Tim De Troyer

A Fast Maximum Likelihood-Based Estimation of a Modal Model

In this paper, the ML-MM estimator, a multivariable frequency-domain maximum likelihood estimator based on a modal model formulation, will be represented and improved in terms of the computational speed and the memory requirements. Basically, the design requirements to be met in the ML-MM estimator were to have accurate estimate for both of the modal parameters and their confidence limits and, meanwhile, having a clear stabilization chart which enables the user to easily select the physical modes within the selected frequency band. The ML-MM method estimates the modal parameters by directly identifying the modal model instead of identifying a rational fraction polynomial model. In the ML-MM estimator, the confidence bounds on the estimated modal parameters (i.e., frequency, damping ratios, mode shapes, etc.) are derived directly by inverting the so-called Fisher information matrix and without using many linearization formulas that are normally used when identifying rational fraction polynomial-based models. Another advantage of the ML-MM estimator lies in its potential to overcome the difficulties that the classical modal parameter estimation methods face when fitting an FRF matrix that consists of many (i.e., 4 or more) columns, i.e., in cases where many input excitation locations have to be used in the modal testing. For instance, the high damping level in acoustic modal analysis requires many excitation locations to get sufficient excitation of the modes. In this contribution, the improved ML-MM estimator will be validated and compared with some other classical modal parameter estimation methods using simulated datasets and real industrial applications.

A time-domain method for prediction of noise radiated from supersonic rotating sources in a moving medium

This paper presents a time-domain method for noise prediction of supersonic rotating sources in a moving medium. The proposed approach can be interpreted as an extensive time-domain solution for the convected permeable Ffowcs Williams and Hawkings equation, which is capable of avoiding the Doppler singularity. The solution requires special treatment for construction of the emission surface. The derived formula can explicitly and efficiently account for subsonic uniform constant flow effects on radiated noise. Implementation of the methodology is realized through the Isom thickness noise case and high-speed impulsive noise prediction from helicopter rotors.

Design of a hydroformed metal blade for vertical-axis wind turbines

Vertical-axis wind turbines (VAWTs) have experienced a renewed impulse during the last few years with important research efforts focused on them. This work explores whether the global profitability of VAWTs can be improved through improved manufacturing techniques. We studied how large-series production techniques from the sheet-metal industry can be used to create blades of H-type Darrieus turbines. Blade size and shape were determined via aerodynamic and structural analyses. The proposed solution is based on the use of hydroforming manufacturing techniques with metal sheets. Our estimations show that with the positive effects of a large-scale use and production (economies of scale), such metal blades have a 90% reduction potential in their production costs compared to fibre-reinforced ones for single turbines.