Roof Model Research Articles

Evaluating the potential of green roofs for greywater treatment

Abstract Greywater, comprising household wastewater excluding toilet waste, represents a significant portion of daily wastewater. Effective greywater treatment is crucial to mitigate environmental pollution, especially when greywater flows directly into water bodies without clear controls, discharge limits, and treatment requirements. Nature-based solution (NBS) approaches, such as green roofs, are gaining popularity for their urban benefits and potential for greywater treatment. However, in Malaysia, the application and literature on green roofs are limited, primarily focusing on stormwater management. The potential for greywater treatment remains understudied, despite numerous successful implementations worldwide. Hence, this study aims to explore the effectiveness of green roofs in improving greywater quality. Two green roof models were constructed: one using commercial materials and the other using recycled coconut waste. Greywater samples from washing and kitchen activities were tested, with influent and effluent samples analyzed for key water quality parameters including pH, turbidity, BOD, COD, TSS, TN, and TP. Both green roof models demonstrated notable effectiveness in reducing BOD concentrations, achieving removal efficiencies between 12% to 33%. The resulting BOD levels ranged from 21 to 25 mg/L, which is slightly above the limit of Standard A but compliant with Standard B of the Environmental Quality Act (EQA) 1974. While green roofs show potential in reducing BOD from greywater, their effectiveness in treating other water quality parameters remains limited. Addressing these shortcomings through system enhancements and integrated treatment approaches can lead to more robust and reliable greywater treatment solutions.

Determining the threshold for variation in indoor temperature reduction capacity of green roofs with different depths in hot and dry climates

To forestall the dangers of overdesign, initial and maintenance costs, and unnecessary loading on the supporting roof, the study was primarily aimed at determining the significant difference in indoor temperature reduction capacity between various green roof models of varying thicknesses within the extensive green roof category. Using a contextualized substrate layer of 25mm as the difference in depth between green roof alternatives, the degree of thermal insulation for the interior was observed on six extensive green roof models of 50mm, 75mm, 100mm, 125mm, and 150mm thicknesses. This is to elucidate the level of significant differences in thermal efficiency between the models. EnergyPlus 8.3.0 simulation software was used to conduct a thermal performance survey on the sampled models. The temperature profiles of all the cases were collected and subjected to statistical analysis using SPSS V 21.0 to conduct an ANOVA and a proceeding Post hoc test to determine where the difference lies between the green roof groups. The results revealed that; no substantial difference in thermal performance exists between alternatives where the difference in depth is around the 25mm mark. Revealing that the threshold for any significant change in thermal insulation is denoted by a 50mm difference between alternatives. This research was carried out to facilitate the initial process of green roof selection, design, detailing, and specifications writing for architect engineers, and other stakeholders.

Building Roof Model Influenced by Environmental Climate

The roof is the main thing in a building that functions to protect the building and occupants. Indonesia has gable and trapezium roof models. Both have advantages and disadvantages. The advantages and disadvantages are managed to become a strength that complements the building. The roof consists of three parts, first the roof frame, second the roof covering frame and the covering material. The roof frame is often called the truss and is made of wood, iron, concrete or mild steel. The covering frame is often called a batten made of bamboo wood or mild steel. The roof is often called tiles made from clay, concrete or metal. Each roof construction has different slope requirements. The slope angle will affect the maintenance, durability and beauty of the building. Determining the angle must be careful and adjusted to the characteristics of the roof covering. The characteristics of the roof angle are influenced by the impermeability of the covering material. The more impermeable it is, the slower the angle will be. The climate also affects the existing roof model. The angle of the roof will be influenced by the environmental climate. The climate affects the use of roof angles.

