CN115384721A - Method for calculating structural strength of foundation stay bar of three-upright-column floating type fan - Google Patents
Method for calculating structural strength of foundation stay bar of three-upright-column floating type fan Download PDFInfo
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Abstract
The invention discloses a method for calculating the structural strength of a foundation stay bar of a three-upright-column floating type fan, which comprises the following steps: selecting four dangerous working conditions and corresponding waveforms of which the fan foundation is easy to lose efficacy or damage; determining the wavelength according to the waveforms of the four dangerous working conditions, and determining the wave period and the wave height under the four dangerous working conditions according to a wave theoretical formula; determining the wave load borne by the wind turbine foundation; step four, establishing a beam system structure model of the fan foundation; step five, applying six boundary conditions on the beam system structure model; carrying out finite element dispersion on the beam system structure model to form a finite element model of a one-dimensional grid; step seven, applying wave load in the finite element model; step eight, performing statics analysis to obtain the maximum axial compressive stress and the maximum combined stress of the stay bar under four dangerous working conditions; and step nine, judging whether the structural strength of the support rod is enough. The invention can obviously improve the calculation efficiency.
Description
Technical Field
The invention relates to a method for calculating structural strength of a foundation stay bar of a three-upright-column floating type fan.
Background
The floating wind power and the fixed wind power correspond to each other, and the definition and the distinction of the floating wind power and the fixed wind power depend on whether the base structure of the wind turbine is a fixed structure or a floating structure. From the experience of offshore oil, the investment cost of the fixed foundation generally increases exponentially with the increase of the water depth due to the increase of the load of the fixed foundation at the seabed and the like caused by the increase of the water depth. When the water depth exceeds a certain depth, the investment gain of the fixed fan becomes worse. According to the related experience of offshore oil, a critical water depth can occur, and after the critical water depth is exceeded, the investment income of the floating wind power is higher than that of the fixed wind power. The floating wind power research significance is to reduce the investment cost of the floating wind power so as to realize the utilization of the offshore wind energy in the deep and distant sea areas.
The three prevailing types of floating wind turbine foundations at present are semi-submersible, TLP (tension leg) and SPAR (mono-pole). The semi-submersible floating type wind turbine foundation which is widely applied and mature in technology is a foundation form which is more suitable for offshore wind power development at the present stage. The semi-submersible floating type fan foundation generally comprises a plurality of upright columns and a connecting structure thereof, the upright columns are mostly made of steel cylinders at the present stage, the connecting structure is mostly made of reinforced plates, round pipes, square pipes and the like, and the support rods are the connecting structure between the upright columns. In order to ensure the wave resistance of the foundation, the distance between the stand columns is often larger, and the load borne by the stay bar is larger, so that the floating type fan foundation has higher requirements on the strength of the stay bar.
At present, a calculation method for the structural strength of an ocean platform in the ocean engineering industry is mature, and a design wave method is generally adopted to analyze the total strength of the ocean platform. The method comprises the steps of firstly designing wave parameters according to the main scale of a platform, calculating the wave load borne by the platform through a potential flow theory, and mapping the wave load in a finite element model to carry out total strength analysis. The method can also be applied to structural strength calculation of the foundation brace rod of the three-upright-column floating type wind turbine, but the method needs to calculate the wave load by using a potential flow theory and map the load in a finite element model, has high requirement on the integrity of the model, is not suitable for the conceptual design stage of structure blurring, is complex, and has complicated steps and time consumption.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a method for calculating the structural strength of a basic stay bar of a three-upright-column floating type fan, which can obviously improve the calculation efficiency and further can quickly and preliminarily determine the size of the stay bar structure.
