Theses supervised by Prof. Dr. Veli Çelik
11 theses · Ankara Yıldırım Beyazıt University
Analytical and numerical analysis of swage autofrettage process applied to thick walled cylinders
Autofrettage is the process of residual stress formation on the walls of the thick walled cylinders before their usage. These residual stresses help to increase the pressure bearing capacity of the thick walled cylinders by eliminating some stresses during the high pressure applications. In practice, there are two different autofrettage methods as hydraulic and swage. Swage autofrettage is a more economical method to form beneficial residual stresses in the thick walled cylinders when it is compared with the hydraulic autofrettage method. In this study, it is investigated how the residual stresses, that occur as a result of the swage autofrettage during manufacturing of a heavy armour barrel, affect the stress distributions that occur at the operating conditions of the barrel. At first, the stress distributions are obtained analytically for both Tresca and Von Mises criteria. Then, the verification of the analytical model is performed by making use of a commercial software which uses the finite element method. In the calculations, the mandrel's outer radius is considered as constant but the bore value of the cylinder is changed and the results for different % interference ratios are compared. The obtained results show that the maximum equivalent stress in an autofrettaged cylinder at operating pressure occurs in the elastic-plastic junction region. The equivalent stress distributions are obtained at 400 MPa operating pressure for different % interference values. The equivalent stress distributions are obtained by the analytical model for both Tresca and Von Mises criteria and the optimum interference value is found as 1% with respect to both two yielding criteria. However, in result of finite element model, the optimum interference value is found as 1% for Tresca criterion whereas it is found as 1,5% for Von Mises criterion. Bauschinger effect is represented by the kinematic hardening model in both analytical model and finite element model. According to the results that are obtained by analytical model, Bauschinger effect does not cause a secondary plastic yielding. However, according to the results that are obtained by finite element model, it is seen that Bauschinger effect causes a secondary plastic yielding.
Investigation of new applications for enhancement of gun barrel performance
Basically, what is expected from a weapon system is that it should be capable of firing the maximum number of shots in the shortest time, contain a larger amount of payload and deliver the ammunition to a greater distance. In addition, the mobility of the weapon system and its ability to move quickly within the area where it is used are also critically important for today's military applications. With the advancing technology, expectations regarding the speed and range of an ammunition used in today's weapon systems could be met by using new generation energetic propellants. The high pressure and temperature generated by such propellants require the barrels to have higher strength. Barrels subjected to higher pressures and temperatures require thicker walls to increase the strength's, which in turn increases the weight of the barrel and thus the weapon system. In order to overcome this disadvantage, a thesis study was carried out, which included a barrel lightening model. The barrel was autofretted at the optimum level for maximum pressure. Afterwards, considering the distribution of the temperature generated by the ammunition on the barrel wall, the wall thinning process was carried out for composite reinforcement application. As a result of the thesis study, the weight of a 105 mm heavy gun barrel with certain dimensions, which was 284.3 kg initial state, was reduced up to 182.4 kg with composite material reinforcement after autofrettage and wall thickness reduction. In this way, it has been shown by analytical and numerical calculations that the barrel can be safely lightened by 35.84 percent. When comparing the results of the analytical calculation and the finite element analysis, the results was found to be compatible with each other and with data in the literature. So, it is assessed that the data for a light and safe design of the barrel have been obtained.
Uçak gövde iskeletinin kıyaslamalı gerilme analizi
Havayollarının emisyonlarını azaltması, hem dünya çapında yaklaşan hükümet düzenlemeleri nedeniyle yakında yaygınlaşacak olan gelişmiş Çevresel, Sosyal ve Yönetişim ölçütleri hem de artan kârlılık açısından hayati önem taşıyor. Azalan emisyonlar, yakıt kullanımının azalmasıyla doğru orantılıdır ve dolayısıyla uçak işletme marjlarını iyileştirmek için kullanışlıdır. Sonuç olarak, havacılık gibi önemli çevresel etkiye sahip endüstrilerin güncel, rekabetçi ve yeni düzenlemelere uyumlu kalabilmek için bu önlemleri yakında benimsemesi gerekmektedir. Bu amaca uygun olarak, etkili bir strateji hava taşıtlarının kütlesinin azaltılması olabilir. Uçakta kütlenin azaltılmasını sağlamak için daha iyi malzemelerin seçimi gibi alternatif yöntemlerle, yapısal bütünlüğün korunması şartıyla bazı bağlantı elemanları çıkartılabilir. Uçak tasarımında ağırlığın önemli bir kısmı tipik olarak gövdede, özellikle de kirişlerle birbirine bağlanan uzunlamasına yerleştirilmiş iskelet yapısında yoğunlaşır. Bu çalışma, yapısal bütünlüğü korurken mekanik analiz araçlarını kullanarak bu konuyu ele almayı ve iyileştirmeyi amaçlamaktadır. Bu kapsamda Al-7475, Al-7075 ve Al-2024 gibi bazı havacılık malzemelerine bir dizi çekme testi uygulanmış ve bulgular kaydedilmiştir. Çekme testlerinden edinilen sonuçlar, sonlu elemanlar metodu yöntemiyle yapısal iyileştirmeler elde etmek amacıyla kullanılmıştır. Bu analizler, Al-7475 için daha yüksek yapısal performans ortaya çıkarırken, güvenlik faktörünü Al-2024'e kıyasla %30,13 artırarak 1,88'den 2,44'e çıkartmış ve ağırlığı yalnızca %1,4 arttırmıştır. Ancak, doğrudan kütle azaltımı, dolayısıyla yakıt tüketimi azaltımı açısından değerlendirildiğinde, en iyi seçeneğin Al-2024 olduğu tespit edilmiştir. Airbus A320neo'da, normal koşullarda kullanılan baz malzeme olan Al-2524 ile kıyaslandığında, güvenlik faktörünü havacılık standartlarında tutmayı sürdürüp %1,77 kütle azaltımının mümkün olduğu ve bu sırada çekme mukavemetinin de %1,81 artabileceği tespit edilmiştir.
