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  • 51.
    Udawalpola, Rajitha
    et al.
    Department of Information Technology, Uppsala University.
    Wadbro, Eddie
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Berggren, Martin
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Optimization of a variable mouth acoustic horn2011In: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 85, no 5, p. 591-606Article in journal (Refereed)
    Abstract [en]

    By using boundary shape optimization on the end part of a semi-infinite waveguide for acoustic waves, we design transmission-efficient interfacial devices without imposing an upper bound on the mouth diameter. The boundary element method solves the Helmholtz equation modeling the exterior wave propagation problem. A gradient-based optimization algorithm solves the resulting least-squares problem and the adjoint method provides the necessary gradients. The results demonstrate that there appears to be a natural limit on the optimal mouth diameter.

  • 52.
    Wadbro, Eddie
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Topology Optimization of an Acoustic Horn2006In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 196, p. 420-436Article in journal (Refereed)
  • 53.
    Wadbro, Eddie
    et al.
    Uppsala University, Department of Information Technology, Division of Scientific Computing.
    Berggren, Martin
    Uppsala University, Department of Information Technology, Division of Scientific Computing.
    High contrast microwave tomography using topology optimization techniques2007In: Proceedings of Waves 2007: The 8th International Conference on Mathematical and Numerical Aspects of Waves / [ed] N. Biggs et al., Reading, U.K.: University of Reading , 2007, p. 448-450Conference paper (Refereed)
  • 54.
    Wadbro, Eddie
    et al.
    Uppsala University, Department of Information Technology, Division of Scientific Computing.
    Berggren, Martin
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Megapixel topology optimization on a graphics processing unit2009In: SIAM Review, ISSN 0036-1445, E-ISSN 1095-7200, Vol. 51, no 4, p. 707-721Article in journal (Refereed)
    Abstract [en]

    We show how the computational power and programmability of modern graphics processing units (GPUs) can be used to efficiently solve large-scale pixel-based material distribution problems using a gradient-based optimality criterion method. To illustrate the principle, a so-called topology optimization problem that results in a constrained nonlinear programming problem with over 4 million decision variables is solved on a commodity GPU.

  • 55.
    Wadbro, Eddie
    et al.
    Uppsala University, Department of Information Technology, Division of Scientific Computing.
    Berggren, Martin
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Microwave tomography using topology optimization techniques2008In: SIAM Journal on Scientific Computing, ISSN 1064-8275, E-ISSN 1095-7197, Vol. 30, no 3, p. 1613-1633Article in journal (Refereed)
    Abstract [en]

    Microwave tomography is a technique in which microwaves illuminate a specimen, and measurements of the scattered electrical field are used to determine and depict the specimen's dielectric and conductive properties. This article presents a new method to perform the reconstruction. The reconstruction method is illustrated by assuming time harmonic scattering in two space dimensions in a setup tailored for medical applications. We prove that the resulting constrained nonlinear least-squares problem admits a solution. The governing Helmholtz equation is discretized by using the finite-element method, and the dielectric properties are allowed to attain different values at each element within a given region. The reconstruction algorithm uses methodologies borrowed from topology optimization of linearly elastic structures. Numerical examples illustrate the reconstruction method in a parameter range typical for human tissue and for the challenging case where the size of the object is in the same order as the wavelength. A reasonable estimate of the dielectric properties is obtained by using one observation per 20 unknowns when the permittivity is allowed to vary continuously within a given interval. Using a priori information that the permittivity attains only certain values results in a good estimate and a sharp image. As opposed to topology optimization for structures, there is no indication of mesh dependency and checkerboarding when forcing the permittivity to attain discrete values.

  • 56.
    Wadbro, Eddie
    et al.
    Uppsala University, Department of Information Technology, Division of Scientific Computing.
    Berggren, Martin
    Uppsala University, Department of Information Technology, Division of Scientific Computing.
    Topology optimization of wave transducers2006In: Topological Design Optimization of Structures, Machines and Materials: Status and Perspectives / [ed] Martin Philip Bendsøe, Niels Olhoff and Ole Sigmund, 2006, p. 301-310Conference paper (Refereed)
  • 57.
    Wadbro, Eddie
    et al.
    Uppsala University, Department of Information Technology, Division of Scientific Computing.
    Udawalpola, Rajitha
    Uppsala University, Department of Information Technology, Division of Scientific Computing.
    Berggren, Martin
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Shape and topology optimization of an acoustic horn-lens combination2010In: Journal of Computational and Applied Mathematics, ISSN 0377-0427, E-ISSN 1879-1778, Vol. 234, no 6, p. 1781-1787Article in journal (Refereed)
    Abstract [en]

    Using gradient-based optimization combined with numerical solutions of the Helmholtz equation, we design an acoustic device with high transmission efficiency and even directivity throughout a two-octave-wide frequency range. The device consists of a horn, whose flare is subject to boundary shape optimization, together with an area in front of the horn, where solid material arbitrarily can be distributed using topology optimization techniques, effectively creating an acoustic lens.

