# George EfthimiouAristotle University of Thessaloniki | AUTH · Sustainability Engineering Laboratory (SEL)

George Efthimiou

PhD Mechanical Engineering

Working on projects,
Writing deliverables,
Writing publications,
Looking for possible collaborations.

## About

98

Publications

20,596

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744

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Introduction

Research Associate in AUTH, Greece. In the past: Research Associate and Postdoc researcher in NCSR Demokritos, Greece. PhD in Mechanical Engineering from the UOWM, Greece.
Research interests: Microscale modelling of environmental flows and pollutant dispersion in urban and industrial environments. Indoor air quality. Wind engineering. Inverse modelling. Member of the Working Committee of COST Action 732 and COST Action ES1006. More information can be found in https://fluenc.gr

Additional affiliations

July 2019 - present

February 2014 - June 2019

May 2013 - August 2014

Education

February 2007 - April 2013

## Publications

Publications (98)

In any health risk related event such as an air hazardous release, a key question that needs to be addressed is, to what extent an individual is exposed to a hazardous pollutant/agent for a specific time interval at a specific location downstream the release. Any systematic and reliable approach on this problem especially at the application/operati...

The aim of this work is to develop an algorithm that is able to provide predictions of wind speed statistics (WSS) in renewable energy environments. The subject is clearly interesting, as predictions of storms and extreme winds are important for decision makers and emergency response teams in renewable energy environments, e.g., in places where win...

When considering accidental or/and deliberate releases of airborne hazardous substances the release duration is often short and in most cases not precisely known. The downstream exposure in those cases is stochastic due to ambient turbulence and strongly dependent on the release duration. Depending on the adopted modelling approach, a relatively la...

The present study main aim is to introduce simplified approaches in estimating exposure due to airborne hazardous releases in urban
environments. The question is to what extend a single suitable continuous release simulation can be utilised in estimating major
exposure parameters statistical behaviour replacing in many cases a prohibitive large num...

In the framework of the Urban Dispersion International Evaluation Exercise (UDINEE) project coordinated by the European Commission’s Joint Research Centre, a case study was conducted of the Joint Urban 2003 (JU2003) experimental campaign in the central area of Oklahoma City, USA. The UDINEE project concerned the cases of puff dispersion of the JU20...

Ιn case of the dispersion of an airborne material from a point source in an urban environment the reliable prediction of the concentration statistical distribution by a numerical dispersion model presupposes the capability of the model to predict at least four statistical moments (mean, variance, skewness and kurtosis). In the present study, the be...

One of the goals of research on indoor air quality is the reduction of human exposure due to the dispersion of hazardous airborne materials. The purpose of this study is to analyse, by using computational fluid dynamics (CFD), the flow and the concentration patterns of floor-emitted pollutants inside a real, mechanically ventilated office of simple...

One of the goals of research on indoor air quality is the reduction of human exposure due to the dispersion of hazardous airborne materials. The purpose of this study is to analyse, by using computational fluid dynamics (CFD), the flow and the concentration patterns of floor-emitted pollutants inside a real, mechanically ventilated office of simple...

An improved inverse modelling method to estimate the location and the emission rate of an unknown point stationary source of passive atmospheric pollutant in a complex urban geometry was incorporated in the Computational Fluid Dynamics code ADREA-HF in Efthimiou et al., (2017). The key improvement lies in a two-step segregated approach. At first on...

Accurate prediction of the wind speed probabilities in the atmospheric surface layer is very important for wind energy assessment studies and many other practical applications such as the design and operation of wind turbines and human exposure to wind extremes. In a recent study, an optimized beta distribution was developed for the prediction of t...

The estimation of a hazardous contaminant unknown source characteristics (i.e., rate and location) in a complex urban environment using efficient inverse modelling techniques is a challenging problem that involves advanced computational fluid dynamics combined with appropriate mathematical algorithms. In this paper we further assess our recently pr...

Large Eddy Simulation (LES) of atmospheric flows has become an increasingly popular modelling approach within the last years, as it has the potential to provide deeper insight into unsteady flow phenomena. LES can be improved and validated using specifically designed and well documented wind tunnel datasets. In this work, we evaluate the performanc...

Accurate prediction of the wind speed probabilities in the atmospheric surface layer is very important for wind energy assessment studies and many other practical applications such as for the design and the operation of wind turbines and human exposure to wind extremes. In a recent study, an optimized beta distribution was developed for the predict...

The intentional or accidental release of airborne toxics poses great risk to the public health. During these incidents, the greatest factor of uncertainty is related to the location and rate of released substance, therefore, an information of high importance for emergency preparedness and response plans. A novel computational algorithm is proposed...

