Monte and Usha Ahuja Distinguished Lecture Series - Speaker: Jayathi Y. Murthy, UCLA Samueli School of Engineering

There has been great interest recently in predicting thermal transport at the nanoscale. Sensitivities or derivatives are used in thermal transport simulations to describe important crystal properties. For example, the Gruneisen parameter is the derivative of phonon frequency with respect to the volume of the crystal. The phonon group velocity is the derivative of the frequency with respect to the wave vector.  A force constant is a derivative of the total potential energy of the system with respect to the displacement of a given atom. Accurate methods to compute these quantities are needed without the approximations inherent in finite difference methods. Derivatives are also needed for gradient-based optimization methods, for example, such as those used in topology optimization. Furthermore, engineers can benefit a great deal from understanding the sensitivity of inputs to outputs.

In this talk, we present the automatic code differentiation technique to perform unintrusive sensitivity analysis and derivative computation.  This method exploits the concepts of templating and operator overloading in C++ and other similar programming languages to unintrusively convert existing codes into those yielding derivatives of arbitrary order. The idea is demonstrated through the computation of thermal properties in nanoscale heat transfer. Phonon properties such as second and third order force constants, the Gruneisen parameter, group velocities, and the temperature sensitivity of specific heat for graphene nanoribbons are computed. Derivative values so computed are compared with those obtained using finite difference approaches or with analytical values. The method is found to yield derivative values to machine accuracy, with none of the round-off issues associated with finite difference approaches. Use of automatic code differentiation is also demonstrated in topology optimization for fluid and heat transfer applications. Furthermore, templating and operator overloading approaches are demonstrated for polynomial chaos based uncertainty quantification in fluid flow applications.

About the speaker:

Jayathi Murthy is the Ronald and Valerie Sugar Dean of the Henry Samueli School of Engineering and Applied Science at the University of California, Los Angeles. Previously she held the Ernest Cockrell Jr. Chair and served as Department Chair of Mechanical Engineering at The University of Texas at Austin. She also served as Director of the $21M NNSA PRISM Center at Purdue for Prediction of Reliability, Integrity and Survivability of Microsystems during 2008-2014. She received her Ph.D degree from the University of Minnesota in the area of numerical heat transfer and has worked in both academia and in industry. She was an early employee of Fluent Inc., a leading vendor of CFD software, where she developed the widely-used unstructured solution-adaptive finite volume methods that underlie their flagship software Fluent, and the electronics cooling software package ICEPAK. More recently, her research has addressed sub-micron thermal transport, multiscale multiphysics simulations of MEMS and NEMS and uncertainty quantification in these systems.  She is the recipient of the IBM Faculty Partnership award 2003-2005, numerous best paper awards, the 2009 ASME EPPD Woman Engineer of the Year Award and the 2012 ASME EPPD Clock Award. In 2012, she was named a distinguished alumna of IIT Kanpur, India. In 2016, she was awarded the ASME Heat Transfer Memorial Award for her contributions to the development of advanced computational techniques. Prof. Murthy serves on the editorial boards of Numerical Heat Transfer and International Journal of Thermal Sciences and is an editor of the 2nd edition of the Handbook of Numerical Heat Transfer. She has served on numerous national committees and panels on electronics thermal management and CFD, and is the author of over 300 technical publications.

The Monte and Usha Ahuja Distinguished Lecture Series aims to attract highly accomplished and illustrious individuals, as well as those on their way to national and international renown. In addition to showcasing the work of current experts in the engineering field, this lecture series will inspire Ohio State students to achieve excellence and eminence in their own future careers in government, industry and academia. As honored and highly accomplished graduates of Ohio State, the Ahujas consider their charitable and philanthropic support of the university as an investment in the next generation of science, technology, engineering and mathematics trailblazers.