| 1. |
- Nilsson, Kristina, et al.
(författare)
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Plastic wave propagation in ductile slabs subjected to dynamic buckling
- 2003
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Ingår i: Mathematical Modelling in Physics, Engineering and Cognitive Science, v. 7. - 1651-0267. ; Mathematical Modelling of Wave Phenomena 2002, s. 207-215
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Konferensbidrag (refereegranskat)abstract
- Plastic wave propagation during dynamic buckling of ductile slabs is investigated numerically using a contour plot method (q-plot) showing contours of normalized effective plastic strain rate as a function of time and position. A non-linear finite element method is used to analyse the buckling problem of the elastic-viscoplastic slab. The contour plot method is quite sufficient to depict the overall development of the localization zones. Wave propagation speeds, relative growth of the localization zones and displacement of non-stationary in-elastic waves may be investigated. The present study also indicates that certain buckling modes may be promoted by selecting particular initial specimen geometries.
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| 2. |
- Vitos, Levente, et al.
(författare)
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Stainless steel alloys from first-principles theory
- 2011
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Ingår i: 7th European Stainless Steel Conference. - : Associazione Italiana di Metallurgia. - 9788885298842
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Konferensbidrag (refereegranskat)abstract
- Gaining an accurate description of materials obviously requires the most advanced atomic-scale techniques from both experimental and theoretical areas. In spite of the vast number of available techniques, however, the experimental study of the atomic-scale properties and phenomena even in simple solids is rather difficult. In steels the challenges become more complex due to the interplay between the structural, chemical and magnetic effects. On the other hand, advanced computational methods based on density functional theory ensure a proper platform for studying the fundamental properties of steel materials from first-principles. Our group at the Royal Institute of Technology in Stockholm has an international position in developing and applying computational codes for such applications. Using our ab initio tools, we have presented an insight to the electronic and magnetic structure, and micromechanical properties of austenitic stainless steel alloys. In the present contribution, we review the most important developments within the ab initio quantum-mechanics-aided steel design with special emphasis on the role of magnetism on the fundamental properties of alloy steels.
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| 3. |
- Ahlström, Petter, et al.
(författare)
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Why space is not enough : Service innovation and service delivery in senior housing
- 2022. - 1
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Ingår i: Management and Information Technology after Digital Transformation. - Abingdon and New York : Routledge. - 9780367612764 - 9780367628789 - 9781003111245 ; , s. 72-80
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Bokkapitel (refereegranskat)abstract
- This chapter discusses senior housing to support the well-being of older individuals through the provision of physical and social resources. The authors show how digital services contribute to these developments by increasing the resources available and the capacity of older people to integrate resources and take advantage of the value-creating opportunities offered by senior housing solutions. They point out that senior users play a crucial role as active co-creators of their own well-being and contributors to both service innovation and service delivery. As digital services become essential for how older people manage their daily lives, they need to be more integrated in the physical spaces where the actions and memories that shape the lives of seniors take place. Digital services have the potential to both create and deliver new services that will enhance these experiences, which makes their integration with the physical space an important and inseparable component of service innovation and delivery in the context of senior housing.
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| 4. |
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| 5. |
- Aksimsek, Sinan, et al.
(författare)
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TEM wave scattering by a step discontinuity on the outer wall of a coaxial waveguide
- 2013
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Ingår i: IEEE transactions on microwave theory and techniques. - : IEEE Press. - 0018-9480 .- 1557-9670. ; 61:8, s. 2783-2791
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the propagation of TEM waves along a coaxial waveguide with a step discontinuity on its outer wall is investigated rigorously by applying the direct Fourier transform and reducing the problem into the solution of a modified Wiener–Hopf equation. The solution for the field terms are determined in terms of an infinite number of unknown coefficients, which satisfy an infinite set of linear algebraic equations. These equations are solved numerically and the effect of area ratio is presented graphically at the end of the analysis. The same problem is also analyzed by applying the mode-matching technique and the results of the two approaches are compared. It is observed numerically that the Wiener–Hopf technique provides a better convergence than the mode-matching technique.
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| 6. |
- Andersson, Anders, et al.
(författare)
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Acoustic Transmission in Ducts of Various Shapes with an Impedance Condition
- 2008
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Ingår i: International Conference on Numerical Analysis and Applied Mathematics 2008. - Melville : AIP, Melville, USA. - 9780735405769 ; , s. 33-36
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Konferensbidrag (refereegranskat)abstract
- Propagation of acoustic waves in a two-dimensional duct with an impedance condition at the boundary, is studied. The duct is assumed to have two ends at infinity being asymptotically straight, but otherwise to be arbitrarily shaped.The so called Building Block Method allows us to synthesize propagation properties for ducts with complicated geometries from results for simpler ducts. Conformal mappings can be used to transform these simple ducts to straight ducts with constant cross-sections.By using recently developed techniques for numerical conformal mappings, it is possible to construct a transformation between an infinite strip and an arbitrarily shaped duct with smooth or piecewise smooth boundary, keeping both smoothness and the well controlled boundary direction towards infinity that the above mentioned method requires.To accomplish a stable formulation of the problem, we express it in terms of scattering operators. The resulting differential equation is solved using wave splitting and invariant embedding techniques. We expand the involved functions in Fourier series, and hence, it is possible to give the operators a matrix representation. Numerical results are produced using truncated matrices.
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| 7. |
- Andersson, Anders, 1957-, et al.
