Elektromanyetik Fırlatıcıların Geçici Etkilerini Modelleme Teknikleri

Although electromagnetic launchers (EMLs) are better than gun-powder-based launchers, they have to endure severe electrical and mechanical conditions. Therefore, the optimal design and accurate simulations of these devices are essential. The inductance and electromotive force (EMF) variations in the transient, which significantly impact the launch process, are modeled. Moreover, velocity skin effect (VSE) is added to the EML calculations in an effective way. Commercial finite element software cannot solve the electromagnetic aspects of such a high-speed application with a transient solver in 3-D. Although 2-D approximations can be used, such an approximation overestimates VSE resistance due to geometry simplifications. In this thesis, a novel quasi-transient 3-D Finite Element Method (FEM) model where the air-armature region's conductivity is varied to emulate the high-speed motion of the armature is proposed. These propositions are compared for experimental results with different EMLs, EMFY-1, and EMFY-2 and showed good agreement.Elektromanyetik fırlatıcılar, barut tabanlı fırlatıcılardan daha iyi olsalar da, ağır elektriksel ve mekanik koşullara dayanmaları gerekir. Bu nedenle, bu cihazların optimum tasarımı ve doğru simülasyonları çok önemlidir. Atış sürecini önemli ölçüde etkileyen geçici olaydaki endüktans ve elektromotor kuvvet (EMF) varyasyonları modellenmiştir. Ayrıca, bu hesaplamalarına etkili bir şekilde hız deri etkisi (HDE) eklenmiştir. Ticari sonlu eleman yazılımı, bu kadar yüksek hızlı bir uygulamanın elektromanyetik yönlerini 3 boyutlu olarak bir geçici çözücü ile çözemez. 2-D yaklaşımları kullanılabilmesine rağmen, böyle bir yaklaşım, geometri basitleştirmelerinden dolayı, VSE direncini olduğundan fazla tahmin etmektedir. Bu tezde, armatürün yüksek hızlı hareketini taklit etmek için hava-armatür bölgesinin iletkenliğinin değiştirildiği ̆yeni bir yarı-geçici 3-D Sonlu Eleman Yöntemi (SEY) modeli önerilmiştir. Bu model, farklı elektromanyetik fırlatıcılarla, EMFY-1 ve EMFY-2 ile, deneysel sonuçlar karşılaştırıldı ve iyi bir uyum gösterdiği görüldü.M.S. - Master of Scienc

Electromagnetic Launcher Speed Control with a Multilevel Fast Triggering Time Algorithm (MFTTA)

Electromagnetic launchers (EMLs) can provide accurate speed control of a projectile compared to gun-powder based alternatives. However large-caliber launchers have several pulse power supply (PPS) modules connected in parallel to reach the required current levels. Determination of the triggering instants of these parallel PPS modules is a crucial part of the launch mechanism. The triggering instants does not only affect the exit velocity but also the forces on the armature which can lead to transition i.e. separation of the armature from the rails. In this study, a triggering sequence optimization method that is faster than other alternatives in the literature and take into account speed-dependent parasitic masses and transition phenomena. Real-coded genetic algorithm (RCGA) and Partical Swarm Optimization (PSO) are used to create bencmarks. 32 capacitive PPS modules with 8 MJ total energy is used. With the achieved accuracy and speed, this study offer: An effective speed control algorithm with several physical constraints

Optimization of a Convex Rail Design for Electromagnetic Launchers

A rail geometry with a convex cross section instead of a rectangular one provides a higher contact area, uniform current density, and less transition on the contact surface, and it increases the performance in electromagnetic launchers. In addition, the design of convex rails should be considered together with armature structure, the distance between rails, rail length, and parasitic masses that all have an influence on the overall efficiency and armature/rail transition. A novel complete rail and launch package optimization method is presented in this article. In the first part of this article, the optimum convex rail cross sections for five different separation values are found to obtain uniform current density distribution on rail cross section. For this part, a transient finite element (FE) model in 2-D is developed to calculate the current density distribution and combined with a real-coded genetic algorithm (GA). Then, the armature and sabot petal masses are calculated for each optimized rail geometry and each separation values. In the second part, the efficiency of each optimum design with different separation values is evaluated by a transient 3-D FE model with transient solver taking the calculated armature and sabot petal masses into account. Finally, the length of the rails of the final design is investigated for the transition phenomena. It is observed that 48-mm rail separation with 12.9- and 21-mm elliptical cross-sectional parameters has the highest exit velocity (2355 m/s) for 400-g projectile with uniform current density at inner rail surfaces

