# Experimental Investigation of the Coupling Effect of Jackup Offshore Platforms, Towers, and Seabed Foundations under Waves of Large Wave Height

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## Abstract

**:**

## 1. Introduction

## 2. Experimental Design

#### 2.1. Experimental Model

^{3}, and the tensile modulus, flexural modulus, and shear modulus were 25 GPa, 9.3 GPa, and 7 GPa, respectively.

#### 2.2. Experimental Procedure

- (1)
- Rinse the flume and the soil box with water before the experiment.
- (2)
- The soil foundation model is made layer by layer, for a total of four layers, each of which is 10 cm high. The platform structure is placed and the pore-pressure sensor is buried according to the design.
- (3)
- (4)
- Water is added to the tank to the prescribed water level for saturation. Considering the poor permeability of the foundation soil, the saturation time of the model’s foundation should be more than 24 h to make the foundation fully saturated.
- (5)
- A preliminary experiment for calibrating the wave parameters is carried out; a total of five wave-height meters are placed at the center of the model and at 1 m intervals before and after it to measure the wave surface process, comparing the test spectrum and the theoretical spectrum.
- (6)
- The experiment of Model A commences, according to the experimental conditions shown in Table 3.
- (7)
- Repeat steps 5–6 for the next wave condition after model A’s testing is completed, and steps 3–6 when model A is changed to model B.
- (8)
- Repeat steps 5–6 for the next wave condition after model B’s testing is completed, and steps 3–6 when model B is changed to model C.

#### 2.3. Experimental Conditions

## 3. Experiment Results

#### 3.1. Simulation Results of the Dynamic Response of the Jackup Offshore Platform Structure under Wavess

#### 3.1.1. Wave Pressure

#### 3.1.2. Pore Pressure

#### 3.1.3. Motion Response

#### 3.1.4. Acceleration

#### 3.1.5. Analysis of Structural Stationary State

#### 3.2. Simulation Test Results of the Coupling Effect of the Offshore Platform, Tower, and Seabed under Wave Impacts

#### 3.2.1. Dynamic Characteristics of Towers

#### 3.2.2. The Motion of the Towers

#### 3.2.3. Acceleration of the Towers

## 4. Discussion

#### 4.1. Stability Control of Jackup Offshore Platforms under Waves of Large Wave Height

#### 4.2. Coupling Effect between the Jackup Offshore Platform, the Tower, and the Seabed Foundation

#### 4.3. The Vibration Control of the Tower on the Offshore Platform

## 5. Conclusions

- (1)
- The wave pressures on the platform structure increase more under waves of large wave height than under normal conditions, and they also increase with the increase in wave height. When the wave height is large enough, the wave is blocked by the platform surface and the water body gathers under the platform surface, causing a pile group effect. The pressure on the platform’s back pile legs is greater than that on the front pile legs.
- (2)
- Due to the reciprocating movement of the structures under waves of large wave height, the soil near the pile legs squeezes the foundation bed in front of and behind the pile legs, causing the pore pressure of the foundation bed near the pile legs to increase cumulatively, and causing local softening of the foundation, which is manifested in the soil near the pile legs becoming soft, and the structure undergoes a certain displacement, revealing the mechanism of instability of the offshore platform’s pile foundation under waves of large wave height.
- (3)
- The platform produces longitudinal movement (along the propagation direction of wave) under normal conditions, and the longitudinal movement of the platform increases under waves of large wave height, accompanied by the vortex-induced vibration of the platform in the lateral direction of the pile legs.
- (4)
- The motion response of the tower structure is significantly greater than that of the platform structure, and a damping device has an obvious impact on the dynamic response characteristics of the tower. The maximum longitudinal movement of the tower without the damping device is 3.13 times that of the tower with the damping device under waves of large wave height.
- (5)
- Under the action of waves, a coupling vibration effect will occur between the tower and the platform, and the installation of the tower can play a certain role in mitigating the vibration of the platform itself.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## References

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**Figure 2.**Sketch of the experimental setup. (A: accelerometer; E: pressure sensor; L: displacement measuring instrument; WH: wave height sensor; P: pore pressure sensor).

**Figure 9.**Wave pressure history of the platform model under waves (${\mathrm{H}}_{\mathrm{w}}$ = 62.5 cm, ${\mathrm{H}}_{\mathrm{s}}$ = 30.0 cm, T = 2.45 s).

**Figure 10.**Pore pressure history of the pile leg under waves (${\mathrm{H}}_{\mathrm{w}}$ = 62.5 cm, ${\mathrm{H}}_{\mathrm{s}}$ = 30.0 cm, T = 2.45 s).

**Figure 16.**Comparison diagram of the surge history of the towers with and without the damping device (${\mathrm{H}}_{\mathrm{w}}$ = 62.5 cm, ${\mathrm{H}}_{\mathrm{s}}$ = 30.0 cm, T = 2.45 s).

**Figure 17.**Comparison diagram of the surge and pitch of the towers with and without the damping device.

**Figure 18.**Comparison diagram of acceleration at the monitoring points on the tower with and without the damping device (wave propagation direction).

