Thesis (MScEng)--Stellenbosch University, 2003. / Some digitised pages may appear illegible due to the condition of the original hard copy. / ENGLISH ABSTRACT: A critical evaluation of provisions for imposed loads in the South African Loading Code for design of structures, SABS 0160-1989 (SABS), by comparison with other codes was performed earlier. The evaluation revealed the SABS loading code to be generally non-conservative in its provisions for imposed loads for a range of general and specialist occupancy classes. The SABS provision for imposed loads for inaccessible roofs was found to be substantially non-conservative in comparison with the other codes. An investigation into the imposed load for inaccessible roofs is subsequently performed in order to establish a scientific rationale through which the codified design values may be measured effectively. Due to the lack of information and the large uncertainties involved in the imposed roof load, stochastic treatment of the loads is implemented. This is in line with the stochastic modelling of loads as implemented in general. The approach applied is to select a type of building that can be regarded as a generic example of buildings to which these loads apply, and to discretisize the load into the various sub-mechanisms that translate into the imposed roof load. The probabilistic models for the load mechanisms are then quantified, either through physical load surveys, or through conducting an expert survey for those variables which are not observable. The use of expert opinion as a resource for information is not readily accessible in terms of yielding scientifically defendable results. Therefore, the expert survey is performed as a calibrated experiment whereby weights were calculated for the individual experts' opinions and their opinions combined accordingly. The probabilistic models for the load mechanisms are then translated into load effects by taking into account the physical process resulting in the load effects. By applying these mechanisms in such a way as to maximise the said load effects, equivalent uniformly distributed loads (EUDL's) were calculated for each mechanism. The probabilistic models obtained in terms of the EUDL's pose an easily accessible format through which existing load models and codified provisions can be evaluated. These load models are then utilised to evaluate the SABS provisions in terms of the level of reliability catered for by SABS ultimate limit-state design criteria. It is concluded that the SABS conservatively provides for maintenance loads on the roof, while the reliability for construction loads is non-conservative for large tributary areas and highly non-conservative for small areas. The load models so obtained can further be applied for structural reliability assessment. / AFRIKAANSE OPSOMMING: "n Kritiese evaluasie van die voorskrifte vir opgelegde belastings in die Suid- Afrikaanse Selastingskode vir die ontwerp van strukture, SASS 0160-1989 (SASS) deur 'n vergelyking met ander kodes is vroeër uitgevoer. Die evaluasie het getoon dat die SASS in die algemeen onkonserwatief is in sy voorsiening vir opgelegde belastings oor 'n bereik van algemene en spesialis okkupasie tipes. Die SASS voorskrif vir opgelegde belastings vir ontoeganklike dakke is hoogs onkonserwatief in vergelyking met die ander kodes. 'n Ondersoek na die opgelegde belasting vir ontoeganklike dakke word gevolglik uitgevoer met die doelom 'n wetenskaplike rasionaal daar te stel waardeur die gekodifiseerde voorskrifte effektief gemeet kan word. As gevolg van die gebrek aan inligting en groot onsekerhede betrokke by die opgelegde dakbelasting word stogastiese modellering geimplimenteer. Die aanslag wat gevolg is, is om 'n tipe gebou te selekteer wat beskou kan word as verteenwoordigend van die geboue waarvoor hierdie belastings van toepassing is, en om die belasting te diskretiseer in die verskeie lasmeganismes wat die opgelegde dakbelasting voortbring. Die waarskynlikheidsmodelle vir die lasmeganismes word dan gekwantifiseer, óf deur fisiese opnames, óf deur die uitvoering van 'n ekspertopname vir daardie veranderlikes wat nie waarneembaar is nie. Die gebruik van ekspert opinie as "n bron van inligting is nie maklik toeganklik in terme daarvan om wetenskaplik verdedigbare resultate te lewer nie. Daarom is die ekspert-opname uitgevoer soos 'n gekalibreerde eksperiment waardeur relatiewe gewigte bereken word vir die individuele eksperts en hulopinies daarvolgens gekombineer word. Die waarskynlikheidsmodelle vir die lasmeganismes word dan omgeskakel in laseffekte deur in agneming van die fisiese proses wat die las-effek voortbring. Deur die lasmeganismes op só 'n manier toe te pas dat die betrokke las-effekte gemaksimeer word, word ekwivalent uniforme belastings (EUS's) bepaal. Die waarskynlikheidsmodelle in terme van EUS's bied "n maklik toeganklike formaat waardeur bestaande lasmodelle en gekodifiseerde voorskrifte evalueer kan word. Die lasmodelle word gevolglik gebruik om die SASS voorskrifte te evalueer in terme van die vlak van betroubaarheid wat gehandhaaf word deur SASS limiet-staat ontwerp kriteria. Dit is bepaal dat die SASS konserwatief voorsiening maak vir onderhoudslaste op die dak, maar onkonserwatief tot hoogs-onkonserwatief is vir konstruksie laste. Die bepaalde lasmodelle kan verder toegepas word in strukturele betroubaarheids analise.

