1,721,216 research outputs found
Design, Analysis and Optimization of Thin Walled Semi-Monocoque Wing Structures Using Different Structural Idealizations in the Preliminary Design Phase
No full textThe article gives a comprehensive study on the effect of using different structural idealizations on the design, analysis and optimization of thin walled semi-monocoque wing structures in the preliminary design phase. In the design part of the article, wing structures are designed by employing two different structural idealizations that are typically used in the preliminary design phase. In the structural analysis part, finite element analysis of one of the designed wing configurations is performed using six different one and two dimensional element pairs which are typically used to model the sub-elements of semi-monocoque wing structures. The effect of using different finite element types on the analysis results of the wing structure, which is designed by the simplified method using two different idealization approaches, is investigated. Comparisons are also made between the analysis results of the finite element solution and the simplified method, and the applicability of the simplified method in the preliminary design phase is investigated for the wing configuration studied in the article. During the analysis study, depending on the mesh size used, conclusions are also inferred with regard to the deficiency of certain element types in handling the true external load acting on the wing structure. Finally in the optimization part, wing structure is optimized for minimum weight by using finite element models which have the same six different element pairs used in the analysis phase. The effect of using different one and two dimensional element pairs on the final optimized configurations of the wing structure is investigated, and conclusions are inferred with regard to the sensitivity of the optimized wing configurations with respect to the choice of different element types in the finite element model. Final optimized wing structure configurations are also compared with the simplified method based designs which are also optimized iteratively
Birinci dereceden yanal kesme deformasyonu dahil edilmiş anizotropik eksenel simetrik kabuk yapılarının gerilme ve deformasyon analizi yarı analitik çalışması.
No full textIn this study, anisotropic shells of revolution subject to symmetric and unsymmetrical static loads are analysed. In derivation of governing equations to be used in the solution, first order transverse shear effects are included in the formulation. The governing equations can be listed as kinematic equations, constitutive equations, and equations of motion. The equations of motion are derived from Hamilton’s principle, the constitutive equations are developed under the assumptions of the classical lamination theory and the kinematic equations are based on the Reissner-Naghdi linear shell theory. In the solution method, these governing equations are manipulated and written as a set called fundamental set of equations. In order to handle anisotropy and first order transverse shear deformations, the fundamental set of equations is transformed into 20 first order ordinary differential equations using finite exponential Fourier decomposition and then solved with multisegment method of integration, after reduction of the two-point boundary value problem to a series of initial value problems. The results are compared with finite element analysis results for a number of sample cases and good agreement is found. Case studies are performed for circular cylindrical shell and truncated spherical shell geometries. While reviewing the results, effects of temperature and pressure loads, both constant and variable throughout the shell, are discussed. Some drawbacks of the first order transverse shear deformation theory are exhibited.M.S. - Master of Scienc
Filament sargı ile üretilen dönel kabuk yapılarda yarı-jeodezik sarımın kabuk yapılarının titreşim özelliklerine olan etkisinin incelenmesi.
No full textIn this thesis, the effect of semi-geodesic winding on the free vibration characteristics of filament wound composite shells of revolution with variable radii of curvature is studied. The analysis is performed by a semi-analytical solution method which is based on the numerical integration of the finite exponential Fourier transform of the fundamental shell of revolution equations. The governing equations for the free vibration analysis are initially obtained in terms of fundamental shell variables, and they are reduced to a system of first order ordinary differential equations by the application of finite exponential Fourier Transform, resulting in a two point boundary value problem. The boundary value problem is then reduced to a series of initial value problems, and the multisegment numerical integration technique is used in combination with the frequency trial method in order to extract the natural frequencies and determine the mode shapes within a given range of natural frequencies. Previous studies on geodesic winding is extended such that the effect of semi-geodesic winding which rely on the preset friction between the fiber and the mandrel surface on the stiffness and vibration characteristics of filament wound shells of revolution is investigated. Additionally, finite element analysis is employed to compare the results obtained from semi-analytical model solved by numerical integration and finite element model solved by finite element method. Sample results are obtained for filament wound truncated conical and spherical shells of revolution and the effect of the winding pattern on the vibration characteristics of shells of revolution is investigated thoroughly.M.S. - Master of Scienc
Kompozit bir taktik insansız hava aracının yapısal tasarım, analiz ve kompozit üretim uygulamaları.