Verification of Numerical Models of Steel Bar Coverings Using Experimental Tests—Preliminary Study

In the design of metal bar coverings, the key problem is to correctly determine the numerical model of the analyzed structure. The description of numerical models may differ from the actual, real behavior of the structure. Therefore, there is a need to verify and calibrate them using experimental studies. The aim of this research will be to verify and assess the accuracy of the numerical model of a metal bar roof by conducting experimental studies. A series of repeatable experimental tests will be conducted on the structure model to determine the path of static equilibrium and the form of stability loss of the steel covering. During the test, as the load increases, data will be collected on the displacements of nodes. The displacements of the nodes will be verified using precise triangulation laser sensors and electronic sensors. Based on the results of the tests, conclusions will be drawn regarding the accuracy of the numerical models. Comparison of the results obtained from the numerical models with the experimental data will allow for the identification of possible discrepancies and understanding how the numerical models can be improved. This in turn will contribute to the development of more advanced and more accurate methods for the analysis of metal bar roof structures in the future.

Evaluation of water richness in coal seam roof aquifer based on factor optimization and random forest method.

Water richness evaluation of coal seam roofs is a crucial prerequisite for preventing and controlling water hazards in coal seam roofs. For this purpose, Spearman correlation and GeoDetector were employed for factor optimization to investigate the significance of lithological and structural factors and the impact of interactions among different factors on the water richness of coal seam roofs. Water richness evaluation models of coal seam roofs were separately established via the entropy weight method (EWM), coefficient of variation method (CVM), and random forest method (RFM), and the predictive accuracies of these models were compared. Eleven lithological and structural factors were collected. Through Spearman correlation analysis, 6 factors were identified to have significant influences on water richness. By utilizing the interaction detection of GeoDetector, the effects of interfactor interactions on water richness were explored, and 3 combination factors were selected. AICc was used to determine the model's superiority. The evaluation results of the study area based on factor optimization and three methods were further compared and validated via pumping tests, workface water inflow tests, and three-dimensional high-density electrical method. The results indicated that the RFM exhibited higher prediction accuracy than did the entropy weight and coefficient of variation methods. Additionally, within each method, factor optimization led to improved model accuracy.

Comparative Evaluation of Evapotranspiration and Optimization Schemes for Green Roof Runoff Simulations Using HYDRUS-1D

The use of green roofs, a low-impact development practice, can be an effective means of reducing direct runoff in urban centers. Green roof modeling can enable efficient design by preliminarily grasping the behavior of the green roof system according to specific configurations. In this study, we aimed to find appropriate evapotranspiration and parameter optimization schemes for HYDRUS-1D, a commonly used modeling tool for green roofs. Comparative studies of this sort in the context of green roof runoff modeling have not been conducted previously and are important in guiding users to overcome the difficulties of choosing the right numerical schemes for an accurate prediction of runoff from a green roof. As a study site, the Portland Building Ecoroof in Portland, Oregon, USA, was chosen, as green roof configurations and observed data for climate and runoff were available. From the simulation results of the runoff volume, the Blaney–Criddle method, which was considered an alternative, was found to be appropriate for calculating evapotranspiration from a green roof (R2 = 0.82) relative to the Hargreaves method built in HYDRUS-1D (R2 = 0.46). In addition, this study showed that the optimization method using the harmony search algorithm, which was proposed as an alternative optimizer, was better (R2 = 0.95) than that of the HYDRUS-1D’s own optimization module (R2 = 0.82) in calibrating HYDRUS-1D for green roof runoff. The findings are thought to be useful in guiding modelers who are considering using HYDRUS-1D for green roof runoff simulations.

Thermally anisotropic building envelope for thermal management: finite element model calibration using field evaluation data

ABSTRACT The thermally anisotropic building envelope (TABE) is an active building envelope that redistributes thermal loads in response to weather conditions and building energy demand. Conductive layers throughout the TABE distribute low-grade heat among hydronic loops, altering heat flow direction and intensity. Finite element models of TABE roof and wall panels were developed and calibrated using field evaluation data. The calibration results showed that heat flux differences between the experimental data and finite element models averaged −0.42% and 3.57%, with a maximum mean square error of 1.78 and 3.96 for roof and wall panels, respectively. A reduction in heat flux from the environment to the building living space over the entire testing period (weeks in July/August) was found to be 85% for roof panels and 335% (load reversed) for wall panels. These results indicate TABE can effectively harness low-grade thermal energy sources to achieve high energy efficiency and promote demand-side management.

