Documents disponibles écrits par cet auteur

Handling uncertainty in model-based optimal experimental design / Tilman Barz in Industrial & engineering chemistry research, Vol. 49 N° 12 (Juin 2010) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 49 N° 12 (Juin 2010) . - pp. 5702–5713 Titre : Handling uncertainty in model-based optimal experimental design Type de document : texte imprimé Auteurs : Tilman Barz, Auteur ; Harvey Arellano-Garcia, Auteur ; Günter Wozny, Auteur Année de publication : 2010 Article en page(s) : pp. 5702–5713 Note générale : Chemical engineering Langues : Anglais (eng) Mots-clés : Uncertainties  Protein  ion-exchange  equilibrium  parameters Résumé : In contrast to the majority of published works in the field of model-based optimal experimental design which focused on numerical studies so as to demonstrate the validity of the OED approach or the development of new criteria or numerical approaches, this work is mainly concerned with the experimental application and practical insights gained from the adaption of an optimal design framework. The presented work is discussed based on the determination of protein ion-exchange equilibrium parameters. For this purpose, special attention is paid to the explicit modeling of all laboratory steps so as to prepare, implement, and analyze experiments in order to have a realistic definition of the numeric design problem and to formally include experimental restrictions and sources of uncertainties in the problem formulation. Moreover, whereas the effect of erroneous assumptions in the initially assumed parameter values have been covered by various authors, in this work, uncertainties are considered in a more general way including those which arise during an imprecise implementation of optimal planned experiments. To compensate for uncertainty influences, a feed-back based approach to optimal design is adopted based on the combination of the parallel and sequential design approaches. Uncertainty identification is done by solution of an augmented parameter estimation problem, where deviations in the experimental design are detected and estimated together with the parameter values. It has been shown that uncertainty influences vanish along with the iterative refinement of the experiment design variables and estimated parameter values. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie901611b [article] Handling uncertainty in model-based optimal experimental design [texte imprimé] / Tilman Barz, Auteur ; Harvey Arellano-Garcia, Auteur ; Günter Wozny, Auteur . - 2010 . - pp. 5702–5713. Chemical engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 49 N° 12 (Juin 2010) . - pp. 5702–5713 Mots-clés : Uncertainties  Protein  ion-exchange  equilibrium  parameters Résumé : In contrast to the majority of published works in the field of model-based optimal experimental design which focused on numerical studies so as to demonstrate the validity of the OED approach or the development of new criteria or numerical approaches, this work is mainly concerned with the experimental application and practical insights gained from the adaption of an optimal design framework. The presented work is discussed based on the determination of protein ion-exchange equilibrium parameters. For this purpose, special attention is paid to the explicit modeling of all laboratory steps so as to prepare, implement, and analyze experiments in order to have a realistic definition of the numeric design problem and to formally include experimental restrictions and sources of uncertainties in the problem formulation. Moreover, whereas the effect of erroneous assumptions in the initially assumed parameter values have been covered by various authors, in this work, uncertainties are considered in a more general way including those which arise during an imprecise implementation of optimal planned experiments. To compensate for uncertainty influences, a feed-back based approach to optimal design is adopted based on the combination of the parallel and sequential design approaches. Uncertainty identification is done by solution of an augmented parameter estimation problem, where deviations in the experimental design are detected and estimated together with the parameter values. It has been shown that uncertainty influences vanish along with the iterative refinement of the experiment design variables and estimated parameter values. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie901611b

