Design of Controlled Pre-Split Blasting in a Hydroelectric Construction Project

Geologic conditions and design requirements around upstream Nachtigal Falls, in Cameroon, for the hydroelectric construction project on the Sanaga River dictated close control of blasting procedures with very precise geometry to obtain safe and economical excavation lines. Various techniques of pre-split blasting were used in the initial stage of all major excavations. Hole diameters for pre-splitting were 89 mm, and hole spacing ranged from 0.8 to 1m. Explosive charges varied from 1 to 7 kg per hole, and the detonating cord linear charge ranged from 12 to 60g. The contour blasting technique is aimed at controlling overbreak and improving remaining slope stability. Over-break or over-excavation needs to be controlled since its occurrence compromises the operations in terms of safety (instability in the remaining slope; loosening rocks that increase the risk for operational people; an irregular free face for subsequent blasting); and costs (need for reinforcement of the remaining rock structure through costly sustainment systems; increase in concrete volumes in civil works). This paper discusses in detail the design and field implementation of pre-split blasts successfully carried out to achieve clean vertical walls in moderately dipping, though complexly sheared and jointed gneiss. Based on the results of the experiments, we were able to design a pre-splitting pattern both experimentally and in a very cost-effective manner. It is felt that the methods developed on this project could have useful applications on other major construction projects. Doi: 10.28991/CEJ-2023-09-03-05 Full Text: PD

Simulation et optimisation des systèmes de production de l’eau chaude sanitaire solaire

