| 1. |
- Wendt, Fabian, et al.
(author)
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Ocean energy systemswave energy modelling task: Modelling, verification and validation ofwave energy converters
- 2019
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In: Journal of Marine Science and Engineering. - : MDPI AG. - 2077-1312. ; 7:11
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Journal article (peer-reviewed)abstract
- The International Energy Agency Technology Collaboration Programme for Ocean Energy Systems (OES) initiated the OES Wave Energy Conversion Modelling Task, which focused on the verification and validation of numerical models for simulating wave energy converters (WECs). The long-term goal is to assess the accuracy of and establish confidence in the use of numerical models used in design as well as power performance assessment of WECs. To establish this confidence, the authors used different existing computational modelling tools to simulate given tasks to identify uncertainties related to simulation methodologies: (i) linear potential flow methods; (ii) weakly nonlinear Froude-Krylov methods; and (iii) fully nonlinear methods (fully nonlinear potential flow and Navier-Stokes models). This article summarizes the code-to-code task and code-to-experiment task that have been performed so far in this project, with a focus on investigating the impact of different levels of nonlinearities in the numerical models. Two different WECs were studied and simulated. The first was a heaving semi-submerged sphere, where free-decay tests and both regular and irregular wave cases were investigated in a code-to-code comparison. The second case was a heaving float corresponding to a physical model tested in a wave tank. We considered radiation, diffraction, and regular wave cases and compared quantities, such as the WEC motion, power output and hydrodynamic loading.
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| 2. |
- Hoffman, Johan, et al.
(author)
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New Theory of Flight
- 2016
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In: Journal of Mathematical Fluid Mechanics. - : Springer. - 1422-6928 .- 1422-6952. ; 18:2, s. 219-241
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Journal article (peer-reviewed)abstract
- We present a new mathematical theory explaining the fluid mechanics of sub-sonic flight, which is fundamentally different from the existing boundary layer-circulation theory by Prandtl-Kutta-Zhukovsky formed 100 year ago. The new the-ory is based on our new resolution of d’Alembert’s paradox showing that slightlyviscous bluff body flow can be viewed as zero-drag/lift potential flow modified by3d rotational slip separation arising from a specific separation instability of po-tential flow, into turbulent flow with nonzero drag/lift. For a wing this separationmechanism maintains the large lift of potential flow generated at the leading edgeat the price of small drag, resulting in a lift to drag quotient of size15
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| 3. |
- Clemente, Francesco, et al.
(author)
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Touch and Hearing Mediate Osseoperception
- 2017
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 7
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Journal article (peer-reviewed)abstract
- Osseoperception is the sensation arising from the mechanical stimulation of a bone-anchored prosthesis. Here we show that not only touch, but also hearing is involved in this phenomenon. Using mechanical vibrations ranging from 0.1 to 6 kHz, we performed four psychophysical measures (perception threshold, sensation discrimination, frequency discrimination and reaction time) on 12 upper and lower limb amputees and found that subjects: consistently reported perceiving a sound when the stimulus was delivered at frequencies equal to or above 400 Hz; were able to discriminate frequency differences between stimuli delivered at high stimulation frequencies (similar to 1500 Hz); improved their reaction time for bimodal stimuli (i.e. when both vibration and sound were perceived). Our results demonstrate that osseoperception is a multisensory perception, which can explain the improved environment perception of bone-anchored prosthesis users. This phenomenon might be exploited in novel prosthetic devices to enhance their control, thus ultimately improving the amputees' quality of life.
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| 4. |
- Degirmenci, Niyazi Cem, et al.
(author)
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A Unified Numerical Simulation of Vowel Production That Comprises Phonation and the Emitted Sound
- 2017
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In: Proceedings of the Annual Conference of the International Speech Communication Association, INTERSPEECH 2017. - : The International Speech Communication Association (ISCA). ; , s. 3492-3496
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Conference paper (peer-reviewed)abstract
- A unified approach for the numerical simulation of vowels is presented, which accounts for the self-oscillations of the vocal folds including contact, the generation of acoustic waves and their propagation through the vocal tract, and the sound emission outwards the mouth. A monolithic incompressible fluid-structure interaction model is used to simulate the interaction between the glottal jet and the vocal folds, whereas the contact model is addressed by means of a level set application of the Eikonal equation. The coupling with acoustics is done through an acoustic analogy stemming from a simplification of the acoustic perturbation equations. This coupling is one-way in the sense that there is no feedback from the acoustics to the flow and mechanical fields. All the involved equations are solved together at each time step and in a single computational run, using the finite element method (FEM). As an application, the production of vowel [i] has been addressed. Despite the complexity of all physical phenomena to be simulated simultaneously, which requires resorting to massively parallel computing, the formant locations of vowel [i] have been well recovered.
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| 5. |
- Jansson, Johan, et al.
(author)
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Adaptive simulation of unsteady flow past the submerged part of a floating wind turbine platform
- 2015
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In: MARINE 2015 - Computational Methods in Marine Engineering VI. - : International Center for Numerical Methods in Engineering (CIMNE). - 9788494392863 ; , s. 35-46
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Conference paper (peer-reviewed)abstract
- Offshore floating platforms for wind turbines represent challenging concepts for designers trying to combine an optimal compromise between cost effectiveness and performance. Modelling of the hydrodynamic behaviour of the structure is still the subject of wide debate in the technical communities. The assessment of the hydrodynamics of the support structure is not an easy task as the floaters consist of an assembly of columns, braces and pontoons, commonly also with heave plates: Each of these components corresponds to a different hydrodynamic model and it further interacts with the other elements. This results in very complex non-linear modeling, which makes it necessary to resort to computational fluid dynamics (CFD) methods for the evaluation of the combined hydrodynamics. In the framework of the collaboration between the Basque Centre for Applied Mathematics (BCAM) and Tecnalia R&I, the interaction of the sea flow with a semisubmersible floating offshore wind platform have been calculated by using the open source solver Unicorn in the FEniCS-HPC framework when subject to a steady inflow. The prototype of the platform consists in a semi-submersible 4-columns column stabilized platform - NAUTILUS Floating Solutions concept-; columns are connected by a rigid ring pontoon provided with heave damping plates at the bottom. The novelty of the approach in FEniCS-HPC hinges upon an implicit formulation for the turbulence, a cheap free slip model of the boundary layer and goal-oriented mesh adaptivity [8, 6, 9, 20, 1]. We find that the results are consistent with experimental results for cylinders at high Reynolds number.
