80 research outputs found
Vehicle surface contamination, unsteady flow and aerodynamic drag
The rear surfaces of blunt-ended vehicles, such as SUVs, are vulnerable to the build-up of contaminants thrown up from wet road surfaces by their tyres. This can compromise driversâ vision, vehicle visibility, sensor performance and aesthetics. Vision will be reduced if the rear screen and lenses of camera systems become obscured. Similarly, sensing methods such as Light Detection and Ranging [LIDAR], introduced to support higher-level Advanced Driver Assistance Systems [ADAS] and autonomous driving are also vulnerable to contaminant accumulation. In addition, vehicle users may find that dirt is transferred to their hands and clothes as they access the rear load space. Finally, rapid soiling of external surfaces can be perceived as degrading the aesthetics of premium vehicles.
Such deposition is a manifestation of unsteady aerodynamics â particularly the interaction between tyre spray, wheel wakes and the vehicle rear wake. These wake structures also strongly influence aerodynamic drag which, in turn affects CO2 emissions for Internal Combustion Engine [ICE] powered cars and the range of Battery Electric Vehicles [BEV]. Hence, automotive manufacturers need a simulation approach that can be used to minimise these characteristics concurrently during vehicle development.
This work met that need by developing and deploying an innovative simulation process which predicts both contaminant accumulation and drag at the same time, by numerically representing unsteady aerodynamics, tyre spray and surface water behaviour. It is now integrated into the vehicle development process at Jaguar Land Rover [J/LR] where it is being used to develop new cars. This has been achieved by using a series of novel simplified vehicle geometry and spray systems to incrementally develop and validate the simulation strategy. The work culminated with its application to a production vehicle and subsequent validation against full scale experiments, providing the first quantification of accuracy for simulations of rear surface contamination.
This novel simulation approach is combined with original experiments to show that reduced vehicle ride heights can lead to increased rear surface contamination, by reducing underbody flow and moving the vehicle wake closer to the highly contaminated wheel wakes. This provides a challenge for vehicle developers as lower ride heights are used to reduce aerodynamic drag; an increasingly important objective for both ICE and BEV product development, to support lower CO2 emissions and enhanced range, respectively. Finally, the first evidence is presented to suggest that aerodynamically improved underfloors can increase rear surface contamination, or at least redistribute it towards the lower regions of the vehicle rear, such as the bumper. This raises a risk for future BEVs which combine aerodynamically advantageous smooth underfloors with vulnerable ADAS features, such as rear bumper mounted LIDAR
Surface contamination of cars : a review
This review surveys the problem of surface contamination for cars, which poses a growing engineering challenge to vehicle manufacturers, operators and users. Both driversâ vision and vehicle visibility need to be maintained under a wide range of environmental conditions. This requires managing the flow of surface water on wind screens and side glazing. The rate of deposition of solid contaminants on glazing, lights, license plates and external mirrors also needs to be minimised. Maintaining vehicle aesthetics and limiting the transfer of contaminants to the hands and clothes of users from soiled surfaces are also significant issues. Recently, keeping camera lenses clean has emerged as a key concern, as these systems transition from occasional manoeuvring aids to sensors for safety systems. The deposition of water and solid contaminants onto car surfaces is strongly influenced by unsteady vehicle aerodynamic effects. Airborne water droplets falling as rain or lifted as spray by tyres interact with wakes, vortices and shear flows and accumulate on vehicle surfaces as a consequence. The same aerodynamic effects also control the movement of surface water droplets, rivulets and films; hence, particular attention is paid to surface water management over the front side-glass and the deposition of contaminants on the rear surfaces. The test methods used in the automotive industry are reviewed, as are numerical simulation techniques
Simulation of rear surface contamination for a simple bluff body
Predicting the accumulation of material on the rear surfaces of square-backed cars is important to vehicle manufacturers, as this progressively compromises rear vision, vehicle visibility and aesthetics. It also reduces the effectiveness of rear mounted cameras. Here, this problem is represented by a simple bluff body with a single sprayer mounted centrally under its rear trailing edge.
A Very Large Eddy Simulation (VLES) solver is used to simulate both the aerodynamics of the body and deposition of contaminant. Aerodynamic drag and lift coefficients were predicted to within +1.3% and â4.2% of their experimental values, respectively. Wake topology was also correctly captured, resulting in a credible prediction of the rear surface deposition pattern.
