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Surface Features
Published in Wolfgang Osten, Optical Inspection of Microsystems, 2019
Segmentation is the next step following on from the edge operator, and it aims to segment the surface topography into regions of interest, for example, to separate and delineate the step planes. These segmentation techniques developed by Scott [19] consider the surface as a continuous function and splits the surface into segments consisting of hills and dales (Figure 2.9). The techniques are based on work by Maxwell (1870) [27], who proposed dividing a landscape into regions consisting of hills and regions consisting of dales. A Maxwellian hill is an area from which maximum uphill paths lead to one particular peak, and a Maxwellian dale is an area from which maximum downhill paths lead to one particular pit. By definition, the boundaries between hills are course lines (watercourses), and the boundaries between dales are ridge lines (watershed lines). Maxwell was able to demonstrate that ridge and course lines are maximum uphill and downhill paths emanating from saddle points and terminating at peaks and pits. Scott formulated this technique [16] for surface metrology and defined the critical points and lines which are crucial to defining hills and dales on a surface representation as texture primitives, as shown in Figure 2.9.
Numerical and experimental analysis of the flow over sinusoidal hills
Published in International Journal of Ambient Energy, 2021
Pramod Kumar Sharma, Vilas Warudkar, Siraj Ahmed
In order to enhance the efficiency of the wind farms, more efforts are placed in finding the optimum locations of the wind turbines. Currently, the flow analysis over complex terrain becoming a critical issue due to rapid variation in the flow conditions with the wind direction. Previously, it observed during experimentation using Wind tunnel and field measurements; significant changes occur in the direction of wind flow over complex terrain (Lange et al. (2016), Lubitz and White (2007), Walmsley et al. (1990)). Several wind tunnel downscale models and numerical simulations can be studied under restricted environments. Cheng, Lubitz, and White (2004) investigated the wind flow model with the diurnal cycle over Altmont Pass in California. It can be difficult to compare the wind flow model in complex terrain with another terrain. This problem can be overcome by idealising the flow problems with simple terrain category. Hunt and Synder (1980) studied the streamlines flow over different hills with changing shapes. The maximum velocity obtained near the crest of the hill due to accelerated wind flow. Webstar, Defraaff, and Eaton (1996) found the distinct features of boundary layer development over the hill in compare to flat surfaces. The local surface characteristic of the hill influences the location of flow separation. Earlier it has been found that the hill slopes steeper than 20 degree causes flow separation more likely than 10 degrees (Arya, Capuano, and Fagen 1987; Finnigan 1988). The location of flow separation point can also change due to a sudden change of the geometry of the hill. Teunissen et al. (1987) investigated about the enhancement of the flow separation due to increase in roughness during the study over Askervein hill. In a neutrally stratified region where speed up effects due to the hill is often less significant (Emeis 2013). When wind flows over complex terrain in a neutrally stratified zone, the formation of lee waves behind hills occurs, this moves further to large distances. It is shown in Figure 1, where blue lines indicate the flow close to the ground. Dale 2016 observed the acceleration phenomenon under the lower parts of the hil and retardation under the crests of the downstream parts of the hill. Nedjari et al. (2017) analyzed the topographic effect on the wind turbine wakes in a complex terrain using CFD. A good agreement has been found of the wind turbine wakes using RANS and SCADA data system for a complex terrain (Astolfi, Castellani, and Terzi 2018). The previous research on the wind turbine wakes has been further modified using integrated Doppler lidar data from Perdigao experiment (Barthelmie et al. 2018).