# Design and analysis of the characteristics of a new vibration reduction system for an in-service long-span transmission tower

### Nonlinear finite element model

The 500 kV nonlinear finite element model ISLSTT with the new vibration reduction system for dynamic simulation is established in the finite element software ANSYS, as shown in Fig. 6. According to the geological and meteorological data of Jiamusi area of ​​Heilongjiang province in China, the design reference wind speed is 27m/s and the ground roughness index is 0.12. The values ​​of the structural parameters are as follows: height of 500 kV ISLSTT H1 is 122.0 m, height of the transom H2 is 97.0 m, height of vibration reduction system H3 is 35.0 m, width 500 kV ISLSTT B1 is 51.0 m, main chord width B2 is 23.0 m, width of vibration reduction system B3 is 45.0 m.

The stress condition is that he imposed full 6 degrees of freedom stresses at the four fulcrums at the bottom of the 500 kV ISLSTT. Since the main chord, diagonal web and cross web of the long span steel pipe tower are steel pipe structures, the beam188 element is selected for the finite element model of the steel pipe. steel, link10 is selected for the steel cable, shell181 is selected for the rectangular plate, and Q345 steel is used for the material of all steel structures.

In order to simulate the wind load on the ISLSTT 500 kV, it is assumed that the wind speed (v(z,;t)) at any height is a time variable, composed of the average wind speed and the fluctuating wind speed, i.e.:

$$v(z,;t) = overline{v}(z) + v_{d} (z,;t)$$

(1)

where (overline{v}(z)) is the average wind speed at height Z can be expressed by Davenport’s formula as follows: (overline{v}(z) = overline{v}_{10} (z/10)^{alpha })in which (overline{v}_{10}) is the average wind speed at a height of 10 m, α is the soil roughness index; (v_{d} (z,;t)) is the fluctuating wind speed at height Z.

Taking the Davenport spectral function as the power spectral density function of the fluctuating wind speed at any point in space, there is:

$$S(f) = 4Koverline{v}_{10}^{2} frac{{x^{2} }}{{f(1 + x^{2} )^{4/3} }}$$

(2)

In which, (x = 1200;f/overline{v}_{10})where F is the wind speed frequency, (Hz); K is the ground roughness coefficient.

Given the spatial correlation of the fluctuating wind speed, and according to the theory of random processes, the power spectral cross-density function of the fluctuating wind speed at any point I and I in space is:

$$S_{i,j} (f) = sqrt {S_{i,i} (f) cdot S_{j,j} (f)} coh(f)$$

(3)

where the exponential form given by Davenport is:

$$coh(f) = exp left[ { – frac{{2fsqrt {c_{y}^{2} (y_{1} – y_{2} )^{2} + c_{z}^{2} (z_{1} – z_{2} )^{2} } }}{{overline{v}(z_{1} ) + overline{v}(z_{2} )}}} right]$$

where (S_{n,n} (f)) is the power spectral density function of the fluctuating wind speed at not points in space, not= I, I ; (coh(f)) is the square root of the coherence function; vsthere and vsz are attenuation coefficients of orthogonal direction in any two-point plane; thereI and zI are the coordinates of the point Iby plane, I= 1, 2.

According to Bernoulli’s theorem, the wind load at any point in space can be expressed by the wind pressureP ( you ), as shown in formula (4):

$$P (4) where γis the apparent density of air; gis the gravitational acceleration; (mu_{s} (z)) is the shape factor at the height Z; (A(z)) is the effective area upwind at height Z. The Spectral Density MatrixS ( ω ) of ISLSTT 500 kV structure under random wind load can be obtained by combining formula (2) and formula (3). Assuming there is notthe load points on the structure, then the wind speed at any point in space can be obtained by the method of harmonic superposition of the multidimensional stationary random process:$$v_{d,j} (z,t) = 2sqrt {Delta omega } sumlimits_{m = 1}^{j} {sumlimits_{l = 1}^{N} {left| {H_{j,m} (omega_{m,l} )} right|} } cos (omega_{m,l} t + phi_{m,l} )$$(5) where,$$Delta omega = (omega_{u} – omega_{d} )/N,quad omega_{m,l} = omega_{d} + (l – 1)Delta omega + frac{m}{n}Delta omega ,quad (l = 1,;2, ldots ,;N),

(H_{j,m} (omega_{m,l} )) is the spectral density matrix, then the Cholesky decomposition method is used, i.e. ({mathbf{S}}(omega ) = {mathbf{H}}(omega ) cdot {mathbf{H}}^{*} (omega )). Where NOTis the large enough positive integer; (phi_{m,l}) is the uniformly distributed random phase angle in[02π);[02π);[02π) ;[02π);(omega_{u}) and(omega_{d}) are the upper and lower limits of the frequency band.

### Wind-induced vibration response simulation analysis

The wind pressure on the tower is calculated according to Eq. (4), the 500 kV ISLSTT is treated in sections in this article, and it is assumed that the wind pressure acts on the discrete nodes shown in Fig. 7a. The magnitude and direction of the wind speed arev( z , you ) and α as shown in Fig. 7b, in which the there direction is the connection direction of conductor and ground wire. Considering the natural mode of the steel pipe tower, when simulating the wind pressure history, the time step is 0.5s and the total duration is 6000s. When the basic wind speed is 27 m/s, the first tower section, the third tower section and the wind speed time fluctuating curves of the seventh tower section and the eleventh tower section are illustrated in Fig. 8. The central heights of each section are 8 m, 38 m, 74.1 m and 106.5 m, respectively. The accuracy of each simulated wind speed fluctuating section in this article is verified by comparing the simulated wind speed power spectrum with the Davenport power spectrum. The results of the comparison are shown in Fig. 9.