O presente trabalho visa o estudo e avaliação de diversos modelos de falha através de ensaios experimentais e análises numéricas. A caracterização do material foi feita por meio de ensaios de tração de espécimes com e sem entalhe e de cisalhamento, para prover dados em uma ampla faixa de triaxialidade. A calibração dos parâmetros necessários para cada modelo de falha ocorreu através da obtenção das componentes de tensões e de deformações na região de ruptura, obtidas por meio de análises numéricas destes ensaios. O critério da máxima deformação plástica equivalente, modelo de dano de Johnson-Cook e critério da máxima tensão cisalhante foram aplicados em um caso de impacto em pára-choque. Diversos ensaios de impacto foram realizados até a que se atingisse a ruptura satisfatória do componente. Os ensaios foram modelados em elementos finitos, através do programa comercial LS-Dyna®, sendo que os modelos de falha calibrados foram aplicados para o ensaio onde se ocorreu ruptura. Houve boa concordância entre os resultados obtidos numericamente e experimentalmente, respeitadas as observações realizadas acerca da especificidade deste caso de impacto em baixa velocidade. / The aim of the present work is an assessment of several fracture models through experiments and numerical simulations. Tensile tests with notched and unnotched specimens were carried out to provide the material characterization in a wide range of stress triaxiality. The calibration of the parameters required by the fracture models was enabled by the parallel numerical simulation of the tensile tests, providing information on the stress and strain components at the failure locus. The constant equivalent strain criterion, the Johnson-Cook failure model and the maximum shear stress failure criterion were applied in a bumper beam impact case study. Several low speed impact tests were carried out in order to result in the components rupture. Numerical simulation of the experiments was performed using commercial finite element code LS-Dyna®. Good correlation of experiments and numerical simulations was achieved when considering this particular low speed case study.

Cette thèse propose de prédire le bruit émis par des ventilateurs à basse vitesse et sa diffraction par des obstacles liés aux contraintes d’installation dans les applications industrielles. Les composantes tonale et à large bande du bruit sont étudiées. Les méthodes existant dans la littérature considèrent des hypothèses et des simplifications afin de traiter le problème du bruit des ventilateurs de façon analytique, comme par exemple l’approximation de champ lointain. Tout d’abord, l’hypothèse de champ lointain dans la formulation du bruit tonal est relaxée. En utilisant des sources artificielles, une comparaison entre deux expressions analytiques et une simulation numérique est effectuée pour la validation en champ libre. Ensuite, la diffraction du bruit tonal est étudiée par des techniques numériques et analytiques. Le champ acoustique d’un rotor fonctionnant dans un conduit fini est d’abord pris comme exemple en combinant les formulations analytiques avec la méthode d’éléments de frontière (BEM). Etant donné que cette dernière serait trop coûteuse en temps de calcul pour des applications haute fréquence, des techniques analytiques pour le problème de diffraction sont également présentées. La réflexion et la diffraction des ondes sonores par une plaque infinie sont d’abord considérées en remplaçant la plaque par une source image. Ensuite, une solution analytique exacte pour la diffraction du bruit tonal par un coin rigide est formulée. Un autre point abordé dans cette thèse est la prévision du bruit à large bande produit par un ventilateur axial à basse vitesse évoluant dans un écoulement turbulent. La théorie d’Amiet pour le bruit d’interaction de turbulence sur un profil fixe est considérée. Nous en proposons dans cette thèse une extension permettant de prédire le bruit du profil dans son champ proche géométrique l’aide d’outils semi-analytiques. La nouvelle formulation est comparée à solution classique d’Amiet et à une solution de référence obtenue par intégration numérique sans hypothèse de champ lointain géométrique. Des expériences sont également menées dans une soufflerie anéchoide où la turbulence est générée en amont du profil par une grille. Une autre hypothèse du modèle d’Amiet concerne l’écoulement uniforme arrivant sur le profil. Cette hypothèse n’est pas vérifiée dans la plupart des applications industrielles. Différentes méthodes existent dans la littérature pour traiter ce problème. Nous proposons une nouvelle approche pour prendre en compte des conditions d’écoulement variables en envergure. En intégrant toutes ces améliorations, la réponse acoustique large bande d’un profil fixe placé dans un jet turbulent et d’un ventilateur axial à basse vitesse placé dans un écoulement turbulent est étudiée et validée par comparaison avec l’expérience. Dans une dernière partie, la diffraction des ondes acoustiques générées par le profil et le ventilateur par des obstacles est déterminée numériquement et analytiquement. Puisque la méthode BEM n’est pas prévue pour résoudre directement le champ d’une source aléatoire, une approche innovante obtenue par la reformulation de la méthode déterministe de BEM est utilisée. Le modèle final est comparé aux solutions numériques, analytiques et expérimentales pour la validation. / This thesis proposes to predict the sound emitted from low-speed fans and its scattered-field by installation effects related to industrial applications. Both