The purpose of the invention is realized by the following steps: a method for calculating structural strength of a foundation stay bar of a three-upright-column floating type fan comprises the following steps:
selecting dangerous working conditions, namely selecting four dangerous working conditions and corresponding waveforms, wherein the fan foundations are easy to lose effectiveness or damage;
determining wave parameters, determining the wavelengths under the four dangerous working conditions according to the waveforms of the four dangerous working conditions, and determining the wave periods and wave heights under the four dangerous working conditions according to a wave theoretical formula;
determining the load, namely determining the wave load on three upright columns of the fan foundation;
step four, building a structural model, namely building a beam system structural model of the fan foundation in an ANSYS Design Modeller module;
applying boundary conditions, namely applying six boundary conditions on the beam system structure model, namely three vertically upward spring constraints, two wave direction horizontal displacement constraints and one horizontal displacement constraint vertical to the wave direction;
carrying out finite element dispersion on the beam system structure model in an ANSYS Static Structural module to form a finite element model of a one-dimensional grid;
step seven, load application, namely applying wave load in the finite element model, wherein the direction of the wave load is determined by the waveforms of the four dangerous working conditions, and the wave load is applied to the centroid of the draught part of the upright column in the form of point load;
step eight, performing statics analysis, namely developing the statics analysis in an ANSYS Static Structural module to obtain the maximum axial compressive stress sigma of the stay rod under four dangerous working conditions dc And maximum combined stress sigma of the stay mc ；
Step nine, checking the strength, namely checking the yield strength of the stay bar material and the maximum combined stress sigma of the stay bar mc Checking the buckling strength of the stay bar material and the maximum axial compressive stress sigma of the stay bar dc Checking is carried out, and whether the structural strength of the stay bar is enough or not is judged.
The method for calculating the structural strength of the foundation stay bar of the three-upright-column floating type fan comprises the following steps of firstly, selecting a first dangerous working condition as a working condition with the maximum separation force at an incident angle of 0 degrees, selecting a second dangerous working condition as a working condition with the maximum extrusion force at an incident angle of 0 degrees, selecting a third dangerous working condition as a working condition with the maximum separation force at an incident angle of 30 degrees, and selecting a fourth dangerous working condition as a working condition with the maximum extrusion force at an incident angle of 30 degrees.
The method for calculating the structural strength of the foundation stay bar of the three-upright floating type fan comprises the following steps of:
A. determining the wavelength, namely determining the relationship between the wavelength L and the distance B of the upright column under the four dangerous working conditions in a one-to-one correspondence manner according to the waveforms under the four dangerous working conditions:
in the formula (1), L 1 The wavelength under the first dangerous working condition; l is a radical of an alcohol 2 The wavelength under the second dangerous working condition; l is 3 The wavelength under the third dangerous working condition; l is 4 The wavelength under the fourth dangerous working condition; b is the distance between the upright posts;
B. determining the wave period, and obtaining a wave period T formula according to a linear wave theory:
in the formula (2), L is a wavelength; k is the number of waves,
d is the water depth;
C. determining the wave height, and calculating the wave height H according to a linear wave height formula (3):
in the formula (3), T is a wave period; h 100 The wave height is one hundred years.
In the method for calculating the structural strength of the foundation stay bar of the three-upright-column floating type wind turbine, the wave load is calculated by adopting the Morisen equation in the third step as follows:
in the formula (4), F N Is a wave load; rho is the density of the seawater; c A For additional mass coefficient, C when the column is cylindrical A ＝1；C D For drag coefficient, C when the column is cylindrical D =1; a is the area of the cross section of the upright post; d is the diameter of the upright column; v. of&The horizontal motion acceleration of water particles; v is the horizontal movement velocity of the water particle;
obtaining the horizontal movement velocity v of water particles in the wave according to a linear wave theory:
obtaining the horizontal motion acceleration of water particles in the waves according to the linear wave theory
In the formulas (5) and (6), H is the wave height; k is the number of waves,
l is the wavelength; d is the water depth; z is the depth of the water particle; x is the direction of wave propagation; ω is the circular frequency of the wave; t is time.
The method for calculating the structural strength of the foundation stay bar of the three-upright-column floating type fan comprises the following stepsIn the fifth step, the set spring stiffness constrained by the spring is equivalent to the water buoyancy load, and the spring stiffness K s The calculation formula of (c) is as follows:
in the formula (7), rho is the density of the seawater; d is the diameter of the upright column; g is the gravity acceleration coefficient of 9.8N/Kg.
