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See detailModel order reduction techniques for thermomechanical systems with nonlinear radiative heat transfer using proper orthogonal decomposition
Hickey, Daryl ULg; Hoffait, Sébastien ULg; Rothkegel Ide, José Ignacio ULg et al

in Proceedings of ISMA 2010 (2010, September)

Analysing large scale, nonlinear, multiphysical, dynamical structures, by using mathematical modelling and simulation, e.g. Finite Element Modelling (FEM), can be computationally very expensive ... [more ▼]

Analysing large scale, nonlinear, multiphysical, dynamical structures, by using mathematical modelling and simulation, e.g. Finite Element Modelling (FEM), can be computationally very expensive, especially if the number of degrees-of-freedom is high. This paper develops modal reduction techniques for such nonlinear multiphysical systems. The paper focuses on Proper Orthogonal Decomposition (POD), a multivariate statistical method that obtains a compact representation of a data set by reducing a large number of interdependent variables to a much smaller number of uncorrelated variables. A fully coupled, thermomechanical model consisting of a multilayered, cantilever beam is described and analysed. This linear benchmark beam is then extended to incorporate an external box. The nonlinear radiative exchanges between the beam and the external box are analysed and a reduction procedure is proposed for this fully coupled, nonlinear, multiphysical, thermomechanical system. Two alternative approaches to the reduction are investigated, a monolithic scaled approach and a partitioned approach that treats the individual physical modes separately. [less ▲]

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See detailModel physical parameters effects on real solar cell characteristics and power curve
Aazou, Safae ULg; ASSAID, El Mahdi

in Global Journal of Physical Chemistry (2011), 2(2), 61-67

The climate change crisis and the running out of fossil resources are motivating the use of renewable energies. Solar energy is the main source of the renewable energies and photovoltaics is one of the ... [more ▼]

The climate change crisis and the running out of fossil resources are motivating the use of renewable energies. Solar energy is the main source of the renewable energies and photovoltaics is one of the main ways of photon conversion. This alternative energy is safe, clean and abundant. The purpose of this paper is the use of Maple software in: - Determining, without any approximation, the model physical parameters of real photovoltaic solar cell as a basic element of photovoltaic conversion. - Analyzing the effects of each physical parameter on real solar cell current-voltage characteristics and output power curve. [less ▲]

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See detailModel polyQ proteins based on the beta-lactamase BlaP: How non-polyQ regions influence the polyQ length-dependent aggregation process
Huynen, Céline ULg

Doctoral thesis (2015)

Neurodegenerative amyloid diseases are fatal disorders representing an important human health and economic burden. Amongst them, nine disorders are classified as polyglutamine (polyQ) diseases, for which ... [more ▼]

