Visualization techniques for representing scalar velocity fields over one- and two dimensional vibrating structures are investigated. High spatial density velocity fields are measured over a vibrating beam and a vibrating plate by a scanning laser velocimeter. The velocity measurements are assumed to contain noise. This thesis proposes a model on which principles and goals of scientific visualization are applied to experimental structural dynamics. Various mathematical functions and parameter estimation techniques are studied to obtain suitable mathematical models for fitting the scattered data sets. A two window displaying method, including a main display window and a zoom window, is adopted for visualizing the two-dimensional velocity data. To visualize three-dimensional velocity fields, four representation methods, the illuminated shade surface, the wireframe surface, the color contour surface, and the three-dimensional vector representation are demonstrated to visualize velocity fields. A dynamic animation of the plate's dynamic response is also demonstrated. Results demonstrate the feasibility of using visualization techniques to manipulate complicated scalar velocity data and visualizes the dynamic response of the free-free beam and completely free rectangular plate vibrations. / Master of Science

Transient modelling of heat fluxes and temperatures in structures was conducted to examine the effect of various characteristics on the temperature response during unusual operating and extreme weather conditions. The analytical model was validated using published experimental data and numerical results from well-known computer codes. The effect of including radiation heat transfer between interior surfaces, using the Mean Radiative Temperature method, on the temperature response was investigated and found to be negligible for a typical commercial building and a house during winter and summer power outages. The effect of thermal mass in the interior and exterior walls on the inside temperature drift after an HVAC system cutoff or a power outage was presented. The inside air temperature response curve is presented for different wall (exterior or interior) constructions of buildings. The effect of insulation position in exterior walls was also shown for several R values. The effect of exterior wall emissivity, sky temperature, outside vertical convective coefficient, furnishings, and ground temperature on the interior temperature response during winter and summer power outages were examined for buildings. The effect of infiltration on the temperature drift in buildings was investigated during winter and summer power outages. Restarting the HVAC after the power outage was examined during both seasons for typical buildings. Outside temperature profiles exceeding the 97.5 design temperature criterion were used to study the effect of extreme weather on the interior temperature of buildings with the HVAC system operating. / Ph. D.

The wooden multi-storey building industry is facing persistent sound transmission problems at low frequencies. Inserting elastomers within wall-floor junctions is common usage nevertheless no accurate studies have elucidated the real behavior of those nonlinear combined materials yet. Deeper knowledge is needed to create a relevant FE model which will help industry to use those materials efficiently.The nonlinear dynamic behavior of the elastomers inserted in wooden junctions is analyzed while the static load acting on them is varying. The specific situation where those elastomers were tested is a scaled room made of two walls and one floor.An experimental study was conducted on this prototype wooden construction and a numerical analysis was performed on the Finite Element model of it. The frequency response functions of several positions were measured on the physical setup.The study showed that loaded structures (up to 2 times the load of the floor) had a lower damping ratio. Having the structure standing on really stiff or elastic material does not differ when comparing experimental and analytical modal parameters.Those results depict the behavior of elastomers for different load cases and are definitely a step forward for the conception of a reliable FE model.

Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: In this thesis, a femtosecond electron diffraction (FED) set-up that is capable of investigating the photo-induced switching of Cu(DCNQI)2 from being an insulator to being a conductor is presented. Movies of atomic structural changes with temporal resolution within the typical photo-switching transition timescales (sub-picoseconds) are obtainable with this set-up by employing a femtosecond laser. The experimental technique and the design of a crucial instrument of the machine, the electron gun, are extensively described and characterised both numerically and experimentally. The interest in observing atomic structural changes of Cu(DCNQI)2 in real time is because of the rich variety of the radical salts available that show alloy-specific Charge Density Wave (CDW) transitions. Valuable insights about the driving mechanisms behind these structural changes that are responsible for a change in conductivity are obtainable, as well as the relation between crystal alloys and their transition characteristics. Electron diffraction patterns of crystals in their metallic phase (room temperature) are shown in this thesis, but diffraction patterns of cryo-cooled Cu(DCNQI)2 in its insulating phase are still to be acquired. The temporal resolution of the atomic movie can be improved by recompression of electron pulses that are debunched due to Coulomb repulsion and electron energy spread within a pulse. Numerical and preliminary experimental results presented in this work expose the potential of a simple compression technique. In this way, more electrons in a single electron pulse can be afforded which allows to perform experiments at shorter integration time or lower repetition rate. / AFRIKAANSE OPSOMMING: In hierdie tesis word ’n femtosekonde elektron diffraksie opstelling aangebied wat daartoe in staat is om die foto-geïnduseerde omskakeling in Cu(DCNQI)2 van nie-geleier tot geleier te ondersoek. Deur gebruik te maak van ’n femtosekonde laser in hierdie opstelling, is ’rolprente’ van strukturele veranderinge op atoomskaal met ’n tyd resolusie beter as die tipiese foto-omskakelings tydskaal (sub-pikosekonde) verkrygbaar. Die eksperimentele tegniek en die ontwerp van ’n noodsaaklike instrument van die masjien, die elektron geweer, word breedvoerig beskryf en numeries en eksperimenteel gekenmerk. Die belangstelling om strukturele veranderinge in Cu(DCNQI)2 op atoom skaal in reële tyd waar te kan neem is as gevolg van die ryke verskeidenheid van radikale soute, wat allooispesifieke ladings digtheid golf (CDW) oorgange toon, wat beskikbaar is. Waardevolle insigte oor die meganismes wat hierdie strukturele veranderinge wat ’n verandering in geleiding veroorsaak dryf is verkrygbaar, sowel as die verwantskap tussen die kristal allooi en die oorgang kenmerke. Diffraksie patrone van kristalle in die metaalagtige fase (kamer temperatuur) word in hierdie tesis getoon, maar diffraksie patrone van cryo-verkoelde Cu(DCNQI)2 in die niegeleier fase moet nog verkry word. Die tyd resolusie van die atomiese rolprent kan verbeter word deur die elektron puls — wat deur Coulomb afstoting en elektron energie spreiding versprei is — weer saam te pers. Numeriese en voorlopige eksperimentele resultate toon die potensiaal van ’n eenvoudige kompressie tegniek. Hierdeur kan meer elektrone in ’n elektron puls gegun word en so die integrasie tyd of die herhalingstempo van die eksperimente verkort kan word.

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.

With an ongoing desire to improve product performance, in combination with the continuously growing complexity of engineering structures, there is a need for well-tested and reliable engineering tools that can aid the decision making and facilitate an efficient and effective product development. The technical assessment of the dynamic characteristics of mechanical systems often relies on linear analysis techniques which are well developed and generally accepted. However, sometimes the errors due to linearization are too large to be acceptable, making it necessary to take nonlinear effects into account. Many existing analysis techniques for nonlinear mechanical systems build on the assumption that the input excitation of the system is periodic and deterministic. This often results in highly inefficient analysis procedures when nonlinear mechanical systems are studied in a non-deterministic environment where the excitation of the system is stochastic. The aim of this thesis is to develop and validate new efficient analysis methods for the theoretical and experimental study of nonlinear mechanical systems under stochastic excitation, with emphasis on two specific problem areas; forced response simulation and system identification from measurement data. A fundamental concept in the presented methodology is to model the nonlinearities as external forces acting on an underlying linear system, and thereby making it possible to use much of the linear theories for simulation and identification. The developed simulation methods utilize a digital filter to achieve a stable and condensed representation of the linear subparts of the system which is then solved recursively at each time step together with the counteracting nonlinear forces. The result is computationally efficient simulation routines, which are particularly suitable for performance predictions when the input excitation consist of long segments of discrete data representing a realization of the stochastic excitation of the system. Similarly, the presented identification methods take advantage of linear Multiple-Input-Multiple-Output theories for random data by using the measured responses to create artificial inputs which can separate the linear system from the nonlinear parameters. The developed methods have been tested with extensive numerical simulations and with experimental test rigs with promising results. Furthermore, an industrial case study of a wave energy converter, with nonlinear characteristics, has been carried out and an analysis procedure capable of evaluating the performance of the system in non-deterministic ocean waves is presented.

