Phononic Band Gaps up to relative 8!

This is my presentation of "Parametric Shape Optimization of Lattice Structures for Phononic Band Gaps" I gave at WCSMO-12 June 2017 in Braunschweig.



I'm quite proud of my phononic band gaps up to relative 8 and normalized 1.6.

I already presented the idea at ECCOMAS 2016 in Crete but there I made the embarrassing mistake of not enforcing square symmetry. However this is a non that uncommon mistake I meanwhile learned. Also my results are much better now.

WCSMO-11 is over

Some time passed since the last WCSMO-11 which was held in Sydney in June 2015. Still I know of no regular conference which comes any close to the World Congress of Structural and Multidisciplinary Optimization. The first OPTi in 2014 held in Kos came close but I see no hint that OPTi will be continued.

To my opinion people were (in the beginning) not happy to travel as far as Australia for a conference - something like the place with the furthest traveling distance for almost everyone I meet at conferences. 

And indeed I missed some participants from the US and Europe where on the other side many speakers came from China. The total number of participant also was a little below the previous numbers. 

I personally was disappointed by the average quality of the presentations. The two worst presentations I attended were from the US and Europe and I had the impression that both speakers did not even understand / could handle the SIMP method at the level of the 99 lines code. But there were more disappointing talks. To my personal opinion there are not too much groups worldwide driving topology optimization further with solid research while there are still plenty of challenging issues and problems, which can be solved by topology optimization. I cannot compare this against the previous WCSMO’s due to too many parallel sessions and I regularly missed some important talks. 

So maybe it would be a good idea to reduce the number of presentations and increase the average quality for the WCSMO but concurrently introduce regional conferences where PhD students have the opportunity to present their works and more importantly can come into contact to their regional experts, especially when they don’t stem from one of the established groups.

My highlight of the WCSMO was the high-performance optimization done at the DTU and I very much acknowledge that they contribute the PETSc base implementation with a parallel linear elasticity, MMA, density filter and PDE filter. More on that in a separate blog post. 

To summarize, the WCSMO-11 2015 in Sydney was again not only a good conference but almost the only conference (to my knowledge) for structural optimization. It was well organized; it was pretty cool to have a conference banquet at “Hogwarts” (the great hall of the University of Sydney). I personally also enjoyed Sydney and my short trip to the Blue Mountains.

What I really missed was that there was no possibility to just sit (and talk) when I did not want to attend a presentation. There was nothing like a lobby or close cafeteria. Especially when it was cold and raining and one could not go outside.

Interpretation of Material Design by an Streamline Approach

At OPT-I 2014, Kos, Greece, 4-6 June 2014, www.opti2014.org I gave the following talk:

Interpretation of local oriented microstructures by a streamline approach to obtain manufacturable structures from fwein

It demonstrates, how a material design result of oriented anisotropic structures (here crosses) can be interpreted.

We are still in the early phase, e.g. removing the blind line segments and going to 3D.

Topology optimization of saturated flows

In 2013 I spent most of my time for a topology optimization project for Procter & Gamble. Technically it we perform transient multi-material optimization for the nonlinear Richards equation which models unsaturated flow. The product behind is a Pampers diaper. The first phase of the project is successfully finished. It was quite hard and computationally and numerically the most complicated and expensive problem I had to deal with up to now.

During summer slump when there is nothing else to report in the local newspaper, we even had two interviews. Well, I doubt this is the career boost a colleague sees in it - and the article is really written for the broad public by non-technicals journalists.

Sorry, all in German.

14. August 2013, Nuerberger Zeitung
Das High-Tech-Produkt für den trockenen Babypopo

15. August 2013, Nordbayrische Nachrichten
Gutes für den Baby-Po: Erlanger Forscher suchen nach der Super-Windel

Here the announcement of the Cluster of Excellence Advanced Materials
http://blogs.fau.de/news/2013/07/30/gutes-fur-den-baby-popo/

Talk on Local Optimal Polarization

I'm just back from the piezo-workshop 2013, correctly, the 9th Int. Workshop on Direct and Inverse Problems in Piezoelectricity in Weimar, organized by Prof. Tom Lahmer, a former colleague.

