Thesis (MScEng)-- Stellenbosch University, 2013. / ENGLISH ABSTRACT: The port of Ngqura is situated on the east coast of South Africa. Since its first operational winter excessive vessel motions have interrupted container shipping operations and lead to mooring line failure. A major component contributing to the excessive motions is the presence of seiching in the port, resonating long waves. This study investigates the long wave generation, penetration into the port and subsequent resonance in the vicinity of the problem berths. An extensive literature review identified two predominant types of long waves along the coast of South Africa. Long waves with periods over 12 min generated by resonant air-water coupling and then shorter long waves between 30 s and 6 min attributed to bound long wave energy and broadly speaking, surf beat. A review of the state of the art long wave modelling techniques was included and contributed to the methodology in this study. Analysis of simultaneous measurements from the outside and inside of the port confirmed the generating mechanism of the long waves to be storm systems also responsible for generating short waves. Long waves outside the port were found to be on average 8% of the height of the short waves. On average 90% of the long wave height outside the port penetrated the port. The measurements further identified distinct resonating periods of the long wave energy inside the port. Calibrated Boussinesq wave models allowed for identification of how long waves penetrated the port and subsequently resonated. Both surface elevation measurements and white noise spectra were used as inputs. The penetration mechanisms were attributed to direct diffraction around the main breakwater as well as reflection off the beach south of the port leading to refraction and reflection off the lee side of the main breakwater. Tests with both free and bound long waves proved that at least for some period intervals the long wave energy was indeed bound to short waves. The excessive vessel motions are attributed to berths positioned in line with nodes created by the resonating long waves; nodes are characterized by strong horizontal currents which can induce surge motions in vessels. Various long waves between the period intervals of 45 s to 125 s resonate in the port to generate nodes at the berths of interest. In conclusion, the port of Ngqura is susceptible to a range of long wave periods resulting in significant basin oscillations which present nodes at mooring places. As a result of the analyses in this study the mechanisms of interaction between the port, port basins and the long waves penetrating into the port directly, or via the surf zone as surf beats, have been modelled, documented and better understood. This provides the potential for better prediction of severe long wave events and for the investigation of feasible mitigation measures to prevent damage to moored ships in the port. / AFRIKAANSE OPSOMMING: Die Ngqura hawe is aan die ooskus van Suid-Afrika geleë. Sedert die hawe se eerste operasionele winterseisoen, het oormatige skeepsbewegings operasies van behoueringskepe onderbreek en gelei tot faling van vasmeertoue. Die teenwoordigheid van langgolf resonansie is ‘n groot bydraende faktor tot die oormatige skeepsbewegings. Hierdie studie ondersoek die opwekking, penetrasie en gevolglike resonansie van langgolwe in die areas aangrensend tot die problematiese kaaie. ‘n Uitgebreide literatuurstudie het twee tipes langgolwe aan die Suid-Afrikaanse kus geïdentifiseer, naamlik langgolwe met periodes langer as 12 minute wat deur resonante lug-water koppeling opgewek word en korter langgolwe met periodes tussen 30 s en 6 min wat aan gebonde langgolfenergie of, meer algemeen, surf beat toegeskryf word. Verder is ‘n studie rakende die jongste langgolfmodelleringstegnieke ook uitgevoer waaruit die metodiek van hierdie studie bepaal is. ‘n Analise van gelyktydige opmetings binne en buite die hawe het bevestig dat kortgolwe wat deur stormsisteme gegenereer word, die opwekkingsmeganisme van lang golwe is. Daar is bevind dat langgolwe buite die hawe gemiddeld 8% so hoog soos kort golwe is. ‘n Gemiddeld van 90% van die langgolfhoogte het die hawe penetreer. Die opmetings het ook verder duidelike resonansieperiodes van langgolfenergie binne die hawe aangedui. Gekalibreerde Boussinsq-golfmodelle is gebruik om te indentifiseer hoe langgolwe die hawe binnedring en gevolglik resoneer. Beide oppervlakmetings en wit geraas spektra is as invoerwaardes vir die model gebruik. Die penetrasiemeganismes is toegeskryf aan diffraksie rondom die hoof hawemuur asook refleksie vanaf die strand, suid van die hawe, wat lei tot refraksie en refleksie teen die lykant van die hoof hawemuur. Toetse met vry langgolwe het bewys dat die langgolfenergie, vir ten minste sommige periode intervalle, aan die kort golwe vebonde is. Die oormatige skeepsbewegings is toegeskryf aan die kaaie wat in lyn met nodes van die langgolfresonansie geposisioneer is. Nodes word gekarakteriseer deur sterk horisontale strome wat surge bewegings in skepe kan veroorsaak. Verskeie langgolwe met periode intervalle tussen 45 s tot 125 s resoneer in die hawe en vorm nodes by die kaaie van belang. Ten slotte, die Ngqura hawe is vatbaar vir ‘n reeks langgolfperiodes wat ossilasies in die bekkens van die hawe veroorsaak en nodes naby kaaie vorm. As gevolg van die analises in hierdie studie is die meganismes van interaksie tussen die hawe, sy bekkens en langgolwe wat die hawe direk of via die brandersone binnedring gemodelleer, gedokumenteer en beter verstaan. Hierdeur is die potensiaal vir beter voorspelling van ernstige langgolftoestande verhoog en is dit moontlik gemaak om lewensvatbare oplossings vir skade aan vasgemeerde skepe te ondersoek.

