2017 Volume 42 Issue 2 Pages 45-56
Accurate prediction of the secondary moment of three-dimensional turbulent wind field is important for structure dynamic analysis, while literatures on turbulence scales for offshore wind field are limited. In this study, an offshore wind field measurement campaign is carried out by an offshore meteorological mast using ultrasonic anemometers at 40, 60 and 80m heights, from which the turbulence integral length scales used in von Karman model are evaluated. It is found that turbulence structure at these heights for offshore wind field can be expressed well by von Karman model. The length scales are evaluated by model fitting for auto-spectrum and spatial coherence. The scales for auto-spectrum showed similar values with the IEC design code for longitudinal, lateral and vertical component. Spatial length scales in vertical direction show similar value with the model provided in ESDU considering surface roughness, but were larger compared to previous measurements in suburban area for longitudinal and lateral components. Spatial length scale in vertical direction for vertical component shows similar value with the previous measurement in lateral direction. Finally, a model for the turbulence length scales of three velocity components in von Karman model is proposed for offshore wind field, based on the measured results and previous studies.
