2,809 research outputs found
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Normal Rack Grid Generation Method for Screw Machines with Large Helix Angles
Improving the efficiency of the screw machine is highly significant for industry. Numerical simulation is an important tool in developing these machines. The 3D computational fluid dynamic simulation can give a valuable insight into the flow parameters of screw machines. However, it is currently difficult to generate high quality computational grids required for screw rotors with large helix angle. This is mainly due to the excessively high cell skewness of the rotors with large helix angel, which would introduce errors in numerical simulation. This paper presents a novel grid generation algorithm used for the screw rotors with large helix angel. This method is based on the principles developed for the grid generation in transverse cross-section. Such mesh is generated by SCORGTM using normal rack grid generation method which means numerical meshes are generated in a plane normal to the pitch helix line. The mesh lines are then parallel to the helix line and thus an orthogonal mesh will be produced. The main flow and leakage flow directions are orthogonal to the mesh, potentially reducing numerical diffusion. This developed algorithm could also be employed for single screw machines
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Numerical investigation of oil injection in a Roots blower operated as expander
The adoption of positive displacement machines as expanders in Organic Rankine Cycles (ORCs) is increasingly common, especially in the low to medium power range. At the same time, these devices often serve as compressor in Vapor-Compression Refrigeration Systems. In both cases, the application of Computation Fluid Dynamics (CFD) to optimize such machines has become an integrated tool in the design process. As a consequence, several challenges associated with the numerical simulation have to be taken into account. For example, the modeling of the gap represents a challenge for the stability of the numerical analysis. The dynamic of the process, combined with deformations of the clearances and of the working chamber has to be considered with extra care. To raise the efficiency of the machine, oil is typically injected. Its numerical modeling imply an extra challenge in the simulation of the actual operation of the machine. The present work is mainly focused on the multi-phase nature of the flow, with a particular analysis of the lubricant oil injected. In this work, a two-lobe Roots blower operated as expander has been simulated with the open-source software OpenFOAM-v1812, using the SCORG-V5.2.2. This analysis highlights the areas that are affected the most by the oil presence in order to highlight the sealing effect it provides
A search for rotating radio transients and fast radio bursts in the Parkes high-latitude pulsar survey
Discoveries of rotating radio transients and fast radio bursts (FRBs) in
pulsar surveys suggest that more of such transient sources await discovery in
archival data sets. Here we report on a single-pulse search for dispersed radio
bursts over a wide range of Galactic latitudes (|b| < ) in data
previously searched for periodic sources by Burgay et al. We re-detected 20 of
the 42 pulsars reported by Burgay et al. and one rotating radio transient
reported by Burke-Spolaor. No FRBs were discovered in this survey. Taking into
account this result, and other recent surveys at Parkes, we corrected for
detection sensitivities based on the search software used in the analyses and
the different backends used in these surveys and find that the all-sky FRB
event rate for sources with a fluence above 4.0 Jy ms at 1.4 GHz to be FRBs day sky, where the
uncertainties represent a confidence interval. While this rate is lower
than inferred from previous studies, as we demonstrate, this combined event
rate is consistent with the results of all systematic FRB searches at Parkes to
date and does not require the need to postulate a dearth of FRBs at
intermediate latitudes.Comment: Accepted, 10 pages, 6 figure
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Grid deformation strategies for CFD analysis of screw compressors
Customized grid generation of twin screw machines for CFD analysis is widely used by the refrigeration and air-conditioning industry today, but is currently not suitable for topologies such as those of single screw, variable pitch or tri screw rotors. This paper investigates a technique called key-frame re-meshing that supplies pre-generated unstructured grids to the CFD solver at different time steps. To evaluate its accuracy, the results of an isentropic compression-expansion process in a reciprocating piston cylinder arrangement have been compared. Three strategies of grid deformation; diffusion equation mesh smoothing, user defined nodal displacement and key-frame remeshing have been assessed. There are many limitations to key-frame re-meshing. It requires time consuming pre-processing, has limited applicability to complex meshes and leads to inaccuracies in conservation of calculated variables. It was concluded that customized tools for generation of CFD grids are required for complex screw machines
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Cage aquaculture requires suitable site, materials to fabricate cage, nutritionally
