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Inverse problems using Artificial Neural Networks in long range atmospheric dispersion

  • P. K. Sharma , B. Gera and A. K. Ghosh
Published/Copyright: April 5, 2013
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Abstract

Scalar dispersion in the atmosphere is an important area wherein different approaches are followed in development of good analytical models. The analyses based on Computational Fluid Dynamics (CFD) codes offer an opportunity of model development based on first principles of physics and hence such models have an edge over the existing models. Both forward and backward calculation methods are being developed for atmospheric dispersion around NPPs at BARC. Forward modeling methods, which describe the atmospheric transport from sources to receptors, use forward-running transport and dispersion models or computational fluid dynamics models which are run many times, and the resulting dispersion field is compared to observations from multiple sensors. Backward or inverse modeling methods use only one model run in the reverse direction from the receptors to estimate the upwind sources. Inverse modeling methods include adjoint and tangent linear models, Kalman filters, and variational data assimilation, and neural network. The present paper is aimed at developing a new approach where the identified specific signatures at receptor points form the basis for source estimation or inversions. This approach is expected to reduce the large transient data sets to reduced and meaningful data sets. In fact this reduces the inherently transient data set into a time independent mean data set. Forward computations were carried out with CFD code for various cases to generate a large set of data to train the Artificial Neural Network (ANN). Specific signature analysis was carried out to find the parameters of interest for ANN training like peak concentration, time to reach peak concentration and time to fall. The ANN was trained with data and source strength and locations were predicted from ANN. The inverse problem was performed using the ANN approach in long range atmospheric dispersion. An illustration of application of CFD code for atmospheric dispersion studies for a hypothetical case is also included in the paper.

Kurzfassung

Skalare Dispersion in der Atmosphäre ist ein wichtiges Gebiet, in dem verschiedene Ansätze bei der Entwicklung guter analytischer Modelle verfolgt werden. Die Analysen auf der Basis der numerischen Strömungsmechanik führen zur Modellentwicklung auf der Basis grundlegender physikalischer Prinzipien und haben deshalb einen Vorteil gegenüber bereits existierenden Modellen. Verschiedene Methoden für die Berechnung der atmosphärische Dispersion um die Kernkraftwerke bei BARC wurden entwickelt. Vorwärts modellierende Verfahren, die den Transport in der Atmosphäre von der Quelle zum Empfänger beschreiben, verwenden vorwärts laufende Transport- und Dispersionsmodelle oder Modelle auf der Basis numerischer Strömungsmechanik mit vielen Durchläufen und das daraus resultierende Dispersionsfeld wird verglichen mit Beobachtungen multipler Sensoren. Rückwärts oder inverse modellierende Methoden verwenden nur einen Modelldurchlauf in inverser Richtung vom Empfänger um die gegen den Wind gerichteten Quellen zu bestimmen. Inverse Modellierungsverfahren umfassen adjungierte und tangentiale lineare Modelle, Kalman Filter, abweichende Datenassimilation und neuronale Netze. Ziel der vorliegenden Arbeit ist die Entwicklung eines neuen Ansatzes bei dem die identifizierten speziellen Signaturen an den Empfängerpunkten die Basis bildet für die Bestimmung der Quelle oder der Inversionen. Es wird erwartet, dass dieser Ansatz die langen Transienten-Datensätze auf aussagekräftige Datensätze reduziert. Tatsächlich reduzieren sich die transienten Datensätze zu zeitabhängigen mittleren Datensätzen. Vorwärtsrechnungen wurden durchgeführt mit Hilfe eines CFD Rechencodes für verschiedene Fälle, um einen großen Datensatz zum Trainieren der künstlichen neuronalen Netze (KNN) zu erzeugen. Die Analyse spezifischer Signaturen wurden durchgeführt um die für das KNN Training interessanten Parameter zu finden, wie z.B. Spitzenwerte der Konzentration, Zeit zum Erreichen dieser Spitzenwerte und Zeit bis zum Abfall der Konzentration. Das KNN wurde trainiert mit Daten und Quellstärke und Positionen wurden damit bestimmt. Inverse Probleme wurden mit Hilfe der KNN gelöst für weitreichender atmosphärische Dispersion. Diese Arbeit beinhaltet auch eine Erläuterung der Anwendung des CFD Codes für Studien der atmosphärischen Dispersion eines hypothetischen Falls.


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Received: 2010-8-20
Published Online: 2013-04-05
Published in Print: 2011-05-01

© 2011, Carl Hanser Verlag, München

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