Laurent Michon
email: laurent.michon@univ-reunion.fr

Valérie Ferrazzini

Andrea Di Muro

Á A Di Muro

Magma Paths at Piton de la Fournaise Volcano

Several patterns of magma paths have been proposed since the 1980s for Piton de la Fournaise volcano. Given the significant differences, which are presented here, we propose a reappraisal of the magma intrusion paths using a 17-years-long database of volcano-tectonic seismic events and a detailed mapping of the scoria cones. At the edifice scale, the magma propagates along two N120 trending rift zones. They are wide, linear, spotted by small to large scoria cones and related lava flows and involving magma resulting from high-pressure fractionation of ol ± cpx and presents an eruption periodicity of around 200 years over the last 30 kiloyears. The upper plumbing system originates at the base of the edifice below the Enclos Fouqué caldera. It feeds frequent (1 eruption every 9 months on average), short-lived summit and distal (flank) eruptions along summit and outer rift zones, respectively. Summit rift zones are short and present an orthogonal pattern restricted to the central active cone of Piton de la Fournaise whereas outer rift zones extend from inside the Enclos Fouqué caldera to the NE and SE volcano flanks. To sum up, rift zones of Piton de la Fournaise present strong geometrical and dynamical differences. On the one hand, the lower plumbing system feeds rift zones showing striking similarities to those developed in Hawaii during the alkaline postshield

stage. On the other hand, the rift zones connected to upper plumbing system can be compared the rift system of Mount Etna, whose dynamics is know to be linked with the lateral displacement of the east flank.

Introduction

On ocean basaltic volcanoes, magma transfer from the source to the surface is generally assumed to occur along sub-vertical ascent paths through the mantle lithosphere, the oceanic crust and the volcanic edifice, eventually followed by lateral propagation at shallower levels along preferential intrusion paths named rift zones (e.g. [START_REF] Macdonald | Volcanoes[END_REF]. At the surface, volcanic rift zones are outlined by a concentration of scoria cones and eruptive fissures, which results from their overall history of activity. Their wide range of geometry, from radial or circumferential diffuse rift zones (e.g. Galapagos; [START_REF] Chadwick | The pattern of circumferential and radial eruptive fissures on the volcanoes of Fernandina and Isabela islands[END_REF] to narrow km-long rift zones (e.g. Hawaiian shields; Walker 1999) is known as dependent, among other parameters, on the dynamics of the plumbing system, the gravitational deformation of the volcanic edifice and the influence of the crustal inheritance [START_REF] Fiske | Orientation and growth of Hawaiian volcanic rifts: the effect of regional structure and gravitational stress[END_REF][START_REF] Macdonald | Volcanoes[END_REF][START_REF] Dieterich | Growth and persistence of Hawaiian volcanic rift zones[END_REF][START_REF] Chadwick | Mechanical modeling of circumferential and radial dike intrusion on galapagos volcanoes[END_REF][START_REF] Walker | Volcanic rift zones and their intrusion swarms[END_REF][START_REF] Walter | Experiments on rift zone evolution in unstable volcanic edifices[END_REF][START_REF] Michon | Role of the structural inheritance of the oceanic lithosphere in the magmato-tectonic evolution of Piton de la Fournaise volcano (La Reunion Island)[END_REF]Chaput et al. 2014a). For the world's most active volcanoes, such as Kilauea and Etna, the rift zones are well identified and provide the opportunity of searching/studying the interrelation between rift zone development, flank displacement and plumbing system dynamics [START_REF] Dieterich | Growth and persistence of Hawaiian volcanic rift zones[END_REF][START_REF] Walter | Rift zone reorganization through flank instability in ocean island volcanoes: an example from Tenerife, Canary Islands[END_REF][START_REF] Montgomery-Brown | Spatiotemporal evolution of dike opening and décollement slip at Kīlauea Volcano, Hawaii[END_REF]. By contrast, the geometry of the rift zones of Piton de la Fournaise (La Réunion hotspot) is still debated and the link between their development and the dynamics of the plumbing system still unclear.

This paper aims first at reviewing the spatial distribution of preferential intrusion paths proposed for Piton de la Fournaise during the last decades using different methodological approaches and, second, at determining the geometry of the plumbing system and its link with the rift zones.

Review of the Intrusion Paths

at Piton de la Fournaise

Magma Paths at the Edifice Scale

Two different approaches have been conducted to determine the rift zone geometry at the edifice scale, taking into account either the concentration of the scoria cones [START_REF] Villeneuve | Revue de la typologie des éruptions au Piton de la Fournaise, processus et risques volcaniques associés[END_REF] or the distribution and the morphometrical parameters of the cinder cones [START_REF] Bonali | Identifying rift zones on volcanoes: an example from La Réunion island[END_REF]. Despite the use of the same 25-m-step digital elevation model of the French Institut Géographique National (IGN), each methodology has produced contrasting results. Only three rift zones were identified from the volcanic cone concentration: two arched rift zones connected to the volcano's summit, prolonged in the NE and SE directions toward the ocean, and a N120 rift zone located between the summits of the Piton des Neiges and Piton de la Fournaise volcanoes (Fig. 7.1a; [START_REF] Villeneuve | Revue de la typologie des éruptions au Piton de la Fournaise, processus et risques volcaniques associés[END_REF]). An additional minor direction of intrusion, corresponding to the Puys Ramond alignment, extends south of the Enclos Fouqué caldera.

Integrating the degradation stage of the scoria cones to the morphometric analysis, [START_REF] Bonali | Identifying rift zones on volcanoes: an example from La Réunion island[END_REF] distinguished active and inactive rift zones. It appears that the intrusion paths identified on the volcano flanks, and most of the N120 rift zone lying between Piton des Neiges and Piton de la Fournaise, were considered as inactive and related to the volcano's ancient history (Fig. 7.1b; [START_REF] Bonali | Identifying rift zones on volcanoes: an example from La Réunion island[END_REF]. All the active rift zones were connected to the summit of Piton de la Fournaise.

Magma Paths Centred on the Enclos Fouqué Caldera

Seismological data indicate that above 7.5 km below sea level (b.s.l.), the plumbing system is almost exclusively restricted to the Enclos Fouqué caldera (Nercessian et al. 1996;[START_REF] Aki | Seismic monitoring and modeling of an active volcano for prediction[END_REF][START_REF] Battaglia | Pre-eruptive migration of earthquakes at the Piton de la Fournaise volcano (Réunion Island)[END_REF][START_REF] Prôno | P-wave velocity structure of Piton de la Fournaise volcano deduced from seismic data recorded between 1996 and 1999[END_REF]. The magmatic activity related to this part of the volcanic system progressively led to the building, on the floor of the Enclos Fouqué caldera, of the 400-m-high Central Cone capped by the Bory crater and the Dolomieu caldera (Fig. 7.2a). This cone and to a lesser extent the Enclos Fouqué caldera are cut by hundreds of eruptive fissures that formed during the recent history of Piton de la Fournaise.

Considering the eruptive fissures orientation, [START_REF] Bachèlery | Le Piton de la Fournaise (Ile de la Réunion). Etude volcanologique, structurale et pétrologique[END_REF], [START_REF] Carter | Pits, rifts and slumps: the summit structure of Piton de la Fournaise[END_REF] proposed that the main shallow intrusion paths fed by the summit plumbing system are organized in two between 1981 and2006 (Fig. 7.2b;[START_REF] Michon | Edifice growth, deformation and rift zone development in basaltic setting: insights from Piton de la Fournaise shield volcano (Reunion Island)[END_REF]. This pattern is supported by the dyke distribution in the wall of the Dolomieu caldera (Fig. 7.2c; [START_REF] Michon | Explosive activity of the summit cone of Piton de la Fournaise volcano (La Réunion island): a historical and geological review[END_REF]. Finally, a much more complex rift zone distribution was recently determined from the scoria cone morphometry (Fig. 7.2d; [START_REF] Bonali | Identifying rift zones on volcanoes: an example from La Réunion island[END_REF]. Magmas ascending through the summit plumbing system could propagate along seven radial rift zones. Noteworthily, this rift zone pattern partly corresponds to the aggregate of preferential intrusion paths described in previous works [START_REF] Bachèlery | Le Piton de la Fournaise (Ile de la Réunion). Etude volcanologique, structurale et pétrologique[END_REF][START_REF] Michon | Role of the structural inheritance of the oceanic lithosphere in the magmato-tectonic evolution of Piton de la Fournaise volcano (La Reunion Island)[END_REF]. Given the important differences in the rift zone geometries (N10/N170 arcuate rift zones, N25-30/N120 perpendicular rift zones or seven radial rift zones), it is worth wondering (1) the cause of these differences and (2) the link between the rift zones identified inside the Enclos Fouqué caldera and the NE and SE rift zones propagating outside the Enclos Fouqué.