Sustainable building envelopes: Evaluating the thermal performance of thatched roofs fabricated using coconut leaves

Excessive heat gain in residential buildings during sunny days, especially in tropical regions, leads to increased reliance on active energy cooling systems, contributing to higher carbon emissions and energy costs. Traditional roofing materials, such as terracotta tiles are often insufficient in mitigating indoor temperature rise, necessitating the exploration of alternative, sustainable solutions. This study investigates the thermal performance of naturally available coconut leaves used as thatch roofing, comparing it with conventional terracotta tiles, to determine their effectiveness in controlling interior temperatures and reducing heat gain in buildings. To mitigate such a problem, the Near Infra-Red (NIR) light reflectivity of dried plant leaves derived from deciduous and coniferous trees was measured. The structural hierarchy of the leaves was confirmed through Field Emission Scanning Electron Microscope (FESEM), Fourier Transform Infrared Spectroscope (FTIR) and X-ray Diffraction (XRD) studies. FTIR spectra reveal characteristic vibrations of ester, cellulosic components, etc., and XRD confirms the amorphous status of cellulosic materials present in the plant biomass. To study the use of thatched roofs made using coconut leaves as a roofing element, two test huts were fabricated - one was covered using terracotta roof tiles and the other was covered using coconut leaves thatches. The thermal performances of two roofing materials were recorded on a sunny day and the results were compared. The temperature data noticed reveal the fact that the maximum average surface temperature of the terracotta roof model was 59.53 °C, while the rooftop covered with coconut thatches exhibits a temperature of 54.26 °C which is 8.8% less than the hut covered with terracotta tiles. The interior temperature recorded in the coconut thatch was 33.36 °C, which was 1.15 °C lower (34.51 °C) than the terracotta tiles-covered test hut, confirming the better thermal comfortability of thatched roof model than a terracotta roof model.

Research on controlled mining of end slope fire-burned area in open-pit mine

To solve the problem of controlling mining in the open-pit mine end slope fire-burned area, applying multivariate function fitting to the roof and floor modeling of multi-coal seam open pit mines, introducing the factor of coal quality changes in the fire-burned area, determining coal quality information at each location through proximate analysis of coal, to establish the net profit model of the mining area, it is determined the net profit of each mining position by numerical integration, the final mining position was determined without failure by calculating the slope stability based on the numerical simulation of strength reduction. Taking the Dananhu No. 2 open-pit mine in Hami, Xinjiang, China as the engineering background, the fire-burned area III within the southern end slope boundary of the first mining area is 240 m. It was finally determined that the optimal mining position is when the advancement degree is 182 m, the ultimate pit slope angle is 25°, the three-dimensional slope stability is 1.305, the profit is 671.96 million yuan, The deep boundary of the southern end slope fire-burned area of the slope is reduced by 58 m. This paper solves the problem of end slope mining in Dananhu No. 2 mine, and maximizes its net profit under the condition of ensuring safe production.

Deformation Characteristics and Response Factors of Rock Bolt Body in Roadway with Layered Composite Roof

