7 research outputs found
The tractive performance of a friction-based prototype track
No full textThesis (PhD (Argricultural Engineering))--University of Pretoria, 2007.In recent years, the interest in the design, construction and utilization of rubber tracks for agriculture and earth moving machinery has increased considerably. The development of such types of tracks was initiated by the efforts to invent a more environmentally friendly vehicle-terrain system. These tracks are also the result of the continuous effort to develop more cost-effective traction systems. A rubber-surfaced and friction-based prototype track was developed and mounted on the patented modification of a new Allis Chalmers four wheel drive tractor. The track is propelled by smooth pneumatic tyres by means of rubber-rubber friction and the tractive effort of the track is mainly generated by soil-rubber friction between the rubber surface of the track elements and terrain. The experimental track layer tractor, based on an Allis Chalmers 8070 tractor (141 kW) was tested on concrete and on cultivated sandy loam soil at 7.8%; 13% and 21% soil water content. The contact pressure and the tangential force on an instrumented track element, as well as the total torque input to one track, was simultaneously recorded during the drawbar pull-slip tests. Soil characteristics for pressure-sinkage and friction-displacement were obtained from the field tests by using an instrumented linear shear and soil sinkage device. By applying the approach based on the classical bevameter technique, analytical methods were implemented for modelling the traction performance of the prototype track system. Different possible pressure distribution profiles under the tracks were considered and compared to the recorded data. Two possible traction models were proposed, one constant pressure model, for minimal inward track deflection and the other a flexible track model with inward deflection and a higher contact pressure at both the front free-wheeling and rear driving tyres. For both models, the traction force was mainly generated by rubber-soil friction and adhesion with limited influence by soil shear. For individual track elements, close agreement between the measured and predicted contact pressure and traction force was observed based on the flexible track model. The recorded and calculated values of the coefficient of traction based on the summation of the traction force for the series of track elements were comparable to the values predicted from modelling. However, the measured values of drawbar pull coefficient were considerably lower than the predicted values, largely caused by internal track friction in addition to energy dissipated by soil compaction. The tractive efficiency for soft surface was also unacceptably low, probably due to the high internal track friction and the low travel speeds applied for the tests. The research undertaken identified and confirmed a model to be used to predict contact pressure and tangential stresses for a single track element. It was capable of predicting the tractive performance for different possible contact pressure values.Civil EngineeringUnrestricte
Performance characteristics of a deep tilling rotavator
No full textThesis (PhD)--University of Pretoria, 2010.This study was undertaken to develop an analytical model that is capable of predicting the torque requirements of a rotavator fitted with commercially available L-shaped blades. An analytical approach based on the limit equilibrium analysis was used to develop the proposed model. The proposed model was verified by comparing the model and measured torque requirements at predetermined rotavator blade angular positions from the horizontal for a down-cut rotavator. The study findings indicated that there was an optimum set tillage depth for each rotavator configuration and operational conditions at which the resultant horizontal thrust generated was greatest. This unique depth was influenced by the bite length. The validation of the proposed model showed that the predicted and measured torque requirements, at different angular blade positions from the horizontal, correlated reasonably well for all the set tillage depths. As the depth of tillage increased, however, the curve for the measured torque requirements exhibited a cyclic behaviour after the peak torque requirements value had been recorded. The cyclic behaviour was probably due to the re-tilling and the instability of the tool-frame carrier, which increased with the set tillage depth. The knowledge contributed by this research will afford the designers of active tillage tools a better understanding of the operations of the rotavator, particularly in deep tillage. The modelling approach, and instrumentation technique used in this research, can be extended to analyze the performance of rotavators fitted with other types of commercial blades.Civil Engineeringunrestricte
The use of gasification ash in cement and concrete
No full textDissertation (MEng(Structural))--University of Pretoria, 2007.Cement is an essential material in today’s society because, as a major constituent of concrete, it forms a fundamental element of any housing or infrastructure development. The chemical process of making cement clinker produces CO2, a major greenhouse gas contributing to climate change. This makes it imperative for us to find ways of using this resource more efficiently. Using waste from other industries, as a raw material is a huge opportunity for the cement industry to reduce its environmental impact. Cement extenders are used as a substitute for some of the Portland cement in concrete. The reasons for the use of extenders, is a growing awareness of the engineering, economical and ecological benefits and the variety of useful enhancements, which they give to the concrete properties. The aim of the research is to determine whether a gasification ash can be used as a cement extender in concrete. In this study the properties of cement and concrete containing gasification ash was compared to the properties of cement and concrete containing fly ash. The physical, chemical and mineralogical composition of a gasification ash sample was investigated, and it was found that gasification ash has an angular shape and a similar chemical composition as fly ash. The chemical requirements of the gasification ash meet the majority of the requirements specified for cement extenders. Where limits are exceeded it is by a very narrow margin. The effect of a gasification ash on the short and long term properties of concrete of both interblending and intergrinding was investigated. The experimental work revealed that gasification ash improves the compressive and tensile strength of concrete in both interblending and intergrinding. Gasification ash does not have a detrimental effect on stiffness of concrete, and did not creep significantly more than concrete containing fly ash. The porosity and permeability does not increase when gasification ash is used as a cement extender. Gasification ash should therefore not decrease the durability of concrete. The use of gasification ash as a cement extender has advantages to both the cement industry and the environment.Civil Engineeringunrestricte