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| 6. |
- Krishnasamy, E., et al.
(author)
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Direct FEM large scale computation of turbulent multiphase flow in urban water systems and marine energy
- 2016
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In: ECCOMAS Congress 2016 - Proceedings of the 7th European Congress on Computational Methods in Applied Sciences and Engineering. - Athens : National Technical University of Athens. - 9786188284401 ; , s. 1339-1351
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Conference paper (peer-reviewed)abstract
- High-Reynolds number turbulent incompressible multiphase flow represents a large class of engineering problems of key relevance to society. Here we describe our work on modeling two such problems: 1. The Consorcio de Aguas Bilbao Bizkaia is constructing a new storm tank system with an automatic cleaning system, based on periodically pushing tank water out in a tunnel 2. In the framework of the collaboration between BCAM - Basque Center for Applied Mathematics and Tecnalia R & I, the interaction of the sea flow with a semi submersible floating offshore wind platform is computationally investigated. We study the MARIA' benchmark modeling breaking waves over objects in marine environments. Both of these problems are modeled in the the Direct FEM/General Galerkin methodology for turbulent incompressible variable-densitv flow 1,2 in the FEniCS software framework.
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| 7. |
- Nguyen, Van Dang, 1985-, et al.
(author)
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Direct Finite Element Simulation of the Turbulent Flow Past a Vertical Axis Wind Turbine
- 2019
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In: Renewable energy. - : Elsevier. - 0960-1481 .- 1879-0682. ; 135, s. 238-247
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Journal article (peer-reviewed)abstract
- There is today a significant interest in harvesting renewable energy, specifically wind energy, in offshore and urban environments. Vertical axis wind turbines get increasing attention since they are able to capture the wind from any direction. They are relatively easy to install and to transport, cheaper to build and maintain, and quite safe for humans and birds. Detailed computer simulations of the fluid dynamics of wind turbines provide an enhanced understanding of the technology and may guide design improvements. In this paper, we simulate the turbulent flow past a vertical axis wind turbine for a range of rotation angles in parked and rotating conditions. We propose the method of Direct Finite Element Simulation in a rotating ALE framework, abbreviated as DFS-ALE. The simulation results are validated against experimental data in the form of force measurements. We find that the simulation results are stable with respect to mesh refinement and that we capture well the general shape of the variation of force measurements over the rotation angles.
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| 8. |
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| 9. |
- Nguyen, Van Dang, et al.
(author)
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Modelling Of Rotating Vertical Axis Turbines Using A Multiphase Finite Element Method
- 2017
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In: VII International Conference on Computational Methods in Marine Engineering (MARINE 2017). - : International Center for Numerical Methods in Engineering (CIMNE). - 9788494690983 ; , s. 950-959
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Conference paper (peer-reviewed)abstract
- We combine the unified continuum fluid-structure interaction method with a multiphase flow model to simulate turbulent flow and fluid-structure interaction of rotating vertical axis turbines in offshore environments. This work is part of a project funded by the Swedish Energy Agency, which focuses on energy systems combining ecological sustainability, competitiveness and reliability of supply. The numerical methods used comprise the Galerkin least-squares finite element method, coupled with the arbitrary Lagrangian-Eulerian method, in order to compute weak solutions of the Navier-Stokes equations for high Reynolds numbers on moving meshes. Mesh smoothing methods help to improve the mesh quality when the mesh undergoes large deformations. The simulations have been performed using the Unicorn solver in the FEniCS-HPC framework, which runs on supercomputers with near optimal weak and strong scaling up to thousands of cores.
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| 10. |
- Janson, Carl-Erik, 1957, et al.
(author)
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Nonlinear computations of heave motions for a generic Wave Energy Converter
- 2018
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In: NAV International Conference on Ship and Shipping Research. - : Associazione Italiana di Tecnica Navale. - 2282-8397. ; 1 January 2018, s. 283 - 290, s. 283-290
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Conference paper (peer-reviewed)abstract
- A benchmarking activity of numerical methods for analysis of Wave Energy Converters (WEC) was proposed under the Ocean Energy Systems (OES) International Energy Agency (IEA) Task 10 in 2015. The purpose of the benchmark is to do a code-2-code comparison of the predicted motions and power take out for a WEC. A heaving sphere was used as a first simple test case. The participants simulated heave decay and regular and irregular wave cases. The numerical methods ranged from linear methods to viscous methods solving the Navier-Stokes equations (CFD). An overview of the results from the first phase of the benchmark was reported in (Wendt et al 2017). The present paper focus on the simulations of the sphere using one fully nonlinear time-domain BEM method one transient RANS method and one transient Direct FE method with no turbulence model. The theory of the three methods as well as the modelling of the sphere are described. Heave decay and heave motions for steep regular waves were selected as test cases in order to study and compare the capability to handle nonlinear effects. Computational efficiency and applicability of the three methods are also discussed.
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