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.
Yavuz E.,ASELSAN Inc. |
Telatar Z.,Ankara University
Digital Signal Processing: A Review Journal | Year: 2013
In this paper, it is shown that there is a fundamental flaw in the paper [Chih-Chin Lai, A digital watermarking scheme based on singular value decomposition and tiny genetic algorithm, Digital Signal Processing 21 (2011) 522-527]. The method has watermark ambiguity problem at detector and could not be used as a proof of ownership as stated in the paper. © 2013 Elsevier Inc. All rights reserved.
Usluer S.N.,ASELSAN Inc. |
Hava A.M.,Middle East Technical University
IEEE International Symposium on Industrial Electronics | Year: 2014
A series active filter (SAF) based method for the damping of resonant harmonics created by the LCL-filter of the grid connected PWM-VSI is proposed. Oscillations in multi-megawatt rated high power inverters with LCL-filters are damped with resistors which create undesired power losses typically up to 1% of the rated power of the system. The method stated in this paper overcomes the stability/oscillation problem while providing a solution to the resistive power loss. The proposed SAF compensated system performs satisfactorily under rated load conditions and the transition from passive damping to SAF is flawless. Adaptability of the proposed method to dynamic loads is also advantageous as opposed to passive damping methods. Simplified circuit diagrams and schematics are provided through the paper. Mathematical model of the passively damped filter is compared and contrasted with the SAF compensated system. The validity of the proposed method is proven via simulations. © 2014 IEEE.
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.
Taskin S.,ASELSAN Inc. |
Lodree Jr. E.J.,University of Alabama
International Journal of Production Economics | Year: 2010
This paper addresses a stochastic inventory control problem for manufacturing and retail firms who face challenging procurement and production decisions associated with hurricane seasons. Specifically, the paper presents a control policy in which stocking decisions are based on a hurricane forecast model that predicts the number of landfall hurricanes for an ensuing hurricane season. The multi-period inventory control problem is formulated as a stochastic programming model with recourse where demand during each pre-hurricane season period is represented as a convolution of the current period's demand and an updated estimate of demand for the ensuing hurricane season. Due to the computational challenges associated with solving stochastic programming problems, recent scenario reduction techniques are discussed and illustrated through an example problem. The proposed model specifies cost minimizing inventory strategies for simultaneously meeting stochastic demands that occur prior to the hurricane season while proactively preparing for potential demand surge during the season. © 2009 Elsevier B.V. All rights reserved.
Cigla C.,ASELSAN Inc. |
Alatan A.A.,Middle East Technical University
Signal Processing: Image Communication | Year: 2013
A novel local stereo matching algorithm is introduced to address the fundamental challenge of stereo algorithms, accuracy and computational complexity dilemma. The time consuming intensity dependent aggregation procedure of local methods is improved in terms of both speed and precision. Providing connected 2D support regions, the proposed approach exploits a new paradigm, namely separable successive weighted summation (SWS) among horizontal and vertical directions enabling constant operational complexity. The weights are determined by four-neighborhood intensity similarity of pixels and utilized to model the information transfer rate, permeability, towards the corresponding direction. The same procedure is also utilized to diffuse information through overlapped pixels during occlusion handling after detecting unreliable disparity assignments. Successive weighted summation adaptively cumulates the support data based on local characteristics, enabling disparity maps to preserve object boundaries and depth discontinuities. According to the experimental results on Middlebury stereo benchmark, the proposed method is one of the most effective local stereo algorithm providing high quality disparity models by unifying constant time filtering and weighted aggregation. Hence, the proposed algorithm provides a competitive alternative for various local methods in terms of achieving precise and consistent disparity maps from stereo video within fast execution time. © 2013 Elsevier B.V. All rights reserved.
Aytekin O.,Middle East Technical University |
Zongur U.,ASELSAN Inc. |
Halici U.,Middle East Technical University
IEEE Geoscience and Remote Sensing Letters | Year: 2013
The automatic detection of airports is essential due to the strategic importance of these targets. In this letter, a runway detection method based on textural properties is proposed since they are the most descriptive element of an airport. Since the best discriminative features for airport runways cannot be trivially predicted, the Adaboost algorithm is employed as a feature selector over a large set of features. Moreover, the selected features with corresponding weights can provide information on the hidden characteristics of runways. Thus, the Adaboost-based selected feature subset can be used for both detecting runways and identifying their textural characteristics. Thus, a coarse representation of possible runway locations is obtained. The performance of the proposed approach was validated by experiments carried on a data set of large images consisting of heavily negative samples. © 2004-2012 IEEE.
Turhan M.,ASELSAN Inc.
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2016
Elicitation of requirements is critical for the conformance of a system. However, collecting user information and deriving it into unambiguous and verifiable design requirements present a challenge. Therefore non-functional design requirements are usually ended up with ambiguous statements like easy to use. Within the framework of this problem, this paper presents a user research conducted at the early stage of the development process of an electronic warfare system’s hand terminal. As a result; the implicit user demands on system functions, the specifications of the hand terminal should provide to its users were collected from the stakeholders’ perspective and the research data were clarified in a way guiding designers to define design requirements and realize the final design. © Springer International Publishing Switzerland 2016.
Guzel G.,ASELSAN Inc. |
Koc I.,ASELSAN Inc.
Communications in Computational Physics | Year: 2015
In this study, the Lattice Boltzmann Method (LBM) is implemented through a finite-volume approach to perform 2-D, incompressible, and turbulent fluid flow analyses on structured grids. Even though the approach followed in this study necessitates more computational effort compared to the standard LBM (the so called stream and collide scheme), using the finite-volume method, the known limitations of the stream and collide scheme on lattice to be uniform and Courant-Friedrichs-Lewy (CFL) number to be one are removed. Moreover, the curved boundaries in the computational domain are handled more accurately with less effort. These improvements pave the way for the possibility of solving fluid flow problems with the LBM using coarser grids that are refined only where it is necessary and the boundary layers might be resolved better. © Global Science Press Limited 2015.
Deniz B.,ASELSAN Inc.
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2015
Static code analysis is a software verification method which analyzes software source code in terms of quality, security and reliability. Unlike other verification activities, static analysis can be automated; thus it can be applied without running the software or creating special test cases. Software metrics are widely practiced by many companies and researchers in order to evaluate their software. In this study, the software component quality measurement method which is developed in an embedded software team will be described. The method is based on automatically collected metrics and predetermined set of rules. First, the measured and calculated metrics under this method will be defined and the reasons for selecting these metrics will be described. Then, the software quality score calculation method using these metrics will be explained. Finally, the gains obtained with this method and the future plans will be related. © Springer International Publishing Switzerland 2015.