Now showing items 1-20 of 20

  • A Generic Framework for Building Heterogeneous Simulations of Parallel and Distributed Computing Systems 

    Authors:Dursun, Taner; Daǧ, Hasan
    Publisher and Date:(Springer Heidelberg, 2017)
    There have been many systems available for parallel and distributed computing (PDC) applications such as grids clusters super-computers clouds peer-to-peer and volunteer computing systems. High-performance computing (HPC) has been an obvious candidate domain to take advantage of PDC systems. Most of the research on HPC has been conducted with simulations and has been generally focused on a specific type of PDC system. This paper however introduces a general purpose simulation model that can be ...

  • A New Preconditioner Design Based on Spectral Division for Power Flow Analysis 

    Solution of large sparse linear systems is the most lime consuming part in many power system simulations. Direct solvers based on LU factorization although robust are known to have limited satiability on parallel platforms. Thus. Krylov subspace based iterative methods (i.e. Conjugate Gradient method Generalized Minimal Residuals (GMRES) method) can be used as alternatives. To achieve competitive performance and robustness however the Krylov subspace methods need a suitable preconditioner. In this ...

  • A Recommender Model Based on Trust Value and Time Decay Improve the Quality of Product Rating Score in E-commerce Platforms 

    Authors:Işık, Muhittin; Daǧ, Hasan
    Publisher and Date:(IEEE, 2017)
    Most of the existing products rating score algorithms do not take fake accounts and time decay of users' ratings into account when creating the list of recommendations. The trust values and the time decay of users' ratings to an item may improve the quality of product rating score in e-commerce platforms especially when it is thought that nowadays the majority of customers read the reviews before making a purchase. In this paper we first introduce the concept trust value of users by explaining its ...

  • A sparsity-preserving spectral preconditioner for power flow analysis 

    Due to the ever-increasing demand for more detailed and accurate power system simulations the dimensions of mathematical models increase. Although the traditional direct linear equation solvers based on LU factorization are robust they have limited scalability on the parallel platforms. On the other hand simulations of the power system events need to be performed at a reasonable time to assess the results of the unwanted events and to take the necessary remedial actions. Hence to obtain faster ...

  • Applications of Eigenvalue Counting and Inclusion Theorems in Model Order Reduction 

    Authors:Yetkin, E. Fatih; Daǧ, Hasan
    Publisher and Date:(Springer-Verlag Berlin, 2010)
    We suggest a simple and an efficient iterative method based on both the Gerschgorin eigenvalue inclusion theorem and the deflation methods to compute a Reduced Order Model (ROM) to lower greatly the order of a given state space system. This method is especially efficient in symmetric state-space systems but it works for the other cases with some modifications.

  • Branch outage simulation based contingency screening by gravitational search algorithm 

    Power systems contingency analysis is an important issue for electric power system operators. This paper performs branch outage simulation based contingency screening using a bounded network approach. Local constrained optimization problem representing the branch outage phenomena is solved by the gravitational search algorithm. The proposed method is applied to IEEE 14 30 57 and 118 Bus Test systems and its performance from the point of capturing violations is evaluated. In addition false alarms ...

  • Distributed Memory Parallel Transient Stability Analysis on a PC Cluster with Ethernet 

    On-line transient stability analysis is a necessity for real-time power system control and security. Parallel processing is a natural technology for achieving real-time solution performance. This paper presents a parallel-in-space algorithm based on a multi-level partitioning scheme in a distributed memory cluster environment. The main aim of the research is to decrease the wallclock time of transient stability analysis of large scale power systems by leveraging open source software and commodity ...

  • Double branch outage modeling and simulation: Bounded network approach 

    Authors:Ceylan, Oǧuzhan; Özdemir, Aydoğan; Daǧ, Hasan
    Publisher and Date:(Elsevier Science, 2015)
    Energy management system operators perform regular outage simulations in order to ensure secure operation of power systems. AC power flow based outage simulations are not preferred because of insufficient computational speed. Hence several outage models and computational methods providing acceptable accuracy have been developed. On the other hand double branch outages are critical rare events which can result in cascading outages and system collapse. This paper presents a double branch outage model ...

  • Feature Extraction Based on Deep Learning for Some Traditional Machine Learning Methods 

    Authors:Çayır, Aykut; Yenidoğan, Işıl; Daǧ, Hasan
    Publisher and Date:(IEEE, 2018)
    Deep learning is a subfield of machine learning and deep neural architectures can extract high level features automatically without handcraft feature engineering unlike traditional machine learning algorithms. In this paper we propose a method which combines feature extraction layers of a convolutional neural network with traditional machine learning algorithms such as support vector machine gradient boosting machines and random forest. All of the proposed hybrid models and the above mentioned ...

  • Heuristic Methods for Postoutage Voltage Magnitude Calculations 

    Power systems play a significant role in every aspect of our daily lives. Hence their continuation without any interruption (or with the least duration of interruption due to faults or scheduled maintenances) is one of the key aims of electrical energy providers. As a result electrical energy providers need to check in great detail the integrity of their power systems by performing regular contingency studies of the equipment involved. Among others line and transformer outage simulations constitute ...

