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Nilsson, Börje
Publications (10 of 85) Show all publications
Nordebo, S., Gustafsson, M., Ivanenko, Y., Nilsson, B. & Sjöberg, D. (2018). Cylindrical multipole expansion for periodic sources with applications for three-phase power cables. Mathematical methods in the applied sciences, 41(3), 959-965
Open this publication in new window or tab >>Cylindrical multipole expansion for periodic sources with applications for three-phase power cables
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2018 (English)In: Mathematical methods in the applied sciences, ISSN 0170-4214, E-ISSN 1099-1476, Vol. 41, no 3, p. 959-965Article in journal (Refereed) Published
Abstract [en]

This paper presents a c ylindrical multipole expansion for periodic sources with applications for three-phase power cables.It is the aim of the contribution to provide some analytical solutions and techniques that can be useful in the calculation ofcable losses. Explicit analytical results are given for the fields generated by a three-phase helical current distribution andwhich can be computed efficiently as an input to other numerical methods such as, for example , the Method of Moments.It is shown that the field computations are numerically stable at low frequencies (such as 50 Hz) as well as in the quasi-magnetostatic limit provided that sources are divergence-free. The cylindrical multipole expansion is fur thermore usedto derive an efficient analytical model of a measurement coil to measure and estimate the complex valued permeability ofmagnetic steel armour in the presence of a strong skin-effect.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2018
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Signal Processing
Research subject
Physics, Waves and Signals
Identifiers
urn:nbn:se:lnu:diva-59497 (URN)10.1002/mma.3992 (DOI)000425834700011 ()
Available from: 2016-12-23 Created: 2016-12-23 Last updated: 2018-03-09Bibliographically approved
Ivanenko, Y., Gustafsson, M., Jonsson, B., Luger, A., Nilsson, B., Nordebo, S. & Toft, J. (2017). Passive approximation and optimization with B-splines.
Open this publication in new window or tab >>Passive approximation and optimization with B-splines
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2017 (English)Report (Other academic)
Abstract [en]

A passive approximation problem is formulated where the target function is an arbitrary complex valued continuous function defined on an approximation domain consisting of a closed interval of the real axis. The approximating function is any Herglotz function with a generating measure that is absolutely continuous with Hölder continuous density in an arbitrary neighborhood of the approximation domain. The norm used is induced by any of the standard Lp-norms where 1 ≤ p ≤ ∞. The problem of interest is to study the convergence properties of simple Herglotz functions where the generating measures are given by finite B-spline expansions, and where the real part of the approximating functions are obtained via the Hilbert transform. In practice, such approximations are readily obtained as the solution to a finite- dimensional convex optimization problem. A constructive convergence proof is given in the case with linear B-splines, which is valid for all Lp-norms with 1 ≤ p ≤ ∞. A number of useful analytical expressions are provided regarding general B-splines and their Hilbert transforms. A typical physical application example is given regarding the passive approximation of a linear system having metamaterial characteristics. Finally, the flexibility of the optimization approach is illustrated with an example concerning the estimation of dielectric material parameters based on given dispersion data. 

Publisher
p. 24
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Physics, Waves and Signals
Identifiers
urn:nbn:se:lnu:diva-63878 (URN)
Funder
Swedish Foundation for Strategic Research , AM13-0011
Available from: 2017-05-18 Created: 2017-05-18 Last updated: 2017-06-09Bibliographically approved
Yanaz Cinar, Ö., Boij, S., Cinar, G. & Nilsson, B. (2017). Sudden area expansion in ducts with flow: A comparison between cylindrical and rectangular modelling. Journal of Sound and Vibration, 396, 307-324
Open this publication in new window or tab >>Sudden area expansion in ducts with flow: A comparison between cylindrical and rectangular modelling
2017 (English)In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 396, p. 307-324Article in journal (Refereed) Published
Abstract [en]

The acoustic properties of an area expansion are analyzed for frequencies where flow acoustic interaction may have a significant influence due to flow separation and vortex shedding. It is investigated why this interaction, which is seen in experimental data on a cylindrical duct as a resonance at a particular Strouhal number of order one, is present in rectangular but not in cylindrical modelling that would be expected to be more realistic; both models consider a plug flow. An analytic method that is suitable for identifying possible reasons for the discrepancies between the two geometries is used. The previously published rectangular model is generalized to the cylindrical case and both models are used to simulate results for all elements in the plane wave scattering matrix and for all parameters for which experimental results are available. The comparison between the two models and between models and measured data is thus not restricted to the flow acoustic induced resonance. The results show that the two geometries in general perform equally when compared with the experimental results, but that the rectangular modelling indeed performs better for some cases. This occurs around a critical Strouhal number, and for higher Mach number. Using the analytic form of the solution, it is shown that the observed discrepancy is related to interaction between the damped hydrodynamic mode and a downstream propagating higher order acoustic mode. Such interaction is not present in the corresponding quiescent duct, and is related to the presence of the shear layer. The analysis shows that the structure of the higher order acoustic modes is different for the cylindrical and rectangular case, respectively, causing the difference in resonant behaviour.

