# Compact Low-Velocity Ocean Current Energy Harvester Using Magnetic Couplings for Long-Term Scientific Seafloor Observation

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## Abstract

**:**

## 1. Introduction

## 2. LOCH Design and Parameter Optimization

#### 2.1. Overall Design

#### 2.2. Turbine Selection

_{in}is

_{P}is the power coefficient of the turbine, ρ is the density of the seawater, r is the radius of the turbine and v is the ocean current velocity. The turbine airfoil is optimized based on the NACA4412 type and the C

_{P}is 0.4 [31].

_{out}is

_{L}is the overall efficiency of the LOCH, thus the radius of the turbine r can be expressed as:

_{L}is 55%, the radius of the turbine r must be at least 0.3 m and P

_{in}is 3.6 W. The turbine parameters are shown in Table 2 and the manufactured turbine is shown in Figure 2.

_{t}is the transmitted torque of the turbine and ω

_{t}is the angular velocity of the turbine.

#### 2.3. Magnetic Coupling Structure

_{r}is 1.25 T. The magnets are sector-shaped and the pole-arc to pole-pitch ratio is 1.

## 3. Magnetic Coupling Parameter Optimization

#### 3.1. D FE Simulation Modeling

#### 3.2. Pole Pairs

#### 3.3. Magnet Thickness

#### 3.4. Iron Yoke Thickness

#### 3.5. Air-Gap Length

## 4. Magnetic Coupling Experiment

#### 4.1. Experimental Platform Design

_{i}and rotating speed n

_{i}of the active rotor and the output torque T

_{o}and rotating speed n

_{o}of the driven rotor can be read directly from the torque/speed sensors, and the input power P

_{i}and output power P

_{o}of the magnetic coupling are expressed as follows:

_{mc}is

#### 4.2. The Static Performance of The Magnetic Coupling

#### 4.3. The Dynamic Performance of The Magnetic Coupling

## 5. LOCH Assembly and Experiment

#### 5.1. Hydrostatic Seal Test

#### 5.2. Underwater Test

## 6. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 11.**The magnetic flux density distribution of magnetic couplings with different iron yoke thickness.

**Figure 16.**The static performance of the magnetic couplings with different air-gap lengths from the three-dimensional finite-element method (3D FEM) and experimental tests.

**Table 1.**Comparison between previous studies and the proposed low-velocity ocean current energy harvester (LOCH).

Reference | Radius of The Turbine (m) | Current Velocity (m/s) | Output Power (W) | Overall Efficiency (%) |
---|---|---|---|---|

[19] | 1.1 | 1.0 | 500 | 64 |

[26] | 0.6 | 0.25 | - | - |

[28] | 0.18 | 0.16 | 0.08 | 40 |

[29] | 1.0 | 0.1 | 0.3 | 39 |

This paper | 0.3 | 0.4 | 2.8 | 75 |

Parameter | Value |
---|---|

Radius r | 0.3 m |

Rated flow velocity v_{r} | 1.0 m/s |

Rated input power P_{rin} | 58 W |

Lowest flow velocity v_{min} | 0.4 m/s |

Input energy at the lowest flow velocity P_{in} | 3.6 W |

Number of blades B | 12 |

Tip speed ratio λ | 3 |

Power coefficient C_{p} | 0.4 |

Parameter | Value |
---|---|

Material of magnet | Nd-Fe-B |

Remanence of the magnet B_{r} | 1.25 T |

Outer radius of the magnet | 54 mm |

Inner radius of the magnet | 12 mm |

Magnet thickness h | 8 mm |

Pole pairs p | 5 |

Air-gap length a | 10 mm |

Iron yoke thickness e | 5 mm |

Isolation layer thickness | 4 mm |

Radius of The Turbine (m) | The Output Power at 0.3 m/s (The Lowest Flow Velocity) (W) | The Output Power at 1.0 m/s (The Rated Flow Velocity) (W) |
---|---|---|

0.3 | 2.8 | 43.5 |

0.6 | 11.1 | 173.9 |

0.9 | 25.0 | 391.2 |

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## Share and Cite

**MDPI and ACS Style**

Huang, L.; Lyu, F.
Compact Low-Velocity Ocean Current Energy Harvester Using Magnetic Couplings for Long-Term Scientific Seafloor Observation. *J. Mar. Sci. Eng.* **2020**, *8*, 410.
https://doi.org/10.3390/jmse8060410

**AMA Style**

Huang L, Lyu F.
Compact Low-Velocity Ocean Current Energy Harvester Using Magnetic Couplings for Long-Term Scientific Seafloor Observation. *Journal of Marine Science and Engineering*. 2020; 8(6):410.
https://doi.org/10.3390/jmse8060410

**Chicago/Turabian Style**

Huang, Longxiang, and Feng Lyu.
2020. "Compact Low-Velocity Ocean Current Energy Harvester Using Magnetic Couplings for Long-Term Scientific Seafloor Observation" *Journal of Marine Science and Engineering* 8, no. 6: 410.
https://doi.org/10.3390/jmse8060410