Η παρούσα διπλωματική εργασία πραγματεύεται την στατική ανάλυση και την ανάλυση κόπωσης διαξονικού ιχνηλάτη φωτοβολταϊκής εγκατάστασης. Η σχεδίαση της κατασκευής γίνεται στο σχεδιαστικό πακέτο Catia V5, τα στατικά φορτία υπολογίζονται με βάσει τον διεθνή κανονισμό Eurocode 1 , τα δυναμικά φορτία ανέμου υπολογίζονται βάσει το Kaimal spectrum ενώ οι αναλύσεις γίνονται στο λογισμικό πεπερασμένων στοιχείων Msc.Patran-Nastran. Η εργασία αποτελείται από επτά (7) κεφάλαια εκ των οποίων το έβδομο είναι τα συμπεράσματα. Στο κεφάλαιο 1 γίνεται μια εισαγωγή για τους τύπους στήριξης των φωτοβολταϊκών πλαισίων και για τις βασικές παραμέτρους της ηλιακής τεχνικής και της τροχιάς του ηλίου. Τέλος, υπολογίζονται οι δύο βασικές ηλιακές γωνιές αζιμούθια και ζενίθια κατά την διάρκεια του έτους ώστε να καθοριστούν οι κινήσεις της διάταξης του tracker. Στο κεφάλαιο 2 αναλύεται ο τρόπος σχεδίασης του ιχνηλάτη στο σχεδιαστικό πρόγραμμα Catia-v5. Συγκεκριμένα, προβάλλονται αναλυτικά τα βασικότερα μέρη της κατασκευής και τα τμήματα που συναρμολογήθηκαν ώστε να δημιουργηθεί η διάταξη.Tέλος, παρουσιάζονται οι σύνδεσμοι που επιτρέπουν την κίνηση του ιχνηλάτη και οι βαθμοί ελευθερίας που περιορίζονται από τον καθένα. Στο κεφάλαιο 3 αρχικά παρουσιάζονται οι μεθοδολογίες υπολογισμού των αδρανειακών φορτίων της ίδιας της κατασκευής, των αδρανειακών φορτίων των φ/β πλαισίων, των φορτίων χιονιού και των φορτίων ανέμου βάσει του Ευρωκώδικα 1. Έπειτα, παρουσιάζεται η μεθοδολογία υπολογισμού των δυναμικών φορτίων ανέμου που επιδρούν στην κατασκευή και ύστερα προβάλλονται τα αποτελέσματα των υπολογισμών. Τέλος, γίνεται μια αναφορά στις ιδιότητες και στην μηχανική συμπεριφορά των υλικών από τα οποία αποτελείται η κατασκευή του tracker. Στο κεφάλαιο 4 γίνεται μια σύντομη αναφορά στην θεωρία και στους τύπους των πεπερασμένων στοιχείων που χρησιμοποιούνται στην μοντελοποίηση του ιχνηλάτη. Και εν συνεχεία παρουσιάζονται διεξοδικά οι διαδικασίες μοντελοποίησης όλης της κατασκευής αλλά και τμημάτων της με στοιχεία δοκού, στοιχεία κελύφους και στοιχεία όγκου. Το κεφάλαιο 5 παρουσιάζει την διαδικασία υπολογισμού της ζωής σε κόπωση που ακολουθεί η υπορουτίνα του Msc.Fatigue στο πρόγραμμα των πεπερασμένων στοιχείων. Τέλος στο κεφάλαιο 6, παρουσιάζονται οι αναλύσεις που έγιναν ώστε να βρεθούν οι δυσμενέστερες καταστάσεις της κατασκευής αλλά και τα αντίστοιχα αποτελέσματα. / Current study deals with the static analysis of the double-axis solar tracker structure and the fatigue analysis of it, using finite elements techniques. The design of structure is done in the Catia V5 design software, the static loads are calculated according to Eurocode 1 Standard , the dynamic wind loads are calculated according to Kaimal Spectrum which is used to model dynamic loads in Sign structures while the analyses are carried out in the Msc. Patran-Nastran Finite Element Analysis program. The study consists of seven (7) parts and the last one refers to conclusions. In the first section, the types of PV panel support and the basic parameters of solar energy and of solar track are mentioned. Finally, the two basic solar angles such as azimuth and zenith are calculated during a year period with the purpose of determination of tracker motion. In section two, the way the sun tracker has been designed in Catia V5 is analyzed. Specifically, the main parts of steel structure and the parts that were assembled so that the order be created are presented. Finally, the connections of two main subparts of structure, which allow the movement of structure, and the degrees of freedom, which are constrained by each one, are presented. In section 3, firstly, the calculation methodology of inertial loads of the structure and of the PV panels and the calculation methodology of snow and wind loads are presented in according to Eurocode 1 Standard. Then, the calculation method of dynamic wind loads, which affect the construction, and the results of calculations are presented. In the end of this section, a report of material properties and behavior, which are used in the tracker structure, is presented. In addition, in section 4, the theory and the types of finite elements, which are used in the structure modeling, are presented. Subsequently, the procedures of structure modeling with beam, shell and 3-d finite elements are analytically presented. In section 5, the background of total-life calculation that is used by the subroutine of Msc.Fatigue in Finite Element Analysis program Msc. Patran-Nastran is reviewed. In section 6, the static and fatigue analyses, which are carried out in order to find the unfavorable load situations of structure and analyses results, are presented.

