Browsing
     by title


0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

or enter first few letters:   
OK
Full Text
See detailNumerical integration over arbitrary surfaces in partition of unity finite elements
Natarajan, Sundararajan; dal Pont, Stefano; Hung, Nguyen-Xuan et al

Scientific Conference (2009, September)

Detailed reference viewed: 114 (0 UL)
See detailNumerical Investigation into the Primary Breakup of Liquid Jets and Sheets
Kannan, Kumar UL

Doctoral thesis (2012)

Detailed reference viewed: 123 (3 UL)
Full Text
See detailNumerical methods for fracture/cutting of heterogeneous materials
Sutula, Danas UL; Agathos, Konstantinos UL; Ziaei Rad, Vahid UL et al

Presentation (2016, December)

Detailed reference viewed: 175 (15 UL)
Full Text
See detailNumerical Modeling of Flow-Driven Piezoelectric Energy Harvesters
Ravi, Srivathsan UL; Zilian, Andreas UL

Scientific Conference (2016, June 09)

A specific class of energy harvester devices for renewable energy resources is investigated, that allow conversion of ambient fluid flow energy to electrical energy via flow-induced vibrations of a piezo ... [more ▼]

A specific class of energy harvester devices for renewable energy resources is investigated, that allow conversion of ambient fluid flow energy to electrical energy via flow-induced vibrations of a piezo-ceramic composite structure positioned in the flow field [3,4]. In this way, potentially harmful flow fluctuations are harnessed to provide independent power supply to small electrical devices. In order to harvest energy from fluid flows by means of piezoelectric materials the kinetic energy of the fluid first has to be transformed to cyclic straining energy of the piezoelectric material which is then transformed to electrical energy under the presence of an attached electrical circuit representing the powered electrical device or charged battery. This energy converter technology simultaneously involves the interaction of a composite structure and a surrounding fluid, the electric charge accumulated in the piezo-ceramic material and a controlling electrical circuit. In order to predict the efficiency and operational properties of such future devices and to increase their robustness and performance, a mathematical and numerical model of the complex physical system is required to allow systematic computational investigation of the involved phenomena and coupling characteristics. The research is devoted to introducing a monolithic approach that provides simultaneous modeling and analysis of the coupled energy harvester, which involves surface-coupled fluid-structure interaction, volume-coupled piezoelectric mechanics and a controlling energy harvesting circuit for applications in energy harvesting. The weak form of the governing equations is discretized by the space-time finite element method based on a mixed velocity-stress/rate form of the potential-dielectric displacement framework. The space-time finite element [2,3] model incorporates a novel method to enforce equipotentiality on the electrodes covering the piezoelectric patches, making the charge unknowns naturally appear in the formulation. This enables to adapt any type of electrical circuit added to the electromechanical problem. To validate the formulation, the case of piezoelectric triple layer EHD driven by base excitations, as described in [1] is chosen. The closed-form solution from [1] is compared to numerical solution proposed in this work. The variation of the electric potential through the thickness of the piezoelectric patch, assumed to be linear in many closed-form solutions, is shown to be quadratic in nature. The research contributes to the mathematical modeling and numerical discretization of complex multi- physics system in an efficient way which facilitates an ideal basis for precise and transient coupling. This may lead to improved convergence and numerical efficiency in comparison with portioned approaches. This methodology also provides new insights and in-depth understanding on design requirements on such energy harvesting devices in terms of their robustness and efficiency. [less ▲]

Detailed reference viewed: 124 (19 UL)
Full Text
See detailNumerical Modelling of Piezoelectric Energy Harvesting Devices
Ravi, Srivathsan UL; Zilian, Andreas UL

in 2nd ECCOMAS Young Investigators Conference (YIC 2013) (2013)

This paper introduces a monolithic approach that provides simultaneous solution to the coupled system which involves volume-coupled piezoelectric mechanics and a controlling energy harvesting circuit for ... [more ▼]

This paper introduces a monolithic approach that provides simultaneous solution to the coupled system which involves volume-coupled piezoelectric mechanics and a controlling energy harvesting circuit for applications in energy harvesting. The weak form of the governing equations is discretized by space-time nite element method based on mixed velocity-stress/ rate of potential-dielectric displacement setting. The results will be compared to the simple cases with closed-form solution available from literature. [less ▲]

Detailed reference viewed: 98 (17 UL)
Full Text
See detailNumerical Modelling of Piezoelectric Energy Harvesting Devices
Ravi, Srivathsan UL; Zilian, Andreas UL

