160 results found
Gros S, Chachuat B, Bonvin D, 2008, NCO tracking for singular control problems using neighboring extremals, IFAC Proceedings Volumes (IFAC-PapersOnline), Vol: 17, ISSN: 1474-6670
A powerful approach for dynamic optimization in the presence of uncertainty is to incorporate measurements into the optimization framework so as to track the necessary conditions of optimality (NCO), the so-called NCO-tracking approach. For nonsingular control problems, this can be done by tracking active constraints along boundary arcs, and using neighboring-extremal (NE) control along interior arcs to force the first-order variation of the NCO to zero. In this paper, an extension of NE control to singular control problems is proposed. The idea is to design NE controllers from successive time differentiations of the first-order variation of the NCO. Based on these results, a NCO-tracking controller that is easily tractable from a real-time optimization perspective is proposed, whose application guarantees that the first-order variation of the NCO converges to zero exponentially. The performance of this NCO-tracking controller is illustrated via the case study of a steered car, a 5th-order two-input dynamical system. Copyright © 2007 International Federation of Automatic Control All Rights Reserved.
Marchetti A, Chachuat B, Bonvin D, 2008, Estimation of experimental gradients for real-time optimization
Mitsos A, Lemonidis P, Bollas GM, et al., 2008, A bilevel framework for process design & operation
Yunt M, Chachuat B, Mitsos A, et al., 2008, Designing man-portable power generation systems for varying power demand, AICHE JOURNAL, Vol: 54, Pages: 1254-1269, ISSN: 0001-1541
Chachuat B, Marchetti A, Bonvin D, 2008, Process optimization via constraints adaptation, JOURNAL OF PROCESS CONTROL, Vol: 18, Pages: 244-257, ISSN: 0959-1524
Marchetti A, Chachuat B, Bonvin D, 2008, Real-Time Optimization via Adaptation and Control of the Constraints, 18th European Symposium on Computer Aided Process Engineering (ESCAPE-18), Publisher: ELSEVIER SCIENCE BV, Pages: 393-398, ISSN: 1570-7946
Chachuat B, Barton PI, 2008, Numerical simulation of a class of PDAEs with a separation of time scales, 14th European Conference for Mathematics in Industry, Publisher: SPRINGER-VERLAG BERLIN, Pages: 512-+, ISSN: 1612-3956
Chachuat B, Srinivasan B, Bonvin D, 2008, Model Parameterization Tailored to Real-time Optimization, 18th European Symposium on Computer Aided Process Engineering (ESCAPE-18), Publisher: ELSEVIER SCIENCE BV, Pages: 1-13, ISSN: 1570-7946
Mitsos A, Chachuat B, Barton PI, 2007, Methodology for the design of man-portable power generation devices, INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, Vol: 46, Pages: 7164-7176, ISSN: 0888-5885
Mitsos A, Chachuat B, Barton PI, 2007, Microfabricated fuel cell systems: Beyond process synthesis, ABSTR PAP AM CHEM S, Vol: 234, ISSN: 0065-7727
Marchetti AG, Chachuat, Bonvin D, 2007, Batch process optimization via run-to-run constraints adaptation, European Control Conference (ECC), Publisher: IEEE, Pages: 2791-2798
© 2007 EUCA. In the batch process industry, the available models carry a large amount of uncertainty and can seldom be used to directly optimize real processes. Several measurement-based optimization methods have been proposed to deal with model mismatch and process disturbances. Constraints often play a dominant role in the dynamic optimization of batch processes. In their presence, the optimal input profiles are characterized by a set of arcs, switching times and active path and terminal constraints. This paper presents a novel method tailored to those problems where the potential of optimization arises mainly from the correct set of path and terminal constraints being active. The input profiles are computed between successive runs by dynamic optimization of a fixed nominal model, and the constraints in the optimization problem are adapted using measured information from previous batches. Note that, unlike many existing optimization schemes, the measurements are not used to update the process model. Moreover, the proposed approach has the potential to uncover the optimal input structure. This is demonstrated on a simple semi-batch reactor example.