In this report we consider the problem of estimating the unknown parameters of a hazardous pollutants release in the atmosphere. The problem known as 'source term estimation' or 'source inversion' is ill-posed and hence extremely difficult to solve. Recently we developed a method [1] in which instead of a commonly used quadratic cost function we as...

In this work, we present an inverse computational method for the identification of the location, start time, duration and quantity of emitted substance of an unknown air pollution source of finite time duration in an urban environment. We considered a problem of transient pollutant dispersion under stationary meteorological fields, which is a reaso...

A dispersion modeling of airborne pollutants in urban environments using RANS CFD codes is usually based on mean and variance concentration Eulerian transport equations. An alternative could be to use simple Lagrangian approaches with the detailed flow parametrization provided by the CFD codes. The Lagrangian approaches have been approved quite suc...

New Lagrangian simulations of the dispersion of puffs in complex urban environments. Evaluation of the new methodology with Michelstadt and Joint Urban 2003.

https://sciencetrends.com/advanced-computational-fluid-dynamics-modeling-for-the-prediction-of-the-dispersion-of-airborne-materials-from-puff-releases-in-complex-urban-environments/

One of the key issues of recent research on the dispersion inside complex urban environments is the ability to predict dosage-based parameters from the puff release of an airborne material from a point source in the atmospheric boundary layer inside the built-up area. The present work addresses the question of whether the computational fluid dynami...

Radiation from the deposited radionuclides is indispensable information for environmental impact assessment of nuclear power plants and emergency management during nuclear accidents. Ground shine estimation is related to multiple physical processes, including atmospheric dispersion, deposition, soil and air radiation shielding. It still remains unc...

An improved inverse method was presented recently for the estimation of the location and the rate of an unknown point stationary source of passive atmospheric pollutant in a complex urban geometry. The inverse method was incorporated in the well-established and updated version of the ADREA-HF Computational Fluid Dynamics code. The key improvement o...

An improved inverse method was presented recently for the estimation of the location and the rate of an unknown point stationary source of passive atmospheric pollutant in a complex urban geometry. The inverse method was incorporated in the well-established and updated version of the ADREA-HF Computational Fluid Dynamics code. The key improvement o...

In this presentation, a detailed description of the research activities of Dr Efthimiou C. George is carried out in the past (e.g. prediction of individual exposure in urban environments) and present (e.g. prediction of the source of airborne pollutants in urban environments and statistics analysis of dynamic systems). Future ideas and plans for re...

State of the art research (unpublished results) on statistical analysis of a turbulent dynamical system.

We recently developed the method for identification of location, start time, duration and release rate of an unknown short-duration source of airborne pollution in urban environment. The method has been integrated in the ADREA-HF CFD code and the testing has been carried out by performing series of source inversion runs using the data of 200 indivi...

Computational Fluid Dynamics (CFD) is applied to analyse the flow and the concentration patterns of floor-emitted pollutants inside a mechanically ventilated office of simple geometry. The simulation results show complex airflow and high heterogeneity of concentration distribution. Alternative scenarios mainly of the vents’ position and airflow str...

We recently developed the method for identification of location, start time, duration and release rate of an unknown short-duration source of airborne pollution in urban environment. The method has been integrated in the ADREA-HF CFD code and the testing has been carried out by performing series of source inversion runs using the data of 200 indivi...

A dispersion modeling of airborne pollutants in urban environments using RANS CFD codes is usually based on mean and variance concentration Eulerian transport equations. An alternative could be to use simple Lagrangian approaches with the detailed flow parametrization provided by the CFD codes. The Lagrangian approaches have been approved quite suc...

Computational Fluid Dynamics (CFD) is applied to analyse the flow and the concentration patterns of floor-emitted pollutants inside a mechanically ventilated office of simple geometry. The simulation results show complex airflow and high heterogeneity of concentration distribution. Alternative scenarios mainly of the vents’ position and airflow str...

Please refer to published version of this article Kovalets et al. (2018) Atmos. Env. 181:82-9 https://www.researchgate.net/publication/323726600_Inverse_identification_of_unknown_finite-duration_air_pollutant_release_from_a_point_source_in_urban_environment

The paper presents a Computational Fluid Dynamics (CFD) approach based on a finite volume technique for the modelling of pollutant dispersion from a real industrial accident, by applying a Large Eddy Simulation (LES) model for the turbulence-related quantities while the sub-grid scale (SGS) modelling is achieved by the classic Smagorinsky model bas...

A dispersion modeling of airborne pollutants in urban environments using RANS CFD codes is usually based on mean and variance concentration Eulerian transport equations. An alternative could be to use simple Lagrangian approaches with the detailed flow parametrization provided by the CFD codes. The Lagrangian approaches have been approved quite suc...

