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  • 1.
    Aoshima, Koji
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Komatsu Ltd..
    Fälldin, Arvid
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wadbro, Eddie
    Umeå University, Faculty of Science and Technology, Department of Computing Science. Karlstad University, Sweden.
    Servin, Martin
    Umeå University, Faculty of Science and Technology, Department of Physics. Algoryx Simulation.
    Data-driven models for predicting the outcome of autonomous wheel loader operationsManuscript (preprint) (Other academic)
    Abstract [en]

    This paper presents a method using data-driven models for selecting actions and predicting the total performance of autonomous wheel loader operations over many loading cycles in a changing environment. The performance includes loaded mass, loading time, work. The data-driven models input the control parameters of a loading action and the heightmap of the initial pile state to output the inference of either the performance or the resulting pile state. By iteratively utilizing the resulting pile state as the initial pile state for consecutive predictions, the prediction method enables long-horizon forecasting. Deep neural networks were trained on data from over 10,000 random loading actions in gravel piles of different shapes using 3D multibody dynamics simulation. The models predict the performance and the resulting pile state with, on average, 95% accuracy in 1.2 ms, and 97% in 4.5 ms, respectively. The performance prediction was found to be even faster in exchange for accuracy by reducing the model size with the lower dimensional representation of the pile state using its slope and curvature. The feasibility of long-horizon predictions was confirmed with 40 sequential loading actions at a large pile. With the aid of a physics-based model, the pile state predictions are kept sufficiently accurate for longer-horizon use.

  • 2.
    Aoshima, Koji
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Komatsu Ltd., Akasaka, Minato-ku, Tokyo, Japan.
    Fälldin, Arvid
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wadbro, Eddie
    Umeå University, Faculty of Science and Technology, Department of Computing Science. Department of Mathematics and Computer Science, Karlstad University, Karlstad, Sweden.
    Servin, Martin
    Umeå University, Faculty of Science and Technology, Department of Physics. Algoryx Simulation AB, Umeå, Sweden.
    World modeling for autonomous wheel loaders2024In: Automation, ISSN 2673-4052, Vol. 5, no 3, p. 259-281Article in journal (Refereed)
    Abstract [en]

    This paper presents a method for learning world models for wheel loaders performing automatic loading actions on a pile of soil. Data-driven models were learned to output the resulting pile state, loaded mass, time, and work for a single loading cycle given inputs that include a heightmap of the initial pile shape and action parameters for an automatic bucket-filling controller. Long-horizon planning of sequential loading in a dynamically changing environment is thus enabled as repeated model inference. The models, consisting of deep neural networks, were trained on data from a 3D multibody dynamics simulation of over 10,000 random loading actions in gravel piles of different shapes. The accuracy and inference time for predicting the loading performance and the resulting pile state were, on average, 95% in 1.21.2 ms and 97% in 4.54.5 ms, respectively. Long-horizon predictions were found feasible over 40 sequential loading actions.

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  • 3.
    Aoshima, Koji
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Komatsu Ltd., Japan.
    Servin, Martin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wadbro, Eddie
    Umeå University, Faculty of Science and Technology, Department of Computing Science. Karlstad University, Sweden.
    Simulation-Based Optimization of High-Performance Wheel Loading2021In: Proceedings of the 38th International Symposium on Automation and Robotics in Construction (ISARC), Dubai: International Association for Automation and Robotics in Construction (IAARC) , 2021, p. 688-695Conference paper (Refereed)
    Abstract [en]

    Having smart and autonomous earthmoving in mind, we explore high-performance wheel loading in a simulated environment. This paper introduces a wheel loader simulator that combines contacting 3D multibody dynamics with a hybrid continuum-particle terrain model, supporting realistic digging forces and soil displacements at real-time performance. A total of 270,000 simulations are run with different loading actions, pile slopes, and soil to analyze how they affect the loading performance. The results suggest that the preferred digging actions should preserve and exploit a steep pile slope. High digging speed favors high productivity, while energy-efficient loading requires a lower dig speed. 

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  • 4.
    Aoshima, Koji
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Komatsu Ltd., Japan.
    Servin, Martin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wadbro, Eddie
    Umeå University, Faculty of Science and Technology, Department of Computing Science. Karlstad University, Karlstad, Sweden.
    Simulation-Based Optimization of High-Performance Wheel Loading2021In: 2021 Proceedings of the 38th ISARC, Dubai, UAE / [ed] Chen Feng; Thomas Linner; Ioannis Brilakis, International Association for Automation and Robotics in Construction (IAARC) , 2021, p. 688-695Conference paper (Refereed)
    Abstract [en]

    Having smart and autonomous earthmoving in mind, we explore high-performance wheel loading in a simulated environment. This paper introduces a wheel loader simulator that combines contacting 3D multibody dynamics with a hybrid continuum-particle terrain model, supporting realistic digging forces and soil displacements at real-time performance. A total of 270,000 simulations are run with different loading actions, pile slopes, and soil to analyze how they affect the loading performance. The results suggest that the preferred digging actions should preserve and exploit a steep pile slope. High digging speed favors high productivity, while energy-efficient loading requires a lower dig speed.

