Thesis--Rostock. / Bibliography: p. [v]-vii.

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Thesis (M.Eng. (Mechanical and Aeronautical Engineering)) -- University of Pretoria, 2008. / Includes bibliographical references.

Thesis (M. Eng.)(Mechanical)--University of Pretoria, 2003. / Summaries in Afrikaans and English. Title as viewed on 9 December 2005. Includes bibliographical references.

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This study examines a specific application of button-head type twist-off bolts. Currently, the Research Council on Structural Connections Specification (2000) removes the requirement for ASTM F436 washers (ASTM 2000a) under the bolt head of twist-off bolts where the head diameter equals or exceeds that of an ASTM F436 washer when oversized and slotted holes are used. The need for washers is also removed for A490 strength bolts used on steels with specified yield strengths less than 40 ksi provided that the head diameter equals or exceeds an ASTM F436 washer. The ASTM F1852 Specification (ASTM 2000b) allows for head diameter dimensions that are slightly smaller than an ASTM F436 washer. Following the RCSC Specification, manufacturers that produce bolts using the ASTM F1852 dimensions are required to use ASTM F436 washers under the bolt head. The discrepancies between the specifications lead to this study, which involved the testing of button-head type twist-off bolts with two different head diameters, both of which were smaller than an ASTM F436 washer. Five bolt diameters between 5/8 in and 1-1/8 in. were tested in standard, oversized, and long-slotted holes. The performance of the twist-off bolts was determined by measuring and comparing the achieved relaxed pretension force in the bolt after tightening. It was found that twist-off bolts with head diameters less than an ASTM F436 washer had no trouble attaining their required minimum pretension force. Bolt head diameter and hole size were found to have no significant influence on the pretension force that was achieved for all bolts tested. / Master of Science

Spatial dependency is commonly measured and tested with Moran's I statistic. The question to be answered is, whether far-off objects affect this statistic and influence the test. Far-off objects are observations that are far apart from all other objects in the dataset, i.e. they do not have spatial links to other design points. In the paper different possibilities of treating such objects are discussed, and their influence on Moran's I and the corresponding spatial autocorrelation test is analysed. (author's abstract) / Series: Research Report Series / Department of Statistics and Mathematics

A leak-off test is one of the most common procedures to test the fracture pressure of the exposed formations. After cementing and drilling out of the casing shoe, the LOT is run to verify that the casing, cement, and formation can withstand the pressure needed to safely drill the next section of the well. The equivalent mud weight obtained from the test is recorded and reported to government agencies as the strength of the casing shoe. Drilling engineers also rely on the reading from the LOT and use it as the maximum pressure that may be imposed on the formation to avoid fracturing. Exceeding the maximum pressure may result in serious consequences such as lost circulation, one of the most costly events in drilling operations. Therefore, accurate determination of formation fracture gradient is critical and can avoid a variety of well control problems. Considerable efforts to model LOT and leak-off behaviors have been done in the past. Altun (2001) and Paknejad (2007) each presented a unique method to estimate leak-off volume by dividing the pressurized system into four sub-systems: mud compression, casing expansion, fluid leakage, and borehole expansion. The volume response from each sub-system is then combined to represent the total volume pumped during a LOT. However, neither model included the expansion volumes of cement sheath and formation rock outside of the casing; these volumes are not trivial and should not be neglected. In addition, both models use only pump pressure to calculate volumes generated during a LOT. The actual downhole pressure and the pressure acting from the outside are ignored. In this study, the volume contributions from cement sheath expansion and formation rock expansion are calculated using single cylinder Lame’s equation. The results are added with Altun’s borehole expansion volume, mud compression volume, and fluid leakage volume to represent the total volume for the enhanced Altun model. Secondly, a Wider Windows mechanical expansion model is developed based on the concentric cylinder theory. This model simulates the compounded effect of casing, cement, and formation expansion along the cased hole based on pressures inside the wellbore and out in the far-field stress region. The volume generated from concentric cylinder expansion is then combined with Altun’s mud compression volume and fluid leakage volume to simulate the total volume pumped during a LOT. The developed models were verified using three sets of field LOT data obtained from literature and compared with the original Altun model. The results confirmed that leak-off volume along the cased hole should be analyzed as a compounded effect of casing, cement, and formation expansion. Overall, the WW models accurately simulate both leak-off volume and leak-off behaviors. / text

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