Non-causal Linear Optimal Control with Adaptive Sliding Mode Observer for Multi-Body Wave Energy Converters

As a non-causal optimal control problem, the performance of wave energy converter (WEC) control relies on the accuracy of the future incoming wave prediction. However, the inevitable prediction errors can degrade WEC performance dramatically especially when a long prediction horizon is needed by a WEC non-causal optimal controller. This paper proposes a novel non-causal linear optimal control with adaptive sliding mode observer (NLOC+ASMO) scheme, which can effectively mitigate the control performance degradation caused by wave prediction errors. This advantage is achieved by embedding the following enabling techniques into the scheme: (i) an adaptive sliding mode observer (ASMO) to estimate current excitation force in real-time with explicitly formulated boundary of estimation error, (ii) an auto-regressive (AR) model to predict the incoming excitation force with explicitly formulated boundary of prediction error using a set of latest historical data of ASMO estimations from (i), and (iii) a compensator to compensate for both the estimation error and the prediction error of excitation force. Moreover, the proposed NLOC+ASMO scheme does not cause heavy computational load enabling its real-time implementation on standard computational hardware, which is especially critical for the control of WECs with complicated dynamics. The proposed NLOC+ASMO framework is generic and can be applied to a wide range of WECs, and in this paper we demonstrate the efficacy by using a multi-float and multi-motion WEC called M4 as a case study, whose control problem is more challenging than the widely studied point absorbers. Simulation results show the effectiveness of the proposed control scheme in a wide range of sea states, and it is also found that the controller is not sensitive to change of ASMO parameters

2-D numerical modeling of rapidly varying shallow water flows by Smoothed Particle Hydrodynamics technique

River engineeringNumerical modelling in river engineerin

High-capacity wave energy conversion by multi-floats, multi-PTO, control and prediction: generalised state-space modelling with linear optimal control and arbitrary headings

Wave energy converters with capacity similar to, or greater than, wind turbines are desirable for the supply of electricity to the grid. It is shown that this may be provided by multiple floats in a hinged raft-type configuration with multimode forcing. The case analysed has 8 floats and 4 power take off (PTO) units. Analysis is based on linear diffraction-radiation modelling, validated in wave basin experiments with a smaller number of floats. Control is desirable to improve energy capture, mainly demonstrated for point absorbers, but this has not previously been applied to such a complex problem with many freedoms. The linear hydrodynamic model in a state-space form makes it possible to implement advanced control algorithms in real time. Linear non-causal optimal control (LNOC) is applied with wave force prediction from auto-regression. For the design case with zero heading, as the configuration heads naturally into the wave direction, energy capture is improved by between 21% and 83%. The energy capture is about 62% the maximum possible from idealised analyses. Off-design, non-zero headings are also analysed to indicate how energy capture can be reduced; this is again improved by control, by several times at 90 degrees heading

Propulsive power contribution of a kite and a Flettner rotor on selected shipping routes

AbstractWind is a renewable energy source that is freely available on the world’s oceans. As shipping faces the challenge of reducing its dependence on fossil fuels and cutting its carbon emissions this paper seeks to explore the potential for harnessing wind power for shipping. Numerical models of two wind power technologies, a Flettner rotor and a towing kite, are linked with wind data along a set of five trade routes. Wind-generated thrust and propulsive power are computed as a function of local wind and ship velocity. The average wind power contribution on a given route ranges between 193kW and 373kW for a single Flettner rotor and between 127kW and 461kW for the towing kite. The variability of the power output from the Flettner rotor is shown to be smaller than that from the towing kite while, due to the different dependencies on wind speed and direction, the average power contribution from a Flettner rotor is higher than that from the kite on some routes and lower on others. While for most forms of international cargo shipping wind may not be suitable as the sole source of propulsive energy, a comparison of average output to main engine power requirements of typical vessels serving the routes indicates that it could deliver a significant share. For instance, installing three Flettner rotors on a 5500dwt general cargo carrier could, on average, provide more than half of the power required by the main engine under typical slow steaming conditions. Uncertainties and simplifying assumptions underlying the model analysis are discussed and implications of the results are considered in light of the urgent need for decarbonisation. This paper demonstrates the significant opportunities for step jump emissions reductions that wind technologies have to offer. It outlines next steps towards realising the potential, highlighting a demand for more detailed studies on socio-economic and technical barriers to implementation, and providing a basis for research into step-change emissions reductions in the shipping sector

