Method for predicting vortex-induced vibration distributed load of steel pipe member of power transmission tower

Abstract

The application discloses a kind of power transmission tower steel pipe component vortex-induced vibration distribution load prediction method, first need according to the measured parameter calculation steel pipe component's natural frequency and midspan amplitude;Again, the vibration displacement amplitude of steel pipe component along the length of rod distribution is determined by the mode shape curve of steel pipe component;Finally, based on forced vibration method, CFD numerical simulation is carried out, and the data set of aerodynamic force coefficient-time history is obtained, and the second-order fitting formula of aerodynamic force coefficient is established according to these data sets;From this, the aerodynamic lift can be obtained.The vortex-induced vibration load of steel pipe component is directly represented by the aerodynamic lift.The significant effect of the application is that the vortex-induced vibration load of steel pipe component can be quickly, directly and relatively accurately quantified and predicted, thereby providing key load sources and data support for fatigue life calculation and reliability analysis of steel pipe component.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power transmission, in particular to a method for predicting wind load of a power transmission tower member. BACKGROUND

[0002] In order to better solve the imbalance between resource distribution and demand in China, in recent years, a large number of long-distance high-capacity ultra-high voltage transmission lines have been constructed, which has opened the era of China's large power grid.

[0003] Compared with angle steel towers, steel tube towers have small wind pressure on components, large stiffness, simple structure, clear force transmission, can fully exert the bearing capacity of materials, and have economic and technical advantages. Therefore, steel tube towers are more suitable for the development trend of large load and large transmission towers, and are widely used in ultra-high voltage transmission lines. However, through investigation, it is found that the main problem restricting the application of steel tube towers is the vortex-induced vibration problem of components.

[0004] In July 2017, it was found that some members near the legs of a steel tube tower in a certain ultra-high voltage AC line project had strong vortex-induced vibration phenomenon; combined with the investigation of weather along the line and the vibration situation on site, it was found that the front of the tower leg, the V-surface inclined material, the horizontal transverse material of the tower leg, the inclined material above the tower leg (1-2 intervals of positive and negative K) and other parts (such as Figure 1

[0005] In April 2019, the node plate at the same position of a 21-base steel tube tower in a certain ultra-high voltage AC project in Puyang, Henan Province, appeared cracks, the cracked plate was located at the horizontal transverse surface of the tower body, the cracks extended from the weld end to both sides, and the cracks were in a straight line, as shown in Figure 2 and Figure 3 The preliminary investigation of the cause of the plate cracking is that the action of welding residual stress and the possible installation error cause the stress concentration at the weld end to be aggravated, combined with the vortex-induced vibration of the suspender, which causes the initial fatigue cracks of the plate at the stress concentration position, and finally leads to the cracking of the plate.

[0006] ​The steel pipe tower structure components are connected by flange bolts, if the steel pipe components continuously vibrate, the connection is easily loosened and the components are easily damaged by fatigue, meanwhile, due to the vibration coupling effect of the tower and the ground wire, the high frequency vibration of the steel pipe components at the hanging point position will resonate with the high order vibration of the ground wire, which affects the damping effect of the ground wire damper. The high frequency vibration of the components which are horizontal or close to horizontal and may be climbed by the maintenance workers will also cause the workers' physical discomfort. The vortex-induced vibration of the steel pipe tower oblique members and cross members will affect the safety of the whole power transmission line and the surrounding area, and once a serious failure occurs, it will cause immeasurable damage to people's life and property. However, due to the lack of vortex-induced vibration theory and experimental research support of the steel pipe tower, the domestic specification is relatively vague on the vortex-induced vibration problem, there is no corresponding calculation formula for operation, and the designer can only reduce the slenderness ratio of the rod to increase the wind speed to avoid possible vortex-induced vibration, which will inevitably cause waste of materials, and whether it is reasonable still needs to be discussed. SUMMARY

[0007] The vortex-induced vibration is the main cause of the fatigue failure of the steel pipe components of the power transmission tower, and is one of the "neck" problems restricting the further popularization and application of the steel pipe tower. In view of this, the purpose of the present application is to provide a method for determining the vortex-induced vibration load of the steel pipe component, so as to fill the gap in the current relevant specification that there is no method for determining the vortex-induced vibration distribution load. The method of the present application can provide accurate load source and data support for the fatigue life calculation and reliability analysis of the steel pipe component.

