# Wind-Based Parametric Design in the Changing Climate
## 2 Materials and Methods
### Steps of the Proposed Wind-Based Form-Finding Method
#### 2.1.2 Parametric Designing Coupled with CFD Simulations  
Parametric designing simplifies the process of working with multiple design alternatives, therefore leading to selecting the most suitable variant within the design context [39]. The parametric architectural software Rhinoceros and its algorithmic plug-in, Grasshopper, enable the exchange of information between the design and simulation software, which, applied to the nature-driven architectural form-finding, leads to the creation of several environment-responsive design choices [40]. Figure 3: The design loop of creating wind-based architecture. The process can, in the future, lead towards designing architecture, morphing its shape in the wind. Concerning the parametric definition in the wind-based design process, the best performance of the design in the wind will be achieved when parametric variables are set correctly, according to the design intentions (Table 1). The wind-based shape optimization, or, in other words, the exploration of multiple design directions in the conceptual design stage, based on their performance in the wind, needs to be as effective as possible. Through examining various CFD software, it was observed that the most efficient for the early design stage, in terms of cost, time, and accuracy, is the CFD analysis within a 3D modeling environment. Swift for Grasshopper, utilizing OpenFOAM for the CFD calculations, enables parametrically setting the virtual wind tunnel (VWT), as well as boundary conditions in the same Grasshopper file. The SimpleFoam (Semi-Implicit Method for Pressure-Linked Equations) iterative algorithm, RAS (Reynolds-Averaged Simulation), and the Standard k-\(\epsilon\) turbulent model are used in Swift for computing Navier-Stokes equations [41]. As the algorithm is iterative, we have to determine when the calculations stop by setting the number of iterations, or convergence criteria, or both. Convergence criteria define when the initial residuals of pressure \(p\), velocity components \(v_{\text{x,y,z}}\), as well as the turbulent kinetic energy \(k\), and turbulent kinetic energy dissipation \(\varepsilon\) stop changing or are small enough. Swift, running on the OpenFOAM platform, uses kinematic pressure within incompressible flow solvers: \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & **The Influence of Architecture** & & **Parametric Variables** \\ \hline \multirow{4}{*}{Minimum resistance} & \(\circ\) & wind pressure reduction with & \(\circ\) & height \(h\) and length \(l\) of the buildings \\  & \(\circ\) & aerodynamic-shape designs & \(\circ\) & frontal area \(A\) on the windward side (first \\  & \(\circ\) & lighter building structures & & wind impact) \\  & \(\circ\) & undisturbed wind flow & & & \\ \hline \multirow{4}{*}{Concentration} & \(\circ\) & natural ventilation & \(\circ\) & specific dimensions of openings (also \\  & \(\circ\) & wind energy harvesting & \(\circ\) & space between buildings) \\ \hline \multirow{4}{*}{Diffusion} & \(\circ\) & pollutant dispersion & \(\circ\) & specific dimensions of openings (also \\  & & & & spaces between buildings) \\  & & & \(\circ\) & the relative position of the openings \\ \hline \multirow{2}{*}{Deflection} & \(\circ\) & shelters from the wind & \(\circ\) & height \(h\) \\  & \(\circ\) & pedestrian wind comfort & \(\circ\) & angle \(\alpha\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The goals of wind-driven designing and possible variables in parametric designing. Figure 4: Left: the colors represent the wind speed, the numbers next to the wind directions represent the percentage of time per year. Right: the colors represent the wind temperature (source of data: EnergyPlus [37]). \[p_{k}=\frac{p_{k}}{\rho} \tag{1}\]  
where \(p_{k}\) is the kinematic pressure [m\({}^{2}\)/s\({}^{2}\)], \(p_{a}\) is the static pressure [Pa], and \(\rho\) is the density of the flow [kg/m\({}^{3}\)]. The kinematic pressure will subsequently be converted to Pa, multiplying it by 1.25 kg/m\({}^{3}\).