CN117113718A - Method, device and medium for measuring scouring power of offshore wind power single pile foundation - Google Patents
Method, device and medium for measuring scouring power of offshore wind power single pile foundation Download PDFInfo
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Abstract
The invention discloses a method, a device and a medium for measuring scouring power of a single pile foundation of offshore wind power, which are used for carrying out numerical simulation research on the power response of a part of wind turbine structures by utilizing a standardized wind turbine model to solve the problem that the working state of a field wind turbine structure is difficult to reflect.
Description
Technical Field
The invention belongs to the technical field of offshore wind power, and particularly relates to a method, a device and a medium for measuring scouring power of an offshore wind power single pile foundation.
Background
The ocean current environment of the offshore wind power plant is complex, the hydrodynamic condition around the pile is changed after the foundation is built, the wave and the current jointly act to break the original sediment transportation balance, and flushing pits with different depths are formed until the dynamic balance of water flow and sediment is achieved again. The scholars at home and abroad develop deep researches on the scouring problem of the wind power pile foundation at sea, and the related research directions comprise: formation and prediction of scouring pits, refer to Wei Kai, wang Shunyi, fur release, etc. marine wind power single pile foundation ocean current local scouring and protection test research [ J ]. Solar school report, 2021,42 (09): 338-343, li Shaowu, yang Hang, cylindrical local scour three-dimensional numerical simulation under water FLOW [ J ]. Water channel harbor, 2018,39 (05): 519-527 ], wang Weiyuan, yang Juan, li Ruiyuan, offshore wind farm fan pile foundation local scour calculation [ J ]. Water channel harbor, 2012,33 (01): 57-60 ], YANG Y, QI M, WANG X, et al.Ex. study of scour around pile groups in steady FLOWs [ J ]. Ocean Engineering,2020,195 (1): 106651 ], scour lower pile foundation load bearing characteristics and dynamic response, reference [ Liu Run, wang Yingchun, wang Jia, etc., unilateral scour is based on the water channel stability simulation of offshore wind farm cylindrical foundation study [ J ]. Solar school, 2022,43 (01): 73-79, QI G W, GAO F P, RANDOLPH M F, et al Scourefens on P-Y curves for shallowly embedded piles in sand [ J ] [ G pile foundation ] G, 2016,66 (see FIG. 35B, 35B, etc., 35-35, 35B, 35, etc., 2013,72:20-38.
The offshore wind power foundation structure is designed to meet the soft-rigid criterion, and the natural frequency of the whole fan system is between one and three times of the blade rotation frequency (see Yuan C, MELVILLE B W, ADAMS K N.Scour at wind turbine tripod foundation under steady flow [ J ]. Ocean Engineering,2017,141:277-282 ], LIJ, GUO Y, LIAN J, et al, mechanics, inspections, counters, and prospects for offshore wind turbine foundation scour research [ J ]. Ocean Engineering,2023,281:114893 ]. At present, the research means of dynamic and static force after the scouring of the offshore wind power mainly comprise numerical simulation and indoor test. In the aspect of numerical simulation, as Liu Gongjun and Yang Ji, the influence of local scouring on the bearing performance of a fan supporting system [ J ]. Rock and soil mechanics, 2018,39 (02): 722-727 ], a finite element model of an offshore fan is built, the vibration characteristics of the fan after scouring are researched, and the change rule of static and dynamic bearing capacity is revealed. The research of the vulnerability of the offshore wind turbine in consideration of the flushing depth [ J ]. The report of water conservancy and water transport engineering, 2022 (4): 123-130 ] researches the dynamics of the wind turbine under the simultaneous action of basic flushing and earthquake, and the research shows that the earthquake load has a significant influence on the normal operation of the wind turbine, but the permanent damage of the structure is difficult to cause.
In the aspect of experiments, the wind turbine dynamic response rules after flushing of foundation with different soil densities and soil rigidity are researched by the 'predergast L J, gavin K, doherty P.an investigation into the effect of scour on the natural frequency of an offshore wind turbine [ J ]. Ocean Engineering,2015, 101:1-11', and the research shows that the wind turbine vibration frequency is remarkably reduced after flushing of loose sandy foundation. Research on the influence of scouring on the natural frequency of a foundation of a wind power single pile at sea [ J ]. Vibration and impact, 2020,39 (22): 16-22., research on the influence rule of a foundation scouring of sandy soil on the natural frequency of a structure, and analysis on the influence of the scouring depth, the compactness of sandy soil and the equivalent embedded length on the natural frequency of the structure. The research aims at working conditions such as different soil properties, scouring depth, earthquakes and the like, a series of rich results are obtained, and a method and a basis are provided for safety evaluation after offshore wind power scouring. However, the onsite monitoring results of the scouring of the offshore wind power are less, and the contrast research of the power response of the fans under different working conditions is still insufficient, mainly because the onsite environment of the offshore wind power is relatively complex, so that the basic monitoring difficulty of the scoured offshore wind power is higher.
The existing single pile power simulation research after flushing is often only aimed at the power response of part of wind turbine structures, and numerical simulation research is carried out by using a standardized wind turbine model, so that the working state of the on-site fan structure is difficult to reflect.
Disclosure of Invention
The present invention has been made to solve the above-mentioned problems occurring in the prior art. Therefore, a method, a device and a medium for measuring the scouring power of the offshore wind power single pile foundation are needed to provide basis and support for the problem of structural vibration caused by different scouring depths in engineering.
