Browsing by Author "Visser, Deon"
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- ItemAccolades and albatrosses : the South African National Defence Force's centenary and the commemoration of milestones in South African military history(Stellenbosch University. Faculty of Military Science (Military Academy), 2012) Visser, DeonPeoples, societies, institutions and other entities frequently record their histories in terms of successive epochs, and commemorate those histories according to perceived milestones or turning points in their development. Since much of human history has been dominated by strife and warfare, national and international milestones are frequently embedded in notions of a military past. Milestones in military history may be divided into three broad categories, namely those representing significant strides in the evolution of warfare, those associated with bravery, heroic sacrifice and great loss, and those of decisive political importance. Defence forces in general, and individual military units in particular, are extremely conscious of their past and often commemorate milestones through customs, traditions, and splendid parades and ceremonial displays. This year (2012), the South African National Defence Force (SANDF) celebrates its centenary against the complex background of South Africa’s long history of internal strife interspaced with participation in foreign conflicts. This article reflects on the commemoration of South Africa’s military history within the context of the divergent historical heritages of the SANDF and its predecessors. It commences with a brief background on memory, identity and the commemoration of history and military history. Thereafter it outlines the commemoration of a few of the foremost milestones in South African military history associated with the evolution of warfare, with bravery, heroic sacrifice and great loss, and with political change within its historical and current context.
- ItemAnalysis of the transition between Tubular Modular Track and ballasted railway(Stellenbosch : Stellenbosch University, 2016-03) Visser, Deon; Strasheim, JAvB; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: Tubular Modular Track (TMT) is a relatively new rail design invented in 1989. The system is ballastless and is designed to continuously support the rails on twin reinforced concrete (RC) beams which are founded on a specially designed subgrade. These RC beams are linked together by galvanised steel gauge bars which encircle the RC beams and provide links to fasten the rails to the RC beams with the use of rail clip fasteners. Elastomeric pads are placed in-between the rail and the RC beam to provide shock and sound absorption and grout is placed below the RC beams to level the TMT beams and ensure constant contact between the RC beams and the subgrade. With the introduction of high speed trains and ballastless rail systems the design of the transitions between ballasted and ballastless rails needs special attention. Multiple studies have been done on transitions between various types of ballastless rail and ballasted rail, but limited research is available on transitions between TMT and ballasted rail. To improve the confidence in the use of the TMT system in a transition various analyses are performed on the RC beam, the main supporting component of the system, for varying train speeds and varying rail irregularity angles due to elevation changes in the rail which occur because of ballast settlement at the track transition. The TMT structure is supported by different layers of subgrade which need to be incorporated in the finite element (FE) model of the system, but modelling the subgrade as a continuum increases the computational cost of the analysis. To simplify the modelling of the subgrade elastic foundation theory with plate bearing test (PBT) models are investigated. The subgrade can then be replaced with an elastic support. The PBT model and the elastic subgrade stiffness are verified by using previous research models which simulate PBT and determine an elastic stiffness to replace the subgrade. To analyse the TMT structural components a static, three-dimensional (3D), FE model is created of the structure. The TMT 3D model is also verified using models used in previous research which analysed the TMT structure. A 3D model of the structure requires a fine mesh to accurately model the cross sections of the TMT components, making the analysis computationally expensive. To simplify the model a two-dimensional (2D) model is created using beam and plane stress elements. For the 2D model a damping factor sensitivity analysis is performed to determine the influence of damping on the behaviour of the structure. The 2D model is then loaded statically and dynamically to determine the dynamic amplification factor (DAF) for the displacements, bending moments and shear forces in the rail and RC beam. In order to create the ballast to the TMT transition model, a model of the ballasted rail is required. A 3D discrete element (DE) model of the ballasted rail was attempted by modelling the ballast as discrete particles in the 3D space and placing the rail and sleepers on the particles. The discrete element method (DEM) was found to be a complex method of modelling the ballast and required time expensive analyses. Convergence errors were encountered in the modelling and analysis process. Due to limited available assistance and knowledge the results of the DEM model were inconclusive. This problem can be attributed to the fact that DEM is a new feature introduced into the available software, i.e. Abaqus. A similar approach to the simpli cation, analysis and results presentation of the TMT 2D model was used for the ballasted model. Plane stress, plane strain and 2D beam elements are used and the ballast and subgrade are modelled according to the elastic foundation theory in order to simplify the ballasted rail model. To calibrate the model results displacement measurements, taken on a reference ballasted rail, are compared to the model displacement results. The model is loaded statically and dynamically to determine the DAF for the displacements of the rail and sleepers and the bending moments and shear forces of the rail are presented. The ballast to TMT transition model is created by combining the simpli ed ballast and TMT 2D models. To calibrate the modelling of a transition with simpli ed 2D methods site displacement measurements are compared to the displacement results of a calibration model. After calibration various dynamic models are created of the ballast to TMT transition to investigate the impact of the transition on the displacements, bending moments and shear forces in the TMT RC beam. Sixteen ballast to TMT transition models with varying train speeds and irregularity angles are created and the results of these models were used in a sensitivity analysis for the response of the RC beam. Results show that RC beam displacements, maximum hogging bending moments and shear forces are sensitive to an increase in train speeds, but are more sensitive to an increase in rail irregularity angle. The maximum sagging bending moments remain constant because wheel loads remain the same for all models. It is concluded that the design of a transition zone should focus on achieving gradual elevation change between supporting structures rather than increasing the stiffness of the ballasted structure at the transition. Regular track maintenance to limit elevation changes at the transitions due to subsidence of the ballasted rail is also of utmost importance to limit the bending moments and resulting stresses in the rail components.
