Thesis--M. Sc., University of Hong Kong, 1982.

This thesis proposes a novel and efficient method (Method of Evolving Junctions) for solving optimal control problems with path constraints, and whose optimal paths are separable. A path is separable if it is the concatenation of finite number of subarcs that are optimal and either entirely constraint active or entirely constraint inactive. In the case when the subarcs can be computed efficiently, the search for the optimal path boils down to determining the junctions that connect those subarcs. In this way, the original infinite dimensional problem of finding the entire path is converted into a finite dimensional problem of determine the optimal junctions. The finite dimensional optimization problem is then solved by a recently developed global optimization strategy, intermittent diffusion. The idea is to add perturbations (noise) to the gradient flow intermittently, which essentially converts the ODE's (gradient descent) into a SDE's problem. It can be shown that the probability of finding the globally optimal path can be arbitrarily close to one. Comparing to existing methods, the method of evolving junctions is fundamentally faster and able to find the globally optimal path as well as a series of locally optimal paths. The efficiency of the algorithm will be demonstrated by solving path planning problems, more specifically, finding the optimal path in cluttered environments with static or dynamic obstacles.

The use of compliant coatings, in particular polyurea, for improved blast protection of structures has been reported recently in the literature. The goal of this research is to develop a comprehensive understanding of the reasons for improved performance of coated structures through experimentation and correlation with simulation. The different factors influencing the response of an elastomer coated ductile metal subjected to a blast load have been examined and quantified. First, dynamic strain localization in the metal is a precursor to ductile failure; this was characterized for the metal of interest with and without the polymer coating. Experiments with the expanding ring/tube and experiments have demonstrated that for Al 6061-O and Al 3003-H14, the localization strain is unaffected by both deformation rate and the polymer coating; however, two important effects of the coating have been explored. First the additional mass of the coating provides an inertial resistance. Second, the flow resistance of the polymer provides continued dissipation of energy even after the metal has yielded potentially preventing failure in the metal, or at least containing fragments. These effects were examined for two different types of polymers – polyurea, an elastomer and polycarbonate, a thermoplastic shear yielding polymer. It is shown that these two effects can be used to tailor the coating to optimize blast protection of the bilayer system. In order to take advantage of this optimization, the constitutive behavior of the elastomer coating must be determined at strain rates and loading conditions that are experienced in the blast loading; these strain rates are in the range of 1000 to 10,000 per second. This has been accomplished through a hybrid method that combines measurements with numerical simulations to extract the constitutive response of the material. The strain rate dependent behavior of polyurea for rates in the range of 800-8000 per second has been determined by measuring the spatio-temporal evolution of the particle velocity and strain in a thin strip subjected to high speed impact loading that generates uniaxial stress conditions and comparing this with numerical simulations of the one-dimensional problem using the method of characteristics. A similar scheme to track the particle velocity and strain during the axisymmetric deformation of a membrane subjected to high speed loading has also been developed; this requires two projections of the deformation to be obtained in order to facilitate the measurement of axial and kink waves in the membrane. The finite volume method is adapted for simulations of these dynamic uniaxial and axisymmetric problems with a view towards simulating shock waves that are expected to form in some loading conditions. The hybrid method is used once again to characterize the constitutive response. The axisymmetric experiments have demonstrated the inability of the uniaxial models for both polyisoprene rubber and polyurea to completely capture their behavior during a more complex loading, and left a need for further work on characterizing the dynamic constitutive response of these polymers. / text

Parking garages have remained fairly outdated even as embedded systems have been introduced virtually everywhere to improve the human existence. Some provide information about whether they are full or not, but that does not offer a better parking experience, it only informs people once they are already there and is inconvenient. This causes people to circle the parking lot numerous times, making the process inefficient and wasteful. The SmartPark parking system fills that gap by providing an automated infrastructure that collects information regarding the availability of parking spaces in a garage. As modern technology grows and expands the connectivity available on automobiles, it would be even possible to interface with the car itself to provide parking information. Each space has an ultrasonic sensor attached to a microcontroller that communicates with a master, who keeps and displays the overall count of spaces available. The purpose of this paper is to provide the capability of dynamically adding and removing slaves, without requiring individual configuration for each slave prior to its deployment. A sequence of communication exchanges will be described in order for a slave to register itself with its master. Through a series of messages, the slave will be able to identify its location and begin reporting the state of its space, and the master will continue to keep track of existing slaves and their states. The result of the research is a protocol that allows successful pairing of a new slave with its master without previous static configuration, which allows an easy deployment of the system without dependence on its original configuration. This functionality will make the system more scalable, allowing the parking system to be extended by connecting new slaves wherever they are needed. It will also make it more maintainable, since slave replacement or relocation will become an easy task. SmartPark can easily be adapted to existing parking structures with only the installation of the master and slave nodes, due to its limited resource requirements. Related work is also discussed and an insight into how this methodology can be used to modernize current automated parking systems is provided. / text

