
Thierry Alex MaraUniversity of Reunion Island · Faculty of Science and Technology
Thierry Alex Mara
PhD
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85
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Introduction
Skills and Expertise
Publications
Publications (85)
Abstract and oral presentation: 10th International Conference on Sensitivity Analysis of Model Output (SAMO 2022) Conference. 14-16 March, Florida State University, Tallahassee.
Abstract submission is now open for the 10th International Conference on Sensitivity Analysis of Model Output (SAMO). The conference will be held at Florida State University, Tallahassee, Florida. The dates of the conference are March 14 -16, 2022, at the Florida State Conference Center.
See: https://samo2022.math.fsu.edu/
European Commission, Report number: JRC122132.
This study compares the performances of two sampling-based strategies for the simultaneous estimation of the first- and total-order variance-based sensitivity indices (a.k.a. Sobol’ indices). The first strategy corresponds to the current approach employed by practitioners and recommended in the literature. The second one was only recently introduce...
In this paper, we discuss the sensitivity analysis of model response when the uncertain model inputs are not independent of one other. In this case, two different kinds of sensitivity indices can be evaluated: (i) the sensitivity indices that account for the dependence/correlation of an input or group of inputs with the remainder and (ii) the sensi...
European Commission, Report number: JRC122132
This study compares the performances of two sampling-based strategies for the simultaneous estimation of the first-and total-orders variance-based sensitivity indices (a.k.a Sobol' indices). The first strategy was introduced by [8] and is the current approach employed by practitioners. The second one was only recently introduced by the authors of t...
Accurate simulation of flow and contaminant transport processes through unsaturated soils requires adequate knowledge of the soil parameters. This study deals with the hydraulic characterization of soils using laboratory experiments. A new strategy is developed by combining global sensitivity analysis (GSA) and Bayesian data-worth analysis (DWA) to...
Uncertainties that commonly exist in mathematical models prevent accurate predictions of solid oxide fuel cell performances and consequently impede the development and application of solid oxide fuel cell technologies. Assessing the impact of uncertain input parameters on cell performance variability is of utmost importance to the improvement of fu...
These notes aim at clarifying different strategies to perform linear regression from given dataset. Methods like the weighted and ordinary least squares, ridge regression or LASSO are proposed in the literature. The present article is my understanding of these methods which are, according to me, better unified in the Bayesian framework. The formula...
In this paper, we present a hybridizable discontinuous Galerkin (HDG) mixed method for second-order diffusion problems using a projective stabilization function and broken Raviart–Thomas functions to approximate the dual variable. The proposed HDG mixed method is inspired by the primal HDG scheme with reduced stabilization suggested by Lehrenfeld a...
Random variables characterized by a joint probability distribution function (jpdf) defined in a Bayesian framework are generally sampled with Markov chain Monte Carlo (MCMC). The latter can be computationally demanding when the number of variables is high. As an alternative, the maximal conditional probability distribution (MCPD) sampler was recent...
In this work, we conducted two laboratory column experiments on an undisturbed sandy soil. The first deals with a percolation-drainage experiment whereas the second deals with an infiltration of a constant water flux at the surface of the unsaturated soil. A Bayesian assessment of the soil parameters is performed for both experiments with the Marko...
Air quality has significantly improved in Europe over the past few decades. Nonetheless we still find high concentrations in measurements mainly in specific regions or cities. This dimensional shift, from EU-wide to hot-spot exceedances, calls for a novel approach to regional air quality management (to complement EU-wide existing policies). The SHE...
We focus on the Bayesian estimation of strongly heterogeneous transmissivity fields conditional on data sampled at a set of locations in an aquifer. Log-transmissivity, Y, is modeled as a stochastic Gaussian process, parameterized through a truncated Karhunen–Loève (KL) expansion. We consider Y fields characterized by a short correlation scale as c...
The quality of statistical calibration of hydraulic and transport soil properties is studied for infiltration experiments in which, over a given period, tracer-contaminated water is injected into an hypothetical column filled with a homogeneous soil. The saturated hydraulic conductivity, the saturated and residual water contents, the Mualem–van Gen...
