#
CFD for Surfboards: Comparison between Three Different Designs in Static and Maneuvering Conditions^{ †}

^{1}

^{2}

^{*}

^{†}

## Abstract

**:**

## 1. Introduction

## 2. Numerical Setup

^{+}lower than 5 on the whole surface. The convective Courant number is defined here as:

_{w}is the water flow velocity, Δt is the physical time step and Δx is the cell with in the x direction. The time step was chosen so that CCN = 0.5 in the finer portion of the grid, which is the necessary condition for the numerical stability of the VOF model.

#### 2.1. Numerical Models

_{w}and kinematic viscosity ν

_{w}and it represents the liquid phase of the mixture. The traveling velocity is modelled by imposing a velocity boundary condition at the inlet boundary, meaning that the velocity u

_{w}= U is prescribed to each of the boundary cells included in the liquid phase of the mixture.

_{a}and kinematic viscosity ν

_{a}and zero speed (U

_{a}= 0). The flow velocities are chosen in order to be representative for paddling speed (U = 4 m/s) and cruising speed (U = 8 m/s).

#### Surfboards

## 3. Results and Discussion

_{w}and the lift along the y-axis and perpendicular to the velocity u

_{w}

_{.}The pivoting point around which the models rotate was placed at Li = 1.5 m. The nondimensional coefficients for lift and drag force can be expressed as follows:

_{i}[m

^{2}] was 0.185 m

^{2}and 0.182 m

^{2}respectively for the Baseline and LR surfboards and for the PT surfboard. While results for the static simulations are presented in form of force coefficients, the output of maneauvering simulations is expressed in form of forces since the wetted area is difficult to measure.

#### 3.1. Static Simulations

**Figure 3**, the pressure distribution on the middle line of the board for the three boards is plotted. Minimal differences are noticeable on the 4 m/s case while larger difference can be seen on the 8 m/s case. At this speed, the LR surfboard generally experiences larger pressures and thus higher forces. The pressure peak is placed at s = 0.72 m and it is constant for all the tested boards and for all the AoA. This allows the surfer to operate and direct the board more easily. In fact, the surfer can change the AoA by moving his body forward or backwards. In principle, by lowering the AoA, the board will experience less drag and its speed will increase while pushing on the tail will allow the surfer to brake. Increasing the AoA will lead to a steep increase in lift which will allow the board to emerge from the water, moving the pivoting point further back on the board but this behavior is not treated in the current paper. If the pressure peak is constant with AoA, the surfer can move his body to change the AoA without losing balance.

#### 3.2. Maneuvers Simulations

## 4. Conclusions

## Conflicts of Interest

## References

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**Figure 1.**Boundary conditions (

**left**) and side and top view of the surfboard models used in the simulations (

**right**).

**Figure 2.**Drag coefficient c

_{D}versus Angle of Attack AoA for baseline, PT and LR models at 4 m/s (

**a**,

**b**) and 8 m/s (

**c**,

**d**). Baseline in red (■) and PT in green (♦) and LR in yellow (♦).

**Figure 3.**Pressure on the middle line of the surfboard bottom. Baseline in red (■) and PT in green (♦) and LR in yellow (♦) for 4m/s (

**a**) and 8m/s (

**b**).

**Figure 4.**Snapshots of the free surface behind the board at different moments in the maneuvering simulation.

Title 1 | h_{1} | h_{2} | h_{0} | Li | Length | Tail Type |
---|---|---|---|---|---|---|

[m] | [m] | [m] | [m] | [m] | [-] | |

Baseline | 0.105 | 0.05 | 0.02 | 0.5 | 1.85 | Squash |

LR | 0.100 | 0.05 | 0.02 | 0.5 | 1.85 | Squash |

PT | 0.105 | 0.05 | 0.02 | 0.5 | 1.85 | Round |

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**MDPI and ACS Style**

Oggiano, L.; Pierella, F.
CFD for Surfboards: Comparison between Three Different Designs in Static and Maneuvering Conditions. *Proceedings* **2018**, *2*, 309.
https://doi.org/10.3390/proceedings2060309

**AMA Style**

Oggiano L, Pierella F.
CFD for Surfboards: Comparison between Three Different Designs in Static and Maneuvering Conditions. *Proceedings*. 2018; 2(6):309.
https://doi.org/10.3390/proceedings2060309

**Chicago/Turabian Style**

Oggiano, Luca, and Fabio Pierella.
2018. "CFD for Surfboards: Comparison between Three Different Designs in Static and Maneuvering Conditions" *Proceedings* 2, no. 6: 309.
https://doi.org/10.3390/proceedings2060309