The world market for solar water heaters (SWH) is in great expansion. In fact, SWHs have become a challenging alternative system to gas and electric heating devices, because of their low CO2 emissions and their explicit involvement in the reduction of the building’s electric bills. L’institut de recherche en énergie solaire et énergies nouvelles (IRESEN-Morocco) is actually providing the necessary funding support to promote research and development field of SWHs in Morocco. Hence, in February 2016, SOL’R SHEMSY project has been defined in order to design and commercialize the first SWH integrating Evacuated Tube Collectors (ETC) with heat pipes, under the constraints of being accessible to the Moroccan public users. For the time being, several technologies of solar collectors with different brands are commercialized in Morocco such as flat plat collectors (FPC) and Evacuated Tube Collectors (ETC), besides to thermosyphon and forced circulation SWHs to convert solar energy to thermal energy, in order to produce hot water with the temperature required in several applications (individual, collective, industrial and the tertiary applications). However, a serious challenge of adjustment, integration and technology transfer should be considered before importing SWHs with ETC into the Moroccan market from supplier countries such as China, Spain, Germany and Turkey described as the leading manufacturer of SWH in the world. Indeed, the imported SWHs in Morocco presented thermo-mechanical failure modes after a short period of use such as the limestone deposited inside the storage tanks, corrosion and cracking of their inner shell... Taking into account the challenge of adjustment, integration and technology transfer of SWHs in Morocco is necessary, because the conditions of use differ from one country to another in terms of climatic conditions, which can be summarized in solar radiations, ambient temperature, wind velocity and the percentage of humidity in the air. In addition, the consumer's random consumption profile usually affects the thermal efficiency of the collector field and the overall solar fraction of SWHs.The main aim of this thesis is to carry out numerical simulations and optimizations of SWHs taking into account the techno-economic context of Morocco and its intrinsic weather conditions. Two simulation approaches were used to achieve this purpose. The first approach was based on unsteady Computational Fluid Dynamics (CFD) numerical simulation in order to enhance the efficiency of the heat pipes integrated inside ETCs and to increase the thermal stratification indicators of horizontal thermal storage tanks with submerged heat pipes. Finally, improve the storage tank’s structure using thermo-mechanical coupling simulations. The second approach is based on dynamic simulations, which have been performed to assess and optimize the energy performance of a collective hot water process intended to produce domestic hot water (DHW) under the climatic conditions of Fez city located in Morocco. Indeed, several parameters have been considered, in particular the effect of the storage tank volume, the brands of collectors and their technology from different manufacturers, the connection between the solar panel and the overall surface of the ETC and FPC which constitute the collector field etc.Le marché mondial des chauffe-eau solaires (CES) est en essor. En effet, les CES sont devenus des systèmes compétitifs aux appareils de chauffage par gaz naturel et énergie électrique, en raison de leurs faibles émissions de CO2 et de leur participation explicite à la réduction des factures d'électricité du consommateur marocain. Actuellement, l'Institut de Recherche en Energie Solaire et Energies Nouvelles (IRESEN-Maroc) pourvoit le soutien financier nécessaire pour promouvoir la recherche et le développement dans le domaine des CES au Maroc. Ainsi, en février 2016, le projet SOL'R SHEMSY a été défini pour concevoir et commercialiser le premier CES intégrant la technologie des capteurs à tubes sous vide (ETC) avec des caloducs, en rendant son acquisition accessible au sociale marocain. Il paraît qu'à l'heure actuelle, plusieurs technologies de capteurs solaires de marques différentes sont commercialisées au Maroc tels que les capteurs plan (FPC) et les capteurs à tube sous vide (ETC), outre le thermosiphon et les CES à circulation forcée pour convertir l'énergie solaire en une énergie thermique, afin de produire de l'eau chaude avec la température requise dans plusieurs applications individuelles, collectives, industrielles et tertiaires. Cependant, une sérieuse problématique d'ajustement, d'intégration et de transfert technologique devrait être envisagée avant d'importer les CES à capteur ETC munis de caloduc sur le marché marocain auprès de pays fournisseurs tels que la Chine, l'Espagne, l'Allemagne et la Turquie considérés comme des leaders internationaux dans le domaine des CES. Car en effet, les CES importés au Maroc ont présenté des modes de défaillances thermomécaniques après une courte période d'utilisation, comme le dépôt de calcaire à l'intérieur des ballons de stockage, la corrosion et la fissuration de leur coque interne...Prendre en considération la problématique d'ajustement, de l'intégration et du transfert technologique des CES au marché marocain est nécessaire, étant donné que les conditions d'utilisation diffèrent d'un pays à un autre en termes de conditions climatiques, qui peuvent être résumées par l’amplitude de l’irradiation solaire, la température ambiante, la vitesse du vent et le pourcentage de l’humidité dans l'air. Par ailleurs, le profil de consommation aléatoire du consommateur affecte à son tour l'efficacité thermique du champ de capteurs et la fraction solaire globale des CES.L'objectif principal de cette thèse est de mener des simulations numériques et des optimisations qui portent sur les CES, en prenant en compte le contexte technico-économique du Maroc et ses conditions climatiques intrinsèques. Deux approches de simulation ont été utilisées pour atteindre cet objectif. La première approche s’est basée sur des simulations numériques CFD (Computational Fluid Dynamics) instationnaires pour améliorer l'efficacité énergétique des caloducs intégrés dans les ETC et d'augmenter les indicateurs de stratification thermique des ballons horizontaux dans lesquels les caloducs sont immergés. Enfin, d’améliorer la structure du réservoir du CES en utilisant des simulations qui permettent de modéliser un couplage thermomécanique. La deuxième approche est basée sur des simulations dynamiques, qui ont été menées pour évaluer et optimiser la performance énergétique d'un système collectif destiné à produire de l'eau chaude sanitaire (ECS) sous les conditions climatiques de la ville de Fès-Maroc. En effet, plusieurs paramètres ont été considérés, en particulier l'effet du volume du réservoir de stockage, les marques des capteurs, leurs rendements et leurs technologies issues de différents fabricants, et finalement l’effet de la connexion série/parallèle et mixte entre les panneaux solaires (ETC et FPC) qui constituent le champ capteur, etc