Scientific Conference (2013)

This paper introduces a monolithic approach that provides simultaneous modeling and analysis of the coupled energy harvester, which involves surface-coupled fluid-structure interaction, volume-coupled ... [more ▼]

This paper introduces a monolithic approach that provides simultaneous modeling and analysis of the coupled energy harvester, which involves surface-coupled fluid-structure interaction, volume-coupled piezoelectric mechanics and a controlling energy harvesting circuit for applications in energy harvesting. The weak form of the governing equations is discretized by the space-time finite element method based on a mixed velocity-stress/rate form of the potential-dielectric displacement framework. The results will be compared to the simple cases with closed-form solution available from literature. [less ▲]

Detailed reference viewed: 118 (16 UL)
Full Text
Peer Reviewed
See detailNumerical Solution of Non-Isothermal Fluid Flows Using Local Radial Basis Functions (LRBF) Interpolation and a Velocity-Correction Method
Bourantas, Georgios UL; Skouras, Eugene; Loukopoulos, Vasilis et al

in Computer Modeling in Engineering & Sciences (2010), 64(2), 187-212

Meshfree point collocation method (MPCM) is developed, solving the velocity-vorticity formulation of Navier-Stokes equations, for two-dimensional, steady state incompressible viscous flow problems in the ... [more ▼]

Meshfree point collocation method (MPCM) is developed, solving the velocity-vorticity formulation of Navier-Stokes equations, for two-dimensional, steady state incompressible viscous flow problems in the presence of heat transfer. Particular emphasis is placed on the application of the velocity-correction method, ensuring the continuity equation. The Gaussian Radial Basis Functions (GRBF) interpolation is employed to construct the shape functions in conjunction with the framework of the point collocation method. The cases of forced, natural and mixed convection in a 2D rectangular enclosure are examined. The accuracy and the sta- bility of the proposed scheme are demonstrated through three representative, well known and established benchmark problems. Results are presented for high values of the characteristics non-dimensional numbers of the flow, that is, the Reynolds, the Rayleigh and the Richardson number [less ▲]

Detailed reference viewed: 64 (0 UL)
Full Text
Peer Reviewed
See detailNumerical study of magnetic particles concentration in biofluid (blood) under the influence of high gradient magnetic field in microchannel
Loukopoulos, Vassilios; Bourantas, Georgios UL; Labropoulos, Dimitrios et al

Scientific Conference (2016, June)

A meshless numerical scheme [1] is developed in order to simulate the magnetically mediated separation of biological mixture used in lab-on-chip devices as solid carriers for capturing, transporting and ... [more ▼]

A meshless numerical scheme [1] is developed in order to simulate the magnetically mediated separation of biological mixture used in lab-on-chip devices as solid carriers for capturing, transporting and detecting biological magnetic labeled entities [2], as well as for drug delivering, magnetic hyperthermia treatment, magnetic resonance imaging, magnetofection, etc. A modified one-way particle-fluid coupling analysis is considered to model the interaction of the base fluid of the mixture with the distributed particles motion. In details, bulk flow influences particle motion (through a simplified Stokes drag relation), while it is strongly dependent on particle motion through (particle) concentration. Due to the imposed magnetic field stagnation regions are developed, leading to the accumulation of the magnetic labeled species and finally to their collection from the heterogeneous mixture. The role of (i) the intensity of magnetic field and its gradient, (ii) the position of magnetic field, (iii) the magnetic susceptibility of magnetic particles, (iv) the volume concentration of magnetic particles (nanoparticles) and their size, (v) the flow velocity in the magnetic- fluidic interactions and interplay between the magnetophoretic mass transfer and molecular diffusion are thoroughly investigated. Both Newtonian and non-Newtonian blood flow models are considered, along with different expressions for the concentration and numerical results are presented for a wide range of physical parameters (Hartmann number (Ha), Reynolds number (Re)). A comprehensive study investigates their impact on the biomagnetic separation. For verification purposes, the numerical results obtained by the proposed meshless scheme were compared with established numerical results from the literature, being in excellent agreement. [less ▲]

Detailed reference viewed: 297 (11 UL)
Full Text
Peer Reviewed
See detailNumerically determined enrichment functions for the extended finite element method and applications to bi-material anisotropic fracture and polycrystals
Menk, Alexander; Bordas, Stéphane UL

in International Journal for Numerical Methods in Engineering (2010), 83(7), 805-828

