Thursday, 28 February 2019

My secondment at IFSTTAR

Secondments are fantastic parts of Marie Curie projects. They give us great experiences in performing research, communication, and cultural orientation.  All these experiences are achieved by working in different research centres, cooperating with experts of the field, and living in several cities and countries. 

I have started my final secondment at IFSTTAR (The French Institute of Science and Technology for Transport, Development and Networks) in Paris in the beginning of February 2019.  The objective of my work at this institute is to study the fatigue phenomenon and crack propagation of welded details in bridges with orthotropic decks. This study has been initiated with cooperation of Cerema (Center for Studies and Expertise on Risks, the Environment, Mobility and Development).  Starting this study gives me the chance to work on the practical cases in the area of structural engineering and learning some advanced methods in finite element analysis such as XFEM in addition to learning some software like GMSHCode-Aster, and Salome-meca

In the end, I hope my work during my secondment would be resourceful and I could cover a big part of our objectives by the help of my supervisors from IFSTTAR and Cerema. In the following you can see some photos of my new working environment. 

Thank you for reading this article, 

ESR10: Morteza Ahmadivala, and ESR6: Mariia Nesterova

Coffee break with supervisors at IFSTTAR

Monday, 15 October 2018

My work in a very small nutshell

In last decades maintenance optimisation of civil structures has gained increasing attention since the number of ageing structures is becoming large while available budget dedicated to maintenance is limited. Fatigue is one of the main degradation processes on steel structures that causes structural failure before the designed lifetime. Therefore, the main goal of our study is to provide an optimal maintenance planning to extend the lifetime of structures against fatigue. Structural health monitoring can help to have a better understanding of the structural condition for a better maintenance funding allocation. To reach our goal we might face different challenges in A: fatigue reliability assessment, B: application of monitoring information, and C: optimisation of maintenance strategies. Addressing these challenges can define different steps of this study. 

Within the first step, fracture mechanism and S-N curves are two regular approaches that are used to evaluate fatigue damage and provide a proper limit state for reliability analysis. Fatigue reliability can be performed within a time-independent or time-dependent framework depending on the choice of fatigue model. The challenge here is related to how to evaluate low probabilities of failure when computationally expensive performance functions are involved. Hence, we have developed an efficient methodology to perform time-dependent reliability analysis. Kriging meta-modelling is used to replace the computationally expensive performance functions while using Monte Carlo simulation. 

The second step is related to how to get benefit from monitoring information. Structural health monitoring provides us with valuable information about the current situation of civil structures. This information can be about crack development, actual loading conditions, etc. The challenge here is related to the way we employ the information coming from monitoring data. With this respect, a study has been developed on long-term monitoring data available at EPFL. Time series methods are employed to prepare a loading model for long-term monitoring data. The aim is to capture seasonality effect in traffic loading and to provide a model that gives more detail about structural fatigue loading. This load model can be used within S-N approach or fracture mechanism with some adjustments.

Finally, methods and approaches in previous steps will be combined to have a proper and updated indicator to apply maintenance actions. The desired indicator would be fatigue reliability index. The challenge in the final step can be related to the cost models for maintenance and monitoring. Therefore, an appropriate cost model will be chosen for the optimisation framework, and overall methodology will be applied on a shared object or another case study.  

Thank you very much for reading this post. 

Wednesday, 3 October 2018

My secondment at EPFL: such a great experience

Secondments are one of the most interesting parts of Mari Curie projects. It gives you the opportunity to work with different researchers in different companies, universities, and research centres. 
I performed my first secondment within the INFRASTAR program at EPFL. It was such a great chance for me to stay as a PhD visitor in one of the well-known engineering schools in the world and to live in Switzerland with its magnificent nature and landscapes. What I have learnt during my secondment is not only related to my work, I also learnt a lot about the Swiss culture, people, and the great international atmosphere of Lausanne. 