tonal and broadband components of fan noise are investigated. Methods existing in the literature contain assumptions and simplifications in order to deal with fan noise problems in analytical manner, such as consideration of an observer located in the far-field of the source. Firstly, the effect of far-field assumption in the tonal fan noise formulation is addressed. Using artificial blade sources, a comparison between two closed-form analytical solutions and a numerical technique is performed for validation in free-field. Secondly, the scattered field of the tonal fan noise is investigated using numerical and analytical techniques. The acoustic field of a rotor operating in a finite duct is first investigated combining the closed-form analytical formulations with the Boundary Element Method (BEM). Since BEM would be computationally demanding for high frequency applications, analytical scattering techniques are also introduced. Reflection and scattering of sound waves by a large plane are first addressed replacing the plane with an image source. Secondly, an exact analytical solution considering scattering of the tonal fan noise by a rigid corner is derived. Another point addressed in this thesis is the prediction of the broadband noise generated by a low-speed axial fan operating in turbulent stream. Amiet’s theory of turbulence-interaction noise for a stationary air foil is considered. One of the key points proposed in this thesis is an extension of Amiet’s method, allowing prediction of the acoustic field of the airfoil in its geometrical near-field in a semi-analytical perspective. The extended formulation is compared with Amiet’s classical solution and a reference solution obtained with numerical integration involving no geometrical far-field assumption. Experiments are also performed in anechoic chamber using an isolated airfoil located in grid generated turbulence. Another assumption made in Amiet’s theory is the consideration of uniform flow impinging onto the airfoil. However this assumption is not valid for most industrial applications. Different methods exist in literature to deal with this problem. A new approach is proposed in order to take the span wise varying flow conditions into account. Including all the improvements, the broadband acoustic responses of a stationary airfoil located in the developing region of a jet and of a low-speed axial fan operating in a turbulent stream are investigated and validated against measurements. Finally, scattering of the sound generated by the considered airfoil and fan by benchmark obstacles is addressed numerically and analytically. Since BEM is not capable to handle statistical source fields directly, an innovative approach obtained by re-formulating the deterministic BEM method is employed. The final model is compared to the numerical, analytical and experimental solutions for validation purposes.

The diploma thesis deals with basic test procedures conducted by companies Euro NCAP and RCAR. It focuses mainly on insurance impact and describes the creation of a model, simulation and crash on barrier. Moreover, it explores the influence of change of yield strength, thickness and hardening of material of energy-absorber on simulation of insurance impact, especially the amount of absorbed energy by energy-absorber.

A permanent magnet synchronous motor is a type of motor that is used in several different application areas, not least in an autonomous robots where it is the motor that drives the wheels. Today, many actors choose simulation as a tool to save money and time when product tests are performed. This thesis covers both the process of modeling a permanent magnet synchronous motor and regulating it at low speeds, in a simulation environment. As previously mentioned, the motor is a permanent magnet synchronous motor and is a direct-driven outrunner, which means that the motor and the wheel are combined and that the rotor is spinning outside the stator. On current robots in production, there is a gear ratio between the motor and wheels to be able to regulate the motor at higher speeds and thus generate a torque. The gearing contributes to losses and is an extra cost, so the examination of a direct-drive motor is interesting. The direct-drive motor has a lower working speed and is therefore by some reasons more difficult to regulate when applying torque load to the motor. The motor is equipped with current sensors and a position sensor, which has a certain resolution. The position sensor is speed-dependent in the sense that at lower RPMs fewer measurements are obtained, which is a problem when regulating the motor. The thesis examines two different control strategies, one of which is a more classic PI control that is often used on the market in various systems and the other is model predictive control (MPC). The latter is an online optimization where, with the help of information about the system, an optimal input signal is calculated and applied. Two different non-linear Kalman filters are also examined, which are implemented with the two different control strategies, to estimate the speed with the help of the measurements from current and the position sensor. The conclusion is an ideal motor model that mimics the physical motor. MPC is able to regulate the motor between 0-50 RPM, both with and without applied torque and even better with speed estimation from a Kalman filter. The PI controller is not able to regulate the motor at 2 RPM but for speeds at 10 RPM and greater, however with over-/undershoot after an acceleration.