Strain singularities appear in many linear elasticity problems. A very fine mesh has to be used in the vicinity of the singularity in order to obtain acceptable numerical solutions with the finite element ... [more ▼]

Strain singularities appear in many linear elasticity problems. A very fine mesh has to be used in the vicinity of the singularity in order to obtain acceptable numerical solutions with the finite element method (FEM). Special enrichment functions describing this singular behavior can be used in the extended finite element method (X-FEM) to circumvent this problem. These functions have to be known in advance, but their analytical form is unknown in many cases. Li et al. described a method to calculate singular strain fields at the tip of a notch numerically. A slight modification of this approach makes it possible to calculate singular fields also in the interior of the structural domain. We will show in numerical experiments that convergence rates can be significantly enhanced by using these approximations in the X-FEM. The convergence rates have been compared with the ones obtained by the FEM. This was done for a series of problems including a polycrystalline structure. [less ▲]

Detailed reference viewed: 63 (0 UL)
Full Text
Peer Reviewed
See detailNumerische Untersuchungen der instationären Strömungstopologie im Nachlauf einer Seehundvibrisse
Witte, Matthias; Michael, Mark UL; Brede, Martin et al

in Ruck, B.; Leder, A.; Dopheide, D. (Eds.) Proceedings der 16.GALA-Fachtagung “Lasermethoden in der Strömungsmesstechnik“ (2008)

Im Rahmen des Schwerpunktprogramms 1207 „Strömungen in Natur und Technik“ wird die Umströmung einer Seehundvibrisse untersucht. Die Vibrissen von Seehunden zeichnen sich durch eine komplizierte ... [more ▼]

Im Rahmen des Schwerpunktprogramms 1207 „Strömungen in Natur und Technik“ wird die Umströmung einer Seehundvibrisse untersucht. Die Vibrissen von Seehunden zeichnen sich durch eine komplizierte dreidimensionale Strukturmodellierung aus. Sie versetzen den See- hund in die Lage, Nachlaufspuren von Beutefischen zu detektieren. Mit Hilfe Stereo- μ Piv Messungen an Seehundvibrissen konnte die stationäre Strömungstopologie des Vibrissen- nachlaufes ermittelt werden. Zum besseren Verständnis der Funktion der Strukturierung der Vibrisse ist es notwendig, die instationäre Strömungstopologie zu kennen. Durch räumlich und zeitlich hochauflösende numerische Verfahren soll die instationäre Strömungstopologie im Nachlauf einer Seehundvibrisse ermittelt werden. [less ▲]

Detailed reference viewed: 78 (3 UL)
Full Text
Peer Reviewed
See detailNURBS-based finite element analysis of functionally graded plates: Static bending, vibration, buckling and flutter
Valizadeh, N; Natarajan, Sundarajan; González-Estrada, Octavio Andrés et al

in Composite Structures (2013), 99

In this paper, a non-uniform rational B-spline based iso-geometric finite element method is used to study the static and dynamic characteristics of functionally graded material (FGM) plates. The material ... [more ▼]

In this paper, a non-uniform rational B-spline based iso-geometric finite element method is used to study the static and dynamic characteristics of functionally graded material (FGM) plates. The material properties are assumed to be graded only in the thickness direction and the effective properties are computed either using the rule of mixtures or by Mori–Tanaka homogenization scheme. The plate kinematics is based on the first order shear deformation plate theory (FSDT). The shear correction factors are evaluated employing the energy equivalence principle and a simple modification to the shear correction factor is presented to alleviate shear locking. Static bending, mechanical and thermal buckling, linear free flexural vibration and supersonic flutter analysis of FGM plates are numerically studied. The accuracy of the present formulation is validated against available three-dimensional solutions. A detailed numerical study is carried out to examine the influence of the gradient index, the plate aspect ratio and the plate thickness on the global response of functionally graded material plates. [less ▲]

Detailed reference viewed: 447 (8 UL)
Full Text
Peer Reviewed
See detailNURBS-based finite element analysis of functionally graded plates: Static bending, vibration, buckling and flutter
Valizadeh, N.; Natarajan, S.; Gonzalez-Estrada, O. A. et al

in Composite Structures (2013), 99

In this paper, a non-uniform rational B-spline based iso-geometric finite element method is used to study the static and dynamic characteristics of functionally graded material (FGM) plates. The material ... [more ▼]

