Stroke has significant impact on dynamic balance during locomotion, with a 73% incidence rate for falls post-stroke. Current clinical assessments often rely on tasks and/or questionnaires that relate to the statistical probability of falls and provide little insight into the mechanisms that impair dynamic balance. Current quantitative measures that assess medial-lateral balance performance do not consider the angular motion of the body, which can be particularly impaired after stroke. Current control methods in bipedal robotics rely on the regulation of angular momentum (H) to maintain dynamic balance during locomotion. This study tests whether frontal-plane H is significantly correlated to clinical balance tests that could be used to provide a detailed assessment of medial-lateral balance impairments in hemiparetic gait. H was measured in post-stroke (n=48) and control (n=20) subjects. Post-stroke there were significant negative relationships between the change in frontal-plane H during paretic single-leg stance and two clinical tests: the Dynamic Gait Index (DGI) (r=-0.57, p<0.001) and the Berg Balance Scale (BBS) (r = -0.54, p<0.001). Control subjects showed timely regulation of frontal-plane H during the first half of single-leg stance, with the level of regulation depending on the initial magnitude. In contrast, the post-stroke subjects who made poorer adjustments to frontal-plane H during initial paretic leg single stance exhibited lower DGI and BBS scores (r = 0.45, p=0.003). We conclude that H is a promising balance indicator during steady-state hemiparetic walking and that paretic single-leg stance is a period with higher instability for stroke patients.
Computationally advanced biomechanical analyses of gait demonstrate the often counter intuitive roles of joint moments on various aspects of gait such as propulsion, swing initiation, and balance. Each joint moment can produce linear and angular acceleration of all body segments (including those on which the moment does not directly act) due to the dynamic coupling inherent in the interconnected musculoskeletal system. This study presents the quantitative relationships between individual joint moments and trunk control with respect to balance during gait to show that the ankle, knee, and hip joint moments all affect the angular acceleration of the trunk. We show that trunk angular acceleration is affected by all the joints in the leg with varying degrees of dependence during the gait cycle. Furthermore, it is shown that inter-planar coupling exists and a two dimensional analysis of trunk balance neglects important out-of-plane joint moments that affect trunk angular acceleration.
The use of soft-computing algorithms in hardware-in-the-loop applications has been investigated. A Proportional-Integral-Derivative (PID) classical controller and a Fuzzy Logic Controller (FLC) were designed and successfully tested on the Turbine Technologies SR-30 turbojet engine for the main-stage operation of the engine. Transfer function model of the plant was obtained using frequency-response method. Closed-loop controllers both with the PID and FLC algorithms were tested in a simulated environment before their application. Additionally, application of Bayesian Belief Networks (BBN) for the start-up sequence of the engine was investigated and a BBN design has been made.
In this paper the design and application of a control algorithm is discussed to control the test conditions within plenum chamber and the test section of a supersonic blow-down, variable throat wind tunnel at the University of Alabama. The artificially intelligent controller algorithm was designed using a gain scheduled Proportional-IntegralDifferential (PID) control approach. The PID controller was augmented to work with time variant properties of the control problem by determining a functional form of the integral term of the controller from the governing equations of the tunnel. The controller was optimized using genetic algorithms (GA) on a neural network (NN) model of the tunnel and was compared to a conventional PID controller using the same NN model. The process was repeated for different throat settings to find the control gains for each setting. The controller algorithm was next applied to the actual wind tunnel at different throat settings and the results were compared. The optimized controller is proven to work very well at every throat setting.
The flow physics of a free round air jet prior to impinging on a convex cylindrical surface is discussed. Two components of mean velocity, normal stress and shear stress profiles were obtained using a novel fibre-optic, two-simultaneous velocity component laser-Doppler velocimetry probe. Velocity profiles obtained at seven axial locations in the impinging jet case are compared to profiles obtained at eight axial locations away from the jet exit to determine the surface effects on the free jet. The Reynolds number of the flow based on the jet diameter was Re = 25 000 and the convex cylinder was located at x/d = 4.0 (jet exit velocity, Uj = 24 m s−1; jet diameter, d = 15.24 mm; circular cylinder diameter, D = 60.5 mm). Flow visualization results show that the initially axisymmetric jet becomes a three-dimensional flow, wraps itself on the cylinder across the cylinder and also behaves similar to a wall jet along the cylinder axis. The jet axial mean velocity starts reducing sharply one diameter (1d) away from the cylinder. The jet axial, radial, tangential normal stresses and the shear stress are not affected by the presence of the surface in the vicinity of the jet axis until 0.05d away from the surface, and are affected near the jet edge about 0.75d away from the surface.
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