Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Optimum Design and Analysis of Torsion Spring Used in Series Elastic Actuators for Rehabilitation Robots(01. Izmir Institute of Technology, 2021) Erten, Hacer İrem; Artem, Hatice SeçilAlong with the developing technology, robotic systems have started to take place in areas where there is one-to-one interaction with people, as well as their use in industrial areas. As the robotic system began to take place in daily life, safety and reliability between humans and robots have become a critical issue. In this context, a series elastic actuator has been developed for the aforementioned robotic systems, which has an elastic element placed in series between the motor output and the mechanical output. In this thesis, the torsion spring, as a critical part for the rotary series elastic actuators of rehabilitation robots, which helps support the extension and flexion of the knee joint during physical therapy of individuals with lower extremity disorders, is discussed. First of all, the data required for modeling was produced by making analyses with the design of experiment and finite element method. In line with the design goal of a light, compact, durable and stiff spring, the torsion spring whose topology was determined was modelled using a hybrid method: Neuro-regression approach and cross-validation technique. To minimize the mass and von Mises stress of the torsion spring, the thickness of the spring and the inner corner radius of the flexible leg are taken as the design variables and multi-objective optimization problems are created. The design and optimization of the torsion spring was done with the help of Differential Evolution, Nelder-Mead, Random Search and Simulated Annealing algorithms. By comparing the obtained optimization results with the finite element method and the results in the literature, it has been seen that the model and optimization methods used in the study are reliable and applicable.Master Thesis Optimization of Buckling Behavior of Hybrid Composite Beam Under Axial Compression(01. Izmir Institute of Technology, 2021) Altıntaş, Hayri; Artem, Hatice SeçilThe use of lighter and high-performance materials in the aerospace sector is of great importance. Optimization methods, which have become very popular with the technological development in the production methods of composite structures in recent years and provide the most suitable design for the purpose, are frequently preferred in the design of parts in the aviation industry. Determining the buckling load capacity of a composite beam under compression load is very important for the design of composite structures. The buckling load capacity of a hybrid composite beam with fiber metal laminate (FML), which is frequently used between aircraft wing and fuselage. The optimum design of the anti-buckling behavior of the hybrid composite beam, which is subjected to compression load, fixed by simple support on both sides, was performed by a genetic algorithm (GA) based on the Tsai-Wu fracture criterion. The robust design of composite hybrid laminates was developed using a design optimization process based on GA with the finite element method. A multi-objective genetic algorithm (MOGA) was used to optimize the design of a hybrid composite beam subjected to buckling. Design variables in the optimization process are considered as fiber material and angle orientations. The purpose of the objective function is to reduce the equivalent stress of hybrid composites while increasing critical buckling load. The design constraint was the Tsai-Wu failure index. As a result, it has been observed that the buckling performance of the beam depends on the structure of the metal material in FML composites. Carbon/epoxy and glass/epoxy structures were proposed and a design was aimed according to the maximum buckling load in the best stacking sequence, taking into account the data in the design constraints.Master Thesis Gravity Compensation of a 2r1t Mechanism With Remote Center of Motion for Minimally Invasive Transnasal Surgery Applications [master Thesis](01. Izmir Institute of Technology, 2021) Aldanmaz, Ataol Behram; Artem, Hatice Seçil; Dede, Mehmet İsmet Can; Artem, Hatice Seçil; Dede, Mehmet İsmet CanIn this work, gravity balancing of a 2URRR-URR parallel manipulator is issued. The manipulator is designed as an endoscope holder for minimally invasive transnasal pituitary gland surgery application. In the surgery, the endoscope is placed through the nostril of the patient where there is a natural path to the pituitary gland. In case of a motor failure, in order to protect the patient and to ease the control of the manipulator static balancing for this manipulator is worked out, the manipulator prototype is balanced and tested. The parallel manipulator has three legs. The payload mass has been distributed to side legs due to workspace limitations. By using counter-mass for two links in each leg, the center of mass of each leg has been reduced to the proximal link which simplified the balancing problem to balancing of a two degree-of-freedom inverted pendulum. By connecting a zero free length spring to the proximal link the total mass of the leg the manipulator has been kept in static balance in its desired workspace. Simulations show that with the applied design, torque effects on the motors have been reduced by 93.5%. Finally, the balancing solution is applied on the manipulator with active motors and the manipulator has been balanced, the torque values mostly has been decreased where the joint clearance, spring tension adjustments and mechanical constraints has affected the results. With the elimination of the joint clearance, mechanical constraints and rearranging the spring tension the required torque could be minimized.Master Thesis Design and Optimization of Shaft Bracket of Drum Brake for Heavy Duty Vehicle(01. Izmir Institute of Technology, 2021) Çetin, Mert; Artem, Hatice SeçilThe automotive industry is one of the leading sectors with a wider market share than any other sector which can quickly adapt to the increasingly competitive environment. However, in addition to the increasing product costs, regulations aiming to reduce fuel consumption and carbon emissions require an optimal design that satisfies design requirements depending on seriously increasing competition in this sector. This situation aims to design lightweight and high-performance vehicle products in a shorter period. In this sense, optimization methods have become very popular especially with the development of computer technologies in recent years. Therefore, they are often preferred in the design of