By means of numerical simulations the aims of this study are as follows: (1) to investigate the dispersion and mixing of ultrafine particles (UFP) with pre-existing size resolved UFP in a street canyon and its vicinity with the ENVI-met 3D microscale model; (2) to show the effects of boundary conditions, like wind direction and traffic emissions, on the UFP concentration in the near vicinity; and (3) to evaluate the importance of deposition and coagulation at the street scale. The decrease in UFP concentration in nucleation mode particles (diameter < 30 nm) and Aitken mode particles (diameter between 30–100 nm) downwind of the street canyon is caused by the large differences in the size distributions of the emissions and the background. Based on the wind direction and traffic emissions, the UFP concentration over the rooftop increases by 23

Currently, KLM's apron processes work in separate silos and there is only minimal integration. The result is that processes tend to work to a local optimum instead of a global optimum. A Transport Logistic Control Tower is a centralized information hub from which integral decisions can be made which could benefit the overall turnaround process at Schiphol airport. There is little knowledge about the effects on the system performance when input parameters are varied. A uniform way of scheduling tasks and making integral decisions is missing. The goal of this research is to determine the integral control scenario that should be used by a Transport Logistic Control Tower in order to optimize the overall performance of KLM's apron processes. The main research question is formulated as: Which integral control scenario should be used by a Transport Logistic Control Tower in order to optimize the overall performance of KLM's apron processes? In the current state analysis the Delft Systems Approach is used in combination with swim lane analyses to analyze the current system. Relations between the different processes, how they interact and the decisions that are made to plan their tasks are analyzed to get a better understanding of the apron processes. To asses the performance of the apron processes, the On Time Start (OTS), On Time Performance (OTP) and the On Time Delivery (OTD) are introduced. The number of flight delays and the corresponding costs are used to combine the process KPIs in order to make a final decision on the best control scenario for KLM. A thorough data analysis is performed by combining the multiple data sources of KLM to get insight in the performance of the system. This showed us that the data quality is not sufficient, and data does not correspond well with the real system. It is therefore recommended to use historical data in combination with the current calculation methods to improve the way the task duration is calculated. This also means that the way data is stored in the HHT should be automated to reduce the amount of measurement errors. A simulation model is designed to assess different control scenarios and the effect they have on the KPIs. The one day run shows significant improvements when dynamic flight priorities are used in combination with a departure oriented control scenario that schedules based on departure time. Compared to the same control scenarios using static priorities, an average improvement of 31,1\% or 1,7 million euros annually could be seen in the delay costs. This control scenario is therefore recommended and shows the necessity to use a uniform way of planning and the potential of the proposed dynamic flight priorities. The recommendations are done based on the analyses and the found results, and used to advice KLM on their future control scenario for their apron processes and improvement levers from which they could benefit in the future.

Waste Electrical and Electronic Equipment (WEEE) is a key resource in the circular economy given its high concentration of valuable materials such as metals. The complexity of recycling this resource, however, is high due to different collection, separation and reprocessing steps. A combined Material Flow Analysis (MFA) and Life Cycle Assessment (LCA) can be used to optimise the environmental performance of this recycling chain. Whereas usually these methodologies are used post-factum, i.e. when data is available, this paper presents how MFA and LCA can be used to predict material flows and the potential environmental benefit of the recycling chain, guiding policy makers and industries towards effective decision making. Based on a case study in Flanders, Belgium, firstly, it is shown that currently only 32% of WEEE materials are recycled towards high-end applications whereas 68% is lost in low-end applications, landfill or incineration. Ferrous and non-ferrous metals such as aluminium and copper achieve the highest high-end material recoveries (54, 46 and 44% respectively), whereas precious metals and plastic achieve lower high-end material recoveries (21-38% and 20% respectively). Secondly, it is shown that the most promising factors to improve material recovery and environmental benefit are consumer behaviour and technological progress (mainly in separation technologies), both potentially doubling the current environmental benefit.

