Browsing by Subject "Optimization method"

Now showing 1 - 5 of 5

Open Access
3D electron density estimation in the ionosphere
(IEEE, 2014) Tuna, Hakan; Arıkan, Orhan; Arıkan, F.
Ionosphere has ion distribution which is variable in space and time. There have been physical and empirical studies for modeling the ionosphere. International Reference Ionosphere extended to Plasmasphere (IRI-Plas) is the most recent model developed for this purpose. However, IRI-Plas presents a model about the ionosphere and its compliance with the instantaneous state of the ionosphere does not provide the accuracy needed for engineering purposes. One of the important information sources about the instantaneous state of the ionosphere is GPS signals. In this study, constructing the ionosphere which is compatible with both the instantaneous ionosphere measurements and the physical structure of the ionosphere is presented as an optimization problem, and solved by using the particle swarm optimization technique. The ionosphere over Turkey is investigated by using the proposed optimization method and the importance of the instantaneous ionosphere measurements obtained from GPS signals is demonstrated.
Open Access
Determining F2 layer parameters via optimization using IRI model and IONOLAB TEC estimations
(IEEE, 2011) Şahin, O.; Sezen, U.; Arıkan, F.; Arıkan, Orhan
We know that F2 layer of the ionosphere is most important layer in the progaration of high frequency (HF) waves. In this study, The relation of the height (HmF2) and the critical frequency (FoF2) of F2 layer-among the parameters of the Internation Reference Ionesphere (IRI) model-to the Total Electron Content (TEC) structure of ionosphere is investigated within their defined parametric range. These two parameters are then optimized using IONOLAB TEC estimations. Performance of the optimization algorithm is examined seperately for the cases of processing daily (24-hour) and hourly TEC data. It is observed that using hourly data produce results with much smaller errors. By using this optimization method, the height and the critical frequency of F2 layer are obtained for countries located on low and high latitudes including Turkey for the same quite day. Results are compared with ionosonde data and it is observed that error norms were in an acceptable range. By this way it is attained the more realistic electrical structure of ionosphere.
Open Access
On reduced order modeling of flexible structures from frequency response data
(IEEE, 2014) Demir, Okan; Özbay, Hitay
In order to identify the dominant flexible modes of a flexible structure with an input/output delay, a numerical method is proposed. The method uses a frequency domain approach (frequency response data) to estimate the resonating frequencies and damping coefficients of the flexible modes, as well as the amount of the time delay. A sequential NLLS (Non-Linear Least Squares) curve fitting procedure is adopted. It is illustrated that such a Newtonian optimization method has the capability of finding the parameters of a reduced order transfer function by minimizing a cost function involving nonlinearities such as exponential and fractional terms.
Open Access
Parçacık sürü Optimizasyonu ile Dağıtık Tespit
(IEEE, 2011-04) İnce, O.; Efe, M.; Arıkan, Orhan
Doğadan esinlenerek geliştirilen optimizasyon yöntemleri, kullanım kolaylıkları ve yüksek performansları nedeniyle pek çok farklı disiplinde kendilerine uygulama alanı bulmaktadırlar. Bu çalışmada, son yıllarda yoğun ilgi gören dağıtık tespit problemine, literatürde Parçacık Sürü Optimizasyonu olarak bilinen yöntem uygulanmıştır. Temel bir paralel dağıtık topoloji üzerinde denenen senaryolarda PSO'nun performansının doğruluk ve güvenilirlik ve hız açısından oldukça yüksek olduğu gözlenmiştir.
Open Access
Quadrupedal bounding with an actuated spinal joint
(IEEE, 2011) Çulha, Utku; Saranlı, Uluç
Most legged vertebrates use flexible spines and supporting muscles to provide auxiliary power and dexterity for dynamic behaviors, resulting in higher speeds and additional maneuverability during locomotion. However, most existing legged robots capable of dynamic locomotion incorporate only a single rigid trunk with actuation limited to legs and associated joints. In this paper, we investigate how quadrupedal bounding can be achieved in the presence of an actuated spinal joint and characterize associated performance improvements compared to bounding with a rigid robot body. In the context of both a new controller structure for bounding with a body joint and existing bounding controllers for the rigid trunk, we use optimization methods to identify the highest performance gait parameters and establish that the spinal joint allows increased forward speeds and hopping heights. © 2011 IEEE.