(författare)
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Electro-Magnetic Scattering in Variously Shaped Waveguides with an Impedance Condition
- 2009
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Ingår i: AIP Conference Proceedings: Third Conference on Mathematical Modeling of Wave Phenomena. - Melville, New York : American Institute of Physics. - 9780735406438 ; , s. 36-45
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Konferensbidrag (refereegranskat)abstract
- Electro-magnetic scattering is studied in a waveguide with varying shape and crosssection. Furthermore, an impedance or admittance condition is applied to two of the waveguide walls. Under the condition that variations in geometry or impedance take place in only one plane at the time, the problem can be solved as a two-dimensional wave-scattering problems. By using newly developed numerical conformal mapping techniques, the problem is transformedinto a wave-scattering problem in a straight two-dimensional channel. A numerically stable formulation is reached in terms of transmission and reflection operators. Numerical results are given for a slowly varying waveguide with a bend and for one more complex geometry.
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| 8. |
- Andersson, Anders, 1957-, et al.
(författare)
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Fourier Methods for harmonic scalar waves in general waveguides
- 2016
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Ingår i: Journal of Engineering Mathematics. - : Springer. - 0022-0833 .- 1573-2703. ; 98:1, s. 21-38
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 9. |
- Andersson, Anders, 1957-
(författare)
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Numerical Conformal mappings for regions Bounded by Smooth Curves
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Inom många tillämpningar används konforma avbildningar för att transformera tvådimensionella områden till områden med enklare utseende. Ett exempel på ett sådant område är en kanal av varierande tjocklek begränsad av en kontinuerligt deriverbar kurva. I de tillämpningar som har motiverat detta arbete, är det viktigt att dessa egenskaper bevaras i det område en approximativ konform avbildning producerar, men det är också viktigt att begränsningskurvans riktning kan kontrolleras, särkilt i kanalens båda ändar. Denna avhandling behandlar tre olika metoder för att numeriskt konstruera konforma avbildningar mellan ett enkelt standardområde, företrädesvis det övre halvplanet eller enhetscirkeln, och ett område begränsat av en kontinuerligt deriverbar kurva, där begränsningskurvans riktning kan kontrolleras, exakt eller approximativt. Den första metoden är en utveckling av en idé, först beskriven av Peter Henrici, där en modifierad Schwarz-Christoffel-avbildning avbildar det övre halvplanet konformt på en polygon med rundade hörn. Med utgångspunkt i denna idé skapas en algoritm för att konstruera avbildningar på godtyckliga områden med släta randkurvor. Den andra metoden bygger också den på Schwarz-Christoffel-avbildningen, och utnyttjar det faktum att om enhetscirkeln eller halvplanet avbildas på en polygon kommer ett område Q i det inre av dessa, som till exempel en cirkel med centrum i origo och radie mindre än 1, eller ett område i övre halvplanet begränsat av två strålar, att avbildas på ett område R i det inre av polygonen begränsat av en slät kurva. Vi utvecklar en metod för att hitta ett polygonalt område P, utanför det Omega som man önskar att skapa en avbildning för, sådant att den Schwarz-Christoffel-avbildning som avbildar enhetscirkeln eller halvplanet på P, avbildar Q på Omega. I båda dessa fall används tangentpolygoner för att numeriskt bestämma den önskade avbildningen. Slutligen beskrivs en metod där en av Don Marshalls så kallade zipper-algoritmer används för att skapa en avbildning mellan det övre halvplanet och en godtycklig kanal, begränsad av släta kurvor, som i båda ändar går mot oändligheten som räta parallella linjer.
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| 10. |
- Andersson, Anders, 1957-
(författare)
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Numerical Conformal Mappings for Waveguides
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Acoustic or electro-magnetic scattering in a waveguide with varying direction and cross-section can be re-formulated as a two-dimensional scattering problem, provided that the variations take place in only one dimension at a time. By using the so-called Building Block Method, it is possible to construct the scattering properties of a combination of scatterers when the properties of each scatterer are known. Hence, variations in the waveguide geometry or in the boundary conditions can be treated one at a time. Using the Building Block Method, the problem takes the form of the Helmholtz equation for stationary waves in a waveguide of infinite length and with smoothly varying geometry and boundary conditions. A conformal mapping is used to transform the problem into a corresponding problem in a straight horizontal waveguide, and by expanding the field in Fourier trigonometric series, the problem can be reformulated as an infinite-dimensional ordinary differential equation. From this, numerically solvable differential equations for the reflection and transmission operators are derived. To be applicable in the Building Block Method, the numerical conformal mapping must be constructed such that the direction of the boundary curve can be controlled. At the channel ends ,it is an indispensable requirement, that the two boundary curves are (at least) asymptotically parallel and straight. Furthermore, to achieve bounded operators in the differential equations, the boundary curves must satisfy different regularity conditions, depending on the boundary conditions. In this work, several methods to accomplish such conformal mappings are presented. The Schwarz–Christoffel mapping, which is a natural starting point and for which also efficient numerical software exists, can be modified in different ways in order to achieve polygons with rounded corners. We present algorithms by which the parameters in the mappings can be determined after such modifications. We show also how the unmodified Schwarz–Christoffel mapping can be used for regions with a smooth boundary. This is done by constructing an appropriate outer polygon to the considered region.Finally, we introduce one method that is not Schwarz–Christoffel-related, by showing how one of the so-called zipper algorithms can be used for waveguides. Keywords: waveguides, building block method, numerical conformalmappings, Schwarz–Christoffel mapping, rounded corners method, approximate curve factors, outer polygon method, boundary curvature, zipper method, geodesic algorithm, acoustic wave scattering, electro-magnetic wave scattering
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