The head box in a tissue machine distributes the fiber suspension to a flat jet along the width of the machine. By adjusting the so-called lip opening, the flow is regulated and the jet is accelerated to match the machine speed. In this work, ideas for alternative solutions for lip opening mechanism is generated and evaluated with a focus on making a cost saving. One of the concepts has been selected for a deeper analysis with respect to the design, strength and cost. The selected concept is based on reducing the number of jacks required by using one jack operating a shaft parallel to the apron beam. Levers convey the movement to the apron beam. The analysis show that the shaft is exposed to high torque which results in large elastic twisting of the shaft, which means that the force that supports the apron beam will not be equal over the entire width. If the difference in force is too big, the apron beam will twist which results in an uneven lip opening. The shaft stiffness is therefore crucial. For the head box with a width of 2946 mm, the number of jacks is reduced from three to one. Wider head boxes may need more than one jack since the shaft cannot be made to long without getting too much twisted. A lip opening mechanism of the current design with six 20 ton jacks can be compared to the new concept in which only two jacks is needed and the cost is reduced by 18%. There is further potential for savings if the jack, separate gear and electric motor are replaced with an actuator that has the motor mounted directly. / Inloppslådan i en tissuemaskin har till uppgift att fördela fibersuspensionen till en flat stråle längs maskinens bredd. Genom att justera den så kallade läppöppningen regleras flödet och strålen accelereras för att passa maskinhastigheten. I detta arbete har idéer till alternativa lösningar för läppöppningsmekanismen genererats och utvärderats med fokus på att göra en kostnadsbesparing. Ett av koncepten har valts ut för en djupare analys med avseende på konstruktion, hållfasthet och kostnad. Det valda konceptet bygger på att reducera antalet domkrafter som behövs genom att en domkraft driver en axel parallell med utloppsbordet. Hävarmar överför rörelsen till utloppsbordet. Analysen visar att axeln utsätts för ett stort moment vilket ger en stor elastisk vridning av axeln, vilket gör att kraften som håller emot utloppsbordet inte blir lika stor över hela bredden. Om skillnaden i kraft är för stor ger det en förvridning av utloppsbordet som resulterar i en ojämn läppöppning. Axelns styvhet är alltså avgörande. För den undersökta lådan med bredden 2946 mm har antalet domkrafter reducerats från tre stycken till en. För bredare inloppslådor behövs fler domkrafter då axeln inte kan göras för lång utan att få för mycket vridning. Ett läppöppningsarrangemang som idag har sex stycken domkrafter kan jämföras med det nya konceptet där det krävs endast två domkrafter och kostnaden minskas med ca. 18%. Ytterligare potential till besparing finns om man byter ut domkraft, separat växel och elmotor till ett ställdon som har motorn direktmonterad.

