Mitigation of urban storm water runoff through application of computational fluid dynamics

This thesis covers computational methods for improving the ability of green roofs to mitigate storm water runoff in urban environments. Roofs with living vegetation, known as green roofs, have been used for this purpose however quantification of their ability to slow and stop rainfall runoff has not been undertaken to a large degree. In this work two different approaches are taken: i) to improve green roof performance by optimizing their location on a building facade; and ii) to optimize the design of the growth substrate by examining the impact of the porous microstructure on infiltrating flow. The approach for optimization by placement makes use of traditional computational fluid dynamics and applies a full turbulence model to an Eulerian multiphase system consisting of a steady-state wind phase and a set of transient rainfall phases. The rainfall phases are determined by droplet size and the quantity incident upon the building facade is calculated and compared to experimental results. The analysis shows that the accuracy varies widely dependent upon location upon the structure and several sources of error are discussed. The second approach makes use of the lattice Boltzmann technique to aid in the deisgn of the growth substrate. Several representative porous media are generated using monodisperse randomly packed particles and gravity-driven infiltration is tracked from an initialized standing water height above the porous subdomain. Many aspects of the flow and properties of the microstructure are analyzed and conclusions are drawn based upon such factors as interfacial area, saturation rate, capillary pressure, and pore size distribution. Guidelines are drawn to aid in the design of thin homogeneous growth substrates based upon the findings. These ideal cases are compared to simulations performed on XMT scans of real growth substrate material and some conclusions are drawn on the observed differences

Modeling stormwater transport through unsaturated green roof substrates

In recent decades there has been an increase in research regarding green roofs and similar technologies. This increased interest is driven by the requirements of urban development and its effects both on humans and the environment. Additionally, the predicted increase in weather severity in the future is raising concerns on the capabilities of urban environments and their stormwater management systems to cope with the increase. Green roofs can be used as a space-conscious solution for improving stormwater management in urban areas as well as contributing to, for example, building protection and pollution and noise reduction. In order to fully utilize them effectively for stormwater runoff reduction it is necessary to quantify their effect and optimize their performance in a given climate. This optimization can take the form of placement on structures or by design within the green roof construction itself. This work focuses on optimization of design by applying computational fluid dynamics and lattice Boltzmann theory to the soil growth substrate. Computational fluid dynamics is used for modeling the flow through the green roof growth substrate (soil layer) at the macrososcopic scale while a lattice Boltzmann model is applied to the mesoscopic (soil particle) scale. Using these methods, the efficacy at water retention and drainage of given soil particles and full-sized green roofs can be determined. This work covers the framework covering both scales however the methodology is applied only to the mesoscopic scale. The focus within the mesoscopic scale is primarily on the hydrophilicity of the particles in the soil and its impact on liquid imbibition. Also included is an exploration on the liquid-air interfacial area and liquid penetration depth to aid in the analysis of the results. The findings of the study suggest particle hydrophilicity plays an important role in the imbibition process, particularly under light to medium rainfall conditions. In addition a pore blocking phenomenon is identified which requires further analysis. Finally, plans for future work and the closure of the two-framework methodology proposed in this work is discussed

On the impact of porous media microstructure on rainfall infiltration of thin homogeneous green roof growth substrates

Green roofs are considered an attractive alternative to standard storm water management methods; however one of the primary issues hindering their proliferation is the lack of data regarding their ability to retain and reduce storm water under a variety of climatic conditions. This lack of data is partly due to the complexity of physical processes involved, namely the heterogeneous microscopic behavior that characterize flows in unsaturated porous media. Such an anomalous behavior is difficult to predict a priori, especially in the presence of layered structures. This paper examines water infiltration of a green roof at the pore-scale with the aim to evaluate the effect of the porous microstructure in thin substrate layers. In such layers, the thickness of the medium and the particle size are within the same order of magnitude and the effect of the packing arrangement on the flow dynamics can be pronounced. In this study, three packing arrangements and two different hydraulic heads, analogous to extreme rainfall events typical of Scandinavia, are investigated by means of direct numerical simulations based on the lattice Boltzmann method. The results show that a wider variability of pore sizes in a thin medium can be linked directly to flow pathing preference and consequently less homogenized flow in the primary flow direction. This situation corresponds to intermittent flow behavior at the pore-scale level and reduced macroscopic infiltration rates. This observation unveils the possibility of designing innovative green roof growth substrates: by tuning the particle size and thickness of the layers composing the medium the desired green roof detention time can be attained