Polynomial chaos expansions are frequently used by engineers and modellers for uncertainty and sensitivity analyses of computer models. They allow representing the input/output relations of computer models. Usually only a few terms are really relevant in such a representation. It is a challenge to infer the best sparse polynomial chaos expansion of...
This paper deals with global sensitivity analysis of computer model output. Given an independent input sample and associated model output vector with possibly the vector of output derivatives with respect to the input variables, we show that it is possible to evaluate the following global sensitivity measures: (i) the Sobol’ indices, (ii) the Borgo...
Several methods are proposed in the literature to perform global sensitivity analysis of computer models with independent inputs. Only a few allow for treating the case of dependent inputs. In the present work, we investigate how to compute variance-based sensitivity indices with the Fourier amplitude sensitivity test. This can be achieved with the...
Uncertainty and risk analyses are important tools for building designs and performance assessment of renewable energy systems. This task requires to account for the variability of the weather data. In the present work, we develop a methodology to characterize and simulate stochastic weather data. The stochastic features of each weather input, such...
A new benchmark with a high accurate solution is proposed for the verification of numerical codes dealing with double-diffusive convection in a heterogeneous porous medium. The new benchmark is inspired by the popular problem of square porous cavity by assuming a stratified porous medium. A high accurate steady state solution is developed using the...
In the present work, we study the quality of the statistical calibration of hydraulic and transport soil properties using an infiltration experiment in which, over a given period, tracer-contaminated water is injected into a laboratory column filled with a homogeneous soil. The numerical model is based on the Richards' equation for solving water fl...
The concept of dual flowing continuum is a promising approach for modeling solute transport in porous media that includes biofilm phases. The highly dispersed transit time distributions often generated by these media are taken into consideration by simply stipulating that advection–dispersion transport occurs through both the porous and the biofilm...
A system of two differential equations is used to model the transmission dynamics of human immunodeficiency virus between
‘persons who inject drugs’ (PWIDs) and their syringes. Our vector-borne disease model hinges on a metaphorical urn from which
PWIDs draw syringes at random which may or may not be infected and may or may not result in one of the...
This paper addresses the issue of performing global sensitivity analysis of model output with dependent inputs. First, we define variance-based sensitivity indices that allow for distinguishing the independent contributions of the inputs to the response variance from their mutual dependent contributions. Then, two sampling strategies are proposed f...
In this paper, we address the issue of conducting a sensitivity analysis of complex models with both static and dynamic uncertain inputs. While several approaches have been proposed to compute the sensitivity indices of the static inputs (i.e. parameters), the one of the dynamic inputs (i.e. stochastic fields) have been rarely addressed. For this p...
We introduce the concept of maximal conditional posterior distribution ( MCPD) to assess the uncertainty of model parameters in a Bayesian framework. Although, Markov Chains Monte Carlo ( MCMC) methods are particularly suited for this task, they become challenging with highly parameterized nonlinear models. The MCPD represents the conditional proba...
In this paper, we address the issue of conducting a sensitivity analysis of complex models with both static and dynamic uncertain inputs. While several approaches have been proposed to compute the sensitivity indices of the static inputs (i.e. parameters), the one of the dynamic inputs (i.e. stochastic fields) have been rarely addressed. For this p...
RESUME. Cet article propose une méthode originale d'échantillonnage des entrées temporelles corrélées an de permettre leur prise en compte dans les analyses de sensibilité et d'incertitude en simulation thermique dynamique. La démarche s'appuie sur les données météorologiques de type TMY associées à EnergyPlus. Ces entrées sont le rayonnement direc...
When a vehicle equipped with tire is manoeuvred on the ground, the tires are submitted to a number of forces – longitudinal force when driving or braking torque is applied to the wheel and/or lateral force when the wheel is steered to turn at a corner. Pacejka model describes these forces that represent the reaction of the road onto the tire. This...
This paper presents a statistical approach for uncertainty and sensitivity analyses applied to 14 inputs whose 10 properties associated with brick material, using the four different EnergyPlus wall models. The variability of inputs has been extracted from several characterization works presented in IEA Annexes 14, 24 and 55, being coherent to the l...
