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  • 51.
    Hansbo, Peter
    et al.
    Jönköping University, School of Engineering, JTH, Mechanical Engineering. Jönköping University, School of Engineering, JTH. Research area Product Development - Simulation and Optimization.
    Larson, Mats
    Intrinsic finite element modeling of a linear membrane shell problem2012Report (Other academic)
    Abstract [en]

    A Galerkin finite element method for the membrane elasticity problem on a meshed surface is constructed by using two-dimensional elements extended into three dimensions. The membrane finite element model is established using the intrinsic approach suggested by Delfour and Zol´esio.

  • 52.
    Hansbo, Peter
    et al.
    Jönköping University, School of Engineering, JTH, Mechanical Engineering. Jönköping University, School of Engineering, JTH. Research area Product Development - Simulation and Optimization.
    Larson, Mats
    Umeå Universitet.
    Locking free quadrilateral continuous/discontinuous finite element methods for the Reissner–Mindlin plate2014In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 269, p. 381-393Article in journal (Refereed)
    Abstract [en]

    We develop a finite element method with continuous displacements and discontinuous rotations for the Reissner-Mindlin plate model on quadrilateral elements. To avoid shear locking, the rotations must have the same polynomial degree in the parametric reference plane as the parametric derivatives of the displacements, and obey the same transforma- tion law to the physical plane as the gradient of displacements. We prove optimal conver- gence, uniformly in the plate thickness, and provide numerical results that confirm our estimates. 

  • 53.
    Hansbo, Peter
    et al.
    Jönköping University, School of Engineering, JTH, Product Development. Jönköping University, School of Engineering, JTH. Research area Product Development - Simulation and Optimization.
    Larson, Mats G.
    Umeå University.
    A posteriori error estimates for continuous/discontinuous Galerkin approximations of the Kirchhoff–Love buckling problem2015In: Computational Mechanics, ISSN 0178-7675, E-ISSN 1432-0924, Vol. 56, no 5, p. 815-827Article in journal (Refereed)
    Abstract [en]

    Second order buckling theory involves a oneway coupled coupled problem where the stress tensor from a plane stress problem appears in an eigenvalue problem for the fourth order Kirchhoff plate. In this paper we present an a posteriori error estimate for the critical buckling load and mode corresponding to the smallest eigenvalue and associated eigenvector. A particular feature of the analysis is that we take the effect of approximate computation of the stress tensor and also provide an error indicator for the plane stress problem. The Kirchhoff plate is discretized using a continuous/discontinuous finite element method based on standard continuous piecewise polynomial finite element spaces. The same finite element spaces can be used to solve the plane stress problem.

  • 54.
    Hansbo, Peter
    et al.
    Jönköping University, School of Engineering, JTH, Product Development. Jönköping University, School of Engineering, JTH. Research area Product Development - Simulation and Optimization.
    Larson, Mats G.
    Department of Mathematics and Mathematical Statistics, Umeå University, Umeå, Sweden.
    A stabilized finite element method for the Darcy problem on surfaces2017In: IMA Journal of Numerical Analysis, ISSN 0272-4979, E-ISSN 1464-3642, Vol. 37, no 3, p. 1274-1299Article in journal (Refereed)
    Abstract [en]

    We consider a stabilized finite element method for the Darcy problem on a surface based on the Masud–Hughes formulation. A special feature of the method is that the tangential condition of the velocity field is weakly enforced through the bilinear form, and that standard parametric continuous polynomial spaces on triangulations can be used. We prove optimal order a priori estimates that take the approximation of the geometry and the solution into account.

  • 55.
    Hansbo, Peter
    et al.
    Jönköping University, School of Engineering, JTH, Product Development. Jönköping University, School of Engineering, JTH. Research area Product Development - Simulation and Optimization.
    Larson, Mats G.
    Department of Mathematics and Mathematical Statistics, Umeå University, Umeå, Sweden.
    Continuous/discontinuous finite element modelling of Kirchhoff plate structures in R3 using tangential differential calculus2017In: Computational Mechanics, ISSN 0178-7675, E-ISSN 1432-0924, Vol. 60, no 4, p. 693-702Article in journal (Refereed)
    Abstract [en]

    We employ surface differential calculus to derive models for Kirchhoff plates including in-plane membrane deformations. We also extend our formulation to structures of plates. For solving the resulting set of partial differential equations, we employ a finite element method based on elements that are continuous for the displacements and discontinuous for the rotations, using (Formula presented.)-elements for the discretisation of the plate as well as for the membrane deformations. Key to the formulation of the method is a convenient definition of jumps and averages of forms that are d-linear in terms of the element edge normals.

