CN114578088B - Method for measuring average flow velocity of strong constraint river section or dragon mouth - Google Patents
Method for measuring average flow velocity of strong constraint river section or dragon mouth Download PDFInfo
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- G01P5/00—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft
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Abstract
A method for measuring the average flow rate of a strong-constraint river section or a tap hole is characterized in that the method is verified by limiting the width of the river in the calculation of the average flow rate of canyons, and limiting the total flow in the calculation of the average flow rate of the tap hole, namely, more accurately measuring the average flow rate in a discontinuous time.
Description
Technical Field
The invention relates to an average flow velocity measurement method, in particular to a method for measuring the average flow velocity of a strong constraint river section or a dragon mouth.
Back shadow technique
The existing average flow velocity measurement method is a formula suitable for all different types of river sections, the deviation between a theoretical calculation value and an actual measurement value is extremely large, the actual measurement is performed by adopting a plurality of means, time and labor are wasted, and the measurement efficiency is influenced.
Disclosure of Invention
The invention provides a method for measuring the average flow rate of a strong constraint river section or a tap, which is verified by limiting conditions, such as limiting the width of the river in the calculation of the average flow rate of canyons and limiting the total flow in the calculation of the average flow rate of the tap, namely more accurately measuring the average flow rate in a discontinuous time.
The technical scheme of the invention is that the method for measuring the average flow velocity of the strong constraint river section or the dragon mouth comprises the following steps:
in the formula (1)Is the average flow velocity, deltaz 0 Is a front head, is->Δz＝z Upper part -z Lower part(s) I.e. strong constraint river section or drop height, v 0 For a near-line flow velocity, general v 0 The calculated section of (1) is selected from the gradual change flow section, and the average width or the average width of the strong constraint river section or the upstream distance of the dragon mouth from the strong constraint river section is usedThe depth of water at the upstream of the length of the tap cofferdam is a base ruler, and the upstream of the tap cofferdam takes the position 3 to 5 times of the base ruler as a control section;
flow velocity coefficient: in order to facilitate the calculation in engineering practice, the general wide top weir flow formula is improved, and the coefficient is the comprehensive flow velocity coefficient integrating the side shrinkage coefficient, the flow coefficient and the inundation coefficient in the original wide top weir flow formula.
Further, the v 0 The method is characterized in that a strong constraint river section or the position of the upstream of a tap opening, which is 3 to 5 times of the average width of the strong constraint river section or the length of the upstream water depth of a tap opening surrounding weir, is used as a control section, and the control section is divided into a plurality of measuring section surfaces, wherein v is 01 、v 02 、v 03 ……v 0n ；
v 0 ＝(v 01 +v 02 +v 03 ……+v 0n )/n (2)。
Further, in the further course of this,therefore, the strong constraint river section or the Longkou period can be used for measuring the flow rate and the water level to solve the +.>And a beta value;
solving the flow velocity coefficient by utilizing the hydrologic data of the early actual measurement, including the flow of the tap, the water level difference delta z=z between the upstream and downstream of the tap Upper part -z Lower part(s) Dragon mouth travel flow velocity v 0 And calculating the maximum flow rate and the average flow rate of the tap by analyzing and calculating the measured flow rate of the ADCP, and then reversely calculating the flow rate coefficientAnd beta value, similar to the coefficient according to the measured data.
Further, β is 1.05;
further, the section of the strongly-constrained river is a canyon, the measurement starting point is a canyon starting point, the measurement end point is a canyon end point, the width of the river channel is relatively consistent, and the water level is increased and raised in unit time.
Furthermore, the closure is a closure, the boundary conditions are continuously changed along with the casting of high-strength stones during closure, and the closure width is narrower along with closure.
Further, the tap is a cofferdam dam break tap, and the width of the tap is wider along with the interception along with the water flow flushing after the cofferdam dam break.
The invention has the advantages that the parameters can be adjusted according to the upstream water flow data, and the calculation of the non-flow velocity is simpler and the accuracy is high.
Drawings
FIG. 1 is a graph of empirical formula predicted portal maximum flow versus measured flow.
FIG. 2 shows a calculation grid layout of a local river reach of a longkou.
FIG. 3 shows the relationship between the water surface width and the split ratio at the narrowest part of the tap.
Fig. 4 shows the comparison of the maximum flow rate of the tap under different methods.
2019.10.12:00 (earlier cut-off, narrowest water surface width 136.71m, maximum flow rate 1.24 m/s) shown in FIG. 5.
2019.10.23:00 (cut-off period, narrowest water surface width 102.11m, maximum flow rate 2.33 m/s) shown in FIG. 6.
2019.10.25:00 (cut-off period, narrowest water surface width 39.0m, maximum water surface flow rate 5.37 m/s) shown in FIG. 7.
Fig. 8 shows a flow field distribution prediction graph for a 35m portal width.
