| 1. |
- Mazur, G. P., et al.
(författare)
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Towards modeling quasi-periodic oscillations of microquasars with oscillating slender tori
- 2013
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 554
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Tidskriftsartikel (refereegranskat)abstract
- Context. One of the often discussed models for high-frequency quasi-periodic oscillations of X-ray binaries is the oscillating torus model, which considers oscillation modes of slender accretion tori. Aims. Here, we aim at developing this model by considering the observable signature of an optically thick slender accretion torus subject to simple periodic deformations. Methods. We compute light curves and power spectra of a slender accretion torus subject to simple periodic deformations: vertical or radial translation, rotation, expansion, and shear. Results. We show that different types of deformations lead to very different Fourier power spectra and therefore could be observationally distinguished. Conclusions. This work is a first step in a longer term study of the observable characteristics of the oscillating torus model. It gives promising perspectives on the possibility of constraining this model by studying the observed power spectra of quasi-periodic oscillations.
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| 2. |
- Grahn, Markus, 1978, et al.
(författare)
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A Diesel Engine Management System Strategy for Transient Engine Operation
- 2013
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Ingår i: IFAC Proceedings Volumes (IFAC-PapersOnline). - 2405-8963. - 9783902823434 ; 7:1, s. 1-6
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Konferensbidrag (refereegranskat)abstract
- A strategy for diesel engine management systems has been introduced and evaluated. The strategy calculates set points for engine management system controllable quantities with an aim to minimize fuel consumption for a given engine speed and requested torque profile, while keeping accumulated emissions below given limits. The strategy is based on existing methodology for steady-state engine operation, but extended to handle transient effects in the engine caused by dynamics in the air system. The strategy has been evaluated using a simulation model of a diesel engine system. The model estimates fuel consumption together with NOX and soot emissions for a transient simulation cycle depending on set points in the engine management system for boost pressure, oxygen fraction in the intake manifold, and injection timing. For the transient simulation scenario used in this paper and with given limits on accumulated emissions, the strategy has been shown to decrease fuel consumption with up to 0.7% compared to a strategy that is based only on steady-state engine operation.
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| 3. |
- Grahn, Markus, 1978, et al.
(författare)
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A Structure and Calibration Method for Data-Driven Modeling of NOX and Soot Emissions from a Diesel Engine
- 2012
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627.
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Tidskriftsartikel (refereegranskat)abstract
- The development and implementation of a new structure for data-driven models for NOX and soot emissions is described. The model structure is a linear regression model, where physically relevant input signals are used as regressors, and all the regression parameters are defined as grid-maps in the engine speed/injected fuel domain. The method of using grid-maps in the engine speed/injected fuel domain for all the regression parameters enables the models to be valid for changes in physical parameters that affect the emissions, without having to include these parameters as input signals to the models. This is possible for parameters that are dependent only on the engine speed and the amount of injected fuel. This means that models can handle changes for different parameters in the complete working range of the engine, without having to include all signals that actually effect the emissions into the models. The approach possibly also enables for the model to handle the main differences between steady-state engine operation and transient engine operation, thus possibly being able to use steady-state engine measurement data to calibrate the model, but still achieve acceptable performance for transient engine operation. This, however, is not evaluated in this study. The model structure has been used to create models for NOX and soot emissions. These models have been calibrated using measured steady-data from a 5 cylinder Volvo passenger car diesel engine with a displacement volume of 2.4 liters, equipped with a turbocharger, an exhaust gas recirculation system, and a common rail injection system. The models estimate NOX mass flow with a root mean square error of 0.0021 g/s and soot mass flow with a root mean square error of 0.59 mg/s for the steady-state engine data used in this study. The models are capable of reacting to different calibratable engine parameters, and they are also fast to execute. This makes them suitable for development of engine management system optimization. The models could also be implemented directly into an engine management system. For comparison, three other fast models of different types for NOX and soot emissions have been implemented and evaluated.
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| 4. |
- Grahn, Markus, 1978, et al.
(författare)
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A Transient Diesel EMS Strategy for Online Implementation
- 2014
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Ingår i: IFAC Proceedings Volumes (IFAC-PapersOnline). - : Elsevier BV. - 2405-8963 .- 1474-6670. - 9783902823625 ; 19, s. 11842-11847
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Konferensbidrag (refereegranskat)abstract
- A recently developed strategy for diesel engine management systems is modified to reduce the implementation complexity. The strategy calculates set points for engine management system controllable quantities with an aim to minimize fuel consumption for a given engine speed and requested torque profile, while keeping accumulated emissions below given limits. The strategy is based on the methodology for steady-state engine operation, but extended to handle transient effects in the engine caused by dynamics in the air system. The strategy leads to the parametrization of mappings with two, three and four input dimensions respectively. In this paper, a modification of the strategy is proposed such that the memory demanding multidimensional mappings can be approximated in an engine management system using only two-dimensional grid maps. The modified strategy has been evaluated using a complete diesel engine vehicle system model simulating the NEDC driving cycle. The performance of the modified strategy has been compared with the original performance of the strategy. It is demonstrated that the modification of the strategy has very little impact on resulting performance of a vehicle but requires considerably less memory for implementation.
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| 5. |
- Grahn, Markus, 1978, et al.