Investigation of new applications for enhancement of gun barrel performance
Basically, what is expected from a weapon system is that it should be capable of firing the maximum number of shots in the shortest time, contain a larger amount of payload and deliver the ammunition to a greater distance. In addition, the mobility of the weapon system and its ability to move quickly within the area where it is used are also critically important for today's military applications. With the advancing technology, expectations regarding the speed and range of an ammunition used in today's weapon systems could be met by using new generation energetic propellants. The high pressure and temperature generated by such propellants require the barrels to have higher strength. Barrels subjected to higher pressures and temperatures require thicker walls to increase the strength's, which in turn increases the weight of the barrel and thus the weapon system. In order to overcome this disadvantage, a thesis study was carried out, which included a barrel lightening model. The barrel was autofretted at the optimum level for maximum pressure. Afterwards, considering the distribution of the temperature generated by the ammunition on the barrel wall, the wall thinning process was carried out for composite reinforcement application. As a result of the thesis study, the weight of a 105 mm heavy gun barrel with certain dimensions, which was 284.3 kg initial state, was reduced up to 182.4 kg with composite material reinforcement after autofrettage and wall thickness reduction. In this way, it has been shown by analytical and numerical calculations that the barrel can be safely lightened by 35.84 percent. When comparing the results of the analytical calculation and the finite element analysis, the results was found to be compatible with each other and with data in the literature. So, it is assessed that the data for a light and safe design of the barrel have been obtained.
Investigation of greenhouse gas emissions originated from public transportation: The case of Ankara
Human induced activities have been increasing the atmospheric abundance of greenhouse gases at an alarming level since pre-industrial times, eventuating in global warming by means of increasing the heat-trapping abilities of the greenhouse gases. Advanced climate models project that global temperature change will exceed 1.5 degrees Celsius at the end of the 21th Century, whereafter the adverse effects of the global warming will be unavoidable. Hence, reducing the atmospheric abundance of the greenhouse gases is of vital importance. Transportation sector is the second largest contributor of the Turkish anthropogenic greenhouse gases with its dominant source being road transportation. In Turkey, road transportation is heavily dependent on individually-owned automobiles. Greater use of public transportation will reduce excessive automobile dependency and greenhouse gas emissions, also providing economic and social benefits. Incidental to both international and domestic regulations, the annual national greenhouse gas inventory covering the Turkish anthropogenic greenhouse gases are being reported adopting the IPCC methodology. The national inventory utilizes fuel sold method in emission calculations from transportation sector. In this thesis, direct greenhouse gas emissions originated from the EGO public transport buses are analyzed with both the highest and the current tier approaches used in the national inventory adapting the IPCC methodology. It is observed that, current approach used estimated emissions in carbon dioxide equivalent ninety five percent less than the highest tier approaches utilized in this thesis. Altering the fuel use habits and vehicle fleet expansion compared to the current trend, hundred and thirty one kilotons of emissions in carbon dioxide equivalent will be avoided and 88,843,822 TL will be saved in a period of next ten years. Keywords: Direct greenhouse gas emissions, IPCC methodology, tier approaches, emission factors.
