The Experts below are selected from a list of 186 Experts worldwide ranked by ideXlab platform
Mohamed Naaim - One of the best experts on this subject based on the ideXlab platform.
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Avalanche risk evaluation and protective dam optimal design using extreme value statistics
Journal of Glaciology, 2016Co-Authors: P. Favier, Thierry Faug, D. Bertrand, N. Eckert, Mohamed NaaimAbstract:In snow avalanche long-term forecasting, existing risk-based methods remain difficult to use in a real engineering context. In this work, we expand a quasi analytical decisional model to obtain simple formulae to quantify risk and to perform the optimal design of an avalanche dam in a quick and efficient way. Specifically, the exponential runout model is replaced by the Generalized Pareto distribution (GPD), which has theoretical justifications that promote its use for modelling the different possible runout tail behaviours. Regarding the Defence Structure/flow interaction, a simple law based on kinetic energy dissipation is compared with a law based on the volume stored upstream of the dam, whose flexibility allows us to cope with various types of snow. We show how a detailed sensitivity study can be conducted, leading to intervals and bounds for risk estimates and optimal design values. Application to a typical case study from the French Alps, highlights potential operational difficulties and how they can be tackled. For instance, the highest sensitivity to the runout tail type and interaction law is found at abscissas of legal importance for hazard zoning (return periods of 10-1000 a), a crucial result for practical purposes.
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Optimal design of snow avalanche passive Defence Structure using reliability approach to quantify buildings vulnerability
2012Co-Authors: Pascale Favier, Nicolas Eckert, D. Bertrand, Mohamed NaaimAbstract:To protect elements at risk (humans, roads, houses, etc.) against snow avalanches, civil engineering Structures, such as dams or mounds, are used. The design of such Defence Structures is done following a deterministic approach which considers European regulation. The minimization of expected total losses is an interesting alternative that generalizes cost-benefit approach to a continuous decision variable. For this purpose, not only the hazard magnitude but also the buildings vulnerability must be evaluated carefully. The aim of this work is therefore to combine state of the art sub-models for the probabilistic description of avalanche flows and the numerical evaluation of damages to buildings. We defined the risk as the expectation of the cost consequences of avalanches activity. Disposal consequences are quantified thanks to reliability methods. In this formulation, the accuracy of both the hazard estimation and the vulnerability calculation has to be consistent according to precision and computational costs. To do so, a numerical approach has been developed to evaluate the physical vulnerability of concrete buildings submitted to avalanche loadings. The ensuing application illustrates our approach. A reinforced concrete slab is considered to model the building with a finite element method. Reliability approach enables to produce a response spectrum of the Structure against avalanche impact. Finally, vulnerability curves are built. Outcomes of the risk calculation are examined to find sensitivity on the optimal design of snow Defence Structures.
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Comparison between three avalanche test sites in northwestern Alps as developed in the DYNAVAL-Alcotra project
2011Co-Authors: L. Pitet, Florence Naaim-bouvet, Mohamed Naaim, V. Segor, H. Bellot, P. Caccamo, F. Ousset, E. Thibert, X. Ravanat, Thierry FaugAbstract:Within the Operational programme 'Italy - France (Alps - ALCOTRA) 'Project DynAval - Dynamique des avalanches: départ et interactions écoulement/obstacles three test sites were built or developed in France and Italy. The goal of the paper is to present the experimental devices and typical pressure generated by avalanches in these 3 sites differing mainly by their scale. (a) Seehore test site is located in Aosta Valley on Monte Rosa Massif. The slope, with an altitude difference of about 300 m (from 2300 to 2570 m a.s.l.), has a mean dip of about 38°. The site is instrumented with a steel obstacle on which load cells and other devices are mounted in order to measure the effects of impact of the avalanche. Surveys are made before and after each artificial event: snow density, front velocity, erosion and deposition are measured and photogrammetric and laser-scanner views are taken. (b) Col du Lautaret test site is located near the Lautaret pass (2058 m a.s.l) between Cerces and Ecrins range. Different avalanche paths are located on the south-east slope of Chaillol Mountain (2600 m a.s.l.). Small to medium avalanches occur at a sufficient frequency (up to 3 or 4 each winter). Avalanche flows are generally dense, wet or dry, with sometimes a small but fast powder cloud (or saltation layer). The dense part is usually less than one meter thick. The run-out distance is 500 to 800 m with an average gradient of 36°. Typical released volume is about 5000 m3 and front velocity can reach 30 m/s. Instrumentation includes a 3 m-high mast recording pressure and velocity each 20 cm, and a one square meter plate integrating the pressure all over the flow height. A high speed photogrammetric system is able to measure the avalanche front velocity. (c) The Taconnaz avalanche path is located in the Arves valley, close to Mont Blanc in France. The Taconnaz path is 7 km long, has a mean slope of 25° and a mean width of 300400 m. A Defence Structure system made of breaking mounds and dams was designed in 2009 based on a 100-year return period event of 1.6 Mm3 volume. In 2010, velocity and pressure sensors were set up on the breaking mounds in order to improve our knowledge of the interaction between avalanches and breaking dams.