According to a first aspect of the invention, there is provided a method for measuring scouring power of a single pile foundation of offshore wind power, the method comprising:
obtaining the equivalent embedded length of the pile foundation, and determining the flushing depth according to the equivalent embedded length of the pile foundation;
constructing a wind turbine structural dynamics model, wherein the wind turbine structural dynamics model is expressed as:
F r +F r * ＝0(r＝1,2,…,N)
wherein F is r Representing generalized main power, which is the sum of gravity, aerodynamic force and elastic force of each component in the wind turbine, F r * Representing generalized inertial force, which is the sum of inertial forces of all components in the wind turbine under an inertial coordinate system, and r represents the number of components in the wind turbine, wherein the components in the wind turbine comprise a foundation, a tower, a cabin, a hub and blades;
generating a turbulent wind field, and calculating wind load generated by turbulent wind to the blades through a phyllanthin momentum theory;
simulating irregular wave frequency distribution by using a P-M spectrum, and solving structural hydrodynamic load by using a radiation diffraction theory as wave load, wherein the wave load is the wave force born by the offshore wind power single pile;
the wind turbine runs in a simulation mode according to set parameters, and power response rules of pile foundations and tower drums under different flushing depths are calculated.
Further, the set parameters comprise simulation total duration, time domain propulsion step length, initial state wind turbine rotating speed, initial pitch angle and pitch rate.
Further, the wind turbine runs in a set parameter simulation mode, calculates a power response rule of pile foundations and tower drums under different flushing depths, and specifically comprises the following steps:
the wind turbine runs in a simulation mode according to set parameters, and obtains a time-frequency domain curve and a time-frequency domain curve of the displacement of the tower top and the displacement of the tower foundation under different scouring depths;
and determining the safe working frequency of the wind turbine according to the time-domain curve and the time-domain curve of the displacement of the tower top and the displacement of the tower base under different scouring depths.
Further, the wind turbine runs in a set parameter simulation mode, calculates a power response rule of pile foundations and tower drums under different flushing depths, and further comprises:
the wind turbine runs in a simulation mode according to set parameters, and pile foundation bending moment response curves under different scouring depths are obtained;
and determining important horizontal loads of the wind turbine according to pile foundation bending moment response curves under different scouring depths.
Further, the wind turbine runs in a set parameter simulation mode, calculates a power response rule of pile foundations and tower drums under different flushing depths, and further comprises:
the wind turbine runs in a simulation mode according to set parameters, and tower top time course curves under different scouring depths are obtained;
FFT conversion is carried out on tower top time course curves under different scouring depths, and the inherent frequency attenuation characteristic of the wind turbine structure is obtained;
and determining a critical flushing depth threshold value causing the fan resonance according to the natural frequency attenuation characteristic of the wind turbine structure and the safe working frequency of the wind turbine.
Further, the determining a critical flushing depth threshold value for causing the fan resonance according to the natural frequency attenuation characteristic of the wind turbine structure and the safe working frequency of the wind turbine specifically includes:
determining the minimum allowable frequency of the wind turbine structure according to the safe working frequency of the wind turbine;
and taking the scouring depth corresponding to the critical point that the natural frequency of the wind turbine structure is lower than the minimum allowable frequency of the wind turbine structure as a critical scouring depth threshold.
Further, the equivalent embedded length of the pile foundation is obtained by the following method:
calculating the distance t from the mud surface to the rigid embedding point of the pile foundation according to the following formula:
t＝αT
wherein α is a coefficient; t is the relative stiffness coefficient of the pile, in units of: m; e (E) p The elastic modulus of the pile material is as follows: kN/m 2 ；I p The unit is pile section moment of inertia: m is m 4 The method comprises the steps of carrying out a first treatment on the surface of the m is the horizontal resistance proportionality coefficient; b 0 Converted width for pile, unit: m;
equivalent embedded length l e The method comprises the following steps:
l e ＝t+l
wherein l is the pile foundation length above the mud surface.
Further, the determining the flushing depth according to the equivalent embedded length of the pile foundation specifically includes:
assuming that the scouring depths are evenly increased according to the set interval, the distance t from the mud surface to the rigid embedded point of the pile foundation is monotonically increased, and performing linear fitting on the equivalent embedded length under each scouring depth to determine a coefficient R 2 =0.99, obtaining a fitted curve;
and determining the flushing depth through the equivalent embedding length of the pile foundation based on the fitting curve.
According to a second technical scheme of the invention, there is provided a device for measuring scouring power of a single pile foundation of offshore wind power, the device comprising:
the flushing depth calculation module is configured to acquire the equivalent embedded length of the pile foundation and determine the flushing depth according to the equivalent embedded length of the pile foundation;
a dynamics module construction module configured to construct a wind turbine structural dynamics model, the wind turbine structural dynamics model being represented as:
F r +F r * ＝0(r＝1,2,…,N)
wherein F is r Represents generalized main power, is the sum of gravity, aerodynamic force and elastic force of each component in the wind turbine,representing generalized inertial force, which is the sum of inertial forces of all components in the wind turbine under an inertial coordinate system, and r represents the number of components in the wind turbine, wherein the components in the wind turbine comprise a foundation, a tower, a cabin, a hub and blades;
the wind load calculation module is configured to generate a turbulent wind field and calculate wind loads generated by turbulent wind on the blades through a phyllin momentum theory;
the wave load calculation module is configured to simulate irregular wave frequency distribution by adopting a P-M spectrum, and solve structural hydrodynamic load by adopting a radiation diffraction theory to serve as wave load, wherein the wave load is the wave force born by the offshore wind power single pile;
and the power response calculation module is configured to enable the wind turbine to run in a simulation mode with set parameters, and calculate the power response rules of the pile foundation and the tower under different flushing depths.
Further, the set parameters comprise simulation total duration, time domain propulsion step length, initial state wind turbine rotating speed, initial pitch angle and pitch rate.