  • 56.
    Hansbo, Peter
    et al.
    Jönköping University, School of Engineering, JTH, Mechanical Engineering. Jönköping University, School of Engineering, JTH. Research area Product Development - Simulation and Optimization.
    Larson, Mats G.
    Umeå University.
    Finite element modeling of a linear membrane shell problem using tangential differential calculus2014In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 270, p. 1-14Article in journal (Refereed)
    Abstract [en]

    We construct a new Galerkin finite element method for the membrane elasticity problem on a meshed surface by using two-dimensional elements extended into three dimensions. The membrane finite element model is established using a tangential differential calculus approach that avoids the use of classical differential geometric methods. The finite element method generalizes the classical flat element shell method where standard plane stress elements are used for membrane problems. This makes our method applicable to a wider range of problems and of surface descriptions, including surfaces defined by distance functions. 

  • 57.
    Hansbo, Peter
    et al.
    Jönköping University, School of Engineering, JTH, Product Development. Jönköping University, School of Engineering, JTH. Research area Product Development - Simulation and Optimization.
    Larson, Mats G.
    Umeå University, Sweden..
    Larsson, Karl
    Umeå universitet, Sweden..
    Cut Finite Element Methods for Linear Elasticity Problems2017In: Geometrically Unfitted Finite Element Methods and Applications: Proceedings of the UCL Workshop 2016 / [ed] Bordas, Stéphane P. A.; Burman, Erik; Larson, Mats G.; Olshanskii, Maxim A., Springer International Publishing , 2017, p. 25-63Conference paper (Refereed)
    Abstract [en]

    We formulate a cut finite element method for linear elasticity based on higher order elements on a fixed background mesh. Key to the method is a stabilization term which provides control of the jumps in the derivatives of the finite element functions across faces in the vicinity of the boundary. We then develop the basic theoretical results including error estimates and estimates of the condition number of the mass and stiffness matrices. We apply the method to the standard displacement problem, the frequency response problem, and the eigenvalue problem. We present several numerical examples including studies of thin bending dominated structures relevant for engineering applications. Finally, we develop a cut finite element method for fibre reinforced materials where the fibres are modeled as a superposition of a truss and a Euler-Bernoulli beam. The beam model leads to a fourth order problem which we discretize using the restriction of the bulk finite element space to the fibre together with a continuous/discontinuous finite element formulation. Here the bulk material stabilizes the problem and it is not necessary to add additional stabilization terms.

  • 58.
    Hansbo, Peter
    et al.
    Jönköping University, School of Engineering, JTH, Mechanical Engineering. Jönköping University, School of Engineering, JTH. Research area Product Development - Simulation and Optimization.
    Larson, Mats G.
    Umeå University.
    Larsson, Karl
    Umeå University.
    Variational formulation of curved beams in global coordinates2014In: Computational Mechanics, ISSN 0178-7675, E-ISSN 1432-0924, Vol. 53, no 4, p. 611-623Article in journal (Refereed)
    Abstract [en]

    In this paper we derive a variational formulation for the static analysis of a linear curved beam natively expressed in global Cartesian coordinates. Using an implicit description of the beam midline during derivation we eliminate the need for local coordinates. The only geometrical information appearing in the final expressions for the governing equations is the tangential direction. As a consequence, zero or discontinuous curvature, for example at inflection points, pose no difficulty in this formulation. Kinematic assumptions encompassing both Timoshenko and Euler-Bernoulli beam theories are considered. With the exception of truly three-dimensional formulations, models for curved beams found in the literature are typically derived in the local Frenet frame. We implement finite element methods with global degrees of freedom and discuss curvature coupling effects and locking. Numerical comparisons with classical solutions for straight and curved cantilever beams under tip load are given, as well as numerical examples illustrating curvature coupling effects. 

  • 59.
    Hansbo, Peter
    et al.
    Jönköping University, School of Engineering, JTH, Product Development. Jönköping University, School of Engineering, JTH. Research area Product Development - Simulation and Optimization.
    Larson, Mats G.
    Umeå University, Sweden.
    Massing, André
    Umeå University, Sweden.
    A stabilized cut finite element method for the Darcy problem on surfaces2017In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 326, p. 298-318Article in journal (Refereed)
    Abstract [en]

