## 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)).

 @page { margin: 2cm } p { margin-bottom: 0.25cm; direction: ltr; line-height: 120%; text-align: left; orphans: 2; widows: 2 } a:link { color: #0563c1 } 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 :)

## Monday, 27 November 2017

### A Great Opportunity to Learn TeamWork

 Infrastar PhD s during second training week
Teamwork is a matter of practice and patience.

Once you start working as a Marie-Curie PhD student, most probably, you will find yourself working with different labs, companies, universities, and research centres having several supervisors from those places. You might have monthly meetings with five or six people to present your improvement and results, therefore, it is necessary to improve your teamwork skills to be able to adapt yourself with such a working conditions.
In the other hand, there will be some other PhD students under the same Marie-Curie program which they can be considered as your classmates. They normally live in another city or country but since PhD topics are somehow related, there is a great opportunity of teamwork and developing ideas together as well. Mari-Curie team allocates some training weeks in which all PhD s under the same program gather together and share their ideas and try to find a way to cooperate with each other.

As a Marie-Curie PhD student I would like to tell you that, not everyone find it easy to work under this highly team-basis conditions. It may look very interesting in the beginning, however, it is amazing, but I would say that seriousness and practice are very important factors to gain this teamwork skill.

In the picture above you can see my classmates and some of our supervisors, however, we are not really in the same school and in the same class.

Stay tuned for next post :)

## Wednesday, 15 November 2017

### Maintenance strategies: Preventive and Corrective

Among different types of maintenance strategies that were introduced before, preventive and corrective maintenance can be called the main strategies.
Preventive maintenance actions are generally referred to those actions that are applied on the structure regularly and that try to maintain the structure from unexpected failures and keep it working.  Preventive maintenance defers the degradation process, hence, it extends the time needed for corrective actions and operational capacity will be increased. In the other hand, because they are performed timely and based on a routine, therefore, less large scale repairs are required. In practice, a preventive maintenance schedule may include things such as cleaning, lubrication, oil changes, adjustments, repairs, etc.

Corrective maintenance is another strategy which will be applied on a structure when a flaw is detected. The purpose of the corrective maintenance is to restore the operational capacity of the structure to an acceptable level. according to the importance of the flaw a corrective action can be applied immediately or deferred for a certain time. There are different types of actions included in corrective maintenance and the application of each depends on the defect situation. In worst case scenario replacement of the component of structure is the final solutions.

 Maintenance strategies, RD/GD-210, 2007

Stay tuned for the next post ;)

## Monday, 2 October 2017

### Structural Maintenance Planning

Maintenance planning for structures, for a long time, was a concept of keeping the structure in a good shape, hence, it can perform its expected duties. Yet, because of financial and physical limitations in the old definition, operational managers had to provide a more comprehensive description for maintenance of structures. Hence, a more professional definition for structural maintenance would be defined as: "Total technical activities in the component level connected to each other and economically balanced, in order to keep or get the structure in such a condition that it can accomplish its duties for a certain period of time with sufficient reliability, availability, serviceability, and durability” Toorn (1996).

According to the new definition, some targets such as maintenance and managerial targets could be identified. Maintenance targets try to assure an adequate level of reliability, availability, etc. and managerial targets mainly aim to minimise the associated maintenance costs. These targets will provide some tools and indicators which are so helpful to mathematically formulate the problems in structural maintenance planning. For instance, Annual reliability index can be used as an indicator if the purpose of maintenance planning is to reach a certain level of reliability or maximise it as affordable as possible.

Structural maintenance can include different kinds of actions which regarding to the type of action and their influence on the degradation process can be divided into four categories:
1- Preventive maintenance, 2- corrective maintenance, 3- observational maintenance, and 4- non-inspection maintenance.

Differences between these categories will be explained in next posts.
 Bridge maintenance: repainting (Photo: Fox Photos / Getty Images)

## Tuesday, 30 May 2017

### Introducing ESR-10

 Collect your stuff and apply for Marie Curie actions; ESR-10 in Paris
Hi Everyone,

Before getting so serious and talking about engineering stuff, let me to introduce myself first. My name is Morteza and I am from Iran (a beautiful country with warm-blooded people). I received my bachelors degree in marine engineering and naval architecture from Amirkabir University of Technology in Tehran. I found this university so interesting and full of great students and faculty board, so I decided to continue my master's education in the same university but in hydro-mechanics. After I finished my first master's, I wanted to have some studies in another field of engineering and to experience living in another country, therefore I moved to Istanbul\Turkey and started studying industrial and systems engineering. I received my second master's degree from Istanbul Sehir University. I would like to mention that living in Istanbul is JUST amazing.

Meanwhile, I got familiar with Marie Skłodowska-Curie actions and I was hoping to become a researcher under this program since they provide you a very good environment to conduct research among different institutions in several countries, and under the supervision of excellent professors and researchers. Finally and gladly, in the right moment, just after I defended my second master's thesis in Reliability Engineering, I found INFRASTAR which is a framework for Innovation and Networking for Fatigue and Reliability Analysis of Structures. I applied for some positions under this program and I was accepted as ESR10 which my project topic is "Optimal maintenance planning of existing structures using monitoring data".

My host institution is PHIMECA Engineering in France which is an engineering company specialised in optimisation,  reliability and robustness of products and structures. Also, I am enrolled as a PhD student in SIGMA Clermont. I work under supervision of five great professors and researchers. Dr. Thierry Yalamas and Guillaume Causse from PHIMECA, Dr. Nicolas Gayton and Dr. Cecile Mattrand from Sigma, and Dr. André Orcesi from IFSTTAR

Thanks in advance for reading my first article 😊