Investigations into the characteristics and underlying mechanism of the circulation of water near the shore are reported. The two main types of circulation, one a cellular system resulting from Haves propagated nearly normally to the shore, and the other an essentially alongshore flow associated with oblique waves, are treated separately. The cellular circulation studies were made in the field at Virginia Beach and more extensively in wave tanks. From the field experiments data were collected about the dimensions of the cells, the way in which the Hater circulated, the rate of exchance of surf zone water and the extent of recycling. A method for measuring the changes in the mean sea level over intervals of time greater than those of the wave periods, was developed. The model experiments carried out in uniform wave tanks showed that the cellular circulations could be well simulated. Measurements were made of the cell dimensions, the velocity of the longshore and rip currents, and of the recycling regime. A finding from the wave tank studies Has the presence of standing waves formed by transverse edge waves. The interaction of these standing waves with the gene rated waves normal to the shore could be the initial cause of rip currents and the cellular circulation. Studies of the alongshore system were made in the field only. A method for measuring the volume of flow of longshore currents was developed, tested, and applied. Calculated volumes of flow using a theory based on continuity and the solitary wave theory (as proposed by Inman and Bagnold) compared tolerably well with the field observations. The calculations of volume of flow required a knowledge of the wave height spectra in the surf. This was established by making wave height recordings in the between-breaker zone . It was found that the characteristics of the spectra compared reasonably well with those pr e dict ed by the Longuet-Higgins theory, previously assumed to apply to deep water waves only. A mechanism for the transition from cellular to alongshore system is proposed. / Thesis (Ph.D.)-University of Natal, 1967.

Ziel dieser Arbeit war, die Auswirkungen von Clocking der Leitreihen eines mehrstufigen Axialverdichters auf Potentiale hinsichtlich der Beeinflussung instationärer und stationärer Effekte zu untersuchen und zum grundlegenden Verständnis der instationären Schaufelinteraktion beizutragen. Dazu wurden über 2000 Leitgitterkonfigurationen vermessen, so dass der Einfluss von Clocking auf den Wirkungsgrad entlang der Kennlinie bei Auslegungsdrehzahl, auf die Schaufelgrenzschichten und auf die Betriebsgrenzen untersucht und dokumentiert werden konnte. Vor allem wurde so eine erhebliche Beeinflussung der Pumpgrenze gefunden, während das Grenzschichtverhalten auf den Schaufeln und der Wirkungsgrad im praktisch relevanten Bereich der Kennlinie kaum verändert wurden. Hauptgegenstand der Untersuchungen war aber der Einfluss von Stator-Clocking auf die instationären Druckverteilungen und die resultierenden instationären Erregerkräfte an den Lauf- und Leitschaufeln. Die Vermessung der Auswirkungen der Positionierung jedes einzelnen Leitgitters wurde genutzt, um durch eine einfache Optimierung zwei geometrische Konfigurationen aller Leitgitter zu entwickeln. Die eine Konfiguration führte zu geringen aerodynamischen Erregerkräften an den Laufschaufeln aller Stufen, während die andere Konfiguration eine gleichmäßig hohe instationäre Anregung zur Folge hatte. Die Unterschiede der instationären Erregerkräfte zwischen den Konfigurationen waren erheblich und über weite Bereiche der Kennlinie unabhängig vom Betriebspunkt, ohne das die Konfiguration der Leitgitter geändert wurde. Für eine umfassende Analyse der periodisch instationären, aerodynamischen Schaufelinteraktion wurden sowohl die Schaufeldruckverteilungen, als auch das Strömungsfeld in den axialen Schaufelzwischenräumen im Mittelschnitt der Beschaufelung für beide Clocking-Konfigurationen zeitgenau vermessen und vergleichend ausgewertet. Aus diesen Analysen konnte mithilfe der Wellenmechanik eine einfache analytische Beschreibung der instationären Interaktion der Potentialfelder der Beschaufelung entwickelt werden. Für eine einzelne Stufe wurde mit diesem Modell die experimentell bestimmte Phasendifferenz der Druckschwankungen auf Druck- und Saugseite auf sehr einfache Weise nachgewiesen. Damit liegt ein einfaches, analytisches Modell für die Beschreibung der komplexen Überlagerung der sich relativ zueinander bewegenden Druckfelder der Beschaufelung axialer Turbomaschinen vor, das für das physikalische Verständnis der instationären Schaufelinteraktion einen wertvollen Beitrag liefert.