Fig. 9 is a flow field distribution prediction graph for a portal width of 25 m.
Fig. 10 shows a flow field distribution prediction graph for 20m of the width of the portal door.
FIG. 11 shows the relationship between the maximum flow rate of the tap and the width of the tap.
FIG. 12 shows the relationship between the maximum flow rate and the minimum water surface width of the spout.
Fig. 13 shows the correlation between the maximum flow rate of the spout and the drop of the spout.
FIG. 14 shows the process lines of the ratio of the maximum flow velocity to the water surface flow velocity of the three lines V4, V6 and V7.
Fig. 15 shows a schematic side view of a portal.
Fig. 16 is a fragmentary transverse view of Q2 (10.9-10.16) of fig. 2.
Detailed Description
A method for measuring the average flow velocity of a strong constraint river section or a dragon mouth comprises the following steps:
in the formula (1)For average flow rate, Δz 0 Is a front head, is->△z＝z Upper part -z Lower part(s) I.e. strong constraint river section or drop height, v 0 For a near-line flow velocity, general v 0 The calculated section of (1) is selected in the gradual change flow section, the water depth of the strong constraint river section or the upstream of the tap opening from the average width of the strong constraint river section or the upstream of the length of the tap opening cofferdam is taken as a base ruler, and the position 3-5 times of the base ruler is taken as a control section on the upstream of the strong constraint river section or the upstream of the tap opening cofferdam (the control section is confirmed according to the water depth length, as shown in fig. 15, the side face of the tap opening marked by F in the figure is taken as an example, the water depth length is that is, the water depth of the upstream of the tap opening F is taken as a base ruler F1, and the control section refers to the section about 3-5 times of the length of the base ruler F1 from the tap opening);
the v is 0 The method is characterized in that a strong constraint river section or a position of the upstream of a tap opening, which is 3-5 times of the average width of the strong constraint river section or the length of the upstream water depth of the tap opening cofferdam, is used as a control section, and the control section is divided into a plurality of measuring section surfaces, wherein v is 01 、v 02 、v 03 …… v 0n ；
v 0 ＝(v 01 +v 02 +v 03 ……+v 0n )/n (2)。
Therefore, the measured flow velocity and water level of the strong constraint river section or the Longkou period can be utilized to solve the +.>And a beta value;
preferably, β is 1.05;
the section of the strongly-constrained river is a canyon, the measurement starting point is a canyon starting point, the measurement end point is a canyon end point, the width of the river is relatively consistent, and the water level is increased and raised in unit time.
The closure is a closure, boundary conditions are continuously changed along with throwing of high-strength stones during closure, and the closure width is narrower along with closure.
The tap is a cofferdam dam break tap, and the width of the tap is wider along with the interception along with the water flow flushing after the cofferdam dam break.
In the earlier stage of closure, the cross section of the tap can be regarded as a trapezoid cross section, the tap is more stable, and the average flow velocity of the cross section can be calculated according to the following formula:
in which Q Dragon In the process of calculating the average flow rate of the cross section, Q is as follows Dragon Q2; and A is the water cross section area of the closure, the cross sections of the closure in different periods are drawn according to the topography of the river channel in the earlier stage and the occupation situation of the dike, and the water cross section area estimation is carried out by combining the water surface width of the closure.
According to the on-site tap flow rate test condition, parameter calibration is carried out on a flow rate calculation empirical formula by adopting real measurement data of the earlier stage of interception and the first stage of interception (10 months 9 days-10 months 23 days), and the later-stage tap flow rate is predicted and forecasted according to the parameter calibration, wherein the maximum flow rate of the tap is the maximum value of the average flow rates of the vertical lines of actual measurement V5, V6 and V7, the average flow rate is the calculated value according to a formula (4), and the water level difference delta Z=Z4-Z5 between the upstream and downstream of the tap is shown in a table 1.
TABLE 1 calculation results of Longkou flow Rate coefficients
As can be seen from Table 1, the average flow rate coefficient for different periods of closureThe valve is stable, the maximum flow velocity coefficient is slightly changed, and the beta value is obviously higher in the whole during the first period of interception than in the earlier period of interception. The empirical formula is used for predicting the flow speed of the closure later-stage closure opening, and a flow speed coefficient value which is calibrated by the first-stage data and is closer in time is selected to obtain the empirical formula for calculating the flow speed of the closure opening:
according to the rated experimental formula of the flow velocity of the tap, the average and maximum flow velocity of the tap in 24-25 days are predicted by combining the tap drop, and the predicted maximum flow velocity value is compared with the actually measured maximum flow velocity value of the tap. The actual measurement value is obtained by multiplying the water surface flow velocity measured by an unmanned aerial vehicle carrier wave flow velocity meter method and an electronic buoy by a correction coefficient of 0.98, wherein the correction coefficient is the average value of the ratio of the average flow velocity of the vertical lines of the interception periods (21 days-23 days) V1-V7 to the maximum flow velocity of the water surface, and the correction coefficient is shown in table 2 and figure 1.