National Category
Fluid Mechanics and Acoustics
Research subject
Mathematics, Applied Mathematics
Identifiers
urn:nbn:se:lnu:diva-61850 (URN)10.1016/j.jsv.2017.02.034 (DOI)000399507200017 ()
Projects
Vågor och signaler
Available from: 2017-03-27 Created: 2017-03-27 Last updated: 2017-05-24Bibliographically approved
Andersson, A., Nilsson, B. & Biro, T. (2016). Fourier Methods for harmonic scalar waves in general waveguides. Journal of Engineering Mathematics, 98(1), 21-38
Open this publication in new window or tab >>Fourier Methods for harmonic scalar waves in general waveguides
2016 (English)In: Journal of Engineering Mathematics, ISSN 0022-0833, E-ISSN 1573-2703, Vol. 98, no 1, p. 21-38Article in journal (Refereed) Published
Abstract [en]

A set of semi-analytic techniques based on Fourier analysis is used to solve wave-scattering problems in variously shaped waveguides with varying normal admittance boundary conditions. Key components are the newly developed conformal mapping methods, wave splitting, Fourier series expansions in eigenfunctions to non-normal operators, the building block method or the cascade technique, Dirichlet-to-Neumann operators, and reformulation in terms of stable differential equations for reflection and transmission matrices. For an example, the results show good correspondence with a finite element method solution to the same problem in the low- and medium-frequency domains. The Fourier method complements finite element analysis as a waveguide simulation tool. For inverse engineering involving tuning of straight waveguide parts joining complicated waveguide elements, the Fourier method is an attractive alternative including time aspects. The prime motivation for the Fourier method is its added physical understanding primarily at low frequencies.

Place, publisher, year, edition, pages
Springer, 2016
Keyword
Building Block Method, Conformal mappings, Dirichlet-to-Neumann operators, Fourier series, Harmonic scalar waves, Normal surface admittance
National Category
Signal Processing
Research subject
Mathematics, Mathematics
Identifiers
urn:nbn:se:lnu:diva-42904 (URN)10.1007/s10665-015-9808-8 (DOI)000376643300003 ()2-s2.0-84938152325 (Scopus ID)
Available from: 2015-04-28 Created: 2015-04-28 Last updated: 2017-12-04Bibliographically approved
Olsson, J., Linderholt, A. & Nilsson, B. (2016). Impact evaluation of a thin hybrid wood based joist floor. In: Sas, P; Moens, D; VanDeWalle, A (Ed.), Proceedings of ISMA 2016, presented at the International Conference on Noise andVibration Engineering (ISMA): . Paper presented at The International Conference on Noise and Vibration Engineering (ISMA) in Leuven, Belgium 19-21 September 2016. (pp. 589-602). Leuven, Belgium: Katholieke University Leuven
Open this publication in new window or tab >>Impact evaluation of a thin hybrid wood based joist floor
2016 (English)In: Proceedings of ISMA 2016, presented at the International Conference on Noise andVibration Engineering (ISMA) / [ed] Sas, P; Moens, D; VanDeWalle, A, Leuven, Belgium: Katholieke University Leuven , 2016, p. 589-602Conference paper, Published paper (Refereed)
Abstract [en]

The purpose of this paper is twofold. The first aim is to develop a numericalanalysis procedure, by combining FRFs from FE-models with analyticalformulas for sound emission and transmission from the ceiling anddownwards within a room with four walls. The aim is to, by applying thisapproach; accomplish a tool which calculates the relative impact soundbetween different joist floors, in the low frequency range. The second aim is tobenchmark a thin hybrid wooden based joist floor with similar thickness,surface weight and global bending stiffness as a concrete hollow core floorstructure. What will be the difference in sound transmission? The question isrelevant since it may be necessary to make thinner wood based joist floors inhigh rise buildings, if wood should stay competitive against concrete. Theresults show that the direct transmissions of impact sound are very similararound the first bending mode. As the frequency increases, the modes in thestructures differ significantly. Below 100 Hz, the concrete floor has 4 modes,while the hybrid joist floor has 9 modes. As the frequency increases the soundradiation characteristics differs. The results show that it is possible to havesimilar sound transmission properties around the first bending modes for ahybrid based joist floor and a hollow core concrete floor structure with similar thicknesses. At the first modes of the structure, the information about thesurface weight and global bending stiffness are useful for prediction of soundtransmission properties but for higher modes, they are not sufficient.

