1,721,070 research outputs found
Robust multi-objective dynamic optimization of chemical processes using the Sigma Point method
No full textDynamic optimization solutions largely rely on the accuracy of the underlying mathematical models. However, these models only represent an approximation of the real dynamic process and their predictions are dependent on a set of parameter values. These parameter values can be hard to estimate exactly (e.g., thermal conductivity) or vary over time (e.g., due to fouling) potentially leading to hazardous situations when applying a model based optimal solution. Robust dynamic optimization deals with the uncertainty related to these parameters in order to quantify their effect and deliver safer (i.e., more robust) operating conditions. This paper discusses a computationally efficient robust dynamic optimization approach based on the Sigma Point method and shows how it outperforms a linearization-based method for a nonlinear dynamic chemical vapor deposition reactor case-study with multiple uncertainties. Moreover, by accounting for uncertainty a trade-off between process safety and performance of the reactor is introduced. This aspect is cast in a multi-objective dynamic optimization framework. In particular, it is illustrated how an increasing robustness (i.e., process safety) induces a worsening of other investigated objective functions and results in robustified Pareto sets
Computer Aided Process Engineering FORUM CAPE FORUM 2019 - BOOK OF ABSTRACTS
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Simuleren en ontwerpen van klassieke en geavanceerde regelschema's in de chemische industrie
No full textEen geschikte procesregeling is onmisbaar voor de veilige en efficiënte werking van industriële chemische installaties. Klassiek wordt PID-regeling (proportioneel, integrerend en differentiërend) gebruikt. Deze is populair, goed gekend en eenvoudig, maar heeft tekortkomingen. Er is maar 1 gemanipuleerde variabele en het kan niet om met beperkingen op (proces-)variabelen. Geavanceerde modelgebaseerde regeltechniek (Model Predictieve Controle of MPC) kan een oplossing zijn voor tekortkomingen van PID-regeling. MPC werkt met een procesmodel en houdt rekening met beperkingen in het proces en kan met meerdere gemanipuleerde variabelen tegelijk overweg.
In deze masterproef zijn PID- en MPC- regelschema's uitgewerkt om op praktische wijze in een educatieve context te gebruiken. De toepasbaarheid van beide regelmethoden werd onderzocht aan de hand van verschillende toepassingen uit de chemische industrie, i.e., tanks met in- en uitstroom en een CSTR-reactor. De complexiteit van de beschouwde processen neemt gradueel toe. Van een lineair proces met één te regelen procesvariabele en één regelingang naar een niet-lineair proces met meerdere procesvariabelen en regelingangen. De 3 beschouwde gevallen zijn uitgewerkt in het softwarepakket MATLAB en Simulink waarbij de code, die voor de betreffende simulaties nodig is, overzichtelijk wordt opgeleverd. De voor- en nadelen van PID en MPC komen naar voren en worden besproken aan de hand van resultaten van simulaties. Uit de resultaten blijkt dat MPC een stap vooruit is ten opzichte van PID
Simuleren en ontwerpen van klassieke en geavanceerde regelschema's in de chemische industrie
No full textEen geschikte procesregeling is onmisbaar voor de veilige en efficiënte werking van industriële chemische installaties. Klassiek wordt PID-regeling (proportioneel, integrerend en differentiërend) gebruikt. Deze is populair, goed gekend en eenvoudig, maar heeft tekortkomingen. Er is maar 1 gemanipuleerde variabele en het kan niet om met beperkingen op (proces-)variabelen. Geavanceerde modelgebaseerde regeltechniek (Model Predictieve Controle of MPC) kan een oplossing zijn voor tekortkomingen van PID-regeling. MPC werkt met een procesmodel en houdt rekening met beperkingen in het proces en kan met meerdere gemanipuleerde variabelen tegelijk overweg.
In deze masterproef zijn PID- en MPC- regelschema's uitgewerkt om op praktische wijze in een educatieve context te gebruiken. De toepasbaarheid van beide regelmethoden werd onderzocht aan de hand van verschillende toepassingen uit de chemische industrie, i.e., tanks met in- en uitstroom en een CSTR-reactor. De complexiteit van de beschouwde processen neemt gradueel toe. Van een lineair proces met één te regelen procesvariabele en één regelingang naar een niet-lineair proces met meerdere procesvariabelen en regelingangen. De 3 beschouwde gevallen zijn uitgewerkt in het softwarepakket MATLAB en Simulink waarbij de code, die voor de betreffende simulaties nodig is, overzichtelijk wordt opgeleverd. De voor- en nadelen van PID en MPC komen naar voren en worden besproken aan de hand van resultaten van simulaties. Uit de resultaten blijkt dat MPC een stap vooruit is ten opzichte van PID
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Optimalisatie-gebaseerde methodologieën en algoritmen voor dynamische metabole fluxanalyse
No full textMathematical models for the growth, survival, inactivation and product formation of microbial organisms are becoming increasingly important for the model-based design, optimization and control of bioreactors in (industrial) biotechnology, and for assessment of food safetynbsp;quality throughout the supply chain in predictive microbiology. However, existing models mostly focus on describing these systemsnbsp;a macroscopic point of view. To further enhance the applicabilitynbsp;robustness of these models, integration of mechanistic knowledge is a necessity.