The question arises whether these rift zones connect to a single or to different magma reservoirs. [START_REF] Lénat | Structure and dynamics of the central zone of Piton de la Fournaise volcano[END_REF] explained the main characteristics of the summit eruptions, i.e. short-lived, small volume of erupted magma and a short duration between the initiation of dyke injection and the opening of eruptive fissures, as resulting from relatively small magma pockets scattered between the volcano's summit and sea level (2.6 km below volcano's summit) (Fig. 7.3). The draining of these shallow magma reservoirs during distal eruptions was thought to trigger summit collapses (pit crater) inside the Dolomieu crater like in 1986 and 2002 [START_REF] Hirn | Episodes of pit-crater collapse documented by seismology at Piton de la Fournaise[END_REF][START_REF] Longpré | The November 2002 eruption at Piton de la Fournaise volcano, La Réunion Island: ground deformation, seismicity, and pit crater collapse[END_REF]. Beside this shallow system, two distinct magma-rich zones have been 1977, 1986and 2007(Nercessian et al. 1996;;[START_REF] Prôno | P-wave velocity structure of Piton de la Fournaise volcano deduced from seismic data recorded between 1996 and 1999[END_REF]. Finally, a quite different picture has been proposed from the inversion of geodetic data [START_REF] Peltier | Cyclic magma storages and transfers at Piton de la Fournaise volcano (La Réunion hotspot) inferred from deformation and geochemical data[END_REF][START_REF] Peltier | Magma transport and storage at Piton de la Fournaise (La Réunion) between 1972 and 2007: a review of geophysical and geochemical data[END_REF]. According to [START_REF] Peltier | Magma transport and storage at Piton de la Fournaise (La Réunion) between 1972 and 2007: a review of geophysical and geochemical data[END_REF], all the eruptions, except for that of 1998, are fed by a single magma reservoir, located above sea level, below the Dolomieu crater and regularly recharged by deeper sources (Fig. 7.3). However, this interpretation does not consider nor explain the intense seismicity that occurs in the proposed magma reservoir.

Reappraisal of the Magma Paths

In order to decipher the rift zone geometry and their current activity or inactivity, an integrated analysis of (1) the recent (<30 kiloyears) volcanic cones distribution, (2) the volcano-tectonic events recorded by the Piton de la Fournaise Volcano Observatory between 1996 and2013, and(3 2012). The occurrence of underplating between 10 and 15 km bsl has been determined by [START_REF] Gallart | Perturbation to the lithosphere along the hotspot track of La Réunion from an offshore-onshore seismic transect[END_REF]. b Distribution of the seismicity at different depths. The solid lines account for the preferential intrusion paths inferred from the scoria cones distribution (Fig. 7.4) underlined by a larger cone concentration (Fig. 7.4a), are dynamically linked to the shallower part of the plumbing system feeding the Central Cone.

At the edifice scale, two further areas of cone concentration can be identified, corresponding to the NW-SE rift zone and the South Volcanic Zone, both trending in the N120 direction (Fig. 7.4b).

The Summit Plumbing System

Magma intrusions are strongly sensitive to the stress distribution (σ 3 and σ 1 , the least and main principal stresses, respectively). In a homogeneous volcanic cone, σ 3 is perpendicular to the slope and σ 1 varies from vertical at depth to a downslope orientation in subsurface [START_REF] Dieterich | Growth and persistence of Hawaiian volcanic rift zones[END_REF][START_REF] Cayol | Three-dimensionnal modeling of the 1983-1984 eruption at Piton de la Fournaise volcano, Réunion Island[END_REF][START_REF] Van Wyk De Vries | Styles of volcano-induced deformation: numerical models of substratum flexure, spreading and extrusion[END_REF]. In such an ideal cone, eruptive fissures and dykes, which correspond to tension cracks are radially distributed [START_REF] Delaney | Deformation of host rocks and flow of magma during growth of minette dikes and -bearing intrusions near Ship Rock, New Mexico[END_REF][START_REF] Pollard | Elementary fracture mechanics applied to the structural interpretation of dykes[END_REF]. However, in nature, additional effects such as magma overpressure, rheological layering, volcano instabilities, faulting activity and structural inheritance may lead to a strongly anisotropic stress field, which influence the dyke intrusion along preferential orientations [START_REF] Chadwick | Mechanical modeling of circumferential and radial dike intrusion on galapagos volcanoes[END_REF][START_REF] Tibaldi | Mutual influence of diking and collapses at Stromboli volcano, Aeolian Arc, Italy[END_REF][START_REF] Tibaldi | Influence of volcanic cone morphology on dikes, Stromboli, Italy[END_REF][START_REF] Walker | Volcanic rift zones and their intrusion swarms[END_REF][START_REF] Marinoni | Dykes, faults and palaeostresses in the Teno and Anaga massifs of Tenerife (Canary Islands)[END_REF][START_REF] Walter | Experiments on rift zone evolution in unstable volcanic edifices[END_REF].

At Piton de la Fournaise, the en échelon pattern of the eruptive fissures related to the same eruption was interpreted as resulting from the eastern displacement of the Central Cone's eastern flank [START_REF] Clermont-Ferrand | Caractères structuraux des éruptions historiques du Piton de la Fournaise (Ile de la Réunion)[END_REF]Lénat et al. 1989a). However a detailed inspection of the eruptive fissures opened between 1998 and 2005 in the Central Cone and the floor of the surrounding Enclos Fouqué caldera clearly shows that almost all fissures develop parallel or subparallel to the slope [START_REF] Michon | Role of the structural inheritance of the oceanic lithosphere in the magmato-tectonic evolution of Piton de la Fournaise volcano (La Reunion Island)[END_REF]). Moreover, geophysical data suggest that the orientation of the en échelon eruptive fissures related to the same eruption can be explained by a single feeding dyke at depth [START_REF] Battaglia | Dynamic dyke propagation deduced from tilt variations preceding the March 9, 1998, eruption of the Piton de la Fournaise volcano[END_REF][START_REF] Fukushima | Finding realistic dike models from interferometric synthetic aperture radar data: the February 2000 eruption at Piton de la Fournaise[END_REF][START_REF] Peltier | Imaging the dynamics of dyke propagation prior to the 2000-2003 flank eruptions at Piton de la Fournaise, Reunion Island[END_REF]. Thus, the radial to subradial distribution of the eruptive fissures on the flanks of the Central Cone and on the floor of the Enclos Fouqué suggests that the fissure orientation is controlled by downslope σ 1 rather than by dyke orientation [START_REF] Michon | Role of the structural inheritance of the oceanic lithosphere in the magmato-tectonic evolution of Piton de la Fournaise volcano (La Reunion Island)[END_REF]). Note that the boundary faults of the summit collapse structures also control the concentric distribution of the eruptive fissures in the summit area [START_REF] Lénat | Structure and dynamics of the central zone of Piton de la Fournaise volcano[END_REF]. We therefore consider that the distribution of the eruptions intruding the Central Cone, e.g. the summit and proximal eruptions in the terminology of [START_REF] Peltier | Cyclic magma storages and transfers at Piton de la Fournaise volcano (La Réunion hotspot) inferred from deformation and geochemical data[END_REF], is best explained by the N25-30 and N120 rift zones. In such a configuration, a few magma intrusions in the cone's eastern flank are controlled by N65 trending faults [START_REF] Michon | Edifice growth, deformation and rift zone development in basaltic setting: insights from Piton de la Fournaise shield volcano (Reunion Island)[END_REF]. What is the link between these summit rift zones and the much broader NE and SE rift zones on the volcano flank?

