Hydrodynamic characterization of floating offshore wind turbines : an experimental and numerical multi-degree of freedom analysis

Wind energy has become a crucial resource in sustainably meeting increasing global energy demands. Recently, offshore wind energy has been gaining traction due to its higher gross resource and larger unclaimed real-estate relative to its onshore counterpart. Floating offshore wind turbines (FOWTs) are increasingly popular, particularly designs with semisubmersible platforms. However, transitioning from bottom-mounted to floating platforms introduces large complexities, e.g., due to wind-wave-structure-mooring interactions, and more research is needed to correctly estimate FOWT behavior. While, intensive validation campaigns with mid-fidelity numerical models could estimate FOWT behavior in the linear wave frequency region, they have consistently underestimated large low-frequency excitation observed in physical experiments. This low-frequency excitation occurred near the system’s surge and pitch natural frequencies, and was determined to be hydrodynamic in nature. Further investigation has suggested that the numerical underprediction was due to a mischaracterization of viscous drag terms and the influence of nonlinear wave hydrodynamics. Several suggested correction methods Have represented the low-frequency surge and pitch excitation, with various levels of success. However, these methods require large amounts of a priori information or are not widely applicable to differing conditions. This study investigates the impact of rotational viscous damping terms on improving the low-frequency hydrodynamic behavior of mid-fidelity FOWT models. The goal was to determine a physically justifiable, low parameter model methodology for accurately capturing the low frequency response. The project included both experimental system identification and numerical validation components. Free decay tests in surge, heave, and pitch were performed on a 1:50 scale model of the DeepCwind semisubmersible platform-supported wind turbine in the O.H. Hinsdale Directional Wave Basin at Oregon State University. Linear and quadratic damping coefficients were extracted from these tests using the PQ methodology and incorporated into the mid-fidelity hydrodynamic simulation program WEC-Sim. The effectiveness of including the rotational damping terms to represent low-frequency surge and pitch response was assessed by comparing experimental wave excitation results against the WEC-Sim models with and without rotational damping terms. Other parameters of interest included heave response, up-wave mooring line tension, and down-wave mooring line tension in the linear wave frequency and low-frequency regions. An additional “Extreme” wave load case was conducted purely numerically to investigate the relative impact that the rotational damping coefficients have on capturing low-frequency excitation for high-intensity sea sates. Results showed that the inclusion of rotational damping coefficients had a negligible impact on platform position and mooring line tension in the linear wave frequency region. Simulations including rotational damping coefficients did show a slight improvement in capturing the low-frequency surge response; however, they were generally still underpredicted. Low-frequency pitch response was significantly overestimated by the three degree of freedom (Baseline) viscous damping model and underestimated by the six degree of freedom (Rotational) viscous damping model. These results suggest that rotational damping does impact low-frequency response but further parameter tuning was required for model predictions to better match experimental results. Additionally, WEC-Sim simulations implementing experimental sea surface elevation timeseries rather than numerically generated elevation timeseries for random wave load cases exhibited reduced error between Rotational viscous damping models and experimental results in the low frequency region. It was hypothesized that the error reduction occurred due increased low-frequency excitation from nonlinear incident wave kinematics inherently included in the real-world timeseries

Effects of correlated and uncorrelated quenched disorder on nearest-neighbor coupled lasers

Quenched disorder is commonly investigated in the context of many body systems such as a varying magnetic field in interacting spin models, or frequency variance of interacting oscillators. It is often difficult to study the effect of disorder on these systems experimentally since it requires a method to change its properties in a controlled fashion. In this work, we study the effect of quenched disorder in the form of frequency detuning on a coupled lasers array using a novel degenerate cavity with tunable disorder and coupling strength. By controlling the properties of the disorder such as its magnitude and spatial correlations, we measure the gradual decrease of phase locking due to the effects of disorder and demonstrate that the effects of disorder depend on the ratio between its correlation length and the size of the phase locked cluster.Comment: 13 pages, 12 figure

Small Signals’ Study of Thermal Induced Current in Nanoscale SOI Sensor

A new nanoscale SOI dual-mode modulator is investigated as a function of optical and thermal activation modes. In order to accurately characterize the device specifications towards its future integration in microelectronics circuitry, current time variations are studied and compared for “large signal” constant temperature changes, as well as for “small signal” fluctuating temperature sources. An equivalent circuit model is presented to define the parameters which are assessed by numerical simulation. Assuring that the thermal response is fast enough, the device can be operated as a modulator via thermal stimulation or, on the other hand, can be used as thermal sensor/imager. We present here the design, simulation, and model of the next generation which seems capable of speeding up the processing capabilities. This novel device can serve as a building block towards the development of optical/thermal data processing while breaking through the way to all optic processors based on silicon chips that are fabricated via typical microelectronics fabrication process

Exact mapping between a laser network loss rate and the classical XY Hamiltonian by laser loss control

Recently, there has been growing interest in the utilization of physical systems as heuristic optimizers for classical spin Hamiltonians. A prominent approach employs gain-dissipative optical oscillator networks for this purpose. Unfortunately, these systems inherently suffer from an inexact mapping between the oscillator network loss rate and the spin Hamiltonian due to additional degrees of freedom present in the system such as oscillation amplitude. In this work, we theoretically analyze and experimentally demonstrate a scheme for the alleviation of this difficulty. The scheme involves control over the laser oscillator amplitude through modification of individual laser oscillator loss. We demonstrate this approach in a laser network classical XY model simulator based on a digital degenerate cavity laser. We prove that for each XY model energy minimum there corresponds a unique set of laser loss values that leads to a network state with identical oscillation amplitudes and to phase values that coincide with the XY model minimum. We experimentally demonstrate an eight fold improvement in the deviation from the minimal XY energy by employing our proposed solution scheme

Chiral states in coupled-lasers lattice by on-site complex potential

The ability to control the chirality of physical devices is of great scientific and technological importance, from investigations of topologically protected edge states in condensed matter systems to wavefront engineering, isolation, and unidirectional communication. When dealing with large networks of oscillators, the control over the chirality of the bulk states becomes significantly more complicated and requires complex apparatus for generating asymmetric coupling or artificial gauge fields. Here we present a new approach for precise control over the chirality of a triangular array of hundreds of symmetrically-coupled lasers, by introducing a weak non-Hermitian complex potential, requiring only local on-site control of loss and frequency. In the unperturbed network, lasing states with opposite chirality (staggered vortex and staggered anti-vortex) are equally probable. We show that by tuning the complex potential to an exceptional point, a nearly pure chiral lasing state is achieved. While our approach is applicable to any oscillators network, we demonstrate how the inherent non-linearity of the lasers effectively pulls the network to the exceptional point, making the chirality extremely resilient against noises and imperfections

Anyonic-parity-time symmetry in complex-coupled lasers

Non-Hermitian Hamiltonians, and particularly parity-time (PT) and anti-PT symmetric Hamiltonians, play an important role in many branches of physics, from quantum mechanics to optical systems and acoustics. Both the PT and anti-PT symmetries are specific instances of a broader class known as anyonic-PT symmetry, where the Hamiltonian and the PT operator satisfy a generalized commutation relation. Here, we study theoretically these novel symmetries and demonstrate them experimentally in coupled lasers systems. We resort to complex coupling of mixed dispersive and dissipative nature, which allows unprecedented control on the location in parameter space where the symmetry and symmetry-breaking occur. Moreover, tuning the coupling in the same physical system, allows us to realize the special cases of PT and anti-PT symmetries. In a more general perspective, we present and experimentally validate a new relation between laser synchronization and the symmetry of the underlying non-Hermitian Hamiltonian