Optimization of a Convex Rail Design for Electromagnetic Launchers

A rail geometry with a convex cross section instead of a rectangular one provides a higher contact area, uniform current density, and less transition on the contact surface, and it increases the performance in electromagnetic launchers. In addition, the design of convex rails should be considered together with armature structure, the distance between rails, rail length, and parasitic masses that all have an influence on the overall efficiency and armature/rail transition. A novel complete rail and launch package optimization method is presented in this article. In the first part of this article, the optimum convex rail cross sections for five different separation values are found to obtain uniform current density distribution on rail cross section. For this part, a transient finite element (FE) model in 2-D is developed to calculate the current density distribution and combined with a real-coded genetic algorithm (GA). Then, the armature and sabot petal masses are calculated for each optimized rail geometry and each separation values. In the second part, the efficiency of each optimum design with different separation values is evaluated by a transient 3-D FE model with transient solver taking the calculated armature and sabot petal masses into account. Finally, the length of the rails of the final design is investigated for the transition phenomena. It is observed that 48-mm rail separation with 12.9- and 21-mm elliptical cross-sectional parameters has the highest exit velocity (2355 m/s) for 400-g projectile with uniform current density at inner rail surfaces

Investigation of Factors Affecting Students' Science Achievement According to Student Science Teachers

In this study, it was aimed to investigate the factors affecting students' science achievement according to student science teachers. The survey model which is one of the quantitative research methods was used. The sample was consisted of total 606 student science teachers from four state universities in Turkey. The data were obtained by using the Questionnaire of Factors Affecting Students' Science Achievement (QFASSA). The data were analyzed by using the descriptive analyzing technique. The factors affecting students' science achievement were analyzed under five dimensions. The result of the study shows that the most important factors affecting student science achievement according to student science teachers are the items in the dimensions of teacher and curriculum. The results also indicates that the most important predictor of science achievement is. teaching the topics in a way that may arouse the students' curiosity. in the teacher dimension of QFASSA

A comparison of velocity skin effect modeling with 2-D transient and 3-D quasi-transient finite element methods

The analysis of the velocity skin effect (VSE) in electromagnetic launchers (EMLs) requires a 3-D transient finite element method, unlike magnetic skin and proximity effects. However, VSE is dominant at high speeds, and this creates convergence problems when moving or deformed mesh physics is used in a transient FEM in the 3-D analysis. Commercial finite element software cannot solve the electromagnetic aspects of such a high-speed application with a transient solver in 3-D. Although 2-D approximations can be used, such an approximation overestimates VSE resistance due to geometry simplifications. In this study, we proposed a novel quasi-transient 3-D FEM model where the air-armature region’s conductivity is varied to emulate the high-speed motion of the armature. Results show that the 2-D approximation overestimates the VSE resistance by almost 40%. The proposed VSE model has been included in the EML model, and simulation results are compared for experimental results with different EMLs, EMFY-1, and EMFY-2 and showed good agreement