I joined the Structural Maintenance and Safety Laboratory (MCS) of Civil Engineering depertment at EPFL.  My work in this lab was devoted to take advantage of valuable long-term monitoring data that is recorded by this lab for about two years. It is worthy to mention that three of the shared objects within INFRASTAR are provided by MCS. Chillion viaduc is one of our shared objects and I was working on the monitoring data of this bridge. I have employed Time Series methods such as ARIMA to prepare a new load model for fatigue analysis while there is seasonality effect. This new model can deal with missing data, it can capture seasonality effect, and it can be used to generate fatigue loading for further analysis (more details about this study will be provided later).  

Apart from work, this period was a great opportunity for me to enjoy the nature of Switzerland. What is very interesting in Switzerland is that one can make a plan to visit any place in the country during a weekend, however, there are plenty of beautiful places out there. Another thing that sounds even more interesting in this small country is that they have four official languages and when you visit different regions you will see the diversity of the languages and cultures. 

In conclusion, I would say that my secondment at EPFL was a great incident for me. I could get benefit of the invaluable experiences of researchers at MCS lab. Also, I could add the experience of living in Switzerland in my memory besides all other beautiful experiences that I had in another countries. 

Thank you for reading this article, 

Chillion Viaduc

A trip with MCS members to visit a newly constructed pedestrianise bridge with UHPFRC that is a new material developed at MCS.  

Monday, 25 June 2018

Training weeks are full of adventures and experiences

I would like to write about interesting training weeks that we had so far within INFRASTAR
We had our Third training week recently at Aalborg University, Denmark, and we performed the previous ones at EPFL (Lausanne, Switzerland) and BAM (Berlin, Germany). 

Apart from the lessons that I have received during our training weeks in different areas of engineering and career development, having the opportunity to visit different labs, structures, materials, and advance technologies in civil engineering domain, gave a me a great insight and experience about what I am currently doing. 

We had our first training week in BAM, Berlin, which is the Federal Institute for Materials Research and Testing in Germany. During this training week, we visited their testing laboratory for concrete structures. They are developing some new tools and methods of none-destructive testing for concrete structures, and we had the chance to get familiar and work with some of their sensors during our visit. 

During the second training week in EPFL (École polytechnique fédérale de Lausanne), we had the chance to get familiar with a new type of material for construction that is a relative of concrete with different properties and it is called UHPFRC (Ultra-High Performance Fibre Reinforced Concrete). We also visited some structures that have already been built using this new type of concrete. 

Finally, we have visited a testing wind farm in Aalborg within our third training week in Aalborg University. Since I was always interested in renewable energy and sustainable development, It was the most amazing experience for me among all visits that I have had so far. We could learn about the recent technologies in the area of wind energy and see some of them working in the wind farm. 

In the end I would like to thank my program (INFRASTAR) that has provided us this amazing training in different and interesting places. 

Thanks a lot for reading this post, 

Training week 1, BAM 

Training week 2, EPFL

Training week 3, Aalborg

Tuesday, 22 May 2018

What is better than having another Marie Curie PhD at your office?

 I would like to devote this post to my colleague Barbara Heitner who is a PhD in TRUSS ITN under Marie Curie actions.

When you want to start a new career particularly when you need to move to another country, in the beginning, you always need some people to assist you with different issues to be able to stand on your own. Apart from the other great members of Phimeca, I would like to admit that I am so lucky to have Barbara as my colleague who has started her PhD one year before me in Phimeca and paved most of the roads before me. Not only for my research and work issues, she is also a great help to tackle personal problems.

With respect to the work, when your work situation and contract is different than other colleagues in the company you may go through different administrative procedure than others and in some cases it might be very boring and time consuming. As Barbara has already started her work before me as Marie Curie PhD at Phimeca, it made my recruitment procedure much easier and more straightforward. Also, it is always a great change when you start working in a company after university and it is not so easy for many people to easily get used to the new environment. It is much easier to adapt to work in a company when there is someone else in the workplace who has the same situation as yours.

In the other hand, since my research project and Barbara's are in the same domain, when I am facing different questions, she is the first person who hears them. Thank to the Phimeca's research team and Barbara, I could make a great progress in structural reliability analysis, probabilistic modelling, and programming in Python.

Apart from being colleagues Barbara is a great friend too. I appreciate her helps regarding my personal life as well. She made it easier for me to get used to live in  Clermont-Ferrand, France. Sometimes when I needed a company to discuss about different topics and maybe having a drink in the evening she was always there.

