Press Room - CFD used to model new bridge

CFD used to model new bridge

A new bridge is to be built over the Svinesund fjord, on the border between Sweden and Norway. The total length of the bridge will be 680 meters and the span will be 242 meters. SMHI have calculated the wind and turbulence conditions in the area around the bridge. The purpose of the study was to predict wind load for the bridge. An image of the planned bridge is shown in figure 1.

From height data, a mesh measuring 10km by 10 km with a height of 1 km was built. As seen from figure 2, the terrain is complex. The light blue colour is the water at sea level and the highest area (red) is about 160 m above sea level.

Land use data for every 25 metres in 20 different classes were used to define ground surface roughness. The data were based on satellite images. Examples of different land use classes are: water (light blue), bog area (blue), different kinds of coniferous forest (green colours), deciduous wood (yellow), rockface (red), open area (light brown) etc. Figure 3 shows the variety of land use data used in
the model.

Figure 4 shows that wind speed is high over the sea due to low friction. When the airflow enters land it is affected by the higher friction there and the topographic landscape. The turbulence increases and the wind speed decreases near the ground. A new boundary layer is built over land. Figure 4 shows how the wind speed differs a lot at the 10 meter level above ground due to differences in the landscape.

In one site not far from the bridge, the three wind components were measured 10 meters above ground. From these data sets we could calculate the turbulent kinetic energy (blue dots) and compare with the CFD calculations (red line). In figure 5, one can see that the agreement between model and measurements is very good for the given wind direction.

Figure 6 shows the vertical wind velocity component in a vertical cross section just where the bridge will be built. The horizontal line is 50 metres above sea level and approximately the height of the bridge.

For more information visit www.smhi.se/cfd, or contact lennart.wern@smhi.se or mikael.magnusson@smhi.se