Circulation control involves tangentially blowing air around a rounded trailing edge in order to augment the lift of a wing. The advantages of this technique over conventional mechanical controls are reduced maintenance and lower observability. Despite the technology first being proposed in the 1960s and well-studied since, circulation control is not in widespread use today. This is largely due to the high mass flow requirements. Increasing the jet velocity increases both the efficiency (in terms of mass flow) and effectiveness. However, as the jet velocity exceeds the speed of sound, shock structures form which cause the jet to separate. Recent developments in the field of fluidic thrust vectoring (FTV) have shown that an asymmetrical convergent-divergent nozzle capable of producing an irrotational vortex (IV) has the potential to prevent separation through eliminating stream-wise pressure gradients. In this study, the feasibility of preventing separation at arbitrarily high jet velocities through the use of asymmetrical nozzle geometries designed to maintain irrotational (and stream-wise pressure gradient free) flow is explored. Furthermore, the usefulness of an adaptive nozzle geometry for the purpose of extending circulation control device efficiency and effectiveness is defined. Through a series of experiments, the flow physics of supersonic curved wall jets is characterised across a range of nozzle geometries. IV and equivalent area ratio symmetrical convergent-divergent nozzles are compared across three slot height to radius ratios (H/R): H/R = 0.1, H/R = 0.15, H/R = 0.2. The conclusion of this study is that at low H/R (0.1 and 0.15), there is no significant difference in behaviour between IV and symmetrical nozzles, whilst at high H/R (0.2), the IV nozzles begin separating whilst correctly expanded due to the propagation of pressure upstream from the edge of the reaction surface via the boundary layer. Consequently, it is shown that symmetrical nozzles of equivalent mass flow at high H/R have a higher separation NPR compared to IV nozzles. Specifically, the elimination of favourable, in addition to adverse stream-wise pressure gradients contradicts the expected behaviour of IV nozzles. The separation NPR for nozzles tested in this study, in addition to past studies is subsequently plotted against the throat height to radius ratios (A*/R). This shows that in fact, no previous experiments have shown a higher separation NPR for IV nozzles compared to symmetrical nozzles of equivalent mass flow. The overall outcome is that neither fixed geometry IV, nor adaptive nozzles are justified to maintain attachment, or to improve efficiency. This is because fixed nozzle geometries designed for higher separation NPR do not show any performance deficit when operating at lower NPRs. However, the throat height could be varied to maximise effectiveness (at the expense of mass flow). The contributions to new knowledge made by this study are as follows: the development of a new method of combining shadowgraph and schlieren images to simplify and enhance visualisation of supersonic flows; the use of pressure sensitive paint (PSP) to study the structure of the supersonic curved wall jet before and after separation; the identification of a clear mechanism for the separation of supersonic curved wall jets, valid over a broad range of nozzle geometries (including a clarification of previously unexplained behaviour witnessed in prior studies); the explanation that reattachment hysteresis occurs due to the upstream movement of the point of local separation at full separation (specifically, this explains why certain geometries such as backward-facing steps prevent reattachment hysteresis).

Statistics show that unstable articulated vehicles pose a serious threat to the occupants driving them as well as the occupants of the vehicles around them. An articulated vehicle typically experiences three types of instability: snaking, jack-knifing and rollover. An articulated vehicle subjected to any of these instabilities can result in major accidents. It is also known that many individuals are unaware of how to properly tow or pack a loaded articulated vehicle. These individuals are, therefore, at a high risk of causing the vehicle system to become unstable. It can hence be confidently said that a method in which an articulated vehicle can stabilise itself is a worthy research question. The method that is implemented in this study is to create a control system, using Nonlinear Model Predictive Control (NMPC), that has the capability of stabilising an articulated vehicle by applying torque vectoring to the trailer. In order for this control system to be applied, a nonlinear articulated vehicle MSC ADAMS model was constructed. The NMPC controller works by using a nonlinear explicit model to predict the future states of the vehicle and then finding the optimal left and right braking forces of the trailer by minimising the cost function using least squares minimisation. The cost function includes the towing vehicle yaw rate, trailer yaw rate and hitch angle and is minimised by minimising the error between the desired vehicle states and the actual states. It was found that the NMPC is capable of not only preventing instability but also causes the vehicle system to behave as if the trailer is unloaded. This conclusion means that this type of control system can be used on all types of articulated vehicles and shall ensure the safety of not only the vehicle occupants but other road users as well. Unfortunately, due to the impact of the 2020 COVID-19 pandemic, the experimental validation of the model had to be delayed significantly. It is for this reason that the experimental validation for the controller could not be done. / Dissertation (MEng (Mechanical Engineering))--University of Pretoria, 2021. / SATC VDG UP / Mechanical and Aeronautical Engineering / MEng (Mechanical Engineering) / Unrestricted