Contribution of dynamic capillary pressure to rainfall infiltration in thin homogeneous growth substrates

The use of green roofs to help mitigate storm water contributions to urban flooding has been gaining popularity but is hindered by the limited data on the performance of such roofs with regard to storm water runoff mitigation. The underlying issue stems from the inherent complexity of modeling subsurface multiphase flow. Modeling of this phenomena requires calculating the contributions of substrate microstructure characteristics, the influence of the wetting and non-wetting phases upon each other, and the effect of the microstructure on the wetting phase. Previously we have observed how the microstructure can affect detention, however the quantification of this relationship is still missing. In the present paper we present numerical simulations of wetting phase infiltration of a thin monodisperse packed bed in order to understand and quantify the impact of microstructure geometry on storm water infiltration of a green roof substrate. For a slightly hydrophilic case, (θ=82\ub0), we find that a dominant mechanism underlying this relationship is the microstructure-induced dynamic behavior of the capillary pressure. We determine that at larger packing ratios (ratio of packed bed depth to particle size), the influence of hydraulic head diminishes and behaves conversely for thinner layers, particularly when larger pores are present. Indeed, thin beds composed of large particles can exhibit high flow velocities that in turn affect the capillary pressure within the substrate. We observe that the capillary pressure can shift from negative values denoting capillary suction to positive ones which cause valve-like blocking effects on the flow; dependent upon the flow velocity as determined by the microstructure. In particular, we find that the capillary pressure depends on the value of the pore-scale gravity-induced flow velocity, quantified through a characteristic Capillary number. The provided quantification of this relationship can be invaluable from a design perspective to understand the behavior of capillary pressure of different substrates under a variety of flow rates prior to testing substrate candidates. In addition, a comparison of the behavior of the dynamic component of capillary pressure to other works is undertaken. Flow homogeneity is also found to be linked to the flow velocity, and consequently to the microstructure

Increased incidence of cancer in systemic lupus erythematosus : a Finnish cohort study with more than 25 years of follow-up