The location of the eruptions, their dynamics and the related deformation pattern for the period spanning between 1972 and 2013 have been taken into account to answer this question. During this time span, Piton de la Fournaise experienced 81 eruptions. The distribution of the eruptive fissures shows that most dykes (58) intruded the Central Cone along the N25-30 and N120 summit rift zones (Table 7.1). Summit eruptions, corresponding to both summit and proximal eruptions in the terminology of [START_REF] Peltier | Cyclic magma storages and transfers at Piton de la Fournaise volcano (La Réunion hotspot) inferred from deformation and geochemical data[END_REF], are characterized by no or limited lateral dyke propagation, which usually stops at the base of the Central Cone. Exceptionally, in November 1987, September 1988 and November 2002, dykes propagated 1-2 km from the cone's base. Twenty-two eruptions, named distal eruptions, started directly on the floor of the Enclos Fouqué caldera and occasionally propagated downslope outside the Enclos Fouqué caldera (1977, 1986 and 1998) or along the northern and southern walls of the Grandes Pentes and Grand Brûlé [START_REF] Swanson | Displacement of the south flank of Kilauea volcano: the result of forceful intrusion of magma into the rift zones[END_REF], 2002, 2005and 2007;Table 7.1;Fig. 7.6a). Interestingly, the eruptive fissures related to distal eruptions in Table 7.1, are concentrated in three areas located South, East and North of the Central Cone. They define three preferential intrusion paths named outer rift zones, that are spatially disconnected from the summit rift zones; the South-East, East and North-East rift zones that gather 12, 4 and 7 distal eruptions respectively (Fig. 7.6). These rift zones roughly correspond to the NE and SE rift zones and the N80 intrusion path identified by [START_REF] Bachèlery | Le Piton de la Fournaise (Ile de la Réunion). Etude volcanologique, structurale et pétrologique[END_REF]. The important new observation brought by the present work is that the outer rift zones are solely fed by distal eruptions rather than by all eruption types. According to [START_REF] Peltier | Magma transport and storage at Piton de la Fournaise (La Réunion) between 1972 and 2007: a review of geophysical and geochemical data[END_REF], between 1998 and 2007, proximal and distal eruptions were fed by two distinct vertical pathways, located below the western and eastern part of the Dolomieu caldera, respectively, and connected to a single magma reservoir lying at about 2300 m depth below the Dolomieu caldera. The inclinometers data recorded during the eruptions of 1983,1984,1985,1986,1988,1990 and 1992 also suggest two different inflation sources located below the western part of Dolomieu and below the eastern flank of the Central Cone for the summit and distal eruptions, respectively (Fig. 7.3; [START_REF] Delorme | March 1986 eruptive episodes at Piton de la Fournaise volcano (Reunion Island)[END_REF]Lénat et al. 1989a, b;[START_REF] Toutain | Real time monitoring of vertical ground deformations during eruptions at Piton de la Fournaise[END_REF][START_REF] Delorme | Apport des déformations à la compréhension des mécanismes éruptifs: le Piton de la Fournaise[END_REF]. We consequently propose that magma intrusions feeding the summit and distal eruptions not only follow different vertical pathways but also propagate laterally along two distinct systems of rift zones, the summit and outer rift zones (Fig. 7.6b). Considering the geophysical data (Nercessian et al. 1996;[START_REF] Prôno | P-wave velocity structure of Piton de la Fournaise volcano deduced from seismic data recorded between 1996 and 1999[END_REF]), the dynamics of the summit and distal eruptions [START_REF] Lénat | Structure and dynamics of the central zone of Piton de la Fournaise volcano[END_REF]) and the observations made in the incised Piton des Neiges volcano [START_REF] Famin | Volcano destabilization by magma injections in a detachment[END_REF]Chaput et al. 2014a), we tentatively propose the existence of a single main magma storage below sea level (Fig. 7.3b). This magmatic zone feeds a superficial storage system below the Central Cone that is involved during the summit eruptions. Magma injections from the eastern part of the main magmatic system occasionally occur, forming sill intrusions that act as detachment levels capable to trigger lateral flank displacement [START_REF] Famin | Volcano destabilization by magma injections in a detachment[END_REF]Chaput et al. 2014b) and subsequent dyke intrusions along the outer rift zones. Finally, among the 81 eruptions, the March-April 1998 Hudson eruption did not follow the summit or outer rift zones. Its magma chemical composition, similar to that of the eccentric cones of the NW-SE rift zone [START_REF] Pietruszka | Crustal contamination of mantle-derived magmas within Piton de la Fournaise, Réunion Island[END_REF][START_REF] Lénat | Anatomy of Piton de la Fournaise volcano (La Réunion, Indian Ocean)[END_REF], and its location south-west of the Central Cone suggest that the magma intrusion was not controlled by the summit or distal rift zones but instead followed the NW-SE rift zone.

The NW-SE Rift Zone, the South Volcanic Zone and the Deep Plumbing System

The scoria cone density map clearly shows that eruptions occurred along the NW-SE rift zone and the South Volcanic Zone, both trend in the N120 direction (Fig. 7.4b). The NW-SE rift zone, 15 km in width, is composed of about 160 scoria cones and pit craters scattered between the Enclos Fouqué caldera in the east and the eastern slopes of Piton des Neiges in the west. The volcanic activity started at least 29 kiloyears ago [START_REF] Mcdougall | The geochronology and evolution of the young volcanic island of Réunion (Indian Ocean)[END_REF] and continued until recently (140 yr BP for Piton Rampe 14), given an average eruption periodicity of around 200 years [START_REF] Morandi | Active volcanoes of the Southwest Indian Ocean: Piton de la Fournaise and Karthala. Active Volcanoes of the World[END_REF]Chap. 8). Interestingly, the NW-SE rift zone is superimposed to a deep seismicity concentrated in a N120 trending zone ranging mostly between 15 and 20 km bsl, i.e. in the mantle lithosphere, just below the oceanic crust (Fig. major eruption, the seismicity progressively migrated down to 7 km bsl. The migration continued after the eruption along the NW-SE rift zone, down to about 30 km below sea level (Fig. 7.5a;[START_REF] Massin | Transferts et Stockages Magmatiques au Piton de la Fournaise[END_REF]. A similar downward migration of the seismicity was recorded during the Eyjafjallajökul 2010 eruption, where it was interpreted as resulting from a downwardpropagating decompression of the plumbing system [START_REF] Tarasewicz | Magma mobilization by downward-propagating decompression of the Eyjafjallajökull volcanic plumbing system[END_REF]. Second, magma involved in the eruptions along the NW-SE rift zone indicates a high-pressure (>0.4 GPa) fractionation of clinopyroxene ± olivine [START_REF] Kornprobst | Le Piton de la Fournaise, île de la Réunion[END_REF][START_REF] Albarède | The geochemical regimes of Piton de la Fournaise volcano (Réunion) during the last 530,000 years[END_REF][START_REF] Famin | Three differentiation stages of a single magma at Piton de la Fournaise volcano (Reunion hot spot)[END_REF][START_REF] Lénat | Anatomy of Piton de la Fournaise volcano (La Réunion, Indian Ocean)[END_REF], which is consistent with the depth of the earthquakes located below the rift zone (depth >15 km). Third, high-pressure fluid inclusions (P up to 400-500 MPa) are common olivine carried by magmas erupted along the N120 rift zone (Piton des Cailles; Chisny; [START_REF] Bureau | A melt and fluid inclusion study of the gas phase at Piton de la Fournaise volcano (Reunion Island)[END_REF]. Combining these geochemical and geophysical data, we tentatively interpret the deep zone of dense seismicity below the Plaine des Cafres and Plaine des Palmistes, in the west, and the NW-SE rift zone toward the east as the deep plumbing system of Piton de la Fournaise. This zone of magma transfer could feed recurrent eruptions and subsequently form a deeply rooted NW-SE rift zone characterized by a low eruption rate.

