| 1. |
- Compere, Gaetan, et al.
(författare)
-
A mesh adaptation framework for dealing with large deforming meshes
- 2010
-
Ingår i: International Journal for Numerical Methods in Engineering. - : Wiley. - 0029-5981 .- 1097-0207. ; 82:7, s. 843-867
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper. we identify and propose solutions for several issues encountered when designing a mesh adaptation package, such as mesh-to-mesh projections and mesh database design, and we describe an algorithm to integrate a mesh adaptation procedure in a physics solver. The open-source MAdLib package is presented as an example of such a mesh adaptation library. A new technique combining global node repositioning and mesh optimization in order to perform arbitrarily large deformations is also proposed. We then present several test cases to evaluate the performances of the proposed techniques and to show their applicability to fluid-structure interaction problems with arbitrarily large deformations. Copyright (C) 2009 John Wiley & Sons, Ltd.
|
|
| 2. |
- 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.
|
|
| 3. |
- Degirmenci, Niyazi Cem, 1982-
(författare)
-
Adaptive Finite Element Methods for Fluid Structure Interaction Problems with Applications to Human Phonation
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work presents a unified framework for numerical solution of Fluid Structure Interaction (FSI) and acoustics problems with focus on human phonation. The Finite Element Method is employed for numerical investigation of partial differential equations that model conservation of momentum and mass. Since the resulting system of equations is very large, an efficient open source high performance implementation is constructed and provided. In order to gain accuracy for the numerical solutions, an adaptive mesh refinement strategy is employed which reduces the computational cost in comparison to a uniform refinement. Adaptive refinement of the mesh relies on computable error indicators which appear as a combination of a computable residual and the solution of a so-called dual problem acting as weights on computed residuals. The first main achievement of this thesis is to apply this strategy to numerical simulations of a benchmark problem for FSI. This FSI model is further extended for contact handling and applied to a realistic vocal folds geometry where the glottic wave formation was captured in the numerical simulations. This is the second achievement in the presented work. The FSI model is further coupled to an acoustics model through an acoustic analogy, for vocal folds with flow induced oscillations for a domain constructed to create the vowel /i/. The comparisons of the obtained pressure signal at specified points with respect to results from literature for the same vowel is reported, which is the final main result presented.
|
|
| 4. |
- Hoffman, Johan, et al.
(författare)
-
A General Galerkin Finite Element Method for the Compressible Euler Equations
- 2008
-
Ingår i: SIAM Journal on Scientific Computing. - 1064-8275 .- 1095-7197.
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we present a General Galerkin (G2) method for the compressible Euler equations, including turbulent ow. The G2 method presented in this paper is a nite element method with linear approximation in space and time, with componentwise stabilization in the form of streamline diusion and shock-capturing modi cations. The method conserves mass, momentum and energy, and we prove an a posteriori version of the 2nd Law of thermodynamics for the method. We illustrate the method for a laminar shock tube problem for which there exists an exact analytical solution, and also for a turbulent flow problem
|
|
| 5. |
- 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.
|
|
| 6. |
- Hoffman, Johan, 1974-, et al.
(författare)
-
Computability and Adaptivity in CFD
- 2018
-
Ingår i: Encyclopedia of Computational Mechanics. - : John Wiley & Sons.
-
Bokkapitel (refereegranskat)
|
|
| 7. |
- 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.
|
|
| 8. |
- Hoffman, Johan, et al.
(författare)
-
FEniCS-HPC : Automated predictive high-performance finite element computing with applications in aerodynamics
- 2016
-
Ingår i: Proceedings of the 11th International Conference on Parallel Processing and Applied Mathematics, PPAM 2015. - Cham : Springer-Verlag New York. ; , s. 356-365
-
Konferensbidrag (refereegranskat)abstract
- Developing multiphysics nite element methods (FEM) andscalable HPC implementations can be very challenging in terms of soft-ware complexity and performance, even more so with the addition ofgoal-oriented adaptive mesh renement. To manage the complexity we inthis work presentgeneraladaptive stabilized methods withautomatedimplementation in the FEniCS-HPCautomatedopen source softwareframework. This allows taking the weak form of a partial dierentialequation (PDE) as input in near-mathematical notation and automati-cally generating the low-level implementation source code and auxiliaryequations and quantities necessary for the adaptivity. We demonstratenew optimal strong scaling results for the whole adaptive frameworkapplied to turbulent ow on massively parallel architectures down to25000 vertices per core with ca. 5000 cores with the MPI-based PETScbackend and for assembly down to 500 vertices per core with ca. 20000cores with the PGAS-based JANPACK backend. As a demonstration ofthe high impact of the combination of the scalability together with theadaptive methodology allowing prediction of gross quantities in turbulent ow we present an application in aerodynamics of a full DLR-F11 aircraftin connection with the HiLift-PW2 benchmarking workshop with goodmatch to experiments.
|
|
| 9. |
- 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.
|
|
| 10. |
- Hoffman, Johan, et al.
(författare)
-
New Theory of Flight
- 2016
-
Ingår i: Journal of Mathematical Fluid Mechanics. - : Springer. - 1422-6928 .- 1422-6952. ; 18:2, s. 219-241
-
Tidskriftsartikel (refereegranskat)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
|
|
