[MUSIC] Hello, close to a rough boundary the flow velocity is not uniform and a vertical shear in the horizontal velocity will occur. Does it impact the power curve of wind or marine turbines? The velocity, V0, used in power turbine relation corresponds to the velocity at the hub height. However, we know that both the atmospheric or the marine boundary layer exhibit a vertical velocity shear. We use a standard power flow for this vertical shear. The upstream kinetic energy will differ from the one calculated with a uniform flow. The power coefficient is defined as the ratio of the output power over the kinetic power of the upstream flow passing through the turbine. But in that case, the estimation of the upstream kinetic power is not correct because the flow is not uniform. Hence, in the case of a shear flow, we should recalculate the upstream kinetic power. Taking into account the vertical variation of the horizontal velocity passing through the turbine of diameter D. We first write the equation of the turbine perimeter. And we consider the elementary area at the altitude z of height dz, then we integrate the cubic velocity for all this elementary area dS inside the turbine perimeter. We replace the velocity with the power law and we get the following integral. We introduce the dimension as viable psi, the ratio of the altitude z over the turbine diameter d. Then a new dimensionless barometer appears naturally. The ratio of the hub height over the turbine diameter labelled here as psi h. It follows that the correction of the extreme kinetic power could be written as a function of the shear exponent alpha And has a parameter psi h. We will consider here that the height of the turbine hub is located approximately 1 diameter above the bottom boundary. The connection function depends now only on the shear exponent alpha, and we can plot on a graph its evolution for various values of alpha from 0 which correspond to your uniform flow to 0.6. We can see that the abstream kinetic power will be slightly reduced for a weak shear, while it will increase for values of the shear exponent above 0.3. Hence the vertical shear could induce negative or positive variations of the output power of a few percent. For more complex flow profiles that cannot be represented by a standard power law, the error on the estimation of the extreme kinetic energy could be much higher. This graph shows real institute measurements. The non-uniform upstream velocity was measured with lidar and the ratio of the upstream kinetic energy passing through the swept area of the turbine over the kinetic energy calculated with the hub velocity is plotted as a function of the shear exponent alpha. We could distinguish here two groups of points. The gray dots correspond to velocity profile that are correctly fitted with a power law. As expected, these points are distributed around the theoretical curve that we derived previously. But, the second group of points, the black dots, exhibit a much wider dispersion with a systematic underestimation of the upstream kinetic energy. These black points correspond to velocity profile that defer significantly from a power law. Hence, for these specific cases, the real flow profile should be taken into account. To sum up the vertical shear of the flow affects the upstream kinetic energy flows. It is therefore important to know the vertical profile of the horizontal speed and not only the speed at the hub height to estimate with high accuracy the power performance of a given turbine. Thank you.