    We develop a cut finite element method for the Darcy problem on surfaces. The cut finite element method is based on embedding the surface in a three dimensional finite element mesh and using finite element spaces defined on the three dimensional mesh as trial and test functions. Since we consider a partial differential equation on a surface, the resulting discrete weak problem might be severely ill conditioned. We propose a full gradient and a normal gradient based stabilization computed on the background mesh to render the proposed formulation stable and well conditioned irrespective of the surface positioning within the mesh. Our formulation extends and simplifies the Masud–Hughes stabilized primal mixed formulation of the Darcy surface problem proposed in Hansbo and Larson (2016) on fitted triangulated surfaces. The tangential condition on the velocity and the pressure gradient is enforced only weakly, avoiding the need for any tangential projection. The presented numerical analysis accounts for different polynomial orders for the velocity, pressure, and geometry approximation which are corroborated by numerical experiments. In particular, we demonstrate both theoretically and through numerical results that the normal gradient stabilized variant results in a high order scheme.

  • 60.
    Hansbo, Peter
    et al.
    Jönköping University, School of Engineering, JTH, Mechanical Engineering.
    Larson, Mats G.
    Umeå University.
    Zahedi, Sara
    Uppsala University.
    A cut finite element method for a Stokes interface problem2014In: Applied Numerical Mathematics, ISSN 0168-9274, E-ISSN 1873-5460, Vol. 85, p. 90-114Article in journal (Refereed)
    Abstract [en]

    We present a finite element method for the Stokes equations involving two immiscible incompressible fluids with different viscosities and with surface tension. The interface separating the two fluids does not need to align with the mesh. We propose a Nitsche formulation which allows for discontinuities along the interface with optimal a priori error estimates. A stabilization procedure is included which ensures that the method produces a well conditioned stiffness matrix independent of the location of the interface. 

  • 61.
    Hansbo, Peter
    et al.
    Jönköping University, School of Engineering, JTH. Research area Product Development - Simulation and Optimization. Jönköping University, School of Engineering, JTH, Product Development.
    Larson, Mats G.
    Department of Mathematics and Mathematical Statistics, Umeå University, Sweden.
    Zahedi, Sara
    Department of Mathematics, KTH Royal Institute of Technology, Sweden.
    A cut finite element method for coupled bulk-surface problems on time-dependent domains2016In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 307, p. 96-116Article in journal (Refereed)
    Abstract [en]

    In this contribution we present a new computational method for coupled bulk-surface problems on time-dependent domains. The method is based on a space–time formulation using discontinuous piecewise linear elements in time and continuous piecewise linear elements in space on a fixed background mesh. The domain is represented using a piecewise linear level set function on the background mesh and a cut finite element method is used to discretize the bulk and surface problems. In the cut finite element method the bilinear forms associated with the weak formulation of the problem are directly evaluated on the bulk domain and the surface defined by the level set, essentially using the restrictions of the piecewise linear functions to the computational domain. In addition a stabilization term is added to stabilize convection as well as the resulting algebraic system that is solved in each time step. We show in numerical examples that the resulting method is accurate and stable and results in well conditioned algebraic systems independent of the position of the interface relative to the background mesh.

  • 62.
    Hansbo, Peter
    et al.
    Jönköping University, School of Engineering, JTH. Research area Product Development - Simulation and Optimization. Jönköping University, School of Engineering, JTH, Product Development.
    Larson, Mats G.
    Umeå University.
    Zahedi, Sara
    KTH Royal Institute of Technology.
    Characteristic cut finite element methods for convection–diffusion problems on time dependent surfaces2015In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 293, p. 431-461Article in journal (Refereed)
    Abstract [en]

    We develop a finite element method for convection–diffusion problems on a given time dependent surface, for instance modeling the evolution of a surfactant. The method is based on a characteristic-Galerkin formulation combined with a piecewise linear cut finite element method in space. The cut finite element method is constructed by embedding the surface in a background grid and then using the restriction to the surface of a finite element space defined on the background grid. The surface is allowed to cut through the background grid in an arbitrary fashion. To ensure stability and well posedness of the resulting algebraic systems of equations, independent of the position of the surface in the background grid, we add a consistent stabilization term. We prove error estimates and present confirming numerical results.

  • 63.
    Hansbo, Peter
    et al.
    Jönköping University, School of Engineering, JTH, Product Development. Jönköping University, School of Engineering, JTH. Research area Product Development - Simulation and Optimization.
    Larson, Mats G.
    Umeå University.
    Zahedi, Sara
    KTH.
    Stabilized finite element approximation of the mean curvature vector on closed surfaces2015In: SIAM Journal on Numerical Analysis, ISSN 0036-1429, E-ISSN 1095-7170, Vol. 53, no 4, p. 1806-1832Article in journal (Refereed)
    Abstract [en]

    The mean curvature vector of a surface is obtained by letting the Laplace--Beltrami operator act on the embedding of the surface in R^3. In this contribution we develop a stabilized finite element approximation of the mean curvature vector of certain piecewise linear surfaces which enjoys first order convergence in L^2. The stabilization involves the jump in the tangent gradient in the direction of the outer co-normals at each edge in the surface mesh. We consider both standard meshed surfaces and so-called cut surfaces that are level sets of piecewise linear distance functions. We prove a priori error estimates and verify the theoretical results numerically.