Simulation and optimization of solar domestic hot water production systems

Le marché mondial des chauffe-eau solaires (CES) est en essor. En effet, les CES sont devenus des systèmes compétitifs aux appareils de chauffage par gaz naturel et énergie électrique, en raison de leurs faibles émissions de CO2 et de leur participation explicite à la réduction des factures d'électricité du consommateur marocain. Actuellement, l'Institut de Recherche en Energie Solaire et Energies Nouvelles (IRESEN-Maroc) pourvoit le soutien financier nécessaire pour promouvoir la recherche et le développement dans le domaine des CES au Maroc. Ainsi, en février 2016, le projet SOL'R SHEMSY a été défini pour concevoir et commercialiser le premier CES intégrant la technologie des capteurs à tubes sous vide (ETC) avec des caloducs, en rendant son acquisition accessible au sociale marocain. Il paraît qu'à l'heure actuelle, plusieurs technologies de capteurs solaires de marques différentes sont commercialisées au Maroc tels que les capteurs plan (FPC) et les capteurs à tube sous vide (ETC), outre le thermosiphon et les CES à circulation forcée pour convertir l'énergie solaire en une énergie thermique, afin de produire de l'eau chaude avec la température requise dans plusieurs applications individuelles, collectives, industrielles et tertiaires. Cependant, une sérieuse problématique d'ajustement, d'intégration et de transfert technologique devrait être envisagée avant d'importer les CES à capteur ETC munis de caloduc sur le marché marocain auprès de pays fournisseurs tels que la Chine, l'Espagne, l'Allemagne et la Turquie considérés comme des leaders internationaux dans le domaine des CES. Car en effet, les CES importés au Maroc ont présenté des modes de défaillances thermomécaniques après une courte période d'utilisation, comme le dépôt de calcaire à l'intérieur des ballons de stockage, la corrosion et la fissuration de leur coque interne...Prendre en considération la problématique d'ajustement, de l'intégration et du transfert technologique des CES au marché marocain est nécessaire, étant donné que les conditions d'utilisation diffèrent d'un pays à un autre en termes de conditions climatiques, qui peuvent être résumées par l’amplitude de l’irradiation solaire, la température ambiante, la vitesse du vent et le pourcentage de l’humidité dans l'air. Par ailleurs, le profil de consommation aléatoire du consommateur affecte à son tour l'efficacité thermique du champ de capteurs et la fraction solaire globale des CES.L'objectif principal de cette thèse est de mener des simulations numériques et des optimisations qui portent sur les CES, en prenant en compte le contexte technico-économique du Maroc et ses conditions climatiques intrinsèques. Deux approches de simulation ont été utilisées pour atteindre cet objectif. La première approche s’est basée sur des simulations numériques CFD (Computational Fluid Dynamics) instationnaires pour améliorer l'efficacité énergétique des caloducs intégrés dans les ETC et d'augmenter les indicateurs de stratification thermique des ballons horizontaux dans lesquels les caloducs sont immergés. Enfin, d’améliorer la structure du réservoir du CES en utilisant des simulations qui permettent de modéliser un couplage thermomécanique. La deuxième approche est basée sur des simulations dynamiques, qui ont été menées pour évaluer et optimiser la performance énergétique d'un système collectif destiné à produire de l'eau chaude sanitaire (ECS) sous les conditions climatiques de la ville de Fès-Maroc. En effet, plusieurs paramètres ont été considérés, en particulier l'effet du volume du réservoir de stockage, les marques des capteurs, leurs rendements et leurs technologies issues de différents fabricants, et finalement l’effet de la connexion série/parallèle et mixte entre les panneaux solaires (ETC et FPC) qui constituent le champ capteur, etc.The world market for solar water heaters (SWH) is in great expansion. In fact, SWHs have become a challenging alternative system to gas and electric heating devices, because of their low CO2 emissions and their explicit involvement in the reduction of the building’s electric bills. L’institut de recherche en énergie solaire et énergies nouvelles (IRESEN-Morocco) is actually providing the necessary funding support to promote research and development field of SWHs in Morocco. Hence, in February 2016, SOL’R SHEMSY project has been defined in order to design and commercialize the first SWH integrating Evacuated Tube Collectors (ETC) with heat pipes, under the constraints of being accessible to the Moroccan public users. For the time being, several technologies of solar collectors with different brands are commercialized in Morocco such as flat plat collectors (FPC) and Evacuated Tube Collectors (ETC), besides to thermosyphon and forced circulation SWHs to convert solar energy to thermal energy, in order to produce hot water with the temperature required in several applications (individual, collective, industrial and the tertiary applications). However, a serious challenge of adjustment, integration and technology transfer should be considered before importing SWHs with ETC into the Moroccan market from supplier countries such as China, Spain, Germany and Turkey described as the leading manufacturer of SWH in the world. Indeed, the imported SWHs in Morocco presented thermo-mechanical failure modes after a short period of use such as the limestone deposited inside the storage tanks, corrosion and cracking of their inner shell... Taking into account the challenge of adjustment, integration and technology transfer of SWHs in Morocco is necessary, because the conditions of use differ from one country to another in terms of climatic conditions, which can be summarized in solar radiations, ambient temperature, wind velocity and the percentage of humidity in the air. In addition, the consumer's random consumption profile usually affects the thermal efficiency of the collector field and the overall solar fraction of SWHs.The main aim of this thesis is to carry out numerical simulations and optimizations of SWHs taking into account the techno-economic context of Morocco and its intrinsic weather conditions. Two simulation approaches were used to achieve this purpose. The first approach was based on unsteady Computational Fluid Dynamics (CFD) numerical simulation in order to enhance the efficiency of the heat pipes integrated inside ETCs and to increase the thermal stratification indicators of horizontal thermal storage tanks with submerged heat pipes. Finally, improve the storage tank’s structure using thermo-mechanical coupling simulations. The second approach is based on dynamic simulations, which have been performed to assess and optimize the energy performance of a collective hot water process intended to produce domestic hot water (DHW) under the climatic conditions of Fez city located in Morocco. Indeed, several parameters have been considered, in particular the effect of the storage tank volume, the brands of collectors and their technology from different manufacturers, the connection between the solar panel and the overall surface of the ETC and FPC which constitute the collector field etc