Numerical investigation of inclined fluidic oscillator in microchannel heat exchanger
The primary aim of this research was to investigate the enhancement of momentum and thermal energy transfer in a microchannel heat exchanger through the use of fluidic oscillators. To this end, a sweeping jet impingement heat transfer performance was evaluated with varying impact angles, distances between fluidic oscillators, and Re numbers. This study employed two fluidic oscillators to investigate heat transfer in a microchannel heat exchanger. To enhance the effectiveness of heat transmission in jet cooling, the fluid was oscillated. This allowed it to be calculated how much the flow rate and, consequently, the local Nu value increased, increasing the heat transfer performance. The study was based on the work of Wu Y. et al. validation studies were carried out on the study from the base study and model is validated for 3 Re numbers. Following the validation research, angles of 30, 45, and 60 degrees were evaluated between the fluid oscillator and the channel. Additionally, the distance between the two oscillators was investigated at distances of 7D, 7.5D, and 8D from the center of the outlet hole. A steady heat flux was applied to the channel surface, which served as the impact surface in the model. The fluid's Reynolds range was identified as 3000 to 10000. The study's findings revealed that increasing the oscillation of the jet flow process improves heat transfer efficiency. Additionally, it was found that when the impact angle grew, the pressure drop and Nu number likewise increased, with a 12 percent improvement in heat transfer being the largest. The heat transmission is found to be positively impacted by shortening the space between the strings, with a maximum improvement of 5.7 percent.
Weight reduction in aircraft with topology optimization
One of the most important parameters in airplanes is weight. Aircraft must be light enough to perform the tasks and capabilities expected of them, while at the same time being structurally resistant to the loads they encounter. Historically, different methodologies have been tried to make lighter aircraft designs. Topology optimization has recently become a preferred weight reduction method in the aviation industry. Lighter designs are obtained by removing the material that does not provide sufficient strength to the structure from the structure. In this study, weight reduction was made in the wing area of Cessna 172 aircraft by topology optimization. Before the topology optimization phase of the wing structure, the initial weight and the forces acting on it were calculated analytically. Based on the real-life weight of the wing structure, a finite element model of its pre-optimization state was created, and its structural strength was checked. A valid model was obtained before the topology optimization by making validation analysis of the created finite element model. In topology optimization, two different topology optimizations were applied to 3-dimensional and 2-dimensional structures. In these structures, weight reduction was achieved by determining the design areas and constraints for optimization. The structure obtained from topology optimization was statically evaluated again in order not to fail.
Modelling and analysis of a hydropneumatic recoil mechanism in artillery
In this study, the recoil movement of heavy weapons with hydropneumatic recoil mechanism is modeled. The primary purpose of the study is to obtain the equation of motion of the recoiling parts in the weapon systems. For this purpose, the forces acting on the recoiling parts were determined, and the effects of each force were examined. Breech force is calculated via LeDuc equations for in bore period and verified by comparing with experimental studies from literature for a typical 105 mm howitzer and from MKEK for a new generation lighter 105 mm weapon system. Additionally, velocity of projectile in barrel is calculated from the model and compared with test data. Breech force which is generated during the discharge of the remaining gases after the projectile leaves the barrel is also calculated and total breech force is obtained. Then, net retarding force that consists of friction, hydraulic brake and recuperator forces are calculated. After determining breech and net retarding forces, the equation of motion is obtained, and solved via MATLAB. Recoil distance, velocity and acceleration of recoiling parts are calculated and effects of firing angle, weight of recoiling parts, orifice discharge coefficient, muzzle brake efficiency are investigated. Comparisons show that model results are compatible with test data and the differences between them is less than three percent. Additionally, it is deduced from this study that if firing angle and orifice discharge coefficient increase, maximum recoil displacement, maximum velocity, and maximum acceleration values of recoiling parts increase. When orifice discharge coefficient is increased by 20 percent, maximum recoil displacement, velocity, and acceleration of recoiling parts are increased from 1109 mm to 1220 mm, from 45.2 m/s to 49.7 m/s and from 21.6 m/s2 to 23.7 m/s2, respectively. In addition, maximum recoil displacement, maximum velocity, and maximum acceleration values of recoiling parts decrease if weight of recoiling parts and muzzle brake efficiency increase. When weight of recoiling parts is increased by 20 percent, maximum recoil displacement, velocity and acceleration of recoiling parts are decreased from 1109 mm to 921 mm, from 45.2 m/s to 37.5 m/s and from 21.6 m/s2 to 17.9 m/s2, respectively. Besides, as the muzzle brake efficiency increases from 1 to 1.5, maximum recoil displacement and velocity of recoiling parts decreased from 1109 mm to 1075 mm, 45.2 m/s to 43.8 m/s, respectively.
