Effects of Sand-Clay Mixtures on Scour Around Vertical Piles Due to Long-Crested and Short-Crested Nonlinear Random Waves

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Dag Myrhaug ◽  
Muk Chen Ong
Keyword(s):  
Coastal Ocean ◽  
Stochastic Method ◽  
Offshore Wind ◽  
Pile Foundations ◽  
Scour Depth ◽  
Regular Wave ◽  
Random Waves ◽  
Offshore Wind Turbines ◽  
Equilibrium Scour Depth ◽  
Nonlinear Random Waves

This note provides a practical stochastic method by which the effects of sand-clay mixtures on the maximum equilibrium scour depth around vertical piles exposed to long-crested (2D) and short-crested (3D) nonlinear random waves can be derived. This is made by using the regular wave formulas for scour depth for sand-clay mixtures by Dey et al. (2011, Scour at Vertical Piles in Sand-Clay Mixtures Under Waves,” J. Waterway, Port, Coastal, Ocean Eng., 137(6), pp. 324–331) and the stochastic method presented by Myrhaug and Ong (2013, “Scour Around Vertical Pile Foundations for Offshore Wind Turbines Due to Long-Crested and Short-Crested Nonlinear Random Waves,” ASME J. Offshore Mech. Arctic Eng., 135(1), p. 011103). Thus the present results are supplementary to those presented in the latter reference. An example calculation is provided.

Scour Around Vertical Pile Foundations for Offshore Wind Turbines Due to Long-Crested and Short-Crested Nonlinear Random Waves

2013 ◽  
Vol 135 (1) ◽  
Author(s):  
Dag Myrhaug ◽  
Muk Chen Ong
Keyword(s):  
Order Theory ◽  
Offshore Wind ◽  
Wave Crest ◽  
Random Wave ◽  
Scour Depth ◽  
Height Distribution ◽  
Random Waves ◽  
Equilibrium Scour Depth ◽  
Nonlinear Random Waves ◽  
Wave Induced

This paper provides a practical stochastic method by which the maximum equilibrium scour depth around vertical piles exposed to long-crested (2D) and short-crested (3D) nonlinear random waves can be derived. The approach is based on assuming the waves to be a stationary narrow-band random process, adopting the Forristall wave crest height distribution (Forristall, 2000, “Wave Crest Distributions: Observations and Second-Order Theory,” J. Phys. Oceanogr., 30, pp. 1931–1943) representing both 2D and 3D nonlinear random waves, and using the regular wave formulas for scour depth by Sumer et al. (1992, “Scour Around Vertical Pile in Waves,” J. Waterway, Port, Coastal, Ocean Eng., 114(5), pp. 599–641). An example calculation is provided. Tentative approaches to related random wave-induced scour cases are also suggested.

Scour Around Vertical Pile Foundations for Offshore Wind Turbines due to Long-Crested and Short-Crested Nonlinear Random Waves

2011 ◽  
Author(s):  
Dag Myrhaug ◽  
Muk Chen Ong
Keyword(s):  
Offshore Wind ◽  
Wave Crest ◽  
Random Wave ◽  
Scour Depth ◽  
Height Distribution ◽  
Random Waves ◽  
Offshore Wind Turbines ◽  
Nonlinear Random Waves ◽  
Wave Induced ◽  
2D And 3D

This paper provides a practical stochastic method by which the maximum scour depth around vertical piles exposed to long-crested (2D) and short-crested (3D) nonlinear random waves can be derived. The approach is based on assuming the waves to be a stationary narrow-band random process, adopting the Forristall (2000) wave crest height distribution representing both 2D and 3D nonlinear random waves, and using the regular wave formulas for scour depth by Sumer et al. (1992b). An example of calculation is provided. Tentative approaches to related random wave-induced scour cases are also suggested.

Time-Varying Wave and Current-Induced Scour Around Offshore Wind Turbines

2007 ◽  
Author(s):  
A. W. Nielsen ◽  
E. A. Hansen
Keyword(s):  
Material Properties ◽  
Time Development ◽  
Offshore Wind ◽  
Scour Depth ◽  
Time Varying ◽  
Engineering Model ◽  
Offshore Wind Turbines ◽  
Industry Standard ◽  
Pile Diameter ◽  
Physical Experiments

The paper presents the engineering model, WiTuS (Wind Turbine Scour), which uses the results of several previous published physical experiments with scour around cylinders to determine the time development of the scour hole around the pile due to the actual and the previous wave and current climate. The WiTuS includes: • Time-varying water level, sea states and current. • Seabed material properties. • Description of the scour geometry around the pile. Simulations presented in the paper show that for typical North Sea conditions the scour depth will be around 0.3 times the pile diameter in periods with larger waves, which is a significant reduction from 1.3 times the pile diameter which is often seen as the industry standard.

scholarly journals EVOLUTION OF LOCAL SCOUR AROUND A COLLARED MONOPILE THROUGH TIDAL CYCLES

2012 ◽  
Vol 1 (33) ◽  
pp. 113 ◽  
Author(s):  
David J McGovern ◽  
Suzana Ilic ◽  
Andrew M Folkard ◽  
Stuart J McLelland ◽  
Brendan J Murphy
Keyword(s):  
Time Development ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Scour Depth ◽  
Half Cycle ◽  
Simplified Approach ◽  
Unidirectional Flow ◽  
Tidal Cycles ◽  
Equilibrium Scour Depth ◽  
Scour Protection

This paper presents the results of an experiment designed to assess the time-development of scour around an offshore wind turbine collared monopile over a number of tidal cycles. One collar shape and location was investigated. The scour developed more slowly and the scour depth was shallower than for the case of a smooth monopile throughout the majority of the first half-cycle. This difference reduced quite rapidly during the second half-cycle and the scour depth at the end of two tidal cycles was essentially the same as for the smooth monopile. The time development of the scour was compared with results from existing empirical models for the time-development of scour under unidirectional flow. As expected, these models give a much smoother evolution of scour and different scour rates than those measured. Time variation in scour depth was better reproduced with a simplified approach for prediction of the time-varying development of scour. This also highlighted a problem with estimation of the time scale for the development of the equilibrium scour depth. Further investigations are needed before this alternative scour protection is completely rejected.

