Eastwood evaluated scaled prototypes in a wind tunnel to determine how Sun-Link™ is loaded during wind exposure. In the wind tunnel, a partial scale model is coupled to an externally mounted six-component force balance to measure three moments and three forces, expressed in terms of yaw, pitch and roll. The force balance is calibrated for the model configuration in order to establish the virtual balance moment center. Under automated control, the model rotates through test positions that correspond to wind approach angles. Forces and moments are obtained directly and recorded as output from transducers (e.g., load cells) integral to the force balance. These datasets relate the specific form of the modules in the Sun-Link™ system to wind loads at various approach angles. In this way, wind tunnel testing enables load path engineering: the process where by design response to defined loads is continuous across the structure and loads are efficiently transferred to ground.



The Sun-Link™ test article set consists of families of components designed to simulate array fields with a 10°, 15° and 20° module tilt angle. For each tilt angle, a 4 x 1 row and a 4 x 4 array field were tested. 4 x 1 rows were evaluated for lift, drag and moment effects over a range of wind approach angles. 4 x 4 array fields were evaluated in a similar manner. Wind tunnel testing established that “per-module” lift on a 4 x 4 array field is a lesser value than the “per-module” lift on a 4 x 1 row; a front row “wind sheltering” effect was clearly observed. Armed with this key information, Eastwood evaluated array test article sets at all tilt angles for response to loading from more than 30 wind approach directions in order to determine the degree to which the sheltering effect is applicable.

The evaluation process requires assessment of over 175 wind tunnel runs corresponding to more than 1,500 data points generated from force balance analog input data acquired at 100 samples per second, then filtered and digitized. For each data point, sampling occurs over a five (5) second interval. Data acquisition, reduction, plotting and analysis are performed under program control. A run-time version of the program enables extended post-test evaluation of data sets. The final stage of the analytic process requires integration of wind load information with structural response. The initial load cases for FEA are basic: wind pressure loading and gravity. This data is replaced with information on loading obtained in the wind tunnel. The result is a final group of design/analyze cycles that define the precise shape and the structural response of primary Sun-Link™ components.