This semester work focuses on the basic characteristics of the VDSl2 and G.fast technologies that allow to transfer data using old telephone lines. The theoretical part of the work describes the main parameters of all currently known profiles for VDSL and G.fast. There is also a description of DMT modulation, used in both types of DSL connections. Moreover, the theoretical part presents a vectoring technique that helps to increase the data transfer rate using a twisted pair. The work also provides methods for testing networks using the recommendations of RFC 2455, ITU-T Y.1564 and RFC6349. The practical part of this thesis contains all conducted tests and measuring, which were described in detail. The results od these tests were presented in the format of graphs and tables.

An examination of parameters affecting the control of a jet vectoring technique used in the Coanda-assisted Spray Manipulation (CSM) is presented. The CSM makes use of an enhanced Coanda effect on axisymmetric geometries through the interaction of a high volume primary jet flowing through the center of a collar and a secondary high-momentum jet parallel to the first and adjacent to the convex collar. The control jet attaches to the convex wall and vectors according to known Coanda effect principles, entraining and vectoring the primary jet, resulting in controllable r-θ directional spraying. Several control slots (both annular and unique sizes) and expansion radii were tested over a range of momentum flux ratios to determine the effects of these variables on the vectored jet angle and profile. Two- and three-component Particle Image Velocimetry (PIV) was used to determine the vectoring angle and the profile of the primary jet in each experiment. The experiments show that the control slot and expansion radius, along with the momentum ratios of the two jets, predominantly affected the vectoring angle and profile of the primary jet. The Reynolds number range for the primary jet at the exit plane was between 20,000 and 80,000. The flow was in the incompressible Mach number range (Mach< 0.3).

This thesis is concerned with electronic stability of an all-wheel drive electric vehicle with independent motors mounted in each wheel. The additional controllability and speed permitted using independent motors can be exploited to improve the handling and stability of electric vehicles. In this thesis, these improvements arise from employing a direct yaw moment control (DYC) system that seeks to adapt the understeer gradient of the vehicle and achieve neutral steer by employing a supervisory controller and simultaneously tracking an ideal yaw rate and ideal sideslip angle. DYC enhances vehicle stability by generating a corrective yaw moment realized by a torque vectoring controller which generates an optimal torque distribution among the four wheels. The torque allocation at each instant is computed by finding a solution to an optimization problem using gradient descent, a well-known algorithm that seeks the minimum cost employing the gradient of the cost function. A cost function seeking to minimize excessive wheel slip is proposed as the basis of the optimization problem, while the constraints come from the physical limitations of the motors and friction limits between the tires and road. The DYC system requires information about the tire forces in real-time, so this study presents a framework for estimating the tire force in all three coordinate directions. The sideslip angle is also a crucial quantity that must be measured or estimated but is outside the scope of this study. A comparative analysis of three different formulations of sliding mode control used for computation of the corrective yaw moment and an evaluation of how successfully they achieve neutral steer is presented. IPG Automotive’s CarMaker software, a high-fidelity vehicle simulator, was used as the plant model. A custom electric powertrain model was developed to enable any CarMaker vehicle to be reconfigured for independent control of the motors. This custom powertrain, called TVC_OpenXWD uses the torque/speed map of a Protean Pd18 implemented with lookup tables for each of the four motors. The TVC_OpenXWD powertrain model and controller were designed in MATLAB and Simulink and exported as C code to run them as plug-ins in CarMaker. Simulations of some common maneuvers, including the J-turn, sinusoidal steer, skid pad, and mu-split, indicate that employing DYC can achieve neutral steer. Additionally, it simultaneously tracks the ideal yaw rate and sideslip angle, while maximizing the traction on each tire[CB1] . The control system performance is evaluated based on its ability to achieve neutral steer by means of tracking the reference yaw rate, stabilizing the vehicle by means of reducing the sideslip angle, and to reduce chattering. A comparative analysis of sliding mode control employing a conventional switching function (CSMC), modified switching function (MSMC), and PID control (HSMC) demonstrates that the MSMC outperforms the other two methods in addition to the open loop system.

