This study proposes a significant improvement on the classical vector field guidance law. Classical vector field method results in imaginary number some cases. In numerical calculation, imaginary part of the number ignores to obtain well-posed solution. However, negligence of imaginary part negatively affects the optimization workflow and it leads to larger cross tracking errors. In this study, classical vector field method was modified to obtain real numbers in all cases. Owing to the modified new method, cross tracking errors were diminished by 10% compared to the traditional vector field method. Second contribution of this study is to integrate the surrogate optimization technique to the developed robust vector field method in order to tune parameters of the guidance law. To the best of our knowledge, we are the first to combine surrogate optimization method with vector field path following algorithm. Vector field path following algorithm requires optimizing four important key parameters. While the unmanned surface vehicle performs the multi-command tasks, determining the optimum values of these four key parameters for each mission increases the computational costs significantly. Since the surrogate optimization method is more suitable for the time-consuming objective functions, it is preferred instead of the most popular optimization technique, genetic algorithm. Surrogate optimization method integrated robust vector field path following algorithm determines optimum parameters approximately 10 times faster than the genetic algorithm integrated vector field method. In addition to the time advantage of the developed model, the proposed method provides a navigation that causes less cross tracking errors compared to classical technique.
In this study, the numerical solutions for the steady-state heat conduction problem with uniform heat source, the steady-state heat conduction problem with convective heat transfer and the transient heat conduction problem have been developed using finite difference method. These numerical solutions have been validated with analytical solutions. After observing the good agreements between numerical solutions and analytical solutions, these three different problems combined to simulate the tandem welding process. The first objective of this study is to present a numerical simulator for the transient heat conduction problem that includes non-uniform moving heat sources and convective heat transfer term. This numerical simulator contains explicit and implicit time discretization methods. In this simulator, it is possible to change the grid sizes, time step sizes, total simulation time, distance between electrodes, magnitude of the sources' power, speed of the sources, etc. Secondly, the temperature distribution of single and twin wire welding processes have been compared using proposed numerical simulator to investigate the premature solidification of liquid metal in low-temperature zone of molten pool. Thirdly, experimental study was carried out using Fluke Thermal Imager to validate numerical results. It was obtained that the maximum temperature of numerical result is very close to the maximum temperature of experimental result with 0.248 % error. Finally, the all Matlab codes related to developed numerical simulator have been added to Appendix to facilitate other researchers’ work.
This study presents a simulator to obtain numerical solution of convection-diffusion equation. It includes explicit, fully implicit and semi-implicit time discretization techniques. In addition to time discretization techniques, this simulator contains several space discretization methods such as first-order upstream and
Bu çalışmada, raylı sistem araç gövdelerinde kullanılan EN AW 6005A T6 alaşımlı profillerin gaz altı kaynağı yapılırken meydana gelen ısı akışının iki boyutlu sayısal bir simülatörü geliştirilmiştir. İş parçası üzerinde oluşan sıcaklık dağılımı, düzgün olmayan hareketli ısı kaynakları ve taşınımla ısı transferi terimini içeren geçici ısı iletimi probleminin sonlu farklar yöntemi kullanılarak çözümlenmesiyle elde edilmiştir. Bu çalışmanın amacı, kaynak işlemindeki erimiş havuzun düşük sıcaklık bölgesinde sıvı metalin erken katılaşmasını önleyecek optimum sıcaklık dağılımını, geliştirilen simülasyon sayesinde araştırabilmektir. Önerilen iki boyutlu simülatör sayesinde, optimum sıcaklık dağılımını elde etmek için yapılacak olan deneylerin sayısı azaltılarak işletme maliyetleri düşürülebilecektir. Geliştirilen simülatörün en belirgin avantajları, zaman adımı boyutlarını, ızgara boyutlarını, toplam simülasyon süresini, kaynakların güç büyüklüklerini, elektrotlar arasındaki mesafeyi, kaynakların hızını değiştirebilmektir. Ayrıca bu simülatör, farklı malzemelerde tek telli kaynak ve tandem kaynak işlemleri için de kullanılabilir. İkinci olarak, sayısal sonuçları doğrulamak için Türkiye Raylı Sistem Araçları Sanayi A.Ş' de (TURASAS) Fluke Thermal Imager kullanılarak deneysel çalışma gerçekleştirilmiştir. Sayısal analizden elde edilen maksimum sıcaklığın, deneysel sonucun maksimum sıcaklığından sadece %1 farklı olduğu görülmüştür. Bu sonuç, önerilen iki boyutlu simülatörün, deneysel çalışma ile uyumlu olduğunu göstermektedir. Son olarak, geliştirilmiş iki boyutlu sayısal simülatör ile ilgili tüm Matlab kodları, bu çalışmanın üç boyutlu sayısal simülasyonu üzerinde çalışmak isteyen diğer araştırmacıların çalışmalarını kolaylaştırmak için makalenin sonuna eklenmiştir.
This study proposes a stable and robust path following algorithm for Unmanned Surface Vehicles (USVs). The main objective of this paper is to optimize a key parameter in the improved algorithm to minimize tracking errors. In this study, firstly a stability criterion is developed to limit this parameter and make stable navigation. This model determines the unique target points for each time step using the optimum and flexible parameter in contrast fixed value used in previous studies. The proposed stability criterion and the turning rate data obtained from the previous time step are used to determine this optimum parameter. It provides smooth and precise navigation at critical points like as sharp turning maneuvers. Moreover, it includes saturation for maximum turning rate to make realistic navigation. The proposed model in this study reduces tracking errors by around 20% compared to the conventional carrot-chasing algorithm. Finally, a numerical simulator for USVs in the Matlab environment has been included in the Appendix to support the work of other researchers.
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