In this paper, a non-uniform rational B-spline based iso-geometric finite element method is used to study the static and dynamic characteristics of functionally graded material (FGM) plates. The material properties are assumed to be graded only in the thickness direction and the effective properties are computed either using the rule of mixtures or by Mori-Tanaka homogenization scheme. The plate kinematics is based on the first order shear deformation plate theory (FSDT). The shear correction factors are evaluated employing the energy equivalence principle and a simple modification to the shear correction factor is presented to alleviate shear locking. Static bending, mechanical and thermal buckling, linear free flexural vibration and supersonic flutter analysis of FGM plates are numerically studied. The accuracy of the present formulation is validated against available three-dimensional solutions. A detailed numerical study is carried out to examine the influence of the gradient index, the plate aspect ratio and the plate thickness on the global response of functionally graded material plates. © 2012 Elsevier Ltd. [less ▲]

Detailed reference viewed: 276 (2 UL)
Full Text
Peer Reviewed
See detailOn the Event-based Attack-tolerant Control: A Polytopic Representation
Bezzaoucha, Souad UL; Voos, Holger UL

in Bezzaoucha, Souad (Ed.) International Conference on Automation, Control and Robots (2019, October)

In the present contribution, we present a new event-based control representation. Based on the polytopic approach, more specifically the sector nonlinear transformation, an event-based attack-tolerant ... [more ▼]

In the present contribution, we present a new event-based control representation. Based on the polytopic approach, more specifically the sector nonlinear transformation, an event-based attack-tolerant control, and scheduling co-design strategy are proposed. From the event triggering definition (sample-and-hold strategy), polytopic writing of the event-triggered feedback control is first presented and then incorporated into the system dynamics for analysis. Our goal is to present a unique model that is able to deal with the co-design problem simultaneously and that can be handled by classical control synthesis tools. The novel representation, including data deception and attack tolerant control is formulated as a BMI optimization problem ensuring both stability and some level performance requirements (L2 attenuation of the cyber-attack). [less ▲]

Detailed reference viewed: 41 (0 UL)
Full Text
Peer Reviewed
See detailOn characterizing the relationship between route choice behavior and optimal traffic control solution space
Rinaldi, Marco UL; Tampère, C. M. J.; Viti, Francesco UL

in Transportation Research Procedia (2017), 23

Explicitly including the dynamics of users' route choice behaviour in optimal traffic control applications has been of interest for researchers in the last five decades. This has been recognized as a very ... [more ▼]

Explicitly including the dynamics of users' route choice behaviour in optimal traffic control applications has been of interest for researchers in the last five decades. This has been recognized as a very challenging problem, due to the added layer of complexity and the considerable non-convexity of the resulting problem, even when dealing with simple static assignment and analytical link cost functions. In this work we establish a direct behavioural connection between the different shapes and structures emerging in the solution space of such problems and the underlying route choice behaviour. We specifically investigate how changes in the active equilibrium route set exert direct influence on the solution space's structure and behaviour. Based on this result, we then formulate and validate a constrained version of the original problem, yielding desirable properties in terms of solution space regularity. © 2017 The Authors. [less ▲]

Detailed reference viewed: 71 (2 UL)
Full Text
Peer Reviewed
See detailOn characterizing the relationship between route choice behaviuor and optimal traffic control solution space
Rinaldi, Marco UL; Tampère, C. M. J.; Viti, Francesco UL

in Transportation Research. Part B : Methodological (2017)

Explicitly including the dynamics of users' route choice behaviour in optimal traffic control applications has been of interest for researchers in the last five decades. This has been recognized as a very ... [more ▼]

Explicitly including the dynamics of users' route choice behaviour in optimal traffic control applications has been of interest for researchers in the last five decades. This has been recognized as a very challenging problem, due to the added layer of complexity and the considerable non-convexity of the resulting problem, even when dealing with simple static assignment and analytical link cost functions. In this work we establish a direct behavioural connection between the different shapes and structures emerging in the solution space of such problems and the underlying route choice behaviour. We specifically investigate how changes in the active equilibrium route set exert direct influence on the solution space's structure and behaviour. Based on this result, we then formulate and validate a constrained version of the original problem, yielding desirable properties in terms of solution space regularity. © 2017. [less ▲]

