External temperature effects on the hysteresis of NiTi wires in dampers for stay-cables

The use of NiTi wires, one of the Shape Memory Alloy (SMA) materials that permits efficient damping in stayed cables for bridges, requires an appropriate behavior when exposed to the external temperature effects. The Clausius-Clapeyron thermodynamic equation establishes a shift of the hysteretic cycle in the stress-temperature representation of about 6 MPa/K for the used wires of diameter 2.46 mm. Hence, an adequate experimental study is necessary to characterize the temperature effects in working conditions. The conducted analysis is twofold. First, the practical evolution of the hysteresis cycle is investigated. The results suggest that the wire permits a completely satisfactory use for temperatures as low as 253 K (i.e., -20 oC). Second, the focus is placed on the effects of extreme winter actions (i.e., as low as 233 K or -40 oC). A preliminary stress aging process at 373K seems adequate to this requirement. Indeed, after the stress aging, the SMA wire increases their working domain by 300 or 400 MPa and the temperature domain is expanded by 30 – 50 K. Measurements visualizing recoverable dynamical actions in the SMA alloys are also outlined.Peer ReviewedPostprint (published version

The SMA: an effective damper in civil engineering that smoothes oscillations

The properties of SMA (Shape Memory Alloys, that are smart materials) are associated to a first order phase transition named martensitic transformation that occurs between metastable phases: austenite and martensite. At upper temperature or at lower stress the austenite is the metastable phase. The martensite appears at lower temperature or higher stresses. The hysteresis of the transformation permits different levels of applications, i.e., in their use as a damper. Two types of applications can be considered in damping of structures in Civil Engineering. The first one is related to diminishing the damage induced by earthquakes. The second one is a reduction of oscillation amplitude associate to an increase of the lifetime for the stayed cables in bridges.Peer Reviewe

Effects of strain aging in NiTi SMA wires for dampers

SMA NiTi wires experience evolution under constrained aging. A strain and temperature aging sequence is designed and experimented, to ascertain the functionality of the dampers exposed to weatheringPostprint (published version

Noves aportacions al coneixement de la flora vascular de les comarques meridionals de Catalunya. IV

En aquest treball aportem dades de 30 plantes vasculars trobades a les muntanyes Catalanídiques centrals i meridionals catalanes. Campanula fastigiata Duf. ex A. DC., Centunculus minimus L., Cephalaria syriaca (L.) Roem. & Schult, Orobanche clausonis Pomel i Rosa andegavensis Bastard, suposen novetats per a aquest territori. S'hi presenten també dades de plantes molt poc citades en aquest territori o a Catalunya: Athyrium filix-femina (L.) Roth, Chaenorhinum rubrifolium (DC.) Fourr. subsp. rubrifolium, Dactylorhiza insularis (Sommier) Ó. Sánchez & Herrero, Milium vernale Bieb., Myosotis discolor Pers., Ophrys insectifera subsp. subinsectifera (C.E. Hermos. & Sabando) O. Bolòs & Vigo, Orobanche alba Stephan ex Willd., Orobanche elatior Sutton subsp. icterica (Pau) A. Pujadas, Potamogeton densus L., Sideritis montana L. o Sisymbrium erysimoides Desf.Here we report data concerning 30 vascular plants recorded in the central and southern Catalanídic's mountains. Campanula fastigiata Duf. ex A. DC., Centunculus minimus L., Cephalaria syriaca (L.) Roem. & Schult, Orobanche clausonis Pomel and Rosa andegavensis Bastard, represent novelties to this territory. We also present data about rare or little cited plants in this area or in Catalonia: Athyrium filix-femina (L.) Roth, Chaenorhinum rubrifolium (DC.) Fourr. subsp. rubrifolium, Dactylorhiza insularis (Sommier) Ó. Sánchez & Herrero, Milium vernale Bieb., Myosotis discolor Pers., Ophrys insectifera subsp. subinsectifera (C.E. Hermos. & Sabando) O. Bolòs & Vigo, Orobanche alba Stephan ex Willd., Orobanche elatior Sutton subsp. icterica (Pau) A. Pujadas, Potamogeton densus L., Sideritis montana L. or Sisymbrium erysimoides Desf

New contributions to the knowledge of the vascular flora of the southern regions of Catalonia. IV

