Browsing by Author "Jacobs, M. J."
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- ItemA low cost, high precision star sensor(Stellenbosch : University of Stellenbosch, 1995-12) Jacobs, M. J.; Steyn, W. H.; University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.; University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: The Sunsat microsatellite is being developed at the University of Stellenbosch. It is equipped with a high resolution earth imager which requires a sophisticated attitude determination and control system. Precise control of the satellite is impossible without high precision attitude sensors. The most accurate attitude sensor presently used by satellites is the star sensor. The aim 'of this thesis is to develop a low cost, high precision star sensor for the Sunsat microsatellite. The development included the selection of electronic and optical hardware followed by the design, construction and testing of the sensor. Software algorithms were developed and programmed to control the imager, extract stars from images and match the observed constellations to a star catalogue. A set of matching observed and reference vectors are passed to the attitude determination and control system which calculates the three axis orientation of the satellite.
- ItemOut-of-plane strength and stiffness prediction of SA pine cross-laminated timber(Stellenbosch : Stellenbosch University, 2023-03) Jacobs, M. J.; Wessels, Brand C.; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.ENGLISH ABSTRACT: South Africa recently adopted a slightly adapted version of ANSI PRG 320:2019 as a standard for performance-rated cross-laminated timber (CLT) – with a local code number of SANS 8892:2020. In ANSI PRG 320:2019 and SANS 8892:2020 there is a table containing unfactored resistance values for standardized CLT layups manufactured with different grades of timber in both the major and the minor strength directions. The grades of timber used in the laminations to produce the unfactored resistance tables are those available in the United States of America and, therefore, this table does not apply to the South African standard as different species of timber under different conditions are used here. Most importantly, South Africa uses a different structural timber grading system. The use of locally grown species to manufacture CLT will ensure that CLT becomes economically feasible and competitive as a high-value green alternative for reinforced concrete. Optimal design will only be possible if sufficient knowledge of local species, and how they perform in the context of CLT, is available. In this study, the locally grown SA pine was used to manufacture CLT specimens which were evaluated for bending and shear stiffness and strength, in both the major and minor strength directions. Bending evaluation was done at a span:thickness ratio of thirty with a 4-point bending test. Shear evaluation was done at a span:thickness ratio of six with a 3-point bending test. The specimens tested consisted of two 3-layer layups with respective thicknesses of 66 mm and 138 mm; these layups relate to layer thicknesses achievable by using the smallest and largest commonly available timber-lamella thicknesses in South Africa. A total of ten specimens for each layup, test and orientation combination were evaluated. The experimentally obtained results were then compared to analytically predicted stiffness results from the most widely used analytical predictive models, namely the shear-analogy and gamma methods. Where possible, all the input parameters for the predictive modelling were determined beforehand to make predictions as specific and accurate as possible. It was found that the shear-analogy method is more broadly applicable and can be used for all span:depth ratios, while the gamma method only produced accurate predictions of bending stiffness for long span:thickness ratios where the percentage of shear deformation was small. Based on the comparisons presented in this thesis, the shear analogy was chosen and used to create an unfactored resistance table for 3- and 5-layer layups using South African-strength class and lamination thickness as inputs. The thinner 66 mm CLT specimens had significantly higher bending and shear strength, and higher bending stiffness when compared to the 138 mm CLT. High rolling-shear strength values were found when compared to values found in literature for European spruce. The main outcomes of this work were (a) the proof that the shear-analogy method was a more broadly applicable prediction model for CLT lay-ups and (b) the creation of unfactored resistance tables for 3- and 5-layer layups using South African pine CLT. Future work should include the determination of rolling- shear modulus and strength of the SA pine resource, with a larger number of specimens from various regions and grades. Furthermore, the influence of layups on mechanical properties should be explored when comparing 5-layer layups to the 3-layer layup. Ways of increasing the effective stiffness of CLT plates in the out-of-plane configuration should be explored, with one such example being the addition of ribs in the long-span direction to increase stiffness.