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This thesis presents the results of a study into the use of H^ꝏ-optimization for the design of feedback control laws for improving the handling qualities of a Lynx helicopter. An important improvement to the H^ꝏ-optimization procedure is the reduction in the number of iterative steps in the γ-iteration before convergence to the optimal γ. Some new algorithms are derived which significantly reduce the computation time for the γ-iteration. Both 2-block and 4-block cases are considered. Control laws are designed for precise control of pitch and roll attitude, yaw rate and heave velocity. Analysis of the raw helicopter showed the need for a stability augmentation system as the dynamic characteristics of the unaugmented helicopter do not comply with military helicopter handling qualities requirements. Results from current research on helicopter handling qualities were used as guidelines in order to define the required dynamic characteristics. A six-degree of freedom nonlinear simulation was used to analyse the helicopter dynamic time histories. A possible solution to the problem of incorporating helicopter handling qualities in the design of robust controllers is to use a two-degree of freedom controller structure. This is illustrated using both H₂ and H^ꝏ-optimization. A piloted simulation study to assess the effectiveness of advanced control laws was initiated at RAE, Bedford. The trials were carried out in the single seat cockpit flight simulator, at the Flight Research Division and represent the first ever real-time piloted simulation using a H^ꝏ-controller.

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During the design of an aircraft it becomes necessary to predict the aircraft handling qualities. Previously, this has been done through the use of pilot opinion ratings of similar vehicles. However, it is desirable to develop more objective means of predicting handling qualities which also do not require the expensive flight testing or simulation necessary to obtain pilot ratings directly. An analysis of the closed-loop pilot-airframe system is performed, utilizing the linear human-pilot transfer function in conjunction with conventional servoanalysis techniques. Boundaries are developed on aircraft frequency and damping ratio for "good" longitudinal short-period control. The lateral phugoid mode is also investigated and the conclusion reached is that this mode cannot be controlled in a manner resulting in "good" pilot ratings. Comparison of the results obtained for the longitudinal short-period mode with experimental data indicates that the analysis is valid. Experimental data is lacking for comparison in the case of the lateral phugoid mode. / M.S.

The aim of the present project was to quantify and compare differences in impact performance and damping effectiveness among various off-road bicycle suspension systems. Two experiments were conducted to compare suspensions. Fork impact performance was tested by measuring peak antero-posterior braking forces and impulses during impact with bumps of 6- and 10-cm height for five mountain bike suspension systems. These results were compared to a rigid fork condition. Comparisons among suspension systems showed small but significant differences in performance. While only marginal differences in peak force were found for the suspension conditions, more substantial differences in braking impulse were observed. Air-Oil design forks had the lowest braking impulse for the range of speeds and impact characteristics of this experiment. In another setting, an analysis of acceleration signals over a range of frequencies on two surface conditions (gravel and trail) was conducted to assess the damping effectiveness of the five suspension systems. The mountain bike was equipped with accelerometers mounted at the axle and frame. A spectral analysis of the signal was performed for each signal to provide a measure of fork effectiveness. Results showed that accelerations ranged from -33 to +40 g at the axle and from -13 to +13 g at the frame, while spectral analyses of the acceleration signals revealed two distinct frequency regions from 0 to 100 Hz and from 300 to 400 Hz. The various suspension systems were all effective in attenuating vibration over the first region. Vibration amplitudes at the frame were considerably less than at the axle for the suspension conditions while similar axle-frame vibrations were observed with the rigid fork. Lower frequency vibration amplitudes were typically greater on the trail than on gravel. In the frequency region between 300-400 Hz, the signal was attenuated at the frame for all conditions including the rigid fork. The quantification and comparison process of the various suspension forks using impulse provided an objective marker for performance, and allowed differentiation between various suspension conditions. Moreover, the effectiveness analysis through the use of accelerometers provided insight into the range of frequencies dampened by a suspension. The lower frequency range dampening suggested that effectiveness of a suspension fork can be quantified even though the experiment did not conclusively differentiate between the forks. / Graduation date: 2001

