Acoustic/Electromagnetic scattering

Acoustic/Electromagnetic scattering
WMtot

Electromagnetic field generated inside human brain

The purpose of this project is to reduce the errors associated with numerical solution of wave propagation problems and their computational costs. In high-frequency regimes, the solution of conventional FEM sufferers from pollution error which is due to dispersion and can be visualized as a phase shift of the numerical solution. To maintain a desired level of pollution error in conventional FEM, it is necessary to increase discretization density faster than the wave number which rapidly increase the computational cost. On the other hand, the geometrical accuracy of the scattering surfaces play an important role in accuracy of the solution. The possibility of representing man-made objects exactly in IGA even with very coarse meshes and the convenience of its refinement makes it a desirable platform to perform scattering analysis. The convergence graphs obtained for scattering problems performed in IGA platform approves the anticipated properties and makes it possible to increase the solution accuracy even for very high-frequency analysis. [http://mechanical907.rssing.com/browser.php?indx=25030677&last=1&item=1], [http://hdl.handle.net/10993/28982].

Sphere_real

Exterior acoustic scattering

p10_IGA

Exterior acoustic scattering problem – The evolution of L2 error with discretization density in IGA. High-order IGA yields low error with very coarse meshes.

Research and Innovation in Luxembourg Number 11 – Surfing the Digital Waves

http://www.luxinnovation.lu/Publications/FOCUS-Research-and-Innovation-in-Luxembourg/FOCUS-Research-and-Innovation-in-Luxembourg-N°11-2016-Surfing-the-Digital-Waves

Link

Automatised selection of load paths to construct reduced-order models in computational damage micromechanics: from dissipation-driven random selection to Bayesian optimizatio

http://hdl.handle.net/10993/27112

Link

 

Jian Deng completes his China Scholarship Council in Cardiff. 

It was great to have you in the Legato team and your work on composite delamination has been a pleasure to discuss with you. Excellent work! Have a safe trip back!

Stéphane Bordas 

Accelerating Monte Carlo estimation with derivatives of high-level finite element models. CMAME paper submitted with Jack and Paul. 

http://hdl.handle.net/10993/28618 Link

In this paper we demonstrate the ability of a derivative-driven Monte Carlo estimator to accelerate the propagation of uncertainty through two high-level non-linear finite element models. The use of derivative information amounts to a correction to the standard Monte Carlo estimation procedure that reduces the variance under certain conditions. We express the finite element models in variational form using the high-level Unified Form Language (UFL). We derive the tangent linear model automatically from this high-level description and use it to efficiently calculate the required derivative information. To study the effectiveness of the derivative-driven method we consider two stochastic PDEs; a one- dimensional Burgers equation with stochastic viscosity and a three-dimensional geometrically non-linear Mooney-Rivlin hyperelastic equation with stochastic density and volumetric material parameter. Our results show that for these problems the first-order derivative-driven Monte Carlo method is around one order of magnitude faster than the standard Monte Carlo method and at the cost of only one extra tangent linear solution per estimation problem. We find similar trends when comparing with a modern non-intrusive multi-level polynomial chaos expansion method. We parallelise the task of the repeated forward model evaluations across a cluster using the ipyparallel and mpi4py software tools. A complete working example showing the solution of the stochastic viscous Burgers equation is included as supplementary material.

Professor Nenad Bićanić passed away

My long-standing colleague Chris Pearce (University of Glasgow) just passed on the sad news of the passing of Professor Nenad Bićanić.

I will remember Nenad as a passionate, gentle and dedicated mentor and I am deeply saddened by his passing. I am sure he inspired many young engineers in the many years he taught the subject and as many researchers to follow the path of knowledge.

I would like to wish all the best to his family in these difficult times.

Stéphane Bordas

Modelling interfacial cracking with non-matching cohesive interface elements Paper out 

http://link.springer.com/article/10.1007/s00466-016-1314-y?wt_mc=Internal.Event.1.SEM.ArticleAuthorAssignedToIssue

Title 

Modelling interfacial cracking with non-matching cohesive interface elements  

Journal 

Computational Mechanics, 58(5), 731-746

DOI 

10.1007/s00466-016-1314-y

Real-time error estimation and adaptivity

https://arxiv.org/submit/1687902
Title: Real-time error controlled adaptive mesh refinement: Application to
  needle insertion simulation

Authors: Huu Phuoc Bui (1 and 2), Satyendra Tomar (2), R\’emi Bessard-Duparc

  (3), Hadrien Courtecuisse (1), St\’ephane Cotin (3), St\’ephane Bordas (2 and

  4) ((1) University of Strasbourg, CNRS, ICube, Strasbourg, France, (2)

  University of Luxembourg, Luxembourg, (3) Inria Nancy Grand Est,

  Villers-les-Nancy, France, (4) Cardiff University, Wales, UK)

Categories: cs.NA

Comments: 20 pages, 15 figures

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

\\

  This paper presents the first real-time discretization-error-driven adaptive

finite element approach for corotational elasticity problems involving strain

localization. We propose a hexahedron-based finite element method, combined

with a posteriori error estimation driven local h-refinement, for simulating

soft tissue deformation. This enables to control the local error and global

error level in the mechanical fields (e.g. displacement or gradient) during the

simulation. The local error level is used to refine the mesh only where it is

needed, while maintaining a coarser mesh elsewhere. We investigate the

convergence of the algorithm on academic examples, and demonstrate its

practical usability on a percutaneous procedure involving needle insertion in a

liver. For the latter case, we compare the force displacement curves obtained

from the proposed adaptive algorithm with that obtained from a uniform

refinement approach.

\\

Real-time error estimation and adaptivity

https://arxiv.org/submit/1687902
Title: Real-time error controlled adaptive mesh refinement: Application to
  needle insertion simulation

Authors: Huu Phuoc Bui (1 and 2), Satyendra Tomar (2), R\’emi Bessard-Duparc

  (3), Hadrien Courtecuisse (1), St\’ephane Cotin (3), St\’ephane Bordas (2 and

  4) ((1) University of Strasbourg, CNRS, ICube, Strasbourg, France, (2)

  University of Luxembourg, Luxembourg, (3) Inria Nancy Grand Est,

  Villers-les-Nancy, France, (4) Cardiff University, Wales, UK)

Categories: cs.NA

Comments: 20 pages, 15 figures

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

\\

  This paper presents the first real-time discretization-error-driven adaptive

finite element approach for corotational elasticity problems involving strain

localization. We propose a hexahedron-based finite element method, combined

with a posteriori error estimation driven local h-refinement, for simulating

soft tissue deformation. This enables to control the local error and global

error level in the mechanical fields (e.g. displacement or gradient) during the

simulation. The local error level is used to refine the mesh only where it is

needed, while maintaining a coarser mesh elsewhere. We investigate the

convergence of the algorithm on academic examples, and demonstrate its

practical usability on a percutaneous procedure involving needle insertion in a

liver. For the latter case, we compare the force displacement curves obtained

from the proposed adaptive algorithm with that obtained from a uniform

refinement approach.

\\