The use of infrared thermography for boundary layer detection was evaluated for use in the Cal Poly Low Speed Wind Tunnel (LSWT) and recommendations for the successful use of this technique were developed. In cooperation with Joby Aviation, an infinite wing model was designed, manufactured and tested for use in the LSWT. The wing was designed around a custom airfoil profile specific for this project, where the nearly-flat pressure gradient at a zero pitch angle would delay the chordwise onset of boundary layer transition. Steady-state, RANS numerical simulations predicted the onset of transition to occur at 0.75 x/c for the design Reynolds Number condition of 6.25x105. The wing was manufactured from 3D printed aluminum, with a wall thickness of 0.125 inches and a chord length of 13.78 inches. Two central rows of static pressure taps were used, each with 12 functional chordwise locations. The taps were able to generate strong correlation to the numerically predicted pressure coefficient distribution. The use of an infrared camera visualized and confirmed the presence of boundary layer transition at the chordline location anticipated by the early simulations. To do so, the model was pre-heated such that the differential cooling properties of laminar and turbulent flow would generate a clear temperature gradient on the surface correlating to boundary layer transition. Adjustment of the model’s pitch angle demonstrated a change in the onset location of boundary layer transition during the infrared testing. The change of onset location was seen to move forward along the chordline as the aerodynamic angle of attack was increased. Testing with a Preston Tube system allowed for the interpolation of local skin friction coefficient values at each static tap location. Application of both laminar and turbulent empirical assumptions, when compared to numerical expectations, allowed for the qualitative assessment of boundary layer transition onset. Overall, the wing model developed for this research proved capable of producing quality and repetitive results for the experimental goals it was designed to meet. The model will next be used in continued tests which will further explore the use of infrared thermography.

In axial compressors with a relatively large blade tip clearance, an unsteady phenomenon denoted as rotating instability (RI) can be detected when the compressor is throttled to the operating points near the stability limit. In the frequency domain, RIs are shown as a hump lower than the blade passing frequency. This indicates an increase in noise level and might cause blade vibration and other undesirable structural issues. In this thesis, a comprehensive study on RIs is performed based on an axial compressor rotor row of the Low Speed Research Compressor at Technische Universität Dresden. Three blade tip clearances are investigated, and a groove casing treatment is mounted over the shroud for flow control. Methods of numerical modeling are evaluated, and zonal large eddy simulation is selected as the numerical model. By analyzing the flow properties and applying the dynamic mode decomposition, the coherent flow structure corresponding to the dominant frequency of RIs is extracted and visualized as the waves located in the blade tip region. The criteria for the appearance of RIs in the investigated research object are concluded.