Neurodegenerative amyloid diseases are fatal disorders representing an important human health and economic burden. Amongst them, nine disorders are classified as polyglutamine (polyQ) diseases, for which no treatment is yet available. They are all characterized by the pathological expansion of a poly(CAG) sequence, above a specific threshold, within the coding sequence of nine unrelated genes, translated in nine polyQ proteins. The polyQ expansion, the only common point, is the critical determinant for polyQ disease development by triggering protein aggregation into amyloid fibrils. More recent studies however indicate that the protein context modulates the polyQ-induced aggregation process and the disease phenotype. The objectives of my thesis are to deeper investigate the molecular determinants of the complex interplay between the propensity of the polyQ tract to trigger protein aggregation and the modulating role of non-polyQ regions in order to allow the identification of strategies to interfere with the pathological aggregation process. For that purpose, model polyQ proteins, referred to as BlaP-polyQ chimeras, based on the β-lactamase BlaP and polyQ sequences (23 – 79Q) inserted at two positions (197, in between or not unstructured peptides, or 216), are used and their aggregation properties are characterized under several conditions. We first observe that the polyQ length is determinant for BlaP-polyQ chimera aggregation. Indeed, there is a Q-threshold for the aggregation into amyloid fibrils and for fibril elongation. Above this threshold, the aggregation in solution and the elongation rate increase with the length of the polyQ tract, with an exponential rise-to-maximum and a linear regression, respectively, independently of the conformation of the BlaP moiety, and of the position of the polyQ tract within BlaP. Longer polyQ tracts are likely to have a larger conformational flexibility allowing them to more easily adopt an amyloid-aggregation prone conformation. However, the Q-threshold for fibril elongation is much lower than for fibril formation in solution: the polyQ tract requires a larger conformational flexibility to nucleate the formation of fibrils than to elongate them. Secondly, the Q-threshold for fibril formation is lower once the BlaP moiety is unfolded, and BlaP-polyQ chimeras aggregate faster into amyloid fibrils under conditions favoring the unfolding of the BlaP moiety. The native structure of BlaP is likely to impose conformational constraints to moderate and long polyQ tracts that block and decrease, respectively, their propensity to form fibrils. The effects of constraints decrease with the polyQ length. Thirdly, BlaP chimeras with the polyQ tract in position 216 have an increased propensity to trigger the nucleation and the elongation of amyloid fibrils compared to chimeras with the polyQ in position 197. Advanced studies confirm that the propensity of the polyQ tract to aggregate into amyloid fibrils is linked to the conformational flexibility of the polyQ tract, which depends on (i) the polyQ length, (ii) the location of the polyQ tract within BlaP, i.e., a terminal location or embedded within a protein domain, and (iii) the structural properties of the polyQ flanking regions. Finally, we observe that the whole region flanking the polyQ tract in position 197 at its N-terminus has an anti-aggregating property that fully counterbalances the pro-aggregating property of that flanking at the C-terminus. The former imposes strong conformational constraints to the polyQ tract that reduce its conformational flexibility and hence its aggregation propensity. Moreover, these regions are likely to differently affect the solubility of the polyQ protein and hence the driving force for insoluble aggregation. Altogether, our data also suggest that BlaP chimeras aggregate via the commonly described nucleation-dependent polymerization mechanism during which the aggregation is first triggered by polyQ-polyQ interactions, and then a subsequent slight reorganization of the BlaP moiety is required for conversion of aggregates into amyloid fibrils. Based on these results, we should allow the development of therapeutic strategies, targeting specifically the molecular features of the complex interplay between the polyQ and non-polyQ regions during the nucleation and/or elongation of the pathological aggregation of polyQ proteins. [less ▲]

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See detailModel predictive control and reinforcement learning as two complementary frameworks
Ernst, Damien ULg; Glavic, Mevludin; Capitanescu, Florin ULg et al

in International Journal of Tomography & Statistics (2007), 6

Model predictive control (MPC) and reinforcement learning (RL) are two popular families of methods to control system dynamics. In their traditional setting, they formulate the control problem as a ... [more ▼]

Model predictive control (MPC) and reinforcement learning (RL) are two popular families of methods to control system dynamics. In their traditional setting, they formulate the control problem as a discrete-time optimal control problem and compute a suboptimal control policy. We present in this paper in a unified framework these two families of methods. We run for MPC and RL algorithms simulations on a benchmark control problem taken from the power system literature and discuss the results obtained. [less ▲]

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See detailModel predictive control and reinforcement learning as two complementary frameworks
Ernst, Damien ULg; Glavic, Mevludin; Capitanescu, Florin ULg et al

in Proceedings of the 13th IFAC Workshop on Control Applications of Optimisation (2006)

Model predictive control (MPC) and reinforcement learning (RL) are two popular families of methods to control system dynamics. In their traditional setting, they formulate the control problem as a ... [more ▼]

Model predictive control (MPC) and reinforcement learning (RL) are two popular families of methods to control system dynamics. In their traditional setting, they formulate the control problem as a discrete-time optimal control problem and compute a suboptimal control policy. We present in this paper in a unified framework these two families of methods. We run for MPC and RL algorithms simulations on a benchmark control problem taken from the power system literature and discuss the results obtained. [less ▲]

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See detailModel Predictive Control for Reference Tracking in Distribution Networks Hosting Dispersed Generation
Soleimani Bidgoli, Hamid ULg; Glavic, Mevludin ULg; Van Cutsem, Thierry ULg

Scientific conference (2015, November 23)

A real-time, centralized control system is presented which is acting on the active and reactive powers of distributed generators when the network experiences voltage and/or thermal limits violation. The ... [more ▼]

A real-time, centralized control system is presented which is acting on the active and reactive powers of distributed generators when the network experiences voltage and/or thermal limits violation. The control resorts to multi-step receding horizon optimization. The objective is to minimize the deviations of Dispersed Generation Units (DGU) active and reactive powers from reference values. Furthermore, the formulation is such that DGU powers are restored to their desired schedule as soon as operating conditions allow doing so. Three modes of operation of the proposed controller are presented, involving dispatchable units as well as DGUs operated to collect maximum power. [less ▲]