Mitsos A, Chachuat B, Barton PI, 2007, What is the design objective for portable power generation: Efficiency or energy density?, JOURNAL OF POWER SOURCES, Vol: 164, Pages: 678-687, ISSN: 0378-7753
Bernard O, Chachuat B, Steyer JP, 2007, State Estimation for Wastewater Treatment Processes, Wastewater Quality Monitoring and Treatment, Pages: 247-263, ISBN: 9780471499299
Marchetti A, Chachuat B, Bonvin D, 2007, Real-time optimization of continuous processes via constraints adaptation, Pages: 45-50, ISSN: 1474-6670
© Copyright 2007 IFAC. In the framework of process optimization, measurements can be used to compensate for the effect of uncertainty. The method studied in this paper combines a process model and measurements to iteratively improve the operation of continuous processes. Unlike many existing real-time optimization schemes, the measurements are not used to update the process model, but to adapt the constraints in the optimization problem. Upon convergence, all the constraints are respected even in the presence of large model mismatch. Moreover, it is shown that constraints adaptation can handle changes in the set of active constraints. The approach is illustrated, via numerical simulation, for the optimization of a continuous stirred-tank reactor.
Chachuat B, Singer AB, Barton PI, 2006, Global methods for dynamic optimization and mixed-integer dynamic optimization, INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, Vol: 45, Pages: 8373-8392, ISSN: 0888-5885
Chachuat B, Bernard O, 2006, Probabilistic observers for a class of uncertain biological processes, INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Vol: 16, Pages: 157-171, ISSN: 1049-8923
Bernard O, Chachuat B, Helias A, et al., 2006, Can we assess the model complexity for a bioprocess: theory and example of the anaerobic digestion process, WATER SCIENCE AND TECHNOLOGY, Vol: 53, Pages: 85-92, ISSN: 0273-1223
Chachuat B, Barton PI, 2005, Constructing tight convex/concave relaxations of the solutions of parameter-dependent nonlinear odes, Pages: 6825-6826
Optimization problems embedding initial value problems in nonlinear ordinary differential equations (ODEs) that depend on parameters are frequently encountered in chemical engineering as well as in many other engineering and scientific fields ẋ ((t, p) = f(t, p, ×)(t, p)), ∀t ∈ (t0, t⌈] x (t0, p) = h (p) with p ∈ P, x (t, p) ∈ ℝnI and P ⊆ ℝnp a nonempty convex set. This paper is concerned with the problem of obtaining pointwise in time convex/concave bounds for the solutions x of (5) on P. More precisely, the general goal is to construct auxiliary differential systems, the solutions of which underestimate/overestimate the solutions of the original differential system (5), and are guaranteed to be pointwise in time convex/concave on P. Note that the idea of constructing such auxiliary differential systems is not new to this paper for it has already been proposed by Singer and Barton . However, in this former work, the authors considered pointwise in time affine relaxations only. The main contribution of this work lies in the development of a theoretical framework enabling the construction of general nonlinear relaxations for the solutions of parameter dependent nonlinear ODEs on subsets of a Euclidean space. The practical application of these results is also closely considered. More precisely, a procedure for constructing such relaxations under mild assumptions is proposed, based on McCormick's relaxation technique , Finally, several illustrative examples are presented which demonstrate the construction and practicality of the relaxations. An important application of these results is in algorithms capable of solving dynamic optimization problems to guaranteed global optimality [3,4,5] as well as mixed-integer dynamic optimization (MIDO)  and hybrid discrete/continuous dynamic optimization  problems.
Mitsos A, Chachuat B, Barton PI, 2005, A design and operation methodology for man-portable power generation, Pages: 7313-7315
A integrated design methodology for portable power generation based on fuel cell systems was presented. Various fuels, including hydrogen, ammonia, various hydrocarbons, and alcohols, and fuel cells including solid oxide fuel cell, polymer electrolyte membrane, single chamber solid oxide fuel cell, direct methanol fuel cell, and proton conducting fuel cell based on ceramic technology were considered. The system level analysis provided limits of performance and could be used to determine at an early stage if a proposed device is worth pursuing; e.g., the use of methane. The use of detailed two- and three-dimensional computational fluid dynamics allowed geometrical improvements as well as the derivation and validation of modeling assumptions that were employed in the system-level and intermediate fidelity models. This is an abstract of a paper presented at the AIChE Annual Meeting and Fall Showcase (Cincinnati, OH 10/30/2005-11/4/2005).
