The Experts below are selected from a list of 4513032 Experts worldwide ranked by ideXlab platform
Björn Holmer - One of the best experts on this subject based on the ideXlab platform.
-
Transmissivity of solar radiation through crowns of single urban trees—application for outdoor thermal comfort modelling
Theoretical and Applied Climatology, 2014Co-Authors: Janina Konarska, Fredrik Lindberg, Annika Larsson, Sofia Thorsson, Björn HolmerAbstract:Trees play an important role in mitigating heat stress on hot summer days, mainly due to their ability to provide shade. However, an important issue is also the reduction of solar radiation caused by trees in winter, in particular at high latitudes. In this study, we examine the Transmissivity of total and direct solar radiation through crowns of single street trees in Göteborg, Sweden. One coniferous and four deciduous trees of species common in northern European cities were selected for case study. Radiation measurements were conducted on nine clear days in 2011–2012 in foliated and leafless tree conditions using two sunshine pyranometers—one located in shade of a tree and the other one on the roof of an adjacent building. The measurements showed a significant reduction of total and direct shortwave radiation in the shade of the studied trees, both foliated and leafless. Average Transmissivity of direct solar radiation through the foliated and defoliated tree crowns ranged from 1.3 to 5.3 % and from 40.2 to 51.9 %, respectively. The results confirm the potential of a single urban tree to reduce heat stress in urban environment. However, the relatively low Transmissivity through defoliated trees should be considered while planning street trees in high latitude cities, where the solar access in winter is limited. The results were used for parameterisation of SOLWEIG model for a better estimation of the mean radiant temperature (T_mrt). Measured values of Transmissivity of solar radiation through both foliated and leafless trees were found to improve the model performance.
-
Transmissivity of solar radiation through crowns of single urban trees application for outdoor thermal comfort modelling
Theoretical and Applied Climatology, 2014Co-Authors: Janina Konarska, Fredrik Lindberg, Annika Larsson, Sofia Thorsson, Björn HolmerAbstract:Trees play an important role in mitigating heat stress on hot summer days, mainly due to their ability to provide shade. However, an important issue is also the reduction of solar radiation caused by trees in winter, in particular at high latitudes. In this study, we examine the Transmissivity of total and direct solar radiation through crowns of single street trees in Goteborg, Sweden. One coniferous and four deciduous trees of species common in northern European cities were selected for case study. Radiation measurements were conducted on nine clear days in 2011–2012 in foliated and leafless tree conditions using two sunshine pyranometers—one located in shade of a tree and the other one on the roof of an adjacent building. The measurements showed a significant reduction of total and direct shortwave radiation in the shade of the studied trees, both foliated and leafless. Average Transmissivity of direct solar radiation through the foliated and defoliated tree crowns ranged from 1.3 to 5.3 % and from 40.2 to 51.9 %, respectively. The results confirm the potential of a single urban tree to reduce heat stress in urban environment. However, the relatively low Transmissivity through defoliated trees should be considered while planning street trees in high latitude cities, where the solar access in winter is limited. The results were used for parameterisation of SOLWEIG model for a better estimation of the mean radiant temperature (Tmrt). Measured values of Transmissivity of solar radiation through both foliated and leafless trees were found to improve the model performance.
Martin Stigsson - One of the best experts on this subject based on the ideXlab platform.
