Abstract
There is an almost everlasting debate on the possibilities of the investigation tools for their applications in a prospective fashion (while solving the engineering tasks) and – against this fact – on the use of these engineering tools while correcting the existing technology problems. A unique chance to compare these needs of research in traffic intentions (while setting the modern road communications through southern Bosnia and Herzegovina) with the natural occurrences in the atmosphere (such is a strong north wind in this geographic region) offers us the highway section Pocitelj-Zvirovici. Exactly in such cases (and before the actual construction of this highway bridge) “for the sake” of prospective engineering, the CFD mechanism (the “toolkit” for performing the computational fluid dynamics) was applied to engage this atmospheric problem. Both as steady-state explorations (while applying the k-ε turbulence treatment) and as the time-dependent CFD-based mode, we explored the wind-strokes of 10 m/s, 20 m/s, 30 m/s and 40 m/s, expected but certainly unwanted strong gaseous flows over the bridge, detecting in this way the traffic safety edge points. The results coming from the explorations performed by the CFD tool are explained and discussed.
Keywords
- Traffic safety
- Highway bridge
- Wind-stroke
- CFD (computational fluid dynamics)
1. Introduction
While establishing the modern road and railway infrastructure that is not only impressive in the construction way but is also needed for accurate and important trafficking, one confronts the reality that is always surrounding such objects: the nature of our planet [1-4]. In spite of evaluations [5-8] and certain suggestions[9], every new object of traffic infrastructure that is exposed to rather strong atmospheric influences is presenting the safety risks and calls for exploring in a large-scale fashion. Such investigations, due to the ever-stronger software and hardware tools [10-12], are performed not only through the physical measuring [13] and scaled testing [14] but also more frequently by applying the CFD (computational fluid dynamics)-based approach[12]. The latter research mode [15] did find application in wind exploring [16, 17] and traffic safety [18] which is the research pathway of the work presented in this paper, offering very satisfying results accomplished in its attempts at “prospective engineering” for particular explored cases of fluid phenomena [19].
All of these research attempts that have been brought up into the CFD community do report on good capability of the numerical approaches used in handling the reactive flows in straight, enclosed traffic infrastructure. Besides the slight denivelation of a few percent, the geometry of the arbitrary objects of interest was relatively a simple one.
Therefore, the aim of the study is to explore the (accidental) wind-strokes over such a bridge that, as a segment of to-be-constructed highway, for sure turns up as an element of this modern traffic road communication and hence suggests some countermeasures serving the overall traffic safety.
2. Numerical approach
2.1. Treatment of turbulence: Mathematical model in this study
For turbulence-modelled conservation equations, for mass and momentum, employing a time-averaged
In cases where the pressure field and face mass fluxes are not known, FLUENT (the software package applied in this research attempt) uses a co-located scheme, whereby pressure and velocity are both stored at cell centres. A need for interfacial values includes an application of an interpolation scheme to compute pressure and velocity out of cell values. The integration over the arbitrary volume (a cell in a computational domain) can be performed and is discretised through an arbitrary surface of a face.
Executing these numerical steps, the equations can express the state for each other cell in the computational grid. This again will result in a set of algebraic equations with a sparse coefficient matrix. In this way, the segregated solver is handling “the updating” of a single variable field, by considering all the cells of the domain at the same time, solving the governing equations sequentially (segregated one from another). Subsequently, the next field of another variable will be solved by again considering the entire cells at the same time. The computational loop for the converged solution had about 5,500 iterations.
3. Procedure of investigation
The estimation of the boundary conditions in this CFD-based investigation was supported by the experience of some previous studies and so were the bridge surrounding space characterised as open (pressure) atmospheric boundaries with minor pressure increase or pressure drop of 2 Pa, respectively. All zones formed around the road bridge an open (pressure) boundary, which was used for initialising the values for the velocity and pressure in the computational domain, while the global temperature was set to 293 K.
The bridge body and bridge road elements as well were presumed to be nonadiabatic in the area where the objects of interest (the investigated bridge crown) are situated. This decision was based on some reality-oriented investigation on modern bridge construction, denoting the thermal conductivity of a reinforced concrete to be
3.1. The explored object of interest
The cross-section shapes of this highway viaduct are distinguished as those between the major carrier pylons. Further, the bridge crown shapes are mounted onto the “bridge legs” of this traffic steady object. Standing with the angle of ca 3.1 °, the road treks of this bridge have the bow-length of 954 m and their arch radius is 983 m. Going partly over the river bed and partly over the terrain valley, the highway bridge “Pocitelj-Zvirovici” demonstrates its highest section to be 96 m. The wide range between the six major pylons is set to 147 m.
