Papers by olivier flamand
Data Processing to Assess Structural Damping of Tall Timber Buildings
Lecture notes in civil engineering, 2023
The cables strategy for the Normandy Bridge
Over the last decades, aerodynamics of inclined cables has become a crucial issue with the develo... more Over the last decades, aerodynamics of inclined cables has become a crucial issue with the development of long-span cable-stayed bridges. In recent years, several phenomena at the origin of vibrations of stay-cables have been identified by full-scale observations and wind-tunnel tests. Among those, research has particularly focused on the rain-wind-induced vibration phenomenon which leads to large amplitudes with relatively moderate wind and rain. Nevertheless, wind induced vibrations of inclined cables without rain have also been reported at full scale and as results of wind-tunnel tests, for instance by Larose (2003) who introduced the idea of dry inclined cable galloping. They explained that a circular cylinder in the critical Re range shows a fast drop in the drag coefficient with increasing Re, due to reattachment of the turbulent boundary layer and formation of laminar separation bubbles, on each side of the cylinder. This paper presents a comparison between various wind tunnel measurements realized on dry circular cables at full scale with various surface roughness, opening the way to an explanation of convergence between rain-wind induced excitation and dry cable galloping. A medium size 400m span cable-stayed bridge, facing the Atlantic ocean in Brest (France) was monitored for more than 3 years. Because some of its stays, covered with smooth PE tube, were seen to be prone to vibrations, these were equipped with accelerometers. Accelerations of the deck and one pylon were also measured and the whole bridge observed by two recording video cameras. Boujard (2007) used these data for his PhD showing that few excitation processes can give rise to cable vibrations on the same bridge, among which numerous vibrations occurred without rain or icing and for a wind speed range clearly different from vortex shedding excitation. Wind direction and speed during these occurrences corresponds to the parameters reported by Larose (2003) for the dry cable galloping (figure ).
HAL (Le Centre pour la Communication Scientifique Directe), Jul 8, 2014
HAL (Le Centre pour la Communication Scientifique Directe), Aug 26, 2013
Rain-Wind Induced Vibration of Stay Cables: Experimental Results and Numerical Interpretation
International Journal of Fluid Mechanics Research, 2002
Influence of Natural Wind Turbulence on Vortex Shedding Excitation, from Real Structure Experience
å®‡å®™èˆªç©ºç ”ç©¶é–‹ç™ºæ©Ÿæ§‹ç‰¹åˆ¥è³‡æ–™ JAXA-SP-(Web), Mar 15, 2017
Vortex shedding is a broadly studied phenomenon, in the well-defined conditions of wind tunnel la... more Vortex shedding is a broadly studied phenomenon, in the well-defined conditions of wind tunnel laboratory. But vortex shedding excitation at is not easy to observe in real life on real structures, as its occurrence depends not only on the instantaneous wind speed, but on the duration of the wind event (stability) and the turbulence of the oncoming flow. On large bridges especially, because they are often monitored by complete systems, recording vibrations as well as the wind speed, it is possible to follow multiple occurrences of vortex shedding, when the bridge is prone to it, and analyze the conditions of this occurrence. This was done from the data issued by the monitoring system of The Charilaos Trikoupis bridge between Rion and Antirion, in Greece which showed that the actual wind turbulence was lower than supposed at design stage. The full set of data running from 2005 to 2014 was analyzed with the aim to show the correlation between the vortex shedding excitation and the wind speed stability, the duration of wind events, the wind turbulence at the time of VS excitation and other sources of excitation on the bridge. One of the main feature is to highlight the relationship between the wind conditions and the birth and vanishing of the aeroelastic phenomenon.
