Force analysis of grouting connection section of offshore wind turbine three pile foundation structure

ABSTRACT

Offshore wind farms are located in marine environments with complex hydrological, meteorological and submarine geological conditions, which pose difficulties for wind turbine foundation design and construction. Therefore, the study of the key technologies of offshore wind turbine foundation design has important theoretical value and practical significance for the assurance of structural safety, the optimization of structural design and the extension of structural service life. In this paper, a numerical simulation model of three pile foundation is established, and a detailed FEA model of grouted area is calculated and analyzed, and influence of grout on performance under different loading conditions is calculated and analyzed. The results show that it is feasible to use the p-y curve method to describe the pile-soil interaction of the three-pile foundation of the offshore wind turbine, the stress check of the whole foundation structure under ultimate load conditions and normal load conditions meets the requirements of the DNV specification, and the result of the fatigue damage check is that the fatigue strength requirement is met in 26.7 years, which indicates that the three-pile foundation structure of the offshore wind turbine is safe and reliable and can be operated safely.

CO EDITOR-IN-CHIEF:

• Ou, Yu-Chen

ASSOCIATE EDITOR:

• Ou, Yu-Chen

KEYWORDS:

• Offshore wind turbine
• grouted connections
• p-y curve
• S-N curve
• fatigue life analysis
• DNV specification
• ANSYS numerical simulation

Nomenclature

A	=	Projected area of the column in the direction of flow per unit length
$A_d$	=	Sectional area of the column
$\mathit{c}$	=	The undrained shear strength of undisturbed cohesive soil
$C_1$$C_2$$C_3$ Depends on the internal friction angle of sand	=
$C_D$	=	Speed force coefficient, take 1.2 for circular section
$C_{\mathit{DD}}$	=	Drag force coefficient
$C_I$	=	Inertial force coefficient
$C_M$	=	Mass force coefficient, take 2.0 for circular cross section
$\mathit{D}$	=	The diameter of the cylinder
$D_p\mathit{\hspace{0.17em}}$	=	The diameter of the pile
$f_{\mathit{cck}}$	=	Characteristic columnar compressive stress strength of the grouting material
$f_s$	=	Tresca stress of the grouting material
$\mathit{J}$	=	Dimensionless empirical constant，the range of variation is 0.25~0.50
$\mathit{k}$	=	Fatigue safety factor, as per the API specification, is considered to be 3
$k^{\prime }\mathit{\hspace{0.17em}}$	=	The ground reaction force of the initial modulus
$\mathit{L}$	=	Length of grouting connection section
$\mathit{m}$	=	Total number of stress amplitudes
$m^{\prime }$	=	The reciprocal of the double logarithmic gradient
$M_T$	=	Design limit axial load
$n_i$	=	Number of actions with alternating stress amplitude${\sigma }_{\mathit{ri}}$
$n_j$	=	Total number of stress cycles in member in sea state j per year
$n_{\mathit{ji}}$	=	Number of actions with alternating stress amplitude$\mathit{\hspace{0.17em}}{\mathit{\sigma }}_{\mathrm{ri}}$
$\mathit{N}$	=	Number of cycles a node can endure without experiencing fatigue when subjected to alternating stress of $\mathrm{\Delta }\mathit{\sigma }$
$N_i$	=	The maximum number of cycles for a node to resist fatigue under an alternating stress amplitude of$\mathit{\hspace{0.17em}}{\mathit{\sigma }}_{\mathrm{ri}}$
$N_{\mathit{ji}}$	=	The maximum number of cycles for a node to resist fatigue under an alternating stress amplitude of$\mathit{\hspace{0.17em}}{\mathit{\sigma }}_{\mathrm{ri}}$
$\mathit{p}\mathit{\hspace{0.17em}}$	=	The actual lateral resistance of soil to pile
$P_D$	=	Velocity component of wave force
$P_I$	=	Inertial component of wave force
$p_u$	=	The ultimate lateral bearing capacity of the pile
$\mathit{P}$	=	Design limit axial load
$\mathit{P}\left(\mathrm{\Delta }{\sigma }_i\right)$	=	Variable amplitude hot spot stress
$r_m$	=	Dimensionless factor
$\mathit{R}$	=	Design value of the structural resistance
$R_p$	=	Outer diameter of inner tube
$\mathit{S}$	=	Design value of the load effect combination
$S_{\mathit{CK}}$	=	permanent load
$S_{\mathit{GK}}$	=	Sub-factor of the self-weight. Here $S_{\mathit{GK}}$is 1.0
$S_{\mathit{Q}1\mathit{K}}$	=	The partial coefficient of wave load and tidal load
$T_e$	=	Stress effective cycle period
$\mathit{X}\mathit{\hspace{0.17em}}$	=	The depth below the mud surface
$X_R$	=	Depth below mud surface to bottom of soil drag reduction zone
$\mathit{y}$	=	The actual lateral displacement of the pile
$y_{50}$	=	Equal to 2.5${\epsilon }_{\mathrm{s}0}$D
$\mathrm{\Delta }{\sigma }_i$	=	Cumulative probability of occurring in given swell
$\mathrm{\Delta }{\sigma }_{\mathit{ref}}$	=	Stress amplitude of the structure at $2\times {10}^6$ cycles
${\mathit{\epsilon }}_{\mathrm{s}0}$	=	Strain of a soil sample reaching half of its maximum stress.
${\gamma }_0$	=	Structural coefficient. Here ${\gamma }_0$=1.1
${\gamma }_G$	=	Sub-factor of the permanent load
${\gamma }_{\mathit{Q}1}$	=	Sub-factor of the $\mathit{i}$-th variable load
${\tau }_{\mathrm{sa}}$	=	Shear stress under the axial force of connecting section
${\tau }_{\mathit{st}}$	=	Shear stress under the axial force of connecting section
${\psi }_{\mathit{ci}}$	=	Combined value coefficient of variable load (wave and current load), usually 0.7
$\mathit{\gamma }$	=	The effective bulk density of soil
$\mathit{\rho }$	=	Percentage of a given swell occurring in a given year
${\rho }^{\prime }$	=	Water density

Acknowledgments

We thank Prof. Yasuhiro Mori for his help in the preparation of this Manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data underlying this article are available in the article and in its online supplementary material.

Declaration of conflicting interests

The authors declare no conflict of interest.

Additional information

Funding

Support for this research was provided by the National Natural Science Foundation of China (Grant No. 50708011), the Research Initiation Project of Xi’an Polytechnic University (Grant No. 310-107020368), and the State Scholarship Fund of China (Grant No. 202108610120).