Contaminant deposition is mainly driven by the lower part of the wake ring vortex, which advects material back onto the rear surface. This leads to a maximum below the rear stagnation point and an association with regions of higher base pressure.
The accumulation of mass is linear with time; the relative distribution changing little as the simulation progresses, implying that shorter simulations can be compared to longer experiments. Further, the rate of accumulation quickly reaches a settled mean value, suggesting utility as a metric for assessing different vehicles
Statistical properties of 12.2 GHz methanol masers associated with a complete sample of 6.7 GHz methanol masers
We present definitive detection statistics for 12.2 GHz methanol masers
towards a complete sample of 6.7 GHz methanol masers detected in the Methanol
Multibeam survey south of declination -20 degrees. In total, we detect 250 12.2
GHz methanol masers towards 580 6.7 GHz methanol masers. This equates to a
detection rate of 43.1%, which is lower than that of previous significant
searches of comparable sensitivity. Both the velocity ranges and the flux
densities of the target 6.7 GHz sources surpass that of their 12.2 GHz
companion in almost all cases. 80 % of the detected 12.2 GHz methanol maser
peaks are coincident in velocity with the 6.7 GHz maser peak. Our data support
an evolutionary scenario whereby the 12.2 GHz sources are associated with a
somewhat later evolutionary stage than the 6.7 GHz sources devoid of this
transition. Furthermore, we find that the 6.7 GHz and 12.2 GHz methanol sources
increase in luminosity as they evolve. In addition to this, evidence for an
increase in velocity range with evolution is presented. This implies that it is
not only the luminosity, but also the volume of gas conducive to the different
maser transitions, that increases as the sources evolve. Comparison with
GLIMPSE mid-infrared sources has revealed a coincidence rate between the
locations of the 6.7 GHz methanol masers and GLIMPSE point sources similar to
that achieved in previous studies. Overall, the properties of the GLIMPSE
sources with and without 12.2 GHz counterparts are similar. There is a higher
12.2 GHz detection rate towards those 6.7 GHz methanol masers that are
coincident with extended green objects.Comment: Accepted to ApJ March 2011. 28 pages, 9 figure
Methanol Masers as Tracers of Circumstellar Disks
We show that in many methanol maser sources the masers are located in lines,
with a velocity gradient along them which suggests that the masers are situated
in edge-on circumstellar, or protoplanetary, disks. We present VLBI
observations of the methanol maser source G309.92+0.48, in the 12.2 GHz
transition, which confirm previous observations that the masers in this source
lie along a line. We show that such sources are not only linear in space but,
in many cases, also have a linear velocity gradient. We then model these and
other data in both the 6.7 GHz and the 12.2 GHz transition from a number of
star formation regions, and show that the observed spatial and velocity
distribution of methanol masers, and the derived Keplerian masses, are
consistent with a circumstellar disk rotating around an OB star. We consider
this and other hypotheses, and conclude that about half of these methanol
masers are probably located in edge-on circumstellar disks around young stars.
This is of particular significance for studies of circumstellar disks because
of the detailed velocity information available from the masers.Comment: 38 pages, 13 figures accepted by Ap
How do methanol masers manage to appear in the youngest star vicinities and isolated molecular clumps?
General characteristics of methanol (CH3OH) maser emission are summarized. It
is shown that methanol maser sources are concentrated in the spiral arms. Most
of the methanol maser sources from the Perseus arm are associated with embedded
stellar clusters and a considerable portion is situated close to compact HII
regions. Almost 1/3 of the Perseus Arm sources lie at the edges of optically
identified HII regions which means that massive star formation in the Perseus
Arm is to a great extent triggered by local phenomena. A multiline analysis of
the methanol masers allows us to determine the physical parameters in the
regions of maser formation. Maser modelling shows that class II methanol masers
can be pumped by the radiation of the warm dust as well as by free-free
emission of a hypercompact region hcHII with a turnover frequency exceeding 100
GHz. Methanol masers of both classes can reside in the vicinity of hcHIIs.
Modelling shows that periodic changes of maser fluxes can be reproduced by
variations of the dust temperature by a few percent which may be caused by
variations in the brightness of the central young stellar object reflecting the
character of the accretion process. Sensitive observations have shown that the
masers with low flux densities can still have considerable amplification
factors. The analysis of class I maser surveys allows us to identify four
distinct regimes that differ by the series of their brightest lines.Comment: 8 pages, 4 figures, invited presentation at IAU242 "Astrophysical
Masers and their environments
Favourable outcomes for the first 10 years of kidney and pancreas transplantation at Wits Donald Gordon Medical Centre, Johannesburg, South Africa
Background. It is important for centres participating in transplantation in South Africa (SA) to audit their outcomes. Wits Donald Gordon Medical Centre (WDGMC), Johannesburg, SA, opened a transplant unit in 2004. The first 10 years of kidney and pancreas transplantation were reviewed to determine outcomes in respect of recipient and graft survival.Methods. A retrospective review was conducted of all kidney-alone and simultaneous kidney-pancreas (SKP) transplants performed at WDGMC from 1 January 2004 to 31 December 2013, with follow-up to 31 December 2014 to ensure at least 1 year of survival data. Information was accessed using the transplant registers and clinical records in the transplant clinic at WDGMC. The Kaplan-Meier method was used to estimate 1-, 5- and 10-year recipient and graft survival rates for primary (first graft) kidney-alone and SKP transplants.Results. The overall 10-year recipient and graft survival rates were 80.4% and 66.8%, respectively, for kidney-alone transplantation. In the kidney-alone group, children tended towards better recipient and graft survival compared with adults, but this was not statistically significant. In adults, recipient survival was significantly better for living than deceased donor type. Recipient and graft survival were significantly lower in black Africans than in the white (largest proportion in the sample) reference group. For SKP transplants, the 10-year recipient survival rate was 84.7%, while kidney and pancreas graft survival rates were 73.1% and 43.2%, respectively.Conclusion. Outcomes of the first 10 years of kidney and pancreas transplantation at WDGMC compare favourably with local and international survival data
12.2-GHz methanol maser MMB follow-up catalogue - I. Longitude range 330 to 10 degrees
We present a catalogue of 12.2-GHz methanol masers detected towards 6.7-GHz
methanol masers observed in the unbiased Methanol Multibeam (MMB) survey in the
longitude range 330\circ (through 360\circ) to 10\circ. This is the first
portion of the catalogue which, when complete, will encompass all of the MMB
detections. We report the detection of 184 12.2-GHz sources towards 400 6.7-GHz
methanol maser targets, equating to a detection rate of 46 per cent. Of the 184
12.2-GHz detections, 117 are reported here for the first time. We draw
attention to a number of 'special' sources, particularly those with emission at
12.2-GHz stronger than their 6.7-GHz counterpart and conclude that these
unusual sources are not associated with a specific evolutionary stage.Comment: accepted to MNRAS 21 Dec 201
12.2-GHz methanol maser MMB follow-up catalogue - II. Longitude range 186 to 330 degrees
We present the second portion of a catalogue of 12.2-GHz methanol masers
detected towards 6.7-GHz methanol masers observed in the unbiased Methanol
Multibeam (MMB) Survey. Using the Parkes radio telescope we have targeted all
207 6.7-GHz methanol masers in the longitude range 186 to 330 degrees for
12.2-GHz counterparts. We report the detection of 83 12.2-GHz methanol masers,
and one additional source which we suspect is thermal emission, equating to a
detection rate of 40 per cent. Of the 83 maser detections, 39 are reported here
for the first time. We discuss source properties, including variability and
highlight a number of unusual sources. We present a list of 45 candidates that
are likely to harbor methanol masers in the 107.0-GHz transition.Comment: Accepted MNRAS 19 July 201
The quiet editor: Ivan VladislaviÄ and South African cultural production
This article examines the literary and sociological significance of Ivan VladislaviÄâs "double lifeâ (Lahire, 2010: n.p.) as both editor and writer. With reference to a number of his editorial roles as well as the joint projects he has worked on with writers and visual artists, the article considers how VladislaviÄâs work with others spreads symbolic value. Described by one of his clients as the âquiet editorâ, VladislaviÄ can be read as a new kind of author; what he terms âcreative editingâ (Steyn, 2012: n.p.) as a new kind of writing, through which more traditional models of authorship and literary production are thrown into question â less Bourdieuâs (1984) âfield of literary productionâ or Casanovaâs (2004: 82) âworld literary spaceâ, red in tooth and claw, amd more Howard Beckerâs âart worldâ: a convivial ânetwork of cooperating people, all of whose work is essential to the final outcomeâ (1982: 25)
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