LEE- Uçak ve Uzay Mühendisliği Lisansüstü Programı

Bu topluluk için Kalıcı Uri

http://hdl.handle.net/11527/19473

Gözat

Yazar "Arıkoğlu, Aytaç" ile LEE- Uçak ve Uzay Mühendisliği Lisansüstü Programı'a göz atma
  • Öge
    A multi-disciplinary design approach for conceptual sizing of advanced rotor blades
    (Lisansüstü Eğitim Enstitüsü, 2022-07-19) İbaçoğlu, Hasan ; Arıkoğlu, Aytaç ; 511072102 ; Aeronautics and Astronautics Engineering
    Rotorcrafts are versatile vehicles with their unique hovering flight capability. However, their forward flight speed limitations and high noise levels are shortened to their usage in much wider areas. Therefore, the rotorcraft industry working on advanced rotorcraft, which are called compound rotorcrafts, development projects increasingly to overcome these problems. The conceptual design phase is the beginning of a development project where the most critical decisions are taken in this stage. So, vehicle-level optimization algorithms are needed for decision-making to lead the project correctly. On the other hand, simplified low-level approaches must be used during conceptual design optimization because of too many design parameters to avoid impractical solution times. Furthermore, rotorcrafts with advanced rotors require advanced design approaches to obtain superior performance, structural, and noise-level characteristics. Therefore, advanced conceptual design approaches are needed to overcome this contradiction. The rotor is the most critical component, which is also the source of the most problems of a rotorcraft such as lack of performance and noise. Therefore, rotor blade optimization is the main issue in the conceptual design phase at the beginning of a project. A multidisciplinary rigid rotor blade design optimization approach that is suitable for the conceptual design, sizing, and evaluation stages of helicopter development processes is suggested. Performance, structural strength of the blade, and noise-level predictions are considered for the objective function. Blade outer surface and structure are represented by a geometrical model in which the chord, thickness ratio, chamber ratio, and twist distributions along the blade radial stations can be defined as linear or nonlinear functions. The distribution of the number of layers for both skin and spar was also defined in the presented model parametrically. Low-level but sufficient fidelity analysis methods were chosen to be able to reduce the computing time. Performance analysis and sizing of the vehicle were obtained by Blade Element Momentum Theory (BEMT) based in-house developed helicopter sizing code called ROTAP. A trim algorithm for compound helicopters that may have additional lifting surfaces and thrust components is suggested. Airfoil Characteristics are calculated by the well-known panel method code Xfoil. Both these codes are modified and embedded in the code developed for this study. Structural analysis was obtained using the 1D FEM approach. Cross-sectional properties of the composite beam are calculated by VABS and displacements under the loads are calculated by GEBT. Reduced FfowcsWilliams-Hawkings equations are used to estimate loading, thickness, and high-speed impulsive noise levels. A hybrid optimization algorithm is suggested to get optimal results. Sequential Quadratic Programming (SQP) can be used to find local optimal points. And then the global optimal point is searched by RSM over local optimal points iteratively. RSM-based surrogate modeling, evaluation, and optimization tool was also developed for manual inspection of the design space. As a case study, multi-objective aerodynamic performance optimization of aircraft propeller is performed.
  • Öge
    Determination of equivalent elastic properties of printed circuit boards
    (Graduate School, 2024-07-10) Yakut, Erdinç ; Arıkoğlu, Aytaç ; 511141118 ; Aeronautics and Astronautics Engineering
    Printed Circuit Boards (PCBs) are indispensable components in modern electronic equipment. They are widely used in various fields such as aerospace, military and defense products, industrial, medical, automotive, telecommunications, maritime, and consumer electronics. Some of these products, the PCBs have a higher volume than other parts of the products. PCBs have significantly effects on these products design and mechanical durability. PCBs are crucial components in the CubeSats and PocketQubes satellites. CubeSats have main six subsystems and these subsystem except one (that is structure) made from PCB or it is controlled from PCB. PocketQubes are made from PCB also structural system. In this application PCBs can affect other systems and be affected by the environment. PCB contains various layers, which are substrate, conductive, solder mask, and silkscreen layers. Each layer has a specific duty. Substrate ensures mechanical and thermal durability, insulation between conductive layers. Solder mask, silkscreen layers are used to help for integrating PCB assemblies. The conductive layers are the main layers of the PCBs, and their number is named PCB. The main duty is conducting electronic parts with electronic ways or surfaces. PCBs are made up of layers that are stacked with epoxy. Due to the variability in design and materials, the mechanical properties of PCBs must be thoroughly tested. However, considering budget and time constraints, this is not always feasible in engineering practice. This study proposes an equivalent model to efficiently and accurately model the mechanical properties of PCBs used in CubeSats