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See detailMODEL PREDICTIVE CONTROL OF CONGESTION AND VOLTAGE PROBLEMS IN ACTIVE DISTRIBUTION NETWORKS
Soleimani Bidgoli, Hamid ULg; Glavic, Mevludin ULg; Van Cutsem, Thierry ULg

in Proc. of CIRED Workshop 2014 (2014, June)

This paper presents a centralized control scheme, inspired of Model Predictive Control (MPC), to manage thermal overloads and correct abnormal voltages in real-time. The control scheme is able to smoothly ... [more ▼]

This paper presents a centralized control scheme, inspired of Model Predictive Control (MPC), to manage thermal overloads and correct abnormal voltages in real-time. The control scheme is able to smoothly bring the system within the desired limits, taking into account its near-future evolution. The control method effectiveness is illustrated on a 20-kV, 32-bus network hosting four distributed generation units. [less ▲]

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See detailModel predictive control of HVDC power flow to improve transient stability in power systems
Phulpin, Yannick; Hazra, Jagabondhu; Ernst, Damien ULg

in Proceedings of the Second IEEE International Conference on Smart Grid Communications (IEEE SmartGridComm) (2011, October)

This paper addresses the problem of HVDC control using real-time information to avoid loss of synchronism phenomena in power systems. It proposes a discrete-time control strategy based on model predictive ... [more ▼]

This paper addresses the problem of HVDC control using real-time information to avoid loss of synchronism phenomena in power systems. It proposes a discrete-time control strategy based on model predictive control, which solves at every time step an open-loop optimal-control problem using an A* event-tree search. Different optimisation criteria based on transient stability indices are compared. The paper presents simulations results for two benchmark systems with 9 and 24 buses, respectively, and an embedded HVDC-link. The results show that the control strategy leads to a modulation of the HVDC power flow that improves significantly the system’s ability to maintain synchronism in the aftermath of a large disturbance. [less ▲]

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See detailModel Predictive Control of Voltages in Active Distribution Networks
Valverde Mora, Gustavo ULg; Van Cutsem, Thierry ULg

in IEEE Transactions on Smart Grid (2013), 4(4), 2152-2161

This paper presents a centralized control scheme to regulate distribution network voltages in the presence of high penetration of distributed generation. The approach is inspired of Model Predictive ... [more ▼]

This paper presents a centralized control scheme to regulate distribution network voltages in the presence of high penetration of distributed generation. The approach is inspired of Model Predictive Control in order to compensate for modeling inaccuracies and measurement noise. The control actions, calculated from a multi-step optimization, are updated and corrected by real-time measurements. The proposed controller uses a linear model to predict the behavior of the system and the optimization is solved using quadratic programming. The proposed corrective control has been tested in a 11-kV distribution network including 75 nodes and hosting 22 distributed generating units. [less ▲]

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See detailModel predictive control to alleviate thermal overloads
Otomega, Bogdan; Marinakis, Adamantios ULg; Glavic, Mevludin et al

in IEEE Transactions on Power Systems (2007), 22(3), 1384-1385

An approach inspired by model predictive control is proposed to determine a sequence of control actions aimed at alleviating thermal overloads. The algorithm brings the line currents below their limits in ... [more ▼]

An approach inspired by model predictive control is proposed to determine a sequence of control actions aimed at alleviating thermal overloads. The algorithm brings the line currents below their limits in the time interval left by protections while accounting for constraints on control changes at each step. Its closed-loop nature allows to compensate for model inaccuracies. [less ▲]

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See detailModel recovery anti-windup for continuous-time rate and magnitude saturated linear plants
Forni, Fulvio ULg; Galeani, Sergio; Zaccarian, Luca

in Automatica (2012), 48(8), 15021513

In this paper two approaches are given for anti-windup design for nonlinear control systems with linear plants subject to limitations both in the magnitude and the rate of variation of the control input ... [more ▼]

In this paper two approaches are given for anti-windup design for nonlinear control systems with linear plants subject to limitations both in the magnitude and the rate of variation of the control input. Both approaches are based on the so-called Model Recovery Anti-windup (MRAW) framework. The first approach is built by treating the rate+magnitude saturation as a single dynamic nonlinearity, while in the second one, the dynamic compensator dynamics is extended with extra states to treat the two saturations separately. Both approaches lead to global stability with exponentially stable plants and local stability in all other cases. For both approaches, stability and performance guarantees are proven, numerical recipes are given and the relative merits are comparatively highlighted on a simulation example. [less ▲]

