Bernhard Kortschak and Bernhard Brandstätter
For the spatial reconstruction of a two phase flow, as it might occur in a pipe, the main problem has always been the blurring of the resulting images.
Abstract
Purpose
For the spatial reconstruction of a two phase flow, as it might occur in a pipe, the main problem has always been the blurring of the resulting images.
Design/methodology/approach
In this paper, we present a method where blurring is implicitly avoided by the use of level sets. The level set method describes the iteratively evolving interface between different materials. The underlying field problem is solved with the boundary element method formulated in the region, where the degrees of freedom are present and the finite element method in all other regions.
Findings
Finally reconstruction results of an electrical capacitance tomography sensor are presented to show the validity of the method.
Originality/value
Presents a method where blurring is avoided by the use of level sets.
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Keywords
Daniel Watzenig, Gerald Steiner, Anton Fuchs, Hubert Zangl and Bernhard Brandstätter
The investigation of the influence of the modeling error on the solution of the inverse problem given uncertain measured data in electrical capacitance tomography (ECT).
Abstract
Purpose
The investigation of the influence of the modeling error on the solution of the inverse problem given uncertain measured data in electrical capacitance tomography (ECT).
Design/methodology/approach
The solution of the nonlinear inverse problem in ECT and hence, the obtainable accuracy of the reconstruction result, highly depends on the numerical modeling of the forward map and on the required regularization. The inherent discretization error propagates through the forward map, the solution of the inverse problem, the subsequent calculation of process parameters and properties and may lead to a substantial estimation error. Within this work different finite element meshes are compared in terms of obtainable reconstruction accuracy. In order to characterize the reconstruction results, two error measures are introduced, a relative integral error and the relative error in material fraction. In addition, the influence of the measurement noise given different meshes is investigated from the statistical point of view using repeated measurements.
Findings
The modeling error, the degree of regularization, and measurement uncertainties are the determining and limiting factors for the obtainable reconstruction accuracy of electrical tomography systems. The impact of these key influence factors on the calculation of process properties given both synthetic as well as measured data is quantified. Practical implications – The obtained results show that especially for measured data, the variability in calculated parameters strongly depends on the efforts put on the forward modeling, i.e. on an appropriate finite element mesh size. Hence, an investigation of the modeling error is highly recommended when real‐world tomography problems have to be solved.
Originality/value
The results presented in this work clearly show how the modeling error as well as inherent measurement uncertainties influence the solution of the inverse problem and the posterior calculation of certain parameters like void fraction in process tomography.
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Bernhard Schweighofer and Bernhard Brandstätter
The accurate simulation of battery cells is of growing interest in automotive industry especially in hybrid vehicle technology. Conventional lumped parameter models are not able…
Abstract
The accurate simulation of battery cells is of growing interest in automotive industry especially in hybrid vehicle technology. Conventional lumped parameter models are not able to predict the battery voltage accurately. Thus models describing the physics of the battery cell are searched. In this paper a model consisting of six partial differential equations is proposed, which predicts the state of charge (SOC) and the battery voltage for given charge and discharge current densities.
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Markus Neumayer, Daniel Watzenig and Bernhard Brandstätter
The purpose of this paper is to demonstrate an inverse problem approach for the determination of stress zones in steel plates of electrical machines. Steel plates of electrical…
Abstract
Purpose
The purpose of this paper is to demonstrate an inverse problem approach for the determination of stress zones in steel plates of electrical machines. Steel plates of electrical machines suffer large mechanical stress by processes like cutting or punching during the fabrication. The mechanical stress has effects on the electrical properties of the steel, and thus on the losses of the machine.
Design/methodology/approach
In this paper, the authors present a sensor arrangement and an appropriate algorithm for determining the spatial permeability distribution in steel plates. The forward problem for stress zone imaging is explained and an appropriate numerical solution technique is proposed. Then an inverse problem formulation is introduced and the nature of the problem is analyzed.
Findings
Based on sensitivity analysis, different measurement procedures are compared and a measurement setup is suggested. Further the ill‐posed nature of the inverse problem is analyzed by the Picard condition.