Further, the dynamic response calculation module is further configured to:
the wind turbine runs in a simulation mode according to set parameters, and obtains a time-frequency domain curve and a time-frequency domain curve of the displacement of the tower top and the displacement of the tower foundation under different scouring depths;
and determining the safe working frequency of the wind turbine according to the time-domain curve and the time-domain curve of the displacement of the tower top and the displacement of the tower base under different scouring depths.
Further, the dynamic response calculation module is further configured to:
the wind turbine runs in a simulation mode according to set parameters, and pile foundation bending moment response curves under different scouring depths are obtained;
and determining important horizontal loads of the wind turbine according to pile foundation bending moment response curves under different scouring depths.
Further, the dynamic response calculation module is further configured to:
the wind turbine runs in a simulation mode according to set parameters, and tower top time course curves under different scouring depths are obtained;
FFT conversion is carried out on tower top time course curves under different scouring depths, and the inherent frequency attenuation characteristic of the wind turbine structure is obtained;
and determining a critical flushing depth threshold value causing the fan resonance according to the natural frequency attenuation characteristic of the wind turbine structure and the safe working frequency of the wind turbine.
Further, the dynamic response calculation module is further configured to:
determining the minimum allowable frequency of the wind turbine structure according to the safe working frequency of the wind turbine;
and taking the scouring depth corresponding to the critical point that the natural frequency of the wind turbine structure is lower than the minimum allowable frequency of the wind turbine structure as a critical scouring depth threshold.
Further, the flush depth calculation module is further configured to obtain an equivalent setting length of the pile foundation by:
calculating the distance t from the mud surface to the rigid embedding point of the pile foundation according to the following formula:
t＝αT
wherein α is a coefficient; t is the relative stiffness coefficient of the pile, in units of: m; e (E) p The elastic modulus of the pile material is as follows: kN/m 2 ；I p The unit is pile section moment of inertia: m is m 4 The method comprises the steps of carrying out a first treatment on the surface of the m is the horizontal resistance proportionality coefficient; b 0 Converted width for pile, unit: m;
equivalent embedded length l e The method comprises the following steps:
l e ＝t+l
wherein l is the pile foundation length above the mud surface.
Further, the flush depth calculation module is further configured to:
assuming that the scouring depths are evenly increased according to the set interval, the distance t from the mud surface to the rigid embedded point of the pile foundation is monotonically increased, and performing linear fitting on the equivalent embedded length under each scouring depth to determine a coefficient R 2 =0.99, obtaining a fitted curve;
and determining the flushing depth through the equivalent embedding length of the pile foundation based on the fitting curve.
It should be noted that, the device of the present invention and the method described in the foregoing belong to the same technical idea, and can achieve the same technical effects, which are not described herein.
According to a third aspect of the present invention, there is provided a readable storage medium storing one or more programs executable by one or more processors to implement the method as described above.
The invention has at least the following beneficial effects:
1) The invention considers the flexible characteristics of pile foundation scouring at different depths, simulates the power response of the offshore wind turbine in the wind-wave-structure-foundation environment by changing the pile foundation embedding length, extracts and analyzes the natural frequency change of the structure, obtains the actual scouring depth of the wind field by multi-beam sweep test, combines the dynamic response rules of simulation models at different scouring depths, provides the single pile type offshore wind turbine foundation safety suggestion after scouring, and provides basis for the maintenance and monitoring of the subsequent wind turbine.
2) The invention obtains the equivalent embedded length of pile foundation under different scouring depths, and the calculation result shows that the equivalent embedded length of the foundation monotonically increases along with the increase of the scouring depth of the pile circumference, and has stronger linear relation between the scouring depth and the equivalent embedded length, and the coefficient R is determined by fitting a straight line 2 0.99.
Drawings
FIG. 1 is a flow chart of a method for measuring scouring power of a single pile foundation of offshore wind power according to an embodiment of the invention;
FIG. 2 is a schematic diagram of the measurement of equivalent setting length of a pile foundation according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of equivalent setting lengths of pile foundations with different flushing depths according to an embodiment of the present invention;
FIG. 4 is a schematic view of a turbulent wind field at about hub elevation in accordance with an embodiment of the present invention;
FIG. 5 is an exemplary view of wave forces experienced by an offshore wind farm single pile according to an embodiment of the invention;
FIG. 6 is Sub>A schematic diagram of the displacement of the column top according to an embodiment of the present invention, wherein (Sub>A) represents the F-A direction and (b) represents the S-S direction;
FIG. 7 is Sub>A schematic view of Sub>A displacement of Sub>A foundation according to an embodiment of the present invention, wherein (Sub>A) represents the F-A direction and (b) represents the S-S direction;
FIG. 8 is a graph of time and frequency for tower top displacement at different flush depths, wherein (a) represents a time domain plot and (b) represents a frequency domain plot, according to an embodiment of the present invention;
FIG. 9 is a graph of time and frequency for tower foundation displacement at different depths of flushing, wherein (a) represents a time domain graph and (b) represents a frequency domain graph;
FIG. 10 illustrates pile foundation bending moments at mud surfaces at different flushing depths according to an embodiment of the present invention, wherein (Sub>A) represents the S-S direction, (b) represents the F-A direction, and (c) represents the Yaw direction;
FIG. 11 is a schematic diagram of natural frequencies of structures corresponding to different flushing depths according to an embodiment of the present invention;
fig. 12 is a schematic diagram of a basic scout multi-beam sweep site according to an embodiment of the present invention;
fig. 13 is a single pile foundation a multi-beam scan result according to an embodiment of the present invention, wherein (a) represents a single pile foundation a plane rendering diagram and (b) represents a single pile foundation a three-dimensional perspective diagram;
fig. 14 is a B multi-beam scan of a single pile foundation according to an embodiment of the present invention, wherein (a) represents a B-plane rendering of the single pile foundation and (B) represents a B-three-dimensional perspective of the single pile foundation;
fig. 15 is a single pile foundation C multi-beam scan result according to an embodiment of the present invention, in which (a) represents a single pile foundation C plane rendering diagram and (b) represents a single pile foundation C three-dimensional perspective diagram.