Contrary to the NW-SE rift zone, the 20-km-long South Volcanic Zone is not associated with recent seismic events. The wide range of degradation stages of the large volcanic cones and the related lava flows, from smooth-recent -to incised-old-morphologies, suggests a recurrent volcanic activity along this intrusion path. Yet, the lack of chronological data combined with the location of the volcanic zone in apparent disconnection with the active volcanic area makes the origin and the dynamics of this volcanic zone enigmatic.

An additional, short vent alignment, the Puys Ramond-Baril volcanic alignment, occurs south of the Enclos Fouqué by the density map (Fig. 7.4b). This narrow, 10-km-long area is composed of several spatter and cinder conesthat are in average significantly smaller than those of the NW-SE rift zone and the South Volcanic Zone, but similar to those found in the Enlos Fouqué and along the SE and NE rift zones. Radiocarbon datings and the occurrence of dykes and buried cones in the southern wall of the Enclos Fouqué caldera indicate a long-lasting activity, which developed until recently (355 BP;[START_REF] Bachèlery | Le Piton de la Fournaise (Ile de la Réunion). Etude volcanologique, structurale et pétrologique[END_REF][START_REF] Tanguy | Archeomagnetism of Piton de la Fournaise: bearing on volcanic activity at La Réunion Island and geomagnetic secular variation in Southern Indian Ocean[END_REF]Morandi et al. 2016, Chap. 8). Despite its location close to the summit plumbing system, the link between this intrusion part and the summit activity and/or the SE rift zone remains unclear.

Comparison with Other Volcanoes

Our work clearly shows that different types of rift zone developed on Piton de la Fournaise since at least 30 kiloyears. On the one hand, the 120 N trending NW-SE rift zone and the South Volcanic Zone present strong similarities with the rift developed in the post shield phase in Mauritius and Hawaii alkaline postshield rift zones in Hawaii [START_REF] Clague | Hawaiian xenolith populations, magma supply rates, and development of magma chambers[END_REF][START_REF] Moore | Evolution of shield-building and rejuvenescent volcanism of Mauritius[END_REF]. In all these cases, they correspond to wide, linear rift zones with eruptions with a secular frequency involving magmas fractionating at minimum depths of 15-20 km (Roeder 1965;[START_REF] Clague | Hawaiian xenolith populations, magma supply rates, and development of magma chambers[END_REF][START_REF] Albarède | The geochemical regimes of Piton de la Fournaise volcano (Réunion) during the last 530,000 years[END_REF][START_REF] Lénat | Anatomy of Piton de la Fournaise volcano (La Réunion, Indian Ocean)[END_REF]). On the other hand, the arched rift zones geometry of the NE and SE outer rift zones resembles to that of the NE and S rift zones of Mount Etna [START_REF] Kieffer | Sur l'existence d'une 'rift zone' à l'Etna (Sicile)[END_REF]. Following the model proposed by [START_REF] Swanson | Displacement of the south flank of Kilauea volcano: the result of forceful intrusion of magma into the rift zones[END_REF] for Kilauea, [START_REF] Bachèlery | Le Piton de la Fournaise (Ile de la Réunion). Etude volcanologique, structurale et pétrologique[END_REF], [START_REF] Duffield | Huge landslide blocks in the growth of Piton de la Fournaise, La Réunion, and Kilauea Volcano, Hawaii[END_REF], Lénat et al. (1989b) postulated that the recurrent dyke intrusions along the NE and SE rift zones forcefully push the east flank and subsequently triggered the lateral collapse of the eastern flank of Piton de la Fournaise. However, determining whether or not dyking along the outer rift zones of Piton de la Fournaise actively pushes the east flank or if it passively follows the upper boundaries of a sliding sectors, like at Mount Etna [START_REF] Acocella | Link between major flank slip and 2002-2003 eruption at Mt. Etna (Italy)[END_REF][START_REF] Neri | Contrasting triggering mechanisms of the 2001 and 2002-2003 eruptions of Mount Etna (Italy)[END_REF] requires at least a thorough inspection of the rift zone and eruption dynamics, which is beyond the scope of this review. Recent work carried out on Piton des Neiges volcano, the inactive twin of Piton de la Fournaise, suggests that rift zone development and flank landslides are linked by a common process, sill injections below the volcano flanks that act as detachment [START_REF] Famin | Volcano destabilization by magma injections in a detachment[END_REF]Chaput et al. 2014a).

  Fig. 7.1 Rift zone distribution determined for Piton de la Fournaise from a the concentration of the scoria cones (Bachèlery 1981; Villeneuve and Bachèlery 2006) and b the distribution and asymmetry of the scoria cones (Bonali et al. 2011). White and grey zones account for recent and old rift zones, whose distinction is based on the degradation stage of the scoria cones. PRB: Puys Ramond Baril volcanic alignment. PdR Plaine des Remparts. RdR Rivière des Remparts

  Fig. 7.2 a Distribution and main orientations of the eruptive fissures opened in the Central Cone of Piton de la Fournaise, enabling to determine two main N10 and N170 rift zones North and South of the Dolomieu caldera (DC), respectively (after Bachèlery 1981). b N25-30 and N120 rift zones inferred from the orientation of recent dykes (black lines) intruding the Central Cone between 1981 and 2006 (after Michon et al. 2009). c Distribution of radial dykes in the walls of the Dolomieu caldera. Numbers refer to the dyke population detected in each of the 18 sectors. The thickness of the white line is proportional to the dyke population. The N25-30 and N120 rift zones previously determined from dyke distribution outside the caldera (Michon et al. 2009) are indicated for comparison. d Rift zone distribution determined from the scoria cone morphometry (after Fig. 12 in Bonali et al. 2011)

  Fig. 7.3 a Seismic events related to the summit and distal eruptions between 1998 and 2010. Structures labelled 1, 2, 3 and 4 account for small magma pockets related to summit eruptions (Lénat and Bachèlery 1990), a low velocity zone inferred from Vp and Vs waves (Nercessian et al. 1996), a low velocity zone deduced from a Vp-wave tomography (Prôno et al. 2009) and the magma reservoir inferred from geodetic data (Peltier et al. 2008), respectively. Red and grey arrows indicate the locus of the pre-eruptive inflation related to summit and distal eruptions. b Interpretative summit plumbing system below the Enclos Fouqué caldera (see text for explanation)

  Fig. 7.4 a Density map of the scoria cones (blue) on the massif of Piton de la Fournaise younger than 60 kiloyears. b Preferential intrusion paths proposed in this study from the density map

Fig

  Fig. 7.5 a Volcano-tectonic seismic hypocenters (black dots) localized between 1996 and 2013 by the Piton de la Fournaise volcano observatory (OVPF/IPGP) on the massif of Piton de la Fournaise. Location is determined by a manual picking of the arrival times at different stations of the network. Depth of the top and the base of the oceanic crust is from Fontaine et al. (2012). The occurrence of underplating between 10 and 15 km bsl has been determined by[START_REF] Gallart | Perturbation to the lithosphere along the hotspot track of La Réunion from an offshore-onshore seismic transect[END_REF]. b Distribution of the seismicity at different depths. The solid lines account for the preferential intrusion paths inferred from the scoria cones distribution (Fig.7.4)

  Fig. 7.6 a Eruptive fissures formed between 1972 and 2010 (black), summit dykes for the period between 1981 and 2007 (red, after Michon et al. 2009) and summit rift zones channeling the summit eruptions. Dates indicate the eruptive vents opened outside the Enclos Fouqué caldera or close to the northern and southern walls of the Grandes Pentes. b Distribution of the outer (grey) and summit (light red) rift zones related to the distal and summit eruptions, respectively. Red and grey circles indicate the location of the edifice inflation triggered by magma intrusions before the summit and distal eruptions, respectively

Table 7 .

