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Experimental investigation of a helicopter rotor with Gurney flaps
Get PDFThe present work describes an experimental activity carried out to investigate the performance of Gurney flaps on a helicopter rotor model in hovering. The four blades of the articulated rotor model were equipped with Gurney flaps positioned at 95% of the aerofoil chord, spanning 14% of the rotor radius. The global aerodynamic loads and torque were measured for three Gurney flap configurations characterised by different heights. The global measurements showed an apparent benefit produced by Gurney flaps in terms of rotor performance with respect to the clean blade configuration. Particle image velocimetry surveys were also performed on the blade section at 65% of the rotor radius with and without the Gurney flaps. The local velocity data was used to complete the characterisation of the blade aerodynamic performance through the evaluation of the sectional aerodynamic loads using the the control volume approach
Risultati di un Confronto Teorico-Sperimentale nello Studio delle Caratteristiche Aerodinamiche di una Fusoliera di Elicottero
No full text3D simulation of Vajont disaster. Part 1: Numerical formulation and validation
No full textThis work presents a numerical method for the simulation of landslides generated impulse waves and its application to the historical Vajont case study. The computational tool is based on the Particle Finite Element Method (PFEM), a Lagrangian strategy that combines the finite element solution of the governing equations with an efficient remeshing strategy to deal with large deformation problems. After presenting the numerical formulation, different landslide impulse wave problems with Froude number ranging from 0.5 to 2.8, are analyzed to validate the proposed methodology. The computational method is shown to be able to reproduce accurately the landslide runout, the momentum transfer between the sliding material and the impounded water, and the consequent wave propagation observed in experimental physical models. Then, the PFEM model is applied to the numerical simulation of the Vajont disaster, which is analyzed with a fully-resolved three-dimensional model. The numerical results are discussed and compared to the post-event observations and the numerical results of other computational methods. The results in terms of landslide velocity and runout, geometry of the deposit, maximum water runup, dam overtopping wave, and water discharge in the downstream valley are in good agreement with observations and reconstructions. The calibration and validation performed for this study form the basis for the PFEM analyses presented in a companion paper finalized to simulate different scenarios of the Vajont rockslide considered in the experimental tests done a year before the disaster
3D simulation of Vajont disaster. Part 2: Multi-failure scenarios
Full text linkPrediction of multi-hazard slope stability events requires an informed and judicious choice of the possible scenarios. An incorrect definition of landslide conditions in terms of expected failure volume, material behavior, or boundary conditions can lead to inaccurate predictions and, in turn, to wrong engineering and risk management decisions. Reduced-scale experiments carried out two years before the Vajont disaster were carried out with a material not representative of the actual rockslide behavior and failed in not considering the simultaneous failure of the whole landslide body. Based on these inappropriate assumptions, the physical models led to wrong estimates of the safety operational level for the Vajont reservoir. This work uses the Particle Finite Element Method (PFEM) to analyze the implications of the wrong hypotheses considered in the pre-event experiments, simulating numerically the Vajont disaster for different sliding volumes and material properties. The use of the PFEM for the accurate assessment of the consequences of landslides impinging in water reservoirs has been already validated in a companion paper. In this work, we demonstrate the capabilities of a robust and reliable numerical modeling approach for the simulation of different scenarios, assessing what could have been a safe operational reservoir level in the case of a landslide generated impulse wave. The three-dimensional analyses were run with a high mesh resolution and demonstrate the suitability and robustness of the PFEM model for large-scale landslide and multi-hazard events simulation
Investigating the influence of block rotation and shape on the impact process
No full textA block impact model based on the elasto-viscoplastic macro element approach is developed for regular base prismatic blocks. This model upgrades a previously conceived model for spherical boulders introducing (i) a rotational degree of freedom; (ii) a moment-rotation relationship; (iii) a toppling mechanism. The model can improve rockfall simulations by considering block geometry and the exchange between translational and rotational energies. Model parameters were calibrated by using laboratory tests on vertical impacts. Parametric analyses were carried out to investigate for both vertical and inclined impacts, the effects of block shape and orientation. The influence of these factors on the impact force, the maximum penetration depth as well as the exchange between translational and rotational energies is discussed. A comparison with the available results for small and large scale laboratory tests shows model capabilities and put in evidence the “nonlinear” relationship between maximum acceleration (or equivalently the maximum contact force) and impact translational velocity. For vertical impacts the trend of the maximum penetration depth is a function of the block shape. Prismatic blocks can experience larger values of maximum penetration than spherical blocks characterized by coincident masses and kinetic energies. In case of bouncing of a prismatic block the increment of normal maximum displacement with respect to spherical blocks ranges from about 66% for triangular base prisms to 132% for hexagonal base blocks. In case of no bouncing, the increments range from about 82% for triangular blocks to −32% for hexagonal blocks. Maximum normal forces also depend on block shape and orientation. In case of a vertex impact with no bouncing, triangular blocks show a decrement in the maximum force of about 43% with respect to the spherical block. The increment of initial block angular velocity generates a reduction in both maximum penetration depths and impact forces
Numerical simulation of water waves generated by landslides impact. Application to Vajont disaster
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