and PocketQubes. The study is divided into two main parts: creating a data pool for elastically equivalent model values and solving an optimization problem to assign coefficients to the equivalent model. Commercial software and software developed for other projects were used. Modal frequency analyses were performed for the equivalent models and detailed natural frequency analyzes were performed using package software. For the optimization problem, the natural frequencies of geometries simulating the primary structure were determined using the differential quadrature method. The database was created with 2-layer, 4-layer, 6-layer, and 8-layer PCBs with two samples of each. Solid models of each conductive layer were extracted from Altium Designer and modeled in CATIA based on the stack-up design. Layer fill ratios were calculated based on maximum dimensions. Due to the small thickness of some conductive (starting at 0.0175 mm) and insulating layers (starting at 0.26 mm), layers were modeled as shells for finite element analysis. Detailed surface models were prepared in Ansys SpaceClaim and transferred to PATRAN for finite element analysis. Results were obtained from NASTRAN and added to the data pool for optimization and validation. To run the optimization code, the natural frequencies were calculated using the differential quadrature method. The material model was based on the Halpin-Tsai model, the normalized root mean square error between the database results and those calculated with quadrature method is minimized for optimization. A brute force approach was used to obtain the material parameters that minimize the selected objective function. The final comparison showed an average difference of around 3.47 % between the equivalent model results obtained with the differential quadrature method and detailed finite element analysis results. One PCB, with a non-rectangular geometry, was solved using finite element analysis due to the inability to use the differential quadrature method. The detailed analysis of the model, solved using a finite element analysis program, took 28,695.00 seconds on a computer with 24 cores and 64 GB of memory, while the analysis modeled with elastic equivalent material model took 1,583.00 seconds on a computer with 12 cores and 32 GB of memory. The solution time was reduced by 94.48 % compared to the detailed finite element analysis with average 2.54 % difference in results. Further validation involved comparing the results with the Voigt model, the Halpin-Tsai model is more accurate than the Voigt model, with their differences being around 3 % compared to detailed model. The primary goal of reducing analysis time was achieved with a 2.54 % mode similarity. Future work could expand creating the database through material property tests and optimizing the equivalent model with more data from more analysis and resonance survey of PCBs with varying fill volumes.
  • Öge
    Static analysis of stiffened laminated composite plates by using GDQM
    (Graduate School, 2023-07-06) Güneytepe, İhsan Berk ; Arıkoğlu, Aytaç ; 511191202 ; Aeronautics and Astronautics Engineering
    Due to their extensive use in the aerospace and maritime industries, stiffened laminated composite plates represent an important study topic in engineering. Due to their superior mechanical qualities and high strength-to-weight ratio, stiffened laminated composite plates are frequently employed in a variety of technical applications. This study examines the static analysis of an eccentric stiffener-equipped laminated composite plate. First-order shear deformation theory is used to mathematically model the main plate under investigation, which includes four layers of carbon/epoxy. In contrast, Timoshenko beam theory is used to describe the isotropic stiffener mathematically. A torsional coefficient is also employed and included in the mathematical beam model for isotropic stiffeners. Also, for modeling an isotropic plate, the Mindlin plate theory is used. The theoretical investigations seek to determine how the insertion of stiffeners impacts the lamination of composite plates' static behavior. The stiffened laminated composite plate's motion equations are derived in the theoretical analysis using Hamilton's principle. A numerical method known as the Generalized Differential Quadrature Method (GDQM) has demonstrated considerable promise in resolving challenging engineering issues. The GDQM approach, which discretizes the partial differential equations into a set of algebraic equations, is used in this study to solve the governing equation that represents the free vibration of eccentrically stiffened laminated composite plates. For each edge of the plate, the clamped boundary conditions are taken into account. The Wolfram Mathematica application is an effective suite of tools for numerical analysis and scientific computing. It is used for numerical problem-solving and result visualization. This study investigates the natural frequencies and mode shapes of an isotropic stiffened plate for isotropic plate, [0,90,90,0] and [45,60,60,45] fiber angle carbon fiber laminated composite. The findings demonstrate that the GDQM method is a reliable and accurate approach for determining the free vibrations of such plates. The results also show that changing the fiber angle orientation significantly affects the mode shapes and can vary the natural frequencies. These findings are applicable in a variety of engineering disciplines for the design and analysis of stiffened laminated composite plates.