Prepare Your Input Geometries

Prepare Your Input Geometries

CAD Model Export Guidelines for CFD Simulation

Proper preparation and cleanup of your CAD model are essential for successful simulation. The following guidelines will help you achieve your first successful simulation iteration.

Export Mistakes - User Guide Archiwind

General Tips

Think in Volumes

Wind patterns at the scale of a city originate from large volumes. Small details like light poles, garden furniture, cars, and intricate thin structures are irrelevant and will only increase the delivery time for your project.

Split is Key

Consider that your project needs to be separated into buildings, surroundings, and terrain. We allocate extra cells to your building of interest. The more resources allocated to your building of interest, the more accurate your results. Reduce the LOD of your surroundings; details will not be captured comprehensively and risk creating instability.

Key Requirements for Successful Simulation

Model Dimensions

Importance of Accurate Dimensions:
Ensure that the model dimensions in your CAD software match the units used in the simulation platform. Discrepancies can lead to unrealistic geometrical dimensions, necessitating scaling operations.

Selecting Units:
When uploading a *.stl file, select the appropriate model dimensions from the dropdown menu. The default unit in the Input page is Meter. This can be changed for files that do not contain unit information.

Complexity Reduction

Simplifying your CAD model can lead to more accurate simulations and shorter computation times. Here are some strategies:


Many CAD models include intricate details such as furniture, door handles, and placeholder mannequins that are irrelevant to simulation. Features like small holes or windings can increase meshing and computing time without affecting results. Remove these details to optimize performance.

Removing Small Entities

Small faces with sharp angles can cause issues during meshing, potentially leading to failures. Merging or removing these small entities can facilitate a smoother meshing process.

The Lighter, the Better

Heavy geometry mostly comes from too-high LOD, internal layers and geometries, furniture, etc. Please follow the previous steps to make your geometries lighter. After 500Mb, your geometry will be wrapped and decimated. The output will conserve the main features but might alter the topology slightly. If you wish to have your exact geometry meshed, please reduce your LOD or proceed to decimation.

By following these guidelines, you can ensure a more efficient and accurate simulation setup. Simplifying your model and understanding the complete workflow will help you avoid common pitfalls and achieve better results in your simulations.

Split Your Scene

ArchiWind allows you to split your scene into three patches: the building, the surroundings, and the terrain.

Guide to Split Your Geometries

Why Should I Bother Splitting My Scene into Patches?

Ensuring that you export your scene into the correct patch is crucial for achieving optimal results. When you run a simulation using ArchiWind, the first step involves meshing your geometry. Meshing decomposes your 3D scene into smaller elements known as cells. The greater the number of cells, the more detailed the resolution of your geometries during the computation phase.

You might think:

“Let’s make the cells as fine as possible to get better results!”

However, this approach is not always beneficial. Increasing the number of cells significantly extends the time required to resolve your case. More cells do not necessarily equate to better results but do guarantee a longer simulation time. Additionally, more cells introduce more opportunities for errors, potentially leading to the simulation diverging (crashing).

Scene example

Therefore, it is essential to avoid creating unnecessary cells. Prioritization is key. For example, if you aim to ensure optimal comfort around a new restaurant you plan to build, this building requires detailed attention. This restaurant is your building of interest and is likely surrounded by other structures (housing, bridges, high-rise buildings). These surrounding buildings influence wind movement based on their volume rather than their intricate details. In other words, the specific design of a façade 100 meters away is less relevant than whether that structure is a small shed or a 39-floor high-rise building.

Hence, defining the Level of Detail (LOD) needed for accurate simulation is crucial. This approach is based on guidelines such as the City of London Wind Microclimate Guidelines.

Building highlighted

By following these principles, you ensure that your simulations are both efficient and accurate, focusing computational resources where they matter most. So, we take care of defining the LOD we need to capture. We base it on the City of London Wind Microclimate Guidelines.