Table 2 Longkou flow empirical formula prediction results and comparison
It can be seen that the maximum flow velocity trend predicted by the empirical formula is basically consistent with the measured flow velocity, the deviation of the flow velocity value measured by the electric wave flow meter method is basically within 0.20m/s, the deviation of the flow velocity value measured by the electronic buoy method is slightly larger, and the maximum deviation is 0.40m/s. From the perspective of errors, the prediction effect of the empirical formula is good before the maximum flow velocity value of the closure is found, when the closure flow velocity reaches the maximum value, the upstream water blocking increases further along with the further advancing of the dike, the closure approaching flow velocity head is basically negligible, at the moment, the prediction value of the empirical formula still continues to increase along with the increase of the closure drop, from the perspective of actual closure experience, the closure gradually decreases after the maximum flow velocity is found, and at the moment, the empirical formula for calibrating the flow velocity coefficient according to the closure earlier-stage data is not applicable any more.
The basic calculation principle is as follows: dragon mouth hydrodynamic mathematical model predictive research
In order to better serve the cut-off of the Dajiang river of the Datengxia water conservancy junction, the reasonable analysis of measured data is carried out in cooperation with the hydrologic data collection during the cut-off of the dragon mouth, a two-dimensional water flow mathematical model of the plane of the cut-off river section is established, parameters are set according to the rolling rate of the measured hydrologic data, the progress situation of the dike and the like, the topography is corrected, and finally, the aim of predicting and forecasting the flow velocity of the dragon mouth is achieved.
Model principle (one)
In order to overcome the difficulty of complex boundary of a calculation area and improve the precision of numerical calculation results, a coordinate transformation method based on curve grids is adopted by the model, so that the calculation grids are attached to the tortuous river boundary. Of these, the orthogonal curve transformation and the general (non-orthogonal) curve transformation methods are two of the most commonly used methods. In comparison with orthogonal curve transformation, general curve transformation is not limited by the strict orthogonality of calculation grids, and grid generation is flexible. Therefore, the numerical simulation adopts a general curve coordinate transformation method to realize accurate coupling of the calculated boundary and the physical boundary. Since the upstream flow rate is not changed much during the shut-off construction period, a constant water flow model is used for calculation.
(1) Model calculation range and boundary processing
Upstream water is split at the longitudinal cofferdam, the split flow of the left bank diversion building is influenced by the opening of the diversion bottom hole, and the split flow of the open river reach is comprehensively influenced by the split flow of the upstream water and the diversion building and the dike supporting progress. The hydraulic model is mainly used for simulating a local river reach of a closure river reach by combining various factors such as river potential, topographic data, hydrologic data and engineering positions of the closure river reach, an inlet calculated by taking the position about 0.9km upstream of the closure section as a model is used, an outlet calculated by taking the position about 2.0km downstream of the closure section as a model is used for calculating the total length of the river reach to be about 2.9km. 1000×110 grids are arranged in the calculated river reach, wherein 1000 grids are arranged along the water flow direction, the average grid length is about 2m-3m, 110 grids are arranged along the river width direction, and the average grid width is about 3m-4m. The calculation grid arrangement of the local river reach of the dragon mouth is shown in fig. 2 and fig. 16. Inlet boundary: in order to reduce the model range and ensure the calculation precision of the portal section, the inlet section is selected at the position about 0.9km above the portal section, the inlet flow is controlled according to the portal flow Q2 so as to ensure that the portal section flow is consistent with the actual situation, and the given inflow single-width flow is distributed along the transverse direction of the section according to the known inlet full-section flow;
outlet boundary: taking the Z12 station water level at the downstream outlet of the measuring area as the outlet section water level;
terrain boundary: taking the outer boundary of the river channel topographic map as a calculated bank boundary, giving a higher Gao Chengling flow velocity of the calculated bank boundary to be zero so as to ensure the sealing of a calculation area, wherein the left bank of the inlet section is controlled according to the elevation of the longitudinal cofferdam;
dynamic boundary: the model adopts a freezing method to carry out dynamic boundary processing, namely judging whether the grid unit is exposed out of the water surface according to the river bottom Gao Chenglai at the water level node. If the rough surface is not exposed, the rough surface takes a normal value; on the contrary, the roughness of the unit is changed (n is 10 10 Magnitude). In order not to affect the solution of the water flow control equation, a thin water layer is required to be given at the junction exposed to the water surface, and the thickness of the water layer is generally given to be 0.5cm.
(2) Shut-off engineering generalization
The model is based on the actual measurement of the terrain of the engineering river reach in 2018 6 months, the terrain is locally corrected according to the new pile of soil at the front edge of the left bank longitudinal cofferdam, and the right bank construction dike carries out engineering generalization in a local terrain modification and local roughness adjustment mode.