  • 64.
    Hansbo, Peter
    et al.
    Jönköping University, School of Engineering, JTH, Mechanical Engineering.
    Larson, Mats
    Zahedi, Sara
    A Nitsche method for a Stokes interface problemManuscript (preprint) (Other academic)
    Abstract [en]

    We present a finite element method for the Stokes equations involving two immiscible incompressible fluids with different viscosities and with surface tension. The interface separating the two fluids does not need to align with the mesh. We propose a Nitsche formulation which allows for discontinuities along the interface with optimal a priori error estimates. A stabilization procedure is included which ensures that the method produces a well conditioned stiffness matrix independent of the location of the interface. 

  • 65.
    Hansbo, Peter
    et al.
    Jönköping University, School of Engineering, JTH, Product Development. Jönköping University, School of Engineering, JTH. Research area Product Development - Simulation and Optimization.
    Larsson, Fredrik
    Department of Applied Mechanics, Chalmers University of Technology, Göteborg, Sweden.
    The nonconforming linear strain tetrahedron for a large deformation elasticity problem2016In: Computational Mechanics, ISSN 0178-7675, E-ISSN 1432-0924, Vol. 58, no 6, p. 929-935Article in journal (Refereed)
    Abstract [en]

    In this paper we investigate the performance of the nonconforming linear strain tetrahedron element introduced by Hansbo (Comput Methods Appl Mech Eng 200(9–12):1311–1316, 2011; J Numer Methods Eng 91(10):1105–1114, 2012). This approximation uses midpoints of edges on tetrahedra in three dimensions with either point continuity or mean continuity along edges of the tetrahedra. Since it contains (rotated) bilinear terms it performs substantially better than the standard constant strain element in bending. It also allows for under-integration in the form of one point Gauss integration of volumetric terms in near incompressible situations. We combine under-integration of the volumetric terms with houglass stabilization for the isochoric terms.

  • 66.
    Johansson, J.
    et al.
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing - Surface technology.
    Belov, I.
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing - Surface technology.
    Johnson, E.
    Leisner, Peter
    Jönköping University, School of Engineering, JTH, Materials and Manufacturing.
    An approach to life consumption monitoring of solder joints in operating temperature environment2012In: Proceedings of 13th IEEE International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems, EuroSimE 2012, Cascais, Portugal, April 16-17-18, 2012, IEEE, 2012, p. -8Conference paper (Refereed)
    Abstract [en]

    This paper elaborates the 3T-approach to life consumption monitoring of solder joints in operating temperature environment without requiring simplification of operating loads. An overview of the 3T-approach is provided including assumptions made for a proposed realization in an avionic application. Associated implementation routines are highlighted and exemplified for a lead-free PBGA256 package with creep strain energy density (SEDcr) as damage metric. Factors that affect the prediction accuracy are investigated. A data resolution has been determined that delivers response surfaces that provide results comparable to 3-D finite-element (FE) simulations, while bearing two orders of magnitude higher computational efficiency. A stress-free temperature modification routine is proposed and proves to further mitigate accuracy problems.

  • 67.
    Johansson, Jonas
    et al.
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing - Surface technology.
    Belov, Ilja
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing - Surface technology.
    Johnson, Erland
    SP Technical Research Institute of Sweden, Borås, Sweden.
    Dudek, Rainer
    Fraunhofer ENAS, Micro Materials Center, Chemnitz, Germany.
    Leisner, Peter
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing - Surface technology.
    Investigation on thermal fatigue of SnAgCu, Sn100C, and SnPbAg solder joints in varying temperature environments2014In: Microelectronics and reliability, ISSN 0026-2714, E-ISSN 1872-941X, Vol. 54, no 11, p. 2523-2535Article in journal (Refereed)
    Abstract [en]