-
A Transmissivity model for deformation zones in fractured crystalline rock and its possible correlation to in situ stress at the proposed high-level nuclear waste repository site at Forsmark, Sweden
Hydrogeology Journal, 2014Co-Authors: Sven Follin, Martin StigssonAbstract:La compagnie de gestion du combustible et des déchets nucléaires suédois a récemment proposé le site de Forsmark pour servir d'emplacement potentiel à la construction d'un futur dépôt géologique de combustible nucléaire haute activité usé à environ 470 m de profondeur dans des roches cristallines fracturées. Les considérations ont inclus, entre autres, la distance des zones de déformation régionalement significatives comprenant des roches sous forte tension, l’homogénéité lithologique, la faible conductivité hydraulique, la salinité des eaux souterraines dans une gamme acceptable, et l’absence de ressources minérales potentielles. Cet article décrit le calcul de la transmissivité des zones de déformation déduites à Forsmark et le modèle de transmissivité utilisé dans un modèle régional d'écoulement d'eaux souterraines réalisé en appui à la description intégrée du site. En plus d’une diminution significative avec l'augmentation de la profondeur (plus de quatre ordres de grandeur pour une profondeur d'environ 1 km), les valeurs calculées de transmissivité indiquent également une variabilité spatiale considérable le long des failles de ces zones, c.-à-d. une hétérogénéité latérale (plus de deux ordres de grandeur). Un couplage hydromécanique est discuté, basé sur les modèles présentés pour l'évolution tectonique et le tenseur de contraintes principales. À titre d'essai, des relations à l’échelle du laboratoire développées à partir d’essais de contraintes normales sur une fracture unique dans une roche cristalline peuvent être utilisées pour estimer les valeurs maximales de transmissivité des zones de déformation déduites à Forsmark. O local de Forsmark foi recentemente proposto pela companhia Sueca de Combustível Nuclear e Gestão de Resíduos para servir como local potencial para a construção de um futuro repositório geológico para combustível nuclear usado de alto nível em rochas cristalinas fraturadas, a cerca de 470 m de profundidade. As considerações incluíram, entre outras coisas, a distância a zonas de deformação com significado regional, com rochas altamente deformadas, homogeneidade litológica, condutividade hidráulica baixa, salinidade da água subterrânea num intervalo aceitável e a inexistência potencial de recursos minerais. Este artigo descreve o cálculo das transmissividades em zonas de deformação inferidas em Forsmark e o modelo de transmissividade usado na modelação do fluxo regional da água subterrânea realizados como apoio à descrição integrada do local. Para além da diminuição significativa com o aumento da profundidade (mais de quatro ordens de magnitude ao longo de uma profundidade de cerca de 1 km) os valores de transmissividade calculados também revelam uma variabilidade espacial considerável ao longo das orientações das zonas, i.e. heterogeneidade lateral (mais de duas ordens de magnitude). É discutida uma ligação hidromecânica, com base nos modelos apresentados para a evolução tectónica, para o tensor principal das tensões. Experimentalmente, as relações à escala de laboratório, desenvolvidas a partir de experiências com tensões normais numa única fratura em rocha cristalina, podem ser usadas para estimar os valores máximos de transmissividade em zonas de deformação inferidas em Forsmark. El sitio de Forsmark fue propuesto recientemente por la Svensk Kärnbränslehantering AB para servir como un lugar potencial para la construcción de un futuro repositorio geológico para combustible nuclear usado de alta radiactividad a alrededor de 470 m en rocas cristalinas fracturadas. Las consideraciones incluían, entre otras cosas, la distancia de zonas de deformación regional significativas con altas deformaciones de la roca, la homogeneidad litológica, la baja conductividad hidráulica, la salinidad del agua subterránea dentro de un rango aceptable, y la carencia de potenciales recursos minerales. Este trabajo describe el cálculo de la transmisividad de las zonas de deformación deducidas en Forsmark y los modelos de transmisividad usados en el modelado del flujo regional del agua subterránea realizados en apoyo de una descripción integrada del sitio. Además de la disminución significativa con el incremento de la profundidad (más que cuatro órdenes de magnitud para una profundidad de alrededor de 1 km), los valores calculados de la transmisividad revelan una considerable variabilidad espacial a lo largo de los rumbos de las zonas, es decir la heterogeneidad lateral (más de dos órdenes de magnitud). Se discute un acoplamiento hidromecánico, basado en los modelos presentes para la evolución tectónica y el tensor principal de tensiones. Tentativamente, relaciones en escala de laboratorio desarrollado a partir de experimentos de tensión normal sobre una sola fractura en rocas cristalinas pueden ser usados para estimar los valores máximos de transmisividad de las zonas de deformación deducidas para Forsmark. The Forsmark site was recently proposed by the Svensk Kärnbränslehantering AB (SKB) to serve as the potential site for construction of a future geological repository for spent high-level nuclear fuel at about 470 m depth in fractured crystalline rock. The considerations included, among other things, distance from regionally significant deformation zones with highly strained rock, lithological homogeneity, low hydraulic conductivity, groundwater salinity with an acceptable range, and lack of potential mineral resources. This report describes the calculation of Transmissivity of deduced deformation zones at Forsmark and the Transmissivity model used in the regional groundwater flow modeling carried out in support of the integrated site description. Besides significant decrease with increasing depth (more than four orders of magnitude over a depth of about 1 km), the calculated Transmissivity values also reveal considerable spatial variability along the strikes of the zones, i.e. lateral heterogeneity (more than two orders of magnitude). A hydro-mechanical coupling is discussed, based on presented models for the tectonic evolution and the principal stress tensor. Tentatively, laboratory-scale relationships developed from normal stress experiments on a single fracture in crystalline rock can be used to estimate the maximum values of Transmissivity of deduced deformation zones at Forsmark.