Detailed Description
The present invention will be described in detail below with reference to the drawings and detailed description to enable those skilled in the art to better understand the technical scheme of the present invention. Embodiments of the present invention will be described in further detail below with reference to the drawings and specific examples, but not by way of limitation. The order in which the steps are described herein by way of example should not be construed as limiting if there is no necessity for a relationship between each other, and it should be understood by those skilled in the art that the steps may be sequentially modified without disrupting the logic of each other so that the overall process is not realized.
The method is applied to a sea wind power plant of the Qingtai Tibet island in Tangshan city in Hebei province, the total installed capacity of the wind power plant is 300MW, 75 wind turbines are built in total, 39 wind turbines are single pile foundations, and 36 high pile cap foundations are formed. The water depth of the project site is 5-26 m. The hub design height of the wind turbine is 90m, wind energy data of nearly 50 years are provided according to a pavilion weather station, the average wind speed at the hub height is 7.4m/s, and the turbulence intensity of the site can be defined as class C by referring to the design requirement of offshore wind turbines, IEC 61400-3. From geological survey data, 14 large layers including sand-mixed silt, silt-mixed sand, clay, fine sand and the like are distributed in a soil layer with the depth of 95.4 m. The area of the wind field belongs to fine sand powder coast, and the scouring speed is about 0.1-0.2 m/a. The scour prevention measures of the single pile foundation are as follows: geotextile is laid in the range of 2-4 times of pile diameter around the pile, and then the pile is covered by a soft mattress of 400mm multiplied by 250mm concrete interlocking blocks, and a sand cover with the thickness of 0.5m is laid on the pile.
The mustine linden island offshore wind farm was started at month 12 of 2021, during which time it was found that there was some flushing of the foundation bed. The offshore wind power is inevitably subjected to long-term cyclic loads such as wind, wave and mechanical in the service period, and the structural dynamics characteristic change of the basic scour is not negligible. Therefore, the embodiment provides a measuring method for the scouring power of the offshore wind power single pile foundation, which is used for researching the vibration characteristics of a fan under the coupling action of various loads so as to evaluate and predict the structural safety of the foundation after scouring. As shown in fig. 1, the method includes the following steps S100-S500.
And step S100, obtaining the equivalent embedded length of the pile foundation, and determining the flushing depth according to the equivalent embedded length of the pile foundation.
Fig. 2 is a schematic diagram of measuring the equivalent embedded length of the pile foundation, wherein the left side of fig. 2 is a single pile embedded schematic diagram, L is the pile foundation length below the mud surface, and L is the pile foundation length above the mud surface. As shown on the right side of FIG. 2, when the pile depth reaches a certain value t, the displacement and the rotation angle of the pile are not obviously changed under the action of load, and the pile foundation is rigidly connected with the soil below t, the pile foundation length unconstrained by the soil is called equivalent embedded length l e The size of which is equal to the sum of l and t.
The distance t from the mud surface to the rigid embedding point of the pile foundation can be calculated according to the following formula:
t＝αT
wherein α is a coefficient, and 2.0 is taken in this embodiment; t is the relative stiffness coefficient (m) of the pile; e (E) p Is the elastic modulus (kN/m) of pile material 2 )；I p Is the pile section moment of inertia (m 4 ) The method comprises the steps of carrying out a first treatment on the surface of the m is the horizontal resistance proportionality coefficient; b 0 Equivalent embedded length l for converted width (m) of pile e Is that
l e ＝t+l
Due to the large number of field soil layers, the study simplified it to sand-mixed silt, silty clay and fine sand, and the m values of each soil layer are shown in table 1. The pile foundation length l above the mud surface corresponding to different flushing depths can be calculated through the steps (1) - (3) e The results are shown in FIG. 3. Neglecting the sediment transport balance after flushing to a certain depth, it is assumed that the flushing depth is changed from 0m to 15m at 1m intervals, and t is monotonically increased from 7.94m to 8.84m, because the lower soil horizontal resistance coefficient m is larger. Equivalent embedding length at each scouring depthLinear fitting of the degree to determine the coefficient R 2 The linearity between the pile equivalent setting length and the flush depth calculated according to this method is high. According to the field data, the pile sinking elevation is controlled to be 10m above MSL (mean sea level), when the water depth of a single pile is 15m, the scouring of a single pile foundation is changed from 0m to 15m, and the distance from the corresponding mud surface to the pile top is 22.94m to 38.84m.
Research shows that the equivalent embedded length of pile foundation under flushing is formed by pile diameter D, soil compactness gamma, cohesive force C and internal friction angleAnd the like. The larger the soil compactness of the mud surface is, the larger the variation of the equivalent embedded length of the pile foundation with the same depth is; for the same soil environment and scouring length, the improvement of the pile diameter will lead to the reduction of the variation of the equivalent embedded length. Therefore, the calculation result of the scouring depth and the equivalent embedded length obtained from the geological data in this embodiment cannot be directly applied to other pile diameters and geological conditions.
Table 1 soil m value for each layer of single pile foundation
| Layer number | Soil layer name | m(MN/m 4 ) | Horizontal displacement (mm) |
| 1 | Sand-mixed silt | 3000 | 10 |
| 2 | Powdery clay | 6000 | 10 |
| 3 | Fine sand | 20000 | 10 |
And step S200, constructing a wind turbine structural dynamics model.