Moderne Kraftfahrzeuge werden mit einer Vielzahl von Fahrerassistenzsystemen ausgestattet um die Sicherheit, die Traktion, die Energieeffzienz, die Agilität und den Komfort noch weiter zu verbessern. Diese Ziele können zu einem Großteil mit einer aktiven Drehmomentverteilung, auch Torque Vectoring genannt, erreicht werden. Dafür sind jedoch Getriebesysteme erforderlich, welche unabhängig vom Fahrzustand und vom Antriebsmoment eine nahezu beliebige Drehmomentverteilung ermöglichen. In der vorliegenden Arbeit werden zunächst Grundlagen zu Getriebesystemen, insbesondere zu Planetengetrieben, und zur Fahrzeugdynamik erläutert. Anschließend wird der Stand der Technik anhand einer Systematik zur Einteilung von aktiven Differenzialgetrieben dargelegt sowie einige Vor- und Nachteile aufgezeigt. Das folgende Kapitel stellt ein Verfahren zur Ermittlung der mechanischen Belastung des aktiven Differenzialgetriebes für beliebige Fahrzeuge und Strecken vor. Damit erfolgt eine Bewertung der bisher bekannten Systeme hinsichtlich Gesamtwirkungsgrad, konstruktiver Aufwand und regelungstechnische Eigenschaften. Im Anschluss wird ein Verfahren zur rechnergestützten Synthese neuer Getriebesysteme beschrieben. Abschließend werden die positiven Auswirkungen der aktiven Drehmomentverteilung auf die Fahrdynamik herausgestellt. Das Ergebnis der Arbeit zeigt drei neue Getriebestrukturen, welche anhand der deffinierten Vergleichskriterien besser sind als alle bekannten Systeme. / Actual passenger cars are equipped with a lot of driver assistant systems to increase safety, traction, efficiency, agility and comfort. These aims can be achieved by a controlled transmission of the engine torque to each driven wheel (active torque distribution, Torque Vectoring). Therefore special gear systems are necessary. In this document firstly the basics on gear systems (planetary gears) and vehicle dynamics are explained. Furthermore the state of the art is shown based on a classification of active differentials and the advantages and disadvantages are envinced. The next chapter describes a method for determining the mechanic load of the active differential for any car and road track. This is used for an evaluation of every differential gear system in view of efficiency, mechanic effort and control properties. The result reveals significant differences between the gear structures. Subsequent a method for a computer synthesis of new gear systems is developped and applied to the demands of a front driven vehicle application. The last chapter points out the positive effects of an active torque distribution on the driving dynamics. As a result of this work three new gear structures are shown which are much better than all existing gear systems in terms of the evaluation properties.

