Karl Janssens

Advanced identification techniques for operational wind turbine data.

During a field test campaign, Sandia National Laboratories acquired operational data both in parked and rotating conditions on a modified MICON wind turbine with the Sensored Rotor 2 experiment. The objective of the test campaign was to acquire data to develop advanced system identification and structural health monitoring techniques. The data includes wind speed, tower deformations, low and high speed shaft rotational speed measurements as well as accelerations and strains on different locations of the blades. Applying Operational Modal Analysis on such data represents a difficult task due to the strong influence of rotor harmonics on the measured data. Accurately identifying and removing the harmonics is required to perform modal parameter identification. In this paper, data acquired with the turbine in both parked and operating conditions will be analyzed and the modal results compared. Several harmonic removal techniques will be applied on the operational data and their efficiency to solve this specific problem analyzed. In addition, a new enhanced identification technique will be applied, that improves the parameter estimation accuracy in the case of very noisy data and also provides uncertainty bounds of the parameters.

Zebra Tape Butt Joint Algorithm for Torsional Vibrations

At the development stage of automobile constructions, many powertrain configurations may be considered. Due to complicated coupling mechanisms, the natural frequencies of the combined system are difficult to predict. It is therefore necessary to run tests on automotive subsystems under realistic operating conditions. To completely understand the dynamic behaviour, a study of both torsional and translational motions along the driveshaft is necessary. Torsional vibrations can conveniently be measured at any point along a rotating shaft by using a zebra tape that overcomes the drawbacks of existing systems which are either expensive or require time-consuming and difficult shaft modifications. Zebra tapes however require a dedicated DSP processing due to the butt joint of the two tape ends. This paper presents a new algorithm to correct the tacho moments obtained from pulses generated with a high quality zebra tape glued on a rotating shaft with torsional vibrations. Due to the misalignment of the stripe pattern at the joint of the two tape ends, the tacho moments are not evenly distributed over the shaft. The angle between subsequent tacho moments is exactly the same except at the butt joint. The algorithm first identifies the position and angular interval at the butt joint by using an angle estimator function and a dedicated spline interpolation and FIR bandpass filter. This information then allows to reconstruct the exact angle evolution and perform a proper torsional vibration analysis. First, the principles of the butt joint correction algorithm are discussed. Then, an error analysis is performed on a simulated dataset, evaluating the accuracy of the algorithm in the presence of torsional vibrations.

Passenger vehicle pass-by noise test using generalized inverse beamforming

Janssens, K., Britte, L., Deblauwe, F., Time-Domain Source Contribution Analysis of in-Room Vehicle Pass-by Noise (2011) International Conference in Sound and Vibration, , Rio de Janeiro, July

Effect of systematic FRF errors on matrix inversion based vibro-acoustic analysis methods

The establishment of a non-parametric system description in terms of a Frequency Response Function matrix is an essential step in many structural and vibro-acoustic analysis approaches such as Modal Analysis, Load Identification, Transfer Path Analysis and Substructuring. A crucial step in many of these applications is the inversion of a matrix of this FRF matrix. Several studies have been reported on the influence of stochastic FRF errors on this matrix inversion, leading to the use of a pseudo-inverse approach, SVD truncation, regularization etc. but little is known about the effect of systematic errors, such as amplitude or frequency shifts and inter-FRF inconsistencies on the matrix inversion result. The present paper investigates the effect of selected systematic FRF measurement errors on applications involving matrix inversion, with emphasis on the Transfer Path Analysis method. The subject is reviewed through analytical considerations and through simulations on a reference numerical model (the Garteur model). In particular, the sensitivity of two Transfer Path Analysis methods with respect to the studied systematic errors is analyzed and considerations on increasing the robustness of these methods are derived.