<p dir="ltr">Low frequency noise has been a challenge to noise control strategies for a long time due to its relatively long wavelength compared with practical thicknesses of acoustical treatments. A series of studies have drawn increasing attention to the acoustical behavior of porous granular materials such as activated carbon due to their good performance at low frequency. To better characterize this type of material, a 1-dimensional poro-elastic model is introduced in this work, which accounts for both the inner particle structure and the elasticity of the granule stack, allowing a better match of resonance features between the model prediction and measurement results. This model was then extended to a 2-dimensional finite difference (2DFD) approach under an axisymmetric assumption, with the depth-dependent stiffness of the granule stack considered. The shape of the computational domain of this 2DFD approach is close to the realistic geometry of the cylindrical standing wave tube, and it provides flexibility in assigning different types of boundary conditions at the circumferential wall of the container. The model is validated by comparing the simulation output and measurements of the acoustic response of porous granular materials in a cylindrical standing wave tube with rigid backing. The comparison demonstrates that the proposed 2DFD model is able to closely match the test results even down to detailed features, thus providing a means of accurate acoustic characterization of granular materials. The application scenarios of porous granular materials are also discussed in this work. A hybrid model based on the classical Johnson-Champoux-Allard (JCA) model and the rigid model describing the multi-level porosity within the granules is proposed to predict the performance of composite materials made of non-woven fiber matrices and porous granular materials. The performance of other practical applications such as that of a sound absorber consisting of a membrane and a cavity partially filled with the porous granular material is also discussed. These applications are shown to be promising strategies of addressing the low frequency noise problems.</p>

Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: A measurement device was developed to accurately determine the pneumatic power performance of an Oscillating Water Column (OWC) model in a wave flume. The analysis of the pneumatic power is significant due to the wave-topneumatic energy being the primary energy conversion process and where the most energy losses can be expected. The aim of the research study is to address the accurate pneumatic power measurement of unsteady and bidirectional airflow in OWC model experiments. The two fundamental measurements required for the pneumatic power measurement are the pressure difference over an orifice on the OWC model and the volumetric flow rate of air through the outlet. The designed, constructed and assembled measurement device comprised of a venturi flow meter, containing a hot-film anemometer, which could measure the pressure drop and the volumetric flow rate in one device. The assembled pneumatic power measurement device was calibrated in a vertical wind tunnel at steady state. The results from the calibration tests showed that the volumetric flow rate measurements from the pneumatic power measurement device was accurate to within 3 % of the wind tunnel’s readings. The pneumatic power measurement device was incorporated onto a constructed Perspex physical model of a simple OWC device. This assembled system was used as the test unit in the wave flume at Stellenbosch University (SUN). The results from the experimental tests underwent comparative analysis with three analytical OWC air-flow models which were simulated as three scenarios using Matlab Simulink. These results showed that the measurement device has the ability to measure the pneumatic power but there is difficulty in modelling the complex air-flow system of the OWC device. This results in varying levels of agreement between the experimental and simulated pneumatic power results. The research study has revealed that there is difficulty in designing an accurate device for a wide range of test parameters due to the variance in output values. The unsteady and bidirectional nature of the air flow is also difficult to accurately simulate using a one-dimensional analytical model. Recommendations for further investigation are for CFD systems to be used for the analysis of the air-flow in an OWC system and to be used to validate future pneumatic power measurement devices. / AFRIKAANSE OPSOMMING: ‘n Meetinstrument was ontwikkel om die pneumatiese kraglewering van ‘n model van die Ossillerende Water Kolom (OWK) golfenergie omsetter in ‘n golf tenk akkuraat te meet. Dit is belangrik om die omskakeling van golf na pneumatiese energie te analiseer siende dat die grootste energieverlies in dié proses plaasvind. Die doel van hierdie navorsingsprojek was om die akkurate pneumatiese