# Numerical and Experimental Investigation on a Moonpool-Buoy Wave Energy Converter

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## Abstract

**:**

## 1. Introduction

## 2. Model Description

#### 2.1. Similar Conditions

#### 2.2. Single Buoy

#### 2.3. Moonpool-Buoy (Cylindrical Shell Housing the Moonpool)

#### 2.4. The Data Acquisition System

## 3. Numerical Approach

#### 3.1. Potential Flow Method

#### 3.2. RANS Method

#### 3.2.1. Computational Domain and Boundary Conditions

#### 3.2.2. Mesh Generation and Convergence Verification

## 4. Experiments Process and Results

#### 4.1. Experimental Facility

#### 4.2. Wave Parameter

#### 4.3. Single Buoy Model Test

#### 4.3.1. Optimum Damping Coefficient

_{B}= 5, 10, 20, 30, 40, and 50 Ω). The PTO damping characteristics change with the resistance due to the current intensity: the larger the resistance, the smaller the PTO damping.

#### 4.3.2. Relative Motion and Power

#### 4.4. Wave Tank Experiment for Moonpool-Buoy and Comparison with Numerical Results

#### 4.4.1. The Moonpool Device

#### 4.4.2. The Optimal Damping

_{B}= 5, 10, 20, 30, 40, and 50 Ω.

#### 4.4.3. Motion Response and Power Output

#### 4.4.4. Motion Response Comparation: Time Domain

## 5. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 3.**Moonpool-buoy device: on the left, 3D Computer Aided Design (CAD) schematics, with the central float in blue and red, the outer cylindrical shell in grey, and the connections to the above structure. On the right, a picture of the device in the tank.

**Figure 9.**The motion curve and power curve in the different sea state: the continuous curve represents the numerical results obtained with a potential flow approach, and the points represent the experimental results. (

**a**) Relative displacement (mm); (

**b**) power output.

**Figure 11.**The motion comparison of the moonpool platform wave energy converter (MPWEC) with CFD results in time domain. (

**a**) T = 2.0 s; (

**b**) T = 2.2 s.

Variables | Entity Symbol | Model Symbol | Scale Factor | Scale Factor |
---|---|---|---|---|

Length | ${L}_{s}$ | ${L}_{m}$ | ${L}_{s}/{L}_{m}=\lambda $ | 10 |

Area | ${A}_{s}$ | ${A}_{m}$ | ${A}_{s}/{A}_{m}={\lambda}^{2}$ | 100 |

Volume | ${V}_{s}$ | ${V}_{m}$ | ${V}_{s}/{V}_{m}={\lambda}^{3}$ | 1000 |

Fluid density | ${\rho}_{s}$ | ${\rho}_{m}$ | ${\rho}_{s}/{\rho}_{m}=\gamma $ | 1.025 |

Displacement | ${\Delta}_{s}$ | ${\Delta}_{m}$ | ${\Delta}_{s}/{\Delta}_{m}=\gamma {\lambda}^{3}$ | 1025 |

Wave period | ${T}_{s}$ | ${T}_{m}$ | ${T}_{s}/{T}_{m}={\lambda}^{1/2}$ | 3.15 |

Wave circular frequency | ${\omega}_{s}$ | ${\omega}_{m}$ | ${\omega}_{s}/{\omega}_{m}={\lambda}^{-1/2}$ | 0.32 |

Velocity | ${v}_{s}$ | ${v}_{m}$ | ${v}_{s}/{v}_{m}={\lambda}^{1/2}$ | 3.15 |

Acceleration | ${a}_{s}$ | ${a}_{m}$ | ${a}_{s}/{a}_{m}=1$ | 1 |

Power | ${P}_{s}$ | ${P}_{m}$ | ${P}_{s}/{P}_{m}=\gamma {\lambda}^{3.5}$ | 3241.3 |

Working Scenario Number | Wave Height (m) | Period (s) | Working Condition | Wave Height (m) | Period (s) |
---|---|---|---|---|---|