  • 5.
    Araujo-Cabarcas, Juan Carlos
    et al.
    Umeå University, Faculty of Science and Technology, Department of Science and Mathematics Education. Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Engström, Christian
    Department of Mathematics, Linnaeus University, Sweden.
    Wadbro, Eddie
    Umeå University, Faculty of Science and Technology, Department of Computing Science. Department of Mathematics and Computer Science, Karlstad University, Sweden.
    Shape optimization for the strong routing of light in periodic diffraction gratings2023In: Journal of Computational Physics, ISSN 0021-9991, E-ISSN 1090-2716, Vol. 472, article id 111684Article in journal (Refereed)
    Abstract [en]

    In the quest for the development of faster and more reliable technologies, the ability to control the propagation, confinement, and emission of light has become crucial. The design of guide mode resonators and perfect absorbers has proven to be of fundamental importance. In this project, we consider the shape optimization of a periodic dielectric slab aiming at efficient directional routing of light to reproduce similar features of a guide mode resonator. For this, the design objective is to maximize the routing efficiency of an incoming wave. That is, the goal is to promote wave propagation along the periodic slab. A Helmholtz problem with a piecewise constant and periodic refractive index medium models the wave propagation, and an accurate Robin-to-Robin map models an exterior domain. We propose an optimal design strategy that consists of representing the dielectric interface by a finite Fourier formula and using its coefficients as the design variables. Moreover, we use a high order finite element (FE) discretization combined with a bilinear Transfinite Interpolation formula. This setting admits explicit differentiation with respect to the design variables, from where an exact discrete adjoint method computes the sensitivities. We show in detail how the sensitivities are obtained in the quasi-periodic discrete setting. The design strategy employs gradient-based numerical optimization, which consists of a BFGS quasi-Newton method with backtracking line search. As a test case example, we present results for the optimization of a so-called single port perfect absorber. We test our strategy for a variety of incoming wave angles and different polarizations. In all cases, we efficiently reach designs featuring high routing efficiencies that satisfy the required criteria.

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  • 6.
    Araujo-Cabarcas, Juan Carlos
    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. Department of Mathematics and Computer Science, Karlstad University, Karlstad, Sweden.
    Shape optimization for the strong directional scattering of dielectric nanorods2021In: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 122, no 15, p. 3683-3704Article in journal (Refereed)
    Abstract [en]

    In this project, we consider the shape optimization of a dielectric scatterer aiming at efficient directional routing of light. In the studied setting, light interacts with a penetrable scatterer with dimension comparable to the wavelength of an incoming planar wave. The design objective is to maximize the scattering efficiency inside a target angle window. For this, a Helmholtz problem with a piecewise constant refractive index medium models the wave propagation, and an accurate Dirichlet-to-Neumann map models an exterior domain. The strategy consists of using a high-order finite element (FE) discretization combined with gradient-based numerical optimization. The latter consists of a quasi-Newton (BFGS) with backtracking line search. A discrete adjoint method is used to compute the sensitivities with respect to the design variables. Particularly, for the FE representation of the curved shape, we use a bilinear transfinite interpolation formula, which admits explicit differentiation with respect to the design variables. We exploit this fact and show in detail how sensitivities are obtained in the discrete setting. We test our strategy for a variety of target angles, different wave frequencies, and refractive indexes. In all cases, we efficiently reach designs featuring high scattering efficiencies that satisfy the required criteria.

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  • 7.
    Bokhari, Ahmad H.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Berggren, Martin
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Noreland, Daniel
    Umeå University, Faculty of Science and Technology, Department of Computing Science. The Forestry Research Institute of Sweden (Skogforsk), Uppsala Science Park, Uppsala, Sweden.
    Wadbro, Eddie
    Umeå University, Faculty of Science and Technology, Department of Computing Science. Department of Mathematics and Computer Science, Karlstad University, Karlstad, Sweden.
    Loudspeaker cabinet design by topology optimization2023In: Scientific Reports, E-ISSN 2045-2322, Vol. 13, no 1, article id 21248Article in journal (Refereed)
    Abstract [en]

    Using material distribution-based topology optimization, we optimize the bandpass design of a loudspeaker cabinet targeting low frequencies. The objective is to maximize the loudspeaker’s output power for a single frequency as well as a range of frequencies. To model the loudspeaker’s performance, we combine a linear electromechanical transducer model with a computationally efficient hybrid 2D–3D model for sound propagation. The adjoint variable approach computes the gradients of the objective function with respect to the design variables, and the Method of Moving Asymptotes (MMA) solves the topology optimization problem. To manage intermediate values of the material indicator function, a quadratic penalty is added to the objective function, and a non-linear filter is used to obtain a mesh independent design. By carefully selecting the target frequency range, we can guide the optimization algorithm to successfully generate a loudspeaker design with the required bandpass character. To the best of our knowledge, this study constitutes the first successful attempt to design the interior structure of a loudspeaker cabinet using topology optimization.