kragmeting van variërende en twee-rigting vloei van lug in ‘n OWK model na te vors. Die twee fundamentele metings wat benodig word vir die pneumatiese kragbepaling is die drukverskil oor die vloei vernouing en die volumetriese vloeitempo van lug deur die uitlaat van die toetstoestel. Die spesiaal ontwerpte meettoestel wat gebruik is in die eksperiment het bestaan uit ‘n venturi vloeimeter wat ‘n verhitte-film anemometer bevat het wat die drukverandering en die volumetriese vloeitempo kan meet in ‘n enkele instrument. Die pneumatiese kragmeting was gekalibreer in ‘n vertikale windtonnel waarin ‘n konstante vloei tempo geïnduseer was. Die kalibrasieproses het bevestig dat die meettoestel metings lewer met ‘n fout van minder as 3 % wanneer dit vergelyk word met die bekende konstante vloei tempo soos bepaal in die windtonnel. ‘n Fisiese model van ‘n vereenvoudigde OWK golfenergie omsetter was ontwerp en gebou uit Perspex om as toetstoestel te gebruik vir die evaluering van die ontwerpte pneumatiese kraglewering meettoestel. Die toetse was uitgevoer in ‘n golftenk by die Universiteit Stellenbosch (SUN). The toetsresultate was vergelyk met drie ander OWK lugvloei modelle wat gesimuleer was deur om die analitiese modelle op te stel en te simuleer in Matlab Simulink. Die vergelyking van modellering resultate het gewys dat die meettoestel die vermoë het om pneumatiese krag te meet. Daar was wel komplikasies met die modellering van die komplekse lugvloei in die OWK toestel, die resultate het geen definitiewe ooreenstemming gewys tussen die eksperimentele en gesimuleerde pneumatiese krag resultate nie. Die navorsingsprojek het gewys dat daar komplikasies is om ‘n enkel toestel te ontwerp wat oor ‘n wye bereik kan meet weens die variasie van die verskillende parameters. Die variërende en twee-rigting lugvloei is ook moeilik om akkuraat te simuleer met ‘n een-dimensionele analitiese simulasie model. Aanbevelings vir verdere navorsing sluit in om die lugvloei in die OWK stelsel te modelleer en te analiseer in ‘n drie-dimensionele model om die lesings van ‘n pneumatiese krag meettoestel te bevestig.

Unique français parmi les fondateurs de la mécanique quantique, Louis de Broglie est une figuremajeure de l’histoire de la physique française du XXème siècle. Il devient grâce à son prix Nobel dephysique en 1929 le personnage central de la physique théorique française. Dans les récits usuelsportant sur la physique française du XXème siècle, la mécanique quantique est décrite comme s’étanttrès lentement diffusée en France, et il est souvent admis que peu de physiciens de ce pays l’utilisèrentavant la fin de la seconde guerre. De Broglie est souvent désigné comme le grand responsable de cetétat de fait et est dépeint comme un représentant type d’une pratique de physique théorique obsolète.De plus, son rôle institutionnel et sa responsabilité dans l’isolationnisme français sont dénoncés.Le but de ce travail est, premièrement, d’éclairer les modalités de la diffusion de la mécaniquequantique en France et le rôle de Louis de Broglie dans ce processus. Ce faisant, mon propos apporterade fortes nuances aux habituels récits portant sur cet aspect de l’histoire de la physique française duXXème siècle. Deuxièmement, je montrerai que l’essor de domaines tels que la physique des particules,la physique du solide et la physique nucléaire après la seconde guerre mondiale introduit unchangement dans les pratiques des jeunes théoriciens par rapport aux pratiques qui régnaient autour deLouis de Broglie. Je serai alors en mesure d’expliquer pourquoi l’héritage de Louis de Broglie au seinde la physique française de la seconde moitié du XXème siècle est si peu revendiqué, tout en évitant detomber dans le piège des jugements rétrospectifs et péjoratifs. / As the only Frenchman among the founding fathers of quantum mechanics, Louis de Broglie has agreat importance in the XXth French physics. With the prestige from the Nobel Prize in 1929, deBroglie became the main characters of the French theoretical physics community since the 30’s andgreat responsibilities on its evolution were entrusted to him. In the usually story of the XXth Frenchphysics, quantum mechanics, which is the core of theoretical physics since 1925, is said to have spreadslowly in France and French theorists who really used it were few before WWII. This story goes on,saying that de Broglie was the principal guilty of this state of fact. In this story, the discoverer ofwave-particle duality of matters becomes a representative of old-fashioned theorists who practice anaive kind of picture-based physics. Furthermore, his institutional action and his responsibility in theisolation of French physics are stigmatized.The aim of this work is, firstly, to throw light on the modality of the diffusion of quantummechanics in France and the role of de Broglie in this process, both on the intellectual and theinstitutional side. Secondly, it will be shown that progress in the area of particle physics, solid statephysics and nuclear physics after WWII introduce a shift in the practice of many young theoristsrelative to the way of practice theoretical physical inside de Broglie’s group. We will thus be able tounderstand why the legacy of Louis de Broglie is not claimed in contemporary French theoreticalphysics without falling into the trap of a retrospective and pejorative assessment of the career of themost famous French theorist of the XXth century.

