| 1. |
- Hoffman, Johan, 1974-, et al.
(författare)
-
Computability and Adaptivity in CFD
- 2018
-
Ingår i: Encyclopedia of Computational Mechanics. - : John Wiley & Sons.
-
Bokkapitel (refereegranskat)
|
|
| 2. |
- Hoffman, Johan, et al.
(författare)
-
Computation of slat noise sources using adaptive FEM and lighthill's analogy
- 2013
-
Ingår i: 19th AIAA/CEAS Aeroacoustics Conference.
-
Konferensbidrag (refereegranskat)abstract
- This is a summary of preliminary results from simulations with the 30P30N high-lift device. We used the General Galerkin finite element method (G2), where no explicit subgrid model is used, and where the computational mesh is adaptively refined with respect to a posteriori error estimates for a quantity of interest. The mesh is fully unstructured and the solutions are time-resolved, which are key ingredients for solving challenging industrial applications in the field of aeroacoustics. We present preliminary results containing time-averaged quantities and snapshots of unsteady quantities, all reasonably agreeing with previous computational efforts. One important finding is that the use of adaptively generated meshes seems to be a more effcient way of computing aeroacoustic sources than by using "handmade" meshes.
|
|
| 3. |
- Hoffman, Johan, et al.
(författare)
-
FEniCS-HPC: Coupled Multiphysics in Computational Fluid Dynamics
- 2017
-
Ingår i: High-Performance Scientific Computing. - Cham : Springer. - 9783319538617 - 9783319538624 ; , s. 58-69
-
Konferensbidrag (refereegranskat)abstract
- We present a framework for coupled multiphysics in computational fluid dynamics, targeting massively parallel systems. Our strategy is based on general problem formulations in the form of partial differential equations and the finite element method, which open for automation, and optimization of a set of fundamental algorithms. We describe these algorithms, including finite element matrix assembly, adaptive mesh refinement and mesh smoothing; and multiphysics coupling methodologies such as unified continuum fluid-structure interaction (FSI), and aeroacoustics by coupled acoustic analogies. The framework is implemented as FEniCS open source software components, optimized for massively parallel computing. Examples of applications are presented, including simulation of aeroacoustic noise generated by an airplane landing gear, simulation of the blood flow in the human heart, and simulation of the human voice organ.
|
|
| 4. |
- Hoffman, Johan, et al.
(författare)
-
Towards a parameter-free method for high Reynolds number turbulent flow simulation based on adaptive finite element approximation
- 2015
-
Ingår i: Computer Methods in Applied Mechanics and Engineering. - : Elsevier. - 0045-7825 .- 1879-2138. ; 288, s. 60-74
-
Tidskriftsartikel (refereegranskat)abstract
- We present work towards a parameter-free method for turbulent flow simulation based on adaptive finite element approximation of the Navier-Stokes equations at high Reynolds numbers. In this model, viscous dissipation is assumed to be dominated by turbulent dissipation proportional to the residual of the equations, and skin friction at solid walls is assumed to be negligible compared to inertial effects. The result is a computational model without empirical data, where the only parameter is the local size of the finite element mesh. Under adaptive refinement of the mesh based on a posteriori error estimation, output quantities of interest in the form of functionals of the finite element solution converge to become independent of the mesh resolution, and thus the resulting method has no adjustable parameters. No ad hoc design of the mesh is needed, instead the mesh is optimised based on solution features, in particular no bounder layer mesh is needed. We connect the computational method to the mathematical concept of a dissipative weak solution of the Euler equations, as a model of high Reynolds number turbulent flow, and we highlight a number of benchmark problems for which the method is validated.
|
|
| 5. |
|
|
| 6. |
- 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.
|
|
| 7. |
- Hoffman, Johan, et al.
(författare)
-
Unicorn : Parallel adaptive finite element simulation of turbulent flow and fluid-structure interaction for deforming domains and complex geometry
- 2011
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We present a framework for adaptive finite element computation of turbulent flow and fluid-structure interaction, with focus on general algorithms that allow for complex geometry and deforming domains. We give basic models and finite element discretization methods, adaptive algorithms and strategies for e cient parallel implementation. To illustrate the capabilities of the computational framework, we show a number of application examples from aerodynamics, aero-acoustics, biomedicine and geophysics. The computational tools are free to download open source as Unicorn, and as a high performance branch of the finite element problem solving environment DOLFIN, both part of the FEniCS project
|
|
| 8. |
- Hoffman, Johan, et al.
(författare)
-
Unicorn : Parallel adaptive finite element simulation of turbulent flow and fluid-structure interaction for deforming domains and complex geometry
- 2013
-
Ingår i: Computers & Fluids. - : Elsevier BV. - 0045-7930 .- 1879-0747. ; 80:SI, s. 310-319
-
Tidskriftsartikel (refereegranskat)abstract
- We present a framework for adaptive finite element computation of turbulent flow and fluid structure interaction, with focus on general algorithms that allow for complex geometry and deforming domains. We give basic models and finite element discretization methods, adaptive algorithms and strategies for efficient parallel implementation. To illustrate the capabilities of the computational framework, we show a number of application examples from aerodynamics, aero-acoustics, biomedicine and geophysics. The computational tools are free to download open source as Unicorn, and as a high performance branch of the finite element problem solving environment DOLFIN, both part of the FEniCS project.
|
|
| 9. |
- Hoffman, Johan, et al.
(författare)
-
Adaptive modeling of turbulent flow with residual based turbulent kinetic energy dissipation
- 2011
-
Ingår i: Computer Methods in Applied Mechanics and Engineering. - : Elsevier BV. - 0045-7825 .- 1879-2138. ; 200:37-40, s. 2758-2767
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we first review our recent work on a new framework for adaptive turbulence simulation: we model turbulence by weak solutions to the Navier-Stokes equations that are wellposed with respect to mean value output in the form of functionals, and we use an adaptive finite element method to compute approximations with a posteriori error control based on the error in the functional output. We then derive a local energy estimate for a particular finite element method, which we connect to related work on dissipative weak Euler solutions with kinetic energy dissipation due to lack of local smoothness of the weak solutions. The ideas are illustrated by numerical results, where we observe a law of finite dissipation with respect to a decreasing mesh size.
|
|
| 10. |
- Jansson, Johan, et al.
(författare)
-
Adaptive simulation of unsteady flow past the submerged part of a floating wind turbine platform
- 2015
-
Ingår i: MARINE 2015 - Computational Methods in Marine Engineering VI. - : International Center for Numerical Methods in Engineering (CIMNE). - 9788494392863 ; , s. 35-46
-
Konferensbidrag (refereegranskat)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.
|
|
