Terms Of Propagation Direction Research Articles

An Improved Approach to Wave Energy Resource Characterization for Sea States with Multiple Wave Systems

Generally, wave energy resource assessment and characterization are performed based on an entire wave spectrum, ignoring the detailed energy features that belong to wave systems, i.e., wind waves and swells. In reality, the energy is separately possessed by multiple wave systems, propagating at different directions and velocities. Therefore, it is the wave system that is the most fundamental unit of the wave energy resource. Although detailed analyses of wind waves and swells can be conducted via wave system partitioning, operational assessment methods that can reveal the detailed wave energy characteristics of wave systems still deserve further development. Following a two-step partitioning procedure, this paper presents an improved approach to the characterization of wave energy resources based on grouped wave systems. Wave systems classified as the same group are consistent in terms of propagation direction, velocity, and other characteristics of wave energy, but these characteristics between the groups are obviously different. Therefore, in comparison with the traditional method, the new approach can reveal more comprehensive and more detailed characteristics of the wave energy resource in terms of (i) wind-sea and swell components, (ii) directionality, and (iii) wave conditions; details that represent valuable information for the improvement of the performance of wave energy converter devices and the optimization of the layout of device arrays in wave farms.

Double-array refraction microtremors

We present a critical analysis of the limitations of the standard ReMi technique, specifically in the case of directional sources, and we propose an alternative approach for the efficient acquisition and processing of passive surface wave data, that exploits a simple and yet effective field layout (two linear orthogonal arrays) and processing strategy. The motivations for using a 2D array for passive surface wave testing are reviewed, together with the limitations of the classical ReMi approach. Using synthetic and real data, the robustness of the method is shown, and the limitations of the simplified processing route are described. The possibility of acquiring active data on the same receiver spread allows a partial validation of the passive results, in terms of propagation direction, in addition to producing a broader band dispersion curve to be used in the inversion process. The proposed approach is an intermediate step towards the full complexity of beamforming analysis, that can be of simple use for practitioners and yet help avoid the most common and dangerous interpretation pitfalls inherent to linear array micro-tremor techniques.

Complex bound and leaky modes in chains of plasmonic nanospheres

Bound and leaky modes with complex wavenumber in chains (linear arrays) of plasmonic nanospheres are characterized for both longitudinal and transverse polarization states (with respect to the array axis). The proposed method allows for the description of each mode evolution when varying frequency. As a consequence, full characterization of the guided modes with complex wavenumber is provided in terms of propagation direction, guidance or radiance, proper or improper, and physical or nonphysical conditions. Each nanosphere is modeled according to the single dipole approximation, and the metal permittivity is described by the Drude model. Modal wavenumbers are obtained by computing the complex zeroes of the homogeneous equation characterizing the field in the one dimensional periodic array. The required periodic Green's function is analytically continued into the complex wavenumber space by using the Ewald method. Furthermore, a parametric analysis of the mode wavenumbers is performed with respect to the geometrical parameters of the array.