The focus of this paper is on the development of validated models for wind turbine blades. Validation of these models is a comprehensive undertaking which requires carefully designing and executing experiments, proposing appropriate physics-based models, and applying correlation techniques to improve these models based on the test data. This paper will cover each of these three aspects of model validation, although the focus is on the third - model calibration. The result of the validation process is an understanding of the credibility of the model when used to make analytical predictions. These general ideas will be applied to a wind turbine blade designed, tested, and modeled at Sandia National Laboratories. The key points of the paper include discussions of the tests which are needed, the required level of detail in these tests to validate models of varying detail, and mathematical techniques for improving blade models. Results from investigations into calibrating simplified blade models are presented.
When measuring the structural dynamic response of test objects, the desired data is sometimes combined with some type of undesired periodic data. This can occur due to N-per-revolution excitation in systems with rotating components or when dither excitation is used. The response due to these (typically unmeasured) periodic excitations causes spikes in system frequency response functions (FRFs) and poor coherence. This paper describes a technique to remove these periodic components from the measured data. The data must be measured as a continuous time history which is initially processed as a single, long record. Given an initial guess for the periodic signal's fundamental frequency, an automated search will identify the actual fundamental frequency to very high accuracy. Then the fundamental and a user-specified number of harmonics are removed from the acquired data to create new time histories. These resulting time histories can then be processed using standard signal processing techniques. An example of this technique will be presented from a test where a vehicle is dithered with a fixed-frequency, sinusoidal force to linearize the behavior of the shock absorbers, while measuring the acceleration responses due to a random force applied elsewhere on the vehicle.
Structural dynamic systems are often attached to a support structure to simulate proper boundary conditions during testing. In some cases the support structure is fairly simple and can be modeled by discrete springs and dampers. In other cases the desired test conditions necessitate the use of a support structural that introduces dynamics of its own. For such cases a more complex structural dynamic model is required to simulate the response of the full combined system. In this paper experimental frequency response functions, admittance function modeling concepts, and least squares reductions are used to develop a support structure model including both translational and rotational degrees of freedom at an attachment location. Subsequently, the modes of the support structure are estimated, and a NASTRAN model is created for attachment to the tested system.