vehicle products which enable to achieve the most suitable design for the specified purpose in a short time. This thesis study aims to realize a new shaft bracket design to be used in Z-Cam drum brakes of heavy duty vehicles by optimization methods. In line with this goal, firstly, the boundaries of material distribution in the given design space for vehicle axle application were obtained with the help of topology optimization. Then shape optimization was applied to bring material distribution having the suitable rough surfaces into the manufacturable form. Here, the Solid Isotropic Microstructure with Penalization (SIMP) algorithm was used for topology optimization and Response Surface Method (RSM) for shape optimization. Finite element analysis (FEA) of the final design obtained due to optimization was repeated and design verification tests were performed on the shaft bracket prototype manufactured according to the final design. The effectiveness and applicability of the optimization method used in the study were examined by comparing the performed test results with the final FEA. As a result of this study, a lighter design having a 72% weight advantage was obtained instead of the existing shaft bracket and the new design showed the similar structural strength compared with the existing shaft bracket as a result of experimental verification tests. Consequently, it has been seen that the optimization methods are very effective for the structural design of vehicle products.Master Thesis Stacking Sequences Optimization of Laminated Composites for Maximum Buckling Strength by Stochastic Search Methods(Izmir Institute of Technology, 2020) Adabaşı, Gökay; Artem, Hatice SeçilBased on materials developed and made available by humans, there are materials that will serve their purpose. Using lighter materials, especially in the field of aviation and space, significantly reduces the costs. However, lightness is not the only feature required in materials. In addition, the physical and mechanical properties of the materials must be at the desired level. Knowing the buckling load capacity of composite materials, which are widely used, is also very important in determining the material properties. Accordingly, an important focus of this thesis is to examine the behavior of different materials against the same loading; the other is to examine the increase in the critical buckling load factor although they have the same geometric structure. Critical buckling load factor is considered when performing the buckling analysis. The mechanical behavior of composite materials used by considering the factors of critical buckling load factor has been investigated and discussed. Different optimization methods have been used while making the optimum design of different composite materials with 48 and 64 layers in total. The verification of mechanical properties of materials was made with the help of coding. Subsequently, the referenced articles were verified to prove the accuracy of this code. Optimization was carried out by using material properties information from reference articles and verifying the code. As a result, considering the buckling strength of different layered composite materials, it has been found that the optimum designs depend on the load, load ratio, and plate aspect ratio.Master Thesis Optimization of Weld Bead Geometric Parameters in a Tig Welding Process(Izmir Institute of Technology, 2019) Dilsiz, Kadriye Çağla; Artem, Hatice SeçilWelding is a process that widely used in many areas of industry. Tungsten Inert Gas (TIG) welding process in several types of welding is often preferred in space and aircraft industry, defense industry, and automotive. The welding should be at the required limits and quality when working under pressure. Visual and physical welding quality determined by welding bead geometric parameters. Weld bead dimensions response variables as front height (FH), front width (FW), back height (BH), and back width (BW). In this thesis, Neuro-regression approach which is hybrid study of conventional regression analysis and artificial neural network. Third order polynomial function is used to design front width response itself. The differences between neuro-regression approach and conventional regression analysis while modeling the weld bead geometric dimensions are examined. Welding speed, wire feed rate, percentage of cleaning, gap, and welding current are taken as input variables of the system during modeling. Effects of welding speed, wire feed rate, percentage of cleaning, gap, and welding current on front height, front width, back height, and back width are expressed. Optimization of weld bead geometric parameters in TIG welding process were carried out by using Differential Evolution, Nelder Mead, Simulated Annealing and Random Search stochastic optimization algorithms. Two different problems of front width are studied. Differential Evolution is selected as stochastic search method to have minimum value of front width as a result of the study. All mathematical calculations are carried in Wolfram Mathematica.Master Thesis Optimization of Surface Roughness on a Milling Process Using Stochastic Methods(Izmir Institute of Technology, 2019) Dinç, Özcan; Artem, Hatice SeçilNowadays, milling process is one of the most widely used metal processing methods in many fields from space and aircraft to automotive industry. The surface roughness values of the workpiece in milling process vary depending on the thermal, chemical and abrasive loads that occur during cutting. Spindle speed, depth of cut and feed rate are the cutting parameters affecting the surface roughness. Hence, these parameters at the time of machining constitute an important issue. Accordingly, in this thesis optimization of surface roughness has been performed using the stochastic search methods. First, using experimental data obtained in the milling process, it was aimed to establish a regression model to determine average surface roughness equation as an objective function. The cutting parameters and average surface roughness value were considered as input and output in regression analysis, respectively. In this study, seven different mathematical models have been established and examined to carry out regression analysis. The reliability and stability of the mathematical models were investigated. The most appropriate mathematical model has been constructed and then used as an objective function for optimization. Nelder-Mead, Random-Search, Simulated Annealing, and Differential Evolution were the stochastic search algorithms to perform the optimization in the present study. In conclusion, it was found that