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Evaluation of sand p–y curves by predicting both monopile lateral response and OWT natural frequency


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Figure 1

Original p–y curves. (a) Piecewise p–y curve proposed by Reese et al., (b) Hyperbolic formula suggested by the API.
Original p–y curves. (a) Piecewise p–y curve proposed by Reese et al., (b) Hyperbolic formula suggested by the API.

Figure 2

FE mesh used to analyze soil–monopile interaction.
FE mesh used to analyze soil–monopile interaction.

Figure 3

Monopile at Horns Rev: (a) monopile structural details, (b) soil layers.
Monopile at Horns Rev: (a) monopile structural details, (b) soil layers.

Figure 4

Profiles of lateral displacements.
Profiles of lateral displacements.

Figure 5

Profiles of bending moments.
Profiles of bending moments.

Figure 6

Profiles of shear forces.
Profiles of shear forces.

Figure 7

Profiles of soil reaction.
Profiles of soil reaction.

Figure 8

Histograms for the monopile head stiffness coefficients provided by the different models.
Histograms for the monopile head stiffness coefficients provided by the different models.

Figure 9

(a) (Substructure/tower/monopile) system, (b) Tower modeling with three springs representing the soil–monopile interaction, (c) Details of substructure and tower.
(a) (Substructure/tower/monopile) system, (b) Tower modeling with three springs representing the soil–monopile interaction, (c) Details of substructure and tower.

Figure 10

Monopile head movements in terms of monopile head applied loading: (a) H-uL, (b) M-θR and (c) H-θR curves.
Monopile head movements in terms of monopile head applied loading: (a) H-uL, (b) M-θR and (c) H-θR curves.

Adopted values for computing the 1st NF at North Hoyle.

α m Substructure mass mS (ton) Substructure bending rigidity EIS (GN m2) Tower top bending rigidity EItop (GN m2) Soil Young’s modulus Es (MPa) λav
0.905 1.739 34.138 254.162 33.547 110.0 3.808

Soil strength and deformation parameters at North Hoyle site.

Cohesion c (kN/m2) Angle of friction ϕ (°) Young’s modulus Es (MPa) Poisson’s ratio νs Shear modulus Gs (MPa) Reference
0.0 40.0 644.0 0.40 230.0 Arany et al. [20]

Soil strata for each soil layer at Horns Rev.

Soil layer Type Depth (m) Es (MPa) γ(γ′) (kN/m3) ϕ (°) ψ (°) νs
1 Sand 0.0–4.5 130.0 20(10) 45.4 15.4 0.28
2 Sand 4.5–6.5 114.3 20(10) 40.7 10.7 0.28
3 Sand to silty sand 6.5–11.9 100.0 20(10) 38.0 8.0 0.28
4 Sand to silty sand 11.9–14.0 104.5 20(10) 36.6 6.6 0.28
5 Sand/silt/organic 14.0–18.2 4.5 17(7) 27.0 0.0 0.28
6 Sand >18.2 168.8 20(10) 38.7 8.7 0.28

Proposed formulae to enhance p–y curves.

