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Upcoming Seminars

Seminars are held Tuesdays and Thursdays in POB 6.304 from 3:30-5:00 pm, unless otherwise noted. Speakers include scientists, researchers, visiting scholars, potential faculty, and ICES/UT Faculty or staff. Everyone is welcome to attend. Refreshments are served at 3:15 pm.

 

ICES Seminar
Tuesday, Sep 26, 2017 from 3:30PM to 5PM
POB 6.304

Multi-field dual and mixed variational principles using non-symmetric stress field in linear elastodynamics with application to shell problems'
by Balazs Toth

Faculty of Mechanical Engineering and Informatics, University of Miskolc, Hungary

Details

The classical displacement-based finite elements (FEs), when modeling the deformation of shells, may suffer from several numerical difficulties even within the framework of linear elasticity. Usually these problems appear when the value of the shell thickness is close to zero, that is when the shell becomes extremely thin. This phenomenon is referred to as the "numerical locking effect". One of the possibilities to avoid these difficulties is to apply a multi-field, dual-mixed variational formulation.

Toward this goal, new multi-field dual and mixed variational principles using (a priori) a non-symmetric stress field for dynamic problems of linearly elastic solids will be presented. The principles form a basis for new hp FE methods for axisymmetric shells with the geometry of shell mid-surfaces modeled with NURBS. The new theory will be illustrated with a number of representative numerical examples.

Bio
Dr. Balazs Toth is Associate Professor in the Institute of Applied Mechanics of the Faculty of Mechanical Engineering and Informatics at the University of Miskolc. He received Ph.D. from the same instutution in 2013. His research is in the area of continuum mechanics, shell theories and other dimensionally-reduced models, variational and energy methods in solid mechanics, as well as h- and p- version finite element methods and computational structural mechanics.

Hosted by Leszek Demkowicz





 

ICES Seminar
Wednesday, Sep 27, 2017 from 1:30PM to 2:30PM
POB 6.304

Uncertainty Quantification in Turbulence Modeling
by Robert D. Moser

Professor, Department of Mechanical Engineering, Institute for Computational Engineering and Sciences, University of Texas at Austin

Details

Many fluid flows of technological interest are turbulent, and in such flows the turbulence has an order-one effect on flow characteristics. Computational models of such flows are commonly used to make predictions in support of design and operations decisions, so the effects of turbulence must be modeled. The most common turbulence modeling approach in applications is Reynolds Averaged Navier-Stokes (RANS) modeling, but it is well known that RANS models are in error in many flow situations. How then can we make reliable predictions of turbulent flows with unreliable RANS models? As it happens, this is possible, provided the uncertainties due to the RANS model errors are accounted for.

In this talk, we discuss the challenge of computational predictions and uncertainties in RANS models. As an examples, we discuss representations of uncertainty due to RANS model error in turbulent channel flow.

Bio
Robert D. Moser holds the W. A. "Tex" Moncrief Jr. Chair in Computational Engineering and Sciences and is Professor of Mechanical Engineering in thermal fluid systems. He serves as the Director of the Center for Predictive Engineering and Computational Sciences (PECOS) and Deputy director of the Institute for Computational Engineering and Sciences (ICES). Moser received his PhD in mechanical engineering from Stanford University. Before coming to the University of Texas, he was a research scientist at the NASA-Ames Research Center and then a Professor of Theoretical and Applied Mechanics at the University of Illinois. Moser conducts research on the modeling and numerical simulation of turbulence and other complex fluid flow phenomena. He also uses direct numerical simulation to investigate and model turbulent flows, particularly the development and evaluation of large eddy simulation models. Moser has also been working to develop new approaches for the validation of and quantification of uncertainty in computational models and to assess their reliability. He has pursued applications to such diverse systems as reentry vehicles, solid propellant rockets, micro-air vehicles, turbulent combustion, tokamak fusion and energy harvesting. He is a Fellow of the American Physical Society, and was awarded the NASA Medal for Exceptional Scientific Achievement.