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return period calculation and passive Structure design at the taconnaz avalanche path france
Annals of Glaciology, 2010Co-Authors: Mohamed Naaim, Thierry Faug, Florence Naaim, Nicolas EckertAbstract:This paper aims to show how recent knowledge developed in the field of avalanche research can be used for a real case study, the Taconnaz avalanche path, where passive Structures already existed but had to be improved. First a morphological analysis of the site is done and historical data are analysed. Second, each recorded event is back-calculated using a numerical model of dense-flow avalanches. For each surveyed avalanche, parameters at the entry of the runout zone upstream of the Defence Structures are defined. Third, a statistical analysis of these parameters allows characterization of 100 year return period events. Fourth, physical and numerical models of dense avalanches interacting with Defence Structures are combined in order to design the most effective passive Structure able to contain the reference scenarios. Finally, physical and numerical modelling of the interaction between the powder avalanche and the designed Defence Structure is performed, to show that the proposed improvements do not increase the residual risk due to the powder part in areas downstream of the Defence Structures.
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An equation for spreading length, centre of mass and maximum run-out shortenings of dense avalanche flows by vertical obstacles
Cold Regions Science and Technology, 2004Co-Authors: Thierry Faug, Mohamed Naaim, Florence Naaim-bouvetAbstract:In this paper, we consider dense snow avalanches interacting with a Defence Structure. The maximum run-out distance of dense snow avalanches is the sum of the centre of mass run-out and the spreading length. We make the simplifying assumptions that the centre of mass run-out is mainly dependent on the velocity of the avalanche flow and the spreading length is mainly linked to the volume of the deposit. The obstacle reduces momentum of the avalanche by (i) velocity reduction and (ii) mass reduction by deposition upstream of the obstacle. The first effect leads to the shortening of the centre of mass run-out and the second one explains the spreading length decrease. Therefore, the maximum run-out reduction is a function of both velocity and volume reductions. An equation is proposed to predict the maximum run-out reduction. This equation is tested on small-scale granular avalanches. For laboratory experiments with confined granular avalanches interacting with a thin vertical dam, velocity and volume reductions are expressed as simple functions of the vertical dam height. The equation for the maximum run-out shortening is then calibrated on experimental data and used to predict the velocity reduction and the critical height for which the granular avalanche is entirely stopped by the vertical dam.
Nicolas Eckert - One of the best experts on this subject based on the ideXlab platform.
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Optimal design of snow avalanche passive Defence Structure using reliability approach to quantify buildings vulnerability
2012Co-Authors: Pascale Favier, Nicolas Eckert, D. Bertrand, Mohamed NaaimAbstract:To protect elements at risk (humans, roads, houses, etc.) against snow avalanches, civil engineering Structures, such as dams or mounds, are used. The design of such Defence Structures is done following a deterministic approach which considers European regulation. The minimization of expected total losses is an interesting alternative that generalizes cost-benefit approach to a continuous decision variable. For this purpose, not only the hazard magnitude but also the buildings vulnerability must be evaluated carefully. The aim of this work is therefore to combine state of the art sub-models for the probabilistic description of avalanche flows and the numerical evaluation of damages to buildings. We defined the risk as the expectation of the cost consequences of avalanches activity. Disposal consequences are quantified thanks to reliability methods. In this formulation, the accuracy of both the hazard estimation and the vulnerability calculation has to be consistent according to precision and computational costs. To do so, a numerical approach has been developed to evaluate the physical vulnerability of concrete buildings submitted to avalanche loadings. The ensuing application illustrates our approach. A reinforced concrete slab is considered to model the building with a finite element method. Reliability approach enables to produce a response spectrum of the Structure against avalanche impact. Finally, vulnerability curves are built. Outcomes of the risk calculation are examined to find sensitivity on the optimal design of snow Defence Structures.
