LEE- Uçak ve Uzay Mühendisliği-Yüksek Lisans
Bu koleksiyon için kalıcı URI
Gözat
Son Başvurular
1 - 5 / 96
-
ÖgeUAV project management and design phases(Graduate School, 2025-01-13)Unmanned Aerial Vehicles (UAVs) have widely become necessities for the military sectors and still the civil sectors because of their multipurpose and high performance. This thesis concentrates on building a comprehensive strategy for managing UAV projects and enshrines the principles of the Theory of Inventive Problem Solving (TRIZ) to boost creativity in solving design problems. A significant contribution of this thesis is the application and validation of TRIZ within the UAV industry, an area where it is typically used in the industrial and automotive sectors. Through 20 detailed examples, this work demonstrates how TRIZ principles can be utilized to solve design challenges in UAVs, thereby expanding the use of TRIZ beyond its traditional applications. This is about the size, range, weight, engines, and configuration that form the initial section of the paper. Taking this into consideration, it points to factors that set UAVs apart from manned aircraft and how such differences affect functionality and technology. This comprehension helps in studying the uses of UAVs for various kinds of operations such as routine missions, perilous operations, secluded operations, research activities, and sensitive operations that affect the environment. It is also important to outline that the thesis considers the advantages the organizations have from the usage of UAVs, with an emphasis on the aspects connected with cost-saving and performance increase. Thus, all the stages and elements of UAV project management are revealed in detail, illustrating the consideration of preliminary and current concepts and final project acceptance and review of a production key. Shows the sizes and definitions of the critical phases, including System Requirements Review (SRR), Preliminary Design Review (PDR), and Critical Design Review (CDR). Methods like Earned Value Management and Critical Path Analysis are applied to coordinate with each sub-process for sufficiently accurate management of the requirements, optimizing developmental phases, and improving project management efficiency. The study covers typical issues in the context of UAV programs and offers information regarding the existing crucial issues related to resource management, new technologies, human factors, and possible regulation. Another key contribution of this thesis is the development of a new methodology for risk management specifically tailored for UAV projects. This methodology introduces a systematic process to calculate risk scores and formulate action plans to mitigate risks. By applying this method, practical examples in the thesis show how it significantly reduces setbacks, saves time, and enhances overall project efficiency, particularly when compared to traditional risk management approaches. Risk management is also an important factor with a clear plan described for operational risks of the UAV operations and the environment. Some factual cases of UAV occurrences are described from which practical conclusions can be drawn and rules and regulations aimed at reducing the risks and increasing the safety and dependability of UAV operations can be developed. By applying the principles of TRIZ, the thesis put forward a methodical framework for stimulating innovations in the area of UAV design and usage. One of the paper's key successes is that it examines different approaches to resolving multi-faceted engineering difficulties, where contradiction analysis and inventive principles are applied to enhance the function and performance of UAVs. Additionally, this thesis makes a substantial contribution to requirement management for UAV systems. While existing literature identifies certain important parameters (such as cruise speed and control stations), this research identifies and expands on additional critical parameters, including payload, UAV configuration, ground control stations, and data links, that must be considered for a comprehensive requirements management framework for UAVs. In addition to theoretical implications, this research provides project managers with practical tools to improve outputs and advance technology in the context of UAVs. In the future, the thesis underlines the importance of the dynamic nature and improvement of the approaches to managing UAV project processes. This work supports the practice of organizational culture change that follows the approach of TRIZ, as well as such measures in managing risks that will advance the development of UAVs further. The aim is to keep the UAV systems as updated as possible in terms of available technologies for them to be useful in military uses as well as in civilian usage. Given this, the thesis presents a suitable management model for overseeing UAV projects, which applies the TRIZ techniques for appropriate challenges' identification and, then, analysis of the UAV projects using the conventional project management approaches to de-risk the projects and encourage innovations. This is because its goal is to make a major contribution to extending understanding and expertise about UAVs; in other words, improving innovation and use of UAV systems across as many industries as possible throughout the world.