The method for calculating the structural strength of the foundation stay bar of the three-upright floating type fan comprises the following steps:
A. checking the yield strength, and determining the allowable yield stress [ sigma ] of the stay bar by the following formula s ]：
[σ s ]＝σ s /S s
Wherein σ s The yield strength of the stay bar material is MPa; s s The yield safety factor of the stay bar material;
B. checking the buckling strength, and determining allowable buckling stress [ sigma ] of the stay bar according to the formula cr ]：
[σ cr ]＝σ cr /S cr
Wherein σ cr The buckling strength of the stay bar material is MPa; s cr The buckling safety factor of the stay bar material.
Buckling strength sigma of compression bar material cr Calculated as follows:
in formula (8): sigma E The tensile stress is the Euler stress, MPa,
l is the length of the rod without support; r is the radius of the rotational inertia of the cross section corresponding to the unsupported length l of the rod; k is an equivalent length coefficient; e is the Young's modulus of the strut material;
when maximum combination of strutsStress sigma mc Less than allowable yield stress [ sigma ] of brace rod s ]I.e. sigma mc ＜[σ s ]While the maximum axial compressive stress σ of the strut dc Allowable buckling stress [ sigma ] less than that of stay cr ]I.e. sigma dc ＜[σ cr ]The structural strength of the strut may be sufficient.
The method for calculating the structural strength of the foundation stay bar of the three-upright-column floating type fan has the following characteristics:
the method has low requirement on the integrity of the model, optimizes and simplifies the calculation steps and the model to the greatest extent, and can obviously improve the calculation efficiency, thereby being capable of rapidly and preliminarily determining the size of the strut structure and being very suitable for the strut strength calculation in the conceptual design stage of structure ambiguity.
Drawings
Fig. 1 is a schematic structural view of a three-upright floating type wind turbine foundation according to the present invention;
FIG. 2 is a flow chart of a method for calculating the structural strength of a foundation brace of a three-upright floating wind turbine according to the present invention;
FIG. 3a is a schematic diagram illustrating a wave force applied to a base of a wind turbine under a first dangerous condition selected in step one of the present invention;
FIG. 3b is a schematic diagram of waveforms under a first dangerous condition selected in step one of the present invention;
FIG. 4a is a schematic diagram illustrating a wave force applied to a base of a wind turbine in a second dangerous condition selected according to the first step of the present invention;
FIG. 4b is a schematic diagram of a waveform under a second dangerous condition selected in step one of the present invention;
FIG. 5a is a schematic diagram illustrating a wave force applied to a base of a wind turbine under a third dangerous condition selected in step one of the present invention;
FIG. 5b is a schematic diagram of a waveform under a third dangerous condition selected in step one of the present invention;
FIG. 6a is a schematic diagram illustrating a wave force applied to a base of a wind turbine under a fourth dangerous condition selected in the first step of the present invention;
FIG. 6b is a schematic diagram of a waveform under a fourth dangerous condition selected in the first step of the present invention;
FIG. 7 is a schematic view of a beam system structural model of the wind turbine foundation built in step four of the present invention;
FIG. 8 is a schematic diagram of boundary conditions imposed on a beam system structure model at step five of the present invention;
FIG. 9 is a schematic diagram of a finite element model obtained after step six of the present invention.
Detailed Description
The invention will be further explained with reference to the drawings.
The invention discloses a method for calculating the structural strength of a strut of a three-upright-column floating type fan foundation, which is applicable to the three-upright-column floating type fan foundation and comprises a first upright column 11, a second upright column 12 and a third upright column 13 which are arranged at three corners of an equilateral triangle, and three groups of struts 2 (shown in figure 1) which are correspondingly connected between the first upright column 11 and the second upright column 12, between the second upright column 12 and the third upright column 13 and between the first upright column 11 and the third upright column 13 one by one, wherein the space between the three upright columns is 160m, the diameter of each upright column is 15m, the height of each upright column is 30m, each strut is a steel round tube and is made of steel
The ultimate strength of the stay bar material is 355MPa, the total weight of the fan foundation is 7570.45t, and the draught of the upright post is 14m.