3.2. Computational domain
The area in which the computation with applied mathematical model approach and additional numerical discretisation was performed is the very volume that a fluid can take without the “walls”, where the solid body is the shape of the explored road bridge. Therefore, the computational domain of the section “Pocitelj-Zvirovici” was set to be 30m x 22m x 14,5 m.
3.2.1. The highway bridge “Pocitelj-Zvirovici”
The mesh of this computational domain (Figs. 4 and 5) is characterised through tetrahedral cells and hexahedral prisms of a random structure. In this case, a denser grid was also applied in the area around the zones where particular mechanical fluid phenomena are expected, having so more grid points to support the major occurrences.
Such an unstructured mesh (sized here to 350 mm) was installed in such zones of whole computational domain. However, the following parts of the 954-m-long bridge are also meshed with unstructured hexahedral cells in the explained way, having subsequent increased cell size up to 400 mm, 800 mm and 1,200 mm – as the distance from the bridge bottom towards the open space was growing.
The “Pocitelj-Zvirovici” bridge body and the road elements were in the computational domain defined as nonadiabatic walls. The fluid domain is air, with the ambient conditions and no fluid movement, onto which the wind-strokes were expected. The computational fluid sides were designed as opened pressure boundaries.
4. Discussion and outlook
Consulting the meteorological survey of the State Weather Service of Bosnia and Herzegovina[25], we performed several investigation scenarios by varying computationally aided, simulative conditions of the unwanted wind-strokes: from both south and north side of the highway bridge “Pocitelj-Zvirovici”. Here (Fig. 4), we have chosen the sketch that presents CFD calculation of a (not seldom) 40 m/s stroke, from the more influencing north wind. Taken alone, this result (that was presented by the time-independent Reynolds-averaged Navier-Stokes numerical research) points up the need for a wind flow disturbing panel fences along the roadsides [26].
Even “weaker”, sudden wind occurrences (out of 10 m/s – Fig. 8) that do turn up more frequently in the roses of wind for the geographic region, where this highway viaduct is to be constructed, do present the traffic hazard for the infrastructure element in this road communication. Our investigation performed in CFD mode does correlate with modern studies [27] and does report [28] on the importance [1] of taking into account security and safety.
During this research, we were able to perform the importance of a prospective engineering approach in treating the (gaseous) fluid phenomena in a large-scale mode. In this case, the traffic safety profits out of our findings – where again those results are “pushing” towards further prospective investigations. Exactly CFD-based research obligates to continuing investigation of the mentioned highway bridge, where the whole set of interacting answers and their questions could be satisfied: by applying another turbulence treatment (while using the
The safety issue caused by atmospheric occurrences varies in different parts of Europe (let alone in various parts of the world); what is inviting or even more is it is “provoking” us to further explore on these traffic safety issues. The landscape of the geographic regions where the future (both road and rail) infrastructure is to be constructed and to them belonging particular meteorological circumstances offers a unique perspective for each of these traffic objects. Modern hardware and software [29] developments [30] in the last 20 years [31] endorsed the computational modelling [32] into the modern and very reliable CFD toolkit [29] for scientific engineering and research [33].
References
- 1.
H.K. Lorenzo Procino, G. Bartoli, A. Borsani, Wind barriers on bridges: the effect of wall porosity , inBBAA VI International Colloquium on: Bluff Bodies Aerodynamics & Applications . 2008. Milano, Italy. - 2.
D. Hembre, C. Otto, J. Payette, G. Pingree, The 50th anniversary of the Golden-Gate Bridge , inLaboratory for Construction Technology, Graduate School of Design 1988, Harward University: Cambridge, Massatchussets, USA. - 3.
P. Bowers, J. Boneck, Charleston's bridges cross troubled waters , inCharleston City Paper 2012: Charleston, South Carolina, USA. - 4.
E. Simiu, P. Vickery, A. Kareem, Relation between Saffir–Simpson hurricane scale wind speeds and peak 3-s gust speeds over open terrain. Journal of Structural Engineering, 2007. 133. - 5.
A. Greeman, Calls for wind shields after lorry falls off bridge , inNew Civil Engineer, www.nce.co.uk 2005. - 6.
Hideharu Yagi, Fumitake Yoshida, Gas absorption by newtonian and non-newtonian fluids in sparged agitated vessels. Industrial & Engineering Chemistry Process Design and Development, 1975. 14(4): p. 15. - 7.
C. Airong, Y. Qingzhong., Z. Xigang, M. Rujin, Z. Zhiyong, Aerodynamic problems of a super-long span cable-stayed bridge , inIABSE SYMPOSIUM 2005: Lisbon, Portugal. - 8.