When an aircraft is aerodynamically or structurally damaged in battle, it may not able to complete the mission and the damage may cause its loss. The subject of aircraft battle survivability is one of critical concern to many disciplines, whether military or civil. This thesis considered and focused on Computational Fluid Dynamics [CFD] predictions and experimental investigations into the effects of simulated battle damage on the low-speed aerodynamics of a fmite aspect ratio wing. Results showed that in two-dimensional [2d] and three-dimensional [3D] CFD simulations, Fluent's® models work reasonably well in predicting jets flow structures, pressure distributions, and pressure-coefficient Cp's contours but not for aerodynamic coefficients. The consequences were therefore that CFD prediction was poor on aerodynamic-coefficients increments. The prediction of Cp's achieved good agreement upstream and near the damage hole, but showed poor agreement at downstream of the hole. For the flow structure visualisation, at both weak and strong jet incidences, the solver always predicted pressure-distribution-coefficient lower at upstream and higher at downstream. The results showed relatively good agreement for the case of transitional and strong jet incidences but slightly poor for weak jet incidences. From the experimental results of Finite Wing, the increments for Aspect-ratio, AR6, AR8 and ARIO showed that as damage moves out towards the tip, aerodynamic-coefficients increments i.e. lift-loss and drag-rise decreased, and pitching-moment-coefficient increment indicated a more positive value at all incidence ranges and at all aspect ratios. Increasing the incidence resulted in greater magnitudes of lift-loss and drag-rise for all damage locations and aspect ratios. At the weak jet incidence 4° for AR8 and in all of the three damage locations, the main characteristics of the weak-jet were illustrated clearly. The increments were relatively small. Whilst at 8°, the flow structure was characterised as transitional to stronger-jet. In Finite Wing tests and for all damage locations, there was always a flow structure asymmetry. This was believed to be due to gravity, surface imperfection, and or genuine feature. An 'early strong jet' that indicated in Finite Wing-AR8 at 'transitional' incidence of 8°, also indicated in twodimensional results but at the weak-jet incidence of 4°. For the application of 2d data to AR6, AR8, and ARIO, an assessment of 2d force results led to the analysis that the tests in the AAE's Low Turbulence Tunnel for 2d were under-predicting the damage effects at low incidence, and over-predicting at high incidences. This suggested therefore that Irwin's 2d results could not be used immediately to predict three-dimensional.

Turbulent mixed convection is a complicated flow where the buoyancy and shear forces compete with each other in affecting the flow dynamics. This thesis deals with the near wall dynamics in a turbulent mixed convection flow over an isothermal horizontal heated plate. We distinguish between two types of mixed convection ; low-speed mixed convection (LSM) and high-speed mixed convection (HSM). In LSM the entire boundary layer, including the near-wall region, is dominated by buoyancy; in HSM the near-wall region, is dominated by shear and the outer region by buoyancy. We show that the value of the parameter (* = ^ determines whether the flow is LSM or HSM. Here yr is the friction length scale and L is the Monin-Obukhov length scale. In the present thesis we proposed a model for the near-wall dynamics in LSM. We assume the coherent structure near-wall for low-speed mixed convection to be streamwise aligned periodic array of laminar plumes and give a 2d model for the near wall dynamics, Here the equation to solve for the streamwise velocity is linear with the vertical and spanwise velocities given by the free convection model of Theerthan and Arakeri [1]. We determine the profiles of streamwise velocity, Reynolds shear stress and RMS of the fluctuations of the three components of velocity. From the model we obtain the scaling for wall shear stress rw as rw oc (UooAT*), where Uoo is the free-stream velocity and AT is the temperature difference between the free-stream and the horizontal surface.A similar scaling for rw was obtained in the experiments of Ingersoll [5] and by Narasimha et al [11] in the atmospheric boundary layer under low wind speed conditions. We also derive a formula for boundary layer thickness 5(x) which predicts the boundary layer growth for the combination free-stream velocity Uoo and AT in the low-speed mixed convection regime.