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  • 8.
    Bokhari, Ahmad Hasnain
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Berggren, Martin
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Noreland, Daniel
    Umeå University, Faculty of Science and Technology, Department of Computing Science. Forest operations Uppsala Science Park SE-751 83 Uppsala.
    Wadbro, Eddie
    Umeå University, Faculty of Science and Technology, Department of Computing Science. Department of Mathematics and Computer Science, Karlstad University.
    Topology optimization of a subwooferManuscript (preprint) (Other academic)
    Abstract [en]

    We use material distribution-based topology optimization to optimize the design of a bandpass subwoofer enclosure. The objective is to maximize the subwoofer's output power for a single frequency as well as for a range of frequencies. A linear electromechanical transducer model is combined with a hybrid 2D-3D model for sound propagation to model the subwoofer's performance. The adjoint variable approach is used to compute the gradients of the objective function with respect to the design variables, and the Method of Moving Asymptotes (MMA) is used to solve the topology optimization problem. To manage intermediate values of the material indicator function, a quadratic penalty is added to the objective function, and a non-linear filter is used to obtain a mesh independent design. By carefully selecting the target frequency range, we can guide the optimization algorithm to successfully generate a subwoofer design with the required bandpass character. This study constitutes, to the best of our knowledge, the first successful attempt to design the interior structure of a loudspeaker using topology optimization. The success is much due to the hybrid 2D-3D approach, which reduces the computational effort significantly with only small effects on the modeling accuracy. 

  • 9.
    Bokhari, Ahmad Hasnain
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Hassan, Emadeldeen
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Department of Electronics and Electrical Communications, Menoufia University, Menouf, Egypt.
    Wadbro, Eddie
    Umeå University, Faculty of Science and Technology, Department of Computing Science. Department of Mathematics and Computer Science, Karlstad University, Karlstad, Sweden.
    Topology optimization of microwave frequency dividing multiplexers2023In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 66, article id 106Article in journal (Refereed)
    Abstract [en]

    We use material-distribution-based topology optimization to design a three-port frequency dividing multiplexer at microwave frequencies. That is, by placing a good electric conductor inside the design domain, we aim to design a passive device that splits the incoming signal's frequencies into two frequency bands and transmits them to their respective output ports. The Helmholtz equation is used to model the time-harmonic wave propagation problem. We use the finite element method to solve the governing equation. The adjoint variable method provides the required gradients, and we solve the topology optimization problem using Svanberg's MMA algorithm. In this study, we present a technique for modeling the distribution of a good electric conductor within the design domain. In addition, we derive a power balance expression, which aids in formulating a series of three objective functions. In each successive objective function, we add more information and evaluate its impact on the results. The results show that by selecting a suitable objective function, we achieve more than 93.7 % transmission for both the frequency bands. Moreover, the numerical experiments suggest that the optimization problem is self penalized and is sensitive to the initial design.

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  • 10.
    Bokhari, Ahmad Hasnain
    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. Department of Mathematics and Computer Science, Karlstad University, Karlstad, Sweden.
    Sensitivity analysis of a coupled plasmonic problem2022Report (Other academic)
    Abstract [en]

    In material distribution-based topology optimization, we place material inside a design domain to extremize an objective function. The optimization problem is solved using a gradient-based algorithm. An efficient way to compute the gradients is to use the adjoint method. This study performs the sensitivity analysis of a coupled plasmonic problem using the adjoint method. More precisely, a TE-polarized Helmholtz equation is coupled to a Poisson equation. The sensitivity analysis of the coupled plasmonic problem poses some challenges stemming from the complex solution of the plasmonic problem. Therefore, we first consider a model problem whose structure is similar to the main problem in some ways but is simpler to study. After examining the model problem, we perform the sensitivity analysis of the coupled plasmonic problem, highlighting key differences between the two problems.

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  • 11.
    Hassan, Emadeldeen
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science. Department of Electronics and Electrical Communication Engineering, Menoufia University.
    Scheiner, Benedict
    Michler, Fabian
    Berggren, Martin
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Wadbro, Eddie
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Röhrl, Franz
    Zorn, Stefan
    Weigel, Robert
    Lurz, Fabian
    Multilayer Topology Optimization of Wideband SIW-to-Waveguide Transitions2020In: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 68, no 4, p. 1326-1339Article in journal (Refereed)
    Abstract [en]

    This article utilizes a topology optimization approach to design planar multilayer transitions between substrate integrated waveguides (SIWs) and rectangular waveguides (RWGs). The optimization problem is formulated based on the modal field analyses and Maxwell's equations in the time domain solved by the finite-difference time-domain (FDTD) method. We present a time-domain boundary condition based on the Klein–Gordon equation to split traveling waves at homogeneous waveguide ports. We employ the boundary condition to compute portal quantities and to devise an adjoint-field system that enabled an efficient computation of the objective function gradient. We solve design problems that include more than 105 000 design variables by using less than 400 solutions of Maxwell's equations. Moreover, a new formulation that effectively combats the development of in-band resonances in the design is presented. The transition configuration allows the direct mount of conventional RWG sections on the circuit board and aims to cover the entire K-band. The guiding structure of the optimized transition requires blind vias, which is realized by a simple and cost-efficient technique. In addition, the transition is optimized for three different setups that can be used to provide different field polarizations. The proposed transitions show less than 1-dB insertion loss and around 15-dB return loss over the frequency interval 18–28 GHz. Several prototypes are fabricated with an excellent match between the simulation and measurement results.