The objective of this research is the development of advanced numerical strategies that take advantage of microscopic, mechanistic knowledge in the form of a biochemical reaction network, to infer intracellular knowledge and to build new generation predictive models. The general framework that is used throughout the work is the dynamic metabolic flux analysis model structure, with its descriptive and predictive modes.
In the first part, a novel algorithm for offline, dynamic estimation of metabolic fluxes based on B-spline flux parameterizations is developed. This algorithm addresses the disadvantages of existing methodologies. Furthermore, a self-contained strategy for choosing the set of free fluxes in the dynamic metabolic flux analysis model is described. The algorithm is illustrated on two simulated case studies.
The second part describes the application of this algorithm in a relevant predictive microbiology case study involving the estimation of metabolic fluxes during a lag phase induced through a sudden shift in temperature. Two bioreactor experiments, performed to gather the necessarynbsp;for the estimation, are described,nbsp;after the definition of the metabolic reaction network, the fluxes are estimated. The evolution of the different metabolic pathways is analyzed and some interesting patterns can be discerned.
Finally, in the last part, also an online methodology for flux estimation based on the predictive dynamic metabolic flux analysis model structure is shown. The methodology uses two black-box kinetic flux models and moving horizon estimation to get continuously updated estimates ofnbsp;fluxes and a predictive model, ready for model-based control. The influence of important methodology parameters is assessed on a small-scalenbsp;study, and the performance of the algorithm with a realistic, medium-scale network is determined.status: Publishe
Op weg naar een duurzame werking in de (bio)chemische industrie: een kader voor computerondersteunde multi-objectieve besluitvorming
No full textIn this research advanced numerical techniques and software are developed to support real-time decision making for the design and optimization of large-scale dynamic (bio)chemical processes. To achieve this aim different steps must be taken. First, improvements and extensions to current state-of-the-art methods for multi-objective optimization (MOO) are elaborated in order to obtain efficient solution strategies for optimizing dynamic (bio)chemical processes. More specically, adapted algorithmic schemes, parallelization strategies and Object-Oriented Programming have to be explored. Second, a software with a user-friendly interface has to be implemented in order to allow an eective application at the industrial level. Last, a validation of the provided techniques and software is required on industry relevant case studies to prove the possibly large contributions in, e.g., reducing costs, limiting waste, lowering energy consumption and improving safety.status: Publishe
Model Based Optimization of Jacketed Tubular Reactors for the Production of Low Density Polyethylene (LDPE)
No full textDue to market saturation, global competition and a worldwide financial c risis, today's chemical industry strives for more efficient processes in order to maximize the production (conversion) and/or to reduce the corr esponding production costs without disregarding safety and environmental limitations. In these current circumstances, the trial-and-error proced ures, mainly based on the experience of operators and engineers, are not adequate anymore and the use of model based strategies is attractive. O ver the past decades, mathematical process models and model based optimi zation techniques have proven to be extremely valuable tools for optimiz ing the operation, control and design of chemical processes.The main objective of this research work is the formulation and solution of a well-defined model based optimization problem with respect to a detailed model of the jacketed tubular reactor for the production of low density polyethylene (LDPE).Setting up a well-defined model based optimization problem of an industrial application is, however, not always as straightforward as it seems. In literature, researchers choos e the shortest way to success by directly developing a high-complexity m odel and using the model to optimize with respect to a certain objective function. Due to the high complexity of the model convergence is not en sured, a good initialization is required and calculation time increases rapidly. Hence, for this research project a sustainable strategy of divide and conquer is chosen to obtain the main objective, i.e., subdividing the aim in three tasks: (i) conduct a conceptual model based design optimization, (ii) develop a detail ed steady state model of the LDPE tubular reactor and (iii) conduc t a design optimization with respect to this detailed steady state model .Before tackling the three subgoals of this dissertation, the ge neral aspects of modelling, simulation and optimization of tubular react ors are reviewed.The first part deals with the necessary steps o f the conceptual approach towards optimal design. Firstly, the multizone LDPE reactor is modelled as a sequence of low-complexity initiated plug flow reactor modules. Secondly, the unknown model parameters are estima ted on industrial simulation data as available experimental data is limi ted due to the extreme process conditions. Finally, a conceptual multi-o bjective design optimization is performed which gives a first suggestion towards the (dis)advantages of additional initiator injections, i.e., a dditional profit oppose to extra investment costs.In the second part, a high-complexity model is obtained and implemented in PEt ER-SiM of which the level of detail is higher than models reported in literature. For instance, via the method of moments, up to t he third order moments of dead and living polymer are determined and the main properties of the molecular weight distribution are more accurately computed. Moreover, the mass balances of all use d reactants and reaction products, the detailed energy balance, the mome ntum balance and the algebraic or differential equations for the physica l properties of the reaction mixture are included. By comparing the simu lation results of PEtER-SiM with the reference simulation dat a, substantial differences are observed. Hence, two steady state simulat ion approaches are discussed and the intrinsic differences are unraveled . Additionally, the influence of discretization during integration is st udied in simulation. Although this aspect is shown to be crucial in orde r to ensure accurate steady-state simulations (i.e., giving rise to devi ations up to 30 %), it is in practice too often overlooked. In the third and last part, the final objective of this dissertation is attained. A model based optimization of the system with two independent cooling water cycles on the basis of the high-complexity model is formul ated and solved. The novelty of a cooling system with two independent co oling cycles introduced a theoretical conversion increase of 19 % as 26& nbsp;% of additional heat of reaction could be removed.status: Publishe
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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