In HEALS Project, in the frame of the development of an integrated external exposure assessment methodology, there was a need to provide comprehensive environmental support data covering important stressors across all environmental media. The HEALS environmental data management system (EDMS) besides accommodating HEALS own datasets is able to retri...

The material intensity (MI) of the economy remains among the most widely cited indicators in international statistics and reports, evaluating the efficient use and productivity of natural resources in the economic process. In the context of the contemporary economy-wide material flow accounting framework, the material intensity of a country is eval...

Published in Atmospheric Environment (2018) , DOI: 10.1016/j.atmosenv.2018.03.028.
Full text freely available here: https://www.researchgate.net/publication/323726600_Inverse_identification_of_unknown_finite-duration_air_pollutant_release_from_a_point_source_in_urban_environment

The deliberate or accidental airborne releases of hazardous chemical, radioactive or bacteriological substances in urban areas is of primary concern in view of increasing urbanization and resulting localization of human living. The basis of efficient emergency management to cope with those problems is the ability to reliably predict the individual...

Wind fields in the atmospheric surface layer (ASL) are highly three-dimensional and characterized by strong spatial and temporal variability. For various applications such as wind-comfort assessments and structural design, an understanding of potentially hazardous wind extremes is important. Statistical models are designed to facilitate conclusions...

The wide range of values observed in a measured concentration time series after the release of a dispersing airborne pollutant from a point source in the atmospheric boundary layer, and the hazard level associated with the peak values, demonstrate the necessity of predicting the concentration probability distribution. For this, statistical models d...

An improved inverse modelling method to estimate the location and the emission rate of an unknown
point stationary source of passive atmospheric pollutant in a complex urban geometry is incorporated in
the Computational Fluid Dynamics code ADREA-HF and presented in this paper. The key improvement in
relation to the previous version of the method li...

This work presents the Computational Fluid Dynamics (CFD) – Reynolds-Averaged Navier Stokes (RANS) simulation and results of the dispersion of a hazardous airborne material which was released during a real accident in an industrial facility. During the event the material was released as flashing liquid from a point located inside a building, partia...

One of the key issues of recent research on the dispersion inside complex urban environments is the ability to predict individual exposure (maximum dosages) of an airborne material which is released continuously from a point source. The present work addresses the question whether the computational fluid dynamics (CFD)–Reynolds-averaged Navier–Stoke...

An improved inverse method was presented recently for the estimation of the location and the rate of an unknown point stationary source of passive at-mospheric pollutant in a complex urban geometry. The inverse method was incorporated in the well-established and updated version of the ADREA-HF Computational Fluid Dynamics code. The key improvement...

The peak values observed in a measured concentration time series of a dispersing gaseous pollutant released continuously from a point source in urban environments, and the hazard level associated with them, demonstrate the necessity of predicting the upper tail of concentration distributions. For the prediction of concentration distributions statis...

In developed countries, office workers spend at least five days a week in the office environment. Consequently, the indoor air quality in these locations must be maintained to a high standard to avoid impacts on human health. Exposure models for indoor air pollution have traditionally focused on primary pollutants, although there is increasing evid...

The atmospheric release of hazardous materials in urban or industrial environments can be the result of an accident, with potential consequences in local or regional scale, or can be an intentional act of violence. In such cases the highest uncertainty is associated with the location of the release and the quantity of the released substance. So far...

In Kovalets et al. (2011), a method was developed to estimate the location and rate of an unknown point stationary source of passive atmospheric pollutant in a complex urban geometry. The algorithm was implemented in the ADREA-HF Computational Fluid Dynamics code and was applied in a complex urban geometry (the MUST wind tunnel experiment). This ap...

A main research task of COST Action ES1006 is the evaluation of atmospheric dispersion models by their comparison against test data from qualified field and laboratory experiments and by a model inter-comparison. The model comparison and evaluation carried out for three test cases is presented, addressing the performance of the different modelling...

New schemes for calculating particles dry and wet deposition have been implemented in the Local Scale Model Chain of RODOS in the frame of Work Package 4 of project PREPARE. Care has been taken not to increase computational times and at the same time, simulations performed with previous deposition schemes to be reproducible. The new schemes take in...

Within the framework of the EPHECT project (Emissions, exposure patterns and health effects of consumer products in the EU), irritative and respiratory health effects were assessed in relation to acute and long-term exposure to key and emerging indoor air pollutants emitted during household use of selected consumer products. In this context, inhala...

The capability to predict short-term maximum individual exposure is very important for several applications including, for example, deliberate/accidental release of hazardous substances, odour fluctuations or material flammability level exceedance. Recently, authors have proposed a simple approach relating maximum individual exposure to parameters...