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Ankara, Turkey

Dursun T.,ASELSAN Inc. | Soutis C.,University of Manchester
Materials and Design | Year: 2014

Aluminium alloys have been the primary material for the structural parts of aircraft for more than 80. years because of their well known performance, well established design methods, manufacturing and reliable inspection techniques. Nearly for a decade composites have started to be used more widely in large commercial jet airliners for the fuselage, wing as well as other structural components in place of aluminium alloys due their high specific properties, reduced weight, fatigue performance and corrosion resistance. Although the increased use of composite materials reduced the role of aluminium up to some extent, high strength aluminium alloys remain important in airframe construction. Aluminium is a relatively low cost, light weight metal that can be heat treated and loaded to relatively high level of stresses, and it is one of the most easily produced of the high performance materials, which results in lower manufacturing and maintenance costs. There have been important recent advances in aluminium aircraft alloys that can effectively compete with modern composite materials. This study covers latest developments in enhanced mechanical properties of aluminium alloys, and high performance joining techniques. The mechanical properties on newly developed 2000, 7000 series aluminium alloys and new generation Al-Li alloys are compared with the traditional aluminium alloys. The advantages and disadvantages of the joining methods, laser beam welding and friction stir welding, are also discussed. © 2013 Elsevier Ltd. Source

Turker T.,Yildiz Technical University | Buyukkeles U.,ASELSAN Inc. | Bakan A.F.,Yildiz Technical University
IEEE Transactions on Industrial Electronics | Year: 2016

High-performance current control is required to obtain a smooth output torque in permanent-magnet synchronous motor (PMSM) drives. In this manner, a new discrete-time robust predictive current controller is presented for PMSM drives. Controller and current prediction schemes are designed based on the dead-beat structure. The dead-beat control has good transient response, but it suffers from parametric uncertainties and unmodeled dynamics. In order to provide robustness, a discrete-time integral term is added to the dead-beat current prediction. The stability analysis is carried out considering the prediction error dynamics, nonlinear uncertain model of PMSM, and the integral action as the states of the overall system. The designed robust predictive controller is tested through numerical simulations and experiments. The proposed controller is easy to implement and suitable for high-performance PMSM applications. © 2016 IEEE. Source

Tap K.,ASELSAN Inc. | Pathak P.H.,Ohio State University | Burkholder R.J.,Ohio State University
IEEE Transactions on Antennas and Propagation | Year: 2011

Complex source point (CSP) beams (or CSPBs) are known to be exact solutions of Maxwell's equations. Hence they can be used as basis functions to represent the electromagnetic fields generated by arbitrary sources. In this work, it is shown that any fully vector electromagnetic field can be represented exactly as an expansion of CSPBs originating from a relatively arbitrary surface enclosing the sources. Three different variants of the CSPB representation are first considered for a spherical expansion surface and their properties are discussed. It is shown that the CSPB expansion set can be conveniently truncated by selecting only the significantly contributing beams for efficient field calculations. The CSPB representations are next extended to the case of relatively arbitrary expansion surfaces. Numerical results are presented to demonstrate and compare the convergence and efficiency of the three approaches. © 2006 IEEE. Source

Subasi Y.,ASELSAN Inc. | Demirekler M.,Middle East Technical University
Automatica | Year: 2014

In this study we define a new observability measure for stochastic systems: The mutual information between the state sequence and the corresponding measurement sequence for a given time horizon. Although the definition is given for a general system representation, the paper focuses on the linear time invariant Gaussian case. Some basic analytical results are derived for this special case. The measure is extended to the observability of a subspace of the state space, specifically an individual state and/or the modes of the system. A single measurement system represented in the observable canonical form is examined in detail. A recursive form of the observability measure for a finite time horizon is derived. The possibility of using this form for designing a sensor selection algorithm is demonstrated by two examples. © 2014 Elsevier Ltd. All rights reserved. Source

Pehlivanoglu Y.V.,Turkish Air force Academy | Yagiz B.,ASELSAN Inc.
Aerospace Science and Technology | Year: 2012

A new optimization algorithm is proposed and tested for four different test cases: benchmark test functions, multi-element airfoil optimization in subsonic flow, active flow control parameter optimization in transonic flow, and a direct shape optimization of an airfoil in transonic flow. The new algorithm emphasizes the use of an aerodynamic design prediction based on a global and a local surrogate modelling in genetic algorithm structure. A global response surface approximation is modelled by using low-order polynomials. A local response surface approximation is constructed by using neural networks. For all the demonstration problems considered herein, remarkable reductions in the computational times have been accomplished. The new approach significantly decreases the required CFD calls by approximately 50% in multi-element airfoil optimization; more than 70% in active flow control parameter optimization; and approximately 50% in direct shape optimization problem. © 2011 Elsevier Masson SAS. All rights reserved. Source

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