 7 1 Eruptions of Piton de la Fournaise since 1972

	Eruption timing		Eruption type	Rift zone	Volume (10 6 m 3 )
	Start (dd/mm/yy)	End (dd/mm/yy)
	09/06/72	11/06/72	Summit	N25-30 SRZ	0.27
	25/07/72	17/08/72	Distal	East RZ	2.9
	07/09/72	26/09/72	Summit	N25-30 SRZ	4
	10/10/72	10/12/72	Distal	South-East RZ	9.3
	10/05/73	28/05/73	Summit	N120 SRZ	1.6
	04/11/75	18/11/75	Summit	N120 SRZ	1.4
	18/12/75	25/01/76	Summit	N120 SRZ	0.03
	12/01/76	06/04/76	Distal	South-East RZ	11.6
	02/11/76	03/11/76	Summit	N25-30 SRZ	0.46
	24/03/77	24/03/77	Distal	South-East RZ	0.06
	05/04/77	16/04/77	Distal	North-East RZ	20
	24/10/77	17/11/77	Summit	N120 SRZ	23
	28/05/79	29/05/79	Summit	N25-30 SRZ	0.2
	13/07/79	14/07/79	Summit	N25-30 SRZ	0.3
	03/02/81	24/02/81	Summit	N25-30 SRZ	3
	24/02/81	31/03/81	Summit	N25-30 SRZ	4
	01/04/81	05/05/81	Distal	East RZ	5
	04/12/83	18/01/84	Summit	N25-30 SRZ	8
	18/01/84	18/02/84	Summit	N25-30 SRZ	9
	14/06/85	15/06/85	Summit	N25-30 SRZ	1
	05/08/85	01/09/85	Summit	N25-30 SRZ	7
	06/09/85	10/10/85	Summit	N120 SRZ	14
	01/12/85	03/12/85	Summit	N25-30 SRZ	0.7
	29/12/85	07/02/86	Summit	N120 SRZ	7
	19/03/86	05/04/86	Distal	South-East RZ	13.5
	13/07/86	13/07/86	Summit	N120 SRZ	0.28
	12/11/86	13/11/86	Summit	N120 SRZ	0.27
	26/11/86	27/11/86	Summit	N120 SRZ	0.24
	06/12/86	07/01/87	Summit	N120 SRZ	2
	07/01/87	10/02/87	Distal	East RZ	10
	10/06/87	29/06/87	Summit	N120 SRZ	1
	19/07/87	20/07/87	Distal	East and South RZ	1
	06/11/87	08/11/87	Summit	N25-30 SRZ	1.6
	30/11/87	01/01/88	Distal	South-East RZ	10
	07/02/88	02/04/88	Distal	South-East RZ	8
	18/05/88	01/08/88	Summit	N25-30 SRZ	7
	31/08/88	12/09/88	Summit	N25-30 SRZ	4
	14/12/88	29/12/88	Distal	North-East RZ	4
					(continued)

Table 7

 7

	.1 (continued)
	Eruption timing		Eruption type	Rift zone	Volume (10 6 m 3 )
	Start (dd/mm/yy)	End (dd/mm/yy)
	18/01/90	19/01/90	Summit	N120 SRZ	0.97
	18/04/90	08/05/90	Distal	South-East RZ	8
	19/07/91	20/07/91	Summit	N120 SRZ	5
	27/08/92	23/09/92	Summit	N120 SRZ	5.5
	09/03/98	21/09/98	Summit	N25-30 SRZ	60
	11/03/98	01/04/98	Other	NW-SE RZ	0.75
	08/08/98	15/09/98	Distal	North-East RZ	0.9
	19/07/99	31/07/99	Summit	N120 SRZ	1.3
	28/09/99	23/10/99	Summit	N25-30 SRZ	1.4
	13/02/00	03/03/00	Summit	N25-30 SRZ	8.2
	23/06/00	30/07/00	Distal	South-East RZ	10
	12/10/00	13/11/00	Summit	N120 SRZ	9
	27/03/01	04/04/01	Summit	N120 SRZ	4.8
	11/06/01	09/07/01	Summit	N120 SRZ	9.5
	05/01/02	16/01/02	Distal	North-East RZ	13
	16/11/02	03/12/02	Summit	N120 SRZ	8
	30/05/03	30/05/03	Summit	N25-30 SRZ	0.16
	04/06/03	09/06/03	Summit	N25-30 SRZ	0.72
	12/06/03	15/06/03	Summit	N25-30 SRZ	0.59
	22/06/03	07/07/03	Summit	N25-30 SRZ	0.69
	22/08/03	27/08/03	Summit	N25-30 SRZ	6.2
	30/09/03	01/10/03	Summit	N25-30 SRZ	1
	07/12/03	25/12/03	Summit	N120 SRZ	1.2
	08/01/04	08/01/04	Distal	North-East RZ	1.9
	02/05/04	18/05/04	Summit	N25-30 SRZ	16.9
	12/08/04	16/10/04	Summit	N120 SRZ	20
	17/02/05	26/02/05	Distal	North-East RZ	19
	04/10/05	17/10/05	Summit	N25-30 SRZ	2
	29/11/05	29/11/05	Summit	N25-30 SRZ	1
	26/12/05	18/01/06	Distal	North-East RZ	20
	20/07/06	14/08/06	Summit	N25-30 SRZ	2
	30/08/06	01/01/07	Summit	N120 SRZ	20
	18/02/07	19/02/07	Summit	N120 SRZ	1
	30/03/07	31/03/07	Distal	South-East RZ	0.6
	02/04/07	01/05/07	Distal	South-East RZ	240
	21/09/08	02/10/08	Summit	N25-30 SRZ	1
	27/11/08	28/11/08	Summit	N25-30 SRZ	0.1
	14/12/08	04/02/09	Summit	N25-30 SRZ	1.5
					(continued)

Table 7

 7

	.1 (continued)
	Eruption timing		Eruption type	Rift zone	Volume (10 6 m 3 )
	Start (dd/mm/yy)	End (dd/mm/yy)
	05/11/09	06/11/09	Summit	N120 SRZ	0.14
	14/12/09	15/12/09	Summit	N25-30 SRZ	0.16
	02/01/10	12/01/10	Summit	N25-30 SRZ	1.2
	14/10/10	31/10/10	Distal	South-East RZ	2.7
	09/12/10	10/12/10	Summit	N25-30 SRZ	0.53
	Emitted volumes from Peltier et al. (2009), Roult et al. (2012)


