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Automated processor for optimizing tractor operation.Lyne, Peter William Liversedge. January 1991 (has links)
The agricultural tractor is designed as a general purpose machine and consequently, does not perform all its tasks at
maximum efficiency. Various methods of increasing the field performance of these vehicles have been studied.
Traction is one of the main factors limiting the field performance of the modern tractor. The process of developing
traction has therefore been investigated by many researchers and although this study has resulted in a better
understanding of the mechanics, it has not to any great extent assisted the operator to optimize performance in the
field. It was concluded that in order to solve the problem the operator required a control system to maintain the dynamic load and inflation pressure at optimum levels. Work was carried out to develop and evaluate such a system using the Single Wheel Traction Research Vehicle at the USDA's National Soil Dynamics Laboratory in Auburn, Alabama, USA. A computer management system was developed to control the dynamic load, net traction and inflation pressure of the test tyre. During a simulated field operation the system was programmed to cycle the tyre over its operating range of dynamic load and inflation pressure while monitoring tractive efficiency. A tractive efficiency response surface was computed for the particular condition and the surface searched for the dynamic load and inflation pressure levels which resulted in maximum tractive efficiency. The tyre was then controlled and operated at maximum tractive efficiency. Evaluation showed that within the operating range of the tyre, tractive efficiency varied considerably with dynamic load, inflation pressure, net traction and soil condition. The results indicated that a considerable advantage could be obtained by using such an arrangement on a tractor. The system would automatically maximize the tractive efficiency of the tractor under the particular field conditions and with the particular implement being used. Implements could be ballasted and the hitch system used to control the weight transfer to ensure maximum tractive efficiency. Systems such as these would result in a significant improvement in the field performance of the machine and a reduction in management time required to optimize the performance of the tractor implement combination. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1991.
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Combustion stress in compression-ignition engines.Taylor, Andrew Bruce. January 1989 (has links)
South Africa produces alternative fuels from a number of different
sources. The properties of a fuel are known to affect the nature
of combustion in compression-ignition engines significantly, and
have occasionally resulted in engine failures. Combustion analyses
have been conducted on a wide range of fuels and combustion has
been thoroughly quantified. However, the role played by the
different combustion variables in failures was not known. The
result was that it was not possible to predict the implications of
variations in the nature of combustion. There was thus a need to
investigate the relative role of combustion variables in the
failure of engines.
The mechanisms of combustion and engine failure were studied. All
the variables required to determine combustion and engine
durability were measured simultaneously. This research required
the development of a complete engine research facility as well as
specialized transducers. Fast response surface thermocouples were
designed and constructed in order to monitor transient surface
temperatures. Heat transfer rates were then calculated with the
aid of Fourier analysis. Dynamic stresses were monitored by
strain-gauges applied to the engine.
A special high speed data
acquisition system was developed. An existing heat release model
was modified and used to calculate combustion rates. A
comprehensive finite element model was developed to calculate
piston temperatures and stresses. The role of each combustion
variable in stress and durability was investigated by statistical
analysis.
The results successfully identified the causes of combustion
related engine failures. The primary cause of engine failure was found to be thermal loading. The principal cause of any variation
in thermal loading and thus engine durability was maximum cylinder
pressure. The life of the engine was proved to be determined
almost entirely by peak cylinder pressure. The role of the rate
of pressure rise was proved to be insignificant.
All the implications of variations in the nature of combustion can
now be determined accurately. It will thus be possible to optimise
engine modifications and fuel properties before validation by
durability testing. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1989.
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A diagnostic quasi-dimensional model of heat transfer and combustion in compression-ignition engines.Hansen, Alan Christopher. 23 September 2013 (has links)
Investigations into the combustion of alternative fuels in
compression-ignition engines in South Africa have underlined the
inadequacies of existing zero-dimensional combustion models. The
major aspect of concern in these models was the computation of
heat transfer which had been singled out by a number of
researchers as the leading cause of inaccuracies in heat release
computations.
The main objective of this research was to develop a combustion
model that was less empirically based than the existing zerodimensional
models for use in evaluating the combustion and
resulting thermal stresses generated by alternative fuels. in
diesel engines. Particular attention was paid to the development
of a spatial and temporal model of convective heat transfer that
was based on gas flow characteristics and to the introduction of
a radiation heat transfer model that made use of fuel properties
and fuel-air ratio. The combustion process was divided into two
zones representing burnt and unburnt constituents and the
resulting temperatures in each zone were used in the calculations
of convective and radiative heat transfer. The complete model
was formulated in such a way that it could be applied with the
aid of a micro-computer.
Calibration and verification of the gas flow sub-models which
involved the squish, swirl and turbulence components necessitated
the use of published data. Good agreement for the squish and
swirl components was obtained between the present model and the
experimental data from three engines, two with a bowl-in-piston
and the other with a flat piston. These gas flow components
dominated the gas velocities in the combustion chamber and
provided a reliable foundation for the calculation of convective
heat transfer. In spite of the well documented difficulties of
characterising turbulence, after calibration the model generated
turbulence levels with acceptable trends and magnitudes. Tests were carried out on a naturally aspirated ADE 236 engine
involving the measurement of cylinder pressure and heat flux at
a single point. Motored engine data were used to verify the
convective heat transfer rates and to ascertain the effects of
soot deposition on the heat flux probe. Close correlation
between predicted and measured heat flux was achieved after
accounting for the effects of chamber geometry at the probe site.
Soot deposition on the probe caused a significant attenuation of
the heat flux within a short period of the engine running under
fired conditions.
The results from fired engine tests showed that the two zone
combustion model was providing plausible trends in the burnt and
unburnt zone temperatures and that the model generated combined
heat transfer rates which were credible not only on a global
basis but also in terms of point predictions in the combustion
chamber. The results also highlighted the considerable variation
in heat transfer that could occur from one point in the chamber
to another. Such variations added considerable weight to the
objective of moving away from a zero-dimensional model to a
quasi-dimensional type where predictions could be made on a more
localised rather than global basis. It was concluded that the
model was a definite improvement over zero-dimensional models and
competed favourably with existing quasi-dimensional models with
advantages in both simplicity and accuracy. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1989.
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The hydrological effects of fire in South African catchments.Scott, David Findlay. January 1994 (has links)
Stream-flow and storm-flow in four small catchments were analysed by the paired
catchment method for a response to fire. Two of the catchments were vegetated with
over-mature fynbos (the indigenous scrub vegetation of the south-western Cape Province,
South Africa), one was afforested to Pinus radiata and the fourth to Eucalyptus fastigata.
One of the fynbos catchments was burned in a prescribed fire in the late dry season. The
other catchments burned in wildfires.
Neither of the fynbos catchments showed a change in storm-flows. Annual total flow
increases of around 16% were in line with predictions, being related to the reductions in
transpiration and interception. The manner of stream-flow and storm-flow generation
appeared to have remained unaltered despite the fire.
The two timber plantation catchments experienced large and significant increases in stormflow
and sediment yields, while total flow increased by 12% in the pine catchment and
decreased marginally in the eucalypt catchment. After fire, storm hydrographs were higher
and steeper though their duration was little changed. These fire effects are considered to
be due to changes in storm-flow generation consistent with an increased delivery of
overland flow to the stream channel. This was caused, in part, by reduced infiltration
resulting from water repellency in the soils of the burned catchments.
The inherent wettability of a wide range of soil types and textures from beneath timber
plantations and other vegetation types over a broad geographic distribution in South Africa
was measured by four methods. Soils with high repellency ratings, unrelated to fire, are
common and are most likely to occur beneath plantations of Eucalyptus and Acacia spp.
and indigenous forest.
Water repellent soils played a role, at two of the three locations, in the generation of
overland flow from small plots exposed to simulated rainfall. However, the inherent
repellency of the dry soils was extreme, such that fire-induced water repellency was not
a factor in the response of the plots. The important role of fire in this experiment was in
burning-off of repellency in the surface layer of the soil and in removing ground cover. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1994.
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Development of network theory approaches to analyse cause and effect relationships in complex integrated sugarcane supply and processing systems.Sanjika, Thawani M. January 2013 (has links)
Network theory has been widely and successfully used to model, analyse and visualise
complex systems. This study aimed to develop approaches to analyse complex integrated
sugarcane supply and processing systems. A literature review includes network theory,
complex systems, the Theory of constraints, indicator analysis and root cause analysis. The
cause-and-effect networks of four sugarcane milling areas in South Africa; viz. Eston,
Felixton, Komati and Umfolozi were developed, where the factors that negatively affected the
performance of the milling areas were represented by vertices, the relationships among the
factors by arcs and the strength of these relationships by weights. Three network theory based
analytical tools namely; (a) primary influence vertex analysis, (b) indicator vertex analysis
and (c) root cause vertex analysis were developed to analyse the networks. The results from
the analyses indicate variations in the numbers and strengths of primary influence factors,
problem indicator factors and root causes of problems between the four milling areas.
Rainfall, drought and high soil content in sugarcane were identified as the strongest primary
influences in the respective milling areas. High crush rate variability, low cutter productivity,
running behind allocation and increases in operating costs were identified as the strongest
indicators of poor performance in the respective milling areas. Rainfall was found to be the
most dominating root cause of poor performance in all the milling areas. Since the South
African integrated sugarcane production and processing system is complex, it is likely that the
unique approaches developed in this study can be used successfully to also analyse other
relatively complex systems. It is recommended that these approaches be tested within other
systems. The main contribution of this study is in the form of a relatively easy-to-use network
theory based comprehensive systems analyses tool. This analytical approach has, to the
author's knowledge, not been used in any agri-industrial application previously. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.
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Crop water requirements for irrigation planning in South Africa.Dent, Mark Clifford. January 1988 (has links)
Irrigation in 1980 accounted for approximately 52 per cent of the water
consumed in Southern Africa. The need for planning water resources in
the agricultural sector is therefore apparent. Much of Southern
Africa's arable farming is carried out on land which, in terms of soil
moisture availability to crops, can be described as marginal. Information
on soil moisture is therefore valuable to the agriculturalist for
planning irrigation schemes and for dryland farming.
The objectives of this study were to provide the information mentioned
above. This was achieved by producing a detailed delimitation of 712
zones throughout Southern Africa, of more or less homogeneous climate
and by providing estimates of crop water requirements under dryland and
irrigated conditions in each zone. At the same time the bulk of information
which is normally forthcoming from such an analysis involving a
large number of combinations of possible input, i.e. crops, soils and
planting dates, was reduced, whilst the essential information content
was retained. The study provided inter alia an estimate of the
frequency of non-exceedance of certain levels of irrigation requirement,
based on analyses of soil moisture budgets using long daily rainfall
records. The soil moisture budgeting models which were used to estimate
the above information were verified inter alia using field measurements
of soil moisture.
The irrigation analysis was designed such that the results should not
became redundant when the inevitable improvement occurs in the estimation of crop factors or soil moisture variables nor if the farming practices
change with respect to planting dates.
A dryland soil moisture budget analysis for a range of crops and soils
was performed in addition to the abovementioned irrigation analysis.
The need for this latter study stemmed from the belief that irrigation
should not be considered in isolation but rather as one of a range of
options, many of them involving dryland farming, facing the agriculturalist.
In addition to the dissertation, this study produced a map of Southern
Africa on which the 712 homogeneous climate zones are depicted. For
each of these zones four pages of computer printout were produced.
These pages contain the results of the crop water requirements study for
irrigated conditions and the crop water requirement deficit, runoff and
an index of stress days for a range of crops, soils and planting dates,
under dryland conditions. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1988.
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