AERODYNAMIC STABILIZING MECHANISM FOR A CABLE...
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1 BBAA VI International Colloquium on: Bluff Bodies Aerodynamics & Applications Milano, Italy, July, 20-24 2008 AERODYNAMIC STABILIZING MECHANISM FOR A CABLE STAYED BRIDGE WITH TWO EDGE BOX GIRDER Sukamta * * * * , Fumiaki Nagao † , Minoru Noda † , and Kazuyuki Muneta + * Graduate School of Engineering The University of Tokushima, Minamijosanjima, Tokushima, 770-8506, Japan e-mail: [email protected], † Department of Civil and Environmental Engineering, Institute of Technology and Science The University of Tokushima, Minamijosanjima, Tokushima, 770-8506, Japan e-mails: [email protected], [email protected] + Center of Technology, Institute of Technology and Science The University of Tokushima, Minamijosanjima, Tokushima, 770-8506, Japan e-mails: muneta@ce.tokushima-u.ac.jp Keywords: Torsional Flutter, Fairing, Flow Visualization, Unsteady Aerodynamic Forces. 1 INTRODUCTION In order to construct long span bridges economically and safely, an excellent wind resistance design is extremely demanded. Lots of aerodynamic stabilizing attachments, such as flaps, fairings, spoilers, etc. were proposed to improve the aerodynamic stability of bridge decks and their stabilizing mechanics were also clarified by experimental researches [1]. In this paper, the aerodynamic effects of fairings on the bridge deck with two edge boxes as shown in Fig. 1 were experimentally investigated. 2.85 2.30 9.85 30 / 2 C L dimension is in meter 0.66 2.40 0.25 0.08 F4415 4430 F 4445 F 4460 F 6030 F 5353 F 5237 F 44° 30° 60° 53° 52° 44° 45° 44° 60° 44° 30° 15° 53° 37° 10 10 Figure 1: Bridge deck section and fairings (mm). 2 MODEL AND EXPERIMENTAL PROCEDURES The model used here was the deck for Suramadu Bridge, which is now being constructed at East Java Island, Indonesia, and the type of main bridge is a cable stayed bridge that has main span of 434 m and two side spans of 192 m. The structural properties are shown in Table 1.
Transcript of AERODYNAMIC STABILIZING MECHANISM FOR A CABLE...
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BBAA VI International Colloquium on: Bluff Bodies Aerodynamics & Applications
Milano, Italy, July, 20-24 2008
AERODYNAMIC STABILIZING MECHANISM FOR A CABLE STAYED BRIDGE WITH TWO EDGE BOX GIRDER
Sukamta∗∗∗∗, Fumiaki Nagao†, Minoru Noda†, and Kazuyuki Muneta+
∗Graduate School of Engineering The University of Tokushima, Minamijosanjima, Tokushima, 770-8506, Japan
e-mail: [email protected],
† Department of Civil and Environmental Engineering, Institute of Technology and Science The University of Tokushima, Minamijosanjima, Tokushima, 770-8506, Japan
e-mails: [email protected], [email protected]
+ Center of Technology, Institute of Technology and Science The University of Tokushima, Minamijosanjima, Tokushima, 770-8506, Japan
e-mails: [email protected]
Keywords: Torsional Flutter, Fairing, Flow Visualization, Unsteady Aerodynamic Forces.
1 INTRODUCTION
In order to construct long span bridges economically and safely, an excellent wind resistance design is extremely demanded. Lots of aerodynamic stabilizing attachments, such as flaps, fairings, spoilers, etc. were proposed to improve the aerodynamic stability of bridge decks and their stabilizing mechanics were also clarified by experimental researches [1].
In this paper, the aerodynamic effects of fairings on the bridge deck with two edge boxes as shown in Fig. 1 were experimentally investigated.
2.85 2.30 9.85
30 / 2
CL
dimension is in meter
0.6
62.4
0
0.2
50.0
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F4415 4430F 4445F 4460F
6030F 5353F 5237F
44°
30°
60° 53° 52°
44°
45°
44°
60°
44°
30°15°
53°37°
10
10
Figure 1: Bridge deck section and fairings (mm).
2 MODEL AND EXPERIMENTAL PROCEDURES
The model used here was the deck for Suramadu Bridge, which is now being constructed at East Java Island, Indonesia, and the type of main bridge is a cable stayed bridge that has main span of 434 m and two side spans of 192 m. The structural properties are shown in Table 1.
Sukamta, F. Nagao, M. Noda and K. Muneta
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The measurement of the aerodynamic responses of bending and torsional modes for sectional model was carried out in uniform flow, where the angle of attack α = 3°. As shown in Fig. 1, first two digits of fairing name is the angle of elevation of lower surface and last two digits expresses that of depression of upper surface. The smoke wire method was used to visualize the flow surrounding the model under going forced vibration. Furthermore, unsteady aerodynamic forces and pressures were obtained by forced oscillation method.
model Properties prototype
required measured width (m) 30 0.353 0.35 depth (m) 3.064 0.042 0.04 equivalent mass (kg/m) 35,212 4.873 4.958 mass of moment inertia (kg m2/m) 2,097,466 0.040 0.039 bending natural frequency fη (Hz) 0.39 3.596 2.977 torsional natural frequency fθ (Hz) 0.54 4.979 4.094 Frequency ratio fθ/ fη 1.385 1.385 1.375 Logarithmic damping δφ (2φ = 1o), δφ (2φ = 2o) 0.008, 0.012 Logarithmic damping δη (2η/B = 0.03) 0.009
Table 1: Structural properties of prototype and model.