-
ÖgeCavitation performance improvement of engine cooling pump(Graduate School, 2025-01-22)As part of this study, the cavitation issue observed at the specific operating point of the water pump used in the cooling system of an off-road vehicle was investigated, and an optimization process was conducted to address the problem. The optimization process consisted of three stages. In the first stage, based on the insights gained from a literature review, different designs for the impeller's blade leading-edge profile were tested. The impact of three different blade leading edge configurations (v0, v1, and v2) on the impeller's cavitation performance was investigated using 3D CFD analysis. The initial analyses were performed in steady-state conditions using ANSYS CFX. Regions on the impeller with pressures below the vapor pressure of the fluid were compared, and the optimal design (v2) was selected. Following the selection of the optimal design, cavitation analyses were conducted on the pump model with the baseline impeller and the pump model with the optimized impeller using ANSYS CFX. These analyses employed the Rayleigh-Plesset cavitation model and were solved under time-dependent conditions. The results demonstrated that the optimized design exhibited superior cavitation performance compared to the baseline design. The optimized impeller was then manufactured and subjected to experimental cavitation tests. These tests revealed that the optimized impeller allowed the pump to operate at 30% lower inlet pressure before cavitation occurred compared to the baseline pump, confirming the significant effectiveness of the optimization process. Subsequently, the final impeller design underwent experimental performance testing, and a validation study was carried out by comparing the experimental results with 3D CFD results. The validation analyses were performed using Siemens StarCCM+ in time-dependent conditions. The comparison between 3D CFD results and experimental data showed a maximum deviation of 3%, confirming the validity of the numerical approach. Performance test results were compared both numerically and experimentally using H-Q curves, which are presented for clarity.
-
ÖgeA metamodel based approach for the shape optimization of a front rail(Graduate School, 2024-12-23)In crash cases, injuries and loss of lifes are inevitable situation most of the time. There are some another considerations in economic, sustainability and production areas from the manufacturer's point of view. There have been some technologic developments in automobile and aerospace industry that pushes manufacturers to produce safer and more profitable products. Bumper, rocker, rail upper and front rail are the main crashworthiness structures for vehicles design. Front rail is one of the most important impact absorber among the all crashworthiness structures in vehicle design area. It is noted that front rail plays the most critical role during the crash in crashworthiness structures. The fuctions of front rail are transmissing the crash force to the middle crumple zone, absorbing impact energy and providing a favorable buckling form during the crash. Absorbing impact energy is the most important parameter among all functions for passenger safety. Before the crash, there is a high kinetic energy for passenger between vehicles or between vehicle and static objects. One of the most considerable condition for crash cases is passenger safety. Crashworthiness structures are the main provider for this case. They absorbs the some portion of kinetic energy and transmits the left part into the passenger zone. It is important for passenger safety that the more energy absorbed by crashworthiness structures because passengers are exposed less impact energy. There have been some optimization studies and design innovations for crashworthiness structures. Also, some material applications are made to overcome in absorbing impact energy consideration for crashworthiness structures. Addition of sub-structures into crashworthiness structures, optimizations for getting less weight structures, structural optimizations are some studies for crashworthiness structures. In real crash test centers, speed of vehicles are specified as encountered in urban areas. Most of the crashes happens in city streets and real tests center used these kind of speed levels. Design modifications, material applications and comparing cases for different speed levels are the main objectives in this study. Firstly, a design approximation is made to absorb more impact energy in optimization cases. Embosses are created on the front rail for this purpose. Relations between embosses and thickness of front rail are specified as design variables. Another purpose of creating embosses on the front rail is getting appropriate buckling form during the crash. Embosses are provides this problem in optimization study. Secondly, some material applications are made for economic and flammability considerations. In crash scenarios, a fire situation can come up and it might melt the crashworthiness structures. Another consideration is fuel consumption. Selecting different materials provide us to have lightweight structure. Specific Energy Absorption (SEA) is another parameter for material selection for crash worthiness structure. Three different materials are used for every optimization process in this study. Lastly, two different speeds are selected to see how front rail behaves under low and high speed conditions and their buckling forms are examined. A stochastic optimizaiton method is selected for optimization processes. Genetic algorithm is used for all optimization studies. Metamodel optimization technics are used with the usage of genetic algorithm. D-optimal point selection is used for sampling process and sequantial response with domain reduction method is used for the selection of next iteration sampling design space. In result section, all six cases are compared with each other for crashworthiness indicators like SEA, peak force, mean crash force et al. After all optimization processes importance of design variables are discussed and metamodels of optimization processes are shown. Von-mises stress distributions of front rails are shown for all six cases to visualize stress distribution. Advantages and disadvantage of all six cases are discussed and their efficiency on this study are indicated.
