CN109915327B - Method for determining natural frequency of reinforced concrete-steel combined fan tower - Google Patents

Method for determining natural frequency of reinforced concrete-steel combined fan tower Download PDF

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CN109915327B
CN109915327B CN201910312180.XA CN201910312180A CN109915327B CN 109915327 B CN109915327 B CN 109915327B CN 201910312180 A CN201910312180 A CN 201910312180A CN 109915327 B CN109915327 B CN 109915327B
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natural frequency
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文锋
杨帆
吴守城
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Shanghai Electric Power Design Institute Co Ltd
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Abstract

The invention discloses a method for determining the natural frequency of a reinforced concrete-steel combined fan tower, which comprises the following steps: step A. determining the bottom of a reinforced concrete towerRadius r of cylindrical wall1Top cylinder wall outer radius r2And the total height h of the reinforced concrete tower1(ii) a Step B, determining the excircle radius r of the cylinder wall at the bottom of the steel tower3Top cylinder wall outer radius r4And total height h of the steel tower2(ii) a C, calculating the equivalent wall thickness t of the tower: equivalent wall thickness t of reinforced concrete tower1Equivalent wall thickness t of steel tower2(ii) a D, determining the total mass m of the fan equipment at the top of the combined fan tower; step E, when the reinforced concrete tower is made of reinforced concrete, determining that the elastic modulus of the material is Ec(ii) a When the steel tower is made of steel, determining the elastic modulus of the material as Es(ii) a And F, calculating the natural frequency of the reinforced concrete-steel combined fan tower. The method can quickly determine the natural frequency of the fan combined tower system without modeling and has certain precision.