(3) Model verification
The initial roughness of the river bed of the cut-off river reach is selected to be 0.028, and model parameters are adjusted according to the measured water level and flow data of 9-10 days of 10 months, so that the variation range of the roughness of the cut-off river reach is 0.025-0.056. Model verification selected 10 months 11 days 8 hours (q=1400 m 3 And/s), verifying that the flow field calculated by the model under the flow condition changes smoothly, and the water flow movement form accords with the boundary condition of the river channel well, wherein the calculated water level of the model is basically consistent with the measured water level, and the general error is within 0.1 m.
The calculation results are comprehensively analyzed, the adopted mathematical model can better simulate the water flow movement characteristics of the cut-off river reach, the calculation results are well matched with the actual measurement results, the calculation method of the mathematical model is correct, the values of relevant parameters in the model are reasonable, and the mathematical model can be used for calculation and analysis of the hydraulic indexes of the cut-off river reach.
(A) Flow rate monitoring and prediction
And monitoring the flow rate of the open river reach according to the actually measured Q2 flow and the Z12 station water level, wherein the flow rate comprises the flow rate of the vertical line of the section of the open, the average flow rate of the section and the maximum flow rate of the open.
The average flow velocity of the vertical lines of the tap section in different periods is compared with the synchronous digital-analog calculated value in the table 3, the average flow velocity of the tap section in different periods is compared with the synchronous digital-analog calculated flow velocity in the table 4, and it can be seen that the variation trend of the digital-analog calculated value and the actual measured value (or calculated value according to the actual measured data) is basically consistent, the absolute error is basically within 0.50m/s, and the calculated result is more accurate no matter the average flow velocity of the vertical line of a specific point or the average flow velocity of the whole section.
Table 3 comparison table of flow velocity digital-analog calculation results of vertical lines of Longkou sections
Table 4 comparison table of results of digital-analog calculation of average flow velocity of the tap section.
TABLE 5 comparison of measured maximum flow Rate and calculated maximum flow Rate for Dragon mouth
The comparison of the measured maximum flow rate in different periods and the same-period digital-analog calculated flow rate, wherein the measured flow rate before 25 days 8 is the average maximum flow rate of the vertical line measured by the ADCP method, the measured flow rate after 25 days 8 is obtained by multiplying the measured value of an electric wave flow rate meter by a correction coefficient of 0.98, the absolute error of the digital-analog calculated value is basically within 0.40m/s, the calculated flow rate better simulates the change process of the Longkou flow rate, and the digital-analog calculated result is more reliable.
Therefore, according to the correlation between the narrowest water surface width of the dragon mouth and the diversion ratio of the dragon mouth (see fig. 3), the flow velocity of the dragon mouth is predicted by combining upstream water supply forecast (see table 6), the result of the digital-analog calculation in the early period is synthesized (see table 5), the maximum flow velocity of the dragon mouth is 5.84m/s when the maximum flow velocity of the dragon mouth occurs for 16 days of 25 days, and then the maximum flow velocity of the dragon mouth starts to decrease along with the further advancing of the dike.
Table 6 a spout flow rate prediction table under different water surface widths.
The observed result of the electric wave flow meter shows that the water surface flow velocity of the dragon mouth reaches the maximum value of 5.37m/s in the period of 25 days 17, the observed result of the electronic buoy shows that the flow velocity reaches the maximum value of 5.62m/s in the period of 15 minutes, the numerical analog calculation result is basically same as the appearance time of the maximum value of the actual measured flow velocity, the numerical value is slightly larger than the maximum value of 5.26m/s of the corrected electric wave flow meter, the maximum value of 5.51m/s of the corrected electronic buoy method is closer, and the calculated result is relatively reasonable.
Further comparing the process of the maximum flow rate test value and the forecast value of the tap obtained by different methods in the cut-off period, wherein the observed values of the electric wave flow rate meter, the electronic buoy and the side sweep radar are multiplied by the correction coefficient of 0.98, as shown in fig. 4. It can be seen that the variation trend of the maximum flow velocity of the tap under different test methods is basically the same, the occurrence time of the maximum flow velocity is distributed between 15 and 17 days of 25 months, compared with actual measurement, the accuracy of the digital-analog calculation in the cut-off earlier stage is higher, the flow velocity is obviously increased after the tap is formed in 24 days, the accuracy of the adopted empirical formula is higher, the digital-analog calculation value is slightly larger, but the overall trend is consistent with the actual measurement value, and the flow velocity forecasting result is basically reasonable.
Typical flow field distribution of the cut-off river reach in different periods and predicted flow field distribution diagrams under different gate widths are shown in fig. 5-10. From the flow field diagram, the water flow can be in different flow states along with the continuous change of the boundary of the closure, and the closure streamline gradually contracts to form 'scissors water' along with the constriction of the closure of the dike.