Illustratively, the Kane method is used for establishing a structural model of the offshore wind turbine, and the dynamic actions among the foundation, the tower, the cabin, the hub and the blades in the ElastoDyn module are mutually transmitted and influenced to form a multi-body dynamics model of the wind turbine. The parameters of the components such as the tower, the cabin, the hub and the like in the single pile wind power simulation model are valued according to prototype design data. For the tower part, the first five-order modes need to be solved by BModes, and then the dynamics simulation of the tower part is realized in Openfast.
The wind turbine structural dynamics model can be written as:
F r +F r * ＝0 (r＝1,2,…,N)
wherein F is r Represents generalized main power, is the sum of gravity, aerodynamic force and elastic force of each component in the wind turbine,the generalized inertial force is represented as the sum of inertial forces of all components in the wind turbine under an inertial coordinate system, and r represents the number of components in the wind turbine, wherein the components in the wind turbine comprise a foundation, a tower, a cabin, a hub and blades.
And step S300, generating a turbulent wind field, and calculating wind load of turbulent wind to the blades through a phyllin momentum theory.
According to design data, the height of the wind wheel hub is 90.0m, the average wind speed is 7.4m/s, the length of the blade is 63.0m, and the diameter of the wind wheel is 130.0m. And a turbulent wind field is generated through turbo sim, a Kametal model recommended by IEC 614001-1 is adopted in the calculation of the turbulent wind field, and the time-varying wind load of the wind wheel is shown in figure 4. The load of turbulent wind on the blade is calculated by the principle of blade element momentum (BMT), and since the fan manufacturer does not publish the aerodynamic parameters of the blade, the model is defined by using the FFA series airfoil profile which is the same as that of the NREL 5MW wind turbine.
Step S400, simulating irregular wave frequency distribution by adopting a P-M spectrum, and solving structural hydrodynamic load by adopting a radiation diffraction theory to serve as wave load, wherein the wave load is wave force born by the offshore wind power single pile;
according to design data, the significant wave height of incident waves is 4.4M, the depth of field water is 15.0M, the peak period of the incident waves is 8.0s, P-M (Pierson-Moskowitz) spectrum is adopted to simulate irregular wave frequency distribution, and the Morison equation has limitation in calculating the wave load of the large-diameter pile. FIG. 5 shows the calculation result of the time domain of the wave force applied to the pile foundation, and the specific calculation method of the wave load is disclosed in documents [ Li Zhi, yue Minnan, yang days, etc. ], the dynamic response of the offshore ultra-large wind turbine and the structural damage analysis [ J ]. Solar report, 2022,43 (7): 366-374 ] under different sea conditions.
And S500, simulating running of the wind turbine by using set parameters, and calculating power response rules of pile foundations and tower cylinders under different flushing depths.
The method comprises two parts, wherein the first part is working condition simulation, and the second part is simulation result analysis.
Regarding the working condition simulation, the total simulation time is t=1000s, the time domain propulsion step length is 0.05s, the initial state wind turbine rotating speed is 0, the pitch angle is 90 degrees, the pitch program is started after 100s, and the simulation wind turbine is started normally, and the pitch rate is 2 degrees/s. The time domain plots of the tower top F-A and S-S directions when not flushed are shown in FIG. 6. Because the wind turbine is in a static state at zero moment, the tower top is influenced by the self weight of the upper structure to generate obvious displacement in an initial state, the tower top is subjected to rapid change after being subjected to the combined action of wind and wave, the wind turbine starts to start normally at the moment of t=100 s, and at the moment, the structural vibration is obvious until the displacement change is relatively stable about 200 s.
The time domain curves of F-A and S-S directions at the tower foundation are shown in FIG. 7. Compared with the displacement of the tower top, the windward direction and the lateral displacement amplitude at the tower foundation are obviously reduced, which is about one tenth of the displacement of the tower top. Overall, the S-S direction displacement of the tower top and tower base positions is significantly less than the F-Sub>A direction, wherein the S-S direction displacement at the tower base is significantly increased upon start-up of the wind turbine, and subsequently the displacement amplitude is smaller and relatively stable. The vibration of the tower barrel in the S-S direction is relatively small in the whole starting process, so that wind load acting in the F-A direction is the main load for causing the vibration of the fan, and the structural vibration in the F-A direction and the fatigue problem of the tower barrel are focused in practical engineering.
And the simulation result analysis comprises the vibration characteristics of the lower flushing tower cylinder, the bending moment response of the lower flushing pile foundation and the natural frequency attenuation of the lower flushing structure.
1) Vibration characteristics of the lower tower drum
As the S-S direction displacement was small, the time domain curve of the column top F-A direction displacement at the flushing depths of 0m,7m and 15m was analyzed, as shown in FIG. 8 (Sub>A). As can be seen by comparing the tower top displacement amplitude values under different flushing depths, the reduction of the pile foundation burial depth caused by flushing can cause the obvious increase of the structural vibration amplitude value. The main reason is that as the flushing depth increases, the length of the free end of the pile foundation increases, the length constrained by the soil decreases, and the increase in the length of the cantilever end further causes the pile end displacement to increase.
Since the fan structure vibration is relatively stable after 200s, time-course data of 200-1000 s is selected for Fast Fourier Transform (FFT), and the result is shown in fig. 8 (b). Compared with the frequency domain curves at 0m,7m and 15m scouring depths, the main frequency amplitude is the largest at 15m scouring depths, because the tower top displacement amplitude of the scouring depths is the largest, and the energy near the corresponding natural frequency is higher. With the increase of the flushing depth, the natural frequency of the structure has obvious descending trend, and the integral working frequency of the fan is required to fall in the range of 1P to 3P according to the soft-rigid design rule followed by the basic design of the wind turbine, so that the structural safety problem caused by different flushing depths is further discussed by combining the rated rotation speed of the fan.