[0008] The main technical scheme adopted is as follows:

[0009] A vortex-induced vibration distribution load prediction method for steel pipe components of a power transmission tower, the key of which lies in the following steps:

[0010] Step 1, measuring parameters, calculating the natural frequency f of the steel pipe component according to formula (1);

[0011]

[0012] Wherein:

[0013] λ is the slenderness ratio of the steel pipe component;

[0014] D is the outer diameter of the steel pipe component;

[0015] d is the inner diameter of the steel pipe component;

[0016] Step 2, predicting the mid-span amplitude A of the steel pipe component according to the following formula (2);

[0017]

[0018] Wherein:

[0019] γ is the modal parameter;

[0020] p a is the density of air;

[0021] p s is the density of the steel tube member;

[0022] E is the elastic modulus;

[0023] St is the Stroganov number;

[0024] c is the damping length;

[0025] L is the length of the steel tube member;

[0026] Step three, the vibration displacement A(x i ) of the steel tube member along the length of the rod is determined according to formula (3) through the mode shape curve of the steel tube member;

[0027]

[0028] wherein:

[0029] is the curve function of the normalized mode shape;

[0030] Step four, CFD numerical simulation is performed based on the forced vibration method to obtain a data set of the aerodynamic force coefficient-time history of the steel tube member under the conditions of vibration displacement A(x i ), and frequency f;

[0031] Step five, a second-order fitting formula of the aerodynamic force coefficient C L (A, f, x) with respect to the natural frequency f, the mid-span amplitude A, and the position x is established based on the above data set;

[0032] C L (A, f, x) = β(1) + β(2)·x + β(3)·A + β(4)·f

[0033] + β(5)·x 2 + β(6)·A 2 + β(7)·f 2 , formula (4);

[0034] wherein:

[0035] β(1), β(2), β(3), β(4), β(5), β(6), β(7) are parameters of each term, which are obtained by fitting;

[0036] Step six, the aerodynamic lift F L (A, f, x) of the steel tube member is calculated according to formula (5);

[0037]

[0038] wherein:

[0039] v is the actual wind speed;

[0040] The vortex-induced vibration load of the steel pipe member is characterized by the aerodynamic lift, i.e., vortex-induced vibration load = aerodynamic lift. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 is a schematic diagram of the position of the member prone to vortex-induced vibration on the tower;

[0042] Figure 2 is a schematic diagram of the vortex-induced fatigue crack position of the node plate of the tower body cross section;

[0043] Figure 3 is a detailed diagram of the vortex-induced fatigue crack of the node plate in Figure 2

[0044] Figure 4 is a flowchart of the present application;

[0045] Figure 5 is a schematic diagram of the segmented calculation of the aerodynamic lift;

[0046] Figure 6 is an F L (8Hz)-x scatter plot;

[0047] Figure 7 is an F L (10Hz)-x scatter plot;

[0048] Figure 8 is an F L (12Hz)-x scatter plot;

[0049] Figure 9 is a comparison diagram of the predicted value and the true value of the aerodynamic lift. DETAILED DESCRIPTION

[0050] The present application is further described below in conjunction with the embodiments and the accompanying drawings.

[0051] As shown in Figure 4 , a vortex-induced vibration load prediction method for a steel pipe member of a power transmission tower, taking the center line point of one end of the steel pipe member as the origin, taking the center line in the length direction of the steel pipe member as the x-axis direction, and taking the direction perpendicular to the length of the steel pipe member as the y-axis direction;

[0052] The following steps are taken:

[0053] Step 1, measure the parameters, and calculate the natural frequency f of the steel pipe member according to formula (1);

[0054] ​

[0055] wherein:

[0056] λ is the slenderness ratio of the steel tube member;

[0057] D is the outer diameter of the steel tube member;

[0058] d is the inner diameter of the steel tube member;

[0059] Step two, predict the mid-span amplitude A of the steel tube member according to the following formula (2);

[0060]

[0061] wherein:

[0062] γ is the modal parameter, and for a single plug plate and a C-shaped plug plate, it is 1.27;

[0063] ρ a is the air density, and in the embodiment, it is 1.225 kg / m 3 ;

[0064] ρ s is the density of the steel tube member, and in the embodiment, it is 7850 kg / m 3 ;

[0065] E is the elastic modulus, and in the embodiment, it is 2.06 GPa;

[0066] St is the Stroganov number, and in the embodiment, it is 0.2;

[0067] c is the damping length, and for a C-shaped plug plate, it is 5.79 kg / s 2 ;

[0068] L is the length of the steel tube member;

[0069] Step three, determine the vibration displacement A(x i ) of the steel tube member along the length of the rod according to formula (3) through the mode shape curve of the steel tube member;

[0070]

[0071] wherein:

[0072] is the curve function of the normalized mode shape;

[0073]

[0074] Step four, perform CFD numerical simulation based on the forced vibration method to obtain the data set of the aerodynamic force coefficient-time history of the steel tube member under the conditions of vibration displacement A(x i ) and frequency f.

[0075] Step five, based on the above data set to establish the aerodynamic force coefficient C L (A, f, x) about the natural frequency f, the cross amplitude A and the second order fitting formula at the position x;

[0076] C L (A, f, x) = β (1) + β (2) x + β (3) A + β (4) f

[0077] + β (5) x 2 + β (6) A 2 + β (7) f 2 , formula (4);

[0078] Step six, according to formula (5) to calculate the aerodynamic lift F of the steel pipe member L (A, f, x);

[0079]

[0080] Wherein:

[0081] v is the actual wind speed, v = fD / St;

[0082] x is the position of the calculation point in the length direction of the steel pipe member, that is, the x-axis coordinate of the calculation point;

[0083] The vortex-induced vibration load of the steel pipe member is characterized by the aerodynamic lift.