(B) Variation law of flow velocity of dragon mouth
In the closure process, along with the approach of the dike, the hydraulic characteristic indexes at the closure position are continuously changed, including closure flow, flow speed, drop, ratio drop and the like, and each hydraulic index is influenced by the closure body type change caused by the closure door width change, so that the mutual change rule of the hydraulic indexes is researched by combining the analysis of the change characteristics of each hydraulic index.
(1) Maximum flow rate of the tap and width of the tap gate
According to field measurement records, the width of the portal opening is the measured water surface width from the longitudinal cofferdam to the dike on the central line of the dike, the minimum water surface width is the water surface distance from the extension of the central line of the dike to the position of the soil pile closest to the dike, and the maximum flow rate of the portal opening has good correlation with the two.
Before the maximum flow velocity occurs, as the dike approaches, the closure is narrowed, the maximum flow velocity of the closure is gradually increased, the closure and the closure gate width are in obvious inverse proportion relation, and the formula is y=0.0002 x 2 -0.1018x+13.5959, the correlation is as high as 0.99, and the correlation between the maximum flow rate and the minimum water surface width is slightly weaker during the period, and the reason is analyzed that the minimum water surface width is brokenThe section where the width of the surface is wider than that of the gate is obviously smaller, when the upstream water inflow amount changes, the fluctuation range of the water level of the section is larger, and the water surface width changes caused by the water level fluctuation are also larger, so that the point data are scattered relatively; after the maximum flow rate appears, along with the further occupation of the dike, the closure is narrower, and relative to the closure width, at the moment, the closure overflow capacity is obviously limited by the minimum water surface width, the maximum flow rate gradually decreases, the relation between the closure and the minimum water surface width is y=0.3101x+0.1627, the correlation reaches 0.91, as shown in fig. 11 and 12 (the closure maximum flow rate value before 24 days 8 is the average maximum flow rate of the ADCP actually measured vertical line, and the water surface flow rate value measured by the electric wave flow rate meter after 25 days 8 is multiplied by the correction coefficient of 0.98).
(2) Maximum flow velocity and drop of the tap
According to the empirical formula for calculating the flow velocity of the wide top weirAnalyzing the relevant index of the flow velocity and the drop of the dragon mouth>As shown in fig. 13 (in the figure, the maximum flow rate value of the portal is the average maximum flow rate of the vertical line measured by ADCP before 24 days 8, and the water surface flow rate value measured by the radio wave flow rate meter after 25 days 8 is multiplied by the correction coefficient 0.98).
It can be seen that the maximum flow rate of the tap and the flow rate before the maximum flow rate is reachedThe method has the advantages that the method is obvious in a direct proportion linear relation, is influenced by a water head of the flow velocity travelling on the weir, is not completely consistent with an empirical formula, has the correlation of y=1.0357x+0.2267, has the correlation of 0.96, has the maximum flow velocity, further increases the drop height of the tap after the maximum flow velocity occurs, and has the inverse proportion correlation between the two, but has the reduced correlation.
(C) Intercepting construction practice
The hydraulic conditions of the open river reach are complex in change during the closure process, in order to smoothly carry out the closure work, the on-site actual measurement data are collected, tidied and analyzed in time, the change of the hydraulic conditions and the influence of the change on the closure in the closure construction process are known and mastered, and the construction plan is adjusted in time, so that the construction difficulty can be reduced, and the smooth completion of the closure is ensured.
Preparation of materials before interception is an important link of interception work, and a sufficient amount of interception materials must be prepared. When the flow rate of the closure opening is not large in the initial stage of closure, common stone slag is firstly used for filling, along with the increase of the flow rate of the closure opening, the casting material is flushed out to a certain extent and then is lost, the casting body is stable, the casting stone with larger particle size is required to be used for casting and filling, and special closure materials such as extra-large stone are required to be used when necessary. Based on the method, the construction side stores 12 square and 140 square throwing materials such as massive stones, reinforcement cages, tetrahedrons and the like, and stacks the materials according to the particle size grades of the materials, so that a plurality of sets of large-scale machines 100 are driven, and the orderly development of the intercepting work is ensured.
The closure dike opening section adopts a full-section pushing and protruding dike upper-choosing angle taking-up mode. In the initial stage of closure, the advancing speed of the dike is slow, the dike is stopped for a plurality of times during the period, the dike is raised, the cofferdam is widened, the stability of the dike foundation is ensured, the advancing operation of more construction vehicles is facilitated, and the section of the flow test Q2 is subjected to two-time position adjustment due to the flow disturbance caused by the dike advancing.