Les alginates, polysaccharides extraits des algues brunes, sont des copolymères à blocs linéaires formés d'unités mannuronates (M) et guluronates (G). Leur structure dépend de la source naturelle. La complexation de cations divalents ou trivalents (sauf Mg2+) par les fonctions carboxylates conduit à la formation d'un hydrogel. Pour approfondir l'étude de la formation des gels ionotropiques d'alginate, des hydrogels et des aérogels séchés en conditions supercritiques ont été caractérisés à plusieurs échelles par différentes techniques. L'analyse orbitalaire ab initio de petits complexes a montré la formation de liaisons covalentes fortes avec les métaux de transition alors que les alcalino-terreux ne mettent en jeu que des interactions électrostatiques. Selon le rapport M/G et la nature des cations, différents régimes structuraux ont pu être identifiés par des mesures SAXS (~10-200Å) : des gels fibrillaires ou formés d'agglomérats interconnectés. Les propriétés mécaniques des hydrogels et les surfaces spécifiques des aérogels correspondants sont directement reliées à ces morphologies. La présence simultanée de plusieurs métaux dans les gels peut induire des effets coopératifs dans la formation mais aussi dans les propriétés des matériaux. De nouvelles méthodes ont été mises au point pour contrôler la synthèse de gels hétéro-cationiques, en considérant les effets d'affinité.Sur la base de cette étude, des synthèses originales de matériaux fonctionnels nano-structurés ont été développées. Certains ont été construits directement dans le réseau d'alginate en exploitant les cations de gélification ; d'autres ont nécessité le sacrifice de la matrice pour former des oxydes simples ou mixtes nanocristallins. / Alginates, polysaccharides produced by brown algae, are linear block-copolymers formed by mannuronate (M) and guluronate (G) units. Their structure depends on the natural source. The coordination of divalent or trivalent cations (except Mg2+) with the carboxylate functions leads to the formation of a hydrogel. In order to get some insight in ionotropic alginate gel formation, hydrogels and supercritical dried aerogels were analysed through various characterizations at different scales. The ab initio molecular orbital analysis on small complexes revealed strong coordination-covalent bonds in the transition metal complexes, whereas only ionic interaction occurs between the alkaline-earth cations and the carboxylates. Depending on the M/G ratio and the nature of the cation, different structural regimes were identified by SAXS analysis (~10-200Å) : well-defined fibrillar gels or gels with multiple junction nature. The mechanical properties of the hydrogels and surface areas of the resulting aerogels are directly related to these morphologies. The concomitant presence of different metals in the gel can bring cooperative effect for the formation but also for the properties of the materials. New methods to control the synthesis of hetero-cationic gels were implemented, taking into account the affinity effects. On the basis of this study, we developed new nanostructured functional materials synthesis. Some were built directly in the alginate network using the gelling cations. Others needed to sacrifice the matrix to form nanocrystalline single or mixed oxides.

