The 2019 study of Tong, Liao and Chen established that a static Coulomb friction contact at the monopile–seabed interface slides and separates under wave loading in a one-way coupled RANS–Biot poroelastic model (RANS: Reynolds-averaged Navier–Stokes, the time-averaged viscous flow equations with a turbulence closure; Biot consolidation: the standard poroelastic theory coupling soil-skeleton deformation with pore-fluid flow), while the pore-pressure field is nearly unaffected and seabed and pile displacements change markedly relative to the usual displacement-continuity (conode) interface. Three omissions remained outside that model: elasto-plastic soil behaviour under repeated pore-pressure cycling, the turbine superstructure and the static and dynamic loads it transmits, and direct hydrodynamic wave forces on the structure above the mudline. Prior work has closed these gaps only pairwise: coupled wind–wave–turbine models with elasto-plastic seabeds retain tied, displacement-continuous pile–soil interfaces; full-structure models with Cam-Clay plasticity (a critical-state elasto-plastic soil model) and frictional contact omit pore-pressure coupling; and the source authors' own follow-up keeps a poroelastic seabed. No published model or experiment combines an elasto-plastic porous seabed, a slip/separation-capable pile–soil contact, and superstructure dynamics with direct hydrodynamic loading in one validated loop. The problem — to build and validate such a coupled model and quantify how each omitted mechanism changes contact pressure, shaft friction, sliding initiation, seabed response and monopile stability — remains open.

Background

Offshore wind turbines are most commonly founded on monopiles: large-diameter (typically 4–10 m) steel pipe piles driven tens of metres into the seabed, which transfer the horizontal thrust and overturning moment from wind, waves and the rotating machinery into the soil. The seabed is a water-saturated porous medium: ocean waves impose an oscillatory pressure on its surface, driving pore-water flow and pressure oscillations described by Biot's quasi-static consolidation equations (the standard poroelastic theory coupling deformation of the soil skeleton with pore-fluid flow). Where wave-induced pore pressure rises toward the overburden effective stress, the seabed can momentarily lose strength or liquefy, degrading the shaft friction and lateral resistance that support the pile.

Most numerical wave–pile–seabed studies before 2019 idealized the pile–soil interface as a 'conode' (displacement-continuity) boundary: soil and pile are forced to move together, which mathematically forbids sliding and separation. The structural-dynamics community, in turn, often represents the foundation with p–y nonlinear springs — empirical lateral soil-resistance curves — which do not resolve the porous-seabed effective-stress physics at all. Tong, Liao and Chen (2019) replaced the conode idealization with a static Coulomb friction contact — sliding initiates when the tangential traction TtT_t exceeds a friction-plus-cohesion threshold νfTn+Tc\nu_f T_n + T_c (with TnT_n the normal contact pressure) — inside a one-way coupled model in which a Reynolds-averaged Navier–Stokes (RANS) wave solver, the time-averaged viscous flow equations with a turbulence closure, supplies wave pressure to a poroelastic seabed and an elastic pile. They found that shaft sliding and separation do occur repeatedly under wave loading, that the pore-pressure field is essentially unaffected by the contact, but that seabed and pile displacements differ markedly from the conode prediction.

Three mechanisms were outside that model. The soil was linear-poroelastic, so irreversible yielding and shear-strength degradation under repeated pore-pressure cycling were unquantified. The superstructure — the tower, nacelle and rotor — and the static and dynamic horizontal forces it transmits through the monopile were absent. And the hydrodynamic wave forces acting on the structure above the mudline were not applied to the pile, so foundation motion was driven only through seabed pressures and contact tractions. The unresolved question is how these mechanisms, acting together with the nonlinear contact, change the contact behaviour and the resulting stability assessment. This matters because the mechanisms interact: structural loads change the normal stress and tangential demand on the shaft and hence the sliding threshold, while soil plasticity changes both the pore-pressure field and the strength available to resist sliding.

