Understanding flow processes of sea and fresh water through complex coastal regions is of utmost importance for a number of applications of interest to the scientific and engineering community, including wetland health and restoration, inland flooding due to tropical storms and hurricanes, and navigation through coastal waters. In such regions, the existence of vegetation increases flow resistance, which is a major factor in determining velocity and water level distribution in wetlands and inland. Commonly, the momentum loss due to vegetation is included in a bottom friction term in the model equations; however, such models may oversimplify the complex resistance characteristics of such a system. With recent increases in computational capabilities, it is now feasible to develop and implement more intricate resistance models that more accurately capture these characteristics. We present two methods for modeling flow through vegetated regions. With the first method, we employ mathematical and computational upscaling techniques from the study of subsurface flow to parametrize drag in a complex heterogeneous region. These parameterizations vary greatly depending on Reynolds number. For the coastal flows in which we are interested the Reynolds number at different locations in the domain may vary from order 1 to order 1000, so we must consider laminar and fully turbulent flows. Large eddy simulation (LES) is used to model the effects of turbulence. The geometry of a periodic cell of vegetative obstacles is completely resolved in the fluid mesh with a standard no-slip boundary condition imposed on the fluid-vegetation boundaries. The corresponding drag coefficient is calculated and upscaling laws from the study of inertial flow through porous media are used to parametrize the drag coefficient over a large range of Reynolds numbers. Simulations are performed using a locally conservative, stabilized continuous Galerkin finite element method on highly-resolved, unstructured 2D and 3D meshes. The second method we present is an immersed structure approach. In this method, separate meshes are used for the fluid domain and vegetative obstacles. Taking techniques from immersed boundary finite element methods, the effects of the fluid on the vegetative structures and vice versa are calculated using integral transforms. This method allows us to model flow over much larger scales and containing much more complicated obstacle geometry. Using a simple elastic structure model we can incorporate bending and moving obstacles which would be extremely computationally expensive for the first method. We model flexible vegetation as thin, elastic, inextensible cantilever beams. We present two numerical methods for modeling the beam motion and analyze their computational expense, stability, and accuracy. Using the immersed structure approach, a fully coupled steady-state fluid-vegetation interaction model is developed as well as a dynamic interaction model assuming dynamic fluid flow and quasi-static beam bending. This method is verified using channel flow and wave tank test problems. We calculate the bulk drag coefficient in these flow scenarios and analyze their trends with changing model parameters including stem population density and flow Reynolds number. These results are compared to well-respected experimental results. We model real-life beds of Spartina alterniflora grass with representative beds of flexible beams and perform similar comparisons. / text

Modeling, simulation, and optimization play vital roles throughout the engineering design process; however, in many design disciplines the cost of simulation is high, and designers are faced with a tradeoff between the number of alternatives that can be evaluated and the accuracy with which they can be evaluated. In this thesis, a methodology is presented for using models of various levels of fidelity during the optimization process. The intent is to use inexpensive, low-fidelity models with limited accuracy to recognize poor design alternatives and reserve the high-fidelity, accurate, but also expensive models only to characterize the best alternatives. Specifically, by setting a user-defined performance threshold, the optimizer can explore the design space using a low-fidelity model by default, and switch to a higher fidelity model only if the performance threshold is attained. In this manner, the high fidelity model is used only to discern the best solution from the set of good solutions, so that computational resources are conserved until the optimizer is close to the solution. This makes the optimization process more efficient without sacrificing the quality of the solution. The method is illustrated by optimizing the trajectory of a hydraulic backhoe. To characterize the robustness and efficiency of the method, a design space exploration is performed using both the low and high fidelity models, and the optimization problem is solved multiple times using the variable fidelity framework.

For over 30 years research has been done concerning the solidification and quenching of light metal alloys for the purpose of improving material properties. This thesis is concerned with an interesting new process for casting metals, by spraying water onto a sand mould, removing the sand and the directly quenching the part. This process is challenging since the component during solidification is extremely fragile, and the rate of cooling that is needed could seriously damage it. The water flow rate to the component needs to be quickly and precisely controlled. Additionally as this a new method there is very little prior art. The purpose of this thesis to develop a control system for the water sprayers flow rates. With this system the flow rate through the nozzles will be controlled indirectly using pressure feedback. The material properties and casting process, and how they influenced the design and construction of the spraying apparatus, are explained first. The hydraulic plant being controlled consists of three proportional valves connected to six spray nozzles. Based on experiments, the plant is extremely nonlinear making it difficult to control. Several controllers were developed and compared experimentally. The best performance was produced by extending a proportional plus integral plus derivative controller by adding an empirical nonlinear feedforward component; smoothing the setpoint; bounding the integration term; adding one bias at time zero and a 2nd bias for the remaining time (to mitigate valve stiction and to prime the hoses). This extended PID controller produced a 0.7% mean error and 1.9% mean absolute error for a multi-step setpoint covering a range of 0 to 80 PSI. Its performance was also highly repeatable. The standard deviations of the mean error, mean absolute error and maximum absolute error were