Description

Method for determining natural frequency of reinforced concrete-steel combined fan tower
Technical Field
The invention relates to the technical field of wind power generation, in particular to a method for determining natural frequency of a reinforced concrete-steel combined fan tower.
Background
At present, the contradiction between wind resource areas and consumption areas exists in the wind power development of China: in areas with rich wind resources, the self power demand is low, and the generated power is difficult to send out or consume on the spot; and the middle east area with large power demand has poor wind resources and belongs to the area with low wind speed. In a low-altitude area, the general wind speed is increased along with the increase of the height above the ground, and if wind power is developed in the low-wind-speed area, the wind power can be obtained by the fan by lifting the tower frame of the fan, so that the generated energy of the fan is improved. The reinforced concrete-steel tower is one of the schemes for lifting the fan tower, and is gradually applied to wind power generation projects in low wind speed areas in China at present. When the reinforced concrete-steel combined fan tower is analyzed, the natural frequency of a tower system must be analyzed, and the frequency must avoid the driving frequency of a fan, so that the natural frequency of the fan tower can be quickly calculated under the condition of the given height of the fan tower and the fan parameters, and the method has important significance for determining the specification and the size of the reinforced concrete-steel tower.
The common method for calculating the natural frequency of the reinforced concrete-steel tower is a finite element method, the obtained result has high precision, but the modeling of the reinforced concrete-steel combined fan tower in the finite element method is complex, the requirement on computer hardware is high, and the efficiency of modifying the size of the tower in a finite element model is low during the primary design, so that a method for quickly determining the natural frequency of the fan combined tower system with certain precision is needed to be found.
Disclosure of Invention
In view of the above defects in the prior art, the technical purpose of the present invention is to provide a method for determining the natural frequency of a reinforced concrete-steel combined wind turbine tower, so as to solve the problems of low modeling efficiency and high requirement on a computer in a finite element method.
In order to achieve the technical purpose, the invention provides a method for determining the natural frequency of a reinforced concrete-steel combined fan tower, which comprises the following steps:
A. determining the excircle radius r of the bottom cylinder wall of the reinforced concrete tower1Top cylinder wall outer radius r2And the total height h of the reinforced concrete tower1；
B. Determining the excircle radius r of the bottom cylinder wall of the steel tower3Top cylinder wall outer radius r4And, the total height h of the steel tower2；
C. Calculating the equivalent wall thickness t of the tower: equivalent wall thickness t of reinforced concrete tower1Equivalent wall thickness t of steel tower2；
D. Determining the total mass m of the fan equipment at the top of the combined fan tower;
E. when the reinforced concrete tower is made of reinforced concrete, determining the elastic modulus of the material as Ec(ii) a When the steel tower is made of steel, determining the elastic modulus of the material as Es；
F. The natural frequency of the reinforced concrete-steel combined fan tower is calculated according to the following formula:
Figure BDA0002031885310000021
δ＝δcF+δcM+(θcF+θcM)h2+δsF(2)
deformation of the top of the reinforced concrete tower:
Figure BDA0002031885310000022
Figure BDA0002031885310000023
Figure BDA0002031885310000024
Figure BDA0002031885310000025
Figure BDA0002031885310000026
Figure BDA0002031885310000027
Figure BDA0002031885310000028
Figure BDA0002031885310000029
deformation of the top of the steel tower relative to the reinforced concrete tower:
Figure BDA0002031885310000031
Figure BDA0002031885310000032
Figure BDA0002031885310000033
in the formulas (1) to (13), f is the natural frequency of the combined fan tower; r is the excircle radius of the tower barrel wall at the position of different height coordinates z, deltacFThe tower horizontal deflection is generated at the top of the reinforced concrete tower by unit horizontal force; deltacMThe horizontal deflection of the tower generated by unit bending moment at the top of the reinforced concrete tower; thetacFA tower corner is generated at the top of the reinforced concrete tower by unit horizontal force; thetacMThe tower corner is generated at the top of the reinforced concrete tower by unit bending moment; deltasFIs the horizontal deflection that is produced only at the steel tower section per horizontal force.
In the step A, the reinforced concrete tower is positioned at the lower section of the combined fan tower, the section of the reinforced concrete tower is circular, and the outer diameter of the section of the reinforced concrete tower along the vertical direction is linearly reduced along with the increase of the height of the tower.
And step B, arranging the steel tower on the upper section of the combined fan tower, wherein the section of the steel tower is circular, and the outer diameter of the section of the steel tower along the vertical direction is linearly reduced along with the increase of the height of the tower.
In the step C, the reinforced concrete tower or the steel tower takes a continuous tower with the same wall thickness as a segmented tower and is divided into n segments of towers in total, and the wall thickness t of the tower is based on the preset segment tower wall thickness0iTower height l corresponding to wall thicknessiEquivalent wall thickness of reinforced concrete tower or steel tower
Figure BDA0002031885310000034
The equivalent wall thickness of the reinforced concrete tower is t through calculation1The equivalent wall thickness of the steel tower is t2。
The invention has the beneficial effects that:
by adopting the steps, the natural frequency of the combined fan tower can be quickly calculated by inputting parameters such as the size, the material parameters, the fan quality and the like of the reinforced concrete-steel combined fan tower, so that whether the frequency is overlapped with the driving frequency interval of the fan or not is judged, the size and the specification of the tower structure are determined, and meanwhile, the wind load and the earthquake load acting on the combined fan tower structure can be further calculated conveniently.
Drawings
FIG. 1 is a schematic view of a reinforced concrete-steel combined wind turbine tower.
In the figure: 1-steel tower, 2-reinforced concrete tower.
Detailed Description
The conception, the specific structure and the technical effects of the present invention will be further described with reference to the accompanying drawings to fully understand the objects, the features and the effects of the present invention.
Taking a certain reinforced concrete-steel combined cylindrical tower as an example, determining the inherent frequency value f: the lower part of the combined fan tower is a reinforced concrete tower 2 with the height h160m, the upper part is a steel tower frame 1, and the height h258.5 m. The section of the reinforced concrete tower 2 is linearly reduced along the height, and the outer radius r of a bottom ring14m, top ring outer radius r22.18m, the reinforced concrete tower 2 has a uniform wall thickness t of 0.3m, and is made of C60 concrete and has an elastic modulus Ec＝3.6×1010Pa; the upper part of the combined fan tower is a steel tower 1 with a height h258.5m, the section is gradually reduced along the height, and the outer radius r of the bottom ring is32.1m, outer radius r of top ring41.5m, the steel tower 1 has uneven wall thickness distribution, see table 1, the steel material is Q345, and the elastic modulus Es＝2.06×1011Pa; the total mass of the fan system is 153000 kg.
TABLE 1 Combined wind turbine tower size table
Height (m) Tower outer diameter (m) Wall thickness (mm) Material
0 8.00 300 C60 concrete
60 4.36 300 C60 concrete
63.33 4.14 25 Q345 steel
66.11 4.08 24 Q345 steel
68.89 4.02 22 Q345 steel
74.45 3.9 20 Q345 steel
80.01 3.783 19 Q345 steel
82.79 3.723 18 Q345 steel
88.35 3.604 17 Q345 steel
93.91 3.484 16 Q345 steel
99.47 3.368 15 Q345 steel
113.37 3.071 14 Q345 steel
118.5 3.005 22 Q345 steel
Referring to fig. 1, according to the foregoing calculation method:
the first step is as follows: determining relevant parameters of the reinforced concrete tower 2:
r1＝4m，r2＝2.18m，h1＝60m；
the second step is that: determining relevant parameters of the steel tower 1:
r3＝2.1m，r4＝1.5m，h2＝58.5m；
the third step: determining the equivalent wall thickness of the tower:
uniform wall thickness of reinforced concrete tower, t1＝0.3m。
Equivalent wall thickness t of steel tower 12The calculation is as follows:
Figure BDA0002031885310000051
the fourth step: determining a mass m of a fan system
m＝153000kg
The fifth step: determining concrete and steel material parameters in combined fan tower
The reinforced concrete tower 2 adopts C60 concrete, and the elastic modulus E of the concretec＝3.6×1010Pa; the steel tower frame 1 adopts Q345 steel with the elastic modulus Es＝2.06×1011Pa。
And a sixth step: determining the natural frequency of a combined wind turbine tower
Substituting the parameters into expressions (3) to (13) to obtain deformation values:
δcF＝5.86×10-8m，δcM＝1.03×10-7m，θcF＝1.76×10-9，θcM＝4.96×10-9，δsF＝8.02×10-7m。
substituting the above results into formulas (1-2), then
δ＝δcF+δcM+(θcF+θcM)h2+δsF＝1.3568×10-6m
Figure BDA0002031885310000052
The combined wind turbine tower natural frequency calculation results in this example are compared with finite element analysis results, as shown in table 1 below.
TABLE 1 comparison table for natural frequency of combined wind turbine tower calculated by different methods
Figure BDA0002031885310000053
The finite element method is adopted to analyze the natural frequency of the combined fan tower, the precision is high, but modeling and calculation are complex, the natural frequency result obtained by calculation of the finite element method in the embodiment can be used as a reference, as can be seen from table 1, the error of the method and the finite element method is less than 5%, the method can be quickly obtained without modeling analysis, the efficiency is high, and the determination method provided by the text is feasible for the cylindrical combined fan tower with the tower section linearly reduced along the height.
The foregoing detailed description of the preferred embodiments of the invention has been presented. It should be understood that numerous modifications and variations could be devised by those skilled in the art in light of the present teachings without departing from the inventive concepts. Therefore, the technical solutions available to those skilled in the art through logic analysis, reasoning and limited experiments based on the prior art according to the concept of the present invention should be within the scope of protection defined by the claims.

