abstract vs conclusion -- examples
Abstract vs Conclusion
structure:
abstract: background, methods, object, results (original conctribution),
implication (future effects)
conclusion: methods, results, limits, further work
Table of Contents
1 2016 effect of wave parameters on MCT
| abstract | conclusion |
| The effect of surface waves on the hydrodynamic performance of a marine current turbine (MCT) is studied using the unsteady BEM method. The calculation are found to be in a very good agreement with experimental results of a small scale MCT. It is shown that a large amplitude wave, but still a long wave can affect the time-averaged coefficient of power and also introduce non-linearity in the time response of the turbine particularly at low tip speed ratio. This can have consequence for an effective control of the turbine. Instantaneous blade loading and power spectra are given and analyzed. | Hydrodynamic calculations based on the unsteady BEM method have been pursued to assess the effect of free surface waves on marine current turbines (MCTs). Very good agreement between the BEM calculations and experimental results of a small scale MCT were found both for the time-averaged and time varying coefficient of power with a small amplitude surface wave. It was shown that large waves, but still long in sense of kA<1 can affect in a different way the turbine performance by changing its time averaged coefficients of thrust and power while introducing non-linear behavior in the time variations of those coefficients, particularly for low TSR. This was also exhibited in a noticeable first harmonic of the surface wave affecting the turbine time-response. Future plans include detailed CFD study of the water surface and sea bed topography coupled with the turbine operation and the development of a control law to mitigate those unsteadiness effects. |
2 2020 dual rotor MCT - RANS
| abstract | conclusion |
| In this study, numerical simulation is used to investigate a counter-rotating dual-rotor marine current turbine (MCT) that is aligned for a rectilinear tidal current. Results of power and thrust coefficients and the mean axial velocity in the wake are compared with that of the blade element momentum (BEM) method coupled with the Park wake model. For a single-rotor MCT, small discrepancies are observed for front rotor, and larger discrepancies for rear rotor when comparing the CFD and BEM results. The mean axial velocity in the wake agrees better with the higher turbulence intensity (TI). CFD results shows that the power coefficient (CP) of rear rotor depends on the ambient turbulence intensity. The maximum CP of dual-rotor turbine is 5% higher than that of just the front rotor. Streamlines show that a large vortex is formed behind the rear rotor. The numerical simulations give more credibility to the BEM Park model, but also points to its sensitivity to the incoming turbulence intensity. | This paper has looked at the hydrodynamics of a dual-rotor MCT with a rotational speed control but with no pitch and yaw controls. The turbine is aligned for a rectilinear tidal current, thus the rotors are oppositely pitched. The RANS-based SST k ω turbulence model was used to simulate both single-rotor and dual-rotor MCTs. Power and thrust coefficients, mean axial velocities in the wake region obtained from the RANS were compared to the BEM-Park model. The CFD results provided more details, such as velocity contours, and streamlines. For a single-rotor MCT, there was a good agreement for CP between BEM and CFD results, except when the rotor operated at high TSRs or having a turbulent wake state with negatively pitched blades. For a dual-rotor MCT, larger discrepancies were observed compared with single rotor cases. The C P of rear rotor obtained from BEM-Park model was higher than its CFD RANS counterpart. Nevertheless, the CFD results shows that the BEM-Park model provides reasonable accuracy for the total performance of the dual-rotor MCT when in presence of high turbulence intensity. A gain of 5% and 4% in the overall CP was recorded as relative to the CP of single-rotor NACA0012 and E387, respectively. The free-stream TI is a key parameter for the C P of rear rotor. A higher TI is preferred for a faster recovery of velocity in the wake region.This analysis shows that there is ground to improve low-order models to better account the incoming TI. It also assumes the rotational plane of rotor is orthogonal to the incoming tidal current. Hence, this study did not account for negative effects from yawed inflow, free surface waves and sea bed. The unsteady RANS simulation can also be used to improve the prediction of performance and load on rear rotor which operates in turbulent windmill state and experiences larger fluctuations during one periodic cycle. Experimental work on dual-rotor case is also recommended for further investigation. |