Layered composite roofs are characterized by developed bedding fissures, resulting in severe deformation and damage of rock bolts at the top of the roadway, as well as a poor roadway support effect. Increasing pretension force is an effective way to enhance the stiffness of the rock bolt support system. To clarify the influence and mechanism of the pretension force on the support effect of rock bolts in the layered roof, a roadway model of the layered roof was established using the interface unit of FLAC3D, and the simulation rock bolts were constructed using the pile unit, which can simulate the mechanical behaviors of rock bolts, such as tension, shear, bending, fracture, and anchor failure, and the pretension force was applied. On this basis, the deformation and failure characteristics and influencing factors of rock bolts in the layered roadway roof under different surrounding rock conditions were simulated and analyzed. The research shows the following: ① Field measurements showed minor shear deformation in the rock bolts at the center of the roadway roof, with lateral displacements of 5.7 cm and 5.3 cm. Significant shear deformation occurred in the rock bolts at the roof corners, with lateral displacements of 18.2 cm and 17.6 cm. ② Simulations of rock bolt deformation characteristics matched the field measurements closely, confirming the reliability of the simulation method, parameter selection, and calculation sequence. ③ The primary factors affecting rock bolt deformation are the structural plane strength and surrounding rock strength. Rock bolts are most susceptible to lateral displacement when the structural plane strength is low, the strength difference between rock layers is large, and the weaker layer is below the structural plane. The presented research can provide a reference for the instability mechanism and support treatment of the layered composite roof roadway.

Contemporary roof pattern for energy efficient buildings: Air conditioning cost alleviation, CO2 emission mitigation potential and acceptable payback period

Buildings account for a significant portion of global energy use and consumption. Buildings have substantial energy consumption due to the use of heating, ventilation, and cooling systems. It is evident that the use of insulation materials and phase change materials (PCMs) in the design of buildings can effectively reduce the cost of air conditioning by reducing external heat gains and losses. Additionally, the use of environmentally friendly, cost-effective, and natural materials can be beneficial from an environmental standpoint. This paper aims to evaluate the potential for cost savings in the air conditioning of various PCMs and insulation-stuffed building roof configurations. In that respect, four types of phase change materials (HS29, HS36, FS42, and FS30) and four insulation materials (Therma cork, sawdust, aerogel, and sheep wool) were selected. The thermophysical properties of PCMs (solid and liquid state), insulation materials, and building elements were determined experimentally as per ASTM D 5334 standards. Ten various building roof models (contemporary roof pattern) are studied with four various PCMs and four various insulations. In addition, novel building roof design integrated with PCM/insulation were analysed numerically, related to environmental conditions that refer to two different scenarios in India (hot dry and composite climates). It further analyses the reduction in greenhouse gas emissions associated with different roof configurations. The aforementioned PCM/insulation materials were stuffed in the void spaces of the contemporary roof pattern. Thermo-economic analysis of novel roof design with PCM/insulation materials on air-conditioning costs, carbon dioxide emissions and payback time are compared with conventional roofs (CR) and contemporary roof patterns (CRP). The thermo-economic analysis was carried out based on the number of degree-hours of heating and cooling to determine the building's annual energy usage. HS29 PCM stuffed roof pattern (HS29RP) saved the highest total energy cost savings of 11.89/14.71 $/m2/year when compared with conventional roof and 11.35/13.89 $/m2/year compared with contemporary roof pattern for Jabalpur/Kota climatic conditions. HS29 PCM stuffed roof pattern (HS29RP) exhibits the maximum carbon emission mitigation of 215.32/275.37 kg/kWh when compared with conventional roof and 204.95/259.57 kg/kWh for climatic conditions of Jabalpur/Kota. While considering shortest payback span, sawdust stuffed roof pattern shows the minimum payback period of 0.69 and 2.15 years when compared with conventional roof and contemporary roof pattern. The findings of this research offer significant contributions to the development of energy-efficient building envelopes applicable to a wider range of buildings, including those with and without air conditioning systems.

