# Seismic Effect of Marine Corrosion and CFRP Reinforcement on Wind Turbine Tower
## 3 Numerical Analysis of Seismic Dynamic Response
### Affect of Corrosion on Dynamic Response of Wind Turbine Tower  
The change rate of peak acceleration at the top of wind turbine tower structure is defined as APRC:  
\[\text{APRC }=\frac{\text{A}_{\text{TP}}-\text{A}_{\text{0P}}}{\text{A}_{\text{0P}}} \tag{5}\]  
Figure 12: Fourier spectrum of seismic wave: (**a**) the El Centro earthquake; (**b**) the Nihonkai-Chubu earthquake; (**c**) the Hyogoken-Nanbu earthquake. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Case Condition** & **PGA** & **HDT (m)** & **Growth Rate** & **HAT (m/s2)** & **Growth Rate** \\ \hline \multirow{2}{*}{El Centro} & 0.07 g & 0.051 & - & 0.388 & - \\  & 0.2 g & 0.120 & 136\% & 1.240 & 220\% \\  & 0.4 g & 0.244 & 378\% & 2.430 & 526\% \\ \hline \multirow{3}{*}{Nihonkai-Chubu} & 0.07 g & 0.210 & - & 1.190 & - \\  & 0.2 g & 0.493 & 135\% & 3.240 & 172\% \\  & 0.4 g & 0.988 & 370\% & 6.380 & 436\% \\ \hline \multirow{3}{*}{Hyogoken-Nanbu} & 0.07 g & 0.031 & - & 0.398 & - \\  & 0.2 g & 0.085 & 174\% & 1.432 & 260\% \\ \cline{1-1}  & 0.4 g & 0.170 & 448\% & 2.635 & 562\% \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Dynamic response of structures under different seismic records. Here: \(\rm{ATP}\) is the peak acceleration of the top of the structure under the seismic action of peak acceleration P for the structure corroded for T years; \(\rm{A_{DP}}\) is the peak acceleration of the top of the structure without corrosion under the seismic action of the peak acceleration P.  
Under the El Center earthquake, the peak acceleration at the top of the structure decreases with the increase in the service time of the structure. The peak acceleration of the top structure acceleration decreases more quickly after 10 years of service. With the increase of PGA, the peak acceleration of top structure increases first and then decreases. When PGA = 0.8\(\sim\)1.0 g, the top acceleration of the structure changes the most and then decreases gradually. Based on the analysis of Figure 13, it can be concluded that when the peak seismic acceleration reaches 1.0 g, the material stress at the top of the wind tower reaches 430 MPa, reaching the material yield state. It can be seen that the structural APRC gradually increases with the increase of PGA before the material at the top of the tower barrel yields. When the material at the top of the tower yields, the tower barrel enters the plastic state in some areas, and the structural APRC value decreases gradually. It can be seen from Figure 14 that under the Nihonkai-Chubu earthquake, the change value of structural acceleration gradually increases with the increase of PGA when PGA is less than 0.6 g. When PGA is greater than 0.6 g, the change value of structural acceleration suddenly decreases. When PGA is greater than 0.8 g, the APRC value increases gradually with the PGA value again, and decreases again when PGA is greater than 1.2 g. Figure 14 shows that when PGA exceeds 0.6 g, the material at the top of the structure yields, the material at the top of the tower barrel yields between 0.8 and 1.2 g, and the structural stress at the corroded area and bottom of the tower barrel gradually increases and approaches the material yield stress. When PGA exceeds 1.2 g, the corroded area and bottom of the structure also reach the material yield. This phenomenon further proves that the structural dynamic response changes before and after material yields during earthquakes. It can be seen from Figure 15 that under the Hyogoken-Nanbu earthquake, when the PGA is greater than 0.6 g, the APRC value increases. Compared with the El Centro earthquake, the peak acceleration of 0.8 g begins to yield because the Hyogoken-Nanbu earthquake contains the action of vertical acceleration. Since the material yield only occurs at the top of the tower, the APRC value of the structure only turns at 0.6 g.  
Figure 13: The El Centro earthquake: (**a**) structural APRC value; (**b**) maximum Mises stress.