Moderne Kraftfahrzeuge werden mit einer Vielzahl von Fahrerassistenzsystemen ausgestattet um die Sicherheit, die Traktion, die Energieeffzienz, die Agilität und den Komfort noch weiter zu verbessern. Diese Ziele können zu einem Großteil mit einer aktiven Drehmomentverteilung, auch Torque Vectoring genannt, erreicht werden. Dafür sind jedoch Getriebesysteme erforderlich, welche unabhängig vom Fahrzustand und vom Antriebsmoment eine nahezu beliebige Drehmomentverteilung ermöglichen. In der vorliegenden Arbeit werden zunächst Grundlagen zu Getriebesystemen, insbesondere zu Planetengetrieben, und zur Fahrzeugdynamik erläutert. Anschließend wird der Stand der Technik anhand einer Systematik zur Einteilung von aktiven Differenzialgetrieben dargelegt sowie einige Vor- und Nachteile aufgezeigt. Das folgende Kapitel stellt ein Verfahren zur Ermittlung der mechanischen Belastung des aktiven Differenzialgetriebes für beliebige Fahrzeuge und Strecken vor. Damit erfolgt eine Bewertung der bisher bekannten Systeme hinsichtlich Gesamtwirkungsgrad, konstruktiver Aufwand und regelungstechnische Eigenschaften. Im Anschluss wird ein Verfahren zur rechnergestützten Synthese neuer Getriebesysteme beschrieben. Abschließend werden die positiven Auswirkungen der aktiven Drehmomentverteilung auf die Fahrdynamik herausgestellt. Das Ergebnis der Arbeit zeigt drei neue Getriebestrukturen, welche anhand der deffinierten Vergleichskriterien besser sind als alle bekannten Systeme.:1 Einleitung 2 Grundlagen 2.1 Getriebesysteme 2.2 Fahrdynamik 3 Stand der Technik 3.1 Getriebesysteme 3.2 Fahrdynamikregelung 4 Analyse bekannter Getriebesysteme 4.1 Zeitlicher Verlauf fahrdynamischer Größen 4.2 Systematische Analyse von Planetengetrieben 4.3 Deffinition der Vergleichskriterien 4.4 Differenziallose Systeme 4.5 Differenzialsysteme 4.6 Elektromotorische Systeme 4.7 Sonderbauformen 4.8 Vergleich bekannter Systeme 5 Synthese neuer Getriebestrukturen 5.1 Anforderungen an aktive Differenzialgetriebe 5.2 Manuelle Struktursynthese 5.3 Rechnergestützte Struktursynthese 5.4 Ergebnisse der Struktursynthese 6 Auswirkung von aktiver Drehmomentverteilung auf die Fahrdynamik 6.1 Komplexe Fahrdynamiksimulation 6.2 Steigerung der Traktion 6.3 Steigerung der Agilität 6.4 Steigerung der Fahrstabilität 6.5 Steigerung des Fahrkomforts 6.6 Verringerung des Kraftstoffverbrauches Zusammenfassung und Ausblick Literaturverzeichnis / Actual passenger cars are equipped with a lot of driver assistant systems to increase safety, traction, efficiency, agility and comfort. These aims can be achieved by a controlled transmission of the engine torque to each driven wheel (active torque distribution, Torque Vectoring). Therefore special gear systems are necessary. In this document firstly the basics on gear systems (planetary gears) and vehicle dynamics are explained. Furthermore the state of the art is shown based on a classification of active differentials and the advantages and disadvantages are envinced. The next chapter describes a method for determining the mechanic load of the active differential for any car and road track. This is used for an evaluation of every differential gear system in view of efficiency, mechanic effort and control properties. The result reveals significant differences between the gear structures. Subsequent a method for a computer synthesis of new gear systems is developped and applied to the demands of a front driven vehicle application. The last chapter points out the positive effects of an active torque distribution on the driving dynamics. As a result of this work three new gear structures are shown which are much better than all existing gear systems in terms of the evaluation properties.:1 Einleitung 2 Grundlagen 2.1 Getriebesysteme 2.2 Fahrdynamik 3 Stand der Technik 3.1 Getriebesysteme 3.2 Fahrdynamikregelung 4 Analyse bekannter Getriebesysteme 4.1 Zeitlicher Verlauf fahrdynamischer Größen 4.2 Systematische Analyse von Planetengetrieben 4.3 Deffinition der Vergleichskriterien 4.4 Differenziallose Systeme 4.5 Differenzialsysteme 4.6 Elektromotorische Systeme 4.7 Sonderbauformen 4.8 Vergleich bekannter Systeme 5 Synthese neuer Getriebestrukturen 5.1 Anforderungen an aktive Differenzialgetriebe 5.2 Manuelle Struktursynthese 5.3 Rechnergestützte Struktursynthese 5.4 Ergebnisse der Struktursynthese 6 Auswirkung von aktiver Drehmomentverteilung auf die Fahrdynamik 6.1 Komplexe Fahrdynamiksimulation 6.2 Steigerung der Traktion 6.3 Steigerung der Agilität 6.4 Steigerung der Fahrstabilität 6.5 Steigerung des Fahrkomforts 6.6 Verringerung des Kraftstoffverbrauches Zusammenfassung und Ausblick Literaturverzeichnis