Nektar++ is an open-source software framework designed to support the development of high-performance scalable solvers for partial differential equations using the spectral/hp element method. High-order methods are gaining prominence in several engineering and biomedical applications due to their improved accuracy over low-order techniques at reduced computational cost for a given number of degrees of freedom. However, their proliferation is often limited by their complexity, which makes these methods challenging to implement and use. Nektar++ is an initiative to overcome this limitation by encapsulating the mathematical complexities of the underlying method within an efficient C++ framework, making the techniques more accessible to the broader scientific and industrial communities. The software supports a variety of discretisation techniques and implementation strategies, supporting methods research as well as application-focused computation, and the multi-layered structure of the framework allows the user to embrace as much or as little of the complexity as they need. The libraries capture the mathematical constructs of spectral/hp element methods, while the associated collection of pre-written PDE solvers provides out-of-the-box application-level functionality and a template for users who wish to develop solutions for addressing questions in their own scientific domains.Program summaryProgram title: Nektar++Catalogue identifier: AEVV_v1_0Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEVV_v1_0.htmlProgram obtainable from: CPC Program Library, Queen's University, Belfast, N. IrelandLicensing provisions: MITNo. of lines in distributed program, including test data, etc.: 1052456No. of bytes in distributed program, including test data, etc.: 42851367Distribution format: tar.gzProgramming language: C++.Computer: Any PC workstation or cluster.Operating system: Linux/UNIX, OS X, Microsoft Windows.RAM: 512 MBClassification: 12.External routines: Boost, PFTW, MPI, BLAS, LAPACK and METIS (www.cs.umn.edu)Nature of problem: The Nektar++ framework is designed to enable the discretisation and solution of time-independent or time-dependent partial differential equations.Solution method: Spectral/hp element methodRunning time: The tests provided take a few minutes to run. Runtime in general depends on mesh size and total integration time. (C) 2015 The Authors. Published by Elsevier B.V.

Effects of vegetation on pollutant dispersion receive increased attention in attempts to reduce air pollutant concentration levels in the urban environment. In this study, we examine the influence of vegetation on the concentrations of traffic pollutants in urban street canyons using numerical simulations with the CFD code OpenFOAM. This CFD approach is validated against literature wind tunnel data of traffic pollutant dispersion in street canyons. The impact of trees is simulated for a variety of vegetation types and the full range of approaching wind directions at 15° interval. All these results are combined using meteo statistics, including effects of seasonal leaf loss, to determine the annual average effect of trees in street canyons. This analysis is performed for two pollutants, elemental carbon (EC) and PM10, using background concentrations and emission strengths for the city of Antwerp, Belgium. The results show that due to the presence of trees the annual average pollutant concentrations increase with about 8% (range of 1% to 13%) for EC and with about 1.4% (range of 0.2 to 2.6%) for PM10. The study indicates that this annual effect is considerably smaller than earlier estimates which are generally based on a specific set of governing conditions (1 wind direction, full leafed trees and peak hour traffic emissions).

Considering climate change and the rapid trend towards urbanization, the analysis of urban microclimate is gaining importance. The Urban Heat Island (UHI) effect and summer-time heat waves can significantly affect urban microclimate with negative consequences for human mortality and morbidity and building energy demand. So far, most studies on urban microclimate employed observational approaches with field measurements. However, in order to provide more information towards the design of climate adaptive urban areas, deterministic analyses are required. In this study, Computational Fluid Dynamics (CFD) simulations are performed to predict urban temperatures in the Bergpolder Zuid region in Rotterdam, which is planned to be renovated to increase its climate resilience. 3D unsteady Reynolds-averaged Navier–Stokes (URANS) simulations with the realizable k–ε turbulence model are performed on a high-resolution computational grid. The simulations include wind flow and heat transfer by conduction, convection and radiation. The resulting surface temperatures are validated using experimental data from high-resolution thermal infrared satellite imagery performed during the heat wave of July 2006. The results show that the CFD simulations are able to predict urban surface temperatures with an average deviation of 7.9% from the experimental data. It is concluded that CFD has the potential of accurately predicting urban microclimate. Results from CFD simulations can therefore be used to identify problem areas and to evaluate the effect of climate adaptation measures in these areas such as urban greening and evaporative cooling.