On the workshop 2012 and at WCSMO-10 I presented piezoelectric Free Material Optimization (FMO), however, this makes not that much sense for piezoelectricity, as weak material is the generally best and the optimum is just controlled by the lower bound. For elasticity, where stiff material is in general good, this is a complete different story.

Doing orientational optimization, which has the physical interpretation of local polarization, the problem makes much sense and indeed has potential.

Local Optimal Polarization of Piezoelectric Material from fwein

Two further examples I want to solve are dynamic problems (can the resonance frequency be moved by polarization, I guess so but it might be a small effect) and a solid auxetic (negative Poisson's ratio) device, what would be really impressing if this is possible.

WCSMO-10 is over

WCSMO-10 is over, and again I realized, that the WCSMO is by far the most interesting conference for me. The whole numerical topology optmization community was there and I enjoyed it very much. I have the impression that I meanwhile know a lot of the important people (at least a little :)).


I held a talk on piezoelectric free material optimization, similar to what I talked about on the last Workshop on Direct and Inverse Problems in Piezoelectricity, but this time not starting with the music of Jean Michel Jarre :)

Free Material Optimization of Piezoelectric Material

People liked our tensor stiffness visualization, maybe I should put the Python code online ...

I also had a poster at the poster session about self-penalization. The content is from a former talk and can be also found in my thesis. My impression is, that private and direct communication/ discussion is best for the topic. The poster can also be downloaded.

This time Jamie Guest was almost omnipresent with a very large group. He appeared on 13 talks as (co-)author compared to 8 talks (co-)authored by Ole Sigmund. Well, numbers are one thing but it's impressive.

My favorite talk was by Alexander Verbart from the group of Fred van Keulen; A new approach for stress-based topology optimization: internal stress penalization. I did a little on stress optimization (e.g. piezoelectric stress optimization) but for me there are two open problems: have not grayness to confirm to the constraints and the miracle of the min vol problem which would be best for rho = rho_min. The idea of Alexander has neither stress penalization nor globalization parameters, subregions or anything else. The approach would allow gray material to confirm with the stresses but with some luck the optimizer won't find this solution. I'll have to give it a try.

The new TopOpt App from DTU

Ole Sigmund's DTU topology optimization team released their TopOpt App for iOS, Android and Web. This is pretty cool stuff. It allows to play with any variant of a compliance problem. With respect to the original TopOpt web application it is interactive and as such it is as interactive as our our iTop web application (eamc080.eam.uni-erlangen.de/iTop. IMHO, the TopOpt app suits better a tablet than a smartphone/ iPod, but on a tablet it is really interactive, and it is real fun to play with it. I let my 5 years old daughter play with the TopOpt app what would not work with iTop.

With the TopOpt app being an off-line app, I started to show almost any person (I have a beer with and who is not escaping fast enough) what this topology optimization stuff is all about on my iPod.

From the technical point of view I'm impressed by the performance. It is clear, that despite their user experience, the ARM processing power is significant slower than our iTop Xenon CPU. I would have guessed that the performance wouldn't be sufficient and I would have been wrong! I wonder about the direct solver and the Heaviside filter parameters.

So what it the difference to iTop? The TopOpt app is self-explaining while iTop deserves explanation (especially as we still did not write any documentation). But using iTop as a demonstrator tool it allows to explain what is behind

• penalization,
• regularization.
• choice of optimizer,
• the phenomenon of self-penalization,
• start designs/ local optima.

I'm pretty sure the force inverter problem will be soon integrated into the TopOpt app, while interactive material design via inverse homogenization might be a unique feature of iTop for a longer time.

Congratulations, Niels, Morten and Casper! :)