[0084] Test example:

[0085] In practical application, when the geometric size of the steel pipe member is within a certain range, the natural frequency and the cross amplitude are relatively close, and the following steel pipes are available:

[0086] The slenderness ratio is 140-180, the outer diameter is 60-127mm, the wall thickness is 3-4mm, and the length is 2.7-6.9m;

[0087] According to formula (1), the natural frequency is 8Hz-20Hz;

[0088] According to formula (2), the cross amplitude is 1-5mm;

[0089] According to the above scheme, the parameters in formula (4) are fitted to be: β (1) = 1.3070; β (2) = 0.6156; β (3) = 0.0380; β (4) = 0.0682; β (5) = -0.6527; β (6) = -0.0021; β (7) = 0.0019.

[0090] Taking several typical working conditions (self-vibration frequency: 8 Hz, 10 Hz, 12 Hz; mid-span amplitude: 2 mm) as examples, the aerodynamic lift of the steel pipe member is calculated according to formula (5).

[0091] Since the amplitude of the steel pipe member is symmetrical about the mid-span when vibrating, the aerodynamic lift of any half thereof can be calculated; more specifically, the portion between the origin of the steel pipe member and the mid-span is divided into five equal parts, obtaining six calculation points (Y1, Y2, Y3, Y4, Y5, Y6), as shown in Figure 5 The aerodynamic lift (F1, F2, F3, F4, F5, F6) of each point is calculated respectively. The corresponding relationship between the aerodynamic lift prediction value F L and the x-axis position under different frequencies is plotted, namely: F L (8 Hz)-x scatter plot, F L (10 Hz)-x scatter plot, F L (12 Hz)-x scatter plot, and compared with the respective CFD simulation results, as shown in Figure 6 , 7 , 8.

[0092] As can be seen from Figure 6 , 7 , 8, the aerodynamic lift calculated by the above method is consistent with the CFD simulation results, and can better predict the lift coefficient of the steel pipe member under typical working conditions.

[0093] After more extensive calculation, a number of aerodynamic lift prediction values are obtained, and the prediction values are compared with the corresponding true values, as shown in Figure 9 The determination coefficient R 2 = 0.8608 is calculated. As can be seen from Figure 9 , the prediction result has a smaller dispersion type and has good applicability, and thus can effectively predict the vortex-induced vibration load of the steel pipe member at any amplitude, frequency and position.

[0094] Beneficial effects: The method of the present application can quickly, directly and relatively accurately quantify and predict the vortex-induced vibration load of the steel pipe member, thereby providing key load sources and data support for fatigue life calculation and reliability analysis of the steel pipe member.

[0095] Finally, it should be noted that the above description is only for the preferred embodiments of the present application, and those skilled in the art can make various similar modifications under the inspiration of the present application without departing from the purpose and scope of the present application. Such modifications fall within the scope of the present application.

Claims

1. A method for predicting the distributed load of vortex-induced vibration in steel pipe components of transmission towers, characterized in that... Follow these steps: Step 1: Measure the parameters and calculate the natural frequency f of the steel pipe component according to formula (1); in: λ is the slenderness ratio of the steel pipe member; D is the outer diameter of the steel pipe component; d is the inner diameter of the steel pipe component; Step 2: Predict the mid-span amplitude A of the steel pipe member according to the following formula (2); in: γ is the modal parameter; ρ a air density; ρ s The density of the steel pipe component; E is the elastic modulus; St is the Storoha number; c is the damping length; L is the length of the steel pipe component; Step 3: Using the mode shape curve of the steel pipe member, determine the vibration displacement A(x) distributed along the length of the steel pipe member according to equation (3). i ); in: The curve function for the normalized mode shape; Step 4: Perform CFD numerical simulation based on the forced vibration method to obtain the vibration displacements A(x) i A dataset of aerodynamic coefficients-time histories of steel pipe components at frequency f. Step 5: Establish the aerodynamic coefficient C based on the above dataset. L (A,f,x) is a second-order fitting formula for natural frequency f, mid-span amplitude A, and arbitrary position x. C L (A, f, x) = β(1) + β(2)·x + β(3)·A + β(4)·f + β(5)·x 2 + β(6)·A 2 + β(7)·f 2 , Equation (4); in: β(1), β(2), β(3), β(4), β(5), β(6), and β(7) are the parameters of each term, obtained by fitting. Step 6: Calculate the aerodynamic lift F of the steel pipe component according to formula (5). L (A,f,x); in: v represents the actual wind speed; The aerodynamic lift is used to characterize the vortex-induced vibration distributed load of the steel pipe component.

2. The method for predicting the vortex-induced vibration distributed load of transmission tower steel pipe components according to claim 1, characterized in that: In step three 3. The method for predicting the vortex-induced vibration distributed load of transmission tower steel pipe components according to claim 1, characterized in that: In step six, v = fD / St.

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