Practical implications
Because of the increased losses due to stress zones, the quantification of stress effects is of interest to adjust the production process. Stress zone imaging is a first approach for the application of an imaging system to quantify these material defects.
Originality/value
This paper presents a simulation study about the applicability of an inverse problem for stress zone imaging and presents first reconstruction results. Further, the paper discusses several issues about stress zone imaging for the ongoing research.
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Bernhard Brandstätter and Christian Magele
Considers, without loss of generality, a simple linear problem, where in a certain domain the magnetic field, generated by infinitely long conductors, whose locations as well as…
Abstract
Considers, without loss of generality, a simple linear problem, where in a certain domain the magnetic field, generated by infinitely long conductors, whose locations as well as the currents are unknown, has to meet a certain figure. The problem is solved by applying hierarchical simulated annealing, which iteratively reduces the dimension of the search space to save computational cost. A Gauss‐Newton scheme, making use of analytical Jacobians, preceding a sequential quadratic program (SQP), will be applied as a second approach to tackle this severely ill‐posed problem. The results of these two techniques will be analyzed and discussed and some comments on future work will be given.
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Bernhard Brandstätter, Gert Holler and Daniel Watzenig
Electrical capacitance tomography (ECT) is a technique for reconstructing information about the spatial distribution of the contents of closed pipes by measuring variations in the…
Abstract
Electrical capacitance tomography (ECT) is a technique for reconstructing information about the spatial distribution of the contents of closed pipes by measuring variations in the dielectric properties of the material inside the pipe. In this paper, we propose a method that solves the non‐linear reconstruction problem directly leading to less iterations and higher accuracy than linear back projection algorithms currently in use in most ECT systems.
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Bernhard Brandstätter, Hermann Scharfetter and Christian Magele
Electrical impedance tomography (EIT) is a non‐invasive method to monitor conductivity changes in regions of the human body. Its robust, miniaturizable instrumentation makes EIT…
Abstract
Electrical impedance tomography (EIT) is a non‐invasive method to monitor conductivity changes in regions of the human body. Its robust, miniaturizable instrumentation makes EIT particularly suitable for online‐monitoring without too much inconvenience for the patient. A major methodological problem is the poor quality of the conductivity images, which is due to the low spatial resolution and low sensitivity for structures far away from the object’s surface as well as large qualitative errors in the reconstructed conductivity values. This paper outlines the advantages of multi‐frequency EIT for a simple two‐dimensional model. In the first part of the paper we assume that some a priori information from MR images is at hand, providing good starting values for the reconstruction process, while in the second part it is assumed that no a priori information about regions of different material values is available.
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Joachim Schauß, Bernhard Hirsch and Matthias Sohn
This paper aims to examine how balanced scorecard (BSC) users change their judgement processes according to qualitative changes in the BSC. Prior experimental studies have found…
Abstract
Purpose
This paper aims to examine how balanced scorecard (BSC) users change their judgement processes according to qualitative changes in the BSC. Prior experimental studies have found that decision-makers do not fully adapt their judgements according to changes in financial reports, known as functional fixation. Although previous research has examined functional fixation in several management accounting-related disciplines, the research has not been completely successful in developing a deeper understanding of the cognitive processes that are responsible for the occurrence of this judgemental bias.
Design/methodology/approach
To fill this gap, a combination of structural modelling and a process tracing method that monitors participants’ information acquisition to better understand the underlying cognitive processes that affect BSC users’ judgements is used.
Findings
Overall, the results indicate that functional fixation is present both from an input–output (structural modelling) and a process tracing perspective. Stable general individual differences, particularly in terms of intuitive versus deliberative preferences in decision-making, influence the probability of functionally fixated behaviour. Additionally, previous findings concerning the over-reliance on financial information in the BSC setting is replicated. Using process data, it was found that BSC users rely more on financial measures than on non-financial measures in the pre-decisional phase of exercising their judgement.
Originality/value
This paper contribute to management accounting research on the BSC by investigating two cognitive biases (functional fixation and overreliance on financial measures) from an input–output and a process tracing perspective.