Referring to fig. 2, the method for calculating the structural strength of the foundation brace of the three-upright-column floating type wind turbine according to the present invention includes the following steps:
firstly, selecting dangerous working conditions, wherein the floating type fan foundation is subjected to waves with different directions and different wavelengths in the service period, but foundation failure or damage often occurs under the dangerous working conditions, so that the selected three-upright floating type fan foundation has four dangerous working conditions, the first dangerous working condition is a working condition with the maximum separation force at an incidence angle of 0 degree, at the moment, the first upright 11 is positioned at the crest position, and the second upright 12 and the third upright 13 are positioned between the crest and the trough, so that a group of support rods 2 connected between the second upright 12 and the third upright 13 are subjected to separation forces which are opposite to each other in the axial direction (see fig. 3a and fig. 3 b); the second dangerous working condition is a working condition with the maximum extrusion force at an incident angle of 0 degree, at the moment, the first upright post 11 is positioned at the position of a wave trough, and the second upright post 12 and the third upright post 13 are positioned between the wave trough and the wave crest, so that a group of support rods 2 connected between the second upright post 12 and the third upright post 13 are subjected to axial opposite extrusion forces (see fig. 4a and 4 b); the third dangerous working condition is a working condition with the maximum separation force at an incident angle of 30 degrees, at this time, the third upright column 13 is positioned between one wave crest and the next wave trough, and the second upright column 12 and the first upright column 11 are positioned between the wave crest and the previous wave trough, so that the group of support rods 2 connected between the third upright column 13 and the second upright column 12 and the group of support rods connected between the third upright column 13 and the first upright column 11 are subjected to the separation force at the incident angle of 30 degrees (see fig. 5a and 5 b); the fourth dangerous working condition is a working condition with the maximum extrusion force at an incident angle of 30 degrees, at this time, the third column 13 is located between one wave trough and the next wave crest, and the second column 12 and the first column 11 are located between the wave trough and the previous wave crest, so that the group of support rods 2 connected between the third column 13 and the second column 12 and the group of support rods 2 connected between the third column 13 and the first column 11 are subjected to the extrusion force at an incident angle of 30 degrees (see fig. 6a and 6 b);
determining wave parameters, determining the wavelengths under the four dangerous working conditions according to the waveforms of the four dangerous working conditions, and determining the wave periods and wave heights under the four dangerous working conditions according to a wave theoretical formula;
A. determining the wavelength, namely determining the relationship between the wavelength L and the distance B of the upright posts under the four dangerous working conditions in a one-to-one correspondence manner according to the waveforms under the four dangerous working conditions:
in the formula (1), B is the distance between the upright posts; l is 1 The wavelength under the first dangerous working condition; l is 2 The wavelength under the second dangerous working condition; l is 3 The wavelength under the third dangerous working condition; l is 4 The wavelength under the fourth dangerous working condition;
B. determining the wave period, and obtaining a wave period T formula (2) according to a linear wave theory:
in the formula (2), L is a wavelength; k is the number of waves,
d is the water depth, and is taken to be 50m;
C. determining the wave height, and calculating the wave height H according to a linear wave height formula (3) recommended in the maritime industry:
in the formula (3), T is a wave period; h 100 Taking 20m for the wave height of one hundred years;
according to the above formulas (1), (2) and (3), the wave parameters under four dangerous working conditions are finally formed, see the following table 1:
TABLE 1
| Working conditions | Wavelength L (m) | Wave cycle T(s) | Wave height H (m) |
| Working |
320 | 16.50 | 18.32 |
| |
320 | 16.50 | 18.32 |
| Working condition 3 | 277.13 | 14.79 | 18.01 |
| Working condition 4 | 277.13 | 14.79 | 18.01 |
Step three, load determination, wherein the size of the stay bar is far smaller than that of the upright post, and the buoyancy and the wave load borne by the stay bar are far smaller than those of the upright post, so that the invention only considers the wave load acting on the upright post; the load on the column is divided into gravity load, buoyancy load and wave load. The total weight load of the wind turbine foundation is determined according to the actual weight of the structure, and due to the size, the influence of gravity on the structural strength of the support rod is small, so that the total weight load of the wind turbine foundation is equally divided and then is only applied to the three upright columns, and due to the triangular characteristic of the three upright column foundation, the three upright columns can counteract the gravity under the action of buoyancy, so that the gravity load and the buoyancy load are not applied to the upright columns finally, and only the wave load on the upright columns needs to be determined; the diameter of an upright post of the existing three-upright-post floating type fan foundation is 15m, the wavelengths of four dangerous working conditions are 270-320 m, the upright post belongs to a small component relative to waves, the using condition of a Morrison equation is met, and the wave load is calculated by adopting the Morrison equation widely applied in ocean engineering as follows:
in the formula (4), F N Is a wave load; rho is the density of the seawater; c A For additional mass coefficient, C when the column is cylindrical A ＝1；C D For drag coefficient, C when the column is cylindrical D =1; a is the area of the cross section of the upright post; d is the diameter of the upright column; v. of&The horizontal motion acceleration of water particles; v is the horizontal movement velocity of the water particle;
obtaining the horizontal movement velocity v of water particles in the wave according to a linear wave theory:
obtaining the horizontal motion acceleration of water particles in the waves according to the linear wave theory
In the formulas (5) and (6), H is the wave height; k is the number of waves,
l is the wavelength; d is the water depth; z is the depth of the water particle; x is the direction of wave propagation; ω is the circular frequency of the wave; t is time;
the wave loads on the first column 11, the second column 12 and the third column 13 under four dangerous working conditions are obtained according to the formulas (4), (5) and (6), and refer to the following table 2
TABLE 2
Step four, building a structural model, namely building a beam system structural model of the fan foundation in an ANSYS Design Modeller module; the main body structure of the fan foundation is the upright post and the stay bar, and the strength of the upright post is not considered in the invention, so that the whole model is simplified into a beam system structure model, the stay bar in the beam system structure model is endowed with an actual stay bar section, the upright post is not endowed with a section, and finally, the actual quality of each part of the fan foundation is endowed to form a complete structure model (see fig. 7);
applying boundary conditions, namely applying three vertical upward spring constraints, two wave direction horizontal displacement constraints and one horizontal displacement constraint vertical to the wave direction on the beam system structure model; namely, a vertically upward spring constraint 31 is respectively applied to the bottoms of the first upright post 11, the second upright post 12 and the third upright post 13, a wave direction horizontal displacement constraint 32 is respectively applied to the bottom of the first upright post 11 and the bottom of the third upright post 13, and a horizontal displacement constraint 33 (see fig. 8) which is perpendicular to the wave direction is applied to the bottom of the first upright post 11; the rigidity of the spring is equivalent to the water buoyancy load, and the rigidity K of the spring s The calculation formula (7) is as follows:
in the formula (7), rho is the density of the seawater; d is the diameter of the upright column; g is the gravity acceleration coefficient of 9.8N/Kg; calculating to obtain the rigidity K of the spring s ＝1.77×10 6 N/m。
Dispersing model finite elements, and carrying out finite element dispersion on the beam system model in an ANSYS Static Structural module to disperse the beam system Structural model into a finite element model of a one-dimensional grid, wherein the size of the grid is determined according to the precision required by calculation (see figure 9);
step seven, load application, namely applying the wave load determined in the step three in a finite element model, wherein the direction of the wave load is determined by the waveforms of the four dangerous working conditions, and the wave load is applied to the centroid of the draught part of the upright column in a point load manner;
step eight, performing Static analysis, namely performing Static analysis on the finite element model applied with the wave load and the boundary condition in an ANSYS Static Structural module to obtain four kinds of finite element modelsMaximum axial compressive stress sigma of stay bar under dangerous working condition dc And maximum combined stress σ mc With particular reference to table 3 below,
TABLE 3
Step nine, checking the strength, namely checking the yield strength of the stay bar material and the maximum combined stress sigma of the stay bar mc Checking the buckling strength of the stay bar material and the maximum axial compressive stress sigma of the stay bar dc Checking and judging whether the structural strength of the stay bar is enough or not;
A. when the yield strength is checked, the allowable yield stress [ sigma ] of the stay bar is determined according to the following formula s ]：
[σ s ]＝σ s /S s
Wherein σ s The yield strength of the stay bar material is MPa; s. the s Taking 1.25 as the yield safety coefficient of the stay bar material;
to obtain [ sigma ] s ]＝284
Combining the yield strength of the strut material with the maximum combined stress σ of the strut mc Checking the maximum combined stress sigma of the stay bar mc =48.26 less than allowable yield stress [ sigma ] of brace rod s ]=284, i.e. sigma mc ＜[σ s ]；
B. When the buckling strength is checked, the allowable buckling stress [ sigma ] of the stay bar is determined according to the following formula cr ]：
[σ cr ]＝σ cr /S cr
Wherein σ cr The buckling strength of the stay bar material is MPa; s cr The buckling safety factor of the stay bar material.