No full textIn this study structural design, analysis and composite manufacturing applications for a tactical UAV, which was designed and manufactured in Aerospace Engineering Department of Middle East Technical University (METU), is introduced. In order to make an accurate structural analysis, the material and loading is modeled properly. Computational fluid dynamics (CFD) was used to determine the 3D pressure distribution around the wing and then the nodal forces were exported into the finite element program by means of interpolation from CFD mesh to finite element mesh. Composite materials which are mainly used in METU TUAV are woven fabrics which are wetted with epoxy resin during manufacturing. In order to find the elastic constants of the woven fabric composites, a FORTRAN code is written which utilizes point-wise lamination theory. After the aerodynamic load calculation and material characterization steps, linear static and dynamic analysis of the METU TUAV’s wing is performed and approximate torsional divergence speed is calculated based on a simplified approach. Lastly, co-cured composite manufacturing of a multi-cell box structure is explained and a co-cured multi-cell box beam is manufactured.M.S. - Master of Scienc
Genetik algoritma kullanarak kafes sistemlerinin tasarım organizasyonu.
Full text linkDesign optimization of truss structures is a popular topic in aerospace, mechanical, civil, and structural engineering due to benefits to industry. Common design problem for the structures is the weight minimization. Especially in aerospace engineering the minimization of the weight of the total structure gets the highest importance in the design. This study focuses on the design optimization of 2D and 3D truss structures. The objective function is the total mass of the structure which is subjected to stress and nodal displacement constraints. To optimize the design, Genetic Algorithm (GA) is preferred due to its efficiency in dealing with problems with discrete design variables as in the case of truss structures. This technique yields more realistic results than linear programming methods. In the thesis, a finite element code is developed for the analysis of planar and space truss structures. The developed finite element solver is coupled with a genetic algorithm optimization code which is also developed as a part of the thesis study. Different truss optimization case studies are performed to demonstrate the performance of the finite element solver and the genetic algorithm optimization code that are developed. It is shown that with the use of adaptive penalty function employing scaled fitnesses, the arbitrariness issue of the factor multiplying the error term in the augmented fitness function can be resolved. It is also shown that significant weight reduction can v be achieved by employing shape optimization together with size optimization compared to pure size optimization.M.S. - Master of Scienc
Low velocity impact analysis of a composite mini unmanned air vehicle during belly landing
Full text linkMini unmanned Air Vehicles (UAV) have high significance among other UAV's, in different categories, due to their ease of production, flexibility of maintenance, decrease in weight due to the elimination of landing gear system and simplicity of use. They are usually built to meet 'hand launching' and 'belly landing' criteria in order to have easy flight and easy landing features. Due to the hand take-off and belly landing features there is no need to have a runway and this feature is a very significant advantage in operational use. In an operation, belly landing mini UAV's may encounter tough landing areas like gravel, concrete or hard soil. Such landing areas may create landing loads which are impulsive in character. The effect of the landing loads on the airframe of the mini unmanned air vehicle must be completely understood and the mini UAV be designed accordingly in order not to damage the mini UAV during belly landing. Typical impact speeds during belly landing is relatively low (<10 m/s) and in general belly landing phenomenon can be treated as low velocity impact. The purpose of this study is to analyze the impact loads on the composite substructures of a mini UAV due to the belly landing. 'Güventürk' Mini UAV which is designed and built in METU Aerospace Engineering Department, is used as the analysis platform. This study is limited to the calculation of stresses and deformation that is caused by the low velocity impact forces encountered during belly landing. The main purpose of this work is to help the designer in making design decisions for a mini UAV that is tolerable to low velocity impact loads. Initial part of the thesis includes analytical treatment of low velocity impact phenomenon. In the simplified analytical approach the loading is assumed as quasistatic and comparisons of such a simplified method of analysis is made with explicit finite element solutions on isotropic and composite plate structures to investigate the applicability of simplified analytical method of analysis. Belly landing analyses of the mini UAV are done by MSC.Dytran, which is an explicit finite element solver. Model building and post processing are done via MSC.Patran. Stress and deformation response of the mini UAV is investigated by performing low velocity impact analysis using sub-structure built-up approach.M.S. - Master of Scienc
Ters taylor çarpma testi ve hız interferometrisi kullanarak yüksek gerinim hızlarındaki malzeme karakterizasyonu.
No full textMetallic materials in aerospace structures are exposed to impact type loads depending on their usage area. High strain rate material characterization of metallic materials is very crucial to properly prepare finite element models to be used in impact loading situations. Johnson-Cook material model is a suitable material model to represent the behaviour of metallic materials at high strain rates. In the present thesis study, parameters of the Johnson-Cook material model for Al 7075-T651 are determined utilizing the tensile test data in quasi-static loading condition and impact test data for impact loading condition. High strain rate material characterization of the metallic material is performed by the modified Taylor impact test and velocity interferometry. Modified Taylor impact test system and how the free surface velocity measurement by the velocity interferometry-VISAR is utilized for the determination of the strain rate constant of the Johnson-Cook material model are described in detail. Experimentally determined material constants are verified by simulating the modified Taylor impact test in Autodyn and comparing the experimentally and numerically determined free surface velocities. M.S. - Master of Scienc
Bir uçağın sadeleştirilmiş aerodinamik ve yapısal modellerini kullanarak yük analizi.