Problem Statement

In the wave–monopile–seabed system with a nonlinear (slip- and separation-capable) pile–soil contact, how do the three mechanisms omitted by Tong, Liao and Chen (2019) — (1) elasto-plastic soil behaviour, i.e. irreversible yielding and shear-strength degradation of the seabed under repeated wave-induced pore-pressure cycling; (2) the turbine superstructure (tower, nacelle, rotor) transmitting static and dynamic horizontal loads, including aerodynamic thrust and rotor inertia, through the monopile; and (3) direct hydrodynamic wave forces acting on the structure above the mudline and coupled to the foundation motion — jointly modify the response?

The task is to develop and validate a coupled model — numerical, or an instrumented physical model — in which all three mechanisms and the nonlinear contact act simultaneously, and to use it to determine how the contact-pressure and shaft-friction histories along the embedded shaft, the initiation, timing and extent of sliding and separation at the interface, the wave-induced pore-pressure and displacement fields in the seabed, and the resulting monopile displacement and stability indicators differ from each of the three single-mechanism-omission models — the coupled model with elasto-plastic soil behaviour suppressed, with the superstructure suppressed, and with direct hydrodynamic loading suppressed. The objective is a defensible quantification of the error each such simplification introduces into monopile stability assessment under realistic wave (and wind) loading. The coupled model must reproduce the source's documented contact-only poroelastic behaviour and the published experimental pore-pressure and displacement measurements for wave–monopile–seabed interaction within the uncertainty those measurements report, and must remain consistent with the displacement-continuity (conode) poroelastic baseline and the source study's contact-only poroelastic model; because no validated full-loop benchmark exists for the fully coupled configuration, that configuration is examined component-wise. A representative combined wind-and-wave sea state over a saturated elasto-plastic seabed profile is a sufficient case in which all four outcome categories and all three single-mechanism-omission comparisons can be evaluated.

