Hybrid Model Predictive Control of Floating Offshore Wind Turbines with Artificial Muscle Actuated Mooring Lines

Floating offshore wind turbines (FOWTs) are subject to undesirable platform motion and significant increase in fatigue loads compared to their onshore counterparts. We have recently proposed using the Fishing Line Artificial Muscle (FLAM) actuators to realize active mooring line force control (AMLFC) for platform stabilization and thus load reduction, which features compact design and no need for turbine redesign. However, as for the thermally activated FLAM actuators, a major control challenge lies in the asymmetric dynamics for the heating and the cooling half cycle of operation. In this paper, for a tension-leg platform (TLP) based FOWT with FLAM actuator based AMLFC, a hybrid dynamic model is obtained with platform pitch and roll degrees of freedom included. Then a hybrid model predictive control (HMPC) strategy is proposed for platform motion stabilization, with preview information on incoming wind and wave. A move blocking scheme is used to achieve reasonable computational efficiency. FAST based simulation study is performed using the NREL 5 MW wind turbine model. Under different combinations of wind speed, wave height and wind directions, simulation results show that the proposed control strategy can significantly reduce the platform roll and tower-base side-to-side bending moment, with mild level of actuator power consumption.

Dimensional Synthesis of a Novel 3-URU Translational Manipulator Implemented through a Novel Method

A dimensional synthesis of parallel manipulators (PMs) consists of determining the values of the geometric parameters that affect the platform motion so that a useful workspace with assigned sizes can be suitably located in a free-from-singularity region of its operational space. The main goal of this preliminary dimensioning is to keep the PM far enough from singularities to avoid high internal loads in the links and guarantee a good positioning precision (i.e., for getting good kinematic performances). This paper presents a novel method for the dimensional synthesis of translational PMs (TPMs) and applies it to a TPM previously proposed by the author. The proposed method, which is based on Jacobians’ properties, exploits the fact that TPM parallel Jacobians are block diagonal matrices to overcome typical drawbacks of indices based on Jacobian properties. The proposed method can be also applied to all the lower-mobility PMs with block diagonal Jacobians that separate platform rotations from platform translations (e.g., parallel wrists).

STEPPING RESPONSE DURING CONSTRAINED AND UNCONSTRAINED STANDING IN MOVING ENVIRONMENTS

The purpose of this study was to determine the differences in human stepping response reaction between constrained and unconstrained standing while being exposed to simulated wave-induced platform motions. Twenty subjects (10 male and 10 female), with limited experience recreating or working in motion-rich environments, performed a constrained and an unconstrained standing task on a six-degrees-of-freedom motion bed while being exposed to two different simulated platform motion conditions. Stepping occurrence was greater during unconstrained standing than constrained standing during all three motion conditions. However, no significant differences in platform kinematics were found between stepping cases. These results suggest that stepping occurs more frequently than originally hypothesized. As such, stepping should not be considered as a last resource when all fixed-support options have been exhausted. This should be taken into consideration to ensure ecological validity when developing models to predict stepping occurrence.

Fine-Scale Velocity Measurement on the Wirewalker Wave-Powered Profiler

The Wirewalker (WW) ocean-wave-powered vertical profiling system allows the collection of high-resolution oceanographic data due to its rapid profiling, hydrodynamically quiet operation, and long endurance. We have assessed the potential for measuring fine-scale ocean velocities from the Wirewalker platform using commercially available acoustic velocimeters. Although the vertical profiling speed is relatively steady, platform motion affects the velocity measurements and requires correction. We present an algorithm to correct our velocity estimates using platform motion calculated from the inertial sensors – accelerometer, gyroscope, and magnetometer – on a Nortek Signature1000 Acoustic Doppler Current Profiler. This correction, carried out ping-by-ping, was effective in removing the vehicle motion from the measured velocities. The motion-corrected velocities contain contributions from surface wave orbital velocities, especially near the surface, and the background currents. To proceed, we use an averaging approach that leverages both the vertical platform profiling of the system and the ~15-20 m vertical profiling range resolution of the down-looking ADCP to separate the surface wave orbital velocities and the background flow. The former can provide information on the wave conditions. From the latter, we are able to estimate fine-scale velocity and shear with spectral wavenumber roll-off at vertical scales around 3 m, a vertical resolution several times finer than that possible from modern shipboard or fixed ADCPs with similar profiling range, and similar to recent glider measurements. When combined with a continuous time-series of buoy drift calculated from the onboard GPS, a highly-resolved total velocity field is obtained, with a unique combination of space and time resolution.

Assessing the contribution of active somatosensory stimulation to self-acceleration perception in dynamic driving simulators

In dynamic driving simulators, the experience of operating a vehicle is reproduced by combining visual stimuli generated by graphical rendering with inertial stimuli generated by platform motion. Due to inherent limitations of the platform workspace, inertial stimulation is subject to shortcomings in the form of missing cues, false cues, and/or scaling errors, which negatively affect simulation fidelity. In the present study, we aim at quantifying the relative contribution of an active somatosensory stimulation to the perceived intensity of self-motion, relative to other sensory systems. Participants judged the intensity of longitudinal and lateral driving maneuvers in a dynamic driving simulator in passive driving conditions, with and without additional active somatosensory stimulation, as provided by an Active Seat (AS) and Active Belts (AB) integrated system (ASB). The results show that ASB enhances the perceived intensity of sustained decelerations, and increases the precision of acceleration perception overall. Our findings are consistent with models of perception, and indicate that active somatosensory stimulation can indeed be used to improve simulation fidelity.

Modeling and analysis of motion with wheel slip of the mobile platform with four wheel drive

The problem of motion with wheel slip of the four wheeled mobile platform has been discussed in this work. Considering the model of dynamics, the formulation of the initial problem of the platform motion and the numerical algorithm for solving this problem has been presented. The Runge-Kutta 4th order method has been used to integrate the equations of motion. Possible cases of motion of the prototype of the mobile platform with four drive modules have been considered. Taking into account the variable values of the active forces caused by the drive torque and changes in the position of the wheels during the platform motion, as well as the resistant forces opposing the active forces at the contact points of the wheels with the ground, the platform motion simulation results have been obtained. Different wheel settings, with controlling the active forces and directions of their settings while driving have been implemented to the model. The results of motion simulations and their analysis have been included. The results presented in the paper show a significant influence of wheel slip on the parameters of the motion of the mobile platform. The computational model presented in the paper enables a good representation of the platform motion parameters, which has been confirmed by comparing the results of simulation tests with the results of experimental tests of motion in relation to a construction solution of the platform other than described in the paper. Further development of the computational model is planned, mainly in order to include the deformability of the wheel suspension systems in the dynamic model of the platform, which will allow for the implementation of wider studies of the motion of such objects, including, for example, in the case of wheels passing through obstacles.