Wave propagation is a common phenomenon in aircraft structures resulting from high velocity transient loadings like bird hit, gust etc. Apart from understanding the behavior of structures under such loading, wave propagation analysis is also important to gain knowledge about their high frequency characteristics, which have several applications. The applications include structural health monitoring using diagnostic waves and control of wave transmission for reduction of noise and vibration. Transient loadings with high frequency content are associated with wave propagation. As a result, the higher modes of the structure participate in the response. Finite element (FE) modeling for such problem requires very fine mesh to capture these higher modes. This leads to large system size and hence large computational cost. Wave propagation problems are usually solved in frequency domain using fast Fourier transform (FFT) and spectral finite element method is one such technique which follows FE procedure in the transformed frequency domain. In this thesis, a novel wavelet based spectral finite element (WSFE) is developed for wave propagation analysis in finite dimension structures. In WSFE for 1-D waveguides, the partial differential wave equations are reduced to a set of ODEs using orthogonal compactly supported Daubechies scaling functions for temporal approximation. The localized nature of the Daubechies basis functions allows finite domain analysis and imposition of the boundary conditions. The reduced ODEs are usually solved exactly, the solution of which gives the dynamic shape functions. The interpolating functions used here are exact solution of the governing differential equation and hence, the exact elemental dynamic stiffness matrix is derived. Thus, In the absence of any discontinuities, one element is sufficient to model 1-D waveguide of any length. This elemental stiffness matrix can be assembled to obtain the global matrix as in FE and after solution, the time domain responses are obtained using the inverse wavelet transform. The developed technique circumvents several serious limitations of the conventional FFT based Spectral Finite Element (FSFE). In FSFE, the wave equations are reduced to ODEs using FFT for time approximation. The remaining part of the formulation is quite similar to that of WSFE. The required assumption of periodicity in FSFE, however, does not allow modeling of finite length structures. It results in “wrap around” problem, which distorts the response simulated using FSFE and a semi-infinite (“throw-off”) element is required for imparting artificial damping. This artificial damping occurs as the “throw off” element allows leakage of energy. In some cases, a very high damping can also be considered instead of “throw off” element to remove wrap around effects. In either cases, the damping introduced is much larger than any inherent damping that may be present in the structure. It should also be mentioned that even in presence of the artificial damping, a larger time window is required for removing the distortions completely. The developed WSFE method is completely free from such problems and can efficiently handle undamped finite length structures irrespective of the time window considered. Apart from this, FSFE allows imposition of only zero initial condition and in contrary any initial conditions can be used in WSFE. Though FSFE has problem in modeling finite length undamped structures for time domain analysis, it is well suited for performing frequency domain study of wave characteristics, namely, the determination of spectrum and dispersion relations. WSFE is also capable of extracting these frequency dependent wave properties, however only up to a certain fraction of the Nyquist frequency. This constraint results from the loss in frequency resolution due to the increase in time resolution in wavelet analysis, where the basis functions are bounded both in time and frequency. A price has to be paid in frequency domain in order to obtain a bound in the time domain. The consequence of this analysis is to impose a constraint on the time sampling rate for the simulation with WSFE, to avoid spurious dispersion. WSFE for 2-D waveguides are formulated using Daubechies scaling functions for both temporal and spatial approximations. The initial and boundary conditions, however, are imposed using two different methods, which are wavelet extrapolation technique and periodic extension or restraint matrix respectively. The 2-D WSFE is bounded in both the spatial