| In recent years,China has been vigorously developing the development and utilization of marine resources.Many offshore wind farms have been built.In recent years,the installed power of single wind turbine and the total installed power have increased.The offshore windpower pile foundation has also been developed.However,the marine environment is complex and changeable.Pile foundation bears various loads in the marine environment such as the self-weight load,wind load,wave load,current load,impact load,etc.These loads act on the marine pile foundation during its service period.At present,the research on flow-induced load such as flow load is not perfect.The existing theories are limited to low Reynolds number and rarely involve practical engineering.The flow load is one of the main loads on the marine pile foundation.Therefore,the analysis of the dynamic characteristics of high Reynolds number multi-cylinder flow around the critical zone are investigated.And the stress law of pile group structure under flow load is studied.The research results can provide a reasonable and reliable theoretical basis for the designing and constructing of offshore windpower pile group fo undation and multi-pile jacket foundation.And there is important th eoretical and practical significance.According to Hangzhou bay of China of an offshore wind farm project summary,referring to the engineering structure parameters and local marine hydrology record data,using the finite volume method,the numerical simulation software FLUENT,the high Reynolds number flow around three columns and four cylindrical numerical model was been established.And the local average currents flow into the sea was taken,to study on hydrodynamic characteristics of three and four pile jacket foundation.Based on the model in different spacing ratio(S=2,3,4,8)and to flow angle(?=0°,30°,45°,90°)of numerical calculation,the drag coefficient and lift coefficient time history curve of circumfluence and pile distribution of flow field in the critical moment,vorticity graph has been obtain of each pile in arriving at a stable state.Combined with the characteristics of the time history curve of flow field and the corresponding time situation.the marine pile group effect in the form of expression under different working conditions and distribution law has been analyzed.Based on the analysis of the actual engineering simulation results and the idea of control variable method,the numerical calculation model of the double cylinder flow around the same marine environment was established.The time history curve of the lift resistance coefficient of each pile is fitted.The formula of the pile lift resistance coefficient after the double cylinder flow around the high Reynolds number is summarized.And based on the distribution of the pile group effect and the mechanism of internal stress analysis,the mechanical model of pile group can be divided into three types:type ?,? and ?.Through the research,the following conclusions are mainly obtained:(1)The main influencing factors of marine pile group effect are inflow angle and spacing ratio.Among them,the inflow Angle determines the relationship between the front and rear piles,and the spacing ratio determines the influence mode between the two piles.It is found that the range of the pile group effect is 0 to 12,and when the spacing ratio is greater than 12,the piles will interact with each other,but the effect can be ignored.For the inlet flow Angle,the pile effect is distributed in the whole domain.(2)There are mainly two types of marine pile group effect,one is the blocking effect of the front pile to the rear pile,the other is the flow field disturbance around the pile and the influence of its shear flow and vortex on other piles.When the spacing is relatively small,the shear flow of each pile has direct contact,which can change the stress mode of the pile group.The current pile is located at a certain Angle directly in front of the rear pile,that is,when the inflow Angle is small,the shielding effect of the front pile is relatively strong,and gradually decreases with the increase of the inflow Angle.However,with the increase of the spacing ratio,the discharge of vortex gradually becomes the medium,which has an impact on the stress of other piles.(3)Based on the distribution regularity of the pile group effect and analysis of the mechanism of internal stress,the stress of the pile group mode can be divided into three types:type ?,? and ?.The type ? is the most common type of mechanical model,namely the spacing is bigger,the pile distance is far away,only the first pile after pile of spiral drain into the circumfluence field,flow field produced disturbance,thus affecting the pile stress,after blocking effect and the action of shear flow is not obvious.And type ? is the stress of the blocking effect significant role model.the mode of pile after coming flow Angle is small,and the relatively small spacing.Type ? to compare the limit,general won't appear in the project,the mode spacing than tiny,shear flow of each pile connected,make the stress of the pile group is completely different from,type ? and ?.(4)Based on the fitting of the calculation results of the two-pile cylindrical circumfluence model,the fitting formula of the lifting resistance coefficient of the rear pile in the two-pile cylindrical circumfluence model is summarized.Considering the influence of the background velocity,strouhal number and pile diameter,the time domain value of the lift resistance coefficient of the rear pile under the influence of the front pile in the circular flow problem of two piles is calculated by taking the spacing ratio and the inlet flow Angle as the main variables.Verified,the formula of ? type stress patterns within the scope of the group of pile stress calculation results are relatively accurate,have reference value for engineering design. |
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