- Dassios, Ioannis K.

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# Dassios, Ioannis K.

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Dassios, Ioannis K.

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Dassios, Ioannis K.

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- PublicationPrimal and Dual Generalized Eigenvalue Problems for Power Systems Small-Signal Stability Analysis(Institute of Electrical and Electronics Engineers (IEEE), 2017-03-07)
; The paper presents a comprehensive study of small-signal stability analysis of power systems based on matrix pencils and the generalized eigenvalue problem. Both primal and dual formulations of the generalized eigenvalue problem are considered and solved through a variety of state-of-the-art solvers. The paper also discusses the impact on the performance of the solvers of two formulations of the equations modelling the power systems, namely, the explicit and semi-implicit form of differential-algebraic equations. The case study illustrates the theoretical aspects and numerical features of these formulations and solvers through two real-world systems, namely, a 1,479-bus model of the all-island Irish system, and a 21,177-bus model of the ENTSO-E network.369Scopus© Citations 23 - PublicationAnalytic loss minimization: Theoretical framework of a second order optimization methodIn power engineering, the Y bus is a symmetric N × N square matrix describing a power system network with N buses. By partitioning, manipulating and using its symmetry properties, it is possible to derive the K GL and Y GGM matrices, which are useful to define a loss minimisation dispatch for generators. This article focuses on the case of constant-current loads and studies the theoretical framework of a second order optimization method for analytic loss minimization by taking into account the symmetry properties of Y bus . We define an appropriate matrix functional of several variables with complex elements and aim to obtain the minimum values of generator voltages.
307Scopus© Citations 20 - PublicationCalculating Nodal Voltages Using the Admittance Matrix Spectrum of an Electrical NetworkCalculating nodal voltages and branch current flows in a meshed network is fundamental to electrical engineering. This work demonstrates how such calculations can be performed using the eigenvalues and eigenvectors of the Laplacian matrix which describes the connectivity of the electrical network. These insights should permit the functioning of electrical networks to be understood in the context of spectral analysis.
290Scopus© Citations 9 - PublicationA mathematical model for plasticity and damage: A discrete calculus formulation(Elsevier BV, 2017-03-01)
; ; ; In this article we propose a discrete lattice model to simulate the elastic, plastic and failure behaviour of isotropic materials. Focus is given on the mathematical derivation of the lattice elements, nodes and edges, in the presence of plastic deformations and damage, i.e. stiffness degradation. By using discrete calculus and introducing non-local potential for plasticity, a force-based approach, we provide a matrix formulation necessary for software implementation. The output is a non-linear system with allowance for elasticity, plasticity and damage in lattices. This is the key tool for explicit analysis of micro-crack generation and population growth in plastically deforming metals, leading to macroscopic degradation of their mechanical properties and fitness for service. An illustrative example, analysing a local region of a node, is given to demonstrate the system performance.269Scopus© Citations 19 - PublicationSpreading of memes on multiplex networksA model for the spreading of online information or 'memes' on multiplex networks is introduced and analyzed using branching-process methods. The model generalizes that of (Gleeson et al 2016 Phys. Rev. X) in two ways. First, even for a monoplex (single-layer) network, the model is defined for any specific network defined by its adjacency matrix, instead of being restricted to an ensemble of random networks. Second, a multiplex version of the model is introduced to capture the behavior of users who post information from one social media platform to another. In both cases the branching process analysis demonstrates that the dynamical system is, in the limit of low innovation, poised near a critical point, which is known to lead to heavy-tailed distributions of meme popularity similar to those observed in empirical data.
202Scopus© Citations 15 - PublicationA stability result for a network of two triple junctions on the planeIn this article, we study the problem of a bounded network of two triple junctions in a planar domain with fixed angle conditions at the junctions and at the points at which the curves intersect with the boundary. We introduce the evolution problem of this type of networks, identify the steady states, and study their stability in terms of the geometry of the boundary.
243Scopus© Citations 12 - PublicationA mathematical model for elasticity using calculus on discrete manifoldsWe propose a mathematical model to represent solid materials with discrete lattices and to analyse their behaviour by calculus on discrete manifolds. Focus is given on the mathematical derivation of the lattice elements by taking into account the stored energy associated with them. We provide a matrix formulation of the nonlinear system describing elasticity with exact kinematics, known as finite strain elasticity in continuum mechanics. This formulation is ready for software implementation and may also be used in atomic scale models as an alternative to existing empirical approach with pair and cohesive potentials. An illustrative example, analysing a local region of a node, is given to demonstrate the model performance.
373Scopus© Citations 11 - PublicationSmall-signal stability analysis of neutral delay differential equationsThis paper focuses on the small-signal stability analysis of systems modeled as Neutral Delay Differential Equations (NDDEs). These systems include delays in both the state variables and their first time derivatives. The proposed approach consists in descriptor model transformation that constructs an equivalent set of Delay Differential Algebraic Equations (DDAEs) of the original NDDE. The resulting DDAE is a non-index-1 Hessenberg form, whose characteristic equation consists of a series of infinite terms corresponding to infinitely many delays. Then, the effect on small-signal stability analysis is evaluated numerically through a Chebyshev discretization of the characteristic equations. Numerical appraisals focus on a variety of physical systems, including a population-growth model, a partial element equivalent circuit and a neutral delayed neural network.
352Scopus© Citations 5 - PublicationOn the Stability Analysis of Systems of Neutral Delay Differential EquationsThis paper focuses on the stability analysis of systems modeled as neutral delay differential equations (NDDEs). These systems include delays in both the state variables and their time derivatives. The proposed approach consists of a descriptor model transformation that constructs an equivalent set of delay differential algebraic equations (DDAEs) of the original NDDEs. We first rigorously prove the equivalency between the original set of NDDEs and the transformed set of DDAEs. Then, the effect on stability analysis is evaluated numerically through a delay-independent stability criterion and the Chebyshev discretization of the characteristic equations.
484Scopus© Citations 39 - PublicationGeometric relation between two different types of initial conditions of singular systems of fractional nabla difference equationsIn this article, we study the geometric relation between two different types of initial conditions (IC) of a class of singular linear systems of fractional nabla difference equations whose coefficients are constant matrices. For these kinds of systems, we analyze how inconsistent and consistent IC are related to the column vector space of the finite and the infinite eigenvalues of the pencil of the system and analyze the geometric connection between these two different types of IC. Numerical examples are given to justify the results.
256Scopus© Citations 17

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