the minimum average surface roughness value depends on spindle speed, depth of cut and feed parameters.Master Thesis Optimum Design of Composite Hydrogen Pressure Vessels by Stochastic Search Methods(Izmir Institute of Technology, 2018) Sayı, Abdülmecit Harun; Artem, Hatice SeçilFiber-reinforced composite materials are extensively used in many engineering applications such as aircraft wings and frames, vehicle drive shafts, sport equipment, and pressure storage vessels. One of the reasons for the extensive use of laminated composite materials is their tailorable nature, which allows them to satisfy specific design objectives in an application. As an application, hydrogen-powered fuel cell vehicles require high amount of hydrogen to increase distance range. Hence, hydrogen is pressurized at elevated rates. Since, it is hard to satisfy safety and weight regulations for high pressure gas, composite storage vessels offering high strength with low weight are preferred. Optimization techniques are applied to the design of composite pressure vessels to maximize strength with comprising weight restrictions. In the thesis, first-ply failure optimizations of stacking sequence design of cylindrical composite pressure vessels with metal liner having 700-bar working pressure and safety factor of 2.0, have been performed using stochastic search algorithms which are Differential Evolution and Nelder Mead. Three separately categorized failure theories; Tsai-Wu, Maximum Stress and Hashin-Rotem criteria have been incorporated to failure analysis of the vessel designs. In addition, the effects of volume on the stacking sequence design have been investigated. Hence, four volumetrically separated pressure vessel designs have been considered. Change in volume has been provided by inner radius. Single objective optimization has been set to minimize failure criteria index which incorporates into classical lamination theory. Fiber orientation angles and number of plies are design variables. CPU time has been calculated to compare the workloads of algorithms. In conclusion, optimized pressure vessels have provided design targets and the difference in volume has caused variable fiber angle orientations, number of plies and CPU time.Master Thesis Design and Mechanical Behaviour of Brazed Plate Heat Exchangers(Izmir Institute of Technology, 2018) Gürler, Yiğit; Artem, Hatice SeçilIn recent years, the developments in clean, renewable and efficient energy policies have been enabled to design new and innovative heat exchangers. The plate heat exchangers have crucial importance among these innovative products due to compact size and thermally efficient behaviour. There are many studies dealing with the thermo-fluidic behaviour of brazed plate heat exchangers. However, since the usage of these products often includes relatively high pressure and toxic fluids, the examination of structural stability of these products is cruical from the point of scientific perspective view. There are very few studies of plate heat exchangers regarding to mechanical aspects. Accordingly, in this thesis it is intended to investigate structural behaviour of brazed plate heat exchangers by numerical methods. For this purpose, the material properties of brazing interface of plate heat exchangers have been determined by experimental methods. The tensile and stress based fatigue experiments are carried out and the material models have been obtained. The validation of material model which is used in numerical analysis has been carried out by explicit method using maximum displacement as a boundary condition. The mechanical behaviour of chevron type brazed plate heat exchangers has been investigated by considering effect of chevron angle under different pressure conditions. The results have been obtained numerically in two stages; static structural analysis results and fatigue analysis. The numerical results show that the chevron angle has a significant effect on the formation of brazing points of plate heat exchangers. The dimensions of brazing points directly affects the overall structural behaviour of plate heat exchanger. It is observed that the single brazing point surface area and homogeneous distribution of brazing points on the plates are more critical than the total surface area. Finally, it is thought that the developed numerical methodology will lead to the structural design of brazed plate heat exchangers before the production of protoype molding and experimental testing. Eventually, it will be advantageous in terms of mold costs and time spent for experimental testing.Master Thesis Stacking Sequence Optimization and Modeling of Laminated Composite Plates for Free Vibration(Izmir Institute of Technology, 2018) Hasanoğlu, Emre Azim; Artem, Hatice SeçilComposite materials, especially fiber reinforced composites, have been extensively used in various engineering fields such as automotive, aerospace, aircrafts, defense, marine and so on due to having their high specific strength to weight and stiffness to weight ratios. In these last years, vibration problem has become more and more important in the structures where thin plates are used. Therefore, free vibration characteristics of composite structures under the influence of dynamic forces should be determined in the design process. Accordingly, in this thesis, optimum designs, which maximize the natural frequencies of laminated composite plate, are investigated by using hybrid algorithm combining the genetic algorithm (GA) and generalized pattern search algorihm (GPSA). Composite plates made of graphite/epoxy have been considered and assumed to be symmetric with continuous fiber angles in the laminate sequences. The natural frequency of plates is obtained bu using the Rayleigh Ritz method analytically. Free vibration equation is taken as objective function and fiber orientation angles are chosen as design variables. The natural frequency is maximized for various boundary conditions, aspect ratios, number of ply and material properties. The optimum designs obtained are verified by finite element method, and mode shapes of laminated composite plates are presented. A comparison between continuous and conventional (laminate in which the orientation angles are limited to the conventional orientations) designs is performed in order to show the reliability of continuous plates. As a results, it is observed that material properties, boundary conditions and dimensions of composite plates play important role on vibration behavior of composite plates. On the other hand, the natural frequencies and the optimum fiber oriantation angles are not affected from the change of number of plies.