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: In this thesis, the investigation into the optimization of low speed communication protocols for narrow band networks will be presented. The main focus will be on analysing commonly used low speed communication protocols and investigate an alternative to these protocols to provide an optimized low speed narrow band network that provides better performance at high and low channel utilization. A study of existing low speed communication networks within the field of water supply has been used to identify the most appropriate protocols to be included in the analysis. The analysis of each protocol discussed includes the development of a simulation and theoretical model, with parameters based on those obtained from implemented communication networks focusing on the parameters used within the Namib water supply scheme of NamWater in Namibia. Of the currently implemented contention protocols, the non-persistent Carrier Sense Multiple Access (CSMA) protocol is implemented the most. Current models used for modelling these protocols make use of various assumptions. These models have been expanded to provide a more accurate representation of the non-persistent CSMA model. The Round Robin Polling (RRP) protocol is another well known protocol used within the telemetry industry and has also been modelled as an alternative to the non-persistent CSMA model. The Adaptive Tree Walk (ATW) protocol has been identified as the limited contention protocol to be modelled as a possible alternative to the conventional methods used. A new model has been developed for modelling this protocol by making use of the same strategies and tools used in the modelling of the non-persistent CSMA and RRP protocols. The Simulation modelling has been developed by making use of DESMO-J, an Object Orientated Simulation API based in Java, developed by the Faculty of Informatics at the University of Hamburg. DESMO-J has been chosen as an alternative to the more traditional simulation languages due to its complete documentation, support structures, ease of use and flexibility. All theoretical models have been implemented in Matlab. / AFRIKAANSE OPSOMMING: In hierdie tesis sal die ondersoek na die optimering van laespoed protokolle vir kommunikasie oor nouband netwerke voorgelê word. Die hoof fokus is op die analise van algemene laespoed kommunikasie protokolle en die ondersoek van alternatiewe wat ’n meer optimale laespoed nouband netwerk sal lewer deur beter werkverigting by lae en hoë kanaalverkeer. ’n Studie van praktiese laespoed nouband netwerke in die veld van waterverspreiding word gebruik om die mees algemene protokolle te identifiseer wat in die analise ingesluit moet word. Die analise van die protokolle sluit in teoretiese en simulasie modelle, met parameters soos geidentifiseer uit die studie van ‘n praktiese netwerk, naamlik die Namib waterverspreidingskema van NamWater in Namibië. Die ’Non-persistent Carrier Sense Multiple Access’ en ’Round Robin Polling’ protokolle is geidentifiseer as dié wat meeste geimplementeer word. Die werkverigting van die protokolle is geanaliseer deur gebruik te maak van teoretiese en simulasie modeleringstegnieke. Huidige modelle van die CSMA protokol is gebaseer op sekere aannames. Hierdie aannames word aangepas en verbeter vir implementering van die teoretiese model. Die model word ook verder uitgebrei om beter resultate te lewer oor ’n groter parameterstel. Die ’Adaptive Tree Walk’ protokol is geidentifiseer as ’n moontlike optimale protokol en word gemodeleer en vergelyk teen die CSMA en RRP protokolle se werkverigting. Die simulasiemodelle is ontwikkel deur gebruik te maak van die DESMO-J sagteware, soos ontwikkel as ’n Java program-koppelvlak deur die Universiteit van Hamburg se Fakulteit van Informatika. DESMO-J is gekies as ’n alternatief vir die meer tradisionele simuleringstale omrede goeie dokumentasie, maklike gebruik en buigbaarheid. Alle teoretiese modelering is uitgevoer in Matlab.

Pracovní podmínky atomizérů v reálných operacích v průmyslu a zemědělství se liší od podmínek laboratorních, ve kterých jsou atomizéry testovány. Částečné přiblížení k realističtějším podmínkám nám může poskytnout použití větrného tunelu. Větrný tunel se používá k simulaci okolního proudění. Studium spreje ve větrném tunelu nám poskytne realističtější představu o chování spreje. Tato diplomová práce se zabývá návrhem malého, nízko rychlostního větrného tunelu pro experimenty s tlakovými vířivými tryskami s obtokem v příčném a podélném proudění. Existuje mnoho typů větrných tunelů, ale jako nejvhodnější typ byl zvolen otevřený, výtlačný větrný tunel s uzavřenou testovací sekcí. Výhodou jsou jeho kompaktní rozměry, ochrana částí tunelu před kapičkami spreje a poměrně jednoduchý návrh. Konstrukce větrného tunelu se skládá z několika částí, každá část je zkonstruována tak, aby bylo dosaženo co nejlepší kvality proudu v testovací sekci. Sprej je zkoumán pomocí optických metod Fázové Dopplerovské anemometrie (PDA), Laserové Dopplerovské anemometrie (LDA), Integrální laserová anemometrie (PIV) a pomocí vysokorychlostního záznamu. Tyto optické metody kladou speciální požadavky na konstrukci tunelu, především na konstrukci testovací sekce, která musí umožňovat optický přístup ke spreji a musí být pro tyto měřící techniky uzpůsobena. Rychlost v testovací sekci se pohybuje v rozmezí 0 až 40 m/s s intenzitou turbulence pod 0,7 %. V závěru práce je ukázka vizualizace spreje, v příčném proudění, pomocí vysokorychlostní kamery. Okolní proudění mění rozpadovou vzdálenost spreje, úhel kužele spreje i jeho tvar. Dochází k vymývání menších kapek, které jsou unášeny okolním proudem.