Search

This paper describes the results of an experimental campaign aimed at the determination of heave hydrodynamic coefficients for a column of a floating wind turbine platform, equipped with a solid heave plate. The tests are carried out with an experimental system that allows performing both heave forced oscillation tests and heave decay tests. A specific characteristic of the system is the reduced mechanical friction, thanks to the use of air bushings. A series of forced oscillation and decay experiments have been carried out with such a model, and the hydrodynamic coefficients obtained in both types of tests are compared. Results show correlation between both methods if the mean of the peaks of the decay process is chosen to represent its Keulegan–Carpenter number (KC), with a fair matching of the results in the KC range where both methods are applicable. With the objective of conducting an uncertainty assessment which can be relevant for the full-scale extrapolation of results, non-dimensional added mass and damping coefficients are proposed. They incorporate the primitive relevant variables and are shown to lead to a notable collapse of the various results in the form of curves with small differences among them. With these coefficients, an uncertainty assessment is carried out, propagating to those coefficients the uncertainties of the primitive variables in place. Such non-dimensional coefficients are useful to develop simple models to estimate the dimensional ones to be used in numerical simulations of the full scale system. The estimated uncertainties can serve to define design safety margins for the values of such coefficients.

In this work, we propose an inertial amplified resonator (IAR) as a building block of a tunable locally resonant metasurface. The IAR consists in a mass–spring resonator coupled with two inerters, realized by two inclined rigid links connected to an additional mass. The IAR has a static behaviour equivalent to that of a standard mass–spring oscillator whereas its dynamic response can be controlled by means of the geometrical configuration and mass of the inerters. We derive the dynamic amplification factor and the base force of the IAR for an imposed harmonic motion and perform a parametric study to unveil its peculiar dynamics. Next, we use an effective medium approach to derive the closed-form dispersion law of a metasurface consisting of IARs coupled to a semi-infinite elastic substrate. We show that the IAR enriches the dynamics of the metasurface providing the ability (1) to shift its bandgap frequency spectrum without changing the mass and stiffness of the resonators, (2) to design single frequency or multi-frequency (metawedges) metasurfaces, (3) to obtain a high-frequency behavior typical of an added dead mass layer (i.e., non-resonant), which confers to the metasurface additional filtering properties.

This work is aimed at the numerical analysis of the vibration response of a plate, carrying one or more concentrated masses, under a stochastic, and convective load. The pressure load is a typical turbulent boundary layer excitation (TBL) and the structural configurations reproduce common experimental situations because the concentrated masses can be considered similar to accelerometer sensors. The models adopt the Corcos TBL model and the concentrated masses are simulated with the Dirac singularity function. The approximations, introduced with the above assumptions on the concentrated masses, and the necessary numerical accuracy, in calculating the structural responses, are discussed. The added masses do not lead to a relevant modification of the global structural response but, on the contrary, the results show that the local effects can be relevant: the paper highlights the differences of the vibration responses from the analogous structural configurations under a stochastic load without convective characteristics.