The frequency domain curves for displacement at the foundation at 0m,7m and 15m scour depths are shown in FIG. 9. Similar to the tower top, the tower foundation is vibrated strongly when the fan is started, and the displacement of the tower bottom is changed periodically and the amplitude is relatively stable along with the fan reaching the rated rotating speed range. The comparison results of the time-frequency domain curves of the tower top and the tower bottom under different flushing depths show that the structure is more obviously vibrated due to the increase of the flushing depths, and the displacement of the tower top is obviously larger than that of the tower base. In addition, the length of the free end of the pile foundation is increased due to the increase of the scouring depth, the amplitude of the main frequency in the frequency domain curve is increased, and the natural frequency of the whole structure is reduced.
Model test researches show that as the soil body around the pile is eroded, the embedding depth is reduced, the tested first-order self-vibration frequency is gradually reduced, and the conclusion is consistent with the rule obtained by numerical simulation. When the scouring depth is shallower, the sensitivity of the first-order natural mode to pile foundation scouring is weaker, and the change of the second-order and third-order natural modes is more obvious along with the increase of the basic scouring depth. On the other hand, the smaller the soil density is, the larger the influence of scouring on the self-vibration frequency of the structure is, and when the scouring depth is increased to 5D, the first-order self-vibration frequency is reduced by 6.5%. In order to prevent the foundation rigidity from being reduced caused by pile foundation scouring, the diameter wall thickness of the steel pipe pile is suggested to be increased. In summary, the basic scouring may cause the overall rigidity of the structure to be insufficient, so that the main frequency of the fan vibration is lower than the rotation frequency 1P of the fan, and the resonance effect of the structure occurs. However, even for the same offshore wind farm and flush depth, the actual natural frequency of the fans at different locations may be different, mainly due to the differences in the physical properties of the soil surrounding the different pile foundations.
2) Moment response of pile foundation under scouring
Since offshore wind power belongs to a typical high-rise structure, bending moment load has an important influence on structural safety. To obtain the bending moment response rule of the pile foundation under different flushing depths, extracting the bending moment loads corresponding to the mud surface heights Cheng Zhuangji S-S, F-A and YAW under 0m,7m and 15m flushing, and then the bending moment response curves of the pile foundation under different flushing depths are shown in figure 10. Because the wind turbine generates larger disturbance in the starting process, the 200-1000 s pile foundation bending moment time curve is analyzed. Overall, F-A direction bend during fan operationMaximum moment of up to 6X 10 7 The bending moment in the direction of N.m and YAW is minimum and is 5 multiplied by 10 3 N.m. Because the rotation angle of the large-diameter fan single pile foundation in actual engineering needs to be strictly controlled, the deflection angle of the pile foundation in the F-A direction should be monitored in the fan operation process. On the other hand, under the action of turbulent wind and irregular waves, the bending moment of the fan in different directions has certain difference. The S-S bending moment and the YAW bending moment change obviously in the starting-up process, when the fan rotates normally under rated power, the bending moment change is relatively stable, and the F-A bending moment changes drastically in the starting-up and normal operation processes of the wind turbine, so that the stress and displacement response of the normally-serving offshore wind power pile foundation in the F-A direction are further described. On the other hand, with the increase of the flushing depth, the S-S, F-A and YAW bending moments are increased to different degrees, the F-A bending moment amplitude is increased most obviously, and the YAW bending moment amplitude is changed relatively little.
Under different flushing depths, the bending moment at the pile foundation mud surface is similar to the change rule of the displacement of the tower top. With the increase of the flushing depth, the bending moment at the mud surface is obviously increased, and the main reason is that the free end length of the pile foundation is increased due to basic flushing, so that the whole cantilever section of the fan is increased. The displacement and bending moment of the pile foundation mud surface are far larger than those of the lateral direction and the vertical direction in the windward direction, which means that wind load is the main horizontal load of the wind turbine, and the lateral bending moment and the vertical bending moment are very weak and can be generally ignored in subsequent analysis.
3) Natural frequency attenuation of structure under scouring
In order to explore the change rule of the natural frequency of the structure corresponding to different flushing depths, FFT conversion is carried out on the tower top time course curve under the flushing depth of 0-15 m, and the natural frequency attenuation characteristic of the structure is extracted and analyzed. Taking the scouring depth of 0m as an example, the equivalent embedding length is 7.94m, so the distance from the pile face to the MSL is 22.94m, the distance from the free end of the pile top to the MSL is 10m, and the equivalent embedding length of the pile face under the scouring depth of 0m to 15m can be calculated in sequence. The natural frequencies of the structures corresponding to different flushing depths are shown in figure 10. The natural frequency of the structure is obviously reduced in the process of flushing 0-2 m, the natural frequency reduction amplitude is about 5%, and the natural frequency of the structure is always monotonically reduced along with the continuous increase of the flushing depth. The natural frequency design of the offshore wind turbine is based on a soft-rigid rule, and a 10% enrichment is reserved, so that the safe passing frequency of the fans 1P-3P is calculated to be 0.28-0.32 Hz, as shown in FIG. 11. The two dashed lines in the figure are the maximum and minimum allowed frequencies, respectively. When the flushing depth is larger than 12m, the integral natural frequency of the fan is lower than the minimum allowable frequency, namely the 1P safety frequency is not met, and the rigidity of the structure is insufficient at the moment, so that the resonance effect is easy to cause. As verification, under the condition of no flushing, the natural frequency of the structure is calculated to be 0.31 based on the dynamic model established herein, the main frequency result of the structure calculated by SACS is 0.29Hz, and compared with the calculation result of the model herein, the error rate of the natural frequency of the structure is 6.9%, and the natural frequency is outside the vibration frequency range needing to be avoided. Therefore, the wind turbine simulation model established based on Openfast can be considered to be accurate and reliable in calculation result.