It is well known that computational fluid dynamics (CFD) models require significant amounts of processing time. Producing annual statistics, which are often required for policy support and EU directive compliance testing, is therefore unfeasible with current typical computing infrastructures. In this contribution, we will describe the application of a meteo-averaging methodology as described in Parra et al, (2010) and similarly Sollazo et al, (2011) for two test cases in Antwerp, partly in the frame of the ATMOSYS (http://www.life-atmosys.be) project cofinanced by the European LIFE+ program. Normalised NOx concentrations for 18 wind directions were simulated as a passive tracer in the ENVI-met model (Bruse et al, 1998) for each of 5 different major line sources in the domain. In-situ measurements were used to parameterize the local NO2/NOx ratio. The simulation results were compared on an hourly basis to the NO2 concentration difference of a curb-side station and a station which is located some 30 m further away from the road. In addition, we will illustrate the approach for an urban development project in the city of Antwerp near the busy ring road. Here, the effect of a row of shielding-houses on the annual averaged NO2 concentrations in the area as calculated by the CFD meteostatistics approach, was estimated and superimposed onto an earlier street-level air quality assessment (Lefebvre et al, 2012).

We present a computational model for simulating the dispersion of traffic emitted particulate matter inside a road tunnel, with an emphasis on the number concentration of ultrafine particles (UFP). The model primarily calculates the size distribution of the particle number concentration at each location inside the tunnel. The proposed model differs from existing models in the sense that it uses a continuous representation of the size distribution based upon the high-order finite element method and that it solves the governing equations using the state-of-the-art discontinuous Galerkin method. Next to the traditional transport processes, the model also implements the most important aerosol transformation processes such as coagulation, condensation and dry deposition. It is shown that based upon parametrisations found in literature, the process of condensation in a traffic tunnel cannot properly be modelled. Therefore, we present a correction factor that allows for a better parametrisation. The adequate performance of the model is demonstrated by both a verification study and a validation study. For the verification we show that the discretisation error converges consistently while for the validation we compare the modelled results with a suitable set of data from a UFP measurement campaign in a Taiwanese traffic tunnel. The model is shown to correctly simulate the observed behaviour and by applying a statistical model evaluation we demonstrate that the proposed model meets widely accepted air quality model acceptance criteria.

Vegetation is often quoted as an effective measure to mitigate urban air quality problems. In this work we demonstrate by the use of computer models that the air quality effect of urban vegetation is more complex than implied by such general assumptions. By modelling a variety of real-life examples we show that roadside urban vegetation rather leads to increased pollutant concentrations than it improves the air quality, at least locally. This can be explained by the fact that trees and other types of vegetation reduce the ventilation that is responsible for diluting the traffic emitted pollutants. This aerodynamic effect is shown to be much stronger than the pollutant removal capacity of vegetation. Although the modelling results may be subject to a certain level of uncertainty, our results strongly indicate that the use of urban vegetation for alleviating a local air pollution hotspot is not expected to be a viable solution.

The aim of this study is to investigate the dispersion of ultrafine particles and its spatial distribution in a street canyon and its neighbourhood with the 3D CFD model ENVI-met®. The performance of the model at street scale is evaluated and the importance of the boundary conditions like wind field and traffic emissions on the UFP concentration is demonstrated. To support and validate the modelled results, a short-term measurement campaign was conducted in a street canyon in Antwerp, Belgium. The UFP concentration was measured simultaneously with P-TRACK (TSI Model 8525) at four different locations in the canyon. The modelled UFP concentrations compare well with the measured data (correlation coefficient R from 0.44 to 0.93) within the standard deviation of the measurements. Despite the moderate traffic flow in the street canyon, UFP concentrations in the canyon are in general double of the background concentrations, indicating the high local contribution for this particle number concentration. Some of the observed concentration profiles are not resembled by the model simulations. For these specific anomalies, further analysis is performed and plausible explanations are put forward. The role of wind direction and traffic emissions is investigated. The performance evaluation of ENVI-met® shows that in general the model qualitatively and quantitatively describes the dispersion of UFP in the street canyon study.

