Events

I³MS - Betancourt Seminar

Location: AICES Seminar Room 115, 1st floor, Schinkelstr. 2, 52062 Aachen

Prof. Michael Betancourt, Ph.D. - A Conceptual Introduction to Scalable Bayesian Inference with Hamiltonian Monte Carlo

Chief Scientist at Symplectomorphic, LLC, New York, USA

Abstract

 

TBA

I³MS - van Brummelen Seminar

Location: AICES Seminar Room 115, 1st floor, Schinkelstr. 2, 52062 Aachen

Prof. Dr. Harald van Brummelen - Adaptive Isogeometric Analysis of Elasto-Capillary Fluid-Solid Interaction

Department of Mechanical Engineering, Eindhoven University of Technology, The Netherlands

Abstract

Binary fluids are fluids that comprise two constituents, viz. two phases of the same fluid (gas or liquid) or two distinct species (e.g. water and air). A distinctive feature of binary-fluids is the presence of a fluid–fluid interface that separates the two components. This interface generally carries surface energy and accordingly it introduces capillary forces. The interaction of a binary-fluid with a deformable solid engenders a variety of intricate physical phenomena, collectively referred to as elasto-capillarity. The solid–fluid interface also carries surface energy and, generally, this surface energy is distinct for the two components of the binary fluid. Consequently, the binary-fluid–solid problem will exhibit wetting behavior [1,2]. Moreover, the fluid-solid surface tension plays an essential role in the elastic deformations in the vicinity of the contact line [3,4]. Elasto-capillarity underlies miscellaneous complex physical phenomena such as durotaxis [5], i.e. seemingly spontaneous migration of liquid droplets on solid substrates with an elasticity gradient; capillary origami [6], i.e. large-scale solid deformations by capillary forces. Binary-fluid–solid interaction is moreover of fundamental technological relevance in a wide variety of high-tech industrial applications, such as inkjet printing and additive manufacturing. As opposed to the significant progress that has been made in the past two decades in modeling and simulation of conventional FSI problems, modeling and simulation of elasto-capillary FSI is still in its infancy, and many aspects are still open, even including fundamental modeling aspects such as the Shuttleworth effect [7].
 
In this presentation, I will present a computational model for elasto-capillary fluid-solid interaction based on a diffuse-interface model for the binary fluid and a hyperelastic-material model for the solid. The diffuse-interface binary-fluid model is described by the incompressible Navier–Stokes–Cahn–Hilliard equations [8] with preferential-wetting boundary conditions at the fluid-solid interface. To resolve the fluid-fluid interface, which is generally several orders of magnitude smaller than  other characteristic length scales in the problem,  as well as the localized displacements in the solid in the vicinity of the contact line, we apply adaptive hierarchical spline approximations. A monolithic solution scheme is applied to enable robust solution of the coupled FSI problem.
 
[1 ] P.-G. de Gennes, F. Brochard-Wyart, and D. Queré. Capillarity and Wetting Phe- nomena: Drops, Bubbles, Pearls, Waves. Springer, 2004.
 
[2] P.-G. de Gennes. Wetting: statics and dynamics. Rev. Mod. Phys., 57:827–863, 1985. 
 
[3] E.H. van Brummelen, H. Shokrpour Roudbari, and G.J. van Zwieten. Elasto- capillarity simulations based on the Navier-Stokes-Cahn-Hilliard equations. 
In Advances in Computational Fluid-Structure Interaction and Flow Simulation, Modeling and Simulation in Science, Engineering and Technology, pages 451–462. Birkhauser, 2016.
 
[4] E.H. van Brummelen, M. Shokrpour Roudbari, G. Simsek, and K.G. van der Zee. Fluid Structure Interaction, volume 20 of Radon Series on Computational and Applied Mathematics, 
chapter Binary-fluid–solid interaction based on the Navier–Stokes– Cahn–Hilliard Equations. De Gruyter, 2017. 
 
[5] R.W. Style et al. Patterning droplets with durotaxis. PNAS, 110(31):12541–12544, 2013. 
 