CFD comparison of 2D and 3D aerodynamics in H-Darrieus prototype wake

In the present study, a comparative assessment is conducted to evaluate the outcomes derived from two-dimensional (2D) and three-dimensional (3D) computational fluid dynamics (CFD) models utilizing the unsteady Reynolds-averaged Navier–Stokes (URANS) approach. The focus lies on the aerodynamic performance of the H-Darrieus vertical axis wind turbine, which has been the subject of numerous numerical investigations since 2010. The k−ω shear stress transport (SST) turbulence model is employed to replicate the flow structures evolving in the turbine wake.The maximum power coefficients attained through 2D and 3D modeling are reported as Cp=0.4016 and Cp=0.5734, respectively, at a tip speed ratio (λ) of 3.0976. The maximum 2D and 3D absolute errors, corresponding to the evaluation of the power coefficients, are determined to be 14.9714% and 29.1582%, respectively. These errors are calculated at λ=2.5183 and λ=3.0976. The parametric study conducted herein reveals that the range of the power coefficient enhancement, considering 3D aerodynamic effects, surpasses that obtained from 2D calculations. In 3D modeling, this range is delineated between λ=1.85 and λ=3.10, whereas, in 2D modeling, it is defined by the interval bounded by λ=2.05 and λ=3.10. The essential contours for comparing the 2D and 3D approaches and for characterizing the flow structures developing around the H-Darrieus turbine are generated and analyzed

Experimental and statistical analysis of blast-induced ground vibrations (BIGV) prediction in Senegal's quarry