-
a Transmissivity model for deformation zones in fractured crystalline rock and its possible correlation to in situ stress at the proposed high level nuclear waste repository site at forsmark sweden
Hydrogeology Journal, 2014Co-Authors: Sven Follin, Martin StigssonAbstract:The Forsmark site was recently proposed by the Svensk Karnbranslehantering AB (SKB) to serve as the potential site for construction of a future geological repository for spent high-level nuclear fuel at about 470 m depth in fractured crystalline rock. The considerations included, among other things, distance from regionally significant deformation zones with highly strained rock, lithological homogeneity, low hydraulic conductivity, groundwater salinity with an acceptable range, and lack of potential mineral resources. This report describes the calculation of Transmissivity of deduced deformation zones at Forsmark and the Transmissivity model used in the regional groundwater flow modeling carried out in support of the integrated site description. Besides significant decrease with increasing depth (more than four orders of magnitude over a depth of about 1 km), the calculated Transmissivity values also reveal considerable spatial variability along the strikes of the zones, i.e. lateral heterogeneity (more than two orders of magnitude). A hydro-mechanical coupling is discussed, based on presented models for the tectonic evolution and the principal stress tensor. Tentatively, laboratory-scale relationships developed from normal stress experiments on a single fracture in crystalline rock can be used to estimate the maximum values of Transmissivity of deduced deformation zones at Forsmark.
Janina Konarska - One of the best experts on this subject based on the ideXlab platform.
-
Transmissivity of solar radiation through crowns of single urban trees—application for outdoor thermal comfort modelling
Theoretical and Applied Climatology, 2014Co-Authors: Janina Konarska, Fredrik Lindberg, Annika Larsson, Sofia Thorsson, Björn HolmerAbstract:Trees play an important role in mitigating heat stress on hot summer days, mainly due to their ability to provide shade. However, an important issue is also the reduction of solar radiation caused by trees in winter, in particular at high latitudes. In this study, we examine the Transmissivity of total and direct solar radiation through crowns of single street trees in Göteborg, Sweden. One coniferous and four deciduous trees of species common in northern European cities were selected for case study. Radiation measurements were conducted on nine clear days in 2011–2012 in foliated and leafless tree conditions using two sunshine pyranometers—one located in shade of a tree and the other one on the roof of an adjacent building. The measurements showed a significant reduction of total and direct shortwave radiation in the shade of the studied trees, both foliated and leafless. Average Transmissivity of direct solar radiation through the foliated and defoliated tree crowns ranged from 1.3 to 5.3 % and from 40.2 to 51.9 %, respectively. The results confirm the potential of a single urban tree to reduce heat stress in urban environment. However, the relatively low Transmissivity through defoliated trees should be considered while planning street trees in high latitude cities, where the solar access in winter is limited. The results were used for parameterisation of SOLWEIG model for a better estimation of the mean radiant temperature (T_mrt). Measured values of Transmissivity of solar radiation through both foliated and leafless trees were found to improve the model performance.