Disambiguation of Vector Magnetograms by Stereoscopic Observations from the Solar Orbiter/Polarimetric and Helioseismic Imager (PHI) and the Solar Dynamic Observatory (SDO)/Helioseismic and Magnetic Imager (HMI)

Spectropolarimetric reconstructions of the photospheric vector magnetic field are intrinsically limited by the 180∘ ambiguity in the orientation of the transverse component. The successful launch and operation of Solar Orbiter have made the removal of the 180∘ ambiguity possible using solely observations obtained from two different vantage points. While the exploitation of such a possibility is straightforward in principle, it is less so in practice, and it is therefore important to assess the accuracy and limitations as a function of both the spacecrafts’ orbits and measurement principles. In this work, we present a stereoscopic disambiguation method (SDM) and discuss thorough testing of its accuracy in applications to modeled active regions and quiet-Sun observations. In the first series of tests, we employ magnetograms extracted from three different numerical simulations as test fields and model observations of the magnetograms from different angles and distances. In these more idealized tests, SDM is proven to reach a 100% disambiguation accuracy when applied to moderately-to-well resolved fields. In such favorable conditions, the accuracy is almost independent of the relative position of the spacecraft with the obvious exceptions of configurations where the spacecraft are within a few degrees of co-alignment or quadrature. Even in the case of disambiguation of quiet-Sun magnetograms with significant under-resolved spatial scales, SDM provides an accuracy between 82% and 98%, depending on the field strength. The accuracy of SDM is found to be mostly sensitive to the variable spatial resolution of Solar Orbiter in its highly elliptic orbit, as well as to the intrinsic spatial scale of the observed field. Additionally, we provide an example of the expected accuracy as a function of time that can be used to optimally place remote-sensing observing windows during Solar Orbiter observation planning. Finally, as a more realistic test, we consider magnetograms that are obtained using a radiative-transfer inversion code and the SO/PHI Software siMulator (SOPHISM) applied to a 3D-simulation of a pore, and we present a preliminary discussion of the effect of the viewing angle on the observed field. In this more realistic test of the application of SDM, the method is able to successfully remove the ambiguity in strong-field areas

Hepatocellular Carcinoma Arising in Non-Cirrhotic Haemochromatosis

Hepatocellular carcinoma arising in a patient with genetic haemachromatosis, without cirrhosis, has only been described once previously. We present a patient with a 15 year history of genetic haemachromatosis who underwent resection of a hepatocellular carcinoma in a liver with normal architecture

OrcaFlex predictions for a multi-float hinged WEC with nonlinear mooring systems: Elastic mooring force and dynamic motion

This is the final version. Available on open access from Elsevier via the DOI in this recordData availability: Data will be made available on request.The mooring system can affect the motion and energy output characteristics of a WEC. This study investigated the effects of an SPM mooring system in a M4 6-float WEC. The scaled model of M4 was modelled via both Orcaflex and experimental approaches. Compared with experimental results, the accuracy of the numerical results was found to be sensitive to the simulation methods in OrcaFlex, and the filter method supplied a better agreement with experimental results in this study. Following the numerical method selection, another two mooring cables were introduced to compare different stiffness properties with respect to tension reduction. Compared with the other two mooring cables, cable 3 with negative bending has the lowest peak spectral density of tension in all wave conditions; however, its stiffness needs to be optimised to reduce the peak tension in some large wave conditions. According to this, the stiffness of cable 3 is initially adjusted, and the new cable 3 can reduce up to 30% offset distance and 50% peak tension. The results also found that the relative rotational motion of the M4 is not sensitive to stiffness properties, which means the future PTO selection could be independent of the mooring cable.EU Marinet2 programmeEngineering and Physical Sciences Research Council (EPSRC