balance feed and healthy seed. The cage farm depending upon intensification generates the
considerable wastes which include uneaten food, excretory products (faecal matter and
urinary products). Many cage aquaculture activities utilize chemicals for prophylactic as well
as therapeutic purpose which further contributes to the total waste discharge. Further,
microorganisms and parasites associated with caged fish also contribute towards cumulative
environmental degradation
Secure Authentication Using Click Draw Based Graphical Password Scheme
Graphical passwords are an alternative to alphanumeric passwords in which users click on images to authenticate themselves rather than type alphanumeric strings. We have developed one such system, called Secure Authentication using Click Draw Based graphical password scheme, and evaluated it with human users. Secure Authentication using Click Draw Based graphical password scheme, including USAbility and security evaluations, and implementation considerations. An important USAbility goal for knowledge-based authentication systems is to support users in selecting passwords of higher security, in the sense of being from an expanded effective security pace. We use the sequence of multiple images along with a dummy image and alsoa pattern on any single image to influence user choice in click draw based graphical passwords, encouraging users to select more random, and hence more difficult to guess patterns
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For the grow-out trials, circular cages of diameter ranging from 6-15 meters have
been tried by CMFRI. However, cage diameter 6-10 is recommended for the culture of
Mullet, Cobia, Pompano, Sea bass and Pearl spot. The grow-out of candidate species in caged
enclosures requires proper planning and management. The critical inputs like right kind of
seed, nutritionally balanced feed and routine cage maintenance activity decide the success of
grow-out production. Unlike closed or semi-closed culture systems, marine environment is
more diverse and dynamic, thus did not offer much scope for the environmental as well as
biological manipulations. After proper site selection and cage installations, cages should be
stocked with recommended numbers of seed depending upon water volume/ cage area
Subarachnoid haemorrhage due to intracranial vertebral artery dissection presenting with atypical cauda equina syndrome features: case report
BACKGROUND: Failing to recognise the signs and symptoms of subarachnoid haemorrhage (SAH) causes diagnostic delay and may result in poorer outcomes. We report a rare case of SAH secondary to a vertebral artery dissection (VAD) that initially presented with cauda equina-like features, followed by symptoms more typical of SAH. CASE PRESENTATION: A 55-year-old man developed severe lower back pain after sudden movement. Over the next 5 days he developed paraesthesiaes in the feet, progressing to the torso gradually, and reported constipation and reduced sensation when passing urine. On day six he developed left facial palsy, and later gradual-onset headache and intermittent confusion. Magnetic resonance imaging of the brain showed diffuse subarachnoid FLAIR hyperintensity, concerning for blood, including a focus of cortical/subcortical high signal in the left superior parietal lobule, which was confirmed by computed tomography. Digital subtraction angiography demonstrated a left VAD with a fusiform aneurysm. CONCLUSION: We present a very rare case of intracranial VAD with SAH initially presenting with spinal symptoms. The majority of subsequent clinical features were consistent with a parietal focus of cortical subarachnoid blood, as observed on neuroimaging
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Numerical and Experimental Investigation of Pressure Losses at Suction of a Twin Screw Compressor
Rotary twin screw machines are used in the wide range of industrial applications and are capable of handling single and multiphase fluids as compressors, expanders and pumps. Concentration of liquid in the inlet flow can influence the performance of the machine significantly. Characteristics of the multiphase flow at the suction of a screw compressor depend on the local flow velocities and concentration. Local flow velocity measurements inside the screw compressors are difficult to obtain. However other flow properties such as local pressures are easier to attain. It is therefore useful to carry out experiments with local pressure variations in the suction which can be used to validate the 3D numerical Computational Fluid Dynamic (CFD) models that could help in studying the single and multiphase flow behaviour in screw compressors.
This paper presents experimental efforts to measure the local pressure losses inside the suction plenum of the screw compressor. Pressure variations are measured at 23 locations in the suction port at various operating conditions and compared with 3D CFD model. The grid generator SCORGTM was used for generating numerical mesh of rotors. The flow calculations were carried out using commercial 3D solver ANSYS CFX. It was found that the local pressure changes predicted by the CFD model are in the good agreement with measured pressures. This validated the use of CFD for modelling of the single phase flows in suction of screw machines
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