    Thermal cycling tests have been performed for a range of electronic components intended for avionic applications, assembled with SAC305, SN100C and SnPbAg solder alloys. Two temperature profiles have been used, the first ranging between −20 °C and +80 °C (TC1), and the second between −55 °C and +125 °C (TC2). High level of detail is provided for the solder alloy composition and the component package dimensions, and statistical analysis, partially supported by FE modeling, is reported. The test results confirm the feasibility of SAC305 as a replacement for SnPbAg under relatively benign thermomechanical loads. Furthermore, the test results serve as a starting point for estimation of damage accumulation in a critical solder joint in field conditions, with increased accuracy by avoiding data reduction. A computationally efficient method that was earlier introduced by the authors and tested on relatively mild temperature environments has been significantly improved to become applicable on extended temperature range, and it has been applied to a PBGA256 component with SAC305 solder in TC1 conditions. The method, which utilizes interpolated response surfaces generated by finite element modeling, extends the range of techniques that can be employed in the design phase to predict thermal fatigue of solder joints under field temperature conditions.

  • 68.
    Johansson, Jonas
    et al.
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing - Surface technology. Electronic Defence Systems, Saab AB, Jönköping, Sweden.
    Belov, Ilja
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing - Surface technology.
    Johnson, Erland
    SP Technical Research Institute of Sweden, Borås, Sweden.
    Leisner, Peter
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing - Surface technology. SP Technical Research Institute of Sweden, Borås, Sweden.
    A computational method for evaluating the damage in a solder joint of an electronic package subjected to thermal loads2014In: Engineering computations, ISSN 0264-4401, E-ISSN 1758-7077, Vol. 31, no 3, p. 467-489Article in journal (Refereed)
    Abstract [en]

    Purpose – The purpose of this paper is to introduce a novel computational method to evaluate damage accumulation in a solder joint of an electronic package, when exposed to operating temperature environment. A procedure to implement the method is suggested, and a discussion of the method and its possible applications is provided in the paper.

    Design/methodology/approach – Methodologically, interpolated response surfaces based on specially designed finite element (FE) simulation runs, are employed to compute a damage metric at regular time intervals of an operating temperature profile. The developed method has been evaluated on a finite-element model of a lead-free PBGA256 package, and accumulated creep strain energy density has been chosen as damage metric.

    Findings – The method has proven to be two orders of magnitude more computationally efficient compared to FE simulation. A general agreement within 3 percent has been found between the results predicted with the new method, and FE simulations when tested on a number of temperature profiles from an avionic application. The solder joint temperature ranges between +25 and +75°C.

    Practical implications – The method can be implemented as part of reliability assessment of electronic packages in the design phase.

    Originality/value – The method enables increased accuracy in thermal fatigue life prediction of solder joints. Combined with other failure mechanisms, it may contribute to the accuracy of reliability assessment of electronic packages.

  • 69.
    Johansson, Jonas
    et al.
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing - Surface technology. Jönköping University, School of Engineering, JTH. Research area Robust Embedded Systems.
    Belov, Ilja
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing - Surface technology. Jönköping University, School of Engineering, JTH. Research area Robust Embedded Systems.
    Leisner, Peter
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing - Surface technology. Jönköping University, School of Engineering, JTH. Research area Robust Embedded Systems.
    An experimental setup for validating a CFD model of a double-sided PCB in a sealed enclosure at various power configurations2005In: Thermal, Mechanical and Multi-Physics Simulation and Experiments in Micro-Electronics and Micro-Systems, 2005: EuroSimE 2005, Piscataway, NJ: IEEE Order Department , 2005, p. 127-133Conference paper (Refereed)
    Abstract [en]

    A flexible experimental setup enabling power control of a fully populated double-sided PCB has been realized, and is described in detail. A CFD model of a double-sided PCB housed in a sealed enclosure has been validated in a 19/spl deg/C environment by means of temperature and flow measurement. The difference between simulated and measured component temperatures has been within 10%. Potential errors both in the model and in the experiments have been discussed and their impact on temperatures has been numerically evaluated.

  • 70.
    Johansson, Jonas
    et al.
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing - Surface technology. Jönköping University, School of Engineering, JTH. Research area Robust Embedded Systems.
    Belov, Ilja
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing - Surface technology. Jönköping University, School of Engineering, JTH. Research area Robust Embedded Systems.
    Leisner, Peter
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing - Surface technology. Jönköping University, School of Engineering, JTH. Research area Robust Embedded Systems.
    CFD Analysis of an Avionic Module for Evaluating Power Distribution as a Thermal Management Measure for a Double-sided PCB2007In: Twenty Third Annual IEEE Semiconductor Thermal Measurement and Management Symposium: SEMI-THERM Proceedings 2007, San Jose, CA USA, March 18-22, 2007, Piscataway, N.J.: IEEE , 2007, p. 233-243Conference paper (Refereed)
    Abstract [en]

    Thermal design aspects of an avionic module including fully populated PCBs housed in a sealed enclosure have been studied by means of computational fluid dynamics. Effect of power distribution between the sides of a double-sided PCB on the case temperature of surface-mounted components has been investigated within a proposed simulation strategy. Simulation-based guidelines have been developed for thermal design of avionic modules, regarding preferable power configuration on a double-sided PCB, representing an alternative approach to thermal management, as compared to introducing additional cooling devices.