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return period calculation and passive Structure design at the taconnaz avalanche path france
Annals of Glaciology, 2010Co-Authors: Mohamed Naaim, Thierry Faug, Florence Naaim, Nicolas EckertAbstract:This paper aims to show how recent knowledge developed in the field of avalanche research can be used for a real case study, the Taconnaz avalanche path, where passive Structures already existed but had to be improved. First a morphological analysis of the site is done and historical data are analysed. Second, each recorded event is back-calculated using a numerical model of dense-flow avalanches. For each surveyed avalanche, parameters at the entry of the runout zone upstream of the Defence Structures are defined. Third, a statistical analysis of these parameters allows characterization of 100 year return period events. Fourth, physical and numerical models of dense avalanches interacting with Defence Structures are combined in order to design the most effective passive Structure able to contain the reference scenarios. Finally, physical and numerical modelling of the interaction between the powder avalanche and the designed Defence Structure is performed, to show that the proposed improvements do not increase the residual risk due to the powder part in areas downstream of the Defence Structures.
Thierry Faug - One of the best experts on this subject based on the ideXlab platform.
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Avalanche risk evaluation and protective dam optimal design using extreme value statistics
Journal of Glaciology, 2016Co-Authors: P. Favier, Thierry Faug, D. Bertrand, N. Eckert, Mohamed NaaimAbstract:In snow avalanche long-term forecasting, existing risk-based methods remain difficult to use in a real engineering context. In this work, we expand a quasi analytical decisional model to obtain simple formulae to quantify risk and to perform the optimal design of an avalanche dam in a quick and efficient way. Specifically, the exponential runout model is replaced by the Generalized Pareto distribution (GPD), which has theoretical justifications that promote its use for modelling the different possible runout tail behaviours. Regarding the Defence Structure/flow interaction, a simple law based on kinetic energy dissipation is compared with a law based on the volume stored upstream of the dam, whose flexibility allows us to cope with various types of snow. We show how a detailed sensitivity study can be conducted, leading to intervals and bounds for risk estimates and optimal design values. Application to a typical case study from the French Alps, highlights potential operational difficulties and how they can be tackled. For instance, the highest sensitivity to the runout tail type and interaction law is found at abscissas of legal importance for hazard zoning (return periods of 10-1000 a), a crucial result for practical purposes.
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Comparison between three avalanche test sites in northwestern Alps as developed in the DYNAVAL-Alcotra project
2011Co-Authors: L. Pitet, Florence Naaim-bouvet, Mohamed Naaim, V. Segor, H. Bellot, P. Caccamo, F. Ousset, E. Thibert, X. Ravanat, Thierry FaugAbstract:Within the Operational programme 'Italy - France (Alps - ALCOTRA) 'Project DynAval - Dynamique des avalanches: départ et interactions écoulement/obstacles three test sites were built or developed in France and Italy. The goal of the paper is to present the experimental devices and typical pressure generated by avalanches in these 3 sites differing mainly by their scale. (a) Seehore test site is located in Aosta Valley on Monte Rosa Massif. The slope, with an altitude difference of about 300 m (from 2300 to 2570 m a.s.l.), has a mean dip of about 38°. The site is instrumented with a steel obstacle on which load cells and other devices are mounted in order to measure the effects of impact of the avalanche. Surveys are made before and after each artificial event: snow density, front velocity, erosion and deposition are measured and photogrammetric and laser-scanner views are taken. (b) Col du Lautaret test site is located near the Lautaret pass (2058 m a.s.l) between Cerces and Ecrins range. Different avalanche paths are located on the south-east slope of Chaillol Mountain (2600 m a.s.l.). Small to medium avalanches occur at a sufficient frequency (up to 3 or 4 each winter). Avalanche flows are generally dense, wet or dry, with sometimes a small but fast powder cloud (or saltation layer). The dense part is usually less than one meter thick. The run-out distance is 500 to 800 m with an average gradient of 36°. Typical released volume is about 5000 m3 and front velocity can reach 30 m/s. Instrumentation includes a 3 m-high mast recording pressure and velocity each 20 cm, and a one square meter plate integrating the pressure all over the flow height. A high speed photogrammetric system is able to measure the avalanche front velocity. (c) The Taconnaz avalanche path is located in the Arves valley, close to Mont Blanc in France. The Taconnaz path is 7 km long, has a mean slope of 25° and a mean width of 300400 m. A Defence Structure system made of breaking mounds and dams was designed in 2009 based on a 100-year return period event of 1.6 Mm3 volume. In 2010, velocity and pressure sensors were set up on the breaking mounds in order to improve our knowledge of the interaction between avalanches and breaking dams.
