| 1. |
- Degirmenci, Niyazi Cem, et al.
(författare)
-
A Unified Numerical Simulation of Vowel Production That Comprises Phonation and the Emitted Sound
- 2017
-
Ingår i: Proceedings of the Annual Conference of the International Speech Communication Association, INTERSPEECH 2017. - : The International Speech Communication Association (ISCA). ; , s. 3492-3496
-
Konferensbidrag (refereegranskat)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.
|
|
| 2. |
- Hoffman, Johan, 1974-, et al.
(författare)
-
Computability and Adaptivity in CFD
- 2018
-
Ingår i: Encyclopedia of Computational Mechanics. - : John Wiley & Sons.
-
Bokkapitel (refereegranskat)
|
|
| 3. |
- Hoffman, Johan, 1974-, et al.
(författare)
-
Turbulent flow and Fluid–structure interaction
- 2012
-
Ingår i: Lecture Notes in Computational Science and Engineering. - : Springer Science and Business Media Deutschland GmbH. ; , s. 543-552
-
Bokkapitel (refereegranskat)abstract
- The FEniCS Project aims towards the goals of generality, efficiency, and simplicity, concerning mathematical methodology, implementation and application, and the Unicorn project is an implementation aimed at FSI and high Re turbulent flow guided by these principles. Unicorn is based on the DOLFIN/FFC/FIAT suite and the linear algebra package PETSc. We here present some key elements of Unicorn, and a set of computational results from applications. The details of the Unicorn implementation are described in Chapter 18.
|
|
| 4. |
- Hoffman, Johan, 1974-, et al.
(författare)
-
Unicorn : A unified continuum mechanics solver
- 2012
-
Ingår i: Lecture Notes in Computational Science and Engineering. - : Springer Science and Business Media Deutschland GmbH. ; , s. 339-361
-
Bokkapitel (refereegranskat)abstract
- This chapter provides a description of the technology of Unicorn focusing on simple, efficient and general algorithms and software for the Unified Continuum (UC) concept and the adaptive General Galerkin (G2) discretization as a unified approach to continuum mechanics. We describe how Unicorn fits into the FEniCS framework, how it interfaces to other FEniCS components, what interfaces and functionality Unicorn provides itself and how the implementation is designed. We also present some examples in fluid–structure interaction and adaptivity computed with Unicorn.
|
|
| 5. |
- Jansson, Johan, et al.
(författare)
-
Adaptive unified continuum FEM modeling of a 3D FSI benchmark problem
- 2017
-
Ingår i: International Journal for Numerical Methods in Biomedical Engineering. - : Wiley-Blackwell. - 2040-7939 .- 2040-7947. ; 33:9
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we address a 3D fluid-structure interaction benchmark problem that represents important characteristics of biomedical modeling. We present a goal-oriented adaptive finite element methodology for incompressible fluid-structure interaction based on a streamline diffusion–type stabilization of the balance equations for mass and momentum for the entire continuum in the domain, which is implemented in the Unicorn/FEniCS software framework. A phase marker function and its corresponding transport equation are introduced to select the constitutive law, where the mesh tracks the discontinuous fluid-structure interface. This results in a unified simulation method for fluids and structures. We present detailed results for the benchmark problem compared with experiments, together with a mesh convergence study.
|
|
| 6. |
- Moragues Ginard, M, et al.
(författare)
-
Simulation of floating platforms for marine energy generation
- 2018
-
Ingår i: 10th International Conference on Computational Fluid Dynamics, ICCFD 2018. - : International Conference on Computational Fluid Dynamics 2018.
-
Konferensbidrag (refereegranskat)abstract
- The goal of this work is to study the dynamics of floating platforms that are designed for marine energy generation. This work is done in collaboration with Tecnalia R&I, a company settled in the Basque Country which designs this kind of platforms. To our purpose we present a method for the simulation of two-phase flow with the presence of floating bodies. We consider the variable density incompressible Navier-Stokes equations and discretize them by the finite element method with a variational multiscale stabilization. A level-set type method is adopted to model the interphase between the two fluids. The mixing or smearing in the interphase is prevented with a compression technique. Turbulence is implicitly modeled by the numerical stabilization. The floating device simulation is done by a rigid body motion scheme where a deforming mesh approach is used. The mesh deforms elastically following the movement of the body. Simulation of a decay test on a cube is performed and the results are presented in this paper. All the simulations are done with the open source finite elements parallel software FEniCS-HPC.
|
|
| 7. |
- Nguyen, Van Dang, 1985-, et al.
(författare)
-
A fluid-structure interaction model with weak slip velocity boundary conditions on conforming internal interfaces
- 2018
-
Konferensbidrag (populärvet., debatt m.m.)abstract
- We develop a PUFEM–Partition of Unity Finite Element Method to impose slip velocity boundary conditions on conforming internal interfaces for a fluid-structure interaction model. The method facilitates a straightforward implementation on the FEniCS/FEniCS-HPC platform. We show two results for 2D model problems with the implementation on FEniCS: (1) optimal convergence rate is shown for a stationary Navier-Stokes flow problem, and (2) the slip velocity conditions give qualitatively the correct result for the Euler flow.
|
|
| 8. |
- Nguyen, Van Dang, 1985-, et al.