Time-stepping algorithms and their implementations are a critical component within the solution of time-dependent partial differential equations (PDEs). In this article, we present a generic framework - both in terms of algorithms and implementations - that allows an almost seamless switch between various explicit, implicit and implicit-explicit (IMEX) time-stepping methods. We put particular emphasis on how to incorporate time-dependent boundary conditions, an issue that goes beyond classical ODE theory but which plays an important role in the time-stepping of the PDEs arising in computational fluid dynamics. Our algorithm is based upon J.C. Butcher's unifying concept of general linear methods that we have extended to accommodate the family of IMEX schemes that are often used in engineering practice. In the article, we discuss design considerations and present an object-oriented implementation. Finally, we illustrate the use of the framework by applications to a model problem as well as to more complex fluid problems.

The presented UFP tunnel model consists of a number of modules that implement the most important transport and transformation processes, i.e. emissions, advection, deposition, coagulation, condensation. The model calculates a continuous UFP number distribution at every location inside the tunnel (assuming a uniform concentration along every cross section). Despite its resemblance with existing Aerosol Box Models, the presented UFP tunnel model differs from existing models in the following sense:

Methodology: The ultrafine particles (UFP) are modelled with the three dimensional computational fluid dynamics (3D CFD) model ENVI-met. The model was extended to account for different transformation processes that could have impact on the size and the number of particles (for example coagulation, deposition, etc).The UFP total number emissions are accounted based on the PARTICULATES project results. In order to validate the results,a measurement campaign was held in a street canyon in Antwerp, Belgium. The study domain contains a small street canyon in combination with a heavily trafficked boulevard perpendicular to it. The concentration of UFP in the street was measured at four different locations (one close to the busy boulevard, two opposite to each other in the middle and one at the other end). Results: Two examples are show the complexity and concerns when modeling the UFP dispersion and analyzing the results. The modelled concentration for total number of UFP was compared with measured UFP concentration at four locations in the street. The modelled trend in the UFP concentration well resembles the measured and it is within the uncertainties of the measurements showing an overall a good agreement. The wind direction is found to be of crucial importance for the dispersion of UFP. Besides there is a need of representative meteorological input suitable for modelling the UFP. Emissions are another parameter that alter the concentration of UFP and need to be addressed adequately. In the analysis averaging over long periods (hours) can mask important details and might lead to wrong conclusions. This model simulation and the comparison results can be used to better understand the dispersion of total number UFP concentrations in urban environment.

There is increasing scientific evidence that the number concentration of (traffic related) ultrafine particles may be a better proxy for the adverse health effects due to particulate matter than the currently regulated PM10 and PM2,5 mass fractions. However, no consensus has been reached whether UFP transformation processes (such as deposition, coagulation, condensation) should be taken into account for appropriately modelling the dispersion of UFP number concentrations within urban environments. Due to their confined space and the controlled conditions, traffic tunnels form the ideal environment to investigate this hypothesis. We have developed a computational model that is able to predict the UFP size-distribution at every location within the tunnel. The model consists of a number of modules that implement the most important transport and transformation processes, i.e. emissions, advection, deposition, coagulation and condensation. The novelty of the model is that it is using state-of-the-art numerical methods that allow for a high-accurate and continuous representation of the solution. We here present the results of a validation study that demonstrates that the model is able to accurately predict the evolution of the UFP sizedistribution inside a traffic tunnel. Moreover, we present a novel approach to identify the dominant processes that govern the UFP size distribution by applying a size-resolved time-scale analysis.