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return period calculation and passive Structure design at the taconnaz avalanche path france
Annals of Glaciology, 2010Co-Authors: Mohamed Naaim, Thierry Faug, Florence Naaim, Nicolas EckertAbstract:This paper aims to show how recent knowledge developed in the field of avalanche research can be used for a real case study, the Taconnaz avalanche path, where passive Structures already existed but had to be improved. First a morphological analysis of the site is done and historical data are analysed. Second, each recorded event is back-calculated using a numerical model of dense-flow avalanches. For each surveyed avalanche, parameters at the entry of the runout zone upstream of the Defence Structures are defined. Third, a statistical analysis of these parameters allows characterization of 100 year return period events. Fourth, physical and numerical models of dense avalanches interacting with Defence Structures are combined in order to design the most effective passive Structure able to contain the reference scenarios. Finally, physical and numerical modelling of the interaction between the powder avalanche and the designed Defence Structure is performed, to show that the proposed improvements do not increase the residual risk due to the powder part in areas downstream of the Defence Structures.
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An equation for spreading length, centre of mass and maximum run-out shortenings of dense avalanche flows by vertical obstacles
Cold Regions Science and Technology, 2004Co-Authors: Thierry Faug, Mohamed Naaim, Florence Naaim-bouvetAbstract:In this paper, we consider dense snow avalanches interacting with a Defence Structure. The maximum run-out distance of dense snow avalanches is the sum of the centre of mass run-out and the spreading length. We make the simplifying assumptions that the centre of mass run-out is mainly dependent on the velocity of the avalanche flow and the spreading length is mainly linked to the volume of the deposit. The obstacle reduces momentum of the avalanche by (i) velocity reduction and (ii) mass reduction by deposition upstream of the obstacle. The first effect leads to the shortening of the centre of mass run-out and the second one explains the spreading length decrease. Therefore, the maximum run-out reduction is a function of both velocity and volume reductions. An equation is proposed to predict the maximum run-out reduction. This equation is tested on small-scale granular avalanches. For laboratory experiments with confined granular avalanches interacting with a thin vertical dam, velocity and volume reductions are expressed as simple functions of the vertical dam height. The equation for the maximum run-out shortening is then calibrated on experimental data and used to predict the velocity reduction and the critical height for which the granular avalanche is entirely stopped by the vertical dam.
Eleonora Ardemagni - One of the best experts on this subject based on the ideXlab platform.
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Yemen’s Defence Structure: Hybridity and Patronage after the State
Journal of Arabian Studies, 2020Co-Authors: Eleonora ArdemagniAbstract:Yemen’s Defence Structure presents a dynamic of “double hybridization”: hybridization due to the overlapping of tribal and military roles and loyalties, and hybridization because of the vague bound...
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yemen s Defence Structure hybridity and patronage after the state
The Journal of Arabian Studies, 2020Co-Authors: Eleonora ArdemagniAbstract:Yemen’s Defence Structure presents a dynamic of “double hybridization”: hybridization due to the overlapping of tribal and military roles and loyalties, and hybridization because of the vague bound...
Wu Zhi-ping - One of the best experts on this subject based on the ideXlab platform.
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Anti-Blast Experimental Study on the Gateway of Civil Defence Structure Strengthened by Steel Plate
Chinese Journal of Underground Space and Engineering, 2007Co-Authors: Wu Zhi-pingAbstract:By similar design to the joint Structure of bonded steel plate to carry out an on-site test in the nuclear blast pressure imitation container,the three dimensional FEM is adopted to a gateway of civil defense Structure of a typical garage closed up by steel plates,obtaining the displacement and strain to move in response to the timing of nodes of vertical abutment steel plate,and the numerical results agree with the analytical results with reasonable reliability.It is proved that the joint Structure of bonded steel plate can be safely used,in case of suffering from grade 6 civil air defensive blast shock wave.In the meantime,this method is proved to be possible and optimal for functional transformation from peacetime to wartime.
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Three Dimensional Finite Element Analysis of the Gateway of Defence Structure Strengthened with Steel Plate
Journal of Shanghai Institute of Technology, 2007Co-Authors: Wu Zhi-pingAbstract:In this paper,by bonding steel plates the desiqn project of a gateway of a typical garage is carried out,and three dimensional FEM is adapted to a gateway of defense Structure of a typical garage streugthened by steel plates.A 3D friction contact element method is developed in this paper.The results show that the technology of strengthening by bonding steel plates can fulfill the design ability of a gateway of defense Structure to close up a typical garage.And the method proves to be of possibility used for functional transformation from peacetime to wartime.