  • The impact of text preprocessing on the prediction of review ratings 

    Authors:Işık, Muhittin; Daǧ, Hasan
    Publisher and Date:(Tubitak, 2020)
    With the increase of e-commerce platforms and online applications, businessmen are looking to have a rating and review system through which they can easily reveal the feelings of customers related to their products and services. It is undeniable from the statistics that online ratings and reviews attract new customers as well as increase sales by means of providing confidence, ratification, opinions, comparisons, merchant credibility, etc. Although considerable research has been devoted to the ...

  • Improving Item-Based Recommendation Accuracy with User's Preferences on Apache Mahout 

    Authors:Jabakji, Ammar; Daǧ, Hasan
    Publisher and Date:(IEEE, 2016)
    Recommendation systems play a critical role in the Information Science application domain especially in e-commerce ecosystems. In almost all recommender systems statistical methods and machine learning techniques are used to recommend items to the users. Although the user-based collaborative filtering approaches have been applied successfully in many different domains some serious challenges remain especially in regards to large e-commerce sites for recommender systems need to manage millions of ...

  • On the selection of ınterpolation points for rational Krylov Methods 

    Authors:Yetkin, E. Fatih; Daǧ, Hasan
    Publisher and Date:(Springer-Verlag Berlin, 2012)
    We suggest a simple and an efficient way of selecting a suitable set of interpolation points for the well-known rational Krylov based model order reduction techniques. To do this some sampling points from the frequency response of the transfer function are taken. These points correspond to the places where the sign of the numerical derivation of transfer function changes. The suggested method requires a set of linear system's solutions several times. But they can be computed concurrently by different ...

  • On-Line Transient Stability Assessment Using Matlab Parallel Programming Environment 

    Authors:Soykan, Gürkan; Daǧ, Hasan
    Publisher and Date:(IEEE, 2010)
    Transient Stability Assessment (TSA) is the major part of Dynamic Security Assessment (DSA) in an electric power system. On-line TSA has gained more importance for power system security in last two decades. The decreasing costs of hardware and advanced package programs and techniques encourage researchers to apply parallel programming to the problems that are either too much time consuming or impossible to solve using serial computers. The real-time evaluation of TSA is now almost possible thanks ...

  • Parallel Contingency Analysis Using Differential Evolution Based Solution For Branch Outage Problem 

    Authors:Ceylan, Oǧuzhan; Daǧ, Hasan; Ozdemir, Aydogan
    Publisher and Date:(IEEE, 2010)
    Contingency analysis is one of the most fundamental work an electricity management center operator has to perform regularly. If both bus voltage magnitudes and reactive power flowing on the branches during any type of outages are within the acceptable limits the system is called secure. In this paper we solve the contingency problem using a recently developed local constrained optimization based branch outage problem. The optimization problem resulted from the formulation of branch outage is solved ...

  • Parallel Implementation Of Iterative Rational Krylov Methods For Model Order Reduction 

    Authors:Yetkin, E. Fatih; Daǧ, Hasan
    Publisher and Date:(IEEE, 2010)
    Model order reduction (MOR) techniques are getting more important in large scale computational tasks like large scale electronic circuit simulations. In this paper we present some experimental work on multiprocessor systems for rational Krylov methods. These methods require huge memory and computational power especially in large scale simulations. Therefore these methods are fairly suitable for parallel computing.

  • Power Consumption Estimation Using In-Memory Database Computation 

    Authors:Daǧ, Hasan; Alamin, Mohamed Abdullah Al
    Publisher and Date:(IEEE, 2016)
    In order to efficiently predict electricity consumption we need to improve both the speed and the reliability of computational environment. Concerning the speed we use inmemory database which is taught to be the best solution that allows manipulating data many times faster than the hard disk. For reliability we use machine learning algorithms. Since the model performance and accuracy may vary depending on data each time we test many algorithms and select the best one. In this study we use SmartMeter ...

  • Protecting openflow switches against Denial of Service Attacks 

    This paper presents a novel approach to protect Openflow switches against a type of Denial of Service (DoS) attacks. Openflow switches are the core of Software Defined Networks (SDN) and they are very flexible programmable and can be used for several functionalities within a network. As the control algorithm of the switch is implemented on a separate computer (Controller) this software can be implemented on any part of the network packet including Layers 2 3 and 4 headers. Therefore an Openflow ...

  • Sparsity Preserving Computation for Spectral Projectors 

    Authors:Yetkin, E. Fatih; Daǧ, Hasan
    Publisher and Date:(Amer Inst Physics, 2011)
    Several areas of applications such as model order reduction preconditioner design and eigenvalue problems for spectral projectors can be found in the literature. In this paper a fast and sparsity preserving approach for computing the spectral projectors is proposed. The suggested approach can be used in both Newton iteration and integral representation based methods. A comparison of the original and the suggested approaches in terms of computation time sparsity preservation and accuracy is presented ...

  • Towards Faster Branch Outage Simulations Using Simulated Annealing and Parallel Programming 

    Authors:Ceylan, Oǧuzhan; Ozdemir, Aydogan; Daǧ, Hasan
    Publisher and Date:(IEEE, 2009)
    Contingency studies such as branch outage and generator outage are among important studies of energy management centers operations. Branch outage modeling on the other hand is one of the basic steps of post-outage state estimation of an electrical power system. Real time implementation of the problem brings the necessity of using high speed methods while providing a reasonable accuracy. This paper presents simulated annealing based solution of the branch outage event which is formulated as a local ...