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Bir Yüksek Hızlı Trenin Aktif Süspansiyonu için Modelleme ve LQR Geribildirim Kontrolü
(2025) Karahan, Mehmet
Yüksek hızlı demiryolu araçlarında sürüş konforu ve yolculuğun kalitesi önemlidir. Tren hareket halindeyken rayların neden olduğu çeşitli titreşimlerle karşılaşır. Bu titreşimlerin uzun süreli yaşanması yolcularda sağlık sorunlarına yol açabilir. Ayrıca trenin titreşimler nedeniyle dayanıklılığı azalır, performansı düşer ve bakım maliyetleri artar. Trenin iyi kullanılabilmesi için rijit bir süspansiyon sistemine ihtiyaç vardır. Geleneksel bir süspansiyon olan pasif süspansiyon, trenin sürüş kalitesi ile yolcu konforu arasında bir denge kurar. Ancak pasif süspansiyon sabit bir süspansiyon sistemidir ve süspansiyon sertliğini değişen koşullara göre ayarlayamaz. Aktif süspansiyon ise süspansiyon sertliğini değişen koşullara göre ayarlayabilir. Bu araştırmada tren gövdesini kontrol etmek için Doğrusal Karesel Düzenleyici tarafından kontrol edilen aktif bir süspansiyon tasarlanmıştır. Böylece titreşimler en aza indirilmiş ve yolcu konforu arttırılmıştır. Pasif ve aktif süspansiyonları karşılaştırmak için çeşitli simülasyonlar yapılmış ve aktif süspansiyonun üstünlüğü kanıtlanmıştır.
Dimensional Optimization of Two-Phase Flow Boiling in Microchannel Heat Sinks
(2021) Jafarı, Rahım
The heat transfer coefficient (HTC) of microchannel heat sinks (MHS) is higher than common heat sinks due to higher area to volume ratio. Its value for two-phase flow boiling is much superior to single-phase flow. In addition, the two-phase flow boiling provides uniform wall temperature close to the coolant’s saturation temperature in low vapor qualities. In the present study, a heat sink is optimized dimensionally after modeling of the boiling of R134a refrigerant in the microchannels. Firstly, mixture two-phase method along with the wall heat flux partitioning are utilized to introduce an applied thermal model to design MHSs. The heat sink mounted on the backside of an Intel core i7-900 desktop processor with dimensions of 19 mm×14.4 mm× 1 mm is numerically simulated to investigate the thermal performance. The HTC and the exit vapor quality are comparable with the available empirical correlations and first law of thermodynamics, respectively. Then the proposed model is developed to optimize the dimensions of the microchannels to design the heat sink with minimized wall temperature. Bound optimization by quadratic approximation (BOBYQA) method results in the optimized dimensions of the microchannels in the heat sink. Optimization of heat sink’s geometry in terms of the dimensions of the microchannels at various boundary conditions will be practical as the unique application of the model.
Citation - Scopus: 2
An Approach for Performance Prediction of Saturated Brushed Permanent Magnet\rdirect Current (dc) Motor From Physical Dimensions
(Tubitak Scientific & Technological Research Council Turkey, 2022) Asl, Rasul Tarvirdilu; Zeinali, Reza; Ertan, Hulusi Bulent; Tarvirdilu-Asl, Rasul; Tarvirdilu–Asl, Rasul
An analytical approach for performance prediction of saturated brushed permanent magnet direct current\r(DC) motors is proposed in this paper. In case of a heavy saturation in the stator back core of electrical machines, some\rflux completes its path through the surrounding air, and the conventional equivalent circuit cannot be used anymore.\rThis issue has not been addressed in the literature. The importance of considering the effect of the flux penetrating\rthe surrounding air is shown in this paper using finite element simulations and experimental results, and an analytical\rapproach is proposed to consider this effect on magnet operating point determination and performance prediction of\rsaturated brushed permanent magnet DC motors. An analytical method is also presented to determine the boundary\rradius of the surrounding air for obtaining accurate results in finite element (FE) solutions and analytical calculations.\rAn analytical approach based on Carter’s coefficient is also proposed to calculate the effective length of the magnet when\rthe length of the magnet and rotor length are not the same. The accuracy of the proposed analytical model is illustrated\rusing finite element simulations and experimental results. With this accuracy, this analytical model is very suitable to\rbe used for reliable and quick mathematical design optimization.