1 | 0.12 | 1.2 | 8 | 0.12 | 2.3 |

2 | 0.12 | 1.4 | 9 | 0.12 | 2.4 |

3 | 0.12 | 1.6 | 10 | 0.12 | 2.5 |

4 | 0.12 | 1.8 | 11 | 0.12 | 2.6 |

5 | 0.12 | 2.0 | 12 | 0.12 | 2.7 |

6 | 0.12 | 2.1 | 13 | 0.12 | 2.8 |

7 | 0.12 | 2.2 | 14 | 0.12 | 3.0 |

The Resistance of the Resistance Box (Ω) | Output Power (W) |
---|---|

5 | 0.56 |

10 | 0.80 |

20 | 0.97 |

30 | 0.95 |

40 | 0.87 |

50 | 0.79 |

Wave Period (s) | Experimental Data (mm) | Numerical Data (mm) | Error Analysis (%) |
---|---|---|---|

1.2 | 21.8 | 29.0 | 33.1 |

1.4 | 38.4 | 36.2 | 5.8 |

1.6 | 50.4 | 40.9 | 18.9 |

1.8 | 45.7 | 44.0 | 3.9 |

2.0 | 44.7 | 45.9 | 2.7 |

2.1 | 43.4 | 46.6 | 7.4 |

2.2 | 48.8 | 47.1 | 3.5 |

2.3 | 50.5 | 47.6 | 5.7 |

2.4 | 49.0 | 47.9 | 2.1 |

2.5 | 48.7 | 48.3 | 0.8 |

2.6 | 49.6 | 48.5 | 2.3 |

2.7 | 47.3 | 48.7 | 2.9 |

2.8 | 46.3 | 48.8 | 5.5 |

3.0 | 48.2 | 49.1 | 1.8 |

The Resistance of Resistance Box (Ω) | Output Power (W) |
---|---|

5 | 0.62 |

10 | 1.55 |

20 | 1.68 |

30 | 0.83 |

40 | 0.86 |

50 | 0.84 |

Wave Period (s) | Experimental Data (mm) | Numerical Data (mm) | Error Analysis (%) |
---|---|---|---|

1.2 | 0.0 | 1.0 | 100 |

1.4 | 8.0 | 6.3 | 21.3 |

1.6 | 18.2 | 20.5 | 12.6 |

1.8 | 88.0 | 100.4 | 14.1 |

2.0 | 40.0 | 30.5 | 23.8 |

2.1 | 62.0 | 40.5 | 34.7 |

2.2 | 79.5 | 80.4 | 1.1 |

2.3 | 69.5 | 70.7 | 1.7 |

2.4 | 64.7 | 56.8 | 12.2 |

2.5 | 58.3 | 48.2 | 17.3 |

2.6 | 50.1 | 45.1 | 10.0 |

2.7 | 47.7 | 43.3 | 9.2 |

2.8 | 47.7 | 42.6 | 10.7 |

3.0 | 45.0 | 40.3 | 10.4 |

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## Share and Cite

**MDPI and ACS Style**

Liu, H.; Yan, F.; Jing, F.; Ao, J.; Han, Z.; Kong, F.
Numerical and Experimental Investigation on a Moonpool-Buoy Wave Energy Converter. *Energies* **2020**, *13*, 2364.
https://doi.org/10.3390/en13092364

**AMA Style**

Liu H, Yan F, Jing F, Ao J, Han Z, Kong F.
Numerical and Experimental Investigation on a Moonpool-Buoy Wave Energy Converter. *Energies*. 2020; 13(9):2364.
https://doi.org/10.3390/en13092364

**Chicago/Turabian Style**

Liu, Hengxu, Feng Yan, Fengmei Jing, Jingtao Ao, Zhaoliang Han, and Fankai Kong.
2020. "Numerical and Experimental Investigation on a Moonpool-Buoy Wave Energy Converter" *Energies* 13, no. 9: 2364.
https://doi.org/10.3390/en13092364