A new parameterization for size resolved ultrafine particles (UFP) traffic emissions is proposed based on the results of PARTICULATES project (Samaras et al., 2005). It includes the emission factors from the Emission Inventory Guidebook (2006) (total number of particles, #/km/veh), the shape of the corresponding particle size distribution given in PARTICULATES and data for the traffic activity. The output of the model UFPEM (UltraFine Particle Emission Model) is a sum of continuous distributions of ultrafine particles emissions per vehicle type (passenger cars and heavy duty vehicles), fuel (petrol and diesel) and average speed representative for urban, rural and highway driving.The results from the parameterization are compared with measured total number of ultrafine particles and size distributions in a tunnel in Antwerp (Belgium). The measured UFP concentration over the entire campaign shows a close relation to the traffic activity. The modelled concentration is found to be lower than the measured in the campaign. The average emission factor from the measurement is 4.29E + 14 #/km/veh whereas the calculated is around 30% lower. A comparison of emission factors with literature is done as well and in overall a good agreement is found.For the size distributions it is found that the measured distributions consist of three modes - Nucleation, Aitken and accumulation and most of the ultrafine particles belong to the Nucleation and the Aitken modes. The modelled Aitken mode (peak around 0.04-0.05 mu m) is found in a good agreement both as amplitude of the peak and the number of particles whereas the modelled Nucleation mode is shifted to smaller diameters and the peak is much lower that the observed.Time scale analysis shows that at 300 m in the tunnel coagulation and deposition are slow and therefore neglected.The UFPEM emission model can be used as a source term in dispersion models. (C) 2011 Elsevier B.V. All rights reserved.

This paper presents the results of two recent case studies which were evaluated with the CFD model ENVI-met. In a first case, the impact of a vegetation barrier along a highway on the local air quality is studied. In a second case, the dispersion of total UFP concentrations within a street canyon is examined. In both cases, ENVI-met model output is compared with measurements resulting in an overall acceptable agreement of the model performance.

Generalized polynomial chaos (gPC) has non-uniform convergence and tends to break down for long-time integration. The reason is that the probability density distribution (PDF) of the solution evolves as a function of time. The set of orthogonal polynomials associated with the initial distribution will therefore not be optimal at later times, thus causing the reduced efficiency of the method for long-time integration. Adaptation of the set of orthogonal polynomials with respect to the changing PDF removes the error with respect to long-time integration. In this method new stochastic variables and orthogonal polynomials are constructed as time progresses. In the new stochastic variable the solution can be represented exactly by linear functions. This allows the method to use only low order polynomial approximations with high accuracy. The method is illustrated with a simple decay model for which an analytic solution is available and subsequently applied to the three mode Kraichnan–Orszag problem with favorable results.

The spectral/hp element method can be considered as bridging the gap between the – traditionally low-order – finite element method on one side and spectral methods on the other side. Consequently, a major challenge which arises in implementing the spectral/hp element methods is to design algorithms that perform efficiently for both low- and high-order spectral/hp discretisations, as well as discretisations in the intermediate regime. In this paper, we explain how the judicious use of different implementation strategies can be employed to achieve high efficiency across a wide range of polynomial orders. Furthermore, based upon this efficient implementation, we analyse which spectral/hp discretisation (which specific combination of mesh-size h and polynomial order P) minimises the computational cost to solve an elliptic problem up to a predefined level of accuracy. We investigate this question for a set of both smooth and non-smooth problems.

Conventional generalized polynomial chaos is known to fail for long time integration, loosing its optimal convergence behaviour and developing unacceptable error levels. The reason for this loss of convergence is the assumption that the probability density function is constant in time. By allowing a probability density function to evolve in time the optimal properties of polynomial chaos are retrieved without resorting to high polynomial degrees.This time‐dependent approach is applied to a system of coupled non‐linear differential equations. These results are compared to the conventional generalized polynomial chaos solutions and Monte Carlo simulations.