Energy recovery at natural gas pressure reduction stations
The energy need of our world increases day by day, but it is seen that the resources are decreasing. For this reason, we need to use our energy more efficiently in every field. This is inevitable, especially for our country, which provides the majority of its energy needs as imported. It is essential to examine all stages of energy consumption to study efficiency and recovery. The amount of natural gas usage in the world and our country is increasing over the years. Natural gas, which is consumed in many areas, enters our country through the national distribution network. Natural gas transported with high pressure is reduced to the desired pressure value for consumers with pressure reduction and measurement stations. In these stations, natural gas is filtered, heated before pressure drop, flow rate measured, and pressure reduced. Gas pressure is reduced by throttling. Meanwhile, sudden drops in the temperature of the gas are observed due to the Joule-Thomson effect. This undesirable situation can damage the pilot controlled regulator due to freezing of the water vapor contained in the gas and the formation of hydrate. Natural gas is heated before it enters the regulator to prevent this. In studies on energy recovery in natural gas stations, it is recommended to use vortex pilot gas heaters in the station to reduce the cost of this preheating process. In this study, the advantages of using a vortex tube and its effect on cost have been examined through a station in Ankara. Using the data of this station for the years 2016-2019, preheating fuel consumption before and after the use of the vortex tube was calculated, and the consumption amounts were compared. In addition, artificial neural network modeling has been made in the study. After completing the training of the model with the data for the specified years, a test was carried out on a monthly value of 2020. Thus, the effectiveness of the vortex tube application in energy recovery was supported, and a resource was provided to other stations to calculate the savings they would achieve if they used a vortex tube.
Research of nuclear waste management and technoeconomical analyses
In short, nuclear energy is the energy derived from a large amount of heat caused by the fragmentation of the atom. When obtaining nuclear energy, fisyon and fusion reactions appear. It is trying to capture the nuclear energy technology that is rising day by day in Turkey by following the countries that have developed more developed in this field. Turkey, which does not have any energy-generating nuclear reactors other than TR-1 and TR-2 research reactors for nuclear energy technology, has signed protocols with Russia and Japan to work in this field and has commissioned Akkuyu Nuclear Inc. with the Russians. Fuel rods will be used when obtaining nuclear energy and nuclear waste will occur. Waste management and disposal are also very important for recycling. Recycling of waste is important in order to prevent situations that will harm the environment. Two types of waste are occurring in nuclear power plants. These are called low-level and high-level waste. Low-level waste can be easily processed and destroyed. High-activity fuels are fuel rods. Used fuel rods are stored in pools near the reactor. Used fuels contain 97% nuclear-worthy substances. Two methods are used for nuclear fuels: open and closed cycle. Fuels used in open cycles are considered direct waste. In the closed cycle, radioactive useful substances in used fuel are re-inserted into the cycle. Open cycle is more economical than closed cycle. In this study, general and up-to-date information on nuclear power, radioactivity and nuclear power plants in Turkey and around the world will be given. Nuclear studies in Turkey will be examined in a comparative manner; fuel types, fuel reserves and availability of these reserves, costs and recommendations for storage or disposal of nuclear waste in more appropriate ways will be presented.
Analytical and numerical analysis of swage autofrettage process applied to thick walled cylinders
Autofrettage is the process of residual stress formation on the walls of the thick walled cylinders before their usage. These residual stresses help to increase the pressure bearing capacity of the thick walled cylinders by eliminating some stresses during the high pressure applications. In practice, there are two different autofrettage methods as hydraulic and swage. Swage autofrettage is a more economical method to form beneficial residual stresses in the thick walled cylinders when it is compared with the hydraulic autofrettage method. In this study, it is investigated how the residual stresses, that occur as a result of the swage autofrettage during manufacturing of a heavy armour barrel, affect the stress distributions that occur at the operating conditions of the barrel. At first, the stress distributions are obtained analytically for both Tresca and Von Mises criteria. Then, the verification of the analytical model is performed by making use of a commercial software which uses the finite element method. In the calculations, the mandrel's outer radius is considered as constant but the bore value of the cylinder is changed and the results for different % interference ratios are compared. The obtained results show that the maximum equivalent stress in an autofrettaged cylinder at operating pressure occurs in the elastic-plastic junction region. The equivalent stress distributions are obtained at 400 MPa operating pressure for different % interference values. The equivalent stress distributions are obtained by the analytical model for both Tresca and Von Mises criteria and the optimum interference value is found as 1% with respect to both two yielding criteria. However, in result of finite element model, the optimum interference value is found as 1% for Tresca criterion whereas it is found as 1,5% for Von Mises criterion. Bauschinger effect is represented by the kinematic hardening model in both analytical model and finite element model. According to the results that are obtained by analytical model, Bauschinger effect does not cause a secondary plastic yielding. However, according to the results that are obtained by finite element model, it is seen that Bauschinger effect causes a secondary plastic yielding.