  • 71.
    Klarbring, Anders
    et al.
    Division of Solid Mechanics, Linköping University, Linköping, Sweden.
    Torstenfelt, Bo
    Division of Solid Mechanics, Linköping University, Linköping, Sweden.
    Hansbo, Peter
    Jönköping University, School of Engineering, JTH, Product Development. Jönköping University, School of Engineering, JTH. Research area Product Development - Simulation and Optimization.
    Larson, Mats G.
    Department of Mathematics and Mathematical Statistics, Umeå University, Umeå, Sweden.
    Optimal design of fibre reinforced membrane structures2017In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 56, no 4, p. 781-789Article in journal (Refereed)
    Abstract [en]

    A design problem of finding an optimally stiff membrane structure by selecting one–dimensional fiber reinforcements is formulated and solved. The membrane model is derived in a novel manner from a particular three-dimensional linear elastic orthotropic model by appropriate assumptions. The design problem is given in the form of two minimization statements. After finite element discretization, the separate treatment of each of the two statements follows from classical results and methods of structural optimization: the stiffest orientation of reinforcing fibers coincides with principal stresses and the separate selection of density of fibers is a convex problem that can be solved by optimality criteria iterations. Numerical solutions are shown for two particular configurations. The first for a statically determined structure and the second for a statically undetermined one. The latter shows related but non-unique solutions. 

  • 72.
    Koneri, Deepak Kumar
    Jönköping University, School of Engineering, JTH, Computer and Electrical Engineering.
    Optimization of PCB Heater Heating Profile for Power-Efficient Humidity Management in Electronics Enclosures2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this master thesis, automated optimization simulation laboratory is developed and implemented for power-efficient humidity management. A concept of local heating as a humidity management measure in electronics enclosure in severe environmental conditions has been evaluated. Environmental conditions included an instant change of the temperature from 0o C to 24o C and relative humidity 30% to 95%. Evaluation process has been developed as an optimization problem solved by integrating CFD modeling and excel data sheet calculations into the automation simulation workflow environment. Heating profile vector has been defined as design variable and optimized objective was defined as the difference between surface temperature of heated IC package and local dew point temperature. The task included interfacing between floTHERM and OPTIMUS tools, sensitivity analysis and CFD model simplification in order to obtain time efficient simulation models subsequently used in optimization process. Ultimate goal in the optimization was to obtain a power efficient heating profile for the local heater that keeps local relative humidity at low level thereby minimizing moisture induced electronic reliability problems.

  • 73.
    Lindgren, Mats
    et al.
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing - Surface technology. Jönköping University, School of Engineering, JTH. Research area Robust Embedded Systems.
    Belov, Ilja
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing - Surface technology. Jönköping University, School of Engineering, JTH. Research area Robust Embedded Systems.
    Leisner, Peter
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing - Surface technology. Jönköping University, School of Engineering, JTH. Research area Robust Embedded Systems.
    Experimental Evaluation of Glob-top Materials for use in Harsh Environments2005In: Journal of Microelectronics and Electronic Packaging, ISSN 1551-4897, E-ISSN 1555-8037, Vol. 2, no 4, p. 253-268Article in journal (Refereed)
    Abstract [en]

    This article presents results of experimental evaluation of glob-top materials for multi-chip-modules (MCM) in harsh environments. Material and process tests have been performed with the purpose to find a material which would fulfill the reliability requirements for use e.g. in military or automotive applications. Seven polymer materials, i.e. four epoxies, two silicones and one polyurethane material have been selected and evaluated in the experiments. The most critical material and process parameters for glob-top have been identified and measured. Based on the experimental results, application-based scoring of studied epoxy materials has been performed. Material evaluation results have been summarized in conclusions about the most suitable glob-top material for use in harsh environments.

