299 research outputs found
The capability enhancement of aluminium casting process by application of the novel CRIMSON method
The conventional foundry not only frequently uses batch melting, where the aluminium
alloys are melted and held in a furnace for long time, sometimes as long as a complete shift,
but also uses the gravity sand casting process where the molten aluminium alloys are
transferred using a ladle from furnace to pour station and are poured into a mould. During the
filling of the mould, the turbulent nature of the liquid metal gives rise to massive entrainment
of the surface oxide films which are the subsequently trapped into the liquid and act as micro
cracks. Also the long exposure time of the liquid surface to the surrounding environment
during melting, transferring and filling will increase the level of hydrogen absorption from
the atmosphere. The abovementioned factors are often the main reasons for casting defect
generation. In this paper the novel CRIMSON aluminium casting method is introduced which
has a number of advantages. Instead of gravity filling method, it uses the single shot upcasting
method to realize the rapid melting and rapid counter-gravity-filling mould operations
which reduce the contact time between the melt and environment thus reducing the
possibility of defect generation. Another advantage is the drastic reduction of energy
consumption due to shortened melting and filling time. A simulation software, FLOW-3D, is
used to compare this new method with the conventional gravity casting process. A tensile bar
case is used as a sample to simulate the filling process
The improvement of aluminium casting process control by application of the new CRIMSON process
All The traditional foundry usually not only uses batch melting where the
aluminium alloys are melted and held in a furnace for long time, but also uses
the gravity filling method in both Sand Casting Process (SCP) and Investment
Casting Process (ICP). In the gravity filling operation, the turbulent behaviour
of the liquid metal causes substantial entrainment of the surface oxide films
which are subsequently trapped into the liquid and generate micro cracks and
casting defects. In this paper a new CRIMSON process is introduced which
features instead of gravity filling method, using the single shot up-casting
method to realize the rapid melting and rapid filling mould operations which
reduce the contact time between the melt and environment thus reducing the
possibility of defect generation. Another advantage of the new process is the
drastic reduction of energy consumption due to shortened melting and filling
time. Two types of casting samples from SCP and ICP were compared with the new
process. The commercial software was used to simulate the filling and
solidification processes of the casting samples. The results show that the new
process has a more improved behaviour during filling a mould and solidification
than the two conventional casting processes
Energy-Efficient UAV Communications in the Presence of Wind: 3D Modeling and Trajectory Design
The rapid development of unmanned aerial vehicle (UAV) technology provides
flexible communication services to terrestrial nodes. Energy efficiency is
crucial to the deployment of UAVs, especially rotary-wing UAVs whose propulsion
power is sensitive to the wind effect. In this paper, we first derive a
three-dimensional (3D) generalised propulsion energy consumption model (GPECM)
for rotary-wing UAVs under the consideration of stochastic wind modeling and 3D
force analysis. Based on the GPECM, we study a UAV-enabled downlink
communication system, where a rotary-wing UAV flies subject to stochastic wind
disturbance and provides communication services for ground users (GUs). We aim
to maximize the energy efficiency (EE) of the UAV by jointly optimizing the 3D
trajectory and user scheduling among the GUs based on the GPECM. We formulate
the problem as stochastic optimization, which is difficult to solve due to the
lack of real-time wind information. To address this issue, we propose an
offline-based online adaptive (OBOA) design with two phases, namely, an offline
phase and an online phase. In the offline phase, we average the wind effect on
the UAV by leveraging stochastic programming (SP) based on wind statistics;
then, in the online phase, we further optimize the instantaneous velocity to
adapt the real-time wind. Simulation results show that the optimized
trajectories of the UAV in both two phases can better adapt to the wind in
changing speed and direction, and achieves a higher EE compared with the
windless scheme. In particular, our proposed OBOA design can be applied in the
scenario with dramatic wind changes, and makes the UAV adjust its velocity
dynamically to achieve a better performance in terms of EE.Comment: 31 pages, 13 figure
Research Letter Surface Adsorption and Replacement of Acid-Oxidized Single-Walled Carbon Nanotubes and Poly(vinyl pyrrolidone) Chains
Quartz crystal microbalance (QCM) was used to investigate the adsorption of acid-oxidized single-walled carbon nanotubes (OxSWNTs) and poly(vinyl pyrrolidone), PVP. It was found for the first time that Ox-SWNTs adsorbed onto the QCM electrode can be effectively replaced by PVP chains in an aqueous solution. This replacement process was also investigated by atomic force miscroscopic (AFM) imaging, which shows good agreement with the QCM measurements. This study provides powerful tools for fundamental investigation of polymer-nanotube interactions and for controlled design/fabrication of functional polymernanotube surfaces for potential applications. Carbon nanotubes have been demonstrated to possess excellent electronic [1], mechanical It is well known that polymer adsorption is a dynamic process, in which adsorbed polymer chains on a particular surface can be desorbed or replaced by other absorbing species that have a greater affinity to the surfac
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