-
Transmissivity of solar radiation through crowns of single urban trees application for outdoor thermal comfort modelling
Theoretical and Applied Climatology, 2014Co-Authors: Janina Konarska, Fredrik Lindberg, Annika Larsson, Sofia Thorsson, Björn HolmerAbstract:Trees play an important role in mitigating heat stress on hot summer days, mainly due to their ability to provide shade. However, an important issue is also the reduction of solar radiation caused by trees in winter, in particular at high latitudes. In this study, we examine the Transmissivity of total and direct solar radiation through crowns of single street trees in Goteborg, Sweden. One coniferous and four deciduous trees of species common in northern European cities were selected for case study. Radiation measurements were conducted on nine clear days in 2011–2012 in foliated and leafless tree conditions using two sunshine pyranometers—one located in shade of a tree and the other one on the roof of an adjacent building. The measurements showed a significant reduction of total and direct shortwave radiation in the shade of the studied trees, both foliated and leafless. Average Transmissivity of direct solar radiation through the foliated and defoliated tree crowns ranged from 1.3 to 5.3 % and from 40.2 to 51.9 %, respectively. The results confirm the potential of a single urban tree to reduce heat stress in urban environment. However, the relatively low Transmissivity through defoliated trees should be considered while planning street trees in high latitude cities, where the solar access in winter is limited. The results were used for parameterisation of SOLWEIG model for a better estimation of the mean radiant temperature (Tmrt). Measured values of Transmissivity of solar radiation through both foliated and leafless trees were found to improve the model performance.
Wei He - One of the best experts on this subject based on the ideXlab platform.
-
A sensitivity study of a hybrid photovoltaic/thermal water-heating system with natural circulation
Applied Energy, 2007Co-Authors: Jie Ji, Jianping Lu, Tin-tai Chow, Wei HeAbstract:A flat-box aluminum-alloy photovoltaic and water-heating system designed for natural circulation was constructed. The hybrid photovoltaic/thermal (PV/T) collector was an integration of single-crystalline silicon cells into a solar thermal collector. The product was able to generate electricity and hot water simultaneously. Outdoor tests on an improved prototype were conducted in a moderate climate zone. Then dynamic simulation runs, using a validated numerical model, were performed. These included sensitivity tests with variations of the system water mass, PV cell covering factor, and front glazing Transmissivity. The test results showed that the characteristic daily primary-energy saving could reach up to 65% for this system with a PV cell covering factor 0.63 and front glazing Transmissivity of 0.83, when the hot water load per unit heat-collecting area exceeded 80Â kg/m2. The simulated results indicated that the higher the PV cell covering factor and the glazing Transmissivity, the better the overall system performance. The effects were quantified.
-
a sensitivity study of a hybrid photovoltaic thermal water heating system with natural circulation
Applied Energy, 2007Co-Authors: Jie Ji, Jianping Lu, Wei He, Tin-tai ChowAbstract:A flat-box aluminum-alloy photovoltaic and water-heating system designed for natural circulation was constructed. The hybrid photovoltaic/thermal (PV/T) collector was an integration of single-crystalline silicon cells into a solar thermal collector. The product was able to generate electricity and hot water simultaneously. Outdoor tests on an improved prototype were conducted in a moderate climate zone. Then dynamic simulation runs, using a validated numerical model, were performed. These included sensitivity tests with variations of the system water mass, PV cell covering factor, and front glazing Transmissivity. The test results showed that the characteristic daily primary-energy saving could reach up to 65% for this system with a PV cell covering factor 0.63 and front glazing Transmissivity of 0.83, when the hot water load per unit heat-collecting area exceeded 80Â kg/m2. The simulated results indicated that the higher the PV cell covering factor and the glazing Transmissivity, the better the overall system performance. The effects were quantified.
Abderrahim Jardani - One of the best experts on this subject based on the ideXlab platform.
-
Hydraulic tomography in time-lapse mode for tracking the clogging effects associated with the colloid injection
Advances in Water Resources, 2019Co-Authors: Abderrahim Jardani, Mohamed Krimissa, Pierre Fischer, Nasre Dine AhfirAbstract:Clogging due to transport and accumulation of the colloids in the pore space has been recognized as one of the most significant challenges in water management research and environmental engineering. This paper proposes an inversion algorithm in time-lapse mode to track that complex process through the assessment of alteration in the Transmissivity field produced by the injection of colloids. The concept is based on a joint inversion of hydraulic head and colloidal particles concentration data acquired during the injection of colloids in the porous aquifer to reconstruct the spatial variability of the Transmissivity field at different times. The inversion code is deterministic and was implemented in the time-lapse scheme by adding in the objective function a temporal geostatistical constraint to control changes of the hydraulic Transmissivity. This algorithm is linked to a forward problem that consists of the groundwater flow and transport equations, which were solved numerically and jointly by considering the effect of particles deposition on the decrease of hydraulic properties. As the inverse problem is deterministic and underdetermined, we have opted to use the efficient adjoint state technique to derive the sensitivity matrices. The approach has been successfully applied to a theoretical case in which the hydraulic head responses have been used alone and jointly to assess the evolution of the clogging impact on hydraulic Transmissivity.