  • 74.
    Lindgren, Mats
    et al.
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing - Surface technology. Jönköping University, School of Engineering, JTH. Research area Robust Embedded Systems.
    Belov, Ilja
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing - Surface technology. Jönköping University, School of Engineering, JTH. Research area Robust Embedded Systems.
    Leisner, Peter
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing - Surface technology. Jönköping University, School of Engineering, JTH. Research area Robust Embedded Systems.
    Thermal and thermo-mechanical analysis for design evaluation of an automotive radar module2004In: Quality and Reliability Engineering International, ISSN 0748-8017, E-ISSN 1099-1638, Vol. 20, no 7, p. 709-726Article in journal (Refereed)
    Abstract [en]

    The influence of the substrate technology, assembly method, and housing material on the thermal, thermo-mechanical and cost performance of a radar module for automotive applications has been studied to address the product reliability aspects during the design phase. Flip chip and wire bonding have been evaluated for Multi-Chip Module—Laminate/Deposition (MCM-L/D) and Multi-Chip Module—Deposition (MCM-D) substrate technologies used for electronic packaging solutions in a harsh environment. Solder ball and direct attachment have been investigated as second-level assembly. As a result of thermal and thermo-mechanical simulations and cost analysis, radar module designs combining MCM-D and MCM-L/D with wire bonding have been revealed, which are preferable for use in different temperature environments with respect to two performance criteria, the maximum junction temperature and the manufacturing cost. Simulation-based guidelines have been developed for designing radar modules used in automotive applications while satisfying temperature and stress constraints provided for the module.

  • 75.
    Lindgren, Mats
    et al.
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing - Surface technology. Jönköping University, School of Engineering, JTH. Research area Robust Embedded Systems.
    Belov, Ilja
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing - Surface technology. Jönköping University, School of Engineering, JTH. Research area Robust Embedded Systems.
    Törnvall, Magnus
    Leisner, Peter
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing - Surface technology. Jönköping University, School of Engineering, JTH. Research area Robust Embedded Systems.
    Application of simulation-based decision making in product development of an RF module2007In: Microelectronics and reliability, ISSN 0026-2714, E-ISSN 1872-941X, Vol. 47, no 2-3, p. 302-309Article in journal (Refereed)
    Abstract [en]

    This paper presents results of simulation-based design evaluation for thermal and thermo-mechanical performance and cost of packaging technology of a RF module for automotive application. Combination of thermal, thermo-mechanical and cost analysis within the multi-attribute decision making enabled design ranking and revealed two MCM-L/D and MCM-D designs with wire bonding assembly preferred for use in automotive applications for different temperature environments. Simulation-based design guidelines were developed for designing electronic modules exhibiting good thermal and thermo-mechanical performance. By application-based partitioning of the importance weights assigned to the reliability and cost criteria, the guidelines were extended to cover other application areas.

  • 76.
    Lindgren, Mats
    et al.
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing - Surface technology. Jönköping University, School of Engineering, JTH. Research area Robust Embedded Systems.
    Belov, Ilja
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing - Surface technology. Jönköping University, School of Engineering, JTH. Research area Robust Embedded Systems.
    Törnvall, Magnus
    Leisner, Peter
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing - Surface technology. Jönköping University, School of Engineering, JTH. Research area Robust Embedded Systems.
    Application of simulation-based decision making in product development of an RF module2004In: 5th IEEE conference in Thermal and Mechanical Simulation and Experiments in Micro-Electronics and Micro-Systems: EuroSimE 2004, 2004, p. 233-240Conference paper (Refereed)
    Abstract [en]

    This paper presents results of simulation-based design evaluation for thermal and thermo-mechanical performance and cost of packaging technology of an RF module for automotive applications. A combination of thermal, thermo-mechanical and cost analysis within the multi-attribute decision making framework enabled design ranking and revealed two MCM-L/D (multi-chip module-laminate/deposition) and MCM-D (deposition) designs with the wire bonding assembly preferred for use in automotive applications for different temperature environments. Simulation-based design guidelines were developed for designing electronic modules exhibiting good thermal and thermo-mechanical performance. By application-based partitioning of the importance weights assigned to the reliability and cost criteria, the guidelines were extended to cover other application areas.

  • 77.
    Linusson, Henrik
    et al.
    Högskolan i Borås, Institutionen Handels- och IT-högskolan.
    Johansson, Ulf
    Högskolan i Borås, Institutionen Handels- och IT-högskolan.
    Löfström, Tuve
    Högskolan i Borås, Institutionen Handels- och IT-högskolan.
    Signed-Error Conformal Regression2014In: Advances in Knowledge Discovery and Data Mining 18th Pacific-Asia Conference, PAKDD 2014 Tainan, Taiwan, May 13-16, 2014 Proceedings, Part I, Springer, 2014, p. 224-236Conference paper (Refereed)
    Abstract [en]

    This paper suggests a modification of the Conformal Prediction framework for regression that will strengthen the associated guarantee of validity. We motivate the need for this modification and argue that our conformal regressors are more closely tied to the actual error distribution of the underlying model, thus allowing for more natural interpretations of the prediction intervals. In the experimentation, we provide an empirical comparison of our conformal regressors to traditional conformal regressors and show that the proposed modification results in more robust two-tailed predictions, and more efficient one-tailed predictions.