Hosted by J. Tinsley Oden





 

ICES Seminar-Babuska Forum Series
Friday, Sep 29, 2017 from 10AM to 11AM
POB 6.304

A Tale of Two Models – Two Exemplary Numerical Models in Soft Tissue Biomechanics
by Manuel Rausch

Department of Aerospace Engineering & Engineering Mechanics, Biomedical Engineering (courtesy)

Details

Biological soft tissues are pervasive in our bodies. Ligaments, tendons, skin, our vascular tissue, and the heart fall within this group of materials. These tissues are characterized by anisotropy, heterogeneity, large deformation mechanics and exhibit other time-dependent phenomena such as active contraction as well as growth and remodeling. Predicting their behavior on the short time scale (acute) and the long time scale (chronic) is as critical as it is difficult. Here I’ll introduce two separate numerical studies that I recently conducted on soft tissue biomechanics that make use of Smoothed Particle Hydrodynamics and the Finite Element Method. The first study is on the damage and failure behavior of soft tissue and makes use of an unorthodox approach employing a mesh-free method originally developed for astrophysical problems. The second study introduces an attempt to capture the evolving constitution and constitutive behavior of thrombus via a multi-physical Finite Element Model. My hope is to provide the audience with an overview over my work and spark interest in the world of computational soft tissue biomechanics.

Bio
Originally from Germany, Dr. Rausch earned his PhD from Stanford University in 2013 before taking on the role of Director of R&D at a small medical device company. After a two year stint in industry, Dr. Rausch returned to academia as a post-doctoral fellow at Yale University. As of 2017, Dr. Rausch is an assistant professor at University of Texas, Austin's Department of Aerospace Engineering & Engineering Mechanics.

Dr. Rausch's research interests are focused on soft tissue biomechanics. He uses experimental as well as computational tools to characterize and understand the mechanical behavior of biological soft tissues such as myocardium, vascular soft tissue, heart valve tissue, and skin to improve diagnostic and therapeutic methods, and medical device design.

Hosted by Federico Fuentes and Sriram Nagaraj





 

ICES Seminar
Tuesday, Oct 10, 2017 from 3:30PM to 5PM
POB 6.304

Guaranteed-Accuracy Fast Algorithms for the Evaluation of Layer Potentials using 'Quadrature by Expansion'
by Andreas Klöckner

Assistant Professor, Computer Science Department, University of Illinois at Urbana-Champaign

Details

Quadrature by Expansion, or 'QBX', is a systematic, high-order approach to singular quadrature that applies to layer potential integrals with general kernels on curves and surfaces. The efficient and accurate evaluation of layer potentials, in turn, is a key building block in the construction of solvers for elliptic PDEs based on integral equation methods.

I will present a new fast algorithm incorporating QBX that evaluates layer potentials on and near surfaces in two and three dimensions with user-specified accuracy, along with supporting theoretical and empirical results on complexity and accuracy. A series of examples on unstructured geometry across a variety of applications in two and three dimensions demonstrates the applicability of the method.

Bio
Dr. Klockner is an assistant professor in the scientific computing group within the Computer Science Department at the University of Illinois at Urbana-Champaign. Prior to being at UIUC, he was at the Courant Institute of Mathematical Sciences at NYU working with Leslie Greengard on various problems in computational electromagnetics and integral equation methods for solving PDEs. Earlier still, he worked on his PhD at the Division of Applied Mathematics at Brown University with Jan Hesthaven on a variety of issues involving linear and nonlinear hyperbolic PDEs and discontinuous Galerkin finite element method. Dr. Klockner studies high-order numerical methods for Partial Differential Equations, in particular for elliptic and hyperbolic problems, as well as parallel computing and the software engineering needed to build useful, robust simulation codes.

