653 research outputs found
Repairing 2024 Aluminum Alloy via Electrospark Deposition Process: A Feasibility Study
The electrospark deposition (ESD) technique has been studied as a potential method to repair locally damaged 2024 rolled sheets supplied in natural-aged (T4) and artificial-aged (T6) conditions. The 2024-T4 and 2024-T6 tensile samples were first notched, and then the notches were filled (repaired) by ESD with the same aluminum alloy. The effect of process parameters on the microstructure of the filling material and the substrate properties was studied by optical and scanning electron microscopy. Tensile and hardness tests were performed. The tensile test showed that T4 and T6 as-repaired specimens had low tensile properties, which was due to defectiveness and residual stress caused by high cooling rate during reparation. However, the as-repaired specimens were heat-treated at either 135°C or 190°C to improve the mechanical properties. A better yield strength was observed for the T4 heat-treated alloy. The ductility and ultimate tensile strength did not change, being mainly affected by voids and microcracks
Task priority control of underwater intervention systems: Theory and applications
This paper presents a unifying task priority control architecture for underwater vehicle manipulator systems. The proposed control framework can be applied to different operative scenarios such as waypoint navigation, assisted teleoperation, interaction, landing and grasping. This work extends the results of the TRIDENT and MARIS projects, which were limited to the execution of grasping actions, to other applications taken from the DexROV and ROBUST projects. In particular, simulation results show how the control framework can be used, for example, for pipeline inspection scenarios and deep sea mining exploration
Definition of a benchmark for low Reynolds number propeller aeroacoustics
Experimental and numerical results of a propeller of 0.3 m diameter operated at 5000 RPM and axial velocity ranging from 0 to 20 m/s and advance ratio ranging from 0 to 0.8 are presented as a preliminary step towards the definition of a benchmark configuration for low Reynolds number propeller aeroacoustics. The corresponding rotational tip Mach number is 0.23 and the Reynolds number based on the blade sectional chord and flow velocity varies from about 46000 to 106000 in the operational domain and in the 30% to 100% blade radial range. Force and noise measurements carried out in a low-speed semi-anechoic wind-tunnel are compared to scale-resolved CFD and low-fidelity numerical predictions. Results identify the experimental and numerical challenges of the benchmark and the relevance of fundamental research questions related to transition and other low Reynolds number effects
Towards the definition of a benchmark for low Reynolds number propeller aeroacoustics
Experimental and numerical results of a propeller of 0.3 m diameter operated in
quiescent standard ambient conditions at 5000 RPM and axial velocity ranging from 0 to 20
m/s and advance ratio ranging from 0 to 0.8 are presented as a preliminary step towards the
definition of a benchmark configuration for low Reynolds number propeller aeroacoustics. The
corresponding rotational tip Mach number is 0.231 and the Reynolds number based on the blade
sectional chord and flow velocity in the whole radial and operational domain ranges from about
54000 to 106000. Force and noise measurements carried out in a low-speed semi-anechoic windtunnel are compared with scale-resolved CFD and low-fidelity numerical results. Results identify
the experimental and numerical challenges of the benchmark and the relevance of fundamental
research questions related to transition and other low Reynolds number effects
Distributed Task-priority Based Control in Area Coverage & Adaptive Sampling
Abstract\u2014The paper presents the first simulative results and
algorithmic developments of the task-priority based control
applied to a distributed sampling network in an area coverage
or adaptive sampling mission scenario. The proposed approach
allowing the fulfilment of a chain of tasks with decreasing priority
each of which directly related to both operability and safety
aspects of the entire mission. The task-priority control is presented
both in the centralized and decentralized implementations
showing a comparison of performance. Finally simulations of
the area coverage mission scenario are provided showing the
effectiveness of the proposed approac
ROBUST project: Control Framework for Deep Sea Mining Exploration
This paper presents the control framework under
development within the ROBUST Horizon 2020 project, whose
goal is the development of an autonomous robotic system for
the exploration of deep-sea mining sites. After a bathymetric
survey of the initial zone of interest, the robotized system selects
a subarea deemed to have the most chances of containing a
manganese nodule field and proceeds with a detailed low altitude
survey. Whenever a possible nodule is found, it performs an insitu
measurement through laser induced spectroscopy. To do so,
the underwater vehicle must first land on the seafloor, with a
certain precision to allow a subsequent fixed-based manipulation,
bringing its manipulator endowed with the laser system in
the position to carry out the measurement. The work reports
the developed control architecture and the simulation results
supporting it
Effect of feed supplementation with Origanum vulgare L. essential oil on sea bass (Dicentrarchus labrax): A preliminary framework on metabolic status and growth performances
This study provided a preliminary framework for the effects of Origanum vulgare L. essential oil (EO) on sea bass (Dicentrarchus labrax) health status over a 60-day feeding trial. Fish were fed twice a day until apparent satiety with three different diets: a control diet (CD), and two experimental diets supplemented with 100 (D100) and 200 (D200) ppm of oregano EO. No mortality was observed in each treatment. Feeding on D100 diet resulted in high growth performances and better food conversion and protein efficiency ratios. Additionally, the supplementation of 100 ppm EO diet also improved (P < 0.05) hepatosomatic and viscerosomatic indices, compared both to control and D200 diets. EO feeding positively affected (P < 0.05) several serum biochemical indices (amylase activity and total proteins, glucose, triglycerides, and cholesterol levels). Focusing on the antioxidant potential of blood, D100 led to the highest (P < 0.05) ferric reducing antioxidant power values and the lowest (P < 0.05) thiobarbituric acid-reactive substances levels in blood
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