Place, publisher, year, edition, pages
Leuven, Belgium: Katholieke University Leuven, 2016
National Category
Construction Management
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-58129 (URN)000392486301010 ()978-90-73802-94-0 (ISBN)
Conference
The International Conference on Noise and Vibration Engineering (ISMA) in Leuven, Belgium 19-21 September 2016.
Available from: 2016-11-15 Created: 2016-11-14 Last updated: 2017-03-08Bibliographically approved
Nilsson, B., Ioannidis, A., Ivanenko, Y. & Nordebo, S. (2016). On absence of sources at infinity and uniqueness for waveguide solutions. In: Proceedings of the 2016 18th International Conference on Electromagnetics in Advanced Applications, ICEEA 2016: . Paper presented at 2016 18th International Conference on Electromagnetics in Advanced Applications, ICEEA, 19-23 Sept. 2016 (pp. 780-783). IEEE Press
Open this publication in new window or tab >>On absence of sources at infinity and uniqueness for waveguide solutions
2016 (English)In: Proceedings of the 2016 18th International Conference on Electromagnetics in Advanced Applications, ICEEA 2016, IEEE Press, 2016, p. 780-783Conference paper, Published paper (Refereed)
Abstract [en]

This paper discusses criteria for establishing uniqueness of wave propagation problems. Causality, or passivity that implies causality, is adopted as the fundamental principle. It is stressed that radiation conditions are not applicable for waveguide modes that carry no active power. The Jones' criteria for causality in the frequency domain, which covers the convectively unstable case, are presented and analysed, the vanishing absorption principle, VAP, in particular. It is proposed to use L2 for a lossy medium but a weighted L2 for the lossless case.

Place, publisher, year, edition, pages
IEEE Press, 2016
National Category
Mathematical Analysis
Research subject
Mathematics, Applied Mathematics; Physics, Waves and Signals
Identifiers
urn:nbn:se:lnu:diva-60614 (URN)10.1109/ICEAA.2016.7731515 (DOI)2-s2.0-85007301251 (Scopus ID)978-1-4673-9811-4 (ISBN)978-1-4673-9810-7 (ISBN)
Conference
2016 18th International Conference on Electromagnetics in Advanced Applications, ICEEA, 19-23 Sept. 2016
Available from: 2017-02-09 Created: 2017-02-09 Last updated: 2017-06-09Bibliographically approved
Nordebo, S., Gustfsson, M., Nilsson, B. & Sjöberg, D. (2015). Cylindrical multipole expansion for helical structures. In: M3ST (2015) Kalamat, Greece, 30 August-1 September: Book of Abstracts. Paper presented at Modern Mathematical Methods in Science and Technology (M3ST), Kalamata, Greece, 30 August-1 september 2015.
Open this publication in new window or tab >>Cylindrical multipole expansion for helical structures
2015 (English)In: M3ST (2015) Kalamat, Greece, 30 August-1 September: Book of Abstracts, 2015Conference paper, Oral presentation with published abstract (Other academic)
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Signal Processing
Research subject
Physics, Waves and Signals
Identifiers
urn:nbn:se:lnu:diva-51412 (URN)
Conference
Modern Mathematical Methods in Science and Technology (M3ST), Kalamata, Greece, 30 August-1 september 2015
Available from: 2016-03-26 Created: 2016-03-26 Last updated: 2017-01-10Bibliographically approved
Nordebo, S., Cinar, G., Gustafsson, S. & Nilsson, B. (2015). Dispersion modeling and analysis for multilayered open coaxial waveguides. IEEE transactions on microwave theory and techniques, 63(6), 1791-1799
Open this publication in new window or tab >>Dispersion modeling and analysis for multilayered open coaxial waveguides
2015 (English)In: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 63, no 6, p. 1791-1799Article in journal (Refereed) Published
Abstract [en]

This paper presents a detailed modeling and analysis regarding the dispersion characteristics ofmultilayered open coaxial waveguides or cables. The electromagnetic model is based on a layer recursive computation of axial-symmetric fields in connection with a magnetic frill generator excitation that can be calibrated to the current measured at the input of the cable. The layer recursive formulation enables a stable and efficient numerical computation of the related dispersion functions, as well as a detailed analysis regarding the analytic and asymptotic properties of the associated determinants. Modal contributions as well as the contribution from the associated branch-cut (nondiscrete radiating modes) are defined and analyzed. Measurements and modeling of pulse propagation on an 82-km-long HVDC power cable are presented as a concrete example. In this example, it is concluded that the contribution from the dominating axial-symmetric transverse magnetic mode is sufficient, and that the contribution from the branch-cut is negligible for all practical purposes, and in particular if the exterior domain is lossy. The main contribution of this paper is to provide the necessary modeling and analysistools for a quantitative study of these phenomena.