Objective: The aim of this study was to assess the cancer risk in a cohort of Finnish systemic lupus erythematosus (SLE) patients when followed long-term. Methods: The cohort consisted of 182 female and 23 male SLE patients treated at the Helsinki University Central Hospital, from 1967 to 1987. The cohort was linked to the Finnish Cancer Registry and followed for cancer incidence from 1967 to 2013. Standardized incidence ratios (SIRs) were calculated by dividing the number of observed cases with the number of expected cases for different types of cancer. Results: The mean duration of follow-up was 25.7 years. 45 patients out of 205 were diagnosed with cancer, with an increased risk of overall malignancy (SIR 1.90, 95% CI 1.39 to 2.54, p<0.001). The incidence for soft-tissue sarcoma (SIR 12.1, 95% CI 1.47 to 43.7, p<0.05), non-Hodgkin lymphoma (SIR 12.1, 95% CI 5.82 to 22.3, p<0.001) and kidney cancer (SIR 7.79, 95% CI 2.53 to 18.2, p<0.01) were significantly elevated. Conclusion: This long-term study confirms that patients with SLE have an increased risk of cancer, particularly non-Hodgkin lymphoma and kidney cancer.Mål: Sambandet mellan autoimmuna sjukdomar och cancer har varit känt i långa tider. Det finns en ökad risk för att utveckla cancer hos patienter med reumatoid artrit, Sjögrens syndrom och systemisk lupus erythematosus (SLE). Detta gäller speciellt risken för Non-Hodgkins lymfom. De autoimmuna reumatiska sjukdomarna innebär en immunologisk dysreglering, minskad apoptos och ökad överlevnad av B-celler, kronisk stimulering av antigener och försämrad funktion av T-celler, dessa mekanismer tillsammans kan förklara den ökade incidensen av lymfom. Målet med denna undersökning var att undersöka risken för cancer hos 205 SLE-patienter vid långtidsuppföljning. Metoder: Kohorten bestod av 182 kvinnor och 23 män som vårdats vid Helsingfors universitetssjukhus från 1967 till 1987. Diagnoserna för olika typer av cancer utreddes i samarbete med Finlands Cancerregister. Vi räknade ut SIR-värden (standardized incidence ratio) för olika typer av cancer genom att dividera mängden cancerfall med den förväntade mängden av cancerfall. Resultat: Patienterna följdes upp i medeltal i 25.7 års tid. 45 patienter diagnostiserades med cancer, med en statistiskt betydelsefull ökad risk för cancer (SIR 1.90, 95% CI 1.39 till 2.54, p<0.001). Incidensen för sarkom (SIR 12.1, 95% CI 1.47 till 43.7, p<0.05), Non-Hodgkins lymfom (SIR 12.1, 95% CI 5.82 till 22.3, p<0.001) och njurcancer (SIR 7.79, 95% CI 2.53 till 18.2, p<0.01) var signifikant förhöjda. Slutsats: Denna långtidsuppföljning bekräftar att patienter med SLE har en ökad risk för cancer, speciellt Non-Hodgkins lymfom och njurcancer

Increased incidence of cancer in systemic lupus erythematosus : a Finnish cohort study with more than 25 years of follow-up

Objective: The aim of this study was to assess the cancer risk in a cohort of Finnish systemic lupus erythematosus (SLE) patients when followed long-term. Methods: The cohort consisted of 182 female and 23 male SLE patients treated at the Helsinki University Central Hospital, from 1967 to 1987. The cohort was linked to the Finnish Cancer Registry and followed for cancer incidence from 1967 to 2013. Standardized incidence ratios (SIRs) were calculated by dividing the number of observed cases with the number of expected cases for different types of cancer. Results: The mean duration of follow-up was 25.7 years. 45 patients out of 205 were diagnosed with cancer, with an increased risk of overall malignancy (SIR 1.90, 95% CI 1.39 to 2.54, p<0.001). The incidence for soft-tissue sarcoma (SIR 12.1, 95% CI 1.47 to 43.7, p<0.05), non-Hodgkin lymphoma (SIR 12.1, 95% CI 5.82 to 22.3, p<0.001) and kidney cancer (SIR 7.79, 95% CI 2.53 to 18.2, p<0.01) were significantly elevated. Conclusion: This long-term study confirms that patients with SLE have an increased risk of cancer, particularly non-Hodgkin lymphoma and kidney cancer.Mål: Sambandet mellan autoimmuna sjukdomar och cancer har varit känt i långa tider. Det finns en ökad risk för att utveckla cancer hos patienter med reumatoid artrit, Sjögrens syndrom och systemisk lupus erythematosus (SLE). Detta gäller speciellt risken för Non-Hodgkins lymfom. De autoimmuna reumatiska sjukdomarna innebär en immunologisk dysreglering, minskad apoptos och ökad överlevnad av B-celler, kronisk stimulering av antigener och försämrad funktion av T-celler, dessa mekanismer tillsammans kan förklara den ökade incidensen av lymfom. Målet med denna undersökning var att undersöka risken för cancer hos 205 SLE-patienter vid långtidsuppföljning. Metoder: Kohorten bestod av 182 kvinnor och 23 män som vårdats vid Helsingfors universitetssjukhus från 1967 till 1987. Diagnoserna för olika typer av cancer utreddes i samarbete med Finlands Cancerregister. Vi räknade ut SIR-värden (standardized incidence ratio) för olika typer av cancer genom att dividera mängden cancerfall med den förväntade mängden av cancerfall. Resultat: Patienterna följdes upp i medeltal i 25.7 års tid. 45 patienter diagnostiserades med cancer, med en statistiskt betydelsefull ökad risk för cancer (SIR 1.90, 95% CI 1.39 till 2.54, p<0.001). Incidensen för sarkom (SIR 12.1, 95% CI 1.47 till 43.7, p<0.05), Non-Hodgkins lymfom (SIR 12.1, 95% CI 5.82 till 22.3, p<0.001) och njurcancer (SIR 7.79, 95% CI 2.53 till 18.2, p<0.01) var signifikant förhöjda. Slutsats: Denna långtidsuppföljning bekräftar att patienter med SLE har en ökad risk för cancer, speciellt Non-Hodgkins lymfom och njurcancer

