# Coupled Interactions Analysis of a Floating Tidal Current Power Station in Uniform Flow

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## Abstract

**:**

## 1. Introduction

## 2. Floating Tidal Current Power Station Design

## 3. Numerical Research on the Performance of Vertical-Axis Twin-Rotors Tidal Current Turbine

#### 3.1. Numerical Verification of CFD Simulation

#### 3.2. Computational Domain Settings

_{0}Y

_{0}Z

_{0}), and two local rotating coordinate systems (X

_{1}Y

_{1}Z

_{1}and X

_{2}Y

_{2}Z

_{2}) has been established in the computational domain. As shown in Figure 5a,b, in the simulation process, the left turbine rotates clockwise in X

_{1}Y

_{1}Z

_{1}by the Z

_{1}-axis, while the right turbine rotates counterclockwise in X

_{2}Y

_{2}Z

_{2}by the Z

_{2}-axis. This internal counter-rotation method can maximize the power output of the twin-rotor system, which has been proved by many researchers [12]. As has been mentioned in Section 3.1, the rotation coordinate (X

_{1}Y

_{1}Z

_{1}and X

_{2}Y

_{2}Z

_{2}) of the twin-rotor turbine is coupled with the platform’s body motion coordinate X

_{0}Y

_{0}Z

_{0}. The carrier is set as a DFBI body. The carrier and the turbine are connected by a virtual hinge. The virtual hinge can transmit the force and momentum between the carrier and the turbine at each time step.

#### 3.3. Validation of the Computational Model

_{p}) first increases and then decreases. The value difference between the experiment and numerical simulation at the best speed ratio is small, and the overall trend is in good agreement. However, since the mechanical friction, free liquid surface, and waves are not considered in the numerical simulation, the computational results are a little higher than the experimental results. The simulation error does not exceed 10% (within the error range) in the low-speed ratio area. In general, the simulation results of the CFD numerical simulation method for the vertical axis turbine are in good agreement with the test results, which verifies the reliability of the CFD numerical simulation method for computing the hydrodynamic performance of the vertical axis turbine.

## 4. Results and Discussions

#### 4.1. Influence of Speed Ratio on the Hydrodynamic Characteristics of Hydraulic Turbine

#### 4.1.1. Power Output

#### 4.1.2. Thrust Coefficient

#### 4.1.3. Lateral Force Coefficient

#### 4.2. Influence of Carrier Motion on the Hydrodynamic Characteristics of Hydraulic Turbine

#### 4.2.1. Power Output

#### 4.2.2. Thrust Coefficient

#### 4.2.3. Lateral Force Coefficient

#### 4.3. Influence of the Turbine on the Hydrodynamic Response of the Carrier

#### 4.3.1. Surge Motion of the Carrier

#### 4.3.2. Pitch Motion of the Carrier

#### 4.3.3. Heave Motion of the Carrier

#### 4.4. Flow Field Analysis

#### 4.4.1. Flow Velocity

#### 4.4.2. Flow Pressure

## 5. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## References

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**Figure 1.**Fixed and floating tidal current turbine worldwide. (

**a**) SeaGen; (

**b**) AK-1000; (

**c**) “Hai Ming” I; (

**d**) BlueTec; (

**e**) Evopod; (

**f**) “Hai Neng” II.

**Figure 5.**Coordinate system establishment. (

**a**) Coordinate system of the twin-rotor turbine; (

**b**) Coordinate system of the FTCPS.

**Figure 9.**Grid settings. (

**a**) Computational domain grid of the turbine; (

**b**) Boundary layer grid; (

**c**) Blade surface mesh.

**Figure 14.**The value of ${C}_{p}$ and ${\overline{C}}_{p}$ at different speed ratios. (

**a**) Average power output; (

**b**) Fluctuation of power output.

**Figure 17.**Time history curves of the lateral force coefficient of a single turbine at different speed ratios.

**Figure 19.**Influence of the carrier motion on the power output efficiency. (

**a**) Time history curves of turbine power output efficiency; (

**b**) Average power output efficiency.

**Figure 25.**Comparison of velocity field between the fixed stand-alone twin-rotor turbine and the twin-rotor turbine with 6-DOF motion. (

**a**) Stand-alone turbine; (

**b**) Turbine with 6-DOF motion.

**Figure 26.**Comparison of horizontal iso-velocity field for the fixed stand-alone turbine and the turbine with 6-DOF motions. (

**a**) Fixed stand-alone turbine; (

**b**) Turbine with 6-DOF motions.

**Figure 27.**Comparison of vertical iso-velocity field for the fixed stand-alone turbine and the turbine with 6-DOF motions. (

**a**) Fixed stand-alone turbine; (

**b**) Turbine with 6-DOF motions.

**Figure 28.**Comparison of the vertical section iso-velocity flow field for the stand-alone carrier and the carrier with twin-rotor turbine. (

**a**) Stand-alone carrier; (

**b**) FTCPS.

**Figure 29.**Comparison of the free surface iso-velocity flow field for the stand-alone carrier and the carrier with twin-rotor turbine. (

**a**) Stand-alone carrier; (

**b**) FTCPS.

Case | Velocity (m/s) | TSR | Computational Domain |
---|---|---|---|

A | 2.5 | 2.0 | Stand-alone turbine |

B | 2.5 | 2.0 | FTCPS |

Case | Velocity (m/s) | TSR | Computational Domain |
---|---|---|---|

C | 2.5 | 2.0 | Stand-alone carrier |

D | 2.5 m/s | 2.0 | FTCPS |

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**MDPI and ACS Style**

Hu, C.; Tang, C.; Yuwen, C.; Ma, Y.
Coupled Interactions Analysis of a Floating Tidal Current Power Station in Uniform Flow. *J. Mar. Sci. Eng.* **2021**, *9*, 958.
https://doi.org/10.3390/jmse9090958

**AMA Style**

Hu C, Tang C, Yuwen C, Ma Y.
Coupled Interactions Analysis of a Floating Tidal Current Power Station in Uniform Flow. *Journal of Marine Science and Engineering*. 2021; 9(9):958.
https://doi.org/10.3390/jmse9090958

**Chicago/Turabian Style**

Hu, Chao, Chenxuan Tang, Chenyang Yuwen, and Yong Ma.
2021. "Coupled Interactions Analysis of a Floating Tidal Current Power Station in Uniform Flow" *Journal of Marine Science and Engineering* 9, no. 9: 958.
https://doi.org/10.3390/jmse9090958