Marc Terracol

Thomas Le Garrec

Daniel-Ciprian Mincu

Eric Manoha

Exa GmbH Damiano Casalino

André Ribeiro

Daniel-Ciprian Mincu

T Le Garrec

D.-C Mincu

Numerical simulations of LEISA2 high-lift configuration at ONERA

de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

1

NUMERICAL SIMULATIONS OF LEISA2 HIGH-LIFT CONFIGURATION AT ONERA

Marc Terracol 1 , Thomas Le Garrec 1 , Daniel-Ciprian Mincu 1 , Eric Manoha 1 , Damiano Casalino 2 , André Ribeiro 2 1 Onera, The French Aerospace Lab, Châtillon, France, danielciprian.mincu@onera.fr 2 Exa GmbH, Stuttgart, Germany, damiano@exa.com For aircraft in approach and landing operations, when the engines are in idle regime, airframe noise becomes predominant. High lift devices, namely the leading edge slats and the trailing edge flaps, deployed to increase lift at low speed, represent one of the main contributor to the airframe noise. A large number of numerical studies have addressed such configurations in the past, using unsteady computations based on either zonal RANS/LES [START_REF] Imamura | Threedimensional unsteady flow computations around a conventional slat of high-lift devices[END_REF][START_REF] Terracol | Investigation of the unsteady flow and noise sources generation in a slat cove: hybrid zonal RANS/LES simulation and dedicated experiment[END_REF][START_REF] Terracol | Simulation of the 3D unsteady flow in a slat cove for noise prediction[END_REF][START_REF] Terracol | Hybrid methods for airframe noise numerical prediction[END_REF] or hybrid RANS/LES [START_REF] Choudhari | Effect of three-dimensional shear-layer structures on slat cove unsteadiness[END_REF][START_REF] Deck | Zonal detached-eddy simulation of the flow around a high-lift configuration[END_REF][START_REF] Deck | Numerical investigation of the flow dynamics past a three-element airfoil[END_REF][START_REF] Knacke | Time-resolved 3D simulation of an aircraft wing with deployed high-lift system[END_REF][START_REF] Knacke | Numerical analysis of slat noise generation[END_REF][START_REF] Lockard | Noise radiation from a leading-edge slat[END_REF][START_REF] Lockard | The effect of cross flow on slat noise[END_REF][START_REF] Zhong | Turbulent flow simulations around a multi-element airfoil using URANS, DES and ILES approaches[END_REF] approaches. However, despite the advanced understanding of flow features, these studies suffered from the lack of mixed experimental measurements to validate conjunctively the aerodynamics and the aeroacoustics. Among the reasons, one can point out the different stream deflections, with direct consequences on the flow around the wing, when such deployed configuration is measured in a closed test section (for aerodynamics) or open test section (for aeroacoustics) measurement wind tunnels. With a view to fill this gap, the French (ONERA) and German (DLR) Aerospace Research Centers unified their competences to address this last topic, and provide, a complete measurement database (with both aerodynamics and acoustics data) to validate computations and to explore in details such configuration. Figure 1 shows some results of this experimental campaign, named LEISA 2. Recently, Onera and DLR made this database available to the com-munity, within the framework of the NASA BANC workshop -Category 6 [START_REF]BANCII_category6 > Summary_BANCII_Category_6_Slat_Noise_DLR _ONERA DG: Summary_BANCII_Category_6_Slat_Noise_DLR_ ONERA[END_REF].

In parallel, several numerical computations were conducted or are still under progress at Onera to perform a detailed numerical flow analysis and to identify the noise mechanisms at approach. Figure 2 shows several results about the acoustic near field and flow features in the slat cove and over the flap using the in-house research CFD/CAA code FUNk working with a structured multiblocks grid [START_REF] Terracol | Wall-resolved Large Eddy Simulation of a high-lift airfoil: detailed flow analysis and noise generation study[END_REF]. Furthermore, recently Onera started to invest in the Lattice Boltzmann methods, firstly through a fruitful cooperation [START_REF] Garrec | Aeroacoustic prediction of the LEISA2 high lift airfoil : Lattice Boltzmann method vs. Navier-Stokes finite volume method and experiments[END_REF] with Exa Corporation, with the objective of evaluating their numerical solution PowerFLOW (Fig. 3, left) and, secondly, by joining the French consortium LaBS, which also develops a LBM solver (Fig. 3, right). The final presentation will include a detailed comparison of Onera's numerical simulations (LES, LBM) with the experimental LEISA2 database for both aerodynamics and acoustics features. The feasibility of alternative methods, such as the Lattice-Boltzmann method, will be discussed to address aeroacoustics simulations of profiled bodies, after setting state of the art of such computations at Onera.

Fig. 1 .

 1 Fig. 1. LEISA2 experiments in F2 Onera closed wind tunnel. Left: 2D PIV test set-up in. Middle: Mean flow PIV map; Right: Example of a noise source map at a given frequency obtained using classical acoustic beamforming.

Fig. 2 .

 2 Fig. 2. FUNk computation, flow visualizations in the mid plane in the spanwise direction. Left: Instantaneous view of the dilatation field. Slat (middle) and flap (right) numerical Schlieren visualizations..

Fig. 3 .

 3 Fig. 3. Flow computations of the LEISA2 configuration with LBM solvers. Left: Instantaneous view of the acoustical pressure field -PowerFLOW; Right: Streamwise flow field -LaBS


Wall-bounded turbulence is ubiquitous in flows of engineering or environmental interest, where the high values of the Reynolds number result in phenomena such as very large scale motions ( [START_REF] Smits | High-Reynolds number wall turbulence[END_REF], [START_REF] Jiménez | Near-wall turbulence[END_REF]). This complex turbulent dynamics determines global parameters such as mean skin friction, contributing for instance to the overall drag and energy consumption of an aircraft.

Although many studies have been devoted to the fluctuations of skin friction, surprisingly less has been achieved towards the understanding of the generation of mean skin friction. It has been suggested that the buffer layer dynamics is involved ( [START_REF] Orlandi | On the generation of turbulent wall friction[END_REF]), but a contribution from the outer layer at high Reynolds numbers may not be excluded. In the case of the incompressible zero-pressure-gradient flat-plate boundary layer, one may wish to quantify the contribution of turbulent fluctuations, as a function of their nature and distance from the wall, to the excess of mean skin friction in comparison with the laminar case. The FIK identity ( [START_REF] Fukagata | Contribution of Reynolds stress distribution to the skin friction in wall-bounded flows[END_REF]) was used in the past to spectrally decompose the turbulent contribution to the mean skin friction coefficient

C f = τ w /(1/2ρU 2 ∞ ) ([2]
). However, the physical interpretation of the terms of this identity is not straightforward. To address this issue, a physical decomposition of mean skin friction generation was recently introduced ([7]):

C f = 2 U 3 ∞ ∞ 0 ν ∂ u ∂y 2 dy C f,a + 2 U 3 ∞ ∞ 0 -u ′ v ′ ∂ u ∂y dy C f,b + 2 U 3 ∞ ∞ 0 ( u -U ∞ ) ∂ ∂y τ ρ dy C f,c (1)
where τ /ρ = ν ∂ u /∂y -u ′ v ′ . The discussion of this new decomposition suggests that at very high Reynolds number, the turbulence-induced excess friction may be essentially related to the production of turbulent kinetic energy (represented by C f,b ) in the logarithmic layer ( [START_REF] Renard | A theoretical decomposition of mean skin friction generation into physical phenomena across the boundary layer[END_REF]). The present study investigates the resolved contribution of turbulence to mean skin friction in a spatially developing flat-plate boundary layer up to Re θ = 13 000 described by a wall-resolved large-eddysimulation database [START_REF] Deck | Large scale contribution to mean wall shear stress in high Reynolds number flat plate boundary layers up to Re θ = 13 650[END_REF] (fig. 2, left) obtained with the Zonal Detached Eddy Simulation technique [START_REF] Deck | Recent improvements in the Zonal Detached Eddy Simulation (ZDES) formulation[END_REF]. The friction decomposition (1) is assessed using this ZDES database and compared with DNS and RANS data in figure 1.

In order to assess the contribution of the resolved large scales of motion in the outer layer to mean skin friction, the velocity time signals from the database may be used to reconstruct turbulent spectra in the streamwise direction, using a suitable convection velocity ( [START_REF] Renard | On the scale-dependent turbulent convection velocity in a spatially developing flat plate turbulent boundary layer at Reynolds number Re θ = 13 000[END_REF]). More specifically, the contribution of turbulence to the excess friction (compared with the laminar case) at high Reynolds numbers is related to the term C f,b (1), i.e. to the overall production of turbulent kinetic energy, as discussed in ref. [START_REF] Renard | A theoretical decomposition of mean skin friction generation into physical phenomena across the boundary layer[END_REF]. The final paper will consequently present streamwise spectra of turbulent kinetic energy production. A preliminary result at Re θ = 13 000 is given in figure 2 (right), suggesting the significant contribution of very large streamwise length scales in the outer layer to the overall TKE production contained within the boundary layer profile. The contribution of given wavelength bands at given wall distances will be quantified from the finalised spectra.

1 1

 1 by TCPDF (www.tcpdf.org) Towards a physical scale decomposition of mean skin friction generation in the turbulent boundary layer Nicolas Renard 1 and Sébastien Deck Applied Aerodynamics Department, Onera -The French Aerospace Lab, Meudon, France key-words: Turbulent boundary layer, Mean skin friction

Figure 1 :

 1 Figure 1: Decomposition (1) of mean skin friction in the zero-pressure-gradient boundary layer.

Figure 2 :

 2 Figure 2: Isosurface of the non-dimensionalised Q criterion Qδ 2 0 /U 2 ∞ = 0.5 coloured by the streamwise velocity near Re θ = 13 000 in the database [2] (left); Premultiplied streamwise spectrum of turbulent kinetic energy production at Re θ = 13 000 (right).