Patriotism as a theme in selected art songs by M.L. de Villiers and Stephen Eyssen
No full textMini Dissertation (MMus (Performance Arts))--University of Pretoria, 2021.Music has long since been used as a tool to disseminate patriotic messages to audiences. Since the early stages of colonisation in Southern Africa, Afrikaner activists have been striving for a uniquely Afrikaans language and musical idiom to express their culture with. Political and cultural events that happen during the composers' lives are mirrored in their music. This means that songs can be studied to understand the past. Marthinus Lourens de Villiers, who today is mostly known for his composition of the former South African national anthem, Die Stem van Suid-Afrika (The Call of South Africa), and Stephen Harry Eyssen, who was at the forefront of the Afrikaans art/folk music scene, were both composers as well as cultural activists during their lifetimes. Therefore, the current study was undertaken to understand what motivated them to write patriotic songs and how the theme of patriotism is reflected in the selected works from their respective oeuvres. Art songs consist of different musical elements that form the final piece. The elements are melody, harmony, accompaniment, rhythm, and text. Content analysis of these individual elements was conducted and then compiled into a style sheet. Style sheets are tools that aid in understanding how different musical elements function together to create a song and convey the message/s inherent in the songs. Style sheets aided in the understanding of how individual elements as well as how they function together, express patriotic messages in the selected songs. The selected pieces are all based on poetry with a patriotic theme and were chosen to understand how the theme of patriotism is reflected in the songs. The selected works for De Villiers are Soet is die stryd (Sweet is the struggle) by I.D. du Plessis, Triomflied (Triumph song) by A.G. Visser, and Trou (Loyalty) by Celliers. The songs by Eyssen that were studied are Segelied (Song of triumph) by Piet du Toit and A.B. Wessels as well as Die Lewerkie by J. Pienaar. Both composers set music to the poem Komaan! by Celliers and the songs were included into the study. The following four patriotic themes were identified in the analysis conducted for the study: action, culture, hope, and ethics and values. Common elements used by the composers to reflect the four identified patriotic themes include word-painting in the form of melodic contouring, melismas and dissonance. Other elements are rhythm, as well as performance directions and indications, such as tenuti and accents on emotive words and descriptive terminology.MusicMMus (Performance Arts)Unrestricte
Force modelling and energy optimization for subsoilers in tandem
No full textThesis (PhD (Engineering))--University of Pretoria, 2004.In the recent past, as more farm power is being demanded on farms, due to increased farm sizes and operating speeds, larger and heavier farm machines are deployed in various farming operations. Their cumulative negative effects have become more apparent with increased incidences of soil compaction problems. This has forced many farmers to practice deep tilling, using subsoilers to break up compacted subsoil layers. In some maize growing regions of South Africa, conventional subsoilers are used in a tandem configuration. The farmers believe that the use of subsoilers in this mode reduces the draft force per unit area tilled. This probably happens because the critical depth for the rear subsoiler is increased beyond its working depth of 600 mm. Operating in this mode necessitated this study, with the ultimate goal of testing an appropriate existing force model for a single tine in predicting the force requirements of the front subsoiler in a tandem configuration. Secondly, to develop an alternative model for the rear subsoiler based on the three-dimensional failed soil-profile and to determine the relative position of the front subsoiler at which energy utilization is optimized. To develop the proposed model, an analytical approach based on limit equilibrium analysis was used and a Matlab-based computer program was coded to solve it. Its verification was conducted through field experiments in sandy clay loam soil. The experiments consisted of a continuous measurement of the horizontal and vertical forces acting on each subsoiler by a two-dimensional force transducer system. At the same time, the three-dimensional and thus the cross-sectional areas of the disturbed soil-profiles at different sections were measured, as well as the soil characteristics. A manual method employing a pin-profile meter was used to measure the vertical cross-sectional areas of the failed soil-profiles at 100 mm intervals. Further more, a technique using an automatic penetrometer and a computer program was developed to identify and map the three-dimensional failed soil-profiles. This technique indicated that the subsoiler failed the soil beyond its maximum operating depth and width. The results also indicated that the soil-failure pattern at close spacing is in phase at both subsoilers, leading to reduced total draft force requirements. At a wider spacing, the soil-failure pattern was out of phase, thus resulting in increased total draft force requirements. At the same time, the cross-sectional area tilled per unit draft force increased with increased spacing. This was because the failed maximum cross-sectional area increased in size faster than the total draft force as the spacing was