References

  1. Tong, Dagui; Liao, Chencong; Chen, Jinjian (2019). Wave-monopile-seabed interaction considering nonlinear pile-soil contact. Computers and Geotechnics 113:103076. DOI 10.1016/j.compgeo.2019.04.021. https://doi.org/10.1016/j.compgeo.2019.04.021
  2. Tong, Dagui; Liao, Chencong; Chen, Jinjian (2023). Hydro-mechanical modelling of interaction between monopiles and cross-anisotropic sandy seabed subjected to wave loadings. Geomechanics and Geoengineering 19:123–138. DOI 10.1080/17486025.2023.2194854. https://doi.org/10.1080/17486025.2023.2194854
  3. Zhao, H. Y.; Jeng, D.-S.; Liao, C. C.; Zhu, J. F. (2017). Three-dimensional modeling of wave-induced residual seabed response around a mono-pile foundation. Coastal Engineering 128:1–21. DOI 10.1016/j.coastaleng.2017.07.002. https://doi.org/10.1016/j.coastaleng.2017.07.002
  4. Lin, Zaibin; Pokrajac, Dubravka; Guo, Yakun; Jeng, Dong-sheng; Tang, Tian; Rey, Nick; Zheng, Jinhai; Zhang, Jisheng (2017). Investigation of nonlinear wave-induced seabed response around mono-pile foundation. Coastal Engineering 121:197–211. DOI 10.1016/j.coastaleng.2017.01.002. https://doi.org/10.1016/j.coastaleng.2017.01.002
  5. Cao, Guangwei; Chen, Zhixiong; Wang, Chenglong; Ding, Xuanming (2020). Dynamic responses of offshore wind turbine considering soil nonlinearity and wind-wave load combinations. Ocean Engineering 217:108155. DOI 10.1016/j.oceaneng.2020.108155. https://doi.org/10.1016/j.oceaneng.2020.108155
  6. Ye, Jianhong; Yu, Dawei (2021). ABAQUS–OlaFlow integrated numerical model for fluid–seabed–structure interaction. Marine Structures 78:103016. DOI 10.1016/j.marstruc.2021.103016. https://doi.org/10.1016/j.marstruc.2021.103016
  7. Ye, Hailin; Yu, Dawei; Ye, Jianhong; Yang, Zhiwen (2022). Numerical Analysis of Dynamics of Jack-Up Offshore Platform and Its Seabed Foundation under Ocean Wave. Applied Sciences 12(7):3299. DOI 10.3390/app12073299. https://doi.org/10.3390/app12073299
  8. Yu, Dawei; Ye, Jianhong; Yin, Changquan (2023). Dynamics of offshore wind turbine and its seabed foundation under combined wind-wave loading. Ocean Engineering 286:115624. DOI 10.1016/j.oceaneng.2023.115624. https://doi.org/10.1016/j.oceaneng.2023.115624
  9. He, Kunpeng; Ye, Jianhong (2023). Dynamics of offshore wind turbine-seabed foundation under hydrodynamic and aerodynamic loads: A coupled numerical way. Renewable Energy 202:453–469. DOI 10.1016/j.renene.2022.11.029. https://doi.org/10.1016/j.renene.2022.11.029
  10. He, Kunpeng; Ye, Jianhong (2023). Seismic dynamics of offshore wind turbine-seabed foundation: Insights from a numerical study. Renewable Energy 205:200–221. DOI 10.1016/j.renene.2023.01.076. https://doi.org/10.1016/j.renene.2023.01.076
  11. Du, Hongyi; Wang, Dunge; Hou, Jiankang; Yu, Ziqin; Liu, Ze; Cheng, Yongzhou (2025). Numerical Simulation of Seabed Response Around Monopile Under Wave–Vibration. Journal of Marine Science and Engineering 13(7):1309. DOI 10.3390/jmse13071309. https://doi.org/10.3390/jmse13071309
  12. Ye, Hailin; Fan, Yaojiang; Bai, Wenjing; Jiang, Chuwei (2024). Experimental study of coupling response characteristics of offshore monopiles, seabed, and waves in various sea conditions. Scientific Reports 14:28560. DOI 10.1038/s41598-024-79858-2. https://doi.org/10.1038/s41598-024-79858-2
  13. Sui, Titi; Liu, Chenglin; Zhang, Jisheng; Zhang, Chi; Zheng, Jinhai (2024). 3D numerical modeling of wave–monopile–seabed interaction in the presence of a scour hole. Ocean Engineering 298:117254. DOI 10.1016/j.oceaneng.2024.117254. https://doi.org/10.1016/j.oceaneng.2024.117254
  14. Lin, Jie; Jeng, Dong-Sheng; Zhao, Hongyi; Gao, Yuan; Liu, Junwei; Guo, Yakun (2023). Recent advances of seabed liquefaction around the vicinity of marine structures. Ocean Engineering 280:114660. DOI 10.1016/j.oceaneng.2023.114660. https://doi.org/10.1016/j.oceaneng.2023.114660
  15. Wang, Tianju; Zou, Degao; Liu, Jingmao; Chen, Kai; Zhang, Xiuyang; Tian, Shanlin (2026). Liquefaction response of monopile offshore wind turbines under different loading conditions during operating and shutdown states. Computers and Geotechnics 196:108125. DOI 10.1016/j.compgeo.2026.108125. https://doi.org/10.1016/j.compgeo.2026.108125
  16. Gkougkoudi-Papaioannou, Maria; Pepi, Yuri; Streicher, Maximilian; Stuyts, Bruno; Troch, Peter (2024). Wave-Structure-Seabed Interaction and Pore Pressure Measurements for Monopile Foundations: A 3D Experimental Study. Proceedings of the ASME 2024 37th International Conference on Ocean, Offshore and Arctic Engineering, paper V008T10A026. DOI 10.1115/omae2024-128227. https://doi.org/10.1115/omae2024-128227
  17. Xu, Simin; Liu, Xiaolei; Zhang, Cheng; Zhang, Hong; Xie, Botao; Guo, Xingsen (2025). Numerical study on the stability of offshore pile-soil systems considering pore pressure response induced by extreme storms. Ocean Engineering 329:121178. DOI 10.1016/j.oceaneng.2025.121178. https://doi.org/10.1016/j.oceaneng.2025.121178
  18. Cheng, Haiyang; Liang, Bingchen; Zhang, Hong; Wang, Dong; Liu, Xiaolei (2025). Coupled numerical simulation of seabed response to focused wave loads around monopile foundation. Ocean Engineering 341:122453. DOI 10.1016/j.oceaneng.2025.122453. https://doi.org/10.1016/j.oceaneng.2025.122453