Buckling strength sigma of compression bar material cr Calculated as follows:
in formula (8): sigma E Is a measure of the euler stress, MPa,
l is the unsupported length of the rod piece; r is the radius of the rotational inertia of the cross section corresponding to the unsupported length l of the rod; k is an equivalent length coefficient and is taken as 0.65; e is the Young's modulus of the strut material;
to obtain [ sigma ] cr ]＝83.04
The buckling strength of the stay bar material and the maximum axial compressive stress sigma of the stay bar dc Checking the maximum axial compressive stress sigma of the stay bar dc =47.44 allowable buckling stress [ sigma ] of stay cr ]=83.04, i.e. σ dc ＜[σ cr ]；
In summary, the maximum combined stress σ of the struts mc Less than allowable yield stress [ sigma ] of brace rod s ]I.e. sigma mc ＜[σ s ]While maximum axial compressive stress σ of the strut dc Allowable buckling stress [ sigma ] less than that of stay cr ]I.e. sigma dc ＜[σ cr ]The structural strength of the stay is sufficient.
The above embodiments are provided only for illustrating the present invention and not for limiting the present invention, and those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, therefore all equivalent technical solutions should also fall into the scope of the present invention, and should be defined by the claims.
Claims (6)
1. A method for calculating structural strength of a foundation stay bar of a three-upright-column floating type wind turbine is characterized by comprising the following steps:
selecting dangerous working conditions, namely selecting four dangerous working conditions and corresponding waveforms, wherein the fan foundation is easy to lose efficacy or damage;
determining wave parameters, determining the wavelengths under the four dangerous working conditions according to the waveforms of the four dangerous working conditions, and determining the wave periods and wave heights under the four dangerous working conditions according to a wave theoretical formula;
determining load, namely determining the wave load on three stand columns of the fan foundation;
step four, building a structural model, namely building a beam system structural model of the fan foundation in an ANSYDSSign Modeller module;
applying boundary conditions, namely applying six boundary conditions on the beam system structure model, namely three vertically upward spring constraints, two wave direction horizontal displacement constraints and one horizontal displacement constraint vertical to the wave direction;
carrying out finite element dispersion on the beam system structure model in an ANSYS Static Structural module to form a finite element model of a one-dimensional grid;
step seven, load application, namely applying wave load in the finite element model, wherein the direction of the wave load is determined by the waveforms of the four dangerous working conditions, and the wave load is applied to the centroid of the draught part of the upright column in the form of point load;
step eight, performing statics analysis, namely developing the statics analysis in an ANSYS Static Structural module to obtain the maximum axial compressive stress sigma of the stay rod under four dangerous working conditions dc And maximum combined stress sigma of the stay mc ；
Step nine, checking the strength, namely checking the yield strength of the stay bar material and the maximum combined stress sigma of the stay bar mc Checking the buckling strength of the stay bar material and the maximum axial compressive stress sigma of the stay bar dc Checking is carried out, and whether the structural strength of the stay bar is enough or not is judged.