T. Martin, I.A. MacLeod, The Tay Rail Bridge disaster revisited , inProceedings of the Institution of Civil Engineers 2004. p. 5. - 9.
D.E. Newland, Vibration of the London Millennium Footbridge: Part 1 - Cure , inDepartment of Engineering 2002, University of Cambridge: CAMBRIDGE CB2 1PZ, UK. - 10.
S. Muzaferija, D. Gosman, F inite-volume CFD procedure and adaptive error control strategy for grids of arbitrary topology. Journal of Computational Physics, 1997. 138(2). - 11.
S. Svaic, I. Boras, M. Andrassy, A numerical approach to hidden defects in thermal non-destructive testing. Journal of Mechanical Engineering, 2007. 53(3): p. 165. - 12.
L. H. Cheng, T.H. Ueng, C. W. Liu, Simulation of ventilation and fire in the underground facilities. Fire Safety Journal, 2001. 36(6): p. 597–619. - 13.
J. Modic, Porocilo o meritvah pri pozernem preizkusu v cestnem tunelu SENTVID , 2008, University in Ljubljana, Mechanical ENgineering: Ljubljana, Slovenia. - 14.
L. ZhouI, Y. Ge., Wind tunnel test for vortex-induced vibration of vehicle-bridge system section model . Journal of the Brazilian Society of Mechanical Sciences and Engineering, 2008. 30(2). - 15.
A. Kareem, Numerical simulation of wind effects: a probabilistic perspective . Journal of Wind Engineering and Industrial Aerodynamics, 2008. 96: p. 25. - 16.
T. Kijewski-Correa, e.a., Validating wind-induced response of tall buildings: synopsis of the Chicago full-scale monitoring program. Journal of Structural Engineering, 2006. 132(10). - 17.
D.-K. Kwon, T. Kijewski-Correa, A. Kareem, e-Analysis of high-rise buildings subjected to wind loads . Journal of Structural Engineering, 2008. 134: p. 1139. - 18.
X. Chen, A. Kareem, Identification of critical structural modes and flutter derivatives for predicting coupled bridge flutter. Journal of Wind Engineering and Industrial Aerodynamics, 2008. 96: p. 14. - 19.
X. Chen, A. Kareem, Revisiting multimode coupled bridge flutter: some new insights . Journal of Structural Engineering, 2006. 132(10). - 20.
http://www.fluent.com. - 21.
H. K. Versteeg, W. Malalasekera, An Introduction to Computational Fluid Dynamics , 1995, London: Longman Group Ltd. - 22.
M. Muhasilovic, M. Deville, Tunnel-curvatire´s influence on the propagation of the consequences of large-scale accidental fire - a CFD-investigation. Turkish Journal of Engineering and Environmental Sciences, 2007. 31: p. 391. - 23.
Hirsch, C., Numerical Computation of Internal and External Flows . Vol. I. 1988, Chichester Brisbane Toronto New York: John Wiley & Sons. p. 515. - 24.
M. Peric, J.H. Ferziger, Computational Methods for Fluid Mechanics , 2001, Berlin: Springer Verlag. p. 423. - 25.
http://www.fhmzbih.gov.ba/. - 26.
K. Ilic, Projekt i Izvedba Viadukta "Hreljin" na Autocesti Rijeka-Zagreb , inInzenjerski Projektni Zavod, Zagreb 2008. - 27.
H. Kozmar, L. Procino, G. Bartoli, A. Borsani, Wind barriers on bridges: effects of wind incidence angle on flow field characteristics , inThe Seventh Asia-Pacific Conference on Wind Engineering 2009: Taipei, Taiwan. - 28.
S. James, Forth Replacement Crossing Study - Windshielding on Bridge Options , 2007, Jacobs UK Ltd. - 29.
S. R. Lee, H.S. Ryou, A numerical study on smoke movement in longitudinal ventilation tunnel fires for different aspect ratio . Building and Environment, 2006. 41(6): p. 719–725. - 30.
M. Deville, A.D., COSMASE , 1996: Lausanne, Switzerland. - 31.
J. S. M. Lee, W.K. Chow., Numerical studies on performance evaluation of tunnel ventilation safety systems . Tunneling and Underground Space Technology, 2003. 18(5): p. 435–452. - 32.
S. Muzaferija, V. Seidl, A. Kneer Parallel multidimensional calculation of steady-state and time-dependent flows with combustion , inEuro-Par '97: the Third International Euro-Par Conference on Parallel Processing 1997. - 33.
C. C. Hwang, J.C. Edwards, The critical ventilation velocity in tunnel fires - a computer simulation. Fire Safety Journal, 2005. 40(3): p. 213–244.