The goal of this diploma thesis is to study and implement selected methods of static code analysis for C# programs translated into the Common Intermediate Language. The results of this work are integrated into the ParallaX Development Environment system. This diploma thesis focuses on Structural, Points-to and Dependence. analysis. Powered by TCPDF (www.tcpdf.org)

Models have become an indispensable tool within most industrial sectors and are used to reduce costs, enhance the performance of a system etc. The computer support within modelling is extensive, whereof the programming language Modelica is eminent, especially for multi-domain models. Dymola, a commercial program, is built on Modelica and is foremost used for simulation purposes, but many applications for which models are useful are not supported by Dymola. Instead other tools, e.g. Matlab, could be used to exploit the full potential of a model, which means that it first would be needed to be translated. This master's thesis examines one of the possible ways to accomplish this. Specifically the possibility to translate Modelica-models via an XML file, generated by Dymola, is examined. The structure and content of this file is explored, and based thereupon a software is implemented in Python, which successfully translates the models constituting the base for this thesis. Specifically the method was developed on a model of a sub-system of Saab 39 Gripen air-plane. Besides porting models between different languages, it is of great interest to determine how well a model describes the system on which it is based. Hence a new method for model validation is developed using the Matlab Fault Diagnosis Toolbox, which also determines the Matlab syntax of the Modelica translation. The novelty with the developed method, compared to traditional model validation methods, is that it is equation based. It is meant to point out specifically which equations are poorly fitted to validation data. On a simple example model the method was successfully used to isolate a poorly fitted equation. This is accomplished by introducing faults to the equations and generating residuals, based on sets of over-determined equations. As a measure of the modelling error the estimation error of the simulated residuals is used, which are weighted together depending on the fault properties of the residuals.

Call number: LD2668 .T4 1986 L43 / Master of Science / Civil Engineering

M.Sc. (Computer Science) / The purpose of this disssertation is to study methods to represent structures in three-dimensions. Due to the fact that chemical molecules are mostly complex three-dimensional structures, we used chemical molecules as our application domain. A literature study of current chemical information systems was undertaken. The whole spectrum of information systems was covered because almost all of these systems represent chemical molecules in one way or another. Various methods of three-dimensional structure representation were found in our literature study. All of these methods were discussed in the context of its own application domain. Structure graph grammars were examined and explained in detail. A small object-based system with structure graph grammars as the underlying principle was developed. We speculated on the use of such "intelligent" graph grammars in structure interpretation and identification. Further research in this area was also identified.

M.Tech. / South African government is one of the countries in the world that has delivered the highest number of houses to the poor through various delivery mechanisms to fulfill her vision to adequate housing for all as reflected in the National Housing Policy framework. Since 1994, about One Million Eight Hundred and Seventy Seven Thousand Nine Hundred and Fifty Eight (1 877 958) houses has been delivered. People’s Housing Process is a state-assisted, self help housing programme and about 3% of the total houses built were delivered through the PHP housing delivery programme. The Government’s goal is, subject to fiscal affordability, to increase housing delivery on a sustainable basis to a peak level of 350 000 units per annum until the housing backlog is overcome (South Africa’s National Housing code policy, 2000:5). The government focused on quantitative housing delivery with qualitative shortcomings. However the focus has now shifted to the quality of the end product delivered. Defects in houses manifest themselves primarily through cracking, dampness, detachment, and water leakages. Defects may be patent or latent, and could be discovered through checking, observations and tests. This research work is a study of structural qualities of houses delivered through PHP. The study investigated the causes of structural inadequacies in PHP houses focusing in the Gauteng Province of South Africa. The findings show that different types of structural defects occurred in houses delivered through PHP scheme, these defects include roof leakages, cracks in walls, wall not being straight and defects in roof trusses. The cause of these defects was as a result of poor quality control mechanism put in place by the Department of Housing.

M.Phil. / “Failure is one of the unfortunate facts of life”. This is the very first statement in the book by Coetzee (1998). This statement is unfortunately true, leading to the fact that failure is a reality, to be dealt with. Dealing with it in a proactive way will provide warnings of an approaching failure. Dealing with it in a reactive way will go through the “surprising pain” of an unexpected breakdown or downtime. In both cases the source of failure must be known to prevent it from happening again. Root Cause Analysis (RCA) is a structured method of determining the reason (root cause) of a failure. On the other hand, Vibration Analysis is one of the best known methods of condition monitoring and has the capability to indicate a reason for failure, although not necessarily the root cause or causes. The objective of this dissertation is to investigate the possibility to combine the RCA method with Vibration Analysis as forensic science to improve the success of finding root causes and their solutions.