This note discusses how to make the superior convergence properties of a Quasi Monte Carlo sample available in Random Balance Design for estimating first order global sensitivity indices. Some findings on bias and bootstrapping are also reported.
This paper deals with neural networks modelling of HVAC systems. In order to
increase the neural networks performances, a method based on sensitivity
analysis is applied. The same technique is also used to compute the relevance
of each input. To avoid the prediction errors in dry coil conditions, a
metamodel for each capacity is derived from the ne...
Validation of building energy simulation programs is of major interest to
both users and modellers. To achieve such a task, it is essential to apply a
methodology based on a priori test and empirical validation. A priori test
consists in verifying that models embedded in a program and their
implementation are correct. this should be achieved before...
Simulation codes of thermal behaviour could significantly improve housing
construction design. Among the existing software, CODYRUN and TRNSYS are
calculations codes of different conceptions. CODYRUN is exclusively dedicated
to housing thermal behaviour, whereas TRNSYS is more generally used on any
thermal system. The purpose of this article is to...
The paper deals with an empirical validation of a building thermal model. We put the emphasis on sensitivity analysis and on research of inputs/residual correlation to improve our model. In this article, we apply a sensitivity analysis technique in the frequency domain to point out the more important parameters of the model. Then, we compare measur...
The calculation of airflows is of great importance for detailed building
thermal simulation computer codes, these airflows most frequently constituting
an important thermal coupling between the building and the outside on one hand,
and the different thermal zones on the other. The driving effects of air
movement, which are the wind and the thermal...
As part of our efforts to complete the software CODYRUN validation, we chose
as test building a block of flats constructed in Reunion Island, which has a
humid tropical climate. The sensitivity analysis allowed us to study the
effects of both diffuse and direct solar radiation on our model of this
building. With regard to the choice and location of...
The paper deals with an empirical validation of a building thermal model. We put the emphasis on sensitivity analysis and on research of inputs/residual correlation to improve our model. In this article, we apply a sensitivity analysis technique in the frequency domain to point out the more important parameters of the model. Then, we compare measur...
The paper deals with an empirical validation of a building thermal model. We put the emphasis on sensitivity analysis and on research of inputs/residual correlation to improve our model. In this paper, we apply a sensitivity analysis technique in the frequency domain to point out the more important parameters of the model. Then, we compare measured...
This paper deals about the presentation of a new software RUNEOLE used to provide weather data in buildings physics. RUNEOLE associates three modules leading to the description, the modelling and the generation of weather data. The first module is dedicated to the description of each climatic variable included in the database. Graphic representatio...
We present in this paper a new strategy based on the use of polynomial chaos expansion (PCE) for both global sensitivity analysis and parameter optimization. To limit the number of evaluations of the direct model, we develop a simple and efficient procedure to construct a sparse PCE where only coefficients that have a significant contribution to th...
In this work, global sensitivity analysis (GSA) was used in conjunction with polynomial chaos expansion (PCE) to help assess unsaturated soil hydraulic parameters from experimental drainage data. The temporal sensitivity of different outputs (cumulative outflow, water content, and pressure head at different positions inside the column) to the Muale...
In this work, we show how the use of global sensitivity analysis (GSA) in conjunction with the polynomial chaos expansion (PCE) methodology can provide relevant information for the interpretation of transport experiments in laboratory-scale heterogeneous porous media. We perform GSA by calculating the Sobol indices, which provide a variance-based i...
Computational models are intensively used in engineering for risk analysis or prediction of future outcomes. Uncertainty and sensitivity analyses are of great help in these purposes. Although several methods exist to perform variance-based sensitivity analysis of model output with independent inputs only a few are proposed in the literature in the...
This paper deals with the sensitivity analysis method named Fourier amplitude sensitivity test (FAST). This method is known to be very robust for the computation of global sensitivity indices but their computational cost remains prohibitive for complex and large dimensional models. Recent developments in the implementation of FAST by use of the ran...
This paper deals with a set of applications of global sensitivity analysis to building thermal modelling. The aim is to demonstrate the interest of such tools for model analysis and to encourage their use. Indeed, since the last ten years important improvements have been made in the field of sensitivity analysis and especially in computational meth...
