Effects of solar radiation and surface roughness on nominally flat coastal rocks

• Online Access: http://hdl.handle.net/2047/D20316389

In this study, the radiative heating of coastal rock surfaces were investigated for scales relevant to the sessile organisms living there. The top surface of the rocks were assumed to be exposed to direct, diffuse and mutual radiative heat flux and convection. Transient heat conduction in the rock was simulated using a commercially available finite element software package. Analysis was carried out for an actual surface, whose surface roughness was imported to the simulation platform. Measured surface temperatures compared favorably with the predictions. Two- and three-dimensional (2/3D) rough surfaces were generated numerically to seek potential relationships between surface temperatures and roughness. The mean temperatures of the surfaces were found to be independent of surface roughness; but the standard deviation and the normalized maxima of surface temperatures were found to vary monotonically with the standard deviation of the surface roughness for both 2D and 3D surfaces. Increasing surface irradiation was found to increase the mean surface temperature monotonically, but a higher increase in the standard deviation was predicted. A mechanism for excessive heating of the surface peaks was identified based on the comparison of direct, mutual, and convective heat flux components and conduction into the rock volume. This work showed that refugia area for sessile organisms depends on the surface roughness. Decrease in refugia area during the diurnal cycle was predicted to be more pronounced for rougher surfaces than smoother ones. The work should be expanded to include thermal analysis of actual coastal rocks, whose surface variations are difficult to create mathematically, and the effects of moisture transport.