Chachuat B, Mitsos A, Barton PI, 2005, Optimal start-up of micro power generation processes employing fuel cells, Pages: 7002-7003
Chachuat B, Singer AB, Barton PI, 2005, Global mixed-integer dynamic optimization, AICHE JOURNAL, Vol: 51, Pages: 2235-2253, ISSN: 0001-1541
Chachuat B, Mitsos A, Barton PI, 2005, Optimal design and steady-state operation of micro power generation employing fuel cells, CHEMICAL ENGINEERING SCIENCE, Vol: 60, Pages: 4535-4556, ISSN: 0009-2509
Fikar M, Chachuat B, Latifi MA, 2005, Optimal operation of alternating activated sludge processes, CONTROL ENGINEERING PRACTICE, Vol: 13, Pages: 853-861, ISSN: 0967-0661
Chachuat B, Roche N, Latifi MA, 2005, Optimal aeration control of industrial alternating activated sludge plants, BIOCHEMICAL ENGINEERING JOURNAL, Vol: 23, Pages: 277-289, ISSN: 1369-703X
Chachuat B, Roche N, Latifi MA, 2005, Long-term optimal aeration strategies for small-size alternating activated sludge treatment plants, CHEMICAL ENGINEERING AND PROCESSING-PROCESS INTENSIFICATION, Vol: 44, Pages: 593-606, ISSN: 0255-2701
Barton PI, Mitsos A, Chachuat B, 2005, Optimal start-up of micro power generation processes, 15th European Symposium on Computer Aided Process Engineering (ESCAPE-15), Publisher: ELSEVIER SCIENCE BV, Pages: 1093-1098, ISSN: 1570-7946
Chachuat B, Singer AB, Barton PI, 2005, Global solution of mixed-integer dynamic optimization problems, 15th European Symposium on Computer Aided Process Engineering (ESCAPE-15), Publisher: ELSEVIER SCIENCE BV, Pages: 133-138, ISSN: 1570-7946
Bernard O, Chachuat B, Helias A, et al., 2005, An integrated system to remote monitor and control anaerobic wastewater treatment plants through the internet, WATER SCIENCE AND TECHNOLOGY, Vol: 52, Pages: 457-464, ISSN: 0273-1223
Chachuat B, Mitsos A, Barton PI, 2004, Optimal design and operation of micro power generation processes, Pages: 2369-2378
This paper presents the optimal design and operation of a micro power generation process that consists of a reactor, a solid-oxide fuel cell (SOFC) and two burners in a stack fed with ammonia and butane fuels. Hydrogen is produced from ammonia decomposition, while butane is catalytically oxidized to produce heat and maintain the stack at a sufficiently high temperature. In the first part, a novel model is developed for predicting the steady-state performance of the process. Subsequently, this model is used as a basis to study and determine the optimal design and operation of the system. The optimization problem is formulated so that the consumption rate of utilities (ammonia and butane) is minimized, while meeting a specified power demand and maintaining the stack at its thermal equilibrium. The dependence of the optimal design and operating strategy on the operating temperature and the heat losses of the system is emphasized.
Chachuat B, Mitsos A, Barton PI, 2004, Optimal design and operation of micro power generation processes, Pages: 7749-7758
The optimal design and operation of a micro power generation process that consists of a reactor, a solid-oxide fuel cell (SOFC), and two burners in a stack fed with ammonia and butane fuels are presented. Hydrogen is produced from ammonia decomposition, while butane is catalytically oxidized to produce heat and maintain the stack at a sufficiently high temperature. The developed steady state model is used as a basis to study and determine the optimal design and operation of the system. The optimization problem is formulated so that the consumption rate of utilities (ammonia and butane) is minimized, while meeting a specified power demand and maintaining the stack in thermic equilibrium. Radiative heat losses play a central role in the operation and design of micro power generation processes. This is an abstract of a paper presented at the AIChE Annual Meeting (Austin, TX 11/7-12/2004).
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