Citation - Scopus: 2
Temperature Effects in Deep Drawing of Advanced High Strengthsteels
(MIM RESEARCH GROUP, 2021) Akcan, Kadir; Billur, Eren; Saraç, H. İbrahim
As advanced high strength steels (AHSS) find more use in automotive industry to meet crashworthiness and light weighting targets, concurrently. AHSS typically have higher strength, but lower formability; often limiting a part’s dimensions and geometric complexity. Several studies have clearly shown that, in sheet metal forming, significant portion of the work done to overcome friction and to plastically deform a sheet is converted into heat. In this study, a thermomechanical finite element model has been developed to calculate the temperature rise in forming DP800 (AHSS). The model was validated with experiments from literature. A multi-cycle model is developed to find out possible problems due to tool heating. The process and material are selected to speed up the heating. Under different realistic press conditions, failures are observed after 20 to 80 hits.
Citation - WoS: 3
On the Yielding of Two-Layer Composite Spherical Pressure Vessels
(Gazi Univ, 2017) Akis, Tolga
The yielding of two-layer composite spherical pressure vessels under either internal or external pressure is investigated analytically in the framework of small deformations and von Mises yield criterion. It is shown for both pressure cases that depending on the material properties and sphere dimensions, different modes of plasticization may take place. Unlike the deformation behavior of a single layer spherical pressure vessel, yielding may commence at the inner layer or at the outer layer or simultaneously at both layers of the assembly.
Launching To an Orbit With a Chemical Propellant Staged Rocket Systems
(2022) Inger, Erk; Inger, Erk
There is one way to explore space by using the space launch vehicles, which is known as rockets, and it can carry useful load named simply as payload of satelite from Earth into Space. In this study, performance predictions of the multi rocket motors are discussed and compared with single rocket motor with the same amount of propellant used for space travel. In this article in serial or tandem staging schemes, the boosting stage is usually the largest, the second stage and subsequent upper stages are above it, usually decreasing in size are used. In boosting stage parallel staging schemes solid or liquid rocket boosters are used to assist with launch. At low level starting to high altitude higher density fuel solid fuels, kerogen and cryogenic hydrogen(-250°C) are used as fuel. In solid propellants oxidizer is generally ammonium per chloride is used but in cryogenic liquid propellants oxygen(183.3°C) are used. In the first stage, both liquid propellant in a booster and five solid rocket propellent are used to reach about a certain altitude and velocity. In second stage, after reducing the weight by ejecting the five solid rocket propellent and only liquid propellant is used only to reach the an extra altitudes and velocities at low earth orbit (LEO). Drag and gravity effects are successfully used in all of the calculations. The added total result of velocities and altidudes found by these staged rockets are higher than the first single staged case. The advantage of multistage rockets, having same amount of propellant in staged rockets where total velocity will be increased by separating and removing waste from the system weight out of the system. Use of staged rocket system are usefull for increasing the amount of payload and decreasing the cost per unit weight as well.
Design and Manufacturing of a Pin on Disk Tribometer
(2024) Küçüköztaş, Korcan; Nassar, Mohammed; Kaftanoğlu, Bilgin; Talay, İlker; Çalışkan, Fatih; Elsakka, Mustafa A.A.
This paper presents the design and manufacturing of a pin on disk tribometer aimed at performing friction and wear testing as accurate as a professional tribometer at a lower cost. Since friction is an important part of our lives and its application varies greatly in size, environment and other factors, testing can be expensive. Tribometers are instruments where these conditions can be simulated experimentally. They are manufactured by various companies abroad and are imported to Turkey. For this reason, the cost of these instruments is very high. The design of the manufactured tribometer prioritizes portability and low cost of manufacturing. The manufacturing process of the various parts are discussed in detail. The tribometer was manufactured in the ATILIM University manufacturing laboratories within a tight budget using CNC machining. The instrument has the full capability to adjust the load, testing radius, motor speed, and the duration of the test before starting the experiments. To handle the electronics and data gathering within the instrument, Arduino boards and software are utilized. Real-time data streaming is made possible for data analysis tasks both during and after the experiments. The paper also provides the results of experiments that are obtained from the newly developed tribometer and comparisons with a mass produced, professional tribometer. The experiments are conducted with the same type of samples and with the same parameters. The manufactured tribometer provides researchers with easily accessible friction data that is within close range to what they would get from a professional tribometer.