<p>The workin this thesis deals with the development of anaeroelastic simulation tool for horizontal axis wind turbineapplications.</p><p>Horizontal axiswind turbines can experience significanttime varying aerodynamic loads, potentially causing adverseeffects on structures, mechanical components, and powerproduction. The need of computational and experimentalprocedures for investigating aeroelastic stability and dynamicresponse have increased as wind turbines become lighter andmore flexible.</p><p>A finite element model for simulation of the dynamicresponse of horizontal axis wind turbines has been developed.The simulations are performed using the commercial finiteelement software SOLVIA, which is a program developed forgeneral analyses, linear as well as non-linear, static as wellas dynamic. The aerodynamic model, used to transform the windflow field to loads on the blades, is a Blade- Element/Momentummodel. The aerodynamic code is developed by FFA (TheAeronautical Research Institute of Sweden) and is astate-of-the-art code incorporating a number of extensions tothe Blade-Element/Momentum formulation. SOSIS-W, developed byTeknikgruppen AB was used to develop wind time series formodelling different wind conditions.</p><p>The model is rather general, and different configurations ofthe structural model and various type of wind conditions couldeasily be simulated. The model is primarily intended for use asa research tool when influences of specific dynamic effects areinvestigated.</p><p>Simulation results for the three-bladed wind turbine Danwin180 kW are presented as a verification example.</p><p><b>Keywords:</b>aeroelastic modelling, rotor aerodynamics,structural dynamics, wind turbine, AERFORCE, SOSIS-W,SOLVIA</p>

Seismically vulnerable buildings constitute a major problem for the safety of human beings. In many parts of the world, reinforced concrete (RC) frame buildings designed and constructed with substandard detailing, no consideration of capacity design principles, and improper or no inclusion of the seismic actions, have been identified. Amongst those vulnerable building, one particular typology representative of the construction practice of the years previous to the 1970’s, that most likely represents the worst case scenario, has been widely investigated in the past. The deficiencies of that building typology are related to non-ductile detailing in beam column joints such as the use of plain round bars, the lack of stirrups inside the joint around the longitudinal reinforcement of the column, the use of 180° end hooks in the beams, the use of lap splices in potential ‘plastic hinge’ regions, and substandard quality of the materials. That type of detailing and the lack of a capacity design philosophy create a very fragile fuse in the structure where brittle inelastic behaviour is expected to occur, which is the panel zone region of exterior beam column joints. The non-ductile typology described above was extensively investigated at the University of Canterbury in the context of the project ‘Retrofit Solutions for New Zealand Multi-Storey Buildings’ (2004-2011), founded by the ‘Foundation for Research, Science and Technology’ Tūāpapa Rangahau Pūtaiao. The experimental campaign prior to the research carried out by the author consisted of quasi-static tests of beam column joint subassemblies subjected to lateral loading regime, with constant and varying axial load in the column. Most of those specimens were representative of a plane 2D frame (knee joint), while others represented a portion of a space 3D frame (corner joints), and only few of them had a floor slab, transverse beams, and lap splices. Using those experiments, several feasible, cost-effective, and non-invasive retrofit techniques were developed, improved, and refined. Nevertheless, the slow motion nature of those experiments did not take into account the dynamical component inherent to earthquake related problems. Amongst the set of techniques investigated, the use of FRP layers for strengthening beam column joints is of particular interest due to its versatility and the momentum that its use has gained in the current state of the practice. That particular retrofit technique was previously used to develop a strengthening scheme suitable for plane 2D and space 3D corner beam column joints, but lacking of floor slabs. In addition, a similar scheme was not developed for exterior joints of internal frames, referred here as ‘cruciform’. In this research a 2/5 scale RC frame model building comprising of two frames in parallel (external and internal) joined together by means of floor slabs and transverse beams, with non-ductile characteristics identical to those of the specimens investigated previously by others, and also including lap splices, was developed. In order to investigate the dynamic response of that building, a series of shake table tests with different ground motions were performed. After the first series of tests, the specimen was modified by connecting the spliced reinforcement in the columns in order to capture a different failure mode. Ground motions recorded during seismic events that occurred during the initial period of the experimental campaign (2010) were used in the subsequent experiments. The hierarchy of strengths and sequence of events in the panel zone region were evaluated in an extended version of the bending moment-axial load (M-N) performance domain developed by others. That extension was required due to the asymmetry in the beam cross section introduced by the floor slab. In addition, the effect of the torsion resistance provided by the spandrel (transverse beam) was included. In order to upgrade the brittle and unstable performance of the as-built/repaired specimen, a practical and suitable ad-hoc FRP retrofit intervention was developed, following a partial retrofit strategy that aimed to strengthen exterior beam column joints only (corner and cruciform). The ability of the new FRP scheme to revert the sequence of events in the panel zone region was evaluated using the extended version of the M-N performance domain as well as the guidelines for strengthening plane joints developed by others. Weakening of the floor slab in a novel configuration was also incorporated with the purpose of reducing the flexural capacity of the beam under negative bending moment (slab in tension), enabling the damage relocation from the joint into the beam. The efficacy of the developed retrofit intervention in upgrading the seismic performance of the as-built specimen was investigated using shake table tests with the input motions used in the experiments of the as-built/repaired specimen. Numerical work aimed to predict the response of the model building during the most relevant shake table tests was carried out. By using a simple numerical model with concentrated plasticity elements constructed in Ruaumoko2D, the results of blind and post-experimental predictions of the response of the specimen were addressed. Differences in the predicted response of the building using the nominal and the actual recorded motions of the shake table were investigated. The dependence of the accuracy of the numerical predictions on the assumed values of the parameters that control the hysteresis rules of key structural members was reviewed. During the execution of the experimental campaign part of this thesis, two major earthquakes affected the central part of Chile (27 of February 2010 Maule earthquake) and the Canterbury region in New Zealand (22 February 2011 Canterbury earthquake), respectively. As the author had the opportunity to experience those events and investigate their consequences in structures, the observations related to non-ductile detailing and drawbacks in the state of the practice related to reinforced concrete walls was also addressed in this research, resulting in preliminary recommendations for the refinement of current seismic code provisions and assessment guidelines. The investigations of the ground motions recorded during those and other earthquakes were used to review the procedures related to the input motions used for nonlinear dynamic analysis of buildings as required by most of the current code provisions. Inelastic displacement spectra were constructed using ground motions recorded during the earthquakes mentioned above, in order to investigate the adequacy of modification factors used to obtain reduced design spectra from elastic counterparts. Finally a simplified assessment procedure for RC walls that incorporates capacity compatible spectral demands is proposed.