3 RESULTS AND DISCUSSIONS
3.1 Aerodynamic responses
For all sections tested here, aerodynamic properties of bending mode were quite stable. Fig. 2(a) shows the chart of double torsional amplitudes, 2φ, to reduced wind velocity,
U/fB. For the basic section, WOF, vortex induced oscillation and torsional flutter were observed. However, for the prototype bridge, the vortex induced oscillation should be disappeared due to large logarithmic damping. Referring to this figure, the flutter speeds for F4430, F6044 and F5237 were as high as 30% of that of WOF.
The effect of the nondimensional height of fairing tip, He/Hf, on flutter speed was summarized in Fig.2 (b). For this cross section, the flutter speed has a sharp peak around He/Hf=0.62.
0
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0 1 2 3 4 5 6U/fB
2 φ ( o )
WOFF 4430F 4460F 6044WOHF 4415F 4445F 6030F 3044F 5237F 5353
3.03.23.43.63.84.04.24.44.64.85.0
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
He/Hf
U/fB
Up
(ms-1)10 40 50 60 70 8020 30
Hf He
Figure 2: Responses at α= 3o (a) and (b) Flutter speed vs. Ratio of fairing tip height to the depth of fairing.
Sukamta, F. Nagao, M. Noda and K. Muneta
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3.2 Flow properties around deck
Fig. 3 shows the instantaneous flows around the model for one cycle of torsional motion of 2φ=2°, under α=3°, U/fB=3, 4, 5 for WOF and the flows at rest entitled “no oscillation”, where the angle of attack is the same with the instantaneous angle of attack for each phase, respectively. The circular arrow in these figures indicates the most outside point where two adjacent smoke lines unified. L is the distance from the leading edge to the circular arrow. H is the representative depth of the separation bubble measured at the point of 0.4B from the leading edge. Referring to these figures with some fairings, the separation flow below the model for all conditions is very similar, because the separation flow below the model is controlled by the edge of the box girder. Therefore, the fairing hardly affects the flow below the model. The separation flow above the model is modified by the attachment of fairings.
Fig. 4 shows the L/B and H/B averaged for one cycle of the motion for WOF, F4430, F4460, and F6044, respectively. H/B decreased in the order of WOF, F4460, F6044 and F4430, and L/B increased in the same order. Moreover, the ratio L/B decreased with increase of the reduced wind velocity, on the other hand, the ratio H/B increased in proportion to the reduced wind velocity. Therefore, for the aerodynamic unstable condition, L/B and H/B became shorter and higher, respectively. In other words, the decrease of L/B and the increase of H/B indicate the increase of separation strength. It is considered that the behaviors of L/B and H/B reflect the flutter instability of the deck. It also shows good agreement with the results of the aerodynamic response. For the lack of the space, it is not shown here; however, it is also coincident with those of unsteady aerodynamic forces as pointed out by Matsumoto et al [2].
NO : No osc illa t ion
0.150
0.1550.1600.165
0.170
0.1750.180
0.1850.1900.195
0.200
2 3 4 5 6 7
U/fB
H/B
WO F
F 4430
F 4460
F 6044
NO . WO F
NO . F 4430
NO . F 4460
NO . F 6044
NO : No osc illa t ion
0.200
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U/fB
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WOF
F 4430
F 4460
F 6044
NO. WO F
NO. F4430
NO. F 4460
NO. F 6044
Figure 4: Ratio H/B and L/H to reduced wind velocity.
4 CONCLUSIONS
• The fairing does not affect the flow below the model.
• The fairing controls the flow above the model.
• The effective fairing reduced the strength of separation flow above the model and increased the aerodynamic stability.
REFERENCES
[1] F. Nagao et al, Aerodynamic efficiency of triangular fairing on box girder bridge. Journal of Wind Engineering and Industrial Aerodynamics, 49, 565-574, 1993.
[2] M. Matsumoto et al, Torsional flutter of bluff bodies. Journal of Wind Engineering and Industrial Aerodynamics, 69-71, 871–882, 1997.
Sukamta, F. Nagao, M. Noda and K. Muneta
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no oscillation U/fB = 3 U/fB = 4 U/fB = 5
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Figure 6 Instantaneous flows around WOF
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45
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H/B = 0.181 H/B = 0.185 H/B = 0.188
L/B = 0.357 L/B = 0.288 L/B = 0.226
L
B
H
H/B = 0.168
L/B = 0.450
Figure 3: Instantaneous flows around basic section (WOF)