Detailed reference viewed: 71 (3 UL)
Full Text
Peer Reviewed
See detailOn Judgment Aggregation in Abstract Argumentation
Caminada, Martin UL; Pigozzi, Gabriella UL

in Autonomous Agents & Multi-Agent Systems (2011), 22(1), 64102

Judgment aggregation is a field in which individuals are required to vote for or against a certain decision (the conclusion) while providing reasons for their choice. The reasons and the conclusion are ... [more ▼]

Judgment aggregation is a field in which individuals are required to vote for or against a certain decision (the conclusion) while providing reasons for their choice. The reasons and the conclusion are logically connected propositions. The problem is how a collective judgment on logically interconnected propositions can be defined from individual judgments on the same propositions. It turns out that, despite the fact that the individuals are logically consistent, the aggregation of their judgments may lead to an inconsistent group outcome, where the reasons do not support the conclusion. However, in this paper we claim that collective irrationality should not be the only worry of judgment aggregation. For example, judgment aggregation would not reject a consistent combination of reasons and conclusion that no member voted for. In our view this may not be a desirable solution. This motivates our research about when a social outcome is ‘compatible’ with the individuals’ judgments. The key notion that we want to capture is that any individual member has to be able to defend the collective decision. This is guaranteed when the group outcome is compatible with its members views. Judgment aggregation problems are usually studied using classical propositional logic. However, for our analysis we use an argumentation approach to judgment aggregation problems. Indeed the question of how individual evaluations can be combined into a collective one can also be addressed in abstract argumentation. We introduce three aggregation operators that satisfy the condition above, and we offer two definitions of compatibility. Not only does our proposal satisfy a good number of standard judgment aggregation postulates, but it also avoids the problem of individual members of a group having to become committed to a group judgment that is in conflict with their own individual positions. [less ▲]

Detailed reference viewed: 63 (1 UL)
Peer Reviewed
See detailOn L2 error bounds between systems
Salinas, A.; Papachristodoulou, A.; Goncalves, Jorge UL

Scientific Conference (2006)

Detailed reference viewed: 27 (1 UL)
Full Text
Peer Reviewed
See detailOn minimal realisations of dynamical structure functions
Yuan, Ye; Glover, Keith; Goncalves, Jorge UL

in Automatica (2015), 55

Motivated by the fact that transfer functions do not contain structural information about networks, dynamical structure functions were introduced to capture causal relationships between measured nodes in ... [more ▼]

Motivated by the fact that transfer functions do not contain structural information about networks, dynamical structure functions were introduced to capture causal relationships between measured nodes in networks. From the dynamical structure functions, a) we show that the actual number of hidden states can be larger than the number of hidden states estimated from the corresponding transfer function; b) we can obtain partial information about the true state-space equation, which cannot in general be obtained from the transfer function. Based on these properties, this paper proposes algorithms to find minimal realisations for a given dynamical structure function. This helps to estimate the minimal number of hidden states, to better understand the complexity of the network, and to identify potential targets for new measurements. [less ▲]

Detailed reference viewed: 154 (15 UL)
Full Text
Peer Reviewed
See detailOn multistability of delayed genetic regulatory networks with multivariable regulation functions
Pan, Wei UL; Wang, Z.; Gao, H. et al

in Mathematical Biosciences (2010), 228(1), 100-109

Many genetic regulatory networks (GRNs) have the capacity to reach different stable states. This capacity is defined as multistability which is an important regulation mechanism. Multiple time delays and ... [more ▼]

Many genetic regulatory networks (GRNs) have the capacity to reach different stable states. This capacity is defined as multistability which is an important regulation mechanism. Multiple time delays and multivariable regulation functions are usually inevitable in such GRNs. In this paper, multistability of GRNs is analyzed by applying the control theory and mathematical tools. This study is to provide a theoretical tool to facilitate the design of synthetic gene circuit with multistability in the perspective of control theory. By transforming such GRNs into a new and uniform mathematical formulation, we put forward a general sector-like regulation function that is capable of quantifying the regulation effects in a more precise way. By resorting to up-to-date techniques, a novel Lyapunov–Krasovskii functional (LKF) is introduced for achieving delay dependence to ensure less conservatism. New conditions are then proposed to ensure the multistability of a GRN in the form of linear matrix inequalities (LMIs) that are dependent on the delays. Our multistability conditions are applicable to several frequently used regulation functions especially the multivariable ones. Two examples are employed to illustrate the applicability and usefulness of the developed theoretical results. [less ▲]

Detailed reference viewed: 60 (0 UL)