scholarly journals The effect of bed roughness uncertainty on tidal stream power estimates for the Pentland Firth

2020 ◽  
Vol 7 (1) ◽  
pp. 191127 ◽  
Author(s):  
M. J. Kreitmair ◽  
T. A. A. Adcock ◽  
A. G. L. Borthwick ◽  
S. Draper ◽  
T. S. van den Bremer
Keyword(s):  
Theoretical Models ◽  
Bottom Friction ◽  
Relative Uncertainty ◽  
Stream Power ◽  
Tidal Power ◽  
Input Uncertainty ◽  
Mean Values ◽  
Tidal Stream ◽  
Bed Roughness ◽  
Tidal Stream Power

Uncertainty affects estimates of the power potential of tidal currents, resulting in large ranges in values reported for sites such as the Pentland Firth, UK. Kreitmair et al. (2019, R. Soc. open sci. 6 , 180941. ( doi:10.1098/rsos.191127 )) have examined the effect of uncertainty in bottom friction on tidal power estimates by considering idealized theoretical models. The present paper considers the role of bottom friction uncertainty in a realistic numerical model of the Pentland Firth spanned by different fence configurations. We find that uncertainty in removable power estimates resulting from bed roughness uncertainty depends on the case considered, with relative uncertainty between 2% (for a fully spanned channel with small values of mean roughness and input uncertainty) and 44% (for an asymmetrically confined channel with high values of bed roughness and input uncertainty). Relative uncertainty in power estimates is generally smaller than (input) relative uncertainty in bottom friction by a factor of between 0.2 and 0.7, except for low turbine deployments and very high mean values of friction. This paper makes a start at quantifying uncertainty in tidal stream power estimates, and motivates further work for proper characterization of the resource, accounting for uncertainty inherent in resource modelling.

scholarly journals Hydrodynamic Effects of Tidal-Stream Power Extraction for Varying Turbine Operating Conditions

Energies ◽  
2020 ◽  
Vol 13 (12) ◽  
pp. 3240
Author(s):  
Lilia Flores Mateos ◽  
Michael Hartnett
Keyword(s):  
Thrust Force ◽  
Operating Conditions ◽  
Blockage Ratio ◽  
Stream Power ◽  
Power Extraction ◽  
Tidal Stream ◽  
Electrical Generation ◽  
Hydrodynamic Effects ◽  
Turbine Wake ◽  
Tidal Stream Power

Realistic evaluation of tidal-stream power extraction effects on local hydrodynamics requires the inclusion of the turbine’s operating conditions (TOC). An alternative approach for simulating the turbine’s array energy capture at a regional scale, momentum sink-TOC, is used to assess the impact of power extraction. The method computes a non-constant thrust force calculated based on the turbine’s operating conditions, and it uses the wake induction factor and blockage ratio to characterise the performance of a turbine. Additionally, the momentum sink-TOC relates the changes produced by power extraction, on the velocity and sea surface within the turbine’s near-field extension, to the turbine’s thrust force. The method was implemented in two hydrodynamic models that solved gradually varying flows (GVF) and rapidly varying flows (RVF). The local hydrodynamic effects produced by tidal-stream power extraction for varying the turbine’s operating conditions was investigated in (i) the thrust and power coefficient calculation, (ii) flow rate reduction, and (iii) tidal currents’ velocity and elevation profiles. Finally, for a turbine array that operates at optimal conditions, the potential energy resource was assessed. The maximisation of power extraction for electrical generation requires the use of an optimum turbine wake induction factor and an adequate blockage ratio, so that the power loss due to turbine wake mixing is reduced. On the other hand, the situations where limiting values of these parameters are used should be avoided as they lead to negligible power available. In terms of hydrodynamical models, an RVF solver provided a more accurate evaluation of the turbine’s operating conditions effect on local hydrodynamics. Particularly satisfactory results were obtained for a partial-fence. In the case of a fence configuration, the GVF solver was found to be a computationally economical tool to pre-assess the resource; however, caution should be taken as the solver did not accurately approximate the velocity decrease produced by energy extraction.

Counter-Rotating Type Tidal-Stream Power Unit Playing Favorable Features in Various Ocean Circumstances

2013 ◽  
Author(s):  
Yuta Usui ◽  
Kohei Takaki ◽  
Toshiaki Kanemoto ◽  
Koju Hiraki
Keyword(s):  
Power Unit ◽  
Axial Force ◽  
Wire Rope ◽  
Stream Velocity ◽  
Vertical Force ◽  
Stream Power ◽  
Tidal Stream ◽  
Tandem Propellers ◽  
Tidal Stream Power ◽  
Cable Wire

The authors have invented the unique counter-rotating type tidal-stream power unit, which is composed of the tandem propellers and the double rotational armature type peculiar generator without the traditional stator. In the unit of the downstream type, the front and the rear propellers counter-drive the outer and the inner armatures of the peculiar generator respectively, in keeping the rotational torque counter-balanced between both propellers/armatures. This paper discusses and verifies experimentally the almighty features of the power unit. The axial force acting on the pillar increases naturally with the increase of not only the stream velocity but also the drag of the tandem propellers. Besides, the tandem propellers bring the symmetrical vertical force from side to side though the single propeller brings the force in one direction. The counter-balanced torque makes it possible to moor the power unit with only one cable/wire/rope, and the behavior of the submerged unit was confirmed experimentally.

scholarly journals Performance Research of Counter-rotating Tidal Stream Power Unit

2016 ◽  
Vol 9 (2) ◽  
pp. 129-136 ◽  
Author(s):  
Xuesong Wei ◽  
Bin Huang ◽  
Pin Liu ◽  
Toshiaki Kanemoto
Keyword(s):  
Power Unit ◽  
Stream Power ◽  
Tidal Stream ◽  
Performance Research ◽  
Tidal Stream Power

scholarly journals 1001 Development of Counter-Rotating Type Tidal Stream Power Unit

2013 ◽  
Vol 2013 (0) ◽  
pp. _1001-01_-_1001-02_
Author(s):  
Kohei TAKAKI ◽  
Yuta USUI ◽  
Toshiaki KANEMOTO
Keyword(s):  
Power Unit ◽  
Stream Power ◽  
Tidal Stream ◽  
Tidal Stream Power

Optimization of the Rear Propeller Profile of a Counter-Rotating Type Tidal Stream Power Unit Based on CFD Simulation

2015 ◽  
Author(s):  
Bin Huang ◽  
Toshiaki Kanemoto ◽  
Ryunosuke Kawashima ◽  
Jin-Hyuk Kim
Keyword(s):  
Power Unit ◽  
Cfd Simulation ◽  
Mutual Effect ◽  
Stream Power ◽  
Power Efficient ◽  
Tidal Turbine ◽  
Tidal Stream ◽  
Tandem Propellers ◽  
Tidal Stream Power ◽  
Blade Element

In order to convert the kinetic energy of tidal stream, the authors have invented a novel counter-rotating type tidal-stream power unit, which is composed of the tandem propellers and the double rotational armature type peculiar generator without the traditional stator. The commercial code (GH-Tidal Bladed) and academic in-house code (SERG-Tidal) based on blade element momentum theory have been proven well applied to performance prediction for the traditional wind turbine and tidal turbine. However, for the counter-rotating type tidal turbine, it is very difficult to simulate the mutual effect between the tandem propellers using blade element momentum. This paper sets up a CFD model for the counter-rotating type tidal turbine and optimizes the chord and pitch distribution of the rear propeller. The predicted results are compared between the original turbine and optimized turbine, which show great improvement in power efficient after optimization.

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