2. The method for calculating the structural strength of the foundation stay bar of the three-upright-column floating type fan according to claim 1, wherein in the step one, the selected first dangerous working condition is the working condition with the maximum separation force at the incident angle of 0 degrees, the selected second dangerous working condition is the working condition with the maximum extrusion force at the incident angle of 0 degrees, the selected third dangerous working condition is the working condition with the maximum separation force at the incident angle of 30 degrees, and the selected fourth dangerous working condition is the working condition with the maximum extrusion force at the incident angle of 30 degrees.
3. The method for calculating the structural strength of the foundation stay bar of the three-upright floating type wind turbine according to claim 1, wherein the second step is performed by:
A. determining the wavelength, namely determining the relationship between the wavelength L and the distance B of the upright column under the four dangerous working conditions in a one-to-one correspondence manner according to the waveforms under the four dangerous working conditions:
in the formula (1), L 1 The wavelength under the first dangerous working condition; l is 2 The wavelength under the second dangerous working condition; l is 3 The wavelength under the third dangerous working condition; l is a radical of an alcohol 4 The wavelength under the fourth dangerous working condition; b is the distance between the upright posts;
B. determining the wave period, and obtaining a wave period T formula according to a linear wave theory:
in the formula (2), L is a wavelength; k is the number of waves and is the number of waves,
d is the water depth;
C. determining the wave height, and calculating the wave height H according to a linear wave height formula (3):
in the formula (3), T is a wave period; h 100 The wave height is one hundred years.
4. The method for calculating the structural strength of the foundation stay bar of the three-upright-column floating type wind turbine according to claim 1, wherein in the third step, the Morison equation is used for calculating the wave load as follows:
in the formula (4), F N Is a wave load; rho is the density of the seawater; c A For adding mass coefficient, C when the column is cylindrical A ＝1；C D For drag coefficient, C when the column is cylindrical D =1; a is the area of the cross section of the upright post; d is the diameter of the upright column; v. of&The horizontal motion acceleration of water particles; v is the horizontal movement velocity of the water particle;
obtaining the horizontal movement velocity v of water particles in the waves according to a linear wave theory:
obtaining the horizontal motion acceleration v &ofwater particle in the wave according to the linear wave theory:
in the formulas (5) and (6), H is the wave height; k is the number of waves,
l is the wavelength; d is the water depth; z is the depth of the water particle; x is the direction of wave propagation; ω is the circular frequency of the wave; t is time.
5. The method for calculating the structural strength of the foundation stay bar of the three-upright-column floating type wind turbine according to claim 1, wherein in the step five, the set spring stiffness constrained by the spring is equivalent to the water buoyancy load, and the spring stiffness K is equal to the water buoyancy load s The calculation formula of (c) is as follows:
in the formula (7), rho is the density of the seawater; d is the diameter of the upright column; g is the gravity acceleration coefficient of 9.8N/Kg.
6. The method for calculating the structural strength of the foundation stay bar of the three-upright floating type wind turbine according to claim 1, wherein the ninth step is performed by:
A. checking the yield strength, and determining the allowable yield stress [ sigma ] of the stay bar by the following formula s ]：
[σ s ]＝σ s /S s
Wherein σ s The yield strength of the stay bar material is MPa; s s The yield safety factor of the stay bar material;
B. the buckling strength is checked, and the allowable buckling stress [ sigma ] of the stay bar is determined according to the following formula cr ]：
[σ cr ]＝σ cr /S cr
Wherein σ cr The buckling strength of the stay bar material is MPa; s cr The buckling safety factor of the stay bar material.
Buckling strength sigma of compression bar material cr Calculated as follows:
in formula (8): sigma E The tensile stress is the Euler stress, MPa,
l is the unsupported length of the rod piece; r is the radius of inertia of the cross section corresponding to the unsupported length l of the rod; k is an equivalent length coefficient; e is the Young's modulus of the strut material;
when maximum combined stress σ of the strut mc Less than allowable yield stress [ sigma ] of brace rod s ]I.e. sigma mc ＜[σ s ]While the maximum axial compressive stress σ of the strut dc Allowable buckling stress [ sigma ] smaller than that of the stay cr ]I.e. sigma dc ＜[σ cr ]The structural strength of the strut may be sufficient.
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