  • 12.
    Hosseini, S. Ahmad
    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. Department of Mathematics and Computer Science, Karlstad University, Karlstad, Sweden.
    A hybrid greedy randomized heuristic for designing uncertain transport network layout2022In: Expert systems with applications, ISSN 0957-4174, E-ISSN 1873-6793, Vol. 190, article id 116151Article in journal (Refereed)
    Abstract [en]

    The foundations of efficient management are laid on transport networks in various scientific and industrial fields. Nonetheless, establishing an optimum transport network design (TND) is complicated due to uncertainty in the operating environment. As a result, an uncertain network may be a more realistic representation of an actual transport network. The present study deals with an uncertain TND problem in which uncertain programming and the greedy randomized adaptive search procedure (GRASP) are used to develop an original optimization framework and propose a solution technique for obtaining cost-efficient designs. To this end, we originally develop the concept of α-shortest cycle (α-SC) employing the pessimistic value criterion, given a user-defined predesignated confidence level α. Employing this concept and the operational law of uncertain programming, a new auxiliary chance-constrained programming model is established for the uncertain TND problem, and we prove the existence of an equivalence relation between TNDs in an uncertain network and those in an auxiliary deterministic network. Specifically, we articulate how to obtain the uncertainty distribution of the overall optimal uncertain network's design cost. After all, the effectiveness and practical performance of the heuristic and optimization model is illustrated by adopting samples with different topology from a case study to show how our approach work in realistic networks and to highlight some of the heuristic's features.

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  • 13.
    Hosseini, S. Ahmad
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science. School of Engineering and Management, University of Nova Gorica, Slovenia.
    Wadbro, Eddie
    Umeå University, Faculty of Science and Technology, Department of Computing Science. Department of Mathematics and Computer Science, Karlstad University, Sweden.
    Ngoc Do, Dung
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Lindroos, Ola
    Department of Forest Biomaterials and Technology, Swedish University of Agricultural Sciences, Umeå, Sweden.
    A scenario-based metaheuristic and optimization framework for cost-effective machine-trail network design in forestry2023In: Computers and Electronics in Agriculture, ISSN 0168-1699, E-ISSN 1872-7107, Vol. 212, article id 108059Article in journal (Refereed)
    Abstract [en]

    Designing an optimal machine trail network is a complex locational problem that requires an understanding of different machines’ operations and terrain features as well as the trade-offs between various objectives. With the overall goal to minimize the operational costs of the logging operation, this paper proposes a mathematical optimization model for the trail network design problem and a greedy heuristic method based on different randomized search scenarios aiming to find the optimal location of machine trails —with potential to reduce negative environmental impact. The network is designed so that all trees can be reached and adapted to how the machines can maneuver while considering the terrain elevation's influence. To examine the effectiveness and practical performance of the heuristic and the optimization model, it was applied in a case study on four harvest units with different topologies and shapes. The computational experiments show that the heuristic can generate solutions that outperform the solutions corresponding to conventional, manual designs within practical time limits for operational planning. Moreover, to highlight certain features of the heuristic and the parameter settings’ effect on its performance, we present an extensive computational sensitivity analysis.

  • 14.
    Mousavi, Abbas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Berggren, Martin
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Hägg, Linus
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Wadbro, Eddie
    Umeå University, Faculty of Science and Technology, Department of Computing Science. Department of Mathematics and Computer Science, Karlstad University, Karlstad, Sweden.
    Topology optimization of a waveguide acoustic black hole for enhanced wave focusing2024In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 155, no 1, p. 742-756Article in journal (Refereed)
    Abstract [en]

    The waveguide acoustic black hole (WAB) effect is a promising approach for controlling wave propagation in various applications, especially for attenuating sound waves. While the wave-focusing effect of structural acoustic black holes has found widespread applications, the classical ribbed design of waveguide acoustic black holes (WABs) acts more as a resonance absorber than a true wave-focusing device. In this study, we employ a computational design optimization approach to achieve a conceptual design of a WAB with enhanced wave-focusing properties. We investigate the influence of viscothermal boundary losses on the optimization process by formulating two distinct cases: one neglecting viscothermal losses and the other incorporating these losses using a recently developed material distribution topology optimization technique. We compare the performance of optimized designs in these two cases with that of the classical ribbed design. Simulations using linearized compressible Navier–Stokes equations are conducted to evaluate the wave-focusing performance of these different designs. The results reveal that considering viscothermal losses in the design optimization process leads to superior wave-focusing capabilities, highlighting the significance of incorporating these losses in the design approach. This study contributes to the advancement of WAB design and opens up new possibilities for its applications in various fields.

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  • 15.
    Mousavi, Abbas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Berggren, Martin
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Wadbro, Eddie
    Umeå University, Faculty of Science and Technology, Department of Computing Science. Department of Mathematics and Computer Science, Karlstad University, Karlstad, Sweden.
    Extending material distribution topology optimization to boundary-effect-dominated problems with applications in viscothermal acoustics2023In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 234, article id 112302Article in journal (Other academic)
    Abstract [en]

    A new formulation is presented that extends the material distribution topology optimization method to address boundary-effect-dominated problems, where specific boundary conditions need to be imposed at solid–fluid interfaces. As an example of such a problem, we focus on the design of acoustic structures with significant viscous and thermal boundary losses. In various acoustic applications, especially for acoustically small devices, the main portion of viscothermal dissipation occurs in the so-called acoustic boundary layer. One way of accounting for these losses is through a generalized acoustic impedance boundary condition. This boundary condition has previously been proven to provide accurate results with significantly less computational effort compared to Navier–Stokes simulations. To incorporate this boundary condition into the optimization process at the solid–fluid interface, we introduce a mapping of jumps in densities between neighboring elements to an edge-based boundary indicator function. Two axisymmetric case studies demonstrate the effectiveness of the proposed design optimization method. In the first case, we enhance the absorption performance of a Helmholtz resonator in a narrow range of frequencies. In the second case, we consider an acoustically larger problem and achieve an almost-perfect broadband absorption. Our findings underscore the potential of our approach for the design optimization of boundary-effect-dominated problems.