Scour Assessment and Measurements for Pile-Supported Wind Turbine Foundations

2013 ◽  
Author(s):  
Bruno Stuyts ◽  
David Cathie ◽  
Yi Xie
Keyword(s):  
Wind Turbine ◽  
Time Scale ◽  
Rapid Development ◽  
Element Model ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Scour Depth ◽  
Central Column ◽  
Pile Interaction ◽  
Equilibrium Scour Depth

With the rapid development of offshore wind energy in Europe, a large number of piled structures are being installed. In areas with sandy seabed conditions, erosion of sediment by the actions of wave and current can negatively influence foundation capacity. An accurate prediction model of scour around the piles is therefore required. Well-accepted scour prediction methods exist; both for the equilibrium scour depth and the time scale of scour [1] around single piles. These standard formulas have been combined with metocean data and a hindcasting model to calculate the expected scour depth around piles of wind turbine tripod foundations. Other causes of scour, such as pile-pile interaction, effect of proximity of structural members to the seabed, and seabed mobility were also assessed in order to determine the amount of global scour to be considered. The scour predictions were compared to measurements taken at an offshore wind turbine foundation at Park Alpha Ventus (PAV) in the German North Sea [2]. The data showed very good agreement with the measured scour around the piles. Both the equilibrium scour depth and time scale of scour were well predicted using the hindcasting model. The measured scour below the central column of the tripod structure exceeded expectations; this is believed to be due to a pumping effect during storm episodes. Finally, the effect of scour on the vertical effective stress around the tripod piles was assessed with a finite element model. Local scour had an important effect while scour below the centre of the structure had a much more limited effect. Considering the combined effects of multiple pile interaction, scour below the central column, and making an allowance for seabed mobility, an equivalent global scour depth for pile capacity calculations was established.

scholarly journals Helical piles: an innovative foundation design option for offshore wind turbines

2015 ◽  
Vol 373 (2035) ◽  
pp. 20140081 ◽  
Author(s):  
B. W. Byrne ◽  
G. T. Houlsby
Keyword(s):  
Wind Turbines ◽  
Offshore Wind ◽  
Pile Foundations ◽  
Clear Understanding ◽  
Foundation Design ◽  
Offshore Wind Turbines ◽  
Critical Design ◽  
Helical Piles ◽  
The Uk ◽  
Driven Pile

Offshore wind turbines play a key part in the renewable energy strategy in the UK and Europe as well as in other parts of the world (for example, China). The majority of current developments, certainly in UK waters, have taken place in relatively shallow water and close to shore. This limits the scale of the engineering to relatively simple structures, such as those using monopile foundations, and these have been the most common design to date, in UK waters. However, as larger turbines are designed, or they are placed in deeper water, it will be necessary to use multi-footing structures such as tripods or jackets. For these designs, the tension on the upwind footing becomes the critical design condition. Driven pile foundations could be used, as could suction-installed foundations. However, in this paper, we present another concept—the use of helical pile foundations. These foundations are routinely applied onshore where large tension capacities are required. However, for use offshore, a significant upscaling of the technology will be needed, particularly of the equipment required for installation of the piles. A clear understanding of the relevant geotechnical engineering will be needed if this upscaling is to be successful.

scholarly journals Scour Characteristics and Equilibrium Scour Depth Prediction around Umbrella Suction Anchor Foundation under Random Waves

2021 ◽  
Vol 9 (8) ◽  
pp. 886
Author(s):  
Ruigeng Hu ◽  
Hongjun Liu ◽  
Hao Leng ◽  
Peng Yu ◽  
Xiuhai Wang
Keyword(s):  
Numerical Simulation ◽  
Present Model ◽  
Euler Number ◽  
Horseshoe Vortex ◽  
Scour Depth ◽  
Random Waves ◽  
Depth Prediction ◽  
Equilibrium Scour Depth ◽  
Scour Morphology ◽  
Good Agreement

A series of numerical simulation were conducted to study the local scour around umbrella suction anchor foundation (USAF) under random waves. In this study, the validation was carried out firstly to verify the accuracy of the present model. Furthermore, the scour evolution and scour mechanism were analyzed respectively. In addition, two revised models were proposed to predict the equilibrium scour depth Seq around USAF. At last, a parametric study was carried out to study the effects of the Froude number Fr and Euler number Eu for the Seq. The results indicate that the present numerical model is accurate and reasonable for depicting the scour morphology under random waves. The revised Raaijmakers’s model shows good agreement with the simulating results of the present study when KCs,p < 8. The predicting results of the revised stochastic model are the most favorable for n = 10 when KCrms,a < 4. The higher Fr and Eu both lead to the more intensive horseshoe vortex and larger Seq.

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