Denys DUTYKH's Blog of an applied mathematician

Recent building physics preprints

Recently we submitted a couple of manuscripts, which report on our progress in the development of new numerical approaches for future building simulation’ tools.

The first preprint is basically the generalization of the Dufort-Frankel method applied earlier to scalar nonlinear models. This time we go to coupled nonlinear heat and moisture transfer. Moreover, we apply our algorithms to realistic configurations of two adjacent rooms together with air temperature inside. So, these results are described in this preprint together with the advantages of using explicit schemes to avoid synchronisation problems and large coupled nonlinear systems:

The second preprint is rather a continuation of our previous investigation on the optimal experimental design. This time we consider more general models including also some advection effects of moisture and we solve an inverse problem to estimate material properties. The experimental part of this work was brilliantly performed by Thomas Busser:

That’s all for the moment. More preprints are coming in the nearest future.

Applied and Computational Mathematics for Kazakhstan

From 20th to 25th of February 2017 I participated in a workshop organized by the Faculty of Mechanics and Mathematics of the Al-Farabi Kazakh National University. The goal of this workshop was mainly to discuss a new Bachelor degree Programme Applied and Computational Mathematics. The particularity of this Programme is that all courses are going to be taught in English. This educational programme is a part of the “Kazakhstan 2050” Strategy.

Among the participants (besides the Author of this post) we had the pleasure to count the following experts:

The conclusions and recommendations issued during this workshop are going to be published in workshop materials to make outcomes available for other Kazakh (and not only Kazakh) Universities.

KazNU Workshop

Fast and accurate computation of cnoidal waves

There are many points to mention and describe briefly today.

First of all, together with my collaborator Didier Clamond, we submitted a manuscript, which describes a new method for the computation of cnoidal waves in the full Euler equations with free surface:

These solutions can be used to validate and check the accuracy of various dynamic solvers for the full water wave problem. Moreover, the Matlab code is freely available at this URL:

This Matlab code computes irrotational 2D periodic steady surface pure gravity waves of arbitrary length in arbitrary depth. The formulation is based on the so-called Babenko equation and pseudo-spectral discretization in the conformal domain. The resulting equation is solved using Petviashvili iteration method.

In the continuation of our previous short publication on peaked solitary capillary-gravity waves, we submitted the full manuscript, which investigates this system of equations (capillary-gravity Serre model) in more details:

In the last manuscript we focus more on the dynamics and properties of smooth solitary wave solutions in various regimes with respect to the Bond number.

Finally, the following week I am going to spend at Al-Farabi Kazakh National University


Open source problems

I would like to share with you a pretty interesting talk given by William Stein, who is the creator and the main developer in the SageMath open source project. You can watch the video here:

The slides can be downloaded separately here.

Personally, I am not a user of SageMath, however, I find that the speaker rises the right questions about open source development and he points out difficulties that the speaker (and his colleagues) encountered on this way.

Just to give some idea about the content, I give here a couple of quotations from this talk:

  • “Every great open source math library is built on the ashes of someone’s academic career.”
  • “I can’t figure out how to create Sage in academia. The money isn’t there. The mathematical community doesn’t care enough. The only option left is for me to build a company.”

I can only endorse the speaker on these points. The software development effort is clearly undervalued in Academia. The general opinion is that if you are a really good mathematician you build a theory. And implicitly, if you are mediocre, you just code. This inadmissible attitude has to change.

Two interesting talks

I would like to share with you a couple of videos coming from the Michigan Engineering (University of Michigan) that I find particularly interesting and informative. The first one is given by Phil Roe, a well-known person in the finite volume community. He gives a critical account of the state-of-the-art in CFD, meshes and existing problems. This talk is to listen absolutely if you are interested in computations.

As a side remark, there is a pretty interesting report produced by NASA on a very close topic:

And as promised, the second video is devoted to common misconceptions in aerodynamics. It is delivered by Doug McLean who made his career at Boeing. To listen absolutely, if you want to understand truly, for example, why airplanes fly (but not only):

Have a pleasant listening!