Hosted by George Biros





 

ICES Seminar-Molecular Biophysics Series
Monday, Oct 23, 2017 from 2PM to 3PM
POB 6.304

Proton Transport in Biomolecular Systems: A Remarkably Complex and Collective Phenomenon
by Gregory A. Voth

The University of Chicago

Details

The hydrated excess proton (aka “hydronium cation”) is critical in many areas of chemistry, biology, and materials science. Despite playing a central role in fundamental chemical (e.g., acid-base) and biological (e.g., bioenergetics) processes, the nature of the excess proton remains mysterious, surprising, and sometimes misunderstood. In this presentation, our longstanding efforts to characterize proton solvation and transport in biomolecular systems will be described. These studies employ a novel, accurate, and computationally efficient multiscale reactive molecular dynamics method combined with large scale computer simulation. The methodology allows for the treatment of explicit (Grotthuss) proton shuttling and charge defect delocalization, which strongly influences proton solvation and transport in proteins such as transmembrane proton channels, pumps, and transporters/antiporters. The unique electrostatics related to the dynamic delocalization of the excess proton charge defect in water chains and amino acid residues will be elaborated, as well as the effects of these complex electrostatics on the proton transport and selectivity properties. The often opposing and asymptotic viewpoints related to electrostatics on one hand and Grotthuss proton shuttling on the other will be reconciled and unified into a single conceptual framework. The intrinsically coupled nature of the excess proton translocation and the water hydration can also be elaborated through these computer simulations. It is found that a prior existing “water wire”, e.g., one seen in an x-ray crystal structure, is not necessary for excess protons to transport through hydrophobic spaces in proteins via water mediated Grotthuss shuttling. The proton translocation process can sometimes create its own transient water wire as needed. Specific simulation results will be given for the M2 proton channel in influenza A, the proton pump cytochrome c oxidase (CcO), and the ClC Cl-/H+ antiporter. A comparison to experimental results will also be provided.

Hosted by Ron Elber





 

ICES Seminar
Thursday, Nov 2, 2017 from 3:30PM to 5PM
POB 6.304

Posterior error control in Bayesian Inverse Problems
by J Andrés Christen

Centro de Investigación en Matemáticas, Guanajuato, México

Details

In the Bayesian analysis of Inverse Problems most relevant cases the forward maps are defined in terms of a system of (O, P)DE's that involve numerical solvers. These then lead to a numerical/approximate posterior distribution. Recently several results have been published on the regularity conditions required on such numerical methods to ensure converge of the numerical to the theoretical posterior. However, more practical guidelines are needed.

I present some recent results that, by using Bayes Factors and in a finite dimensional setting, one can see that the numerical posterior tends to the theoretical posterior in the same order as the numerical solver used in the forward map. Moreover, when error estimates are available for the solver we can use a bound on this errors, proven to lead to basically error free posteriors. That is, given that we are observing noisy data, we may tolerate an amount (relative to the data noise) of numerical error in the solver, and end up with a basically error free posterior. In this talk I will show these results, present some examples in ODEs and PDEs and comment on the generalizations to the infinite dimensional setting.

Bio
Dr J Andres Christen has a BSc in mathematics from Universidad Nacional Autonoma de Mexico (1989, UNAM, Mexico city) and a PhD in mathematics from the University of Nottingham (1994, Nottingham, UK). His expertise is in Bayesian Statistics. Dr Christen has been working on the field for more than 25 years in applied as well as theoretical aspects of the discipline. His areas of application include ecology, paleoecolgy, environmental change, bioinformatics, among others. Moreover, recently at CIMAT he has helped to create a group on the study of inverse problems using Bayesian statistics (Bayesian UQ). In particular, Dr Christen and the group at CIMAT are working on the analysis of complex biological systems, epidemiology, sound wave scattering and other applications in physics, as well as some theoretical aspects involved in the practice of Bayesian UQ. Dr Christen holds a tenure position at CIMAT (part of the national network of research centers of CONACyT) since 2003 and is a Investigador Nacional, Sistema Nacional de Investigadores level III. He is a member of the International Society for Bayesian Analysis (ISBA), participated in the Scientific Committee of ISBA 2009{2012 and was the chair of the Local Organizing Committee,
2014 ISBA World Congress. (Personal home page www.cimat.mx/~jac/. See also uq.cimat.mx for more details on the UQ group at CIMAT.)

Hosted by Tan Bui-Thanh