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  • 16.
    Mousavi, Abbas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Berggren, Martin
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Wadbro, Eddie
    Department of Mathematics and Computer Science, Karlstad University, Karlstad, Sweden.
    How the waveguide acoustic black hole works: A study of possible damping mechanisms2022In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 151, no 6, p. 4279-4290Article in journal (Refereed)
    Abstract [en]

    The acoustic black hole (ABH) effect in waveguides is studied using frequency-domain finite element simulations of a cylindrical waveguide with an embedded ABH termination composed of retarding rings. This design is adopted from an experimental study in the literature, which surprisingly showed, contrary to the structural counterpart, that the addition of damping material to the end of the waveguide does not significantly reduce the reflection coefficient any further. To investigate this unexpected behavior, we model different damping mechanisms involved in the attenuation of sound waves in this setup. A sequence of computed pressure distributions indicates occurrences of frequency-dependent resonances in the device. The axial position of the cavity where the resonance occurs can be predicted by a more elaborate wall admittance model than the one that was initially used to study and design ABHs. The results of our simulations show that at higher frequencies, the visco-thermal losses and the damping material added to the end of the setup do not contribute significantly to the performance of the device. Our results suggest that the primary source of damping, responsible for the low reflection coefficients at higher frequencies, is local absorption effects at the outer surface of the cylinder.

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  • 17.
    Mousavi, Abbas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Berggren, Martin
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Wadbro, Eddie
    Department of Mathematics and Computer Science, Karlstad University, Karlstad, Sweden.
    On the acoustic black-hole effect in waveguides2021In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 149, no 4, article id A108Article in journal (Refereed)
    Abstract [en]

    The acoustic black-hole (ABH) effect is a well-known way of controlling structural vibrations in solid beams and plates. The theory behind this effect is to reduce the velocity of waves by altering the physical properties of the domain according to a power-law profile. For an ideal ABH, this leads to vanishing reflections from the end of the termination. In practice, there will be a truncation in the profile, which leads to some reflections. A well-known way of minimizing this truncation error is to add damping material to the end of the ABH termination.

    For a waveguide embedding a set of rings with retarding inner radius according to a power-law profile, the velocity of sound waves tends to zero. However, unlike the structural counterpart, experimental results in the literature show that adding damping material to reduce the truncation error is not effective for waveguides. Here, we present a finite element simulation of the considered cylindrical setup. Our results confirm that the addition of damping material to the end of the waveguide is ineffective while suggesting that the local absorption effects at the lateral surface of the cylinder are a primary source of damping to achieve the ABH effect.

  • 18.
    Mousavi, Abbas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Uihlein, Andrian
    Department of Mathematics, Chair of Applied Mathematics (Continuous Optimization), Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany.
    Pflug, Lukas
    Department of Mathematics, Chair of Applied Mathematics (Continuous Optimization), Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany; FAU Competence Center Scientific Computing, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany.
    Wadbro, Eddie
    Umeå University, Faculty of Science and Technology, Department of Computing Science. Department of Mathematics and Computer Science, Karlstad University, Karlstad, Sweden.
    Topology optimization of broadband acoustic transition section: a comparison between deterministic and stochastic approaches2024In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 67, no 5, article id 67Article in journal (Refereed)
    Abstract [en]

    This paper focuses on the topology optimization of a broadband acoustic transition section that connects two cylindricalwaveguides with different radii. The primary objective is to design a transition section that maximizes the transmission of aplanar acoustic wave while ensuring that the transmitted wave exhibits a planar shape. Helmholtz equation is used to modellinear wave propagation in the device. We utilize the finite element method to solve the state equation on a structured meshof square elements. Subsequently, a material distribution topology optimization problem is formulated to optimize the dis-tribution of sound-hard material in the transition section. We employ two different gradient-based approaches to solve theoptimization problem: namely, a deterministic approach using the method of moving asymptotes (MMA), and a stochasticapproach utilizing both stochastic gradient (SG) and continuous stochastic gradient (CSG) methods. A comparative analysisis provided among these methodologies concerning the design feasibility and the transmission performance of the optimizeddesigns, and the computational efficiency. The outcomes highlight the effectiveness of stochastic techniques in achievingenhanced broadband acoustic performance with reduced computational demands and improved design practicality. Theinsights from this investigation demonstrate the potential of stochastic approaches in acoustic applications, especially whenbroadband acoustic performance is desired.