A scroll vortex intake is a hydraulic structure that transfers water stably from one elevation to a lower one by generating a swirling vortex flow down a vertical drop- shaft. Scroll vortex intakes are applied widely in water supply, stormwater drainage and sewerage systems. For a good engineering design, a sufficiently large and stable air core needs to be maintained within the dropshaft. Although a number of the- oretical and experimental investigations have been conducted, the understanding and predictions of the vortex flow is still far from complete due to a lack of de- tailed velocity field and air core measurements. This study aims to achieve a better understanding of the scroll vortex intake flow. The hydraulic theory of scroll vortex intake is revisited and detailed measurements of air core and velocity field of the vortex flow is conducted. A 1:15 physical model of a scroll vortex intake has been designed according to dynamic Froude similitude and constructed. Experiments have been conducted to measure the head-discharge relation. Piezometric head and air core size are measured at the throat of the vortex flow. Velocity fields are measured using Laser Doppler Anemometry (LDA). The measurements show that the vortex flow in the chamber resembles a free vortex and the circulation is approximately equal to that at the inlet to chamber. The chamber flow is not affected by the bottom boundary effect at bottom above a depth of the order of the dropshaft diameter. The throat section of the vor- tex flow is located slightly below the chamber bottom and within the bellmouth at the entrance to dropshaft. For the vortex flow in and downstream of the bell- mouth, the tangential velocity distribution can be described by a Rankine vortex (combination of forced and free vortex); the transition from forced to free vortex occurs at around the middle of the vortex flow layer. The pressure is positive for all locations and all discharges. Due to viscous effect, the maximum circulation is found to be lower than the inlet circulation. Consistent with the free vortex theory, the vertical velocity in the dropshaft is approximately constant. By accounting for the loss of circulation between chamber inlet and the dropshaft, a new 1D theory is proposed. Unlike previous models, the new theory gives good predictions of head-discharge relation and minimum air core size without the need of physically unrealistic assumptions. This study has revealed the structure of a scroll vortex intake flow for the first time. Characteristic flow features of the scroll vortex intake have been elucidated. The findings have helped to explain and resolve the long-standing discrepancies between the theoretical predictions of three representative 1D hydraulic theories. The vortex flow measurements also provide a basis for the development of a new theory and the validation of 3D numerical models. / published_or_final_version / Civil Engineering / Master / Master of Philosophy

published_or_final_version / Civil Engineering / Master / Master of Philosophy

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No description available.

A 1-D dynamic simulation model of a new cooling system for the upcoming Gripen E aircraft has been developed in the Modelica-based tool Dymola in order to examine the cooling performance. These types of low-dimensioned simulation models, which generally are described by ordinary differential equations or differential-algebraic equations, are often used to describe entire fluid systems. These equations are easier to solve than partial differential equations, which are used in 2-D and 3-D simulation models. Some approximations and assumptions of the physical system have to be made when developing this type of 1-D dynamic simulation model. The impact from these approximations and assumptions can be examined with an uncertainty analysis in order to increase the understanding of the simulation results. Most uncertainty analysis methods are not practically feasible when analyzing large 1-D dynamic simulation models with many uncertainties, implying the importance to simplify these methods in order to make them practically feasible. This study was aimed at finding a method that is easy to realize with low computational expense and engineering workload. The evaluated simulation model consists of several sub-models that are linked together. These sub-models run much faster when simulated as standalone models, compared to running the total simulation model as a whole. It has been found that this feature of the sub-models can be utilized in an interval-based uncertainty analysis where the uncertainty parameter settings that give the minimum and maximum simulation model response can be derived. The number of simulations needed of the total simulation model, in order to perform an uncertainty analysis, is thereby significantly reduced. The interval-based method has been found to be enough for most simulations since the control software in the simulation model controls the liquid cooling temperature to a specific reference value. The control system might be able to keep this reference value, even for the worst case uncertainty combinations, implying no need to further analyze these simulations with a more refined uncertainty propagation, such as a probabilistic propagation approach, where different uncertainty combinations are examined. While the interval-based uncertainty analysis method lacks probability information it can still increase the understanding of the simulation results. It is also computationally inexpensive and does not rely on an accurate and time-consuming characterization of the probability distribution of the uncertainties. Uncertainties from all sub-models in the evaluated simulation model have not been included in the uncertainty analysis made in this thesis. These neglected sub-model uncertainties can be included using the interval-based method, as a future work. Also, a method for combining the interval-based method with aleatory uncertainties is proposed in the end of this thesis and can be examined.