-
ÖgeQuantitative analysis of aircraft aerodynamic derivatives using the least squares method in a six degrees of freedom flight simulation environment(Graduate School, 2024-08-21)This thesis presents an in-depth analysis of aircraft aerodynamic derivatives using the Least Squares Method (LSM) within a six degrees of freedom (6-DOF) flight simulation environment. The primary objective is to evaluate and compare the performance of Ordinary Least Squares (OLS) and Recursive Least Squares (RLS) methods in estimating aerodynamic parameters under various flight conditions, including ideal, turbulent, and error-induced scenarios. A detailed 6-DOF flight simulation model was developed using data from the SIAI Marchetti S211 aircraft. This model integrates various subsystems, including equations of motion, aerodynamics, engine dynamics, and atmospheric conditions. The Newton-Raphson method was employed to maintain steady-state conditions, ensuring the aircraft's trim state was accurately represented. For solving the differential equations derived from the equations of motion, the Runge-Kutta method was chosen due to its robustness and accuracy in handling the nonlinearities associated with flight dynamics in the simulation model. The aerodynamic forces and moments were linearized using the small disturbance theorem, which simplifies the complex nonlinear equations into a more manageable linear form. This linearization allowed for the formulation of force and moment coefficients as functions of aerodynamic derivatives. These derivatives, critical for understanding the aircraft's behavior, were estimated using both OLS and RLS methods. Realistic flight data was simulated under various conditions, including ideal scenarios without any disturbances, scenarios with atmospheric turbulence, and scenarios with systematic sensor errors. The Dryden turbulence model was used to simulate realistic atmospheric disturbances, providing a continuous representation of turbulence that affects the aircraft during flight. Systematic sensor errors were introduced to understand their impact on the accuracy of parameter estimation. The OLS method provided single-step parameter estimates by processing all data points simultaneously, making it straightforward and computationally efficient. In contrast, the RLS method updated parameter estimates incrementally as new data became available. This dynamic approach allowed the RLS method to adapt to changes over time, making it particularly suitable for real-time applications where system characteristics may vary. Performance metrics such as the $R^2$ statistic and standard deviation were used to evaluate the estimation accuracy. These metrics provided quantitative measures of how well the estimated parameters matched the true values, with the $R^2$ statistic indicating the proportion of variance explained by the model and the standard deviation providing a measure of the estimation precision. The analysis revealed that both OLS and RLS methods produced accurate results under ideal and turbulent conditions. The presence of atmospheric turbulence did not significantly affect the estimation accuracy, as the average error introduced by the turbulence was zero. This robustness highlights the effectiveness of LSM in handling real-world flight data with environmental disturbances. However, when systematic sensor errors were introduced, both OLS and RLS methods showed biased estimation results. The bias was evident in the deviation of the estimated aerodynamic derivatives from their true values, underscoring the importance of accurate and error-free measurement data for reliable parameter estimation. Further analysis demonstrated that increasing the sampling frequency improved the performance of the RLS method. At higher frequencies, such as 50 kHz, the RLS estimates converged more closely to the true values, even in the presence of systematic sensor errors. This improvement is attributed to the reduced information loss in higher frequency sampling, which captures more details and variations in the data that might be missed at lower frequencies. This finding suggests that higher sampling rates can effectively mitigate the adverse effects of sensor errors on parameter estimation. The design of control surface inputs was identified as a crucial factor influencing the accuracy of aerodynamic parameter estimation. Optimal input design, which involves selecting appropriate control surface deflections, ensured