Planting trees is widely considered an effective way to create a good urban wind environment, improve air quality, mitigate heat island effects, improve pedestrian wind comfort and reduce building energy consumption. To assess tree effects and find suitable tree setups in urban areas, Computational Fluid Dynamic (CFD) simulations can be used.
To handle trees in CFD simulations, the implicit tree modeling approach, i.e, the porosity model, is widely used where finite volume cells that roughly account for trees are marked as porous zones. Some studies have also attempted to model trees as obstacles rather than porous zones, which can be referred to as an explicit tree modeling approach. The difference between these two approaches deserves further study. Also, for practical purposes and lack of information, the geometric features of trees are usually oversimplified or even ignored in CFD simulations.
This thesis investigates the difference between implicit and explicit tree modeling approaches and analyzes the impact of tree Level of Detail (LoD) and shapes on the flow structure. For comparative analysis, several numerical test cases with different urban complexities, tree modeling approaches, tree LoDs, tree shapes, Leaf Area Density (LAD) values, and wind directions were used for CFD simulations.
The results show: (a) the implicit models always allow some of the wind flow into the porous cells no matter how high the LAD values are, resulting in smaller wind acceleration on the lateral sides of implicit tree models; (b) for the idealized street canyon and realistic urban geometry test cases simulated in this thesis, the velocity magnitude differences between the LoD2 cases and the LoD3 cases are rather limited, with maximum differences in the order of 0.5 m/s; (c) differences in tree shapes, LAD values, and wind directions will change the effects of tree modeling approaches and tree LoDs on wind. For instance, the case using an isolated explicit LoD2 conifer tree model has a different wake flow pattern from other explicit cases. Also, with the inflow direction perpendicular to buildings, the higher the LAD values, the larger the velocity magnitude difference between cases using LoD2 tree models and those using LoD3 tree models.

In 2017, the ‘Kustpact’, a Dutch national agreement, was signed to develop the Dutch coast without damaging its ecosystem nor its aesthetics. Consequently, the formation and protection of coastal dunes have become a focal point for research and development. For this reason, based on the idea of Performance-Based Design (PBD), this Master thesis aims to investigate the impact of certain geometric design parameters of beach house configurations on wind turbulence for the purpose of widening the dunes.

A parametric design space was set up to easily automate Computational Fluid Dynamics (CFD) simulations for different purposes throughout this study. The sediment mobility estimation was the objective function for all simulations conducted. It is based on the difference of transport rate between two lines from the beginning of the plateau to the foot of the dunes. To simplify the parametric model, a Sensitivity Analysis (SA) was conducted to statistically identify the most influential parameters in the model. Afterward, the filtered parameters from the SA are used to build a surrogate model to detect the trends that result from combining the most influential parameters. Finally, a Surrogate-Based Optimisation (SBO) is conducted based on the former surrogate and using a Genetic Algorithm (GA). Three generations were run and used to increase the accuracy of the surrogate and predict an optimum solution for widening the dunes.

The study concludes on a list of design criteria to respect in order to widen the dunes mainly pertaining to the consistent position of the configuration relative to the dunes, the important overlap between houses and the larger wind-facing direction of the configuration.

In the Netherlands, the coastal dunes are essential to protect the country against flooding. However, the rising sea levels increase the risk of flooding along these sandy shores. Moreover, due to a combination of human and natural activities, dune erosion has increased and will continue to do so in the coming decades. Besides flood protection, the Dutch shoreline is important for preserving biodiversity, the generation of drinking water and recreation. In recent year, the number of recreational buildings on the beach, such as bars and holiday homes has increased. This is relevant because previous studies show that such beach buildings affect the wind flow and limit aeolian transport of sediment towards the dunes.

This research studies the impact of beach house configurations on dune-ward sediment transport to limit the adverse effects on dune development. We use CFD simulations to study the wind flow around a 3D model of a beach with holiday houses, based on a section of the Noordwijk beach in the Netherlands. We implement the CFD software OpenFOAM to solve the RANS equations for turbulent, steady-state flow. The sediment transport that occurs is calculated using the wind direction and speed near the ground surface of the solution.

The study consists of multiple 3D models in which the placement of the houses is varied systematically, to study the effects of beach house configurations. Variations are made by rotating houses, individually or within a row, and changing the distance between the houses and dunes. We determine the annual effect on sediment transport by applying varying wind conditions based on historical wind data from Noordwijk.
As we have many simulations to run, and all need different parameters and settings, we automated the process. First, a PostgreSQL database is used to store all requirements for the CFD simulations, the metadata and the results the simulations give. Then, a Python script links the information stored in the database to the correct settings in OpenFOAM. This way, many simulations are run in a row, and the results area to compare.

The results show that rotating the houses individually towards the prevailing wind direction appears to improve the amount of dune-ward sediment that takes place, compared to beach houses placed perpendicular to the shore. Rotating a row of houses as a whole has a limited effect on the amount of sediment transport. However, combining the rotation of the row of houses and the houses individually towards the prevailing wind direction shows the best improvement in sediment transport. Changing the distance between the houses and the dune foot so that a row of houses forms a funnel shape pointing towards the dunes also yields promising results.
Because we use a simplified model and do not take factors such as moisture levels or fetch distance into account, the results of this study overestimate the amount of sediment transport that takes place and might not quite resemble the reality. Further research using scale models or wind tunnels is necessary to confirm the suggestions made in this thesis.