P Pernelle

T Carron

S Elkadiri

A Bissay

J.-C Marty

PLM Serious Game Approach available both for Change Management and Knowledge Assessment

Minimizing the reluctance of actors in change management is a wellknown and key issue that can be resolved thanks to a serious game approach during the upstream PLM deployment phase. If our initial choices have already allowed us to validate the relevance of a serious game for change management process, we found that the participants, who were familiar with the area of technology in question, have systematically initiated a high level discussion about the models used in the PLM. We tried thus to take into account these unexpected observation results to also address the downstream phase concerning knowledge identification and assessment. Indeed, the capitalization of industrial knowledge is an important issue for enterprises who wish to master the development and the innovative element of their product. A substantial amount of knowledge extraction methods has the drawback to require expensive work by KM experts. We witnessed that besides this, it is necessary to evaluate both knowledge and knowledge use. In this article, we present the two uses synthesized in a same Serious Game Environment. From an identification methodology based on an analysis under a PLM (Product Lifecycle Management) deployment, we developed and experimented a Serious Game platform to both minimize the reluctance of actors and validate the identification work of KM experts.

Introduction

The deployment of a PLM project is an opportunity for companies, even for SMEs / SMIs, to reconsider their work methods. It involves a formalization of the processes currently in place. The MPPI method (fig. 1) is based on this observation and offers a combined approach to take into account capitalization of know-how dur-ing stages of PLM project discussions. This approach is called combined because it combines three different objectives (deployment methodology , change management and knowledge capitalization approach). The first part of this paper will present the methodology MPPI (Methodology for PLM Project Implementation) that is a global approach for coupling a deployment methodology (implementation of a new information system) and a phase for integrating knowledge (company specific configuration). Thanks to our previous works on PLM system deployment, we acknowledged that this phase is particularly favorable to identify tacit knowledge. Nevertheless, these method presents some drawbacks in terms of cost and attractiveness. We decided then to bare on recent educational trends where playful approaches are supporting learning content.

The second part of this article focuses thus on the integration of the use of gaming techniques inside the MPPI method. In this part, we will characterize the gamification of industrial processes as well as the emergence of new usages and some specific scenarios to facilitate change management and knowledge integration in two particular and relevant steps of the method.

The third section will describe the serious game platform designed for supporting this integration method. This section is then illustrated by the way of a real case study concerning a project of coupling between a PLM platform and a Serious Game environment.

The last part will focus on results and feedback concerning the experiments that have been set up.

Methodology for PLM Project Implementation

The companies which deploy a PLM system wish to reduce the development cycle to promote innovation. For the implementation of a PLM system, these companies must analyze their information and processes. It seems interesting to take advantage of this revision of information system to make explicit the crucial knowledge in order to manage it more efficiently. Through MPPI method, we want to integrate and capitalize on the knowledge generated by a process in a PLM system.

Description of the approach

The following figure (Fig. 1) schematizes the approach proposed in MPPI [START_REF] Bissay | Deployment methodology of is[END_REF] [START_REF] Bissay | Integration of business processes and performance indicators in a plm[END_REF]. Thus, MPPI is structured around two processes: the process of draft (pre-project) and deployment process. We can note that the accompanying and adaptation process must be considered as a transversal subprocess included in the first two.

The overall approach MPPI exhibits a comprehensive process implementation modeling of an information system focused on the product. A specific part concerning the deployment process is called MPPI-KI (for Knowledge-Integration). MPPI-KI approach can be divided into two cycles. In the first cycle (Identify, Modeling, Use, Evaluate), the goal is to characterize the global model of the information system called "PPO model" (Product / Process / Organization). In the second cycle (outer circle), the objective is then the integration of a specifically "knowledge perspective".

As for the PPO model cycle, this integration is performed through 4 steps: Identify, Modeling, Use and Evaluate. In this article, we are interested in the problems that concern the first two stages. Thus, the identification step consists in characterizing from the PPO model, the activities which contain knowledge. From these activities (built from business processes), the knowledge expert makes explicit the elements of the data model that are knowledge-containing and enriches this model with the necessary attributes. Subsequently, the modeling phase will consist in completing the PPO model enriched by the business rules that formalizes this knowledge. The advantage of this approach is to facilitate this expertise by mapping relevant areas from the viewpoint of business processes.

Discussion

As explained before, these steps are difficult, expensive to exploit and do not resolve the problem of reluctance of the users. In this article, our main proposal concerns the use of a serious game for specific stages of MPPI approach. From our experience and in the context of our work, the use of a serious game is suitable for two aspects of the MPPI method. The first aspect concerns the transversal process of change Fig. 1 Principles of the MPPI method management, the second aspect relates to the stages of evaluation of the MPPI-KI process.

In the next section, we will then focus on the integration of gaming concepts into the MPPI method.

3 Gaming integration into a PLM Method

Gamification of industrial context

In the context of change management within MPPI, we used a gamification approach [START_REF] Mayer | The gaming of policy and the politics of gaming: A review[END_REF] for industrial processes. In this approach, the game designer must choose some specific target characteristics of the platform (e.g. what has to be learnt) [START_REF] Galarneau | Games and Simulations in Online Learning: Research and Development Frameworks[END_REF]. From the previous example (section 2.2), we initiated gamification process with the following choices:

• A contemporary and realistic world, quite close of the real enterprise (with the complete modeling of a production building of the enterprise). • A first linear scenario, multi-user : every player has the same scenario. Being together simultaneously in the same "virtual world" strengthens the feeling of immersion and the user's motivation (implicit competition, possibility of exchanging messages, etc.). • Another, nonlinear scenario, multi-user, multi-role, collaborative: in this context, the game actions are not necessarily predetermined. Players may have different roles and must work together to continue to advance.

As we will see now, our main assumption is to use a role play approach where the user with her/his avatar is faced with practical problems of her/his everyday work (see below screenshots in Fig. 4 and3).

Change management process

Indeed, the change management (identified in the MPPI method as a transversal process ) is a sensitive issue at the origin of many failures. The causes of these problems are diverse (system malfunctions, poor ergonomics, ...). But they are often due to the reluctance of actors to use a new information system. The real cause of these rejections is relatively conventional: the user is forced to change from an informal environment to a formal one (their personal information becomes collective). It is thus important to make the user experiment effectively the gain brought by the new system.

Finally, the analysis of these results underscores the need to conduct a policy of change management that clearly explains the constraints of the system and the overall gain for the company and each of its actors. As it was defined, this approach is based on scenarios designed for including connections with the PLM system, as well as metaphors to introduce the game concepts concerning business process.

We thus experimented several scenarios for change management [START_REF] Pernelle | Serious gaming: A new way to introduce product lifecycle management[END_REF]. The following figure shows an example of scenario around the RFQ1 process. In these scenarios, the players must perform both game activities and business activities without then with a PLM system to better understand the benefits of these systems.

For example, the part without a PLM system exhibits the difficulty to retrieve a correct product reference at the right moment, at the right place. As everybody knows, a company with services, protocols, agents is always evolving and there is a gap between theory and practice.

Knowledge use and evaluation step

Concerning the second step, the final approach is similar but the cause is different. It is well-known that it is difficult to extract tacit expert knowledge from the workers. We faced with same problems when exploiting the method or even conceiving the serious game. Nevertheless each serious game is finished with a debriefing discussion in order to better incorporate the acquired knowledge and surprisingly, we observed that the experts have naturally exposed their reticences or doubts concerning the models they found in the game during such a discussion with the others.

We decided then to adapt our scenarios in order to actively promote the identification and validation of knowledge. Our proposal is to provide additional context that allows the player to explicitly validate his skills about the domain. We have established a dual strategy to answer this question : on the one hand, we added some quests specifically dedicated to the knowledge use; on the other hand, we have added new artifacts in the game.

