PSI - Issue 6

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

324

3

Fig. 2. The graph of the dependence of the aerodynamic coefficients of the drag force CD and the lifting force CL on the angle of attack α , º

Table 1 The values of the aerodynamic drag coefficients C D and lift C L and the Glowrt-Den-Hartog criterion H and critical wind velocity V CG from the angle α Angle α , ° C D C L H V CG , m/s 5 1.35 2.98 -1.24 14.37 35 4.19 5.29 -3.35 2.10 55 5.56 3.79 -0.25 22.67 75 6.45 1.75 -0.18 28.27 85 6.50 0.79 -0.09 55.59 Further, from a sufficient condition, critical velocity at which galloping occurs was found. The expression for this velocity is also given in Eurocode [2] and has the form: (2) where f i - frequency of natural vibrations of i-th mode bending shape in the direction transverse to the direction of the action of the wind ( f i = 0.13 Hz); B - cross sectional width across the wind flow ( B = 2.45 m); g a - coefficient of instability at galloping, equal S H k  , where S k is assumed equal 0.9, H - the Glowrt-Den-Hartog criterion; Sc - the Skruton number: g i a Sc f B CG V     2

m

2

B     

(3)

Sc



2

1.185   kg/m 3 ); m - mass per unit length

0.03   );  - air density (

where  - logarithmic decrement (

( m =4250 kg/m). According to Eurocode [2], aerodynamics instability during galloping occurs when the wind speed reaches a value at which the oscillating process begins with an increasing amplitude.

V

V

 1.25



(4)

CG

m