En aquest treball aportem dades de 30 plantes vasculars trobades a les muntanyes Catalanídiques centrals i meridionals catalanes. Campanula fastigiata Duf. ex A. DC. , Centunculus minimus L. , Cephalaria syriaca (L. ) Roem. & Schult, Orobanche clausonis Pomel i Rosa andegavensis Bastard, suposen novetats per a aquest territori. S’hi presenten també dades de plantes molt poc citades en aquest territori o a Catalunya: Athyrium filix-femina (L. ) Roth, Chaenorhinum rubrifolium (DC. ) Fourr. subsp. rubrifolium, Dactylorhiza insularis (Sommier) Ó. Sánchez & Herrero, Milium vernale Bieb. , Myosotis discolor Pers. , Ophrys insectifera subsp. subinsectifera (C. E. Hermos. & Sabando) O. Bolòs & Vigo, Orobanche alba Stephan ex Willd. , Orobanche elatior Sutton subsp. icterica (Pau) A. Pujadas, Potamogeton densus L. , Sideritis montana L. o Sisymbrium erysimoides Desf.Here we report data concerning 30 vascular plants recorded in the central and southern Catalanídic’s mountains. Campanula fastigiata Duf. ex A. DC. , Centunculus minimus L. , Cephalaria syriaca (L. ) Roem. & Schult, Orobanche clausonis Pomel and Rosa andegavensis Bastard, represent novelties to this territory. We also present data about rare or little cited plants in this area or in Catalonia: Athyrium filix-femina (L. ) Roth, Chaenorhinum rubrifolium (DC. ) Fourr. subsp. rubrifolium, Dactylorhiza insularis (Sommier) Ó. Sánchez & Herrero, Milium vernale Bieb. , Myosotis discolor Pers. , Ophrys insectifera subsp. subinsectifera (C. E. Hermos. & Sabando) O. Bolòs & Vigo, Orobanche alba Stephan ex Willd. , Orobanche elatior Sutton subsp. icterica (Pau) A. Pujadas, Potamogeton densus L. , Sideritis montana L. or Sisymbrium erysimoides Desf

Simultaneous mapping and planning for autonomous underwater vehicles in unknown environments

New potential applications of autonomous underwater vehicles (AUVs) involve operations in unknown and cluttered environments, therefore increasing the vehicle exposure to collisions. To cope with these situations, we use an AUV framework for planning collision-free paths in unknown environments, which adapt and replan the paths according to nearby obstacles perceived during the mission execution using different range sensing sonar. We present simulation and real-world results for the SPARUS-II AUV, a torpedo-shaped vehicle, performing autonomous missions

SMA in mitigation of extreme loads in civil engineering: study of their application in a realistic steel portico

Guaranteeing the use of Shape Memory Alloys (SMA) in mitigation of extreme load effects requires a deep study of the SMA behavior according to the specific requirements of the applications in damping. The damper was defined according the expected requirements (length of SMA and number of SMA wires). It is applied to two types of alloys (CuAlBe and NiTi) in the diagonals of a realistic steel portico (2.47 m x 4.10 m). The measurements establish that the used SMA reduces the oscillation amplitude to a less than a half.Preprin

Online path planning for autonomous underwater vehicles in unknown environments

We present a framework for planning collision-free paths online for autonomous underwater vehicles (AUVs) in unknown environments. It is composed of three main modules (mapping, planning and mission handler) that incrementally explore the environment while solving start-to-goal queries. We use an octree-based representation of the environment and we extend the optimal rapidly-exploring random tree (RRT*) using concepts of anytime algorithms and lazy collision evaluation, thus including the capability to replan paths according to nearby obstacles perceived during the execution of the mission. To validate our approach, we plan paths for the SPARUS-II AUV, a torpedo-shaped vehicle performing autonomous missions in a 2-dimensional workspace. We demonstrate its feasibility with the SPARUS-II AUV in both simulation and real-world in-water trials

On-line 3D path planning for close-proximity surveying with AUVs

We present an approach for planning collision-free paths on-line for an underwater multi-robot system, which is composed by a leading Autonomous Underwater Vehicle (AUV) endowed with a multibeam sonar and high processing capabilities and a second AUV. While the leading AUV follows a safe, pre-planned survey path, the second vehicle, herein referred to as Camera Vehicle (CV), must survey the bottom in close proximity while following the leader, complementing its survey capabilities. Due to their proximity to the bottom, the CV is exposed to a collision threat. We address this problem by incrementally building a 3D map of the environment onboard the leading vehicle by means of its multibeam sonar. Using this map, we plan on-line 3D paths that are transferred to the CV for close and safe surveying of the bottom. These paths are planned using the Transition-based RRT (T-RRT) algorithm, which is an RRT-variant that considers a cost function defined over the vehicle’s configuration space, or costmap for short. By defining a costmap in terms of distance to the bottom and path distance, we are able to keep the paths at a desired offset distance from the bottom for constant-resolution surveying. We have integrated our path planning system with the software architecture of the SPARUS-II and GIRONA500 AUVs. We demonstrate the feasibility of our approach in simulation. The multi-robot system presented is based on the context of the MORPH FP7 EU project