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The Relevance of Damper Pre-Optimization and its Effectiveness on the Forced Response of Blades
No full textThe paper presents a calculation procedure for the design of turbine blades with underplatform dampers. The procedure involves damper "pre-optimization" before the coupled calculation with the blades. The pre-optimization procedure excludes, since the early design stage, all those damper configurations leading to low damping performance. Pre-optimization involves plotting a design "damper map" with forbidden areas, corresponding to poorly performing damper geometries and admissible design areas, where effective solutions for the damper shape can be explored. Once the candidate damper configurations have been selected, the damper equilibrium equations are solved by using both the multi-harmonic balance (MHB) method, and the direct time integration method (DTI). Direct time integration of the damper dynamic equations is implemented in order to compute the trend of the contact forces in time and the shape of the hysteresis cycles at the different contact points. Based on these trends, the correct number of Fourier terms to represent the contact forces on the damper is chosen. It is shown that one harmonic term together with the static term, are enough in the MHB calculation of a pre-optimized damper. The proposed method is applied to a test case of a damper coupled with two blades. Experimental forced response functions of the test case with a nominal damper are available for comparison. The purpose of this paper is to show the effectiveness of the "damper maps" in excluding all those damper configurations, leading to undesirable damper behavior and to highlight the strong influence of the blades mode of vibration on the damper effectiveness. From the comparison of dampers with different geometrical parameters, the pre-optimized damper proved to be not only the most effective, in terms of damping capability, but also the one that leads to a faster and more flexible calculation of the damper, coupled with the blades
Art and Colour in the Requalification of Urban Areas and Landscapes
No full textFor contemporary research, peripheral realities, urban voids or dismantled areas and structures represent important opportunities for urban regeneration and redevelopment. The Color, through the "Color Design", becomes an approach that can achieve remarkable and immediate results with low cost. It is capable of transforming the visual impact of a building, a road, an entire neighbourhood; it orientes and creates harmony through the Visual rules and hierarchies, it can recover the identity and image of a place; it can highlights and enhances paths, obstacles, zones, functions, services, or informs through their universally recognizable codes. Even today, Bruno Taut's idea of improving the quality of life in popular neighborhoods with the creation of polychrome architectures is a reference: the color therefore constitutes the "accessible" decoration even for the most deprived areas. Like Color, Art is a tool for social and urban upbringing. Nowaday, Art no longer needs to be confined in museums or galleries, but can be placed outdoors in an urban or landscape dimension, becoming public art (made of installations and large sculptures). The contribution, through the study of critically selected and analyzed case studies, tends to verify the validity of this thesis, confirming that Art and Color constitute both retraining tools and valuable media to promote the recognition of sites and services, attraction poles, urban presence, constituting a real urban communication strategy, without forgetting the role of social and cultural exchanges. Of course, the great challenge will be to combine, if possible, the above approaches with the "ways of sustainability"
Experimental investigation of out-of-plane constraint effect on fracture toughness of the SE(T) specimens
No full textIn the study, the experiments are performed to determine thickness effect on critical crack tip opening displacement (δ_IC) of the single-edge tension (SE(T)) specimen with side-groove. The applicability and thickness sensitivity of several fracture toughness estimation procedures are also investigated by the experimental data. Referring to the results by the double clip gauge method, it is found that the critical crack initiation toughness decreases significantly as specimen thickness increases until the thickness-to-width ratio equal to 4, beyond which thickness effect becomes relatively weak. Accordingly, a dimension size is recommended for the fracture toughness testing to take the out-of-plane constraint into account for SE(T) specimen. The further analyses based on the plastic zone size confirm the result as well
A study on the different finite element approaches for laser cutting of aluminum alloy sheet
No full textThe effectiveness of finite element simulation techniques for laser cutting of 1.2-mm-thick aluminium sheets has been studied. Lagrangian and Arbitrary Lagrangian-Eulerian techniques were used to model and simulate laser cutting process. The reliability of finite element results were evaluated by general energy balance analysis and experimental results. Temperature and stress distribution along with heat-affected zone were predicted during the laser-induced process in line with experimental conditions under ABAQUS finite element code. Heat transfer analysis relying on thermal loading was employed to reach the best efficiency. By using field-emission scanning electron microscope, morphological, structural, and elemental changes in the cutting sections were analyzed along with the X-ray diffraction technique. Obtained stress and heat-affected zone are highly dependent on the element type as well as numerical method. Both numerical method, ALE and Lagrangian, are compared to each other in terms of power absorption, cut surface morphology, and cutting efficiency. The results show that ALE method is in good agreement with experimental data. A study on the different finite element approaches for laser cutting of aluminum alloy sheet. Available from: https://www.researchgate.net/publication/317579195_A_study_on_the_different_finite_element_approaches_for_laser_cutting_of_aluminum_alloy_sheet [accessed Jul 3, 2017]
Motion control of mobile robots with Particle Filter Model Predictive Equilibrium Point Control
No full textThis paper describes an optimal motion control for mobile robots with differential drive. We propose a novel method called Particle Filter Model Predictive Equilibrium Point Control (PF-MPEPC) that implements robot navigation with obstacle avoidance in a structured environment. This control evaluates the near future behaviour continuously to generate an optimal trajectory that is safe and smooth. The Model Predictive Control approach minimizes a defined cost function by solving a non-linear optimization problem. It evaluates robot dynamics and control constraints. Our method uses the Equilibrium Point Control approach. It searches for an equilibrium point near the robot in order to satisfy the navigation requirements. Moreover the use of particle filters allows safety to be improved. This method is validated in a real case scenario with simple obstacles. The obtained results demonstrate that the robot executes safe, smooth and comfortable trajectories
La Maddalena exploratory tunnel
No full textThe Lyon-Turin high-speed rail project includes a 57.5 km long twin-tube base tunnel. The design uses data collected from four exploratory tunnels, three in France, completed in 2010, and one in Italy, named "La Maddalena". Excavation of this 7 km long Italian exploration tunnel was completed in February 2017 using a 6.3 m diameter main beam TBM under exceptionally high overburden of more than 2,000 m under the Ambin mountain slopes, where mild rockbursts were systematically experienced along nearly half of the alignment. The TBM excavated through gneiss and mica schists. Intercepted water inflows were lower than expected in the design phase, with temperature and chemical composition giving useful information. This exploration tunnel is the subject of the present paper
Improved Lp-Poincaré inequalities on the hyperbolic space
No full textWe investigate the possibility of improving the p-Poincare inequality parallel to on the hyperbolic space, where p > 1. We prove several different, and independent, improved inequalities, one of which is a Poincare-Hardy inequality, namely an improvement of the best p-Poincare inequality in terms of the Hardy weight 1/r^p, r being geodesic distance from a given pole. Certain Hardy-Mazya type inequalities in the Euclidean half-space are also obtained