Local optima in model - based optimal experimental design / Jan C. Schoneberger in Industrial & engineering chemistry research, Vol. 49 N° 20 (Octobre 2010) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 49 N° 20 (Octobre 2010) . - pp. 10059–10073 Titre : Local optima in model - based optimal experimental design Type de document : texte imprimé Auteurs : Jan C. Schoneberger, Auteur ; Harvey Arellano-Garcia, Auteur ; Günter Wozny, Auteur Année de publication : 2011 Article en page(s) : pp. 10059–10073 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Optimal Résumé : Model-based nonlinear optimal experimental design (OED) has advanced to a relevant systematic tool in model development. However, the high nonlinearity of OED problems and their required high computational effort makes the optimization a challenging task. The objective of this work is to point out a crucial aspect of OED problems, namely, the existence of local minima. For this purpose, general characteristics of OED problems are presented and discussed, using different OED criteria and approaches (sequential/parallel). Furthermore, five different approaches are compared to overcome the local minima problem. Tuning options to improve the computation time of hybrid approaches are derived and discussed. The approaches are compared, based on the results of two case studies. To solve high-dimensional complex OED problems, a proposed hybrid framework is found to be a promising approach. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie9016094 [article] Local optima in model - based optimal experimental design [texte imprimé] / Jan C. Schoneberger, Auteur ; Harvey Arellano-Garcia, Auteur ; Günter Wozny, Auteur . - 2011 . - pp. 10059–10073. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 49 N° 20 (Octobre 2010) . - pp. 10059–10073 Mots-clés : Optimal Résumé : Model-based nonlinear optimal experimental design (OED) has advanced to a relevant systematic tool in model development. However, the high nonlinearity of OED problems and their required high computational effort makes the optimization a challenging task. The objective of this work is to point out a crucial aspect of OED problems, namely, the existence of local minima. For this purpose, general characteristics of OED problems are presented and discussed, using different OED criteria and approaches (sequential/parallel). Furthermore, five different approaches are compared to overcome the local minima problem. Tuning options to improve the computation time of hybrid approaches are derived and discussed. The approaches are compared, based on the results of two case studies. To solve high-dimensional complex OED problems, a proposed hybrid framework is found to be a promising approach. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie9016094

Robust implementation of optimal decisions using a two-layer chance-constrained approach / Tilman Barz in Industrial & engineering chemistry research, Vol. 50 N° 9 (Mai 2011) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 50 N° 9 (Mai 2011) . - pp. 5050-5063 Titre : Robust implementation of optimal decisions using a two-layer chance-constrained approach Type de document : texte imprimé Auteurs : Tilman Barz, Auteur ; Günter Wozny, Auteur ; Harvey Arellano-Garcia, Auteur Année de publication : 2011 Article en page(s) : pp. 5050-5063 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Optimization Résumé : In this work, the implementation of optimal and robust decisions in the presence of various uncertainties comprising model parameters, external conditions, and the closed loop behavior of basic controllers is presented. In order to compute the optimal and reliable decisions, a chance-constrained optimization problem is formulated. The efhcient solution approach is based on the relaxation of the original stochastic optimization problem formulation to a standard nonlinear programming problem. By this means, nominal optimal solutions and operating points are regularly adapted in order to guarantee both feasibility and process operation as close as possible to the nominal optimum. The solution implies the minimization of additional costs, which come from conservative strategies that compensate for uncertainty. The experimental verification of the developed approach is carried out on a high-pressure distillation pilot plant for the separation of an azeotropic mixture. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie1014525 [article] Robust implementation of optimal decisions using a two-layer chance-constrained approach [texte imprimé] / Tilman Barz, Auteur ; Günter Wozny, Auteur ; Harvey Arellano-Garcia, Auteur . - 2011 . - pp. 5050-5063. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 50 N° 9 (Mai 2011) . - pp. 5050-5063 Mots-clés : Optimization Résumé : In this work, the implementation of optimal and robust decisions in the presence of various uncertainties comprising model parameters, external conditions, and the closed loop behavior of basic controllers is presented. In order to compute the optimal and reliable decisions, a chance-constrained optimization problem is formulated. The efhcient solution approach is based on the relaxation of the original stochastic optimization problem formulation to a standard nonlinear programming problem. By this means, nominal optimal solutions and operating points are regularly adapted in order to guarantee both feasibility and process operation as close as possible to the nominal optimum. The solution implies the minimization of additional costs, which come from conservative strategies that compensate for uncertainty. The experimental verification of the developed approach is carried out on a high-pressure distillation pilot plant for the separation of an azeotropic mixture. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie1014525