**Figure 19.**Comparison diagram of acceleration at the monitoring points on the top face of the platform with and without the tower.

Specific gravity of the soil particle ${G}_{s}$ | 2.71 |

Moisture content $\omega $ | 25.59% |

Saturated density ${\rho}_{sat}$ (g/cm^{3}) | 1.780 |

Maximum saturated density ${\rho}_{dmax}$ (g/cm^{3}) | 1.719 |

Minimum saturated density ${\rho}_{dmin}$ (g/cm^{3}) | 1.286 |

Designed dry density ${\rho}_{d}$ (g/cm^{3}) | 1.502 |

Minimum porosity rate e_{min} | 0.357 |

Maximum porosity rate e_{max} | 0.525 |

Module | Parameters | Real Value | Proportional Scale | Experimental Model Value |
---|---|---|---|---|

Platform | Width (m) | 14.4 | ${\lambda}_{W}=24$ | 0.6 |

Length (m) | 14.4 | ${\lambda}_{L}=24$ | 0.6 | |

Height (m) | 0.48 | ${\lambda}_{H}=24$ | 0.02 | |

Diameter of pillars (m) | 1.92 | ${\lambda}_{D}=24$ | 0.08 | |

Length of pillars | 24 | ${\lambda}_{L}=24$ | 1 | |

Wave | Wave height H (m) | 1; 2; 3; 4.46; 5.60; 7.2 | ${\lambda}_{H}=24$ | 0.042; 0.083; 0.125; 0.186; 0.233; 0.30 |

Wave period T (s) | 8; 10; 12 | ${\lambda}_{T}$ = 24^{0.5} = 4.9 | 1.63; 2.04; 2.45 | |

Water depth h (m) | 10; 12; 15 | ${\lambda}_{d}=24$ | 0.417; 0.50; 0.625 | |

Monitoring objects | Pressure (kPa) | - | ${\lambda}_{p}=24$ | - |

Acceleration (g) | - | ${\lambda}_{a}=1$ | - | |

Displacement (m) | - | ${\lambda}_{s}=24$ | - |

Test Number | $\mathbf{Water}\mathbf{Depth}{\mathbf{H}}_{\mathbf{w}}\left(\mathbf{cm}\right)$ | $\mathbf{Wave}\mathbf{Height}{\mathbf{H}}_{\mathit{s}}\left(\mathbf{cm}\right)$ | Wave Period T (s) | $\mathbf{Wave}\mathbf{Length}\mathit{\lambda}$ (m) | Wave Celerity C (m/s) | |
---|---|---|---|---|---|---|

Normal conditions | 1 | 41.7 | 4.2 | 1.63 | 2.95 | 1.81 |

2 | 41.7 | 8.3 | 1.63 | 2.95 | 1.81 | |

3 | 41.7 | 18.6 | 1.63 | 2.95 | 1.81 | |

Extreme conditions with waves of large wave height | 4 | 41.7 | 23.3 | 1.63 | 2.95 | 1.81 |

5 | 50.0 | 30.0 | 2.04 | 4.15 | 2.03 | |

6 | 62.5 | 20.8 | 2.45 | 5.64 | 2.30 |

Conditions | ${\mathbf{H}}_{\mathbf{w}}\left(\mathbf{cm}\right)$ | ${\mathbf{H}}_{\mathbf{s}}\left(\mathbf{cm}\right)$ | T (s) | Stationary State |
---|---|---|---|---|

Normal operating conditions | 41.7 | 4.2 | 1.63 | Yes |

41.7 | 8.3 | 1.63 | Yes | |

41.7 | 12.5 | 1.63 | Yes | |

Extreme conditions with waves of large wave height | 41.7 | 18.6 | 1.63 | No |

50.0 | 23.3 | 2.04 | No | |

62.5 | 30.0 | 2.45 | No |

Tower Type | Period (s) | Equivalent Damping | ||
---|---|---|---|---|

Surge | Pitch | Surge | Pitch | |

Tower without damping device | 0.18 | 0.21 | 0.364 | 0.354 |

Tower with damping device | 0.20 | 0.23 | 0.500 | 0.473 |

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**MDPI and ACS Style**

Ye, H.; Zu, F.; Jiang, C.; Bai, W.; Fan, Y. Experimental Investigation of the Coupling Effect of Jackup Offshore Platforms, Towers, and Seabed Foundations under Waves of Large Wave Height. *Water* **2023**, *15*, 24.
https://doi.org/10.3390/w15010024

**AMA Style**

Ye H, Zu F, Jiang C, Bai W, Fan Y. Experimental Investigation of the Coupling Effect of Jackup Offshore Platforms, Towers, and Seabed Foundations under Waves of Large Wave Height. *Water*. 2023; 15(1):24.
https://doi.org/10.3390/w15010024

**Chicago/Turabian Style**

Ye, Hailin, Feng Zu, Chuwei Jiang, Wenjing Bai, and Yaojiang Fan. 2023. "Experimental Investigation of the Coupling Effect of Jackup Offshore Platforms, Towers, and Seabed Foundations under Waves of Large Wave Height" *Water* 15, no. 1: 24.
https://doi.org/10.3390/w15010024