From the time of 21 days of 10 months and 0 days, according to the announcement of the harbour and navigation administration, the crossbow beach at the outlet of the big rattan cany is subjected to interception and navigation breaking for 163 days, the maximum flow rate of the banquette at the time of 21 days and 8 days reaches 1.64m/s, the water surface width at the narrowest part is 114.48m, the on-site banquette intake is accelerated at the time of day, and the night construction operation is started; on the basis of the actual condition of the site, the excavation plan of the upstream diversion port sub-dike of the original longitudinal cofferdam cannot be implemented for 10 months and 22 days, so that the diversion pressure of the closure period is increased, the water level of the upper cofferdam is increased, the drop of the closure is increased, the flow velocity of the closure is relatively increased, and on the basis of the forecast of upstream water, the flow rate of the 25-day late dam site reaches 3800m 3 The flow rate of the closure is up to 4.4m/s, and the current closure is increased from 27.07m to 29.87m according to design requirements in order to ensure the stability of the closure due to the aggravated variation of hydrodynamic conditions of the closure; the maximum flow rate of the vertical line of the dike is increased to 2.33m/s after 10 months and 23 daysThe flow speed of the upper corner reaches 1.47m/s, the flow speed of the lower corner reaches 1.22m/s, the flow speed of the dike is larger at the axis and the upper corner, in order to reduce the influence of water flow scouring loss on the throwing material, it is suggested that a part of large and medium stones are thrown at the upper corner of the front edge of the dike, under the protection of the large and medium stones, the water flow of the dike forms a backflow slow flow area at the downstream side, and then the slag is thrown in the middle of the dike and at the downstream side close to the dike.
The method is characterized in that the advancing of the dike is accelerated in 10 months and 24 days, a dragon mouth is formed, the flow rate at the dike is 3.11m/s, the angle-picking flow rate at the dike is 1.19m/s, the angle-picking flow rate at the dike is 2.46m/s, the maximum flow rate at the dike is gradually transferred to the downstream, and according to engineering experience, scour prevention and reinforcement measures are carried out at the positions of the riverbed dike and the dragon mouth when the dragon mouth appears, so that the stability of the dike head is ensured; 10. the predicted maximum flow rate may appear in 16-17 pm when the width of the tap is 30-40 m, at the moment, water flow is strong to wash the two banks, the method of taking up the upper corner by about 30-45 degrees is adopted according to actual conditions, tetrahedron is used for pushing at the slope angle of the banked dike, when the casting material at the upper corner is stable and not washed away, the material taking up of other particle size stones is timely filled at the downstream of the upper corner, so that the casting material loss is reduced, meanwhile, the monitoring density of the tap flow rate and the drop is enhanced on site, and the maximum flow rate of the tap when 17 is accurately obtained by 5.37m/s; after 17 days 25, the dike is further pushed forward, the width of the closure mouth is reduced from 39.04m to 0m, the flow rate of the closure mouth is reduced from 5.37m/s to 0.00m/s, the closure mouth is narrow, the water level drop is large, especially the downstream and the bottom of the dike are easy to brush, the bottom and the left side of the closure mouth are protected in advance, at the moment, large stones, medium stones and stone residues are mainly thrown, the mixed use of the thrown materials is noted, the phenomenon of large-area collapse is avoided, and the stable proceeding of final closure inlet is ensured.
(II) vertical line distribution characteristics of Dragon mouth flow velocity
From a hydraulic perspective, the water flow at the opening is a weir flow, and only the boundary of the weir flow is changed continuously, so that the water flow presents different outflow forms, such as submerged flow and non-submerged flow. The water flow enters the contraction section of the dragon mouth, enters the rapid flow section of the dragon mouth and forms a water tongue, and finally forms a diffusion section, and a forward flow area, a slow flow area and a backflow area are formed between the upper cofferdam and the lower cofferdam. As the gate narrows, the spout streamline gradually contracts to form "scissors water", i.e., a water tongue is formed at the intersection of the streamlines, with the maximum flow rate typically occurring near the water tongue. The position of the water tongue is related to the width of the closure, the depth of the closure water and the like, the closure is narrowed and the depth of the closure becomes shallow along with the occupation of the closure, the water tongue is from far to near, finally, water drops are formed at the axial line of the closure, and the drop of the closure is more concentrated at the axial line of the closure.
The distribution of the flow velocity of the tap reflects the motion characteristics of the water flow and mainly comprises resistance characteristics, flow velocity distribution, turbulence intensity distribution, energy distribution and the like. These characteristics are influenced on the one hand by the boundary conditions of the river bed and on the other hand by the sand content. For natural rivers, research results show that clear water flow, low-sand-content water flow and high-sand-content water flow have commonality and have the specificity of respective movement rules. For the closure of the closure dike, the high-strength sand throwing material makes the form of the closure dike wall, the bed surface, the sand content and the like changeable instantaneously and permanently. This change affects the change in resistance characteristics and also affects the constant change in water flow characteristics. The distribution of the flow velocity of the tap is mainly influenced by the shape of the bed surface and the water flow resistance, and the shape of the bed surface and the water flow resistance are also influenced by factors such as water depth, specific drop, fluid density, fine sand content, bed sand size and grading, sediment settling speed, river bed section shape and the like.
