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How to Model Trees with Porous Media — Pedestrian Wind Comfort

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For architects, engineers, urban planners, and other AEC professionals working in sustainability, porous media for LBM and Pedestrian Wind Comfort analysis can offer an insight into innovative wind effect mitigation solutions. This presentation demonstrates how to use SimScale's advanced features, like porous media, for urban flow simulation and, more specifically, to evaluate the effect of trees as windbreaks.

Watch the webinar recording here: https://www.youtube.com/watch?v=r9c4t0tsvpA

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How to Model Trees with Porous Media — Pedestrian Wind Comfort

  1. 1. With Arnaud Girin CFD webinar How to Model Trees with Porous Media — Pedestrian Wind Comfort CFD webinar How to Model Trees with Porous Media — Pedestrian Wind Comfort
  2. 2. About SimScale Who we are ● Founded in 2012 ● Offices in Munich, Boston, and New York ● 80+ employees across 6+ time zones ● 150,000 users worldwide ● More than 300k simulation projects ● Knowledge base and tutorials
  3. 3. We created the world’s first cloud-based engineering simulation platform. ● Fluid dynamics (CFD) ● Solid mechanics (FEA) ● Thermodynamics All accessible via a web browser. About SimScale What we do
  4. 4. What are the effects produced by trees and other porous urban furnitures and buildings on the comfort of pedestrian? Today’s application Porous media and pedestrian wind comfort
  5. 5. Setup and run a simulation Lawson Criteria Assess directional results 1 3 part workflow 1. Run 2 simulations of the same model ○ With trees modeled ○ Without trees modeled 2. Wind comfort criteria ○ At which location did the trees help with the comfort? 3. Wind speed results in the predominant direction ○ How did the trees impact on the flow pattern? How do we assess trees impact on pedestrian comfort? 2 3
  6. 6. Overview Reports [2] show the different outcomes in regards to pedestrian wind comfort : ● Shops untenanted ● Parks under utilized ● Personal injury ● Venturi effect in passages ● Wind-blocking What is wind comfort? Today’s application Example for mechanical wind comfort criteria [1] [1] Adamek, Kimberley.,Vasan, Neetha., Elshaer, Ahmed., English, Elizabeth.,& Bitsuamlak,Girma.,Pedestrian Level Wind Assessment through City Development:A Study of the Financial Districtin Toronto. [2] http://www.urbanphysics.net/windcomfort.htm
  7. 7. How can we combat the undesired effects of the wind? Today’s application Case scenario 1: New construction General shape and layout Canopies & Panels Placement of entrances Case scenario 2: Existing buildings Implement trees Implement urban furnitures or art pieces https://www.sciencedirect.com/science/article/pii/S0167610516307644?via%3Dihub https://www.sciencedirect.com/science/article/abs/pii/S0360132317300884?via%3Dihub https://sci-hub.tw/https://www.tandfonline.com/doi/abs/10.1080/00038628.2018.1492899 https://www.sciencedirect.com/science/article/pii/S0360132319305037
  8. 8. Why are trees important for cities? Today’s application http://www.fao.org/zhc/detail-events/en/c/454543/ https://www.smartcitiesdive.com/ex/sustainablecitiescollective/why-we-need-trees-our-cities/1100050/ https://www.theguardian.com/cities/2016/oct/12/importance-urban-forests-money-grow-trees 1. Increase property value 2. Reduce carbon emissions 3. Regulate water flow 4. Improve physical and mental health 5. Filters for urban pollutants 6. Climate change mitigation 7. Increasing urban biodiversity 8. Food and nutrition security
  9. 9. What is a porous media? Today’s application A porous medium is a solid with interconnected voids distributed more or less uniformly through the bulk of the body. For trees, porosity is defined:
  10. 10. Why is it useful? How does it affect the flow pattern? Today’s application In CFD, trees are defined as porous materials because: ● The physical structure is complex (we cannot model each leaf) ● The value of porosity and inertial resistance are essential for accurate results The windbreak trees affect: ● The trajectory of the flow ● The wind speed ● The pressure drop windward/leeward
  11. 11. How is the porosity of trees modeled on SimScale? Today’s application There are different ways to define a tree zone in SimScale: A Global Database of Field-observed Leaf Area Index in Woody Plant Species GFDL and Creative Commons CC-BY 2.5 Option 1: Pick a predefined tree from the library Option 2: Create a custom tree definition with 1. Leaf Area Index 2. Drag Coefficient Leaf Area Index = Total Leaf Area/Total Ground Area The dimensionless drag coefficient can be understood as the ratio of the pressure difference of windward and leeward and the dynamic force.
  12. 12. How trees should be modeled on SimScale? Today’s application The standard tree representative in Revit NON ACCEPTABLE An ideal representative of a tree for PWC Solid representation of the foliage
  13. 13. Assessing the level of comfort with and without trees Porous Media and Wind Comfort Example 1
  14. 14. ● Assessing the level of pedestrian comfort in front of the Grace building and Bryant Park ● Identify areas that are uncomfortable for the main activities involved ● Investigate the causes of uncomfortable zones, taking into account wind effects generated by the surrounding buildings ● Evaluating the impact of the presence of trees in the urban layout What is the goal of this simulation? Example 1
  15. 15. Today’s example 1. This model represents the vicinity of Bryant park and the main buildings around it, including’ a. The Grace building b. NYC library c. The Bank of America tower CAD upload Google (n.d.).[Google Maps of Bryant Park and its surrounding.. Retrieved April 18, 2020.
  16. 16. Define region of Interest Define wind rose Define pedestrian zones 1 3 2 minute setup It’s that simple. 2 4 Define porous regions
  17. 17. What effect do the tree have on the pedestrian wind comfort? Example 1
  18. 18. What effect do trees have on the flow pattern? Example 1
  19. 19. Assessing the level of comfort with and without trees Porous Media and Wind Comfort Example 2: A bustling city center
  20. 20. ● Assessing the level of pedestrian comfort in a specific urban area ○ Using year-round meteorological data ○ With multiple directions of wind ● Identify areas that are uncomfortable for the designated activity ● Investigate the causes of uncomfortable zones, taking into account wind effects generated by the surrounding buildings ● Evaluating the impact of the presence of trees in the urban layout What is the goal of this simulation? Example 2
  21. 21. Today’s example 1. The model used represent a bustling city center with trees along pavements and squares CAD upload
  22. 22. What effect do the trees have on the pedestrian wind comfort? Example 2
  23. 23. ● In some locations and directions, the differences, in both transient and average are significant What effect do the tree have on the flow pattern? Example 2
  24. 24. ● In some locations and directions, the differences, in both transient and average are significant What effect do the tree have on the flow pattern? Example 2
  25. 25. ● We simulate trees with porous media simplification ● For our first example : ○ The park is a lot more comfortable with tree since they alleviate the downdraft effect of the wind coming against the facade ● For our second example: ○ Implementing trees along pavement, especially at street corners mitigate the cornering and channeling effects Trees make great windbreakers! Summary
  26. 26. Want to Learn more? Check out the articles below. Additional Resources ● A wind tunnel study on aerodynamic porosity and windbreak drag ● Computational Fluid Dynamics Simulation of Tree Effects on Pedestrian Wind Comfort in an Urban Area ● Including trees in the numerical simulations of the wind flow in urban areas: Should we care? ● A Global Database of Field-observed Leaf Area Index in Woody Plant Species ● How to Upload an STL File With Separate Layers

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