No full textAircraft must be light enough to fly but also strong enough to endure the loads they experience during flight. Designing such a structure is one of the most demanding works in an aircraft design project. In order to design such a structure, accurate evaluation of loads is important. Once the loads applied to the structure are calculated precisely, then the deflections and stresses can be calculated and sizing of the structures can be performed accordingly. Therefore, in aircraft design projects, loads group lies at the heart of the design cycle. It receives inputs from various design groups such as aerodynamics group, structures group, weight and balance group, systems groups, airworthiness group, and so on. Not only receiving these inputs, but load group also provides outputs to various groups, mainly structural design and analysis. Those interactions make aircraft loads one of the most multidisciplinary subjects in aircraft design and analysis. On the other hand, because of those interactions with all disciplines of the design cycle, load analyses are also quite complex, requires systematic work, ability to process massive amounts of data, adequate insight of both aerodynamic and structural issues and communication with not only within the company but also with certification authorities. The objective of this study is provide a comprehensive overview of load analysis process, to develop methods for simplification of aircraft structural and aerodynamic models to make it possible to perform the load analysis in a fast and integrated way during conceptual and preliminary design phases, then to perform a load analysis of an ultralight aircraft as a case study for the demonstration of the load analysis process.M.S. - Master of Scienc
Sabit ve döner kanatların çırpınma kararsızlığı analizi.
No full textFlutter is a critical stability problem that needs to be considered for the design of fixed and rotary wings. Although flutter susceptibility is addressed during the test phases of the most of the aircraft, an analytical model is required for the determination of flutter boundaries and most importantly for supplying feedback to the design procedure in order to have a structure that is free from flutter. In this thesis, several flutter analysis methodologies are investigated for both fixed and rotary wing structures. For the analytical models, a theoretical background is given for Theodorsen, Loewy, Wagner unsteady aerodynamic theories and Pitt-Peters and Peters-He inflow theories. In addition, derivation of the simple beam theory is explained with the expansion methods of Rayleigh-Ritz and Galerkin. Three different solution types; k-method, modified k-method and p-method are studied based on the aerodynamic theory implemented. The flutter analysis results are verified and compared with the results given in the literature. The fixed wing analyses are validated with Goland’s fixed wing results, rotary wing analyses are validated both with helicopter blade and wind turbine blade analyses results. Case studies are performed to investigate the effects of the shear center and center of gravity locations and the forward velocity of the helicopter on the flutter analysis results.Thesis (M.S.) -- Graduate School of Natural and Applied Sciences. Aerospace Engineering
Kompozit rüzgâr türbin kanadının sabit rüzgâr koşullarında zamana bağlı ve neredeyse statik aeroelastik analizlerinin karşılaştırmalı çalışması.
No full textThe objective of this study is to conduct a comparative study of the transient and quasi-steady aeroelastic analysis of a composite wind turbine blade in steady wind conditions. Transient analysis of the wind turbine blade is performed by the multi-body dynamic code Samcef Wind Turbine which uses blade element momentum theory for aerodynamic load calculation. For this purpose, a multi-body wind turbine model is generated with rigid components except for the turbine blades. For the purposes of the study, a reference three dimensional blade is designed using inverse design methodology. Dynamic superelement of the turbine blades are created and introduced into multi-body model of the wind turbine system, and transient aeroelastic analysis of the multi-body wind turbine system is performed in steady wind conditions. As a follow-up study, quasi-steady aeroelastic analysis of the same composite wind turbine blade is performed by coupling a structural finite element solver with an aerodynamic tool based on blade element momentum theory. Quasi-steady aeroelastic analysis of the blade is performed at different azimuthal positions of the blade and transient effects due to the rotation of the blade are ignored. The article aims at investigating the applicability of quasi-steady aeroelastic modeling of the turbine blade in steady wind conditions by comparing the deformations obtained by quasi-steady aeroelastic analysis and transient aeroelastic analysis of the complete turbine system at the same azimuthal positions of the blade. The presented results conclude that the quasi-steady aeroelastic analysis and transient aeroelastic analysis have a close match and the coupling between the finite element solver with a blade element momentum based aerodynamic tool can be used for static aeroelastic analysis at preliminary design state of a composite wind turbine blade.M.S. - Master of Scienc
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