Since the next two weeks will be our final weeks that we spend together in Phimeca, by this post I would like to appreciate her help and support and I want to say that I was so lucky and glad to have her as my colleague.

Thank you very much for reading this post.

Me and Barbara after preparing the Christmas tree for 2018 in Phimeca

Thursday, 5 April 2018

A short introduction on Meta-Modelling and Kriging

In many branches of science and particularly Engineering, there are lots of complex physical models that are very hard to evaluate, or in the other hand there might be some data available that there is no physical model to describe them. Regarding to these issues, Surrogate models or Meta-models provide a very appropriate tool to be able to address such problems. Meta-models can replace a very complex mathematical model which is very expensive to evaluate with a simpler model, therefore,  applying available numerical methods on the meta-model will be much cheaper. Also, for those data that there in no model available, one can say that surrogate models are the only remedy. 

Having a good design of experiment is adequate to prepare the meta-mode and this is a great advantage for this approach since design of experiment is a small set of realisations of input variables and the corresponding output of the complex original model. Hence, the effective cost of meta-model goes for the choice of design of experiment. 

There are different types of meta-modelling such as functional basis methods, Gaussian regression and spectral methods. Choosing among these methods depends on the quality of the method and their ability to address high dimensional problems with a good accuracy. 

Gaussian process regression (Kriging) 

Among different methods of meta-modelling Kriging meta-modelling or Gaussian process regression is one of the most interesting methods. Kriging metamodeling has been formulated by a French mathematician George Matheron around 1963 and he named the methodology after a South African mining engineer D. G. Krige who applied this methodology for the first time in geo-statistical problems. In fact, Kriging is the best linear and unbiased prediction of the unknown value of a random function M at any voluntary location. 

Kriging meta-modelling is based on this idea that any physical model can be formulated by combining a regression model with a stochastic process. By using the design of experiment, regression model tries to find the general trend of the original model and stochastic part reduces the distance of the approximation by regression and the points in design of experiment to zero. Different steps of Kriging is illustrated in Figure 1. 

Kriging meta-models can provide a very helpful tool in the area of structural reliability analysis. There are different methods developed out of kriging for reliability analysis such as EGRA, Independent EGO, Mixed EGO, AK-MCS, etc. ((H. Zhen & D. Xiaoping, 2015), (W. Fauriat & N. Gayton 2013 ), (B. Echard et al. 2011)). 

Figure 1 Kriging modelling steps 

Thursday, 1 February 2018

One year in France

Since I am about to celebrate the first anniversary of my new job in France. I would like to devote this post to some of my living experience in France in a very short version. 

Living in another country, especially in the beginning, is like having lessons for every day in which even a small kid can be your teacher while you are learning their language. Of course, this learning process in not only about the language, you can learn a lot from people about their behaviour in different situation such as public transportation, classrooms, pubs, shopping, etc. In my opinion, when you want to know more about a country or a culture, the best way is to live among locals. 

When it comes to France, most of us can guess about different things that is famous in this country, however, depending on the person the first guess might be different since there are a lot of good stuff in France. In my own case I was always wondering about French wine and cheese. I did not have  any idea that consuming French cheese might be very addictive but gladly I was able to control myself against all those tasty cheese to become an addict. Although, French wine is super, beer is very expensive. I think they have intentionally increased the price of beer to persuade people to spend more on wine :)

During the last year I learnt a lot in this country. I found French people so polite while facing strangers especially when they are going to do something and that might be different in their friend's culture, so they ask first to make sure if it is not gonna be offensive for them. But, the most interesting characteristics that I realised about French people is that they expect you to learn their language very fast, however French is a very difficult language. They easily become tired of speaking English even if they are very fluent in English. 

In the end I would mention that, if one  wants to enjoy his/her life in France, there are too many things you can do. There are a lot of beautiful regions and cities in France to visit with their own specialities, also, there are a lot of good facilities to study, to do sport, music, etc. 

Thanks for reading this post,
Stay tuned for next one :)

My secondment at IFSTTAR

Secondments are fantastic parts of Marie Curie projects. They give us great experiences in performing research, communication, and cultura...