En introduktion till dagvattenfl\uf6desmodellering i gr\uf6na tak

Gr\uf6na tak ses idag som ett alternativ f\uf6r dagvattenhantering i urbana omr\ue5den d\ue4r det lokala ledningsn\ue4tet inte har kapacitet nog att hantera framtidens regnm\ue4ngder. I detta projekt utvecklas modeller som syftar till att optimera och validera gr\uf6na tak s\ue5 att deras funktion kan anv\ue4ndas p\ue5 b\ue4sta s\ue4tt med st\uf6rst effekt. M\ue5let \ue4r att utveckla verktyg och riktlinjer f\uf6r hur gr\uf6na tak kan anv\ue4ndas

Simulating wind-driven rain on building facades using Eulerian multiphase with rain phase turbulence model

Wind-driven rain (WDR) is responsible for many types of damage to building fa\ue7ades and contributes to storm water management problems in urban environments. Consequently there is significant interest in accurately predicting WDR using computational fluid dynamics (CFD) simulations. In this paper an Eulerian multiphase (EM) method is proposed which includes applying a turbulence model for solving the rain phase equation closure rather than a response coefficient to approximate turbulent behaviour. The simulations are conducted using AVL FIRE™ with standard k−ε model and are validated against experimental data for two cases. The results produce an error ranging from 5% to 39% in the first case and from 9% to 72% in the second case. The discrepancies are attributed largely to the unsuitability of the standard k−ε in predicting the flow accurately as well as the limited number of raindrop phases. While the results are not as accurate as other research has shown, the method described in this paper allows for greater flexibility when working with transient rainfall conditions and gives an alternative to the previously proposed response coefficient for modelling turbulent dispersion. The method is viable for calculating general WDR distribution patterns on a fa\ue7ade and can be improved to offer more accurate results

Wind pressure coefficients for roof ventilation purposes

Wind pressure coefficients (cp) are important inputs for analytical calculations of wind load. The aim of this research is to investigate wind pressure coefficients on a test house located in Norway in order to pave the way for improved analysis of wind-driven roofing ventilation. The large-scale test measurements show that the wind pressure coefficient along the eaves of the house varies with different wind approach angles. Assuming wind-driven air flow through the air cavity beneath the roofing, an average View the MathML source value of 0.7 is derived for practical engineering purposes. The results from the study are applicable for single or two-storey houses with pitched roofs at different roof angles

Wind pressure coefficients for roof ventilation purposes

Wind pressure coefficients (c p ) are important inputs for analytical calculations of wind load. The aim of this research is to investigate wind pressure coefficients on a test house located in Norway in order to pave the way for improved analysis of wind-driven roofing ventilation. The large-scale test measurements show that the wind pressure coefficient along the eaves of the house varies with different wind approach angles. Assuming wind-driven air flow through the air cavity beneath the roofing, an average Δc p \uaf value of 0.7 is derived for practical engineering purposes. The results from the study are applicable for single or two-storey houses with pitched roofs at different roof angles