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NIST has evaluated the model ’ s performance under design gravity loads and is identifying credible failure sequences using the model to analyze the effect of component failures on the structural system stability . Admittedly , the results of such tests may reflect more on our methods of approximating a solution to the model , or on our choice of relevant free parameters , than on the fundamental assumptions of the model itself , but that ’ s part of the problem of testing the model — find ways to confront the central assumptions with crucial tests , ie , tests whose evaluation is not overly dependent on incidental aspects of the model ’ s formulation . These forecasts were used to develop improvements in the model ’ s ability to realistically render urban boundary-layer properties .