Search

Cable-driven parallel robots are a type of parallel manipulators where rigid links are replaced by actuated cables. Although in many cases dynamic models that neglect the cables mass and elasticity are employed to simulate the robot behavior and test the control approach to be used, there are several situations in which their effect cannot be disregarded, especially when large span cables are used, and the cable mass density generates important cable sagging. This work proposes a dynamic model for planar cable-driven parallel robots with 3 degrees-of-freedom considering cables mass and elasticity. Furthermore, the effect of using control approaches based on massless inelastic cables dynamic models on robots with non-negligible cable mass and elasticity is finally assessed.

Masonry structures represent large part of the historical and cultural built heritage in Europe. The assessment of their structural behaviour is critical for the preservation and conservation of buildings, monuments and infrastructures especially in seismic areas. In particular, one relevant issue is the evaluation of damage and residual load-bearing capacity of historical masonry structures affected by earthquakes. Such evaluation is necessary to assess structural safety, in order to define posteriori actions such as evacuation, retrofitting or demolition. A successful technique aimed at better knowing the dynamical behaviour of a structure is Operational Modal Analysis (OMA), in which the modal properties of the system are identified based on vibration data collected when the structure is under operating conditions. In Structural Health Monitoring (SHM) analysis, any variation of such modal properties could be considered as an indicator of modifications induced in the structure, such as change in mass or stiffness due to environmental agents or development and propagation of damage. The identification of the location, the type and the severity of the damage entails the solution of a further inverse problem, in which modal data, possibly coupled to other sources of information, are exploited for the assessment of such damage. In this paper, a novel comprehensive procedure is proposed for the identification of damage in masonry structures after a seismic event. The procedure relies on the acquisition of operational vibration data before and after an earthquake. In a first phase, those data are analysed by means of Stochastic Subspace Identification (SSI) to estimate frequencies and modal shapes of the linear system in undamaged and damaged conditions respectively. Afterwards, such modal properties are used as input for the inverse problem of estimating material parameters for an approximate numerical model representing the structure. The proposed methodology is applied to a pseudo-experimental case study in which the acceleration data are provided as the output of a mesoscale numerical representation of a 3D masonry building. The same building is then modelled with a macroscale approach using a homogenous isotropic model, whose damaged and undamaged features are identified by means of inverse analysis against the SSI output. The results show the potential of the proposed approach, where simple and non-destructive measurements are coupled to advanced computational methodologies to provide a comprehensive framework for damage identification after seismic events.

Shell has developed a novel mono-diameter well concept for oil and gas wells as opposed to the traditional telescopic well design. A Mono- diameter well contains multiple casing sections with the same internal diameter. This is achieved by expansion of the casing sections concerned using an expansion cone. Since the well is drilled in stages and casings are inserted to support the open hole, an overlap section between two consecutive (expandable) casings exists which has to be expanded. When the cone enters the overlap section, the expansion force increases dramatically due to the expansion of two casings, cured cement and formation layers. When the cone finalizes the expansion of the overlap section it pops out, the expansion force vanishes and the cone accelerates upwards and it generates an empty volume to be filled by the well fluid (mud). As a result of this, fluid starts to flow through the drill pipe, around the cone and the fluid volume below the cone starts to decompress. This induces a surge pressure wave traveling upwards and a swab pressure wave in the expanded casing traveling downwards. If the pressure difference between outside and inside of the expanded casing exceeds the collapse rating of the casing, the casing will collapse which leads to the loss of the concerned well section. Repair of such a failure costs time and money, therefore this swab pressure must be well predicted to enable the installation process to be designed such that this collapse can be avoided. A model of fully coupled fluid-structure interaction between cone and the well fluid is built for calculating the swab pressure propagating downward and surge pressure propagating upward resulted from transient process occurring after cone pops out. This model has shown an effective tool for predicting the swabbing pressure in field deployments performed lately in Gulf of Mexico and according to its output the suitable cone is selected in order to avoid the casing collapse.