  • 58.
    Wadbro, Eddie
    et al.
    Uppsala University, Department of Information Technology, Division of Scientific Computing.
    Udawalpola, Rajitha
    Uppsala University, Department of Information Technology, Division of Scientific Computing.
    Berggren, Martin
    Uppsala University, Department of Information Technology, Division of Scientific Computing.
    Shape and topology optimization of an acoustic horn-lens combination2007In: Proceedings of Waves 2007: The 8th International Conference on Mathematical and Numerical Aspects of Waves / [ed] N. Biggs et al., Reading, U.K.: University of Reading , 2007, p. 451-453Conference paper (Refereed)
  • 59.
    Wadbro, Eddie
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Zahedi, Sara
    Department of Information Technology, Uppsala University, Uppsala.
    Kreiss, Gunilla
    Department of Information Technology, Uppsala University, Uppsala.
    Berggren, Martin
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    A uniformly well-conditioned, unfitted Nitsche method for interface problems2013In: BIT Numerical Mathematics, ISSN 0006-3835, E-ISSN 1572-9125, Vol. 53, no 3, p. 791-820Article in journal (Refereed)
    Abstract [en]

    A finite element method for elliptic partial differential equations that allows for discontinuities along an interface not aligned with the mesh is presented. The solution on each side of the interface is separately expanded in standard continuous, piecewise-linear functions, and jump conditions at the interface are weakly enforced using a variant of Nitsche’s method. In our method, the solutions on each side of the interface are extended to the entire domain which results in a fixed number of unknowns independent of the location of the interface. A stabilization procedure is included to ensure well-defined extensions. We prove that the method provides optimal convergence order in the energy and the L2 norms and a condition number of the system matrix that is independent of the position of the interface relative to the mesh. Numerical experiments confirm the theoretical results and demonstrate optimal convergence order also for the pointwise errors.

  • 60.
    Yedeg, Esubalewe Lakie
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Wadbro, Eddie
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Berggren, Martin
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Anisotropic Topology Optimization of a Reactive Muffler with a Perforated PipeArticle in journal (Other academic)
  • 61.
    Yedeg, Esubalewe Lakie
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Wadbro, Eddie
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Berggren, Martin
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Interior layout topology optimization of a reactive muffler2016In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 53, no 4, p. 645-656Article in journal (Refereed)
    Abstract [en]

    This article presents a material distribution method that is tailored to the interior design of reactive mufflers. Such devices are typically acoustically small, except in the length direction, and their interior consists of a combination of pipes, expansions, contractions, and Helmholtz resonators. In order to design the interior layout using material distribution optimization, it is necessary to be able to resolve thin sound-hard materials as well as thin sheets with a given acoustic impedance, such as perforated plates, and manage small channels to Helmholtz resonators. We develop a method that uses an anisotropic design filter in combination with a fine mesh in order to control the minimum thickness separately in different directions. A two-stage post processing procedure is used to control openings to resonators, and embedded thin impedance surfaces are modeled by a mortar-element method. Numerical results demonstrate that the approach can produce mufflers with high transmission loss for a broad range of frequencies. The optimized mufflers include components that resemble combinations of expansion chambers, cylindrical pipes, and Helmholtz resonators.

  • 62.
    Yedeg, Esubalewe Lakie
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Wadbro, Eddie
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Berggren, Martin
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Layout optimization of thin sound-hard material to improve the far-field directivity properties of an acoustic horn2017In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 55, no 3, p. 795-808Article in journal (Refereed)
    Abstract [en]

    To improve the far-field directivity properties of a given mid-range acoustic horn, previously designed by shape optimization to exhibit almost ideal transmission properties in the frequency range 1.6–9.05 kHz, we apply layout optimization of thin sound-hard material in the interior of the horn. The purpose of the optimization is to place scattering material to prevent the sound intensity to increasingly be concentrated, with increasing frequency, along the horn axis. Absence or presence of thin sound-hard material is modeled by an equivalent surface transmission impedance, and the optimization algorithm determines the distribution of air or sound-hard material along a “ground structure” in the form of a grid inside the horn. The surface impedance is numerically handled using a newly developed finite-element formulation that allows exact enforcement of a vanishing impedance, corresponding to air, which would not be possible using a standard formulation. Horns provided with the optimized scatterers show a much improved angular coverage, compared to the initial configuration, with beam widths that exceed 60 ∘ uniformly over the operational frequency range, without destroying the good transmission properties of the initial horn.

  • 63.
    Yedeg, Esubalewe Lakie
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Wadbro, Eddie
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Hansbo, Peter
    Larson, Mats G.
    Umeå University, Faculty of Science and Technology, Department of Mathematics and Mathematical Statistics.
    Berggren, Martin
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    A Nitsche-type Method for Helmholtz Equation with an Embedded Acoustically Permeable Interface2016In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 304, p. 479-500Article in journal (Refereed)
    Abstract [en]

    We propose a new finite element method for Helmholtz equation in the situation where an acoustically permeable interface is embedded in the computational domain. A variant of Nitsche's method, different from the standard one, weakly enforces the impedance conditions for transmission through the interface. As opposed to a standard finite-element discretization of the problem, our method seamlessly handles a complex-valued impedance function Z that is allowed to vanish. In the case of a vanishing impedance, the proposed method reduces to the classic Nitsche method to weakly enforce continuity over the interface. We show stability of the method, in terms of a discrete Gårding inequality, for a quite general class of surface impedance functions, provided that possible surface waves are sufficiently resolved by the mesh. Moreover, we prove an a priori error estimate under the assumption that the absolute value of the impedance is bounded away from zero almost everywhere. Numerical experiments illustrate the performance of the method for a number of test cases in 2D and 3D with different interface conditions. 

12 51 - 63 of 63
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  • ieee
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  • en-GB
  • en-US
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  • nn-NO
  • nn-NB
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  • Other locale
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  • text
  • asciidoc
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