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  • 19.
    Nguyen, Quoc Khanh
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Serra-Capizzano, Stefano
    Department of Humanities and Innovation, University of Insubria, INDAM Unit, Como, Italy; Department of Information Technology, Uppsala University, Uppsala, Sweden.
    Tablino-Possio, Cristina
    Dipartimento di Matematica e Applicazioni, Università di Milano Bicocca, Milano, Italy.
    Wadbro, Eddie
    Umeå University, Faculty of Science and Technology, Department of Computing Science. Department of Mathematics and Computer Science, Karlstad University, Karlstad, Sweden.
    Spectral analysis of the finite element matrices approximating 2D linearly elastic structures and multigrid proposals2022In: Numerical Linear Algebra with Applications, ISSN 1070-5325, E-ISSN 1099-1506, Vol. 29, no 4, article id e2433Article in journal (Refereed)
    Abstract [en]

    Topology optimization aims to find the best material layout subject to given constraints. The so-called material distribution methods cast the governing equation as an extended or fictitious domain problem, in which a coefficient field represents the design. When solving the governing equation using the finite element method, a large number of elements are used to discretize the design domain, and an element-wise constant function approximates the coefficient field in the considered design domain. This article presents a spectral analysis of the (large) coefficient matrices associated with the linear systems stemming from the finite element discretization of a linearly elastic problem for an arbitrary coefficient field. Based on the spectral information, we design a multigrid method which turns out to be optimal, in the sense that the (arithmetic) cost for solving the related linear systems, up to a fixed desired accuracy, is proportional to the matrix-vector cost, which is linear in the corresponding matrix size. The method is tested, and the numerical results are very satisfactory in terms of linear cost and number of iterations, which is bounded by a constant independent of the matrix size.

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  • 20.
    Niu, Bin
    et al.
    Key Laboratory for Precision and Non-traditional Machining Technology of Ministry of Education, School of Mechanical Engineering, Dalian University of Technology, Dalian, China.
    Wadbro, Eddie
    Umeå University, Faculty of Science and Technology, Department of Computing Science. Department of Mathematics and Computer Science, Karlstad University, Karlstad, Sweden.
    Multiscale design of coated structures with periodic uniform infill for vibration suppression2021In: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 255, article id 106622Article in journal (Refereed)
    Abstract [en]

    In this paper, a novel design strategy to minimize the dynamic compliance of a vibrating infill structure with a solid outer coating and a periodic uniform infill lattice is presented. The vibration of the linearly elastic infill structure is excited by time-harmonic external mechanical loading. The design optimization of the infill lattice is performed simultaneously with the topology optimization of the macroscale structure, which also includes the coating. Multiscale topological designs of infill structures are presented in numerical examples for different excitation frequencies, different limits on static compliance, different damping properties, and different boundary conditions. The results are obtained by the finite element method and gradient-based optimization using analytical sensitivity analysis, which is derived and presented in the fully discrete setting. The influences of excitation frequencies, static constraints, damping properties, coating thicknesses, and boundary conditions on the optimized macrostructures and microstructures are discussed in the numerical examples. In general, the optimized microstructures reflect the shape characteristics of the macrostructure configuration, where Kagome-like microstructures have been obtained in some examples. Moreover, in the optimized results the microstructures include more but finer structural members for the design optimized for low excitation frequencies.

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  • 21.
    Nobis, Harrison
    et al.
    FLOW Centre and Swedish e-Science Research Centre (SeRC), KTH Mechanics, Royal Institute of Technology, Stockholm, Sweden.
    Schlatter, Philipp
    FLOW Centre and Swedish e-Science Research Centre (SeRC), KTH Mechanics, Royal Institute of Technology, Stockholm, Sweden.
    Wadbro, Eddie
    Umeå University, Faculty of Science and Technology, Department of Computing Science. Department of Mathematics and Computer Science, Karlstad University, Karlstad, Sweden.
    Berggren, Martin
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Henningson, Dan S.
    FLOW Centre and Swedish e-Science Research Centre (SeRC), KTH Mechanics, Royal Institute of Technology, Stockholm, Sweden.
    Modal laminar–turbulent transition delay by means of topology optimization of superhydrophobic surfaces2023In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 403, article id 115721Article in journal (Refereed)
    Abstract [en]

    When submerged under a liquid, the microstructure of a SuperHydrophobic Surface (SHS) traps a lubricating layer of gas pockets, which has been seen to reduce the skin friction of the overlying liquid flow in both laminar and turbulent regimes. More recently, spatially homogeneous SHS have also been shown to delay laminar–turbulent transition in channel flows, where transition is triggered by modal mechanisms. In this study, we investigate, by means of topology optimization, whether a spatially inhomogeneous SHS can be designed to further delay transition in channel flows. Unsteady direct numerical simulations are conducted using the spectral element method in a 3D periodic wall-bounded channel. The effect of the SHS is modelled using a partial slip length on the walls, forming a 2D periodic optimization domain. Following a density-based approach, the optimization procedure uses the adjoint-variable method to compute gradients and a checkpointing strategy to reduce storage requirements. This methodology is adapted to optimizing over an ensemble of initial perturbations. This study presents the first application of topology optimization to laminar–turbulent transition. We show that this method can design surfaces that delay transition significantly compared to a homogeneous counterpart, by inhibiting the growth of secondary instability modes. By optimizing over an ensemble of streamwise phase-shifted perturbations, designs have been found with comparable mean transition time and lower variance.