[6] C. Py, P. Reverdy, L. Doppler, J. Bico, B. Roman, and C.N. Baroud. Capillary origami: Spontaneous wrapping of a droplet with an elastic sheet. Phys. Rev. Lett., 98:156103, Apr 2007. 
 
[7] J.H. Snoeijer, E. Rolley, and B. Andreotti, The paradox of contact angle selection on stretched soft solids, arXiv:1803.04428 [cond-mat.soft] (2018).
 
[8] M. Shokrpour Roudbari, G. Simsek, E.H. van Brummelen, and K.G. van der Zee, Diffuse-interface two-phase flow models with different densities: a new quasi-incompressible form 
and a linear energy-stable method, Math. Mod. Meth. Appl. Sci. (online) (2018).

 

EU Regional School - Fonnesbeck Seminar

Location: AICES Seminar Room 115, 1st floor, Schinkelstr. 2, 52062 Aachen

Prof. Christopher Fonnesbeck, Ph.D. - Probabilistic Programming with Python

Department of Biostatistics, Vanderbilt University Medical Center, USA

Abstract

This intermediate-level course will provide students with hands-on experience applying practical Bayesian statistical modeling methods on real data. PyMC3 is a high-level Python library for building statistical models using probabilistic programming, and fitting them using modern Bayesian computational methods. I will provide an introduction to Bayesian inference and prediction, followed by a tutorial on probabilistic programming with PyMC3, including the use of Markov chain Monte Carlo (MCMC) and Variational Inference (VI), using real-world datasets. The last part of the course will focus on modeling strategies and how to avoid various pitfalls when applying Bayesian statistics to your own work. The course will assume familiarity with Python and with basic statistics (e.g. probability), but does not require previous experience with Bayesian methods or probabilistic programming.

I³MS - Saxena Seminar

Location: AICES Seminar Room 115, 1st floor, Schinkelstr. 2, 52062 Aachen

Prof. Dr. Anupam Saxena - Contact in Topology Optimization: Challenges and Solution Strategies

Department of Mechanical Engineering, Indian Institute of Technology, Kanpur

Abstract

Topology Optimization of large deformation planar continua will be
formulated. Two parameterization schemes, namely, frame- and continuum-
based, will be exemplified using small deformation theory for familiarity
with existing, gradient- and function- based, topology optimization
schemes. Within continuum parameterization, rectangular and hexagonal
tessellations will be discussed. The first set of challenges pertaining to
connectivity singularities, namely, checkerboards and point flexures will
be highlighted, and remedies will be mentioned. Constituents of planar
continua undergoing large deformation have a tendency to come in contact.
This aspect can either be avoided, or used to advantage
to design continua that can deliver the desired, intricate deformation
characteristics. Many challenges, when adapting topology optimization to
incorporate contact interactions, will be highlighted and solution
strategies will be discussed. These challenges pertain to mesh handling,
generation/evaluation of binary continua, non-convergence in finite
element analysis, generation of rigid contact surfaces in vicinity of
largely deforming constituents, and other factors. It will be argued that
zero-order searches, albeit computationally costly, seem more viable in
addressing these problems. The talk will culminate with examples on large
deformation monolithic gripper-manipulator, and path generating continua
that can exhibit one or more desired kinks in the path by effectively
employing contact interactions. Some open problems will also be
highlighted.

EU Regional School - Püschel Seminar

Location: AICES Seminar Room 115, 1st floor, Schinkelstr. 2, 52062 Aachen

Prof. Dr. Markus Püschel - Optimal Performance Numerical Code: Challenges and Solutions

Department of Computer Science, ETH Zürich, Switzerland

Abstract

The complexity of modern computing platforms has made it extremely difficult to write numerical code that achieves the best possible performance. Straightforward implementations in C based on algorithms that minimize the operations count often fall short in performance by at least one order of magnitude. The reason are the inherent limitations of compilers to optimize for deep memory hierarchies, vector instruction sets, and multiple cores. The goal of this short course is to explain the problem and techniques for performance optimization using matrix multiplication and the fast Fourier transform as examples. Finally, I will discuss program generators as a way to reduce the implementation and optimization effort.

Click here for his slides.