directions unlike 2-D FSFE, which is essentially unbounded in one spatial direction. Apart from this, 2-D WSFE is also free from “wrap around” problem similar to 1-D WSFE due to the localized nature of the basis functions used for temporal approximation. In this thesis, WSFE is developed for isotropic 1-D and 2-D waveguides for time and frequency domain analysis. These include elementary rod, Euler-Bernoulli and Timoshenko beams in 1-D modeling, and plates and axisymmetric cylinders in 2-D modeling. The wave propagation responses simulated using WSFE for these waveguides are validated using FE results. The advantages of the proposed technique over the corresponding FSFE method are also highlighted all through the numerical examples. Next part of the thesis involves the extension of the developed WSFE technique for modeling composite and nano-composite structures to study their wave propagation behavior. Due to their anisotropic nature, analysis of composite structures, particularly high frequency transient analysis is much more complicated compared to the corresponding metallic structures. This is due to the presence of stiffness coupling in these structures. Superior mechanical properties of composites, however, are making them integral parts of an aircraft and thus they often experience such short duration, high velocity impact Loadings. Very few literatures report the response of composite structures subjected to such high frequency excitations. Here, WSFE is formulated for a higher order composite beam with axial, flexural, shear and contractional degrees of freedom. WSFE is also formulated for composite plates using classical laminated plate theory with axial and flexural degrees of freedom. Simulations performed using these WSFE models are used to study the higher order and elastic coupling effects on the wave propagation responses. Carbon nanotubes (CNTs) and their composites are attracting a great deal of experimental and theoretical research world-wide. The recent trend in the literature shows a great interest in the dynamic and wave characteristics of CNTs and nano-composites because of their several applications. In most of these applications, CNTs are used in the embedded form as it does not requires precise alignment of the nano-tubes. In addition, the extraordinary mechanical properties of CNTs are being exploited to achieve high strength nano-composite. Apart from the experimental studies and atomistic simulation to study the mechanical properties of CNTs and nano-composites, continuum modeling is also receiving much attention, mainly due to its computational viability. In this thesis, a 1-D WSFE is formulated for multi-wall carbon nanotube (MWNT) embedded composite modeled as beam using higher order layer-wise theory. This theory allows to model partial interfacial shear stress transfer, which normally occurs due to improper dispersion of CNTs in nano-composites. The effects of different matrix materials and fraction of shear stress transfer on the wave characteristics are studied. The responses obtained using other beam theories are also compared. The beam modeling does not allow capturing the radial motions of the CNT, which are important for several applications. These can be effectively captured by modeling the CNT using a 2-D axisymmetric model. Hence, a 2-D WSFE model is constructed to capture the high frequency characteristics of single-walled carbon nanotubes (SWNTs). The response of SWNT simulated using the developed model is validated with experimental and atomistic simulation results reported in the literature. The comparison are done for dispersion relation and also radial breathing mode frequencies. The effects of geometrical parameters, namely the radius and the wall thickness of the SWNT on the higher radial, longitudinal and coupled radial-longitudinal vibrational modes are analyzed. These behaviors are studied in both time and frequency domains. Such time domain analyses of finite length SWNT are not possible with the Fourier transform based techniques reported in literature, although, such analyses are important particularly for sensor applications of SWNT. Spectral finite element method is very much suited for solution of inverse problems like force reconstruction from the measured wave response. This is because the technique is based on the concept of transfer function between the displacements (output) and applied forces (input). In the present work, WSFE is implemented for identification of impact force from the wave propagation responses simulated with FE and used as surrogate experimental results. The results show that WSFE can accurately reconstruct the impulse load applied to 1-D waveguides which include rod, Euler-Bernoulli beam and connected 2-D frame, even with highly truncated response. This is unlike FSFE, where the accuracy of the identified force depends largely on the time window of the measured responses. The detection of damage from the wave propagation analysis is another