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  • 22.
    Nobis, Harrison
    et al.
    FLOW and SeRC, KTH Engineering Mechanics, Royal Institute of Technology, Stockholm, Sweden.
    Schlatter, Philipp
    FLOW and SeRC, KTH Engineering Mechanics, Royal Institute of Technology, Stockholm, Sweden; Friedrich-Alexander-Universität (FAU) Erlangen–Nürnberg, Germany.
    Wadbro, Eddie
    Department of Mathematics and Computer Science, Karlstad University, Karlstad, Sweden.
    Berggren, Martin
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Henningson, Dan S.
    FLOW and SeRC, KTH Engineering Mechanics, Royal Institute of Technology, Stockholm, Sweden.
    Topology optimization of Superhydrophobic Surfaces to delay spatially developing modal laminar–turbulent transition2023In: International Journal of Heat and Fluid Flow, ISSN 0142-727X, E-ISSN 1879-2278, Vol. 104, article id 109231Article in journal (Refereed)
    Abstract [en]

    Super-Hydrophobic Surfaces (SHSs) have been shown to reduce skin friction of an overlying fluid as a consequence of gas pockets trapped within the surface's microstructure. More recently, they have also been shown capable of delaying laminar–turbulent transition. This article investigates the applicability of topology optimization in designing the macroscopic layout of SHSs in a channel that are able to further delay K-type transition in a spatial setting. Unsteady direct numerical simulations are performed to simulate the transition scenario. This is coupled with adjoint–based sensitivity analysis and gradient based optimization. The optimized designs found through this procedure are capable of moving the transition location further downstream compared to a homogeneous counterpart by inhibiting the growth of secondary instability modes. This article provides the first application of topology optimization to a spatially developing transition scenario.

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  • 23.
    Nobis, Harrison
    et al.
    FLOW Centre and Swedish e-Science Research Centre (SeRC), KTH Mechanics, Royal Institute of Technology, Stockholm, Sweden.
    Schlatter, Philipp
    FLOW Centre and Swedish e-Science Research Centre (SeRC), KTH Mechanics, Royal Institute of Technology, Stockholm, Sweden.
    Wadbro, Eddie
    Umeå University, Faculty of Science and Technology, Department of Computing Science. Department of Mathematics and Computer Science, Karlstad University, Karlstad, Sweden.
    Berggren, Martin
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Henningson, Dan S.
    FLOW Centre and Swedish e-Science Research Centre (SeRC), KTH Mechanics, Royal Institute of Technology, Stockholm, Sweden.
    Topology optimization of unsteady flows using the spectral element method2022In: Computers & Fluids, ISSN 0045-7930, E-ISSN 1879-0747, Vol. 239, article id 105387Article in journal (Refereed)
    Abstract [en]

    We investigate the applicability of a high-order Spectral Element Method (SEM) to density based topology optimization of unsteady flows in two dimensions. Direct Numerical Simulations (DNS) are conducted relying on Brinkman penalization to describe the presence of solid within the domain. The optimization procedure uses the adjoint-variable method to compute gradients and a checkpointing strategy to reduce storage requirements. A nonlinear filtering strategy is used to both enforce a minimum length scale and to provide smoothing across the fluid–solid interface, preventing Gibbs oscillations. This method has been successfully applied to the design of a channel bend and an oscillating pump, and demonstrates good agreement with body fitted meshes. The precise design of the pump is shown to depend on the initial material distribution. However, the underlying topology and pumping mechanism is the same. The effect of a minimum length scale has been studied, revealing it to be a necessary regularization constraint for the oscillating pump to produce meaningful designs. The combination of SEM and density based optimization offer some unique challenges which are addressed and discussed, namely a lack of explicit boundary tracking exacerbated by the interface smoothing. Nevertheless, SEM can achieve equivalent levels of precision to traditional finite element methods, while requiring fewer degrees of freedom. Hence, the use of SEM addresses the two major bottlenecks associated with optimizing unsteady flows: computation cost and data storage.

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  • 24.
    Saglietti, Clio
    et al.
    Linné FLOW Centre, Swedish e-Science Research Centre (SeRC), KTH Mechanics Royal Institute of Technology, Stockholm, Sweden.
    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.
    Henningson, Dan S.
    Linné FLOW Centre, Swedish e-Science Research Centre (SeRC), KTH Mechanics Royal Institute of Technology, Stockholm, Sweden.
    Heat transfer maximization in a three dimensional conductive differentially heated cavity by means of topology optimization2020In: Proceedings of the 6th European Conference on Computational Mechanics: Solids, Structures and Coupled Problems, ECCM 2018 and 7th European Conference on Computational Fluid Dynamics, ECFD 2018, International Centre for Numerical Methods in Engineering, CIMNE , 2020, p. 3258-3269Conference paper (Refereed)
    Abstract [en]

    The thermal performance of heat sinks is enhanced, in the present paper, by applying a material distribution topology optimization approach. We consider solid structures enclosed in three dimensional steady-state conductive differentially heated cavities. The algorithm iteratively updates the geometry of a heat sink, relying on gradient information. The gradient information are computed using adjoint sensitivity methods, combined with high-order accuracy direct numerical simulations. A complete conjugated problem is solved, in which we describe the effect of the solid material on the surrounding flow through the action of a Brinkman friction term in the Navier-Stokes equations, and we map the material distribution function onto the thermal conductivity and heat capacity in the energy conservation equation. Additionally, advanced filtering techniques are applied for enforcing a desired length scale to the solid structure. The success of the method is presented with a thorough physical investigation of the optimal results, which deliver a substantial increase of the heat transfer.

