Multifractal characteristics of sediment pass by the Xiangjiaba Hydropower Station
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Abstract:
The power generation efficiency problem and hydropower stations turbine abrasion overwhelmed water conservancy engineers,especially during the flood season,when heavy rains,and the inflow and sediment concentration have reached their peaks.The power generation efficiency of hydropower stations is the best during this period,while the flow components of the turbine are also subject to abrasion.The Xiangjiaba Hydropower Station is located in the lower reaches of the Jinsha River.After its completion,it exerts tremendous flood control and power generation benefits.As the core equipment of the power station,the performance of the hydraulic turbine and the reliability of its operation are some of the keys to whether it can exert engineering benefits.To understand the rules of damage to hydraulic turbines by sediment in time,and to study various protective measures to reduce the abrasion damage to the surface of the turbine′s flowpassing parts by the sand-containing water flow,it is necessary to carry out the medium– and long–term monitoring of the sediment of the typical units on the left and right banks of the Xiangjiaba Hydropower Station to provide data support for the subsequent development of hydraulic turbine protection measures. The Xiangjiaba Hydropower Station flood season from June to September is taken as the research object.The maximum sediment concentration is selected twice a month by taking into account the time difference of the sediment particle size distribution during the flood season.The silt is sampled by the machine.For each sample,the left and right bank typical units are selected and enter the designated water intake inside the turbine volute for water sample collection.A total of 8 samples were taken during the entire flood season.After sampling the laser particle size analyzer was used to analyze the volume percentage of the machinesilt particle size gradation.The characteristic law of particle size distribution was studied using multifractal analysis. The results show that the particle size of the machined sediment has good multifractal characteristics.Combined with the multifractal theory,the overall average inhomogeneity of the particle size distribution is D1（B2）＞D1（C1）＞D1（C2）＞D1（A2）＞D1（B1）＞D1（A1）＞D1（D2）＞D1（D1）.There is a certain threshold,so that when,the uneven size of the largest subset particle size distribution is D≥5(B2)＞D≥5(B1)＞D≥5(D2)＞D≥5(C2)＞D≥5(A2)＞D≥5(C1)＞D≥5(A1)＞D≥(D1),at that time,the unevensize of the smallest subset particle size distribution isD≤-7，D≤-7(C1)＞D≤-7(B2)＞D≤-7(A1)＞D≤-7(D1)＞D≤-7(C2)＞D≤-7(A2)＞D≤-7(D2)＞D≤-7(B1)(A1,B1,C1,D1 are the sediment sample numbers of the left bank unit,and A2,B2,C2,D2 is the sediment sample number of the right bank unit).Combined with the generalized dimensional spectrum,the nonuniform distribution of the largest subset and the smallest subset of the sediment size of the Xiangjiaba Hydropower Station can not be effectively compared.Combined with the multifractal singularity,the spectrum width is Δα1 and Δα2,and the uneven size of the largest subset particle size distribution is Δα1 (B2)>Δα1 (B1)>Δα1(D2)>Δα1 (C2)>Δα1 (A2)>Δα1 (C1)>Δα1 (A1)>Δα1 (D1).The smallest subset particle size distribution is Δα2 (C1)>Δα2 (B2)>Δα2 (A1)>Δα2 (D1)>Δα2 (C2)>Δα2 (A2)>Δα2 (D2)>Δα2 (B1). Combining the generalized dimensional spectrum and the multifractal singular spectrum,the two conclusions are the same regarding the local unevenness of the particle size distribution.Combined with the correlation analysis,the sediment refinement and the maximum subset distribution unevenness show good results.The negative correlation of the silt refinement has nothing to do with the uneven size of the smallest subset distribution.
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