Recently, mostly due to global warming concerns and high oil prices, electric vehicles have attracted a great deal of interest as an elegant solution to environmental and energy problems. In addition to the fact that electric vehicles have no tailpipe emissions and are more efficient than internal combustion engine vehicles, they represent more versatile platforms on which to apply advanced motion control techniques, since motor torque and speed can be generated and controlled quickly and precisely. The chassis control systems developed today are distinguished by the way the individual subsystems work in order to provide vehicle stability and control. However, the optimum driving dynamics can only be achieved when the tire forces on all wheels and in all three directions can be influenced and controlled precisely. This level of control requires that the vehicle is equipped with various chassis control systems that are integrated and networked together. Drive-by-wire electric vehicles with in-wheel motors provide the ideal platform for developing the required control system in such a situation. The focus of this thesis is to develop effective control strategies to improve driving dynamics and safety based on the philosophy of individually monitoring and controlling the tire forces on each wheel. A two-passenger electric all-wheel-drive urban vehicle (AUTO21EV) with four direct-drive in-wheel motors and an active steering system is designed and developed in this work. Based on this platform, an advanced fuzzy slip control system, a genetic fuzzy yaw moment controller, an advanced torque vectoring controller, and a genetic fuzzy active steering controller are developed, and the performance and effectiveness of each is evaluated using some standard test maneuvers. Finally, these control systems are integrated with each other by taking advantage of the strengths of each chassis control system and by distributing the required control effort between the in-wheel motors and the active steering system. The performance and effectiveness of the integrated control approach is evaluated and compared to the individual stability control systems, again based on some predefined standard test maneuvers.

Recently, mostly due to global warming concerns and high oil prices, electric vehicles have attracted a great deal of interest as an elegant solution to environmental and energy problems. In addition to the fact that electric vehicles have no tailpipe emissions and are more efficient than internal combustion engine vehicles, they represent more versatile platforms on which to apply advanced motion control techniques, since motor torque and speed can be generated and controlled quickly and precisely. The chassis control systems developed today are distinguished by the way the individual subsystems work in order to provide vehicle stability and control. However, the optimum driving dynamics can only be achieved when the tire forces on all wheels and in all three directions can be influenced and controlled precisely. This level of control requires that the vehicle is equipped with various chassis control systems that are integrated and networked together. Drive-by-wire electric vehicles with in-wheel motors provide the ideal platform for developing the required control system in such a situation. The focus of this thesis is to develop effective control strategies to improve driving dynamics and safety based on the philosophy of individually monitoring and controlling the tire forces on each wheel. A two-passenger electric all-wheel-drive urban vehicle (AUTO21EV) with four direct-drive in-wheel motors and an active steering system is designed and developed in this work. Based on this platform, an advanced fuzzy slip control system, a genetic fuzzy yaw moment controller, an advanced torque vectoring controller, and a genetic fuzzy active steering controller are developed, and the performance and effectiveness of each is evaluated using some standard test maneuvers. Finally, these control systems are integrated with each other by taking advantage of the strengths of each chassis control system and by distributing the required control effort between the in-wheel motors and the active steering system. The performance and effectiveness of the integrated control approach is evaluated and compared to the individual stability control systems, again based on some predefined standard test maneuvers.

This work deals with the design of right-and-left torque vectoring systems used in heavy commercial vehicle powertrains. It is a new device for a commonly used vehicle differential. This study recommends design, kinematic and load parameters. Also the overall effect of the mechanism on vehicle dynamics and design of the experimental vehicle chassis is described. The study further describes how the mechatronic system works with necessary control systems. Purpose of this thesis is to summarize available information on a right-and-left torque vectoring and possible practical applications for further development of torque vectoring systems.