National Category
Physical Sciences Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Technology (byts ev till Engineering)
Identifiers
urn:nbn:se:lnu:diva-40649 (URN)10.1109/TMTT.2015.2420555 (DOI)000355930300002 ()2-s2.0-84957962336 (Scopus ID)
Available from: 2015-03-07 Created: 2015-03-07 Last updated: 2017-12-04Bibliographically approved
Sjödén, T., Nordebo, S. & Nilsson, B. (2015). On the accuracy and resolution in inverse imaging.
Open this publication in new window or tab >>On the accuracy and resolution in inverse imaging
2015 (English)Manuscript (preprint) (Other academic)
Abstract [en]

This paper provides a quantitative analysis of the optimal accuracy and resolution in inverse imaging based on the Cram ́er-Rao lower bound. The imaging problem is characterized by the forward operator and its Jacobian. The Fisher information operator is defined for a deterministic parameter in a real Hilbert space and a stochastic measurement in a finite-dimensional complex Hilbert space with Gaussian measure. The connection between the Fisher information and the Singular Value Decomposition (SVD) based on the Maximum Likelihood (ML) criterion (the ML-based SVD) is established. It is shown that the eigenspaces of the Fisher information provide a suitable basis to quantify the trade-off between the accuracy and the resolution of the (non-linear) inverse problem. It is also shown that the truncated ML-based pseudo-inverse is a suitable regularization strategy for a linearized problem, which exploits a sufficient statistics for estimation within these subspaces.

The statistical-based Cram ́er-Rao lower bound provides a complement to the deterministic upper bounds and the L-curve techniques that are employed with linearized inversion. To this end, the Electrical Impedance Tomography (EIT) provides an interesting example where the eigenvalues of the SVD usually do not exhibit a very sharp cut-off, and a trade-off between the accuracy and the resolution may be of practical importance. A numerical study of EIT is described, including a statistical analysis of the model errors due to the linearization.

Keyword
inverse imaging, Maximum Likelihood (ML), Singular Value Decompo- sition (SVD), Electrical Impedance Tomography (EIT), accuracy, resolution, Cram ́er- Rao bound (CRB)
National Category
Signal Processing Other Physics Topics
Research subject
Physics, Waves and Signals
Identifiers
urn:nbn:se:lnu:diva-18688 (URN)
Available from: 2012-05-15 Created: 2012-05-15 Last updated: 2017-01-10Bibliographically approved
Gustafsson, S., Nilsson, B., Nordebo, S. & Sjöberg, M. (2015). Wave propagation characteristics and model uncertainties for HVDC power cables. IEEE Transactions on Power Delivery, 30(6), 2527-2534
Open this publication in new window or tab >>Wave propagation characteristics and model uncertainties for HVDC power cables
2015 (English)In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 30, no 6, p. 2527-2534Article in journal (Refereed) Published
Abstract [en]

This paper presents a stable and efficient fullwave cable model and a detailed study of the relatedmodel uncertainties regarding the wave propagation characteristics of very long HVDC power cables at low frequencies. The model can be used to predict the dispersion characteristics of the cable with respect to its electromagnetic parameters, or as an inverse problem to estimate some parameters of the cable (armour permeability, metal layer conductivities, temperature, length, etc.) based on measurements. The electromagnetic model is based on a magnetic frill generator that can be calibrated to the current measured at the input of the cable, and a layer recursive computation of the axial-symmetric fields. Measurements of pulse propagation on an 82 km long HVDC power cable over a bandwidth of 100 kHz have been used to validate the model. The main conclusion of the study is that the conductivity (and thus the temperature) of the conductor and the lead sheath are of utmost importance to achieve an accurate model. At the same time, some parameters are in principle insignificant regarding the dispersion characteristics in the low-frequency regime, such as the permittivity and the conductivity of the semi-conducting screens. The paper contains an investigation and a discussion on the electromagnetic properties of all layers of a typical HVDC power cable.

Place, publisher, year, edition, pages
IEEE Press, 2015
National Category
Physical Sciences Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:lnu:diva-40650 (URN)10.1109/TPWRD.2015.2456237 (DOI)000365316700019 ()2-s2.0-84960844790 (Scopus ID)
Available from: 2015-03-07 Created: 2015-03-07 Last updated: 2017-12-04Bibliographically approved
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