class of inverse problems considered in this thesis and is of utmost importance in the area of aircraft structural health monitoring. Here, the detection scheme is based on arrival time of the waves reflected from the damage. A novel detection technique based on wavelet filtering is proposed here and it is shown to work efficiently even in the presence of noise in the measured wave responses. Detection of damage requires an efficient damage model to simulate the mode of structural failure. In this regard, two spectrally formulated wavelet elements are proposed, one to model isotropic beam with through-width notch and the second to model composite beam with embedded de-lamination. In the first case, the response of the damaged beam is considered as the perturbation of the undamaged response and the linear perturbation analysis leads to a completely new set of dynamic stiffness matrix. In the second case, the delamination is modeled by subdividing the de-laminated region into separate waveguides and full damage model is established by imposing the kinematics. These models help to simulate wave propagation in such damaged beams to study the effect of damage on the wave response. Noise and vibration are often transmitted from the source to the other parts of the structure in the form of wave propagation. Thus, control of such wave transmission is essential for reduction of noise and vibration, which are the main cause of discomfort and in many cases cause failure of structure. Here, techniques for both passive and active controls of wave are proposed. For active control, a closed loop system is modeled using WSFE with magnetostrictive actuator for control of axial and flexural wave propagations in connected isotropic 1-D waveguides. The feedback is negative velocity and/or acceleration measured at different sensor points. A very new application of CNT reinforced composite for passive control of vibration and wave response is explored in this thesis. For this, a novel concept of nano-composite inserts is proposed. This insert can be made from CNTs dispersed in polymer. The high stiffness of the inserts helps to regulate the power flow in the form of wave propagation from the point of application of the loads to other parts of the structures. The length of the insert, volume fraction of CNTs and position are changed to achieve the required reduction in wave amplitudes. The entire thesis is split up into eight chapters. Chapter 1 presents a brief introduction, the motivation and objective of the thesis. Chapters 2 and 3 give a detail account of wavelet spectral finite element formulation for 1-D and 2-D isotropic waveguides, while Chapter 4 gives the same for composite waveguides. Chapter 5 brings out essential wave characteristics in carbon nanotubes and nano-composite structures, while Chapters 6 and 7 exclusively deal with application of WSFE to some real world problems. The thesis ends with summary and directions of future research. In summary, the thesis has brought out several new aspects of wave propagation in isotropic, composite and nano-composite structures. In addition to establishing wavelet spectral finite element as a useful tool for wave propagation analysis, several new techniques are presented, several new algorithm are proposed and several new concepts are explored.

The topic of this thesis is about experimental study of phenomena which are associated with light propagation in nonlinear dielectric media. In the first part of this work, we study experimentally the snake instability of the bright soliton stripe of the (2+1)-dimensional hyperbolic nonlinear Schrödinger equation. The instability is observed, through spectral measurements, on spatially extended femtosecond pulses propagating in a normally dispersive self-defocusing semiconductor planar waveguide. The second part of this thesis is about light propagation in nonlinear periodic media. We experimentally observe a stationary spatial gap (or Bragg) soliton in a periodic semiconductor planar waveguide. Based on the interference pattern of the soliton beam, we measure the power parameter of the soliton which is related to the position of the spatial spectrum in the linear band gap. <p><p><p>Cette thèse de doctorat a pour sujet l’étude expérimentale de phénomènes associés à la propagation de la lumière dans les milieux diélectriques non linéaires. La première partie porte sur la démonstration expérimentale de l’instabilité serpentine d’une bande solitonique dans un système décrit par une équation de Schrödinger non linéaire à (2+1)-dimensions. L’instabilité est observée sur base de mesures du spectre spatial ainsi que du profil spatio-fréquentiel d’une impulsion femtoseconde après propagation dans un guide plan semi-conducteur qui présente une dispersion normale et une non-linéarité défocalisante. Le second thème abordé concerne la propagation de la lumière dans les milieux non linéaires périodiques. Les expériences réalisées ont montré l’existence du soliton de Bragg spatial stationnaire sous forme de faisceaux se propageant dans des guides plans semi-conducteurs périodiquement gravés. Sur base du profil de la distribution modale en intensité du faisceau soliton, il a été possible de mesurer le paramètre de puissance du soliton de Bragg qui détermine la position du spectre spatial dans la bande interdite linéaire. <p> / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished

Micro-assembly is of crucial importance in industry nowadays. Nevertheless, currently applied processes require improvements. Indeed, when dealing with the assembly of submillimetric components, usually neglected surface forces disturb the manipulation task. They are responsible for the component sticking to the gripper, because of downscaling laws. A promising strategy to tackle adhesion consists in working without contact. The present dissertation is focused on contactless handling with acoustic levitation.<p>The advantages of contactless handling, the physical principles suitable for levitation and their applications are detailed. The opportunity for new handling strategies are shown. Acoustic levitation appears as the most fitted principle for micro-assembly. The elements to model acoustic forces are analysed and performances of existing modellings are assessed. A general numerical model of acoustic forces is implemented and theoretically validated with literature benchmarks. A fully automated modular levitator prototype is designed and used to experimentally validate the implemented numerical model. Specific instrumentations and protocols are developed for the acoustic force measurements.<p>The numerical model is finally applied to the real levitator. Modelling results are used to support experimental observations: the optimisation of the levitator resonance, the influence of the reflector shape, the dynamical study of the component oscillations, the stability with lateral centring forces and rotation torques, the component insertion and extraction from the levitator, the effect of pressure harmonics on the acoustic forces, and the manipulation of non spherical components. Acoustic forces are experimentally measured and a very good agreement with the modellings is obtained. Consequently, the implemented simulation tool can successfully be applied to a complex manipulation task with a component of any shape in a real levitator. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Ziel dieser Arbeit war, die Auswirkungen von Clocking der Leitreihen eines mehrstufigen Axialverdichters auf Potentiale hinsichtlich der Beeinflussung instationärer und stationärer Effekte zu untersuchen und zum grundlegenden Verständnis der instationären Schaufelinteraktion beizutragen. Dazu wurden über 2000 Leitgitterkonfigurationen vermessen, so dass der Einfluss von Clocking auf den Wirkungsgrad entlang der Kennlinie bei Auslegungsdrehzahl, auf die Schaufelgrenzschichten und auf die Betriebsgrenzen untersucht und dokumentiert werden konnte. Vor allem wurde so eine erhebliche Beeinflussung der Pumpgrenze gefunden, während das Grenzschichtverhalten auf den Schaufeln und der Wirkungsgrad im praktisch relevanten Bereich der Kennlinie kaum verändert wurden. Hauptgegenstand der Untersuchungen war aber der Einfluss von Stator-Clocking auf die instationären Druckverteilungen und die resultierenden instationären Erregerkräfte an den Lauf- und Leitschaufeln. Die Vermessung der Auswirkungen der Positionierung jedes einzelnen Leitgitters wurde genutzt, um durch eine einfache Optimierung zwei geometrische Konfigurationen aller Leitgitter zu entwickeln. Die eine Konfiguration führte zu geringen aerodynamischen Erregerkräften an den Laufschaufeln aller Stufen, während die andere Konfiguration eine gleichmäßig hohe instationäre Anregung zur Folge hatte. Die Unterschiede der instationären Erregerkräfte zwischen den Konfigurationen waren erheblich und über weite Bereiche der Kennlinie unabhängig vom Betriebspunkt, ohne das die Konfiguration der Leitgitter geändert wurde. Für eine umfassende Analyse der periodisch instationären, aerodynamischen Schaufelinteraktion wurden sowohl die Schaufeldruckverteilungen, als auch das Strömungsfeld in den axialen Schaufelzwischenräumen im Mittelschnitt der Beschaufelung für beide Clocking-Konfigurationen zeitgenau vermessen und vergleichend ausgewertet. Aus diesen Analysen konnte mithilfe der Wellenmechanik eine einfache analytische Beschreibung der instationären Interaktion der Potentialfelder der Beschaufelung entwickelt werden. Für eine einzelne Stufe wurde mit diesem Modell die experimentell bestimmte Phasendifferenz der Druckschwankungen auf Druck- und Saugseite auf sehr einfache Weise nachgewiesen. Damit liegt ein einfaches, analytisches Modell für die Beschreibung der komplexen Überlagerung der sich relativ zueinander bewegenden Druckfelder der Beschaufelung axialer Turbomaschinen vor, das für das physikalische Verständnis der instationären Schaufelinteraktion einen wertvollen Beitrag liefert.