# Computational Fluid Dynamic Analysis of a Floating Offshore Wind Turbine Experiencing Platform Pitching Motion

^{1}

^{2}

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## Abstract

**:**

## 1. Introduction

## 2. Methodology

#### 2.1. Computational Fluid Dynamic Approach

#### 2.2. Overset Mesh Methods

## 3. Simulation Conditions

#### 3.1. Computational Modeling of a Wind Turbine Blade

**Figure 3.**(

**a**) Illustration of the computational mesh domain; (

**b**) Zoon-in refine overset grid area; (

**c**) A view of layer grid adjustment blade surface; and (

**d**) Blade surface tip area.

CFD Mesh Type | Case 1 | Case 2 | Case 3 | Case 4 |
---|---|---|---|---|

Maximum size (m) | 0.030 | 0.024 | 0.015 | 0.012 |

Maximum size (m) | 0.090 | 0.072 | 0.045 | 0.036 |

Total number of elements (Million) | 6.8 | 9.7 | 16.9 | 23.7 |

#### 3.2. Boundary Condition

_{pitch}= Amp ∙ sin(2π ∙ Frep ∙ t)

^{−3}, and then the unsteady computation used the steady state flow solution as the initial condition. The blade completed one cycle of revolution in 5 s with a time step size of 0.02778 s that corresponded to a blade rotation of 2.0°. All computations were effectively performed on a personal clustered of parallel machines that had 6-CPU Intel i7 processor, and 64 GB of RAM. For 10 sub-iterations of each global time step, the computation approximately required 3 min of 12 CPU parallel processing time.

## 4. Results and Discussion

**Figure 5.**Computational flowchart for computational fluid dynamic (CFD) approaches. (

**a**) Computational fluid dynamic with multiple reference frames (CFD-MRF); and (

**b**) Computational fluid dynamic with rigid body motion (CFD-RBM).

**Figure 6.**Mesh convergence study for the grid size on NREL 5-MW wind turbine surface. (

**a**) Aerodynamic Power; and (

**b**) Aerodynamic Thrust.

**Figure 7.**Unsteady aerodynamic comparison using the UBEM, CFD and FAST (NREL) methods for a platform pitching motion with an amplitude of 1° and a frequency of 0.1 Hz. (

**a**) Aerodynamic Power; and (

**b**) Aerodynamic Thrust.

**Figure 8.**Unsteady aerodynamic comparison using the UBEM, CFD and FAST (NREL) methods for a platform pitching motion with an amplitude of 4° and a frequency of 0.1 Hz. (

**a**) Aerodynamic Power; (

**b**) Aerodynamic Thrust.

**Figure 9.**Aerodynamic comparisons using the UBEM, CFD and FAST (NREL) methods for different pitching amplitudes of a FOWT (Freq = 0.1 Hz).

**Figure 10.**Visualisation of instantaneous computed vortices for unsteady pitching of a FOWT simulation represented by an isosurface of vorticity (Amp = 4°, Freq = 0.1 Hz). (

**a**) Downstream zone (Top: T

_{1}→ T

_{6}) and (

**b**) Upstream zone (Bottom: T

_{7}→ T

_{12}).

**Figure 11.**Unsteady aerodynamic load on the blade coordinate system by the CFD–RBM approach (Amp = 4°, Freq = 0.1 Hz).

## 5. Conclusions

## Acknowledgments

## Conflicts of Interest

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**MDPI and ACS Style**

Tran, T.; Kim, D.; Song, J.
Computational Fluid Dynamic Analysis of a Floating Offshore Wind Turbine Experiencing Platform Pitching Motion. *Energies* **2014**, *7*, 5011-5026.
https://doi.org/10.3390/en7085011

**AMA Style**

Tran T, Kim D, Song J.
Computational Fluid Dynamic Analysis of a Floating Offshore Wind Turbine Experiencing Platform Pitching Motion. *Energies*. 2014; 7(8):5011-5026.
https://doi.org/10.3390/en7085011

**Chicago/Turabian Style**

Tran, Thanhtoan, Donghyun Kim, and Jinseop Song.
2014. "Computational Fluid Dynamic Analysis of a Floating Offshore Wind Turbine Experiencing Platform Pitching Motion" *Energies* 7, no. 8: 5011-5026.
https://doi.org/10.3390/en7085011