Extractive industries often use explosives to destroy rocks, and productivity requirements tend to increase the charges of the explosives. The blasts induce vibrations, which result in a potential damage of the surrounding structures. Therefore, the prediction of vibrations should be described with accuracy, in order to ensure the safety of engineered structures. However, the prediction of vibrations' levels remain a complicated issue, because it involves numerous parameters correlated to the quarry site. In this paper, statistical analysis based on the peak particle velocity (PPV) and the attenuation law has been carried out to assess the safety charges (Q) for different distances (R) between the blast and the considered structure to secure. Moreover, the experimental investigations were conducted on the quarry site of "Sococim", which is located on the south coast of Senegal. To ensure the safety of the "Conveyor belt" and "Panel 1 (Upper exploitation level)" sites, the PPV should be less than 10 mm/s. In fact, the attenuation model has been used to assess the safe charge weights of the explosive (Q) to be used at the "Conveyor belt" site and at the "Panel 1 (Upper exploitation level)" site. Therefore, the safe charge weights per delay (Q) were respectively 116 kg and 13.75 kg

Experimental and statistical analysis of blast-induced ground vibrations ( BIGV

Extractive industries often use explosives to destroy rocks, and productivity requirements tend to increase the charges of the explosives. The blasts induce vibrations, which result in a potential damage of the surrounding structures. Therefore, the prediction of vibrations should be described with accuracy, in order to ensure the safety of engineered structures. However, the prediction of vibrations' levels remain a complicated issue, because it involves numerous parameters correlated to the quarry site. In this paper, statistical analysis based on the peak particle velocity (PPV) and the attenuation law has been carried out to assess the safety charges (Q) for different distances (R) between the blast and the considered structure to secure. Moreover, the experimental investigations were conducted on the quarry site of "Sococim", which is located on the south coast of Senegal. To ensure the safety of the "Conveyor belt" and "Panel 1 (Upper exploitation level)" sites, the PPV should be less than 10 mm/s. In fact, the attenuation model has been used to assess the safe charge weights of the explosive (Q) to be used at the "Conveyor belt" site and at the "Panel 1 (Upper exploitation level)" site. Therefore, the safe charge weights per delay (Q) were respectively 116 kg and 13.75 kg

Experimental and statistical analysis of blast-induced ground vibrations (BIGV) prediction in Senegal’s quarry

Extractive industries often use explosives to destroy rocks, and productivity requirements tend to increase the charges of the explosives. The blasts induce vibrations, which result in a potential damage of the surrounding structures. Therefore, the prediction of vibrations should be described with accuracy, in order to ensure the safety of engineered structures. However, the prediction of vibrations’ levels remain a complicated issue, because it involves numerous parameters correlated to the quarry site

Numerical analysis of PCM melting filling a rectangular cavity with horizontal partial fins

The present numerical study is conducted to analyze melting process within a rectangular enclosure filled by phase change material (PCM) vertically heated from one side. The right hot wall and the left cold wall are maintained at temperatures, Th=38.3 °C and Tc =28.3 °C, respectively, and it was filled by solid PCM Gallium initially at temperature Tc. The horizontal walls are insulated. A transient numerical model is developed to study the heat transfer and melting behaviours, and the natural convection is accounted. To enhance the heat transfer and the melting process of the PCM, fins with a rectangular and triangular shape are proposed. Moreover, the effects of both thermophysical properties and fins integration on the flow structure and heat transfer characteristics are investigated in detail. The melt fraction contours with the natural convection driven flow are performed and compared, as well as the temperature distributions for a Rayleigh number of around Ra= 106. It is found that the rate of the melting increases with the elevation in the values of specific heat capacity Cp as well as the thermal conductivity λ of the PCM Gallium. The results show also that the rectangular fin accelerates the PCM melting faster than the triangular fin’s shape thanks to the increased exchange area