AB3080 L. Learning Objectives: About the Speaker:

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1 AB3080 L While architects have tested their designs in wind tunnels for many years, the process is typically outsourced to engineering firms and not easily accessible to architects during the conceptual phase. As Computational Fluid Dynamics (CFD) software like Autodesk Simulation CFD becomes more affordable and easier to use, architects are for the first time able to incorporate wind data into their design process and harness the wind for structural loading, passive ventilation, passive cooling, and building integrated wind generation. In this hands on lab, we will look at a project that integrates quantitative analysis in Autodesk Simulation CFD into a thorough, multi staged aerodynamic performance driven design process for supertall buildings based on the multidisciplinary optimization borrowed from the aerospace industry. We will also demonstrate the involvement of computational design software like Autodesk Vasari and Grasshopper in the process. Learning Objectives: Introduction to Multi Disciplinary Optimization Design process of supertall s aerodynamic performance design. Hands on learning of setting up an external incompressible flow case for supertall analysis, and analyze the results About the Speaker: Darren s main interest is in performance driven architecture design. He has worked on a variety of cultural, public, hospitality, mixed used, and urban design projects in Asia and America. After graduating from Harvard with a Master in Architecture (I) degree, Darren has worked for OMA in Beijing, ZNA, and RTKL. Before becoming an architect, Darren obtained his Dual Master of Science in Aero/Astro and Systems Engineering from MIT and Bachelor of Science in Mechanical and Aerospace Engineering from Cornell University. Contact information:, (available ) Page 1 of 8

2 What is CFD? Computational Fluid Dynamics (CFD) Wikipedia: A branch of fluid mechanics that uses numerical methods and algorithms to solve and analyze problems that involve fluid flows. My definition: a computer simulation of fluid flow, with modeling based on the laws of the conservation of mass, momentum, and energy. Initial conditions, boundary conditions, and material properties are the givens; fluid pressure, temperature, velocity, etc. are the unknowns to be solved. What is Autodesk Simulation CFD? A CFD software that returns reasonably reliable results in timely and graphical manner. Compatible with geometries generated by most 3D software. Good for: Compare different design options during conceptual phase Graphics generation for marketing purpose LC: Left Click, RC: Right Click, MB: Middle Button How to set up? Step 1. Prep the model In Rhino, trim and join everything, no gap, no broken pieces (same as for 3D printing) Step 2. Build a wind tunnel and place the model inside Build a wind tunnel using surfaces. The upstream and downstream dimensions need to be 5x to 10x the characteristic length of the model, the width needs to be 3x to 4x, and the height needs to be 1.5x to 2x. Page 2 of 8

3 The model should better be attached to the wind tunnel and joined. Step 3. Export the file as.sat (from Revit or ProE, can also directly launch Simulation CFD) Inside Simulation CFD Step 1. Set up new design study and import geometry Application Button New New Design Study Browse for the.sat file exported from Rhino, and give a name to the design study LC Create new design study, and a folder containing all the computational data will be automatically created. Simulation CFD checks the geometry, and gives an error message if the geometry is not fully closed. Step 2. Set materials Orient the view using the view cube on upper right corner Under Design Study Bar Scenario 1 Material, select Unassigned and Double Click Use default setup: Air Apply. The model s color becomes cyan. Page 3 of 8

4 Step 3. Set initial and boundary conditions Under Design Study Bar Select Boundary Conditions Select the inlet by RC the surface at Y = 0, click on Edit In Boundary Conditions, assign a velocity to inlet. In this case, 36m/s, equivalent to 80 mph. A black strap will appear on the inlet surface Similarly, assign Pressure = 0 to the outlet surface, and Slip/Symmetry to the side and top walls. Leave the bottom (ground) and building what they are Step 4. Set Mesh Size Select Mesh Size LC on Autosize for a crude grid LC on Regions, add Region 1 around the building, form a finer grid. Include more area in the downstream direction if want to capture the wake. In Mesh Refinement Regions, under Step 2: Define region, assign region size and location LC on Get local mesh size, then give a grid size smaller than the number in the text box, and spread changes. Click OK. Page 4 of 8

5 Repeat again to add Region 2 if want to capture more details Step 5. Solve Click on Solve in the Simulation panel Under Solve, Save Intervals Results, assign an interval for saving results Under Iteration to Run, assign 50, then click on Solve. If the case is set up properly, it will run for 50 iterations. Then under Continue From, enter 50. Under Iterations to Run, enter 1000 or a large number. Case will stop either if converged or reaches the limit. Solve Solution Control Advanced Automatic convergence assessment. Change the convergence criteria here if desired. Page 5 of 8

6 Step 6. Result Analysis Under Results tab, in Results Tasks ribbon, the most commonly used tools are Planes and Wall Calculator To have unobstructed view of inside the wind tunnel, hide walls by View Surface Blanking under Appearance ribbon Mid Button Click on walls to be hidden Add Plane by Results Planes Add LC on Plane to change normal direction (x, y, z). Can change location of Plane by dragging on the arrows or entering different values by RC on Plane Edit Plane Control. Under Planes ribbon, Result, select the type of result to be displayed: Velocity Magnitude, Static Pressure, Temperature, etc. To change legend range, RL on legend to the left Legend Options change Min, Max, and other options Page 6 of 8

7 To use Wall Calculator by RC in the empty space Show All Then Results Tab Wall Calculator select Surface Select All (green double check mark) then LC on the walls of the wind tunnel to deselect them, so the result will be calculated only for the building walls in Wall Results window, check results to be calculated, such as Force, Torque, etc. click Calculate Under Output tab, click Write to file to save Excel sheet Open Excel, scroll down to the bottom for the results of total forces and moments in different directions. Summary Total area m^2 TOTAL FX 2.01E+06 Newton TOTAL FY 2.44E+07 Newton TOTAL FZ 2.19E+06 Newton Center of Force about X Axis (Y Z) m Center of Force about Y Axis (X Z) m Center of Force about Z Axis (X Y) m TOTAL MX 6.44E+09 N m TOTAL MY 4.70E+08 N m TOTAL MZ 3.78E+07 N m Torque 3.78E+07 N m Page 7 of 8

8 Use Iso Surface by Results tab Iso Surfaces Add select under Quantity the result to be visualized Change the value of the Iso Surface by RC on Iso Surface Edit Iso Surface Control drag the bar Use Traces by first giving a Plane in the direction normal to the traces, then Results tab Planes ribbon Traces select a Seeding method (Rectangular grid) Add points click on the Plane to define the rows and columns Add trace set To optimize the view, RC on Set in Traces window Set properties change Appearance, Width, etc. Can also change background color, etc. to make the view more legible Page 8 of 8