PSI - Issue 6

A.M. Belostotsky et al. / Procedia Structural Integrity 6 (2017) 322–329 Author name / Structural Integrity Procedia 00 (2017) 000 – 000

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4

1.2. Divergence

According to Eurocode [2], such types of dynamic instability as divergence and flutter arising if structural deformations cause variable aerodynamics loads should be excluded in principle. To be susceptible to divergence or flutter, the design must simultaneously fulfill all three conditions specified in Eurocode [2]. If all the conditions are met, it is necessary to check the investigated design for the possibility of a flutter or divergence arising from the condition:

m div V V   2

(5)

The critical wind speed for divergence is calculated using the following formula: 2 1

     

     

k

2



(6)

V





d dc

div

L







2

M



where  k - torsion stiffness of section (  k =1,2·10  d dc M - rate of change of aerodynamic moment coefficient with respect to rotation about the torsional centre; L - in wind depth (chord) ( L =11.9 m). Below, there are results of calculations performed using the software ANSYS CFX. Using the ANSYS CFX, the aerodynamic moment of the C MZ was determined at different angles of attack (Fig. 3). Further, according to the formula (6), the critical wind velocity for divergence was calculated for angles of attack. In Table 2, those angles for which the critical wind velocity does not exceed 20 2   m V m/s are marked in red. For these angles, when a corresponding wind speed is reached, a divergence may occur (Table 2). 4 Nm/rad); M c - aerodynamic moment coefficient;

Fig. 3. The graph of the dependence of the aerodynamics moment coefficients C MZ on the angle of attack α , º