Claims (4)

1. A method for determining the natural frequency of a reinforced concrete-steel combined fan tower is characterized by comprising the following steps:
A. determining the excircle radius r of the bottom cylinder wall of the reinforced concrete tower1Top cylinder wall outer radius r2And the total height h of the reinforced concrete tower1；
B. Determining the excircle radius r of the bottom cylinder wall of the steel tower3Top cylinder wall outer radius r4And total height h of the steel tower2；
C. Calculating the equivalent wall thickness t of the tower: equivalent wall thickness t of reinforced concrete tower1Equivalent wall thickness t of steel tower2；
D. Determining the total mass m of the fan equipment at the top of the combined fan tower;
E. when the reinforced concrete tower is made of reinforced concrete, determining the elastic modulus of the material as Ec(ii) a When the steel tower is made of steel, determining the elastic modulus of the material as Es；
F. The natural frequency of the reinforced concrete-steel combined fan tower is calculated according to the following formula:
Figure FDA0002392384400000011
δ＝δcF+δcM+(θcF+θcM)h2+δsF(2)
deformation of the top of the reinforced concrete tower:
Figure FDA0002392384400000012
Figure FDA0002392384400000013
Figure FDA0002392384400000014
Figure FDA0002392384400000015
Figure FDA0002392384400000016
Figure FDA0002392384400000017
Figure FDA0002392384400000018
Figure FDA0002392384400000019
deformation of the top of the steel tower relative to the reinforced concrete tower:
Figure FDA0002392384400000021
Figure FDA0002392384400000022
Figure FDA0002392384400000023
in the formulas (1) to (13), f is the natural frequency of the combined fan tower; r is the excircle radius of the tower barrel wall at the position of different height coordinates z, deltacFThe tower horizontal deflection is generated at the top of the reinforced concrete tower by unit horizontal force; deltacMThe horizontal deflection of the tower generated by unit bending moment at the top of the reinforced concrete tower; thetacFA tower corner is generated at the top of the reinforced concrete tower by unit horizontal force; thetacMThe tower corner is generated at the top of the reinforced concrete tower by unit bending moment; deltasFIs the horizontal deflection that is produced only at the steel tower section per horizontal force.
2. The method for determining the natural frequency of the reinforced concrete-steel combined blower tower is characterized in that in the step A, the reinforced concrete tower is positioned at the lower section of the combined blower tower, the section of the reinforced concrete tower is circular, and the external diameter of the section of the reinforced concrete tower in the vertical direction linearly decreases along with the increase of the height of the tower.
3. The method for determining the natural frequency of the reinforced concrete-steel combined blower tower as claimed in claim 1, wherein in the step B, the steel tower is arranged at the upper section of the combined blower tower, the section of the steel tower is circular, and the outer diameter of the section of the steel tower in the vertical direction linearly decreases along with the increase of the height of the steel tower.
4. A method as claimed in claim 1The method for determining the natural frequency of the reinforced concrete-steel combined fan tower is characterized in that in the step C, the reinforced concrete tower or the steel tower takes the tower with continuous same wall thickness as a segmented tower and is divided into n segments of towers in total, and the wall thickness t of the tower is based on the preset segment of tower wall thickness0iTower height l corresponding to wall thicknessiEquivalent wall thickness of reinforced concrete tower or steel tower
Figure FDA0002392384400000024
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