(författare)
-
A partition of unity finite element method for computational diffusion MRI
- 2018
-
Ingår i: Journal of Computational Physics. - : Elsevier. - 0021-9991 .- 1090-2716. ; 375, s. 271-290
-
Tidskriftsartikel (refereegranskat)abstract
- The Bloch–Torrey equation describes the evolution of the spin (usually water proton) magnetization under the influence of applied magnetic field gradients and is commonly used in numerical simulations for diffusion MRI and NMR. Microscopic heterogeneity inside the imaging voxel is modeled by interfaces inside the simulation domain, where a discontinuity in the magnetization across the interfaces is produced via a permeability coefficient on the interfaces. To avoid having to simulate on a computational domain that is the size of an entire imaging voxel, which is often much larger than the scale of the microscopic heterogeneity as well as the mean spin diffusion displacement, smaller representative volumes of the imaging medium can be used as the simulation domain. In this case, the exterior boundaries of a representative volume either must be far away from the initial positions of the spins or suitable boundary conditions must be found to allow the movement of spins across these exterior boundaries.Many approaches have been taken to solve the Bloch–Torrey equation but an efficient high-performance computing framework is still missing. In this paper, we present formulations of the interface as well as the exterior boundary conditions that are computationally efficient and suitable for arbitrary order finite elements and parallelization. In particular, the formulations are based on the partition of unity concept which allows for a discontinuous solution across interfaces conforming with the mesh with weak enforcement of real (in the case of interior interfaces) and artificial (in the case of exterior boundaries) permeability conditions as well as an operator splitting for the exterior boundary conditions. The method is straightforward to implement and it is available in FEniCS for moderate-scale simulations and in FEniCS-HPC for large-scale simulations. The order of accuracy of the resulting method is validated in numerical tests and a good scalability is shown for the parallel implementation. We show that the simulated dMRI signals offer good approximations to reference signals in cases where the latter are available and we performed simulations for a realistic model of a neuron to show that the method can be used for complex geometries.
|
|
| 9. |
- Nguyen, Van Dang, et al.
(författare)
-
A partition of unity finite element method for computational diffusion MRI
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The Bloch-Torrey equation describes the evolution of the spin (usually water proton) magnetization under the influence of applied magnetic field gradients and is commonly used in numerical simulations for diffusion MRI and NMR. Microscopic heterogeneity inside the imaging voxel is modeled by interfaces inside the simulation domain, where a discontinuity in the magnetization across the interfaces is produced via a permeability coefficient on the interfaces. To avoid having to simulate on a computational domain that is the size of an entire imaging voxel, which is often much larger than the scale of the microscopic heterogeneity as well as the mean spin diffusion displacement, smaller representative volumes of the imaging medium can be used as the simulation domain. In this case, the exterior boundaries of a representative volume either must be far away from the initial positions of the spins or suitable boundary conditions must be found to allow the movement of spins across these exterior boundaries. Many efforts have been made to solve the equation but there is still missing an efficient high performance computing framework. In this work, we present formulations of the interface as well as the exterior boundary conditions that are computationally efficient and suitable for arbitrary order finite elements and parallelization. In particular, the formulations use extended finite elements with weak enforcement of real (in the case of interior interfaces) and artificial (in the case of exterior boundaries) permeability conditions as well as operator splitting for the exterior boundary conditions. The method appears to be straightforward to implement and it is implemented in the FEniCS for moderate-scale simulations and in the FEniCS-HPC for the large-scale simulations. The accuracy of the resulting method is validated numerically and a good scalability is shown for the parallel implementation. We show that the simulated dMRI signals offer good approximations to reference signals in cases where the latter are available. Finally, we do simulations on a complex neuron to study how the signals decay under the effect of the permeable membrane and to show that the method can be used to simulate for complex geometries that we have not done before.Highlights:The discontinuity in the magnetization across the interior interfaces of the medium is weakly imposed, allowing generalization to arbitrary order finite elements.Spin exchange across the external boundaries is implemented by weakly imposing an artificial, high permeability, condition, allowing generalization to non-matching meshes.Thus, optimal convergence with respect to the space discretization is achieved.The second-order Crank-Nicolson method is chosen for the time discretization to reduce oscillations at high gradient strengths and allows for larger time-step sizes.The method is of a high level of simplicity and suitable for parallelization.An efficient open-source code is implemented in the FEniCS and FEniCS-HPC platforms.
|
|
| 10. |
- Nguyen, Van Dang, 1985-, et al.
(författare)
-
Direct Finite Element Simulation of the Turbulent Flow Past a Vertical Axis Wind Turbine
- 2019
-
Ingår i: Renewable energy. - : Elsevier. - 0960-1481 .- 1879-0682. ; 135, s. 238-247
-
Tidskriftsartikel (refereegranskat)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.
|
|
