Analytical based modeling of damage induced by electromagnetic pressure impact of lightning on aerodynamic surfaces: Aircraft wing and wind turbine blade

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Tarih
2024-05-08
Yazarlar
Soysal, Aysun
Süreli Yayın başlığı
Süreli Yayın ISSN
Cilt Başlığı
Yayınevi
Graduate School
Özet
The survivability of systems (e.g., aircrafts and wind turbine blades) routinely operating in open terrain and weather-independent conditions is generally defined as the ability of the systems to avoid or resist harsh environments, including man-made and non-man-made. One of the non-man-made enemy environments is the lightning strike. Thus, the interaction of lightning strike and the materials of such systems must be considered in the procedures regarding design, production, certification requirements, and hence survivability of the systems. In the present thesis, the interaction of lightning strike with an aeronautical material is investigated. In this context, firstly, an analytical-based improved electromagnetic pressure impact model (IEPIM) of lightning is established. Subsequently, with the help of the pressure impact model established, two analytical-based damage models are established. The first one is the damage model for an aircraft wing and the latter one is the damage model for a wind turbine blade. For each damage model, two different beam theories are considered: Bernoulli- Euler beam theory and Timoshenko beam theory. Then, some applications of the pressure model and damage models established are performed, and then the results obtained are confirmed with appropriate studies in open the literature whenever the comparison is possible. According to the findings of the thesis, it was found that the pressure model (IEPIM) established in the thesis study was in good agreement with the experimental studies taken from the open literature for 100 kA and 200 kA lightning current. Moreover, it was observed that the pressure model provided quite correct results during the first 25 μs for 100 kA current and the first 50 μs for 200 kA current. In the damage model of an aircraft wing, which is one of the models developed in the thesis, the damage caused by the pressure impact of lightning on an aircraft wing was obtained with respect to the Timoshenko type damage model and the Bernoulli-Euler type damage model. Then, the amounts of the damage when lightning struck the root, middle and tip of the aircraft wing were calculated according to both the Timoshenko type damage model and the Bernoulli-Euler type damage model. Considering the results of the Bernoulli-Euler type damage model and the Timoshenko type damage model, it was seen that at the wing root, middle of the wing and wing tip, the largest deflections were respectively the bending deflection, torsional deflection, and bending-induced rotational deflection. In the aircraft wing damage model established, even though there was a flexural forcing function, not only bending deflection but also both torsional deflection and rotational deflection caused by cross-sectional area rotation emerged in the aircraft wing. The reason for this is that the damage model developed is established in a coupled (i.e., interactive) form. This chosen approximation is closer to the physical nature of the aircraft wing system. When the Timoshenko type damage model and the Bernoulli-Euler type damage model are compared in terms of efficiency, it has been determined that the Timoshenko type model provides less deviation than the Bernoulli-Euler type model in terms of the maximum positive damage amount, based on the lightning strike points considered. In the applications of structural analysis problems, when a Timoshenko type model is compared with a Bernoulli-Euler type model for the same material properties, it is claimed that the Bernoulli-Euler type model is used for more rigid structures and therefore gives less deflection. However, in the damage model we have established, there is a dynamic analysis and the forcing function considered in the damage model has a more complex structure than the known standard forcing functions. For these reasons, it is expected that the results of this study can be different from the known standard results. Moreover, in the free vibration analysis subsection performed before the forced vibration analysis subsection of the thesis study, it was seen that the Timoshenko type model gave lower vibration frequencies than the Bernoulli-Euler type model for the same material properties. Furthermore, it was found that the vibration mode shapes associated with these vibration frequencies had lower amplitudes compared to those obtained from the Bernoulli-Euler type model. Thus, it is an expected result that the amounts of the deflection obtained from the Timoshenko type model are lower than the amounts of the deflection obtained from the Bernoulli-Euler type model. Additionally, regarding the deflected shape of the aircraft wing, it was found that in both models, even if lightning strikes a single point on the wing, the deflections in the wing spread throughout the wing. This is because the physical behavior of the forcing function considered in the damage model corresponds to a distributed load form. In the case of the damage model of the wind turbine blade, when lightning strikes the middle of a wind turbine blade, the amount of damage to the blade caused by the pressure impact of the lightning is calculated according to both the Timoshenko type damage model and the Bernoulli-Euler type damage model for the clamped-free (C-F), clamped-clamped (C-C), and simply supported-simply supported (S-S) boundary conditions and then the results obtained were compared for both models. Accordingly, firstly, the damage model was solved by free vibration analysis and then by forced vibration analysis. Then, using the solution of the model, results were obtained for both the Timoshenko type damage model and the Bernoulli-Euler type damage model for the same material properties. Compared the both models with each other for different boundary conditions, when lightning strikes the middle of a wind turbine blade with C-C boundary condition, the Bernoulli-Euler type damage model provides better result in terms of the result of an experimental study with similar conditions taken from the literature than the Timoshenko type damage model in calculating the damage caused by the electromagnetic pressure impact of lightning. The reason for this is that wind turbine blades are relatively slender structures (i.e., structures with width ratios of at least 1/10 of the length ratios), which makes them more suitable for Bernoulli-Euler type models. On the other hand, the Timoshenko type model is more suitable for relatively shorter and thicker (stubby) structures. When the effect of the boundary conditions of the blade on the occurrence of lightning-induced damage on the wind turbine blade is investigated, in case of neglect of the axial load caused by the rotation of the blade, lightning-induced damage occurs most in the C-C, C-F and S-S boundary conditions, respectively. Among these boundary conditions, in the case of the absence of axial load, when a comparison is made on the basis of the damage model, the Bernoulli-Euler type damage model gives more damage in terms of bending deflection than the Timoshenko type damage model. In addition, while the Bernoulli-Euler type damage model gives larger results in terms of torsional deflection in the C-C and C-F boundary conditions, the Timoshenko type damage model gives more torsional deflection in the S-S boundary condition. Additionally, again in the absence of axial load, the largest damage types are bending, bending-induced rotational and torsional damage, respectively. As in the lightning damage model of the aircraft wing, even though there is only a flexural forcing function in the lightning damage model of the wind turbine blade, torsional and bending-induced rotational deflections as well as bending deflection occur due to the coupled form of the model. Furthermore, as in the aircraft wing damage model, the forcing function in the damage model has a distributed load effect. Therefore, even if the lightning strike hits a single point in the middle of the wind turbine blade, a pressure spread occurs on the blade surface due to the impact of the lightning, and this pressure spread acts in a radial direction along the blade. On the other hand, in the presence of axial load for the C-F boundary condition, the Timoshenko type damage model gives more deflection amount in terms of bending and torsional deflection than the Bernoulli-Euler type damage model.
Açıklama
Thesis (Ph.D.) -- Istanbul Technical University, Graduate School, 2024
Anahtar kelimeler
damage analysis, hasar analizi, damage, hasar, damage detection, hasar tespiti, wind turbines, rüzgar türbinleri, aircraft wings, rüzgar kanatları, aircraft performance, uçak performansı, aircraft design method, uçak tasarım yöntemi, lightning, yıldırım
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