And finally, carrying out scouring safety analysis based on multi-beam scanning.
The offshore wind power model calculation method based on AFL is applied to the offshore wind power plant of the Tangshan pavilion in Hebei province, and supports and references are provided for subsequent wind power foundation safety evaluation and maintenance. And carrying out multi-beam sweep test on the actual scouring depth of the 39 single-pile wind power foundations, and grasping and knowing the actual scouring depth. The sweep site is shown in fig. 12. The wind field sea area scouring and sweeping measurement mainly uses equipment names, models, purposes and the like as shown in the table, and the measuring instruments are checked and qualified by a metering station authenticated by the country according to regulations and are in the effective period.
Table 2 wind power foundation scouring and scanning instrument
Because of limited space, only plane and three-dimensional rendering diagrams of typical pile foundations (A-C) are selected for display, as shown in FIGS. 13-15. For pile foundation a, there are suspected scour pits on the northwest and south sides of the fan pile, with the northwest pit being deeper, about 3m. For pile foundation B, the western side of the fan pile has suspected scouring phenomenon, the scouring depth is about 2m, and the rest part of the topography is slightly fluctuated. For pile foundation C, the topography around the fan single pile foundation is obviously higher than the natural seabed surface, suspected to be caused by manual reinforcement, slight scouring phenomenon exists on the south and north sides, the rest topography is rough and flat, and suspected scouring pits are not found.
And according to the AFL model calculation result, the on-site scouring sweep result is combined to deeply analyze the fan power response rule under scouring. The minimum allowable natural frequency of the fan is 0.28 through numerical simulation, the corresponding basic flushing depth is 12.0m, and the maximum pile foundation flushing depth in 39 single pile fans is 3.0m, so that the on-site flushing depth does not reach the critical depth causing structural resonance. On the other hand, the on-site scouring depth is 7.0m smaller than the designed reserved critical scouring depth, so that the bearing capacity of offshore wind power meets the requirement, and the structure can be further judged to be still in a safe state. Because the service time of the wind field is shorter, sediment transportation at the foundation is still in an unbalanced state, and the scouring monitoring of the follow-up wind field single pile foundation is required to be enhanced. The increase of the scouring depth not only causes the attenuation of the natural frequency of the structure, but also causes the increase of the vibration amplitude of the structure, and the vibration amplitude of the pile foundation and the tower barrel in the windward direction is more obvious by combining the numerical simulation result, so that the fatigue life problem of the foundation and the supporting structure of the offshore wind turbine can be caused. Therefore, the monitoring of the parameters such as stress, strain and the like at the key positions is added later, and the long-term safe service of the offshore wind power under flushing is ensured.
In summary, the invention considers the flexible characteristics of pile foundation scouring at different depths, simulates the power response of the offshore wind turbine in the wind-wave-structure-foundation environment by changing the pile foundation embedding length, extracts and analyzes the natural frequency change of the structure, obtains the actual scouring depth of the wind field through multi-beam sweep test, combines the simulation model power response rules at different scouring depths, provides the single pile type offshore wind power foundation safety suggestion after scouring, and provides basis for the maintenance and monitoring of the subsequent wind turbine. The main conclusions drawn by this example are as follows:
(1) The pile foundation equivalent embedding lengths under different scouring depths are obtained based on an AFL method, and the calculation result shows that the equivalent embedding length of a foundation monotonically increases along with the increase of the scouring depth around the pile, the scouring depth and the equivalent embedding length have a stronger linear relation, and the fitting straight line determining coefficient R is 0.99;
(2) The offshore wind power integrated simulation result considering wind-wave-structure-foundation shows that the instantaneous displacement of the top of the wind turbine tower is larger when the wind turbine is started, and the displacement amplitude is relatively stable after normal operation; the displacement of the windward tower and the pile foundation is far greater than the displacement of S-S, which indicates that wind load is a main cause of structural vibration, and the damage caused by the windward load is suggested to be emphasized in the subsequent operation and maintenance process of the wind farm foundation.
(3) The scouring depth of 39 single-pile offshore wind power foundations is obtained through multi-beam scanning, and the maximum scouring depth is 3.0m. The natural frequency of the structure is 0.29Hz when not flushed, and when the flushing depth reaches 12.0m and the main frequency of the fan is lower than the allowable frequency of the fan 1P by 0.28Hz, resonance of the fan structure can be caused, and the conclusion also verifies that the design data provides the feasibility of reserving the flushing depth of 7.0 m.
The above description is intended to be illustrative and not restrictive. For example, the above-described examples (or one or more aspects thereof) may be used in combination with each other. For example, other embodiments may be used by those of ordinary skill in the art upon reading the above description. In addition, in the above detailed description, various features may be grouped together to streamline the invention. This is not to be interpreted as an intention that the features of the claimed invention are essential to any of the claims. Rather, inventive subject matter may lie in less than all features of a particular inventive embodiment. Thus, the following claims are hereby incorporated into the detailed description as examples or embodiments, with each claim standing on its own as a separate embodiment, and it is contemplated that these embodiments may be combined with one another in various combinations or permutations. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.