- ItemBetween history, amnesia and selective memory : the South African armed forces, a century's perspective(Stellenbosch University. Faculty of Military Science (Military Academy), 2012) Van der Waag, Ian; Visser, Deon2012 has a double significance for this year sees the centenary of the founding of the African National Congress (8 January) and of the creation of the Union Defence Forces (1 July), two organisations that have for much of the twentieth century shared a contested history. Yet, in a remarkable bouleversement, South Africa has come through this difficult past and, over the past two decades, a new South African society has been recreated following an interesting period of adjustment following the end of the Cold War and the growth of democracy in the developing world. These changes have necessarily affected her armed forces and the roles defined for them. Some commentators, particularly in the years immediately following 1994, asserted that military power had lost all of its vaunted, Cold-War importance in a new postmodern environment. Others still, recognising future challenges, argued that South Africa, beset with far-reaching socio-economic crises, could no longer afford the burden of military forces. Most scholars agree now that these perspectives were short-sighted and that, while the risk of major conflict has receded, the events of 9/11, and its consequences, demonstrate that the continental and international landscapes are less certain, less stable and less predictable, than that for which many had hoped. Clearly, South African interests are intertwined inextricably in regional and global affairs and if she is to protect these interests and ensure her security, she must maintain credible military force capable of meeting an array of contingencies. It was with this in mind that the strategic arms deal, since the subject of much debate, was passed by parliament:[i] the promise of a full technological transformation, to accompany the human transformation, offered.
- ItemBlack workers, typhoid fever and the construction of the Berg River : Saldanha military water pipeline, 1942 – 1943(AOSIS, 2008-04-11) Visser, Deon; Monama, FankieWar creates a huge need for labour to support the war efforts of the belligerent parties. In South Africa tens of thousands of ‘non-white’ workers were mobilised during the Second World War to satisfy the Union Defence Force’s (UDF’s) labour needs at home and abroad. This article, firstly, outlines the role of ‘non-white people’, particularly black Africans, in the UDF with special reference to those employed within the Union of South Africa. Secondly, it briefly delineates typhoid fever as an historical thorn in the flesh of military forces up to the early 20th century. It then looks briefly into the incidence of and perceptions on typhoid fever as a killer disease in South Africa on the eve of the Second World War. Against that background, the article investigates the employment of black workers on the construction of the Berg River-Saldanha Bay military water pipeline and the UDF’s response to the threat and subsequent outbreak of typhoid fever amongst the workers at the Berg River intake site in 1943. The article concludes that the public health authorities and UDF were aware of the threat of typhoid fever with regard to the Berg River water scheme, but did not take sufficient precautionary measures, which could have had serious repercussions for the Allied war effort. This incident should serve as a warning to the South African National Defence Force when deploying on peace support operations on the African continent where typhoid fever remains a serious threat next to Hiv/Aids.
- ItemChange, organisational culture and the development of the South African Military Academy to 2009(AOSIS, 2011-12-31) Visser, Deon; Van Dyk, G. A. J.This article investigates the impact of change and organisational culture on the growth and development of the South African Military Academy. It explores the impact of Nationalist Party rule since 1948 and black majority rule since 1994 on the institutional culture of the South African military and how that influenced the development of the Military Academy. This is intertwined with an investigation of the nature and impact of the diverging military and academic subcultures at the Academy. The article contends that, together with the historical exclusion of blacks and women from the military, the marginalisation of white English-speaking citizens by Nationalist Party rule denied the Academy the exploitation of a significant portion of the country’s human resource potential in the interest of institutional development. The same happened with the introduction of racial quotas and the marginalisation of whites since 1994. The Military Academy has, furthermore, historically been too reflective of the organisational culture of the South African National Defence Force and its predecessors instead of informing that culture to meet the challenges of military professionalism. The Academy has a potentially vital educational role to play in the South African and Sub-Saharan African militaries, but requires some changes in its organisational culture to fulfil that mission.
- ItemNamibiese bosoorlog uit die pen van deurwinterde kryshistorikus(AOSIS, 2009-04-04) Visser, DeonNo abstract available