied to the bearing through a number of orifices and any unevenness in the size of these orifices will affect the performance of the system. The size difference could be due to manufacturing error and/or blockage of the orifice because of foreign materials in the air system. In this study, the performance of an aerostatic bearing with a partially blocked orifice is numerically investigated. Firstly, the airflow in the bearing clearance was modeled with Reynolds equation and this equation was numerically solved with the finite difference and differential transform hybrid method to obtain the pressure distribution. Then, the force and the stiffness are calculated from the pressure distribution for different blockage cases of the orifice and different blockage ratios. The results show that the partial blockage of the orifice significantly changes the performance of the system in a positive or a negative way according to the feeding hole position, and the blockage ratio also affects performance.
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    Pneumatic hammer instability in the aerostatic journal bearing-rotor system: A theoretical and experimental analyses
    (Sage Publications Ltd, 2021) Dal, Abdurrahim; Karacay, Tuncay
    In this study, the pneumatic hammer instability phenomena in the aerostatic journal bearing-rotor system is analysed and discussed for different feeding hole configurations theoretically and experimentally. The influences of the configuration of the feeding holes on the nonlinear dynamics of the system are also investigated. The air flow between the surfaces is modelled with Reynold's equation and it is numerically solved with differential transform and finite difference hybrid method. Three different aerostatic bearings are modelled and simulated to investigate the influences of the configuration of the holes for different angular speeds. An experimental test rig is designed and tested for different rotor speeds to validate the obtained numerical results. The dynamic response of the system is analysed using waterfall plots, bifurcation diagrams, orbit plots, phase portrait and Poincare map, which are drawn to determine the pneumatic hammer instability region of the modelled system. The results reveal a nonlinear dynamic response of the rotor centre. In addition, the analysis shows that the feeding hole configuration affects the rotor dynamics and the pneumatic hammer instability region.
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    Pneumatic hammer instability in the aerostatic journal bearing-rotor system: A theoretical and experimental analyses
    (Sage Publications Ltd, 2021) Dal, Abdurrahim; Karacay, Tuncay
    In this study, the pneumatic hammer instability phenomena in the aerostatic journal bearing-rotor system is analysed and discussed for different feeding hole configurations theoretically and experimentally. The influences of the configuration of the feeding holes on the nonlinear dynamics of the system are also investigated. The air flow between the surfaces is modelled with Reynold's equation and it is numerically solved with differential transform and finite difference hybrid method. Three different aerostatic bearings are modelled and simulated to investigate the influences of the configuration of the holes for different angular speeds. An experimental test rig is designed and tested for different rotor speeds to validate the obtained numerical results. The dynamic response of the system is analysed using waterfall plots, bifurcation diagrams, orbit plots, phase portrait and Poincare map, which are drawn to determine the pneumatic hammer instability region of the modelled system. The results reveal a nonlinear dynamic response of the rotor centre. In addition, the analysis shows that the feeding hole configuration affects the rotor dynamics and the pneumatic hammer instability region.
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    Vibration Analysis of a Hybrid Polymer Ball Bearing with 3D-Printed Races
    (Springer Heidelberg, 2024) Dogan, Burcu Kucukoglu; Dal, Abdurrahim; Agoren, Gorkem; Karacay, Tuncay
    BackgroundThe use of polymer bearings in some industries has increased in recent years because of their advantages, such as resistance to dirt and dust, no need for maintenance and lubrication, and chemical resistance, especially in hygienic areas. Additive manufacturing (AD) or 3D printing is also a popular method that makes complex geometric shapes easily produced using polymer material, layer by layer, of the defined component.PurposeThe study aims to investigate the applicability of producing polymer ball bearing with additive manufacturing techniques by experimentally observing the bearing's vibrations, temperature, and rolling resistance.MethodsA set of ball-bearing races-inner and outer-are produced with the stereolithography (SLA) method using polymeric resin and tested under a certain load.ResultsVibrations and load cell data for rolling resistance are analyzed through its lifetime to investigate the evolution of the bearing under the test.ConclusionThe additive manufacturing method could be preferred to produce a ball bearing with limited life.
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    Vibration behavior of a 3D-printed hybrid polymer bearing with outer race defect
    (Emerald Group Publishing Ltd, 2024) Dogan, Burcu Kucukoglu; Dal, Abdurrahim; Agoren, Gorkem; Karacay, Tuncay
    PurposeIn industry applications, polymer hybrid bearings have become widespread in recent years owing to the lack of lubricant requirements, particularly in areas requiring hygiene. The additive manufacturing method gives significant advantages to have complex machinery parts, and it has become popular in the industry in recent years. However, it has some inherent disadvantages caused by layered deposition/addition of the materials, and the probability of the localized defect is much higher than in the conventional manufacturing methods. This study aims to investigate the effect of the outer race defect on the characteristics of vibration and service lifetime of hybrid polymer ball bearings produced with the stereolithography (SLA) additive manufacturing method.Design/methodology/approachIn this study, polymer bearings' races were produced with the additive manufacturing SLA method, and the outer race defect was analyzed with measured vibrations.FindingsThe results show that the additive manufacturing method suggests a practical solution for producing a polymer hybrid ball bearing. On the other hand, the hybrid three-dimensional-printed bearing, which has an outer race defect, worked for approximately 8 h without any problems under a 1 kg load and a shaft speed of around 1,000 rpm. In addition, when there is a defect in the outer and/or inner race of the ball bearing, the crest factor and kurtosis of the vibration are higher than faultless ball bearing, as expected.Originality/valueThis paper provides valuable information on the lifetime and vibration characteristics of polymer hybrid ball bearing produced by means of additive manufacturing.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-06-2023-0183/
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    Vibration behavior of a 3D-printed hybrid polymer bearing with outer race defect
    (Emerald Group Publishing Ltd, 2024) Dogan, Burcu Kucukoglu; Dal, Abdurrahim; Agoren, Gorkem; Karacay, Tuncay
    PurposeIn industry applications, polymer hybrid bearings have become widespread in recent years owing to the lack of lubricant requirements, particularly in areas requiring hygiene. The additive manufacturing method gives significant advantages to have complex machinery parts, and it has become popular in the industry in recent years. However, it has some inherent disadvantages caused by layered deposition/addition of the materials, and the probability of the localized defect is much higher than in the conventional manufacturing methods. This study aims to investigate the effect of the outer race defect on the characteristics of vibration and service lifetime of hybrid polymer ball bearings produced with the stereolithography (SLA) additive manufacturing method.Design/methodology/approachIn this study, polymer bearings' races were produced with the additive manufacturing SLA method, and the outer race defect was analyzed with measured vibrations.FindingsThe results show that the additive manufacturing method suggests a practical solution for producing a polymer hybrid ball bearing. On the other hand, the hybrid three-dimensional-printed bearing, which has an outer race defect, worked for approximately 8 h without any problems under a 1 kg load and a shaft speed of around 1,000 rpm. In addition, when there is a defect in the outer and/or inner race of the ball bearing, the crest factor and kurtosis of the vibration are higher than faultless ball bearing, as expected.Originality/valueThis paper provides valuable information on the lifetime and vibration characteristics of polymer hybrid ball bearing produced by means of additive manufacturing.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-06-2023-0183/