Study on the Tensile Failure Characteristics and Energy Calculation Model of Coal Seam Hard Roof Considering the Mining Speed

To reveal the influence mechanism of mining speed on roof fracture-type rockburst, the Brazilian split technique combined with acoustic emission monitoring technology was employed to study the effects of loading rates on the tensile failure characteristics and acoustic emission parameters of coal series sandstone. The linear relationship between the tensile strength of the samples and the change rate of tensile stress was determined. The mining speed was introduced into the mechanical model of initial and cyclic fracture of the hard roof, and the quantitative relationship between the maximum rate of change of tensile stress within the hard roof and the mining speed was derived. Based on this, a computational model for the bending elastic energy of the hard roof during initial and cyclic fractures, considering the mining speed, was established. The main findings are as follows: As the loading rate increases, the distribution range of acoustic emission energy in sandstone Brazilian split samples before failure widens, with a significant rise in acoustic emission ring-down counts and energy at failure. At lower loading rates, acoustic emission events primarily occur near sample failure, whereas at higher rates, they mostly happen in the early loading stage. The higher the mining speed, the less opportunity there is for internal micro-fractures to develop and expand before the hard roof fractures, which macroscopically results in increased tensile strength and a larger amount of energy released at the moment of fracture. Bending elastic energy rises approximately linearly with mining speed, and the thicker the hard roof, the more sensitive the bending elastic energy is to changes in mining speed. This effect is even more pronounced during cyclic fractures. Optimizing mining speed is crucial for preventing roof fracture-type rockbursts, especially in mining workfaces with thick and hard roofs.

Effect of connection and grouting level on mechanical behavior of pipe roof

ABSTRACT Pipe roof support suffers from engineering defects such as connection and insufficient grouting in tunnel engineering. To analyze the influence of connection and grouting level on the mechanical behavior of pipe roof support during tunnel construction, a series of pure bending tests were conducted to measure the mechanical property of pipe roof, and quantitatively analyze the influence of the connection and grouting level on the bearing capacity and bending stiffness of the pipe roof. In addition, the double shear mechanical analysis model of pipe roof based on the Timoshenko beam theory and the Pasternak elastic foundation theory was established by considering the shear deformation of pipe roof, the supporting effect of surrounding rock of tunnel face and the delayed effect of shotcrete for primary support. Then, the solution methods for pipe roof deflection and internal force were derived based on this model. Based on an engineering case, the deflection and internal force distribution, as well as the effect of connection and grouting levels on the pipe roof were discussed. Corresponding construction suggestions were proposed and had achieved good results in the case. This research can provide reference for the design and construction of pipe roof.

Application of Research on Risk Assessment of Roadway Roof Falls Based on Combined Weight Matter Element Extension Model

Roof falls in coal mine roadways are the main causes of many casualties, shutdowns and production plan delays. To understand the relationship between the influencing factors of roadway roof fall accidents and the importance ranking of the accidents, we will reduce safety accidents in coal mines. To enable the timely prediction and control of roadway roof fall risks, based on the investigation of many roadway roof fall risk factors, 12 evaluation indexes such as the roadway roof rock thickness, geological conditions and roadway section shape were selected. An evaluation index system of roadway roof fall risks is constructed. A risk degree standard of roadway roof falls is proposed. The risk evaluation model of roadway roof falls was established by using the combination weight of the analytic hierarchy process (AHP), entropy weight method (EW) and matter element extension theory. According to the principle of the maximum membership degree, the risk degree of roadway roof falls is determined. Based on Java Web, a risk assessment system for roadway roof falls was developed. We name the system Multiple Weight-Material Element Web (MW-MEW). The MW-MEW system was used to evaluate the risk degree of roof falls in the C9 return airway of the Xingu Coal Mine. Compared with the evaluation results of the AHP matter element extension model, it is found that the evaluation results of the MW-MEW system are more in line with the actual engineering conditions. The successful application of the MW-MEW system will provide new avenues for the quantitative evaluation of roof fall risks in coal mine roadways.