The vertical flow field test is carried out in the whole area by using the navigation ADCP, and the focus is near the closure, so as to know the change of the vertical flow field represented by each dike in the process of occupying the dike.
(1) Flow velocity distribution characteristics of vertical line in dragon mouth formation period
According to the actual measurement data, the formation of the closure dike is insufficient to generate obvious constraint effect on the river channel, and the water flow state of the closure dike is still close to that of the natural river channel. The position change of the vertical maximum flow velocity still has the regularity of a natural river bed, generally, the vertical maximum flow velocity mainly appears near the water surface of the relative position of 0.4, when the flow velocity at the upstream of the banquette is less than 1.0m/s, the position of the vertical maximum flow velocity is scattered, and when the flow velocity is larger and larger, the maximum flow velocity gradually approaches to the area of 0.2-0.4. In particular, the average relative water depths of the maximum flow velocity in the period of the formation of the dragon mouth are respectively 0.26 and 0.37 in the lines 6 and 7 with the maximum flow velocity.
The maximum flow rate occurrence position of each vertical line in the formation period of the spout and the ratio of the maximum flow rate to the vertical line water surface flow rate are shown in tables 7 and 8.
TABLE 7 statistics of relative position of maximum flow velocity to depth of water at each vertical line
TABLE 8 ratio of maximum flow Rate of each vertical line to Water surface flow Rate
(2) Vertical line flow velocity distribution characteristic of forced inlet period
Starting at day 09 and after 12 days of dyke advancement, dyke closure has gradually formed and upstream water retention effects gradually develop. Along with the change of boundary conditions, the water flow morphology of the dragon mouth section of the diversion river section is changed greatly, and the main body is obviously moved to the left to the middle section of the dragon mouth. And the closure engineering enters a strong occupying period at the beginning of the 21 day 8, and under the condition that the flow rate of a closure opening is gradually increased, a construction unit begins to throw in a concrete frame tetrahedron, so that the advancing speed of the dike is obviously increased.
According to the actual measurement data, the strong-advanced dike has obvious constraint effect on the river channel, and the water flow form of the river channel is obviously changed compared with that of the natural river channel. The vertical lines V1 and V4 with smaller flow velocity have the flow velocity distribution of the vertical lines which are big in top and small in bottom and are similar to natural water flow, and unstable flow phenomena such as backflow vortex and the like occur nearby; as the flow rate increases, the vertical flow rate distribution becomes very uniform, with the maximum flow rate gradually approaching the 0.4-0.6 region. The average relative water depths of the maximum flow velocity in the portal forming period are respectively 0.62, 0.38 and 0.45 on the lines No. 5, no. 6 and No. 7 of the portal section with the maximum flow velocity. In addition, the ratio of the maximum flow velocity of the vertical line to the average flow velocity of the vertical line can be used as an index of the uniformity of the flow velocity distribution of the vertical line, except for V1 and V5 near the right bank, the ratio of the other vertical lines is 1.04-1.06, and the vertical line flow velocity distribution of the area which is close to the hip bank head and the closure section and generates constant flow due to the narrow closure beam is very uniform.
The position of occurrence of the maximum flow velocity of each vertical line in the aggressive period and the ratio of the maximum flow velocity to the vertical line water surface flow velocity are shown in tables 9 and 10.
TABLE 9 statistics of relative position of maximum flow velocity to depth of water at each vertical line
Table 10 ratio of maximum flow velocity of each vertical line to flow velocity of water surface
(3) Vertical line flow velocity distribution characteristics during closure
The closure period is called closure period when the closure of the Dajiang river is completed from the time of 8 days of 10 months to 24 days of 10 months to 14 days of 26 months. And during the period, the navigation ADCP is continuously adopted to carry out vertical flow field test on the upstream of the cross section of the portal (which is moved up by 30m than the previous cross section for safety consideration), and the flow velocity at the portal is tested by adopting methods such as an electronic buoy, an unmanned airborne wave flow rate meter, a side scanning radar and the like.
Average flow velocity position of maximum vertical line
From actual measurement data, after the width of the dike opening is narrowed to 90m in the closure period, the central axis of the closure is arranged at the downstream of the V4 currently tested, and the flows of the flows such as reflux or stagnation and the like are generated at different degrees by the V1-V3, so that the average flow velocity of the vertical lines from the V1-V4 is gradually increased, and the flow velocity distribution uniformity degree of the vertical lines is gradually improved. The cross section of the tap is not reached, and other methods are adopted for testing. Whichever test method, it was confirmed that the maximum flow rate of the cross section of the tap occurred near the central axis of the tap, and as the dyke further advanced, the maximum flow rate position was gradually shifted to about 30m downstream of the dyke (at the front of the fin).
Vertical distribution of flow velocity of dragon mouth
It is evident from a combination of tables 11 and 12 that as the dike advances, the stoma narrows and the hydrodynamic conditions of the water flow through the stoma change again.