  • 78.
    Lundin, Rolf A.
    Jönköping University, Jönköping International Business School, JIBS, Media, Management and Transformation Centre (MMTC).
    Metodproblem vid simulering1972Book (Other academic)
  • 79.
    Smedberg, Patrick
    et al.
    Jönköping University, School of Education and Communication, HLK, School Based Research, Mathematics Education Research.
    Uhlin, Anton
    Jönköping University, School of Education and Communication, HLK, School Based Research, Mathematics Education Research.
    Elevers uppfattningar av operationer med negativa tal2013Independent thesis Advanced level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Negativa tal har inte alltid varit lika självklara som de är idag. En elev som aldrig tidigare mött ne-gativa tal, än mindre räknat med dem, kommer troligtvis anse att det är ologiskt att tala om äpplen. Forskning visar på att det finns en mängd svårigheter och missuppfattningar om operatio-ner med negativa tal. En del av dessa missuppfattningar grundas i den tvetydighet som finns be-träffande minustecknets funktioner - då minustecknet både används som operator och som be-teckning för negativitet. Den negativa talmängden är en del av kursplanen i matematik för årskurs 4 till 6. Vanligtvis är det dock först i årskurs 8 som elever undervisas om operationer med negativa tal.

    Syftet med denna studie är att undersöka hur elever i årskurs 7 uppfattar addition och subtraktion av negativa tal. Detta ämnar vi att uppfylla genom att besvara följande frågeställning; På vilka kva-litativ skilda sätt uppfattar elever operationer med negativa tal?

    Som grund för urvalet genomfördes ett förtest varifrån åtta elever valdes ut till att delta i kvalitati-va intervjuer. Dessa intervjuer resulterade i att fem kvalitativt åtskilda beskrivningskategorier kun-de urskiljas;

    det finns inget under noll, eliminering av termer, omvända räkneoperationer till vänster om noll, posi-tiva och negativa tal samarbetar ej samt positiv eller negativ differens. Vi hoppas att denna studie kan bidra till en ökad förståelse om vilka olika elevuppfattningar det finns av operationer med negativa tal.

  • 80.
    Smedberg, Patrick
    et al.
    Jönköping University, School of Education and Communication, HLK, School Based Research, Mathematics Education Research.
    Uhlin, Anton
    Jönköping University, School of Education and Communication, HLK, School Based Research, Mathematics Education Research.
    Lärares ämneskunskaper och pedagogiska ämneskunskaper om division med bråk2012Independent thesis Advanced level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Division med bråk är ett av de områden av skolans matematiska innehåll som både elever och lärare har svå-righeter med. I flera internationella studier har man funnit att lärares svårigheter delvis grundas i ett proce-durellt förhållningssätt till de lösningsmetoder som används vid division med bråk. Detta, i kombination med att lärare har svårt att konstruera realistiska förklaringsmodeller till sådana typer av uppgifter, påverkar även lärares undervisning.

    Syftet med denna uppsats är att undersöka svenska högstadielärares ämneskunskaper och pedagogiska äm-neskunskaper om division med bråk. De frågeställningar studien ämnar besvara är vilka vanliga ämneskun-skaper och specialiserade ämneskunskaper lärare visar samt vilka pedagogiska ämneskunskaper om under-visning och pedagogiska ämneskunskaper om elever lärare visar om division med bråk.

    Fem matematiklärare i årskurs 7-9 utvaldes för kvalitativ intervju, där de både fick beräkna uppgifter med division med bråk samt beskriva hur de själva resonerar kring sin undervisning, elevers svårigheter och in-troduktion av division med bråk. I intervjuerna framkom att lärarna generellt visade prov på både goda äm-neskunskaper och goda pedagogiska ämneskunskaper.

  • 81.
    Yedeg, Esubalewe Lakie
    et al.
    Umeå University.
    Wadbro, Eddie
    Umeå University.
    Hansbo, Peter
    Jönköping University, School of Engineering, JTH, Product Development. Jönköping University, School of Engineering, JTH. Research area Product Development - Simulation and Optimization.
    Larson, Mats G.
    Umeå University.
    Berggren, Martin
    Umeå University.
    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.

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