-
A hybrid inverse method for hydraulic tomography in fractured and karstic media
Journal of Hydrology, 2017Co-Authors: Xiaoguang Wang, Abderrahim Jardani, Hervé JourdeAbstract:We apply a stochastic Newton (SN) approach to solve a high-dimensional hydraulic inverse problem in highly heterogeneous geological media. By recognizing the connection between the cost function of deterministic optimizations and the posterior probability density of stochastic inversions, the Markov chain Monte Carlo (MCMC) sampler of SN is constructed by two parts: a deterministic part, which corresponds to a Newton step of deterministic optimization, and a stochastic part, which is a Gaussian distribution with the inverse of the local Hessian as the covariance matrix. The hybrid inverse method exploits the efficient tools for fast solution of deterministic inversions to improve the efficiency of the MCMC sampler. To address the ill-posedness of the inverse problem, a priori models, generated by a transition-probability geostatistical method, and conditioned to inter-well connection data, are used as regularization constraints. The effectiveness of the stochastic Newton method is first demonstrated by a synthetic test. The Transmissivity field of the synthetic model is highly heterogeneous, and includes sharp variations. The inverse approach was then applied to a field hydraulic tomography investigation in a fractured and karstified aquifer to reconstruct its Transmissivity field from a collection of real hydraulic head measurements. From the inversions, a series of Transmissivity fields that produce good correlations between the inverted and the measured hydraulic heads were obtained. The inverse approach produced slightly different a posteriori Transmissivity patterns for different a priori structure models of Transmissivity; however, the trend and location of the high-Transmissivity channels are consistent among various realizations. In addition, the uncertainty associated with each realization of the inverted Transmissivity fields was quantified.
-
Characterisation of the Transmissivity field of a fractured and karstic aquifer, Southern France
Advances in Water Resources, 2016Co-Authors: Xiaoguang Wang, Abderrahim Jardani, Hervé Jourde, Lidia Lonergan, John Cosgrove, Olivier Gosselin, Gérard MassonnatAbstract:Geological and hydrological data collected at the Terrieu experimental site north of Montpellier, in a confined carbonate aquifer indicates that both fracture clusters and a major bedding plane form the main flow paths of this highly heterogeneous karst aquifer. However, characterising the geometry and spatial location of the main flow channels and estimating their flow properties remain difficult. These challenges can be addressed by solving an inverse problem using the available hydraulic head data recorded during a set of interference pumping tests. We first constructed a 2D equivalent porous medium model to represent the test site domain and then employed regular zoning parameterisation, on which the inverse modelling was performed. Because we aim to resolve the fine-scale characteristics of the Transmissivity field, the problem undertaken is essentially a large-scale inverse model, i.e. the dimension of the unknown parameters is high. In order to deal with the high computational demands in such a large-scale inverse problem, a gradient-based, non-linear algorithm (SNOPT) was used to estimate the Transmissivity field on the experimental site scale through the inversion of steady-state, hydraulic head measurements recorded at 22 boreholes during 8 sequential cross-hole pumping tests. We used the data from outcrops, borehole fracture measurements and interpretations of inter-well connectivities from interference test responses as initial models to trigger the inversion. Constraints for hydraulic conductivities, based on analytical interpretations of pumping tests, were also added to the inversion models. In addition, the efficiency of the adopted inverse algorithm enables us to increase dramatically the number of unknown parameters to investigate the influence of elementary discretisation on the reconstruction of the Transmissivity fields in both synthetic and field studies. By following the above approach, Transmissivity fields that produce similar hydrodynamic behaviours to the real head measurements were obtained. The inverted Transmissivity fields show complex, spatial heterogeneities with highly conductive channels embedded in a low Transmissivity matrix region. The spatial trend of the main flow channels is in a good agreement with that of the main fracture sets mapped on outcrops in the vicinity of the Terrieu site suggesting that the hydraulic anisotropy is consistent with the structural anisotropy. These results from the inverse modelling enable the main flow paths to be located and their hydrodynamic properties to be estimated.