In this thesis, A nonlinear methodology for the control of the highly maneuverable, high performance aircraft HARV (F-18) is studied by using sliding-mode control (SMC). This control law, which takes a continuous function when the input constraints are not considered, satisfies the reachability condition by which concerned states are driven to their sliding surfaces. Especially, this SMC is generalized for the so-called (square) uncoupled multi-input multi-output (MIMO) system by the use of error dynamics and applied directly to the nonlinear aircraft system without linearizing the system. For the practical application of the SMC to aircraft with input constraints, two control schemes are used, considering that variations of pitch rate q directly affect variations of the angle of attack. The first scheme consists of an ��-q control for the fast response. The second scheme consists an a-control for making the output approach its sliding surface slowly by setting boundary layers and adjusting reachable speeds to the sliding surface. Robustness to parameter uncertainties and disturbances is also studied for the SMC. Especially, when the effect of parameter uncertainties is severe, then multiple boundary layers are set in the neighborhood of sliding surface, in which different reachable speeds to the sliding surface are used to sustain the concerned state within the boundary layer and to reduce the effect of chattering. / Graduation date: 1994

Thesis (M.Tech.: Chiropractic)-Dept. of Chiropractic, Durban Institute of Technology, 2006 129, [21] leaves / The first objective was to investigate the injury profiles of South African cyclists, especially those relating to mountain bicycle use on the road, as there appears to be no knowledge available on mountain bicycle use on the road and related injuries. Secondly, to see if there is an association between injuries and bicycle set-up in a South African context.

The purpose of this study was to determine if the viscosity of MTA Angelus Fluid is lower than that of Pro Root MTA and MTA Angelus; and to compare the viscosity, leakage and particle size of these materials to determine whether a relationship exists between these properties. The viscosity of each material was measured and compared with the Student's t test. MTA Angelus Fluid's viscosity was significantly lower than the other two materials tested. Microleakage of root end fillings was assessed in a passive diffusion model. Leakage groups were compared with a one-way ANOVA (p < 0.05). No significant difference was found. Particle size and shape were evaluated with the SEM. MTA Angelus Fluid has a lower viscosity than the other materials tested. There was no significant difference in the sealing ability of the three materials tested and there was no apparent variation in each material's particle size or shape.

Thesis (M.Tech.: Chiropractic)-Dept. of Chiropractic, Durban Institute of Technology, 2006 129, [21] leaves / The first objective was to investigate the injury profiles of South African cyclists, especially those relating to mountain bicycle use on the road, as there appears to be no knowledge available on mountain bicycle use on the road and related injuries. Secondly, to see if there is an association between injuries and bicycle set-up in a South African context.

Simulation of maneuvers with multibody models of rotorcraft vehicles is an important research area due to its complexity. During the maneuvering flight, some important design limitations are encountered such as maximum loads and maximum turning rates near the proximity of the flight envelope. This increases the demand on high fidelity models in order to define appropriate controls to steer the model close to the desired trajectory while staying inside the boundaries. A framework based on the hierarchical decomposition of the problem is used for this study. The system should be capable of generating the track by itself based on the given criteria and also capable of piloting the model of the vehicle along this track. The generated track must be compatible with the dynamic characteristics of the vehicle. Defining the constraints for the maneuver is of crucial importance when the vehicle is operating close to its performance boundaries. In order to make the problem computationally feasible, two models of the same vehicle are used where the reduced model captures the coarse level flight dynamics, while the fine scale comprehensive model represents the plant. The problem is defined by introducing planning layer and control layer strategies. The planning layer stands for solving the optimal control problem for a specific maneuver of a reduced vehicle model. The control layer takes the resulting optimal trajectory as an optimal reference path, then tracks it by using a non-linear model predictive formulation and accordingly steers the multibody model. Reduced models for the planning and tracking layers are adapted by using neural network approach online to optimize the predictive capabilities of planner and tracker. Optimal neural network architecture is obtained to augment the reduced model in the best way. The methodology of adaptive learning rate is experimented with different strategies. Some useful training modes and algorithms are proposed for these type of applications. It is observed that the neural network increased the predictive capabilities of the reduced model in a robust way. The proposed framework is demonstrated on a maneuvering problem by studying an obstacle avoidance example with violent pull-up and pull-down.