Kristal Plastisite Modellemesi ile Inconel 718 Alaşımının İşlenmesinde Artık Gerilmelerin Doğru Tahmini
(2023) Kesriklioğlu, Sinan; Kapçı, Mehmet Fazıl; Buyukcapar, Ridvan; Çetin, Barış; Yılmaz, Okan Deniz; Bal, Burak
Artık gerilmelerin belirlenmesi ve değerlendirilmesi, savunma, havacılık ve otomotiv endüstrilerinde kullanılan bileşenlerin arızalanmasını önlemede çok önemlidir. Bu çalışmanın amacı, Inconel 718'in işlenmesi sırasında oluşan artık gerilmeleri doğru bir şekilde tahmin etmek için bir malzeme modeli sunmaktır. Ortogonal talaşlı imalat testleri, çeşitli kesme ve ilerleme hızlarında gerçekleştirilerek, Inconel 718'in işlenmesinden sonraki artık gerilmeler, X-Ray ışın kırınımı ile karakterize edildi. Bu süper alaşımın mikroyapısal girdilerini ticari olarak temin edilebilen bir sonlu eleman yazılımına (Deform 2D) aktarmak için bir viskoplastik kendi içinde tutarlı kristal plastisite modeli geliştirildi. Ayrıca simülasyonlar klasik Johnson - Cook malzeme modeli ile aynı işleme parametrelerinde yapıldı. Bu çalışmada elde edilen simülasyon ve deneysel sonuçlar, kristal plastisite tabanlı çok ölçekli ve çok ölçekli malzeme modelinin, mevcut modele kıyasla Inconel 718'in işleme kaynaklı kalıntı gerilmelerinin tahmin doğruluğunu önemli ölçüde geliştirdiğini ve yüzey kusurlarını en aza indirmek için kullanılabileceğini göstermiştir. Geliştirilen bu model, kesilmesi zor malzemelerin işlenmesinde yüzey kusurlarını ve üretim denemelerinin maliyetini en aza indirmek için kullanılabilir.
Structural behavior of shear connectors embedded in different types of concrete
(2020) Wardi, Adil Hadi; Tunc, Gokhan; Ibraheem, Khalil
Push-out tests are used to determine shear connectors’ properties where two smallreinforced concrete walls are attached to the top and bottom flanges of an I-sectionthrough four shear studs located on both its flanges. In this study, the structural behavior of shear connectors was examined by testing a total of 36 push-out specimens.In these specimens, various test parameters were used. The types of shear connectors and their strengths, their connection types, and the strength of the concrete inwhich they were embedded were all investigated. Headed, L-shaped, and C-shapedstuds were selected in this experimental study to represent different types of shearconnectors. These shear connectors were assumed to be either ordinary or highstrength steel-embedded in three different types of concrete: ordinary, high strength,and reactive powder concretes. In these tests, the shear connectors were connectedthrough welding or epoxy bonding. The objective of this study was to investigate thestructural behaviors of these different types of shear connectors by focusing on theirshear force capacities and slip values. The test results indicate that the reactive powder concrete increased the mechanical properties of concrete as the concrete age increased. The specimens with C-shaped studs made of high-strength steel with weldedstuds embedded in normal weight, high strength and reactive powder concretes, generated the maximum shear resistance values.
Mechanical Properties of Trip Aided Bainitic Ferrite (tbf) Steels in Production and Service Conditions
(2018) Billur, Eren; Karabulut, Semih; Yılmaz, İmren Öztürk; Erzincanoğlu, Samet; Çelik, Hafize; Altınok, Evren; Başer, Tanya
In the automotive industry, one of the most common methods to reduce the weight of the body components is to downgage the sheets using higher strength steels. In the design phase, engineers typically use the material properties of the incoming material, suchas the yield strength and the elongation. For forming analyses, however, more detailedcharacterization is required (flow curves, anisotropy, forming limit curves, etc.). Once thecomponents are formed in the press shop, the yield strength increases due to work (strain)hardening. The parts are then welded in the body shop, and the body-in-white goes to thepaint shop where it is baked to cure the paint. Most steels’ yield strength changes duringthis paint bake cycle, which determines its final properties in service. Bake hardening (andin some cases, bake softening) is measured by Bake Hardening Index (BHI) as defined byEN 10325-2006. The standard dictates relatively low pre-strain (2%) and baking temperature (170°C). In real production conditions however, higher strains are achieved andbaking temperatures may exceed 170°C to shorten the baking time. In this study, a newgeneration Advanced High Strength Steel (AHSS) grade TBF 1050 was characterized formetal forming purposes and its bake hardening response was studied both as the standardsuggests and as the real production cycle dictates.

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