The initial stiffness E*py Parameters involved Nature of sand Reference
kAPIz As in equation (2) Silica API [4], DNV [5]
kWz=zkAPI(DprefDp)4(1-a)4+a {{\boldsymbol{k}}_{\boldsymbol{W}}}{\boldsymbol{z = z}}\,{{\boldsymbol{k}}_{{\bf{API}}}}{\left({{{{\boldsymbol{D}}_{\boldsymbol{p}}^{{\bf{ref}}}} \over {{{\boldsymbol{D}}_{\boldsymbol{p}}}}}} \right)^{{{{\boldsymbol{4(1 - a)}}} \over {{\boldsymbol{4 + a}}}}}} a=0.6 for a medium dense sanda=0.5 for a dense sandDpref=1.0 m Silica Wiemann et al. [12]
kS1z=a(ZZref)b(DpDpref)cϕd {{\boldsymbol{k}}_{{\boldsymbol{S1}}}}\,{\boldsymbol{z = a}}{\left({{{\boldsymbol{Z}} \over {{{\boldsymbol{Z}}_{{\bf{ref}}}}}}} \right)^{\boldsymbol{b}}}{\left({{{{{\boldsymbol{D}}_{\boldsymbol{p}}}} \over {{\boldsymbol{D}}_{\boldsymbol{p}}^{{\bf{ref}}}}}} \right)^{\boldsymbol{c}}}\,{\phi ^{\boldsymbol{d}}} a=50,000, zref=1 m, Dpref=1.0 mb=0.6, c=0.5, d=3.6, ϕ in radians Silica Sorensen et al. [13]
kKz=kAPIzref(ZZref)m(DpDpref)0.5 {{\boldsymbol{k}}_{\boldsymbol{K}}}\,{\boldsymbol{z =}}{{\boldsymbol{k}}_{{\bf{API}}}}{{\boldsymbol{z}}_{{\bf{ref}}}}{\left({{{\boldsymbol{Z}} \over {{{\boldsymbol{Z}}_{{\bf{ref}}}}}}} \right)^{\boldsymbol{m}}}{\left({{{{{\boldsymbol{D}}_{\boldsymbol{p}}}} \over {{\boldsymbol{D}}_{\boldsymbol{p}}^{{\bf{ref}}}}}} \right)^{{\boldsymbol{0}}{\boldsymbol{.5}}}} m=0.6, zref=2.5 m, Dpref=0.61 m Silica Kallehave et al. [14]
kS2z=a(ZZref)b(DpDpref)c(EsEsref)d {{\boldsymbol{k}}_{{\boldsymbol{S2}}}}\,{\boldsymbol{z = a}}{\left({{{\boldsymbol{Z}} \over {{{\boldsymbol{Z}}_{{\bf{ref}}}}}}} \right)^{\boldsymbol{b}}}{\left({{{{{\boldsymbol{D}}_{\boldsymbol{p}}}} \over {{\boldsymbol{D}}_{\boldsymbol{p}}^{{\bf{ref}}}}}} \right)^{\boldsymbol{c}}}\,{\left({{{{{\boldsymbol{E}}_{\boldsymbol{s}}}} \over {{\boldsymbol{E}}_{\boldsymbol{s}}^{{\bf{ref}}}}}} \right)^{\boldsymbol{d}}} a=1 MPa, zref=1 m, Dpref=1 mEsref=1 MPa, b=0.3, c=0.5, d=0.8 Silica Sorensen [15]

North Hoyle OWT’s structural details.

OWT component Symbol (unit) Value
Tower height LT (m) 67.0
Substructure height Ls (m) 7.0
Structure height L (m) 74.0
Tower top diameter Dt (m) 2.3
Tower bottom diameter Db (m) 4.0
Tower wall thickness tT (mm) 35.0
Substructure diameter Ds (m) 4.0
Substructure wall thickness ts (mm) 50
Tower material Young's modulus ET (GPa) 210.0
Tower mass mT (ton) 130.0
Top mass Mtop (ton) 100.0
Monopile diameter Dp (m) 4.0
Monopile wall thickness tp (mm) 50
Monopile material Young's modulus Ep (GPa) 210.0
Monopile depth Lp (m) 33.0
Measured frequency fmeasured (Hz) 0.35

Stiffness coefficients, interaction factors, and the different 1st NFs computed for the OWT at North Hoyle.

Parameters ABAQUS FE Analysis WILDPOWER 1.0
Reese et al. (1974) O’Neil and Murchison (1983) Kallehave et al. (2012) Sorensen et al. (2010) Sorensen (2012) Wiemann et al. (2004)
KL (MN/m) 771.64 1293.02 1471.54 2307.26 744.07 1335.67 1101.32
KR (MN m/rad) 54,172.94 63,519.50 66,491.98 74,640.81 50,676.57 63,667.97 60,458.79
KLR (MN) 5065.43 7109.84 7770.27 10,061.80 4689.59 7141.61 6412.90
CR 0.8693 0.8859 0.8900 0.9072 0.8703 0.8901 0.8802
CL 0.9977 0.9986 0.9988 0.9993 0.9978 0.9987 0.9984
Fixed base NF fFB (Hz) 0.417
1st NF f1 (Hz) 0.361 0.369 0.371 0.378 0.362 0.371 0.367
Measured NF f measured (Hz) 0.35
Deviation(%)=|fmeasuredf1fmeasured|100 {\rm{Deviation}}\,(\%) = \left| {{{{f_{{\rm{measured}}}} - {f_1}} \over {{f_{{\rm{measured}}}}}}} \right|\,100 100 3.14 5.43 6.00 8.00 3.43 6.00 4.86

Monopile head flexibility coefficients.

Flexibility coefficients ABAQUS FE analysis WILDPOWER 1.0
Reese et al. (1974) O’Neill and Murchison (1983) Kallehave et al. (2012) Sorensen et al. (2010) Sorensen (2012) Wiemann et al. (2004)
IL (m/MN) 0.003356 0.002011 0.001775 0.001052 0.003225 0.001871 0.002375
IR (rad/MN m) 0.000048 0.000041 0.000039 0.000033 0.000047 0.000039 0.000043
ILR (1/MN) 0.000314 0.000225 0.000207 0.000142 0.000298 0.000210 0.000252
eISSN:
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Language:
English
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Journal Subjects:
Geosciences, other, Materials Sciences, Composites, Porous Materials, Physics, Mechanics and Fluid Dynamics