Middle, high school and university students’ predictors of science achievement

Bu çalışmada, farklı öğretim seviyelerindeki öğrencilerin algılarına dayalı olarak fen derslerinde öğrencilerin akademik başarılarını etkileyen faktörleri belirlemek amaçlanmıştır. Bu araştırma tarama türü araştırma yönteminde gerçekleştirilmiştir. Araştırmanın örneklemini Bartın, Hatay, Kilis ve Uşak illerindeki 179 ortaokul, 128 lise ve 206 üniversite olmak üzere toplam 513 öğrenci oluşturmaktadır. Veri toplama aracı olarak Fen Başarısını Etkileyen Faktörler Anketi (FBEFA) adında nitel bir anket kullanılarak öğrencilerin fen başarısı üzerine etki eden faktörler hakkındaki görüşlerinin belirlenmesi amaçlanmıştır. Elde edilen veriler içerik analizi yönteminden yararlanılarak çözümlenmiştir. Çalışmada elde edilen kategorilere göre bulgular incelendiğinde, ortaokul, lise ve üniversite düzeylerindeki öğrencilerin büyük bir bölümünün fen başarısında en önemli faktörlerin öğrenci merkezli, sonra ise öğretmen merkezli olduğunu ifade ettikleri belirlenmiştir. Öğrencilerin fen başarısını etkileyen ilk on faktör ortaokul, lise ve üniversite düzeylerinde karşılaştırmalı olarak incelendiğinde ise ortak faktörlerin; konu tekrarı, deney yapmak ve öğretmenin ders anlatım yöntem ve tekniği şeklinde olduğu belirlenmiştirThis study has aimed to identify the factors that influence the academic success based on the perceptions of students with different education levels. This research was conducted using survey research method. The sample involved 179 middle school students, 128 high school students, and 206 university students (Department of Science Teaching) from Bartın, Hatay, Kilis and Uşak provinces. A qualitative survey called Survey on Factors Influencing Success in Science (SFISS) was used to identify students’ opinions about the factors that influence their success in science. The data was analyze using content analysis method, which is the most preferred method in qualitative studies. When the results of the study were generally examined according to the categories obtained from the study, it was observed that most students studying at middle schools, high schools and universities stated that the most important factors for the success in science classes is first studentcentered, then teacher-centered. It was identified that the most important 10 factors that influence students’ success in science classes vary according to their levels of education. When the first 10 factors that influence success of students in science were compared with regards to middle school, high school and university levels, common factors appeared as review the subjects, do the experiments, and teaching methods, and techniques used by the teache

Solar Power Generation Analysis and Forecasting Real-World Data Using LSTM and Autoregressive CNN

Generated power of a solar panel is volatile and susceptible to environmental conditions. In this study, we have analyzed variables affecting the generated power of a 17.5 kW real-world solar power plant with respect to five independent variables over the generated power: irradiance, time of measurement, panel's temperature, ambient temperature and cloudiness of the weather at the time of measurement. After our analysis, we have trained three different models to predict intra-day solar power forecasts of the plant. Our models are able to predict future power output of the solar power plant with less than 10% RMSE without requiring additional sensor data, e.g. a camera to observe clouds. Based on our forecasting accuracy, our study promises: fast, scaleable and effective solutions to solar power plant maintainers and may facilitate grid safety on a large scale

Öğrencilerin Fen Bilimleri Derslerindeki Başarılarına Etki Eden Faktörlerin Belirlenmesine Yönelik Bir Ölçeğin Geliştirilmesi

Bu çalışma, öğrencilerin fen başarılarına etki eden faktörleri tespit etmeye yönelik geçerli ve güvenilir bir ölçeğin geliştirilmesi amaçlanmıştır. Fen Başarısına Etki Eden Faktörler Ölçeği (FBEFÖ) geliştirilirken öncelikle öğrenci görüşlerine başvurularak ve ilgili eğitim literatüründen faydalanılarak madde havuzu oluşturulmuştur. Ölçeğin kapsam geçerliğinin belirlenmesi amacıyla uzman görüşü alınmıştır. Uzman görüşü doğrultusunda revize edilen ölçek 681 üniversite öğrencisine uygulanmıştır. Yapılan madde analizi sonucunda madde toplam korelasyon değeri .30’dan küçük olan maddeler ölçekten çıkarılmıştır. Açımlayıcı faktör analizi yapıldıktan sonra binişik olduğu düşünülen maddeler çıkarılmış ve son haliyle ölçeğin toplam varyansın %45.045’ini açıkladığı görülmüştür. Öğrenci, öğretmen, materyal, öğrenme ortamı ve öğretim programı şeklinde beş alt boyuttan oluşan toplam 29 maddelik ölçeğin tamamı için Cronbach-Alpha iç tutarlık katsayısı .865 olarak hesaplanmıştır. Çalışma sonucunda geçerlik ve güvenirliği ortaya konan geliştirilen ölçeğin, ilerde fen başarısı belirleyicileri üzerinde yapılan araştırmalar için ışık tutacağı düşünülen geçerli, güvenilir ve kullanışlı bir ölçek olduğu düşünülmektedir