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See detailModel Recovery Anti-Windup for plants with rate and magnitude saturation
Forni, Fulvio ULg; Galeani, Sergio; Zaccarian, Luca

in European Control Conference (2009) (2009)

In this paper two alternative approaches are provided to design an anti-windup compensator for control systems subject to limitations both in the magnitude and the rate of variation of the plant input ... [more ▼]

In this paper two alternative approaches are provided to design an anti-windup compensator for control systems subject to limitations both in the magnitude and the rate of variation of the plant input. For both approaches, constructive numerical recipes are given and the relative merits are highlighted. [less ▲]

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See detailA model reduction algorithm for solving multiple scattering problems at high-frequencies
Geuzaine, Christophe ULg

in Proceedings of the Frontiers in Applied and Computational Mathematics (FACM '10) conference (2010)

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See detailA Model Reduction Algorithm for Solving Multiple Scattering Problems Using Iterative Methods
Vion, Alexandre ULg; Vazquez Sabariego, Ruth ULg; Geuzaine, Christophe ULg

in IEEE Transactions on Magnetics (2011), 47(5), 1470-1473

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See detailA model reduction algorithm for solving multiple scattering problems using iterative methods
Vion, Alexandre ULg; V Sabariego, Ruth ULg; Geuzaine, Christophe ULg

in Proceedings of the 14th Biennial IEEE Conference on Electromagnetic Field Computation (CEFC2010) (2010, May)

This paper presents a new method for solving scattering problems by multiple objects. A model reduction algorithm based on the Macro Basis Functions (MBFs) method is used to find an approximate solution ... [more ▼]

This paper presents a new method for solving scattering problems by multiple objects. A model reduction algorithm based on the Macro Basis Functions (MBFs) method is used to find an approximate solution within a subspace of solutions, that are the solutions of several single scattering subproblems. Different iterative methods for the generation of the MBFs are compared. The whole process relies on a finite element approach and is applied to convex obstacles scattering. [less ▲]

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See detailModel reduction for simulating the dynamic behavior of parabolic troughs and a thermocline energy storage in a micro-solar power unit
Dickes, Rémi ULg; Desideri, Adriano ULg; Lemort, Vincent ULg et al

in Proceedings of ECOS 2015 (2015, July)

Micro-scale concentrated solar power plants are characterized by strong transients and mostly operate in off-design working conditions. Both the sizing and the control of these systems are key challenges ... [more ▼]

Micro-scale concentrated solar power plants are characterized by strong transients and mostly operate in off-design working conditions. Both the sizing and the control of these systems are key challenges whose optimization requires powerful dynamic modeling tools. In this context, a system featuring a solar field of parabolic troughs, a thermocline thermal energy storage and a 5kWe organic Rankine cycle (ORC) power unit is modeled in the Modelica language. Model reduction methods applied to the solar field and the thermal storage are investigated and analyzed to improve the computational efficiency of the problem. Each model is described and integrated in the open-source ThermoCycle library. Results of simulation under identical operating conditions are compared and the benefits and limitations of model reduction are assessed. [less ▲]

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See detailModel Reduction in Biological Systems Applied to a MAP Kinase Model
Bullinger, Eric ULg; Sauter, T.; Schoeberl, B. et al

Conference (2002, November 04)

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See detailA model reduction method for the control of rigid mechanisms
Bruls, Olivier ULg; Duysinx, Pierre ULg; Golinval, Jean-Claude ULg

in Multibody System Dynamics (2006), 15(3), 213-227

This paper presents a reduction method to build closed-form dynamic equations for rigid multibody systems with a minimal kinematic description. Relying on an initial parameterization with absolute ... [more ▼]

This paper presents a reduction method to build closed-form dynamic equations for rigid multibody systems with a minimal kinematic description. Relying on an initial parameterization with absolute displacements and rotations, the method is able to tackle complex topologies with closed-loops in a systematic way and its extension to flexible multibody systems will be investigated in the future. Thus, it would be of great use in the framework of model-based control of mechanisms. The method is based on an interpolation strategy. The initial model is built and reduced for a number of selected points in the configuration space. Then, a piecewise polynomial model is adjusted to match the collected data. After the presentation of the reduction procedure and of the interpolation strategy, two applications of the reduction method are considered: a four-bar mechanism and a parallel kinematic machine-tool called "Orthoglide". [less ▲]

Detailed reference viewed: 45 (12 ULg)