Lateral Undrained Capacity of a Multiline Ring Anchor in Clay
Publication: International Journal of Geomechanics
Volume 21, Issue 5
Abstract
Offshore wind energy is an attractive alternative in pursuing the nation's clean energy goals due to the significant demand for electricity in the coastal areas of the United States. Locating sites further offshore in deeper water can provide stronger, more consistent wind power resources and can mitigate aesthetic concerns. This motivates a need for improvements in the floating offshore wind turbine (FOWT) technology. As foundation costs comprise a significant fraction of the total cost for offshore wind power development, reducing the cost of the mooring system can play a significant role in making floating offshore wind economically competitive. Previous studies led to the development of a novel, efficient multiline ring anchor (MRA) system that can provide significant capital cost savings. Preliminary research shows that the MRA has a clear advantage under lateral loading by attaching wing plates to the cylindrical core of the anchor. In this study, two-dimensional finite-element (2D FE) analyses were performed to understand how wing plates affect the MRA performance under horizontal loading and provide reliable estimates of the ultimate load capacity. The results show the collapse mechanisms and bearing factors can be affected by width, the total number of wing plates, and load angles. This study also presents plastic limit analysis (PLA), based on the upper bound solution, to validate the 2D FE results by comparison and to confirm whether the postulated collapse mechanism was correct. The results obtained in the current study indicated that PLA can be a benchmark solution to evaluate the ultimate load capacity of the MRA with a satisfactory agreement with the FE-computed values.
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Data Availability Statement
All data, models, and codes generated or used during the study appear in the published article.
Acknowledgments
The authors acknowledge the support for the second author from the National Science Foundation, award number CMMI-1936901, and the Texas A&M High Performance Research Computing facility for the use of their resources in running the numerous finite-element analyses supporting this study.
Notation
The following symbols are used in this paper:
- Ap
- projected area of the MRA;
- D
- diameter of the cylinder part of the MRA;
- rate of energy dissipation;
- E
- Young's modulus;
- F
- applied load;
- H
- lateral resistance of the MRA per unit length;
- L
- characteristic width of MRA;
- Lp
- projected width of MRA normal to load direction;
- Np
- dimensionless unit lateral bearing factor;
- Npc
- H/(suD), lateral bearing factor based on D;
- Npp
- H/(suLp), lateral bearing factor based on Lp;
- Nw
- number of wing plates;
- su
- undrained shear strength;
- v0
- velocity of the anchor in the loading direction;
- vn
- v0 cos β, v0 cos δ;
- vt
- v0 sin β, v0 sin δ;
- Ww
- width of the wing plates;
- α
- adhesion factor between pile and soil;
- β, δ
- angle of the triangular wedge;
- θ
- angle between applied load and the closest wing; and
- θa
- load angle from bisector between two wing plates.
References
Aubeny, C. 2017. Geomechanics of marine anchors. Boca Raton, FL: CRC Press.
Aubeny, C., J. Murf, and S. Moon. 2001. “Lateral undrained resistance of suction caisson anchors.” Int. J. Offshore Polar Eng. 11 (3): 211–219.
Aubeny, C. P., S. W. Han, and J. D. Murff. 2003. “Inclined load capacity of suction caissons.” Int. J. Numer. Anal. Methods Geomech. 27 (14): 1235–1254. https://doi.org/10.1002/nag.319.
Aubeny, C. P., and J. Lee. 2020. “Horizontal load capacity of multiline ring anchor in soft clay.” In Int. Symp. on Frontiers in Offshore Geotechnics. Austin, TX: Deep Foundations Institute.
Bang, S., Y. Cho, Y. Kim, D. Kwag, and T. Lee. 2003. “Embedded suction anchors for floating breakwaters.” WIT Trans. Built. Environ. 70: 469–477.
Benson, D. J. 1989. “An efficient, accurate, simple ale method for nonlinear finite element programs.” Comput. Methods Appl. Mech. Eng. 72 (3): 305–350. https://doi.org/10.1016/0045-7825(89)90003-0.
Chen, J., C. F. Leung, Z. Chen, K. K. Tho, and Y. K. Chow. 2015. Centrifuge model study on pullout behavior of plate anchors in clay with linearly increasing strength, 839–844. Leiden, Netherlands: Taylor & Francis Books.
Chen, W.-F. 1975. Limit analysis and soil plasticity. Amsterdam, Netherlands: Elsevier.
Chen, Z., K. K. Tho, C. F. Leung, and Y. K. Chow. 2013. “Influence of overburden pressure and soil rigidity on uplift behavior of square plate anchor in uniform clay.” Comput. Geotech. 52: 71–81. https://doi.org/10.1016/j.compgeo.2013.04.002.
Chung, S. F., M. F. Randolph, and J. A. Schneider. 2006. “Effect of penetration rate on penetrometer resistance in clay.” J. Geotech. Geoenviron. Eng. 132 (9): 1188–1196. https://doi.org/10.1061/(ASCE)1090-0241(2006)132:9(1188).
de Sousa, J. R. M., C. S. de Aguiar, G. B. Ellwanger, E. C. Porto, D. Foppa, and C. J. de Medeiros. 2011. “Undrained load capacity of torpedo anchors embedded in cohesive soils.” J. Offshore Mech. Arct. Eng. 133 (2): 021102. https://doi.org/10.1115/1.4001953.
Diaz, B. D., M. Rasulo, C. P. Aubeny, C. M. Fontana, S. R. Arwade, D. J. DeGroot, and M. Landon. 2016. “Multiline anchors for floating offshore wind towers.” In OCEANS 2016 MTS/IEEE Monterey, 1–9. New York: IEEE.
Fontana, C., S. Arwade, D. DeGroot, S. Hallowell, C. Aubeny, B. Diaz, M. Landon, S. Ozmutlu, and A. Myers. 2019. “Force dynamics and stationkeeping costs for multiline anchor systems in floating wind farms with different spatial parameters.” In Proc., 38th Int. Conf. on Ocean, Offshore and Arctic Engineering, 1–11. New York: ASME.
Hu, Y., and M. Randolph. 1998. “A practical numerical approach for large deformation problems in soil.” Int. J. Numer. Anal. Methods Geomech. 22 (5): 327–350. https://doi.org/10.1002/(SICI)1096-9853(199805)22:5%3C327::AID-NAG920%3E3.0.CO;2-X.
Huang, Y., and X. Han. 2020. “Features of earthquake-induced seabed liquefaction and mitigation strategies of novel marine structures.” J. Mar. Sci. Eng. 8 (5): 310. https://doi.org/10.3390/jmse8050310.
Lee, J., and C. P. Aubeny. 2019. “Effect of wing plates on a multiline ring anchor system in cohesive soils.” In OCEANS 2019 MTS/IEEE SEATTLE, 1–6. New York: IEEE. https://doi.org/10.23919/OCEANS40490.2019.8962734.
Lee, J., and C. P. Aubeny. 2020. “Multiline ring anchor system for floating offshore wind turbines.” J. Phys.: Conf. Series 1452 (1): 012036.
Lee, J., M. Khan, L. Bello, and L. P., Aubeny. 2020. “Cost analysis of multiline ring anchor systems for offshore wind farm.” Deep Foundation Institute 45th Conf., 484–493. National Harbor, MD: Deep Foundations Institute.
Li, H., H. Liu, and S. Liu. 2017. “Dynamic analysis of umbrella suction anchor foundation embedded in seabed for offshore wind turbines.” Geomech. Energy Environ. 10: 12–20. https://doi.org/10.1016/j.gete.2017.05.002.
Malvern, L. E. 1969. Introduction to the mechanics of a continuous medium. Upper Saddle River, NJ: Prentice Hall.
Merifield, R. S., S. W. Sloan, and H. S. Yu. 2001. “Stability of plate anchors in undrained clay.” Géotechnique 51 (2): 141–153. https://doi.org/10.1680/geot.2001.51.2.141.
Murff, J., M. Randolph, S. Elkhatib, H. Kolk, R. Ruinen, P. Strom, and C. Thorne. 2005. “Vertically loaded plate anchors for deepwater applications.” In PInt. Symp. on Frontiers in Offshore Geotechnics, 31–48. Boca Raton, FL: CRC Press.
Murff, J. D., and J. M. Hamilton. 1993. “P-ultimate for undrained analysis of laterally loaded piles.” J. Geotech. Eng. 119 (1): 91–107. https://doi.org/10.1061/(ASCE)0733-9410(1993)119:1(91).
Musial, W., D. Heimiller, P. Beiter, G. Scott, and C. Draxl. 2016. 2016 offshore wind energy resource assessment for the United States. Golden, CO: NREL.
O’Loughlin, C., D. White, and S. Stanier. 2015. “Novel anchoring solutions for FLNG-opportunities driven by scale.” In Vol. 6 of Offshore Technology Conf., 4314–4345. Houston: Offshore Technology Conference.
O’Neill, M. P., M. F. Bransby, and M. F. Randolph. 2003. “Drag anchor fluke–soil interaction in clays.” Can. Geotech. J. 40 (1): 78–94. https://doi.org/10.1139/t02-096.
Potts, D. M., L. Zdravkovic, and L. Zdravković. 2001. Finite element analysis in geotechnical engineering: Application. London: Thomas Telford.
Randolph, M. F., and G. T. Houlsby. 1984. “The limiting pressure on a circular pile loaded laterally in cohesive soil.” Géotechnique 34 (4): 613–623. https://doi.org/10.1680/geot.1984.34.4.613.
Ranjan, G., and V. Arora. 1980. “Model studies on anchors under horizontal pull in clay.” In Proc., 3rd Australia-New Zealand Conf. on Geomechanics, 65–70. Wellington, New Zealand: Institution of Professional Engineers New Zealand.
Rowe, R. K., and E. H. Davis. 1982. “The behaviour of anchor plates in clay.” Géotechnique 32 (1): 9–23. https://doi.org/10.1680/geot.1982.32.1.9.
SIMULIA. 2018. ABAQUS/standard user’s manual, version 2018. Providence, RI: SIMULIA.
Song, Z., Y. Hu, D. Wang, and C. O’Loughlin. 2006. “Pullout capacity and rotational behaviour of square anchors.” In Proc., 6th Int. Conf. on Physical Modelling in Geotechnics, 1325–1331. London: Taylor & Francis.
Wang, D., B. Bienen, M. Nazem, Y. Tian, J. Zheng, T. Pucker, and M. F. Randolph. 2015. “Large deformation finite element analyses in geotechnical engineering.” Comput. Geotech. 65: 104–114. https://doi.org/10.1016/j.compgeo.2014.12.005.
Yang, M., J. D. Murff, and C. P. Aubeny. 2010. “Undrained capacity of plate anchors under general loading.” J. Geotech. Geoenviron. Eng. 136 (10): 1383–1393. https://doi.org/10.1061/(ASCE)GT.1943-5606.0000343.
Yu, L., J. Liu, X.-J. Kong, and Y. Hu. 2011. “Numerical study on plate anchor stability in clay.” Géotechnique 61 (3): 235–246. https://doi.org/10.1680/geot.8.P.071.
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© 2021 American Society of Civil Engineers.
History
Received: Jun 11, 2020
Accepted: Dec 2, 2020
Published online: Feb 23, 2021
Published in print: May 1, 2021
Discussion open until: Jul 23, 2021
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