# Influence of Porosity on Drag Coefficient of Perforated Road Signs
## 1 Introduction
They found that gusting winds must also be considered for the safety of road signs, because they are not considered in windbreak wall design standards. [PERSON] et al. [15] proposed installation criteria to ensure the structural stability of windbreak walls installed on bridges. They conducted a wind tunnel test on the wind resistance characteristics of windbreak walls according to porosity and height. The results showed that the drag coefficient of windbreak walls increased as the windbreak wall height increased and the porosity decreased. [PERSON] [16] calculated the drag coefficient of a rectangular signboard using various variables. In the study, the width/height ratio of the signboard, the height ratio between the signboard and the ground and the porosity of the signboard were applied as variables. However, the final proposed drag coefficient was the experimental result of applying only the basic wind speed of 10 m/s. In other words, various wind speeds were not reflected in the final result. [PERSON] et al. [17] studied the wind load of panels with various porosities and proposed the drag coefficient of the panels according to the porosity. However, in the analysis, only panels installed on the ground were considered; the drag coefficient of elevated panels was ignored. [PERSON] et al. [18] conducted CFD analysis on panels perforated using various shapes and standards. They analyzed the wind load reduction effect by setting the diameter and spacing of the holes drilled in the panels as variables. However, the drag coefficient was fixed at 1.2, thereby ignoring the changes in drag coefficient due to the wind speed. [PERSON] et al. [19] conducted a wind tunnel test to assess the drag coefficient of an insect net used for agriculture. The porosity of the applied insect net was 65%, and the wind speed ranged from 1 to 22 m/s. When the drag was measured by increasing the wind speed, the drag coefficient of the insect net converged to 0.7 at a low wind speed of less than 10 m/s and showed a tendency to decrease at a high wind speed of more than 20 m/s. [PERSON] et al. [20] analyzed the characteristics of airflow around fences with various porosities. They analyzed the relationships among the porosity, height and wind speed of the fences. The drag was found to be high at a porosity of less than 20%, which later converged to a certain value as the porosity increased. The Korea Institute of Civil Engineering and Building Technology [2] proposed a road sign installation technology that applies a perforated plate and analyzed its effect. They proposed a structural form of the post and its manufacturing technology to facilitate the application of the perforated plate. Furthermore, they conducted a legibility test by installing a road sign with the perforated plate. [PERSON] et al. [21] determined the drag coefficients for longitudinal finned tubes, considering various wind directions. Numerical analysis was performed by CFD analysis, and experimental testing was performed in a wind tunnel test. [PERSON] et al. [22] conducted CFD analysis to examine the wind loads on spherical structures with different height and diameter ratios. The results show that the largest pressure coefficient at the windward surface increased with the height and diameter ratios. In this study, the drag coefficient was analyzed to enable the detailed design of perforated road signs with porosity less than 30%. CFD analysis was conducted and implemented to reflect the existing conditions in the actual environment. The aspect ratio, clearance ratio and porosity of the actual perforated road signs were applied, and the drag coefficient of perforated road signs was calculated according to the porosity and wind speed. Finally, based on the analysis results, the drag coefficient reduction effect of perforated road signs with porosity less than 30% was analyzed.