(författare)
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B-splines for Diesel Engine Emission Modeling
- 2012
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Ingår i: IFAC Proceedings Volumes (IFAC-PapersOnline). - 2405-8963. - 9783902823168 ; , s. 416-423
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Konferensbidrag (refereegranskat)abstract
- The equivalence between linear interpolation and B-spline functions of degree 1 is described. The equivalence is used to express interpolation based diesel engine NOX and soot emission models as B-spline functions, and to apply data fitting methods for B-spline functions to perform calibration of the models. This strategy leads to that the model calibration can be calculated directly by means of analytically solving a minimization problem. The B-spline representation also makes it possible to control the smoothness and extrapolation behavior of the interpolation maps in the models in a controlled manner. The models have been calibrated using measured steady-state data from a 5-cylinder Volvo passenger car diesel engine with a displacement volume of 2.4 liters, equipped with a turbocharger, an exhaust gas recirculation system, and a common rail injection system. The calibrated model for NOX emissions predicts the NOX mass ow with a root mean square error of 1.6 mg/s, and the calibrated model for soot emissions predicts the soot mass ow with a root mean square error of 0.65 mg/s. The described equivalence between linear interpolation and B-spline functions of degree 1 could also be used for calibration of other models of similar structure.
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| 6. |
- Grahn, Markus, 1978, et al.
(författare)
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Data-driven emission model structures for diesel engine management system development
- 2014
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Ingår i: International Journal of Engine Research. - : SAGE Publications. - 1468-0874 .- 2041-3149. ; 15:8, s. 906-917
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Tidskriftsartikel (refereegranskat)abstract
- This article discusses some specific data-driven model structures suitable for prediction of NOx and soot emissions from a diesel engine. The model structures can be described as local linear regression models where the regression parameters are defined by two-dimensional lookup tables. It is highlighted that this structure can be interpreted as a B-spline function. Using the model structure, models are derived from measured engine data. The smoothness of the derived models is controlled by using an additional regularization term, and the globally optimal model parameters can be found by solving a linear least squares problem. Experimental data from a five-cylinder Volvo passenger car diesel engine is used to derive NOx and soot models, using a leave-one-out cross-validation strategy to determine the optimal degree of regularization. The model for NOx emissions predicts the NOx mass flow with an average relative error of 5.1% and the model for soot emissions predicts the soot mass flow with an average relative error of 29% for the mea- surement data used in this study. The behavior of the models for different engine management system settings regarding boost pressure, amount of exhaust gas recirculation, and injection timing has been studied. The models react to the dif- ferent engine management system settings in an expected way, making them suitable for optimization of engine manage- ment system settings. Finally, the model performance dependence on the selected model complexity and on the number of measurement data points used to derive the models has been studied.
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| 7. |
- Grahn, Markus, 1978, et al.
(författare)
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Model-based diesel Engine Management System optimization for transient engine operation
- 2014
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Ingår i: Control Engineering Practice. - : Elsevier BV. - 0967-0661. ; 29, s. 103-114
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Tidskriftsartikel (refereegranskat)abstract
- A recently developed strategy to calculate set points for controllable diesel engine systems is described, further developed, and evaluated. The strategy calculates set points with an aim to minimize fuel consumption for a given dynamic vehicle driving cycle, while keeping accumulated emissions below given limits. The strategy is based on existing methodology for steady-state engine operation, but extended to handle transient effects in the engine caused by dynamics in the engine air system. Using the strategy, set points for the complete operating range of the engine can be calculated off-line and stored in an Engine Management System, hence set points can be derived for any (steady-state or transient) driving scenario. The strategy has been evaluated using a simulation model of a complete diesel engine vehicle system. The model estimates fuel consumption, NOX, and soot emissions for a dynamic vehicle driving cycle depending on set points for boost pressure, oxygen fraction in the intake manifold, and injection timing, throughout the simulation. Using this simulation model, the strategy has been shown to decrease fuel consumption for the New European Driving Cycle with 0.56%, the Federal Test Procedure with 1.04%, and the Japanese JC08 cycle with 0.84% compared to a strategy based on steady-state engine operation.
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| 8. |
- Johansson, Markus, 1978, et al.
(författare)
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Comparison between Two Phase Retrieval Methods for Electromagnetic Source Modeling
- 2011
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Ingår i: Progress in Electromagnetics Research B. - 1937-6472. ; 30, s. 239-253
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Tidskriftsartikel (refereegranskat)abstract
- Phase-retrieval from measured phaseless field data is of interest for various applications including electromagnetic dosimetry, electromagnetic compatibility investigations, near-field to far-field transformations and antenna diagnostics. In this study two phaseretrieval methods are compared. The first method, the adjoint field method, employs a gradient-based optimization algorithm based on the adjoint fields. The second method, the phase angle gradient method, uses an optimization algorithm based on the phase angle gradients of a functional. The methods are tested with numerical test cases and the phase angle gradient method is found to retrieve the phase with the best accuracy. Moreover it gives results that agree well with correct phase.
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| 9. |
- Johansson, Markus, 1978
(författare)
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Complex source modeling for electromagnetic dosimetry
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Electromagnetic modeling of complex sources is useful in dosimetry applications as well as for near-field to far-field transformations and antennadiagnostics. In order to determine whether exposure safety guidelines, such as the EU directive 2004/40/EC, are complied with, it is important to be able tomodel the field distribution from electromagnetic sources.Two methods of determining the total field, including phase information, when only field amplitudes have been measured on a set of planes in front of an electromagnetic source have been developed. The first method, the adjoint field method, is a gradient based optimization algorithm based on the adjoint fields. The second method, the phase angle gradient method, employs an optimization algorithm based on the phase angle gradients of a functional.The methods have been tested with numerical test cases. The adjoint field method is functioning well in 2D and the phase angle gradient method gives good results for 3D test cases. The phase angle gradient method was also tested for measured magnetic flux density with low frequency from a transformer and for electric field with high frequency from a mobile phone. For the cases with measured field the obtained phase angles on the measurement plane closest to the source gave calculated field on other measurement planes that agrees well with measured field.The developed methods are useful for coupling of measured field amplitudes in front of a source, to numerical calculations of the fields inside humans.
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| 10. |
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