In this paper, three methods to compute the factors main effect on model responses are compared. The first one is the improved Fourier amplitude sensitivity test [Tarantola, S., Gatelli, D. and Mara, T.A., 2006, Random balance designs for the estimation of first-order global sensitivity indices. Reliability Engineering and System Safety, 91(6), 717...
A simplified model of indoor short wave couplings adapted to multizone simulation context is proposed, thanks to some simplified hypothesis and the introduction of an indoor short wave exchange matrix. Through specific properties of this matrix, it appears as a useful step to quantify exchanges between zones separated by windows or large openings....
We present two methods for the estimation of main effects in global sensitivity analysis. The methods adopt Satterthwaite's application of random balance designs in regression problems, and extend it to sensitivity analysis of model output for non-linear, non-additive models. Finite as well as infinite ranges for model input factors are allowed. Th...
In this paper, we propose a new pruning algorithm to obtain the optimal number of hidden units of a single layer of a fully connected neural network (NN). The technique relies on a global sensitivity analysis of model output. The relevance of the hidden nodes is determined by analysing the Fourier decomposition of the variance of the model output....
This paper deals with a new model of HVAC systems for hourly simulations. The former is derived from a short time step model that is priory described. The hourly model is appraised by comparing its predictions to those of the short time step simulations. Finally, a sensitivity analysis is carried out to understand the cause of the discrepancies bet...
This paper deals with a new saliency measure for ranking and removing the less important inputs and hidden nodes. This new metric is the result of a global sensitivity analysis, EFAST, performed on the neural network. EFAST is model independent, does not interact with the training stage and does not rely on any assumption regards to local minima fo...
This paper deals with the empirical validation of a building thermal model, which includes a roof-mounted radiant barrier. We first present the thermal model, developed with a building simulation code prototype, the objective being to increase understanding of the thermal phenomena that govern the behaviour of the whole building. We then describe t...
This paper deals with a method of performing a parametric sensitivity analysis. Such a study is very important for modellers as it can provide useful information. Indeed, it can point out a model's weaknesses and allow us to identify the most important parameters in the model, which the modeller must know accurately to provide reliable results. Aft...
The cooling system/building coupling encounters several modeling difficulties. First, the lack of manufacturer's data for cooling equipment (manufacturers are often not very keen on giving this information) prevent the development of an accurate model. Secondly, building simulation codes often give good results for the estimation of the loads but n...
This paper deals with a method for performing a parametric sensitivity analysis. Such a study is very important for modellers as it can provide useful information. Indeed, it can point out a model's weaknesses and allow us to identify the most important parameters in the model, which the modeller must know accurately to provide reliable results. Af...
In early 1995, a DSM pilot initiative was launched in the French islands of Guadeloupe and La Reunion through a partnership between several public and private partners (the French Public Utility EDF, the University of Reunion Island, low cost housing companies, architects, energy consultants, etc…) to set up standards to improve thermal design of n...
As part of our efforts to complete the software CODYRUN validation, we chose as test building a block of flats constructed in Reunion island, which has a humid tropical climate, ne sensitivity analysis allowed us to study the effects of both diffuse and direct solar radiation on our model of this building. With regard to the choice and location of...
Simulations are conducted using CODYRUN software to evaluate indoor confort conditions in Mauritius Island dwellings
Les logiciels de simulation du comportement thermique jouent un rôle capital dans l'amélioration des performances énergétiques des bâtiments. Se pose cependant le problème du crédit à apporter aux résultats de simulations de ces logiciels, autrement dit, de l'aptitude de ces derniers et des modèles intégrés à représenter la réalité. Dans ces travau...
ISBN : 2-84299-200-8 EAN : 9782842992002
ISBN : 2-84299-200-8 EAN : 9782842992002
The calculation of airflows is of great importance for detailed building thermal simulation computer codes, these airflows most frequently constituting an important thermal coupling between the building and the outside on one hand, and the different thermal zones on the other. The driving effects of air movement, which are the wind and the thermal...
The sky temperature is an important parameter for simulation codes in building studies. A preliminary campaign of validation of a simulation software CODYRUN has demonstrated the misinterpretation of the radiative exchanges of long waves between the building and its environment. A bibliographical research has then led to the use models using dry ai...
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