After the closure period, the vertical line distribution change trend of V4 positioned on the main flow is as follows: the vertical line distribution is gradually flat, the upper-lower difference distance is reduced, the ratio of the maximum flow rate to the average flow rate of the vertical line gradually approaches to a number slightly larger than 1, and the maximum flow rate distribution point gradually moves down to the vicinity of 0.4-0.6. V1, V2 and V3 which are still obviously constrained by boundary conditions are characterized in opposite directions, the water flow is unstable, the turbulence is increased, the ratio of the maximum flow velocity to the average flow velocity of the section is gradually increased, and the appearance position of the maximum flow velocity is near the relative position of the water depth of 0.3-0.5.
TABLE 11 maximum flow velocity for each vertical line relative water depth
Table 12 ratio of maximum flow velocity of each vertical line to flow velocity of water surface
(3) Analysis of ratio of maximum flow rate of closure period portal to water surface flow rate
As can be seen from the above tables 10, 11, 12, the ratio of the maximum flow rate of each vertical line to the flow rate of the water surface exhibits different change laws as the engineering progresses. The positions of the V1, V2 and V5 and the later V3 vertical lines are continuously changed along with the progress of engineering (the positions are closer to the left bank), but the relative positions are always at the side closest to the right bank, the ratio of the relative positions is larger than other vertical lines, and the relative positions generally have the tendency of becoming larger gradually, so that the flow velocity distribution of the vertical lines is more and more uneven. This is consistent with the actual situation observed. The vertical lines such as V4, V6 and V7 are always on the main flow of the section where the vertical lines are positioned, so that the vertical line flow velocity distribution is relatively more uniform. And the change rule of the ratio is gradually reduced along with the increasing concentration of water flow. The stability is about 1.04-1.05 in the late stage. The process line for making this ratio for each vertical line is shown in fig. 14.
The flow velocity distribution rule of three lines V4, V6 and V7 (the water surface is narrowed in the three cut-off periods, namely, the flow velocity vertical line of a dragon mouth) without flow velocity actual measurement data from the time of 8 days of 10 months and 24 days is considered as follows: the vertical line flow velocity distribution is very uniform, the maximum flow velocity appears near the relative water depth of 0.6-0.8, and the ratio of the maximum flow velocity to the water surface flow velocity is about 1.03, so that the water surface flow velocity of the three-stage interception electronic buoy, the unmanned airborne electric wave flow velocity meter method and the side-sweep radar can be corrected, and the maximum flow velocity of the vertical line of the dragon mouth is obtained.
Through the verification, the measurement data of the formula (1) and the formula (3) are accurate, wherein beta can be adjusted according to the upstream flow, beta values can be corresponding to the beta values through hydrologic conditions, and beta parameters corresponding to different canyon forms and different closure openings (warehouse entering flow) can be established.
Claims (3)
1. A method for measuring the average flow velocity of a strongly-constrained river section or a dragon mouth is characterized by comprising the following steps: the method comprises the following steps:
(1),is the average flow velocity, deltaz 0 Is a front head, is->Δz＝z Upper part -z Lower part(s) I.e. strongly constrained river section or drop height, v 0 For a near-line flow velocity, general v 0 The calculated section of the (2) is selected in the gradual change flow section, the average width of the strong constraint river section or the upstream of the tap opening from the strong constraint river section or the water depth of the upstream of the length of the tap opening cofferdam is taken as a base ruler, and the position 3-5 times of the base ruler is taken as a control section at the upstream of the base ruler>Is the flow velocity systemA number;
the v is 0 The method is characterized in that a strong constraint river section or a position of the upstream of a tap opening, which is 3-5 times of the average width of the strong constraint river section or the length of the upstream water depth of the tap opening cofferdam, is used as a control section, and the control section is divided into a plurality of measuring section surfaces, wherein v is 01 、v 02 、v 03 ……v 0n ；
v 0 ＝(v 01 +v 02 +v 03 ……+v 0n )/n (2)；
Therefore, the flow speed and the water level can be measured by using the strong constraint river section or the Longkou period to solve +.>And a beta value;
the section of the strongly-constrained river is a canyon, the measurement starting point is a canyon starting point, the measurement end point is a canyon end point, the width of the river is relatively consistent, and the water level is increased and raised in unit time;
the tap is a cofferdam dam break tap, and the width of the tap is wider along with the interception along with the water flow flushing after the cofferdam dam break.
2. The method for measuring the average flow velocity of a strongly restrained river section or a tap according to claim 1, which is characterized in that: beta is 1.05;
3. the method for measuring the average flow rate of a strongly-constrained river section or a closure according to claim 1, wherein the method comprises the following steps: the closure is a closure, boundary conditions are continuously changed along with the casting of high-strength stones during closure, and the closure width is narrower along with closure.
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