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.

L'objectif de cette thèse est de démontrer comment faire une analyse théorique de fatigue et de mécanique de la rupture d'une structure éolienne à l'axe horizontal. La chaîne des calculs nécessaires pour atteindre cet objectif s'avère être particulièrement longue pour deux raisons : d'abord, la vitesse du vent varie aléatoirement avec le temps ; deuxièmement, l'amplitude de vibration du mât est amplifié en raison des ses fréquences naturelles de vibration. Un chapitre entier est consacré à la modélisation de la vitesse du vent dans l'espace et dans le temps. Ce même chapitre démontre comment synthétiser un signal aléatoire à partir d'une fonction de densité spectrale de puissance (DSP). La force axiale du rotor est le chargement le plus important sur une structure éolienne à l'axe horizontal. Cette force a un rapport non linéaire avec la vitesse du vent. Cela implique la nécessité de déterminer la DSP de la force axiale à partir de son signal, en se servant d'une technique d'estimation spectrale. La méthode Thomson Multitaper s'est avéré la plus satisfaisante pour cette application. La DSP des déplacements du mât est déterminée en associant la réceptance du système structurel avec la DSP de la force qui représente tous les chargements. Un signal de contrainte peut finalement être synthétisé à partir de sa DSP. La technique de comptage de cycles de chargement connue sous le nom de rainflow est abordée et appliquée. Le fait que le signal de contraintes a une amplitude variable implique la nécessité d'employer une technique plus avancée de simulation de propagation de fissures. La technique choisie pour cette thèse est connue sous le nom de strip-yield (bande d'écoulement). / The objective of this thesis is to demonstrate how to do theoretical analyses of fatigue and fracture mechanics in a structure for horizontal axis wind turbine. The chain of calculations required to reach this objective is particularly long for two reasons : firstly, the wind speed varies randomly with time , secondly, the vibration amplitude of the mast is amplified due to its natural frequencies of vibration. A whole chapter is dedicated to modeling the wind speed in space and time. The same chapter shows how to synthesize a random signal by employing a power spectral density function (PSD). The axial force of the rotor is the most important loading on a structure for horizontal axis wind turbine. This force has a non linear relation with the wind speed. This implies the need to determine the PSD of the axial force from its signal, by employing a spectral estimation method. The Thomson Multitaper method revealed to be the most satisfactory for this application. The PSD of displacement of the mast is determined by associating the receptance of the structural system and the PSD of the force representing all loadings. Finally, a signal of stress can be synthesized from its PSD. The fatigue cycle counting method known as rainflow is discussed and employed. The fact that the signal of stress has a variable amplitude implies the need of a more sophisticated method to simulate a crack propagation. The method chosen in this thesis is called strip-yield.