## 2 Materials and Methods
### CFD Simulation  
The numerical simulations were performed with the use of the ANSYS 2022R2 Fluent with Fluent Meshing software in the Workbench environment. The main aim of the CFD simulations was the estimation of the aerodynamic forces acting on the investigated models of the crane trusses. The models of the tower truss and the jib truss (Figures 3 and 5) were placed in a rectangular volume filled with air, as shown in Figure 13. The cross-section of this volume is a rectangle with geometrical dimensions of 2200 mm \(\times\) 1400 mm (hydraulic diameter \(\mathrm{D_{H}}=1.711\) m). The model was placed 1500 mm from the inlet (blue wall in Figure 13) and 2000 mm from the outlet. The assumed dimensions of the aerodynamic tunnel precisely correspond to the geometric dimensions of the real aerodynamic tunnel. In the simulations, the standard air properties were assumed; therefore, \(\rho=1.225\) kg/m\({}^{3}\), T = 15 \({}^{\circ}\)C, and p\({}_{0}\) = 101,325.25 Pa. The walls of the aerodynamic tunnel as well as the whole surface of the studied models were assumed to be stationary boundaries and a steady state of airflow was assumed. One of the most important problems is the appropriate choice of the turbulent model. In the current work, the three most frequently applied models were used: the Reynolds stress model, k-\(\omega\) model, and k-\(\varepsilon\) model. The first model, used by [PERSON] et al. [40], causes the computations to converge unacceptably slowly. The second model, used by [PERSON] et al. [33], [PERSON] et al. [34], and [PERSON] et al. [36], requires preparing a specific mesh at the boundary conditions. In the estimation made for the studied structure using a special calculator available online [59], the first layer of the finite volume should be about 10 \(\times\) 10\({}^{-5}\) m in height. Unfortunately, this leads to an enormous number of nodes and finite element volumes. Finally, the standard k-\(\varepsilon\) model with a standard wall function was used. It is  
Figure 12: Diagram of the measuring system. 1—the model of the truss; 2—the five-component aerodynamic balance, 3—amplifier module with data acquisition systems, 4—the turntable with stepper motor, 5—the motor step control system, 6—the pressure sensor Pitot pipes located on the x, z plane, 7—the pressure scanner, 8—the wind sensor, 9—thermo-anemometer AMD 2000, 10—DaqBoard/2000 card, 11—PC. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Model** & **A\({}_{\text{ref}}\) (m\({}^{2}\))** & **b\({}_{\text{ref}}\) (m)** \\ \hline Part of the tower truss & 0.021438 & 0.552 \\ Part of the jib truss & 0.017304 & 0.138 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The reference values for the force coefficients. worth noting that this model is still in use, for example, in the works of [PERSON] et al. [19], [PERSON] et al. [21], [PERSON] et al. [32], and [PERSON] et al. [57]. In order to generate the appropriate mesh, a relatively new approach was used, namely the shape of the elements was assumed to be polytetrahedral. Moreover, it was assumed that the approximate edge length of the faces of the elements, which cover the surface of the truss model, is equal to \(l_{c}=1.5\) mm. The length of the edges of the faces of the elements that belong to the circular plates and the vertical rod is equal to \(l_{c}=3.4\) mm. The maximal length of the rest cells is equal to \(l_{c}=108.867\) mm. Figure 14 represents the cell mesh generated for the tower truss model. Table 4 presents the values of the aerodynamic forces and corresponding coefficients, computed according to Equation (6), for different sizes of cells. The convergence test was performed for the part of the tower truss where the angle \(\beta=0^{\circ}\) (Figure 7), air speed V = 15 m/s, and the turbulent intensity \(I_{v}=9\%\). Table 5 shows the corresponding number of the nodes, faces, and cells.