  • 25.
    Wiberg, Viktor
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wallin, Erik
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Fälldin, Arvid
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Semberg, Tobias
    Skogforsk (the Forestry Research Institute of Sweden), Uppsala, Sweden.
    Rossander, Morgan
    Skogforsk (the Forestry Research Institute of Sweden), Uppsala, Sweden.
    Wadbro, Eddie
    Umeå University, Faculty of Science and Technology, Department of Computing Science. Karlstad University, Karlstad, Sweden.
    Servin, Martin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sim-to-real transfer of active suspension control using deep reinforcement learningManuscript (preprint) (Other academic)
    Abstract [en]

    We explore sim-to-real transfer of deep reinforcement learning controllers for a heavy vehicle with active suspensions designed for traversing rough terrain. While related research primarily focuses on lightweight robots with electric motors and fast actuation, this study uses a forestry vehicle with a complex hydraulic driveline and slow actuation. We simulate the vehicle using multibody dynamics and apply system identification to find an appropriate set of simulation parameters. We then train policies in simulation using various techniques to mitigate the sim-to-real gap, including domain randomization, action delays, and a reward penalty to encourage smooth control. In reality, the policies trained with action delays and a penalty for erratic actions perform at nearly the same level as in simulation. In experiments on level ground, the motion trajectories closely overlap when turning to either side, as well as in a route tracking scenario. When faced with a ramp that requires active use of the suspensions, the simulated and real motions are in close alignment. This shows that the actuator model together with system identification yields a sufficiently accurate model of the actuators. We observe that policies trained without the additional action penalty exhibit fast switching or bang-bang control. These present smooth motions and high performance in simulation but transfer poorly to reality. We find that policies make marginal use of the local height map for perception, showing no indications of look-ahead planning. However, the strong transfer capabilities entail that further development concerning perception and performance can be largely confined to simulation. 

  • 26.
    Wiberg, Viktor
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Algoryx Simulation AB, Umeå, Sweden.
    Wallin, Erik
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Fälldin, Arvid
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Semberg, Tobias
    Skogforsk (the Forestry Research Institute of Sweden), Uppsala, Sweden.
    Rossander, Morgan
    Skogforsk (the Forestry Research Institute of Sweden), Uppsala, Sweden.
    Wadbro, Eddie
    Umeå University, Faculty of Science and Technology, Department of Computing Science. Karlstad University, Karlstad, Sweden.
    Servin, Martin
    Umeå University, Faculty of Science and Technology, Department of Physics. Algoryx Simulation AB, Umeå, Sweden.
    Sim-to-real transfer of active suspension control using deep reinforcement learning2024In: Robotics and Autonomous Systems, ISSN 0921-8890, E-ISSN 1872-793X, Vol. 179, article id 104731Article in journal (Refereed)
    Abstract [en]

    We explore sim-to-real transfer of deep reinforcement learning controllers for a heavy vehicle with active suspensions designed for traversing rough terrain. While related research primarily focuses on lightweight robots with electric motors and fast actuation, this study uses a forestry vehicle with a complex hydraulic driveline and slow actuation. We simulate the vehicle using multibody dynamics and apply system identification to find an appropriate set of simulation parameters. We then train policies in simulation using various techniques to mitigate the sim-to-real gap, including domain randomization, action delays, and a reward penalty to encourage smooth control. In reality, the policies trained with action delays and a penalty for erratic actions perform nearly at the same level as in simulation. In experiments on level ground, the motion trajectories closely overlap when turning to either side, as well as in a route tracking scenario. When faced with a ramp that requires active use of the suspensions, the simulated and real motions are in close alignment. This shows that the actuator model together with system identification yields a sufficiently accurate model of the actuators. We observe that policies trained without the additional action penalty exhibit fast switching or bang–bang control. These present smooth motions and high performance in simulation but transfer poorly to reality. We find that policies make marginal use of the local height map for perception, showing no indications of predictive planning. However, the strong transfer capabilities entail that further development concerning perception and performance can be largely confined to simulation.

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  • 27.
    Wiberg, Viktor
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wallin, Erik
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wadbro, Eddie
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Rosander, Morgan
    Skogforsk.
    Servin, Martin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Simulation-to-reality transfer to control a forwarder with active suspensions through deep reinforcement learning2022In: International Conference of Forest Engineering COFE-FORMEC-IUFRO, Corvallis, Oregon, USA, 2022Conference paper (Other academic)
    Abstract [en]

    Automating the loaded and unloaded driving of a forwarder has the potential to reduce operational costsup to 10% in cut-to-length logging, but remains a challening and unsolved task. The complex interaction between the vehicle and terrain requires the controller to percieve its surroundings and thestate of the vehicle to plan for traversal. Because the state space is high dimensional and the systemdynamics cannot be formulated in closed form or easily approximated, traditional control methods areinadequate. Under these conditions, where learning to act in the environement is easier than learning thesystem dynamics, model free reinforcement learning is a promising option. We use deep reinforcementlearning for control of a 16-tonne forwarder with actively articulated suspensions. To efficiently gathergeneralizable experience, the control policies were safetly trained in simulation while varying severaldomain parameters. Each policy is trained during what correponds to roughly one month of real time.In simulation, the controller shows the ability to traverse rough terrains reconstruced from high-densitylaser scans and handles slopes up to 27◦. To compare the simulated to real performance we transfer thecontrol policies to the physical vehicle. Our results provide insight on how to improve policy transfer toheavy and expensive forest machines.

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