This new game context is characterized by new indicators, an annotation tool and the ability to learn new skills (Fig. 3):

• The new K-quests are game activities (or industrial activities in PLM) concerning knowledge or result from an acquaintance. A K-quest can be individual or collective.

• The K-indicators that may be individual (or collective) ones, represent the level of expertise of the player (or group of players). This indicator is viewable by the player and the value of its skill level is affected by some particular game actions including the use of the annotation tool. • The K-annotation tool is an artifact that the player can use in some situations (interaction with NPC 2 , object, ...). Annotation is a simple marking (grading system equivalent to "i like") or a marking type description (with additional text). The use of this tool automatically modifies the previous indicator. • New K-skills explicitly characterize the actors (or groups of actors) whose expertise level indicator is considered relevant at the end of the scenario.

In order to be able to evaluate dynamically the concept acquisition, the whole system is traced: the business system and the serious game environment as we will see later. This allow us to assess the skills and the expertise level.

Skills and expertise level

Traces collection aims to be able and provide indicators and also to calculate the user model of each player. This user model characterizes the whole user skills. We define a user model simply from a declarative manner as the following set:

UM p = {(p, skill i )/p = player, skill i = ( f ield, value)i > 0} (1)
The user model is used to calculate, for each player, a set of characteristics acquired during the game. In our case, game activities, activities within the PLM and annotations will provide traces needed to calculate the user model of each player.

The user model skills have two uses: On one hand, it allows to obtain game artifacts that increase player motivation; on the other hand, it identifies motivated people and those who are able to validate a specific knowledge. The definition of K-skill can be seen as a motivating factor, but it should help especially characterized objectively the actors expertise according to activities that have been traced in the game.

Finally, it is the combined use of these tools (K-Quest, K-Annotation, K-Indicator, K-Skill) which allows us to define a global scenario of knowledge validation. All these scenarios have been experimented several times in real situations with a specific serious game environment that will be described in the following sections.

A Serious Game use for MPPI enactment

A generic Serious Game platform : Learning Adventure

Learning Adventure (L.A.) is a generic Serious Game based on a role-play approach [START_REF] Baptista | Funchal 500 years: Learning through role play games[END_REF][START_REF] Yu | Learning in the virtual world : the pedagogical potentials of massively multiplayer online role playing games[END_REF]. The players (students or teachers), possibly represented by their own avatars, can move through the environment, performing a sequence of sub activities in order to acquire knowledge. This environment is generic in the sense that the teacher can adapt the environment before the session by setting pre-requisites between sub activities and by providing different resources (documents, videos, quizzes) linked to the course. The collaboration takes place in L.A. by constituting groups of users. The NonPlayableCharacters (NPCs) give objectives to the members of a group and provide them with access to collaborative tools. As said before, we have modeled a Fig. 3 Additional device for knowledge company building from the actual architectural plans in order to ensure the players' immersion. Indeed, it is easier for them to find the different locations (e.g. coffee room, secretary's office) in the game if they are situated in the same places as in the real building. A compass to help players reach a specific place is however available in the game (see the upper right circle in Fig. 4). Moreover, the fact that the users understand that this game or formation is specifically dedicated to them is a great factor of motivation.

As mentioned in the previous section, in the game environment we also get a lot of trace left by the users in order to adapt the system.

Traces analysis and indicators

The implemented system uses all significant traces : game traces (interactions, movement, etc.) and activity traces within the PLM system (document consultation, creation, etc.). The aim of these traces is to improve the user monitoring for individual actions but also and especially during interactions and group actions. Annotation traces will complement game traces and activity traces. The interest of these annotation traces is twofold : on the one hand, they are used to validate PLM data and Fig. 4 The Learning Adventure Serious Game Environment business rules that were identified as holder of knowledge by expert. On the other hand, they can implicitly define an "organizational mapping" of knowledge. Here, the meaning of mapping concerns actors' identification with a level of professional expertise in relation to the formalized knowledge.

In the previous example, relevant traces for the expert analysis are:

• Moves and passed time in interaction with the NPC that informs the mini-quest.

• Dialogues (with "chat" = instant messaging) between the players during this period • Consultations within the PLM system on the data related to the injection speed • Players' responses to the proposal • Number of annotation by player and their descriptions They are used by the trainer to validate with the business expert, the relevance of formalized knowledge and the actors identified as mastering this knowledge.

Aggregating different indicators allows us to define a K-indicator. This Kindicator is a visual element of motivation for the players.

Concerning the experiments, the system is now used in education for several years (more than 500 persons) but there are each year some slight evolutions in order to improve the system or to adapt to a changing context (sessions with industrial experts for example). In the following section, we will describe the general conditions of experiments in formation context and give some feedback concerning the user acceptation of the system.

Conditions of experiments and results

Experiments have taken place in general training programs (master's degrees) as well as in a further training course for interested professionals. All experiments were conducted in the same experimental context. During the experiments, all groups of people were present with a teacher and an external observer. Concerning the social presence perception [START_REF] De Kort | People, places, and play: Player experience in a sociospatial context[END_REF], players were oriented one behind the other, limiting mutual eye contact, in a row of four students. Each student accessed the virtual environment through her/his workstation and had a personal (adapted) view on the world. They were explicitly allowed to communicate through the chat tool provided with the system and were warned that they would be observed and filmed concerning the use of the system.

We did two types of experiment. The first one dealt with students who had a basic level of knowledge concerning PLM (for change management). This experiment took place in a PLM training module for the Institute of Technology in Lyon. This training module is an introductory module lasting 15 hours with second year students. These students did not know the PLM but had skills in mechanical engineering. 254 students from 18 to 21 years old were split into 20 practical work groups. 10 groups started the module by playing the game scenario, without any theoretical lesson. The other ten groups did have two hours of theoretical training on PLM before their experiment in order to evaluate the benefit of the learning game session. All the experiments took place in the same room belonging to AIP-Primeca (Regional Engineering platform organization).

The second experiment was carried out with students who had no knowledge on PLM (For knowledge evaluation). This experiment took place with a group of students preparing a master's degree in the PLM domain. Each student involved in this one-year program works part-time for his/her company (one week at the university, three weeks in his/her company). The experiment took place on the last day of the first week at the university. At this time, the students had attended theoretical lessons and practical classes concerning another PLM system than the one included in the Serious Game Scenario. The students were aged from 24 to 50 years old. They had all chosen this training program for new opportunities and jobs offered in this domain. The initial skills of the students were diverse (computer science, electrical engineering, industrial engineering).

Thanks to traces and indicators, correct actions were automatically rewarded with the relevant skill level up. Concerning these experiments, two evaluation methods were chosen:

• Quantitative, thanks to collaborative indicators elaborated with traces left by the users when collaborating, • Qualitative, with live questions at the end of the session and explicit feedback from the teacher/PLM expert.

We can observe :

• 90 % of the participants have identified the features and goals of the systems and 40 % would have recommended them to their manager (3% before using the game). • The number of student requests for collaborative projects has been multiplied by two. In the second experiment, the sequence of the game session has had no measurable impact on student achievement. • The work on the knowledge validation has implicitly validated 70% of structural models defined in the PLM system.

Conclusion

In this article, we explained that we tried to couple a methodology for PLM integration and a serious game in order to facilitate the change management and the knowledge capitalization. From our point of view, the results are satisfying. Indeed, these approaches are very attractive thanks to their novelty and thus reinforce the motivation of the users. The immersion is also used to help the users to exhibit tacit or expert knowledge more easily. Some drawbacks remains: some parts concerning the game elaboration are always costly in time and expensive in code/design development. The sessions are limited to around 20 persons at the same time for the moment. Nevertheless, some reuse possibilities are more and more evident when we are elaborating new scenarios indicating a certain maturity for the approach. The PLM domain is also evolving and for future work, we are studying the possibilities of extension given by Service Lifecycle Management (SLM) or Knowledge Lifecycle Management (KLM),

Fig. 2

 2 Fig. 2 Steps in the MPPI-KI method

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