Claims (10)
1. The method for measuring the scouring power of the offshore wind power single pile foundation is characterized by comprising the following steps of:
obtaining the equivalent embedded length of the pile foundation, and determining the flushing depth according to the equivalent embedded length of the pile foundation;
constructing a wind turbine structural dynamics model, wherein the wind turbine structural dynamics model is expressed as:
F r +F r * ＝0(r＝1,2,…,N)
wherein F is r Represents generalized main power, is the sum of gravity, aerodynamic force and elastic force of each component in the wind turbine,representing generalized inertial force, which is the sum of inertial forces of all components in the wind turbine under an inertial coordinate system, and r represents the number of components in the wind turbine, wherein the components in the wind turbine comprise a foundation, a tower, a cabin, a hub and blades;
generating a turbulent wind field, and calculating wind load generated by turbulent wind to the blades through a phyllanthin momentum theory;
simulating irregular wave frequency distribution by using a P-M spectrum, and solving structural hydrodynamic load by using a radiation diffraction theory as wave load, wherein the wave load is the wave force born by the offshore wind power single pile;
the wind turbine runs in a simulation mode according to set parameters, and power response rules of pile foundations and tower drums under different flushing depths are calculated.
2. A method according to claim 1, wherein the set parameters include a simulated total time period, a time domain propulsion step size, an initial state wind turbine rotational speed, an initial pitch angle and a pitch rate.
3. The method according to claim 2, wherein the wind turbine operates in a set parameter simulation mode, and calculates power response rules of pile foundations and tower drums under different flushing depths, and the method specifically comprises the following steps:
the wind turbine runs in a simulation mode according to set parameters, and obtains a time-frequency domain curve and a time-frequency domain curve of the displacement of the tower top and the displacement of the tower foundation under different scouring depths;
and determining the safe working frequency of the wind turbine according to the time-domain curve and the time-domain curve of the displacement of the tower top and the displacement of the tower base under different scouring depths.
4. A method according to claim 3, wherein the wind turbine is operated in a set parameter simulation, and the power response rules of pile foundations and tower drums under different flushing depths are calculated, and the method further comprises:
the wind turbine runs in a simulation mode according to set parameters, and pile foundation bending moment response curves under different scouring depths are obtained;
and determining important horizontal loads of the wind turbine according to pile foundation bending moment response curves under different scouring depths.
5. The method of claim 4, wherein the wind turbine operates in a set parameter simulation, calculates a dynamic response law of pile foundations and tower drums at different flushing depths, and further comprises:
the wind turbine runs in a simulation mode according to set parameters, and tower top time course curves under different scouring depths are obtained;
FFT conversion is carried out on tower top time course curves under different scouring depths, and the inherent frequency attenuation characteristic of the wind turbine structure is obtained;
and determining a critical flushing depth threshold value causing the fan resonance according to the natural frequency attenuation characteristic of the wind turbine structure and the safe working frequency of the wind turbine.
6. The method according to claim 5, wherein the determining the critical flush depth threshold value causing the fan resonance according to the natural frequency attenuation characteristic of the wind turbine structure and the safe operating frequency of the wind turbine, specifically comprises:
determining the minimum allowable frequency of the wind turbine structure according to the safe working frequency of the wind turbine;
and taking the scouring depth corresponding to the critical point that the natural frequency of the wind turbine structure is lower than the minimum allowable frequency of the wind turbine structure as a critical scouring depth threshold.
7. The method of claim 1, wherein the equivalent set length of the pile foundation is obtained by:
calculating the distance t from the mud surface to the rigid embedding point of the pile foundation according to the following formula:
t＝αT
wherein α is a coefficient; t is the relative stiffness coefficient of the pile, in units of: m; e (E) p The elastic modulus of the pile material is as follows: kN/m 2 ；I p The unit is pile section moment of inertia: m is m 4 The method comprises the steps of carrying out a first treatment on the surface of the m is the horizontal resistance proportionality coefficient; b 0 Converted width for pile, unit: m;
equivalent embedded length l e The method comprises the following steps:
l e ＝t+l
wherein l is the pile foundation length above the mud surface.
8. The method of claim 7, wherein the determining the flush depth based on the equivalent setting length of the pile foundation comprises:
assuming that the scouring depths are evenly increased according to the set interval, the distance t from the mud surface to the rigid embedded point of the pile foundation is monotonically increased, and performing linear fitting on the equivalent embedded length under each scouring depth to determine a coefficient R 2 =0.99, obtaining a fitted curve;
and determining the flushing depth through the equivalent embedding length of the pile foundation based on the fitting curve.
9. An offshore wind power single pile foundation scouring power measurement method device is characterized in that the device comprises:
the flushing depth calculation module is configured to acquire the equivalent embedded length of the pile foundation and determine the flushing depth according to the equivalent embedded length of the pile foundation;
a dynamics module construction module configured to construct a wind turbine structural dynamics model, the wind turbine structural dynamics model being represented as:
F r +F r * ＝0 (r＝1,2,…,N)
wherein F is r Representing generalized main power, which is the sum of gravity, aerodynamic force and elastic force of each component in the wind turbine, F r * Representing generalized inertial force, which is the sum of inertial forces of all components in the wind turbine under an inertial coordinate system, and r represents the number of components in the wind turbine, wherein the components in the wind turbine comprise a foundation, a tower, a cabin, a hub and blades;
the wind load calculation module is configured to generate a turbulent wind field and calculate wind loads generated by turbulent wind on the blades through a phyllin momentum theory;
the wave load calculation module is configured to simulate irregular wave frequency distribution by adopting a P-M spectrum, and solve structural hydrodynamic load by adopting a radiation diffraction theory to serve as wave load, wherein the wave load is the wave force born by the offshore wind power single pile;
and the power response calculation module is configured to enable the wind turbine to run in a simulation mode with set parameters, and calculate the power response rules of the pile foundation and the tower under different flushing depths.
10. A readable storage medium storing one or more programs executable by one or more processors to implement the method of any of claims 1-8.
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