Estimating nonlinear wind-induced response of roof cable nets by aeroelastic experiments and ML modeling

The paper examines the structural engineering challenges related to the assessment of the wind-induced vertical displacements of lightweight, hyperbolic-paraboloid cable-supported membrane roofs. Analysis and comparisons are conducted using three distinct methods for calculating the roof vertical, out-of-plane displacements. Finite element method (FEM) analysis is employed using: (i) estimated static nodal forces obtained from wind pressure coefficients determined by aerodynamic wind tunnel tests on a rigid building model, and (ii) loads found from wind pressure coefficients, estimated through machine learning (ML) methods, and (iii) measured roof response found from aeroelastic wind tunnel tests on a flexible model. The study examines three different roof geometries (square, rectangular and circular) and two distinct membrane curvatures for each geometry. Furthermore, wind directionality (three mean-wind incidence angles) and Reynolds number effects (seven mean wind velocities) are studied. Comparisons show that the non-linear FEM analysis, based on estimated static wind loads, underestimates the roof displacements at the roof center, compared to the direct measurements on the aeroelastic model. The main contribution of the study consists of a novel application of ML models, and Artificial Neural Networks (ANNs) in particular, which are employed to correct roof displacement estimations, found by simplified aerodynamic test pressure measurements on rigid roof models. The goal is to better describe the complex fluid-structure interaction of the roof membranes, which can only be achieved by direct aeroelastic tests that are difficult to design and execute. Finally, the study demonstrates that ANNs can be used not only for the preliminary design of the full-scale structure but also for construction of wind tunnel scale models.

Wind resistance performance analysis of metal roof system of the long-span integrated photovoltaic building

Wind resistance is an important factor in the operation of Building Integrated Photovoltaic (BIPV) systems, especially for long-span roofs, where lifting of the roof can result in significant economic losses. This paper proposes a periodic boundary numerical simulation method for long-span metal roof systems to address the problem of meshes and contact pairs in the numerical simulation of wind resistance. In order to calibrate the BIPV metal roof's material parameters, indoor tensile test was conducted, and the results of the global metal roof model were compared with those of the single metal roof model with periodic boundaries for verification of periodic boundary efficiency and accuracy. The wind-resistant capacity of laboratory and long-span sizes for the BIPV metal roof system are compared, and a conversion formula between them is proposed to enable the rapid calculation from the laboratory to long-span roof system. The results show that the periodic boundary is suitable for the analysis of wind resistance of the long-span BIPV metal roof. Wind resistance of the long-span BIPV metal roof system is 1.77 kPa, whereas that of the laboratory size is 4.50 kPa. According to the proposed formula, the wind-resistant capacity of the long-span metal roof can be converted from the laboratory test, which can provide technical support for the design of BIPV systems.

Assessing energy saving potential of wavelength-dependent passive daytime radiative cooler implemented with EnergyPlus by a roof model

The Passive Daytime Radiative Cooler (PDRC) exhibits potential in enhancing building energy conservation due to its high emissivity in wavelength between 8 μm and 13 μm. However, current building energy simulation programs, e.g., EnergyPlus, generally adopt a constant emissivity. To implement the wavelength-dependent PDRC model into EnergyPlus, a roof model was introduced to couple it with EnergyPlus to assess the energy saving potential of PDRC more reasonably. To assess the PDRC roofs, the impact of buildings constructed in different eras, building heights, and climatic conditions in China on building energy saving was investigated. The results showed that more energy was saved in regions with high cooling demands e.g., Shanghai and Guangzhou. Applying PDRC on roofs of buildings constructed pre 2001 in severe cold regions increased building energy consumptions. Furthermore, buildings with well insulated roofs coated by PDRC were not equally beneficial for reducing cooling demands in summer compared to buildings with non-insulated roofs, but heating demands in winter could be reduced. With an increase in building height, the energy saving potential of PDRC roofs was reduced. Therefore, a comprehensive analysis was imperative considering the local climates as well as the building itself when PDRC is to be applied.