accurate estimation results. Conversely, non-optimal inputs led to discrepancies between the estimated and true values. This emphasizes the need for carefully designed excitation maneuvers during flight tests to obtain reliable aerodynamic data. The RLS method demonstrated particular advantages in dynamic environments due to its ability to update estimates in real-time. This adaptive capability allowed it to maintain accuracy even when the system characteristics changed over time. However, the OLS method exhibited slightly better performance at lower frequencies, showing less sensitivity to variations in sampling rates. Both methods showed distinct strengths, with OLS excelling in stable, low-frequency scenarios and RLS proving superior in dynamic, high-frequency conditions. The theoretical expected value formulas for the parameter estimates were validated using the simulation model outputs. This validation confirmed the presence of bias when systematic errors were introduced and reinforced the high accuracy of estimates under both ideal and turbulent conditions. In conclusion, this thesis provides a comprehensive evaluation of OLS and RLS methods for estimating aerodynamic derivatives in a 6-DOF flight simulation environment. The findings demonstrate the robustness of these methods under various flight conditions, highlight the impact of systematic sensor errors, and underscore the importance of optimal input design and high-frequency data sampling under linear database.
-
ÖgeEffect of elastic rotor modelling on helicopter rotor performance and control(Graduate School, 2023)Aim of this study is to investigate the effect on rotor blade elasticity on rotor performance and control angles at hover and forward flight conditions by comparing elsatic rotor solutions to rigid rotor solutions at same flight conditions. Helicopters are air vehicles that can fly at zero airspeed(hover), forward, sideward and even backwards, unlike fixed wing aircrafts which can only fly forward with a minimum flight speed that is defined as stall speed. Helicopters ability to fly like this comes from its main rotor, which is essentially consists of number of wings rotating along a shaft axis By this way, helicopter rotor blades can produce lift, regardless of helicopter flight speeds at any direction. Unlike a fixed wing aircraft, both lift, control and propulsion is happening at main rotor, whereas fixed wing aircrafts produce lift via their wings and produce thrust via their jet engines/propellers. Unique abilities of helicopter rotor come from its ability to control individual blade pitch through azimuth and flapping ability of rotor blades. However, availability of these functionalities requires many parts, which adds cost, design complexity and maintenance problems compared to fixed wing aircraft. Also, rotation of main rotor and complex aerodynamic interactions causes higher vibrations than fixed wing counterparts. Analysis of helicopter rotor is a complex topic due to many moving parts, rotor aerodynamic interactions and blade elasticity. Rotor blades rotate at shaft axis and flaps at flap hinge and has lead-lag motion at lead-lag hinges and also rotor blade pitch varies with azimuth with applied cyclic controls. Since all of this motions changes lift of rotor blade and flapping motion is caused by lift, problem cannot be separated into two different parts and all of rotor lift and rotor dynamics must be solved together. Rotor aerodynamic solution is a complex topic, especially in forward flight where rotor blade tips can approach speed of sound and experiences compressibility related problems at advancing side, and same blade can experience blade stall at retreating side, all in one revolution, periodically. Elastic deformation of rotor blade is dependent all of the mentioned parameters above, and has an effect on both rotor aerodynamics and blade motion. To solve these problems and compare rigid and elastic rotor blades, a blade element momentum theory code in MATLAB is developed and isolated rotor results is validated with FLIGHTLAB rotorcraft analysis tool at same fidelity and at same flight conditions. Then elasticity is implemented into written code and result of rigid and elastic rotor is compared for different forward flight conditions. In the end, results show that effect of elastic rotor is minimal on power requirement for same thrust, however, achieving same lift and propulsive forces requires different control inputs.