A round robin study of wind tunnel estimates of wind effects on a building model: test-related uncertainties
Aerodynamic Study of Two Cable Stayed Bridges in Poland
International Journal of Fluid Mechanics Research, 2002
A simplified method of flutter assessment: first steps towards flutter derivative generalization
Wind studies for the Millau Viaduct
Monitoring systems are prone to record huge amount of data, only a minor part of which could be o... more Monitoring systems are prone to record huge amount of data, only a minor part of which could be of interest. Maintaining a giant data base from the monitoring system of a large structure equipped with dozens of sensors is a costly challenge. One way for solving this question lies in discarding everything that does not enter in the scope of what was considered as "interesting event " at the design stage, with a big risk of missing an unattended but essential event. Another way could be to store less data, making a kind of "survey " instead of recording continuously, with a possibility to rebuild events from the discontinuous records. This way of doing is suitable in the case of minutes lasting phenomena only, it is clear that a sudden and brief phenomenon could be missed in such a configuration. This method was used in the case of vortex shedding excitation of the deck of a large cable stayed bridge, in order to rebuild the history of passed excitations and evalua...
Bulletin of the American Physical Society, 2015
Dry galloping on bridge cables: roughness and shape effects on an inclined circular cylinder
Dry galloping of stays in cable-stayed bridges is a phenomenon that is still of interest to the s... more Dry galloping of stays in cable-stayed bridges is a phenomenon that is still of interest to the scientific community. Over the course of the current three-year research project numerous experiments will be carried out to investigate the effect of turbulence and inclination angle on dry galloping. The novel aspect of this study consists of an in-depth investigation into the effect of non uniformity of the pipe surrounding the stay cables on the dry galloping excitation mechanism. Previous studies reported that dry galloping is caused by the appearance of a negative pressure bubble on one side of the circular cylinder at the critical Reynolds number range, leading to a rapid drop in the drag coefficient and the appearance of a non negligible lift force. This paper presents results from initial experiments in the wind tunnel at CSTB – Nantes, France
Springer Tracts on Transportation and Traffic, 2015
Proceedings of the 4th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COMPDYN 2013), 2014
The Grande Ravine Viaduct, at the Reunion Island, is a girder bridge crossing an abrupt volcanic ... more The Grande Ravine Viaduct, at the Reunion Island, is a girder bridge crossing an abrupt volcanic breach conceived and designed by Alain Spielmann and the design office SETEC TPI . The location in a zone frequently affected by typhoons and the typology of the bridge, for which limited experience existed previously in terms of description of the wind behaviour, motivated the installation of a monitoring system, in order to characterise the wind loads acting on the bridge, the corresponding aerodynamic behaviour and the structure dynamic response. The monitoring system comprehends various anemometers distributed along and outside the bridge, pressure and temperature sensors and accelerometers. In this context, it is the purpose of this paper to present and discuss preliminary results of the prototype monitoring during a 2-year period, describing in particular numerical tools implemented with the purpose of selecting relevant data, processing signals and extracting relevant effects in terms of the wind response.
Twin Strouhal numbers in pressure loading of circular cylinder at high Reynolds numbers
Journal of Fluids and Structures
HAL (Le Centre pour la Communication Scientifique Directe), Jul 4, 2017
The work here presented results from the study of the monitored data collected during a 2-year pe... more The work here presented results from the study of the monitored data collected during a 2-year period at the viaduct of Grande Ravine at the Reunion Island. Based on the records collected by a set of anemometers, pressure sensors and accelerometers, it was possible to establish a wind model for the Grande Ravine implantation site, to estimate force coefficients for the deck, and to identify modal properties (vibration frequencies, damping and modal configurations). From the analysis of the structural response, it was possible specifically to identify a case of very slight vortex induced vibration, which is described in detail in this paper.
HAL (Le Centre pour la Communication Scientifique Directe), Jul 4, 2017
The paper aims at showing the evolution of methods to design a large wind tunnel. The current Jul... more The paper aims at showing the evolution of methods to design a large wind tunnel. The current Jules Verne facility was designed with a scale model of the wind tunnel which enabled hot wire local wind speed measurements. The new facility is designed according a numerical modelling approach which parameters were validated by PIV measurements in the reduced scale physical model.
On the mechanism of divergent cable movement: Contribution of the bistable flow activity in the critical flow regime
Journal of Wind Engineering and Industrial Aerodynamics
Uploads
Papers by olivier flamand