Geometric Analysis of Greenhouse Roofs for Energy Efficiency Optimization and Condensation Drip Reduction

Greenhouses are instrumental in the advancement of regions globally. The geometric arrangement of these structures plays a pivotal role in governing sunlight distribution, facilitating ventilation, and managing condensation. The roof’s shape significantly affects energy efficiency and the accumulation of condensation water, which, when dripping onto crops, can induce diseases and diminish production. This study introduces a Matlab program designed for defining and analyzing greenhouse roof geometry that is adaptable to both single-span and multispan structures. Various roof shapes were examined, and angles along their length were determined to facilitate condensation droplet runoff. In the ogival roof shape, water droplets adhering to the roof surface were found to slide off, preventing interior dripping. However, in all semicylindrical roof structures, dripping occurred on more than 50% of the cultivated ground surface. Furthermore, the greenhouse’s energy efficiency was evaluated by analyzing diverse roof models, accounting for the surface area and internal air volume. There was little difference in the volume of air inside the greenhouse attributable to the roof shape. Increasing the arch height relative to the span width enhanced solar energy capture and the roof surface, with the semicylindrical shape being more efficient in this case. The results aim to aid in the selection of the optimal greenhouse type based on the climate and latitude. This study offers a valuable decision-making tool for the planning and design of agricultural structures, providing insights to enhance their overall sustainability and performance in diverse environmental contexts. Hence, in cold climates and high latitudes, the steeper roof angle of the ogival shape type 2l and its smaller surface area promote solar energy capture and reduce convective heat losses. In warmer climates, a larger roof surface facilitates natural cooling, making the ogival shape type 3l/2 recommended.

Eco-friendly green roof from biodegradable substrate for stormwater quality improvement

Currently, there is a significant surge of interest in green roof technology for construction buildings due to its numerous environmental benefits, such as stormwater management, energy efficiency, and enhanced urban biodiversity. However, the issue of potential pollutant release from green roof substrates into runoff water, causing water pollution, needs to be addressed. To tackle this concern, a lab-scale green roof model was assessed, utilizing a biodegradable substrate made from banana peels and eggshell waste (organic fertilizer). Three models were tested: a conventional green roof (control), a green roof with chemical fertilizer, and a green roof with organic fertilizer. Various water quality parameters, including pH, total suspended solids (TSS), nitrogen, phosphorus, and potassium (NPK), and chemical oxygen demand (COD), were evaluated. The results demonstrated the effectiveness of organic fertilizer in reducing TSS and COD levels, where the eco-friendly green roof with biodegradable substrate exhibited an impressive performance, achieving a higher COD removal percentage (78%) compared to the green roof with chemical fertilizer (50%). The utilization of organic fertilizer led to an enhancement in the quality of stormwater runoff, resulting in NPK removal percentages ranging from 17% to 25%. Additionally, the organic fertilizer fostered healthier vegetation growth, leading to a greater number of leaves compared to the chemical fertilizer. These findings highlight the potential of eco-friendly green roofs as a sustainable and effective tool for stormwater management, provided suitable substrate materials are employed.

Numerical method used for the simulation of fluid–solid transitions based on the VOF and SAM models and prediction of snow distributions on large-span roofs

During a snowfall, the surfaces of the snow beds on roofs change dynamically with time and wind conditions. The generation of body-fitted computational fluid dynamics grids for simulating dynamic snow surfaces using the moving-grid method remains challenging. Therefore, a numerical method was developed to simulate the fluid–solid transition based on the volume of the fluid model and solidification and melting models. The snowfall process was divided into n stable steps, and a stable state calculation method was adopted to calculate the air and snow phases. The dynamic snow boundary was simulated at each stage by converting the fluid or solid characteristics of the domain in which the grids resided. Based on the results of the (n−1)th stage, the fluid domain grids buried by the snow were filled with liquid and frozen into the solid domain. Instead, the fluid in the frozen grids, where snow was about to be eroded, was evacuated and converted into fluid-domain grids. Thus, a complex and changeable snow boundary could be adapted without re-meshing. A modified wall friction velocity equation was derived to correct the wall friction velocity at the snow boundary owing to the serrated boundary of the solidified grids, thereby improving calculation accuracy. The numerical simulation results were verified via field observations of snow distribution on the stepped flat and gable roof models. The snow variation on a full-scale, three-span, suspended cable roof under snow-fall conditions was predicted using the proposed method.