increased. The proposed model verification results show that the predicted and recorded forces at the rear subsoiler correlated reasonably well at a wider spacing. When the front subsoiler was shallow working and close to the rear subsoiler, the model under- predicted the measured forces on the rear subsoiler, whilst the Swick-Perumpral model over predicted the applied forces to the front subsoiler and this was generally the case at wider spacings. Furthermore the efficiency of the subsoilers was maximized when the longitudinal spacing was such that it allowed the soil failed by the front subsoiler to stabilize before the rear subsoiler reached it. The maximum cross-sectional area failed per unit draft force was recorded when the depth of the front subsoiler was equal to about 80% of the rear subsoiler-operating depth. The knowledge contributed by this research will not only facilitate qualitative field operations and optimize energy use, but also promote better management decisions.Civil Engineeringunrestricte
Evaluation of an indirect method for measuring irrigation water abstracted from rivers with centrifugal pumps
No full textDissertation (M Eng (Agricultural Engineering))--University of Pretoria, 2005.Although a wide range of flow measurement devices and methods already exist for the measurement of irrigation water, water users and water management officials still claim there is a need for more appropriate devices that are non-intrusive, reliable, easy to install and maintain, and cost effective. Meters that are typically used for irrigation water measurement were tested in a laboratory as an initial part of the research and measurement errors larger than ±10 % of the actual discharge was recorded. This study was aimed at evaluating an experimental measuring method that may meet the requirements of the users. The experimental method is based on the unique relationship between the differential pressure and the discharge of a specific pump. By determining this relationship for a specific pump over a range of operating conditions (but for specific installation conditions), a curve similar to the pump curve as developed by the pump manufacturer can be established. If this relationship is inversed (into a discharge-differential pressure relationship), it can be used to calculate the discharge of the pump by measuring the differential pressure. The volume of water discharged by the pump over a period of time can then be determined by integrating the calculated discharge over time. Laboratory tests were conducted to evaluate the validity of the proposed measuring method. The tests entailed the development of the discharge-differential pressure relationship for the specific pump being used, by simultaneously measuring the system discharge, and pressure at both the suction and delivery sides of the pump. Once the relationship had been developed, a set of independent tests was conducted and the pressure measurements used to calculate the discharge through the system. The calculated discharge values were then compared with the measured values. The experimental measuring method was also evaluated in the field through empirical testing of its application in the field. The necessary equipment was installed and calibrated at an irrigation system pump station at the Orange-Riet Water User Association, and data collected over a two week period. The laboratory evaluation of the proposed measurement method produced favourable results, with the analyses showing that discharge can be "measured" with this method at errors smaller than ± 5.4 % of the reference reading within a specified range of flow rates, which is better than the errors produced by the conventional meters evaluated during the initial part of the research. The field tests showed that the method can be applied successfully to monitor pump abstractions. The method's results were compared to two reference measurements and it was found that the volume of water abstracted according to the experimental method was within ± 2.6 % of the reference measurements. The field work also showed that from a practical application point of view, the method has definite advantages over the conventional meters, although it is not less expensive than other measuring devices. The advantages include easier installation, high turn-down ratios, low maintenance requirements, no additional head loss, and suitable for telemetric data collection. Further work that is required include investigations on the use of a differential pressure transducer (rather than two separate suction and delivery side transducers), since this may reduce costs and the number of recorded data points, as well as evaluations of the validity of the discharge - differential pressure relationship over a long period of time, since it may change due to wear on the pump or motor.Civil Engineeringunrestricte
Effect of grinding time on the particle size distribution of gasification ash and Portland cement clinker
No full textIn recent years the cement and concrete industry has reduced its environmental impact by increasing the use of waste materials as both cement extenders and fillers in concrete. Fly ash has been widely used as a cement extender in concrete for many years but the use of ash from other industries has been limited. In this study the use of ground coarse gasification ash as cement extender is investigated. The effect of grinding time on the particle size distribution (PSD) of gasification ash (GA) and Portland cement (PC) clinker was investigated. The PSD was determined for both blended GA and PC clinker that were first ground separately and interground GA and PC clinker. There appeared to be an optimum grinding time for the GA and interground of GA and PC clinker beyond which the fineness did not increase significantly. The particle size range was narrow after two hours' grinding and any increase in grinding time made it wider for GA and the blended cement. The fineness and Blaine specific surface area of GA and PC clinker increased with an increase in grinding time. However, this increase was less significant beyond two hours. The fineness had an effect on the rate of strength development of the blended cement. The compressive strength, particle size and Rosin-Rammler distribution parameters clearly indicated that grinding time should not be shorter than two hours for interblending and intergrinding of GA and PC clinke
