题目: Predicting long term performance of offshore wind turbine foundation using experimental tests and DEM simulations
报告人: Dr Liang Cui (University of Surrey, UK)
Many offshore wind turbines are supported by large-diameter piles (known as monopiles) and are subjected to 107 to 108 cycles of dynamic loadings in their designed service life. There are evidences suggesting that foundation stiffness are changing with cycles of loading and this may lead to changes in the natural frequency of the system with the potential for unplanned system resonances. There are other consequences such as excessive tilt leading to expensive repair or even complete shutdown. Therefore, it is vital to understand the long-term response of wind turbine foundation so that a method to predict the change in frequency and long-term tilt could be established. The first part of the presentation shows the experimental work of small-scale physical modelling and discrete element modelling of the interactions between a monopile and the surrounding soil. Changes in soil stiffness under cyclic loading of various strain amplitudes were examined for both physical modelling and discrete element modelling. Micromechanics of soils underlying the soil stiffness change was investigated using discrete element method. Variation of force distribution along the monopile under cyclic loading was analysed to show the influence of monopile stability.
The second part of the presentation considers the local soil behaviour adjacent to monopile under cyclic loading by a series of cyclic simple shear tests. The effects of cycles of shear loading with different shear strain amplitudes and vertical stresses were investigated. The results correlated quite well with the observations from scaled model tests. Specifically, the test results showed that shear modulus increases rapidly in the initial loading cycles and then the rate of increase diminishes; the rate of increase depends on strain amplitude, initial relative density and vertical pressure. Complementary DEM simulations were performed using PFC2D to analyse the micromechanics underlying the cyclic behaviour of soils. It shows that the change of soil behaviour strongly related to the rotation of principle axes of fabric and degree of fabric anisotropy.
Dr Liang Cui joined the University of Surrey as a Lecturer in Geotechnics in June 2009. Her main expertise is in developing Discrete Element Method (DEM) for modelling granular materials. She has endeavoured to develop DEM codes to analyse the micromechanics in the geotechnical element tests and a wide range of geotechnical applications, including
DEM modelling of direct shear test, triaxial test and simple shear test;
the complex soil-structure interactions for offshore wind farms;
locomotion of the off-road vehicles in the terrestrial and extra-terrestrial environments (analysed using both DEM and FEM);
aggregate breakage mechanism for permeable pavements;
cyclic behaviour of rubberised backfill soil for integral abutment bridges, etc.
Her second research area is energy absorption capacities of porous materials, including polymeric foam materials and granular materials. She is also interested in the wave propagation behaviours through porous materials. She obtained the PhD degree from UCD in 2006 on the development of virtual test environment for granular materials using Discrete Element Method. She gained the BE degree from Tsinghua University in China in 2002.
She has published over 20 journal papers with over 700 citations and h-index of 12 based on Scopus as well as two book chapters and over 20 conference publications. She served on the Editorial board of ASCE Journal of Computing in Civil Engineering between 2010 and 2017. Key publications include:
Lopez-Querol S., L. Cui and S. Bhattacharya (2017) “Numerical Methods for SSI Analysis of Offshore Wind Turbine Foundations”, in T. Letcher ed. Wind Energy Engineering: A Handbook for Onshore and Offshore Wind Turbines. ISBN 9780128094518. Publisher: Academic Press.
L. Cui, A. Moqsud, M. Hyodo, S. Bhattacharya (2018) Methane hydrate as a “new energy”, in Managing Global Warming. Publisher: Academic Press. In Press.
M.J. Jiang, Y.S. Dai, L. Cui and B.L. Xi (2017). Experimental and DEM analyses on wheel-soil interaction. Journal of Terramechanics. Vol 76, 15-28.
M.J. Jiang, Y.S. Dai, L. Cui and B.L. Xi (2017) Soil-mechanics based testbed setup and corresponding experimental investigation. Journal of Aerospace Engineering. Vol 30 (6).
M.J. Jiang, J Sima, L.Q. Li, C.B. Zhou, L. Cui (2017). Investigation of influence of particle characteristics on the non-coaxiality of anisotropic granular materials using DEM. International Journal for Numerical and Analytical Methods in Geomechanics. Vol 41 (2), 198-222.
M.J. Jiang, C. Fu, L. Cui, Z.F. Shen, F.Y. Zhu, (2016) DEM simulations of methane hydrate exploitation by thermal recovery and depressurization methods. Computers and Geotecnics. Vol 80, 410-426.
Cui, L. and Bhattacharya, S. (2016) Soil–monopile interactions for offshore wind turbines. Proceedings of the ICE - Engineering and Computational Mechanics. Vol 169(4), 171-182.
Cui, L. and Bhattacharya, S. (2015) “Choice of aggregates for permeable pavements based on laboratory tests and DEM simulations”. International Journal of Pavement Engineering. Vol 18 (2), 162-170
M.J. Jiang, N. Zhang, L. Cui, Shulou Jin (2015). A size-dependent bond failure criterion for cemented granules based on experimental studies. Computers and Geotecnics. Vol 69, pp182-198.
M.J. Jiang, Y.S. Dai, L. Cui and Z.F. Shen (2014). “Investigating mechanism of inclined CPT in granular ground using DEM”. Granular Matter. Vol 16(5), pp 785-796.
O’Sullivan, C. and Cui, L. (2009) “Micromechanics of Granular Material Response During Load Reversals: Combined DEM and Experimental Study” Powder Technology. Vol 193(3), pp 289-302.
O’Sullivan, C., Cui, L. and S. O’Neil (2008) “Discrete element analysis of the response of granular materials during cyclic loading” Soils and Foundations. Vol.48(4), pp 511-530.
Cui, L., C. O’Sullivan and S. O’Neil (2007) “An analysis of the triaxial apparatus using a mixed boundary three-dimensional discrete element model” Geotechnique Vol 57(10), pp 831-844.
Cui, L. and C. O’Sullivan (2006) “Exploring the macro- and micro-scale response characteristics of an idealized granular material in the direct shear apparatus” Geotechnique Vol 56(7), pp 455-468.
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