947 research outputs found
Numerical study on parametrical design of long shrouded contra-rotating propulsion system in hovering
The parametrical study of Shrouded Contra-rotating Rotor was done in this paper based on 2D axisymmetric simulations. The calculations were made with an actuator disk as double rotor model. It objects to explore and quantify the effects of different shroud geometry parameters mainly using the performance of power loading (PL), which could evaluate the whole propulsion system capability as 5 Newton total thrust generation for hover demand. The numerical results show that: The increase of nozzle radius is desired but limited by the flow separation, its optimal design is around 1.15 times rotor radius, the viscosity effects greatly constraint the influence of nozzle shape, the divergent angle around 10.5° performs best for any chosen nozzle length; The parameters of inlet such as leading edge curvature, radius and internal shape do not affect thrust greatly but play an important role in pressure distribution which could produce most part of shroud thrust, they should be chosen according to the reduction of adverse pressure gradients to avoid the risk of boundary separation
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Formation mechanism of streamer discharges in liquids: A review
Streamer discharges in liquids have received lots of attention with respect to their considerable applications in various disciplines. Much effort has been spent to understand the basis of streamer ignition and propagation in dielectric liquids, but a comprehensive mechanism is far from conclusive. In this review, based on an introduction to the streamer physics and experimentally observed characteristics in various liquids, the authors emphasise on the current status of streamer discharge ignition mechanisms and present their understanding for each theory
Performance improvement of the LM device and its application to precise measurement of motion trajectories within a small range with a machining centre
In order to apply the LM device previously developed to precisely measuring small motion trajectories located on the different motion planes, three major improvements are successfully performed under the condition of completely maintaining the advantages of the device. These improvements include 1) development of a novel connection mechanism to smoothly attach the device to the spindle of a machining centre; 2) employment of a new data sampling method to achieve a high sampling frequency independent of the operating system of the control computer; and 3) proposal of a set-up method to conveniently install the device on the test machining centre with respect to different motion planes. Practical measurement experiment results with the improved device on a machining centre sufficiently demonstrate the effectiveness of the improvements and confirm several features including a very good response to small displacement close to the resolution of the device, high precision, repeatability and reliance. Moreover, based on the measurement results for a number of trajectories for a wide range of motion conditions, the error characteristics of small size motions are systematically discussed and the effect of the movement size and feed rate on the motion accuracy is verified for the machining centre tested
Mathematical simulation of a dipole delivery system for in-situ remediation
Abstract
In-situ remediation using reactive zones is a promising groundwater contaminant treatment technology that involves the injection of a reagent(s) into the subsurface to destruct harmful target chemicals. For efficient and effective treatment the reagent has to be delivered into a specific contaminated zone for the desired chemical reaction(s) to occur. The most commonly used delivery method is a conventional well where the distribution of injected reagent is mainly controlled by the surrounding hydraulic conductivity field. In this case, the reagent is easily delivered into the higher hydraulic conductivity zones but the lower hydraulic conductivity zones are missed. The goal of this research effort is to investigate a novel delivery method involving a single well vertical recirculation system or a dipole well. The configuration of this single dipole well is that injection and extraction occurs from two chambers separated by an impermeable central packer. Thus, this dipole well system can induce predominantly vertical flow across bedding plane features and it is therefore hypothesised that this delivery system can overcome physical heterogeneities creating a more uniform reactive zone. The objective of this research was to demonstrate that the dipole well is a useful delivery tool compared to the commonly used single injection well.
Mathematical simulations were used to investigate the delivery performance of a dipole well using steady-state and transient approaches. A simple analytical model was used to determine the steady-state dipole flow field and observe the impact of system parameters on reagent delivery behaviour. The size of coverage area (the area swept by the injected reagent) was used as the performance metric to assess the impact of each system parameter on the dipole well performance. Numerical simulations were used to extend this investigation to homogeneous and heterogeneous (structured or randomly correlated hydraulic conductivity) aquifers under pulsed operation to identify those situations where the dipole delivery system is more efficient or effective. Both forward and backward particle path lines were used to identify reagent coverage areas around the injection well and down gradient. The impact of each system parameters on the dipole well performance was studied.
The shoulder length and the injection cost are characteristic parameters that affect dipole delivery performance. A relationship between the down gradient coverage area vs. characteristic system parameters was developed and can be used to predict the dipole well performance in homogenous aquifers. The impact of the hydraulic conductivity distribution on dipole well performance is consistent with either a structured hydraulic conductivity field or randomly correlated hydraulic conductivity fields. Regions of lower hydraulic conductivity can be swept by the dipole well and the dipole well outperforms a single injection well, which is analyzed as a base case in terms of the shape of down gradient coverage area. However, the advantage of dipole well over a single well delivery is small if the degree of heterogeneity is large or the horizontal extent of the bedding plane is small
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Eradication of unresectable liver metastasis through induction of tumour specific energy depletion.
Treatment of liver metastasis experiences slow progress owing to the severe side effects. In this study, we demonstrate a strategy capable of eliminating metastatic cancer cells in a selective manner. Nucleus-targeting W18O49 nanoparticles (WONPs) are conjugated to mitochondria-selective mesoporous silica nanoparticles (MSNs) containing photosensitizer (Ce6) through a Cathepsin B-cleavable peptide. In hepatocytes, upon the laser irradiation, the generated singlet oxygen species are consumed by WONPs, in turn leading to the loss of their photothermally heating capacity, thereby sparing hepatocyte from thermal damage induced by the laser illumination. By contrast, in cancer cells, the cleaved peptide linker allows WONPs and MSNs to respectively target nucleus and mitochondria, where the therapeutic powers could be unleashed, both photodynamically and photothermally. This ensures the energy production of cancer cells can be abolished. We further assess the underlying molecular mechanism at both gene and protein levels to better understand the therapeutic outcome
Revisiting Froude’s Theory for Hovering Shrouded Rotor
This paper extends Froude’s momentum theory for free propellers to the analysis of shrouded rotors. A one-dimensional analytical approach is provided, and a homokinetic normal inlet surface model is proposed. Formulations of thrusts and power for each system component are derived, leading to the definition of optimum design criteria and providing insight into the global aerodynamics of shrouded rotors. In the context of micro-air vehicles applications, assessment of the model is conducted with respect to numerical data. Overall, comparison between numerical and analytical results shows good agreement and highlights the sensitivity of the model to viscous effects
The and decays with the fourth generation
If the fourth generation fermions exist, the new quarks could influence the
branching ratios of the decays of and . We
obtain two solutions of the fourth generation CKM factor
from the decay of . We use these
two solutions to calculate the new contributions of the fourth generation quark
to Wilson coefficients of the decay of . The branching ratio
and the forward-backward asymmetry of the decay of in the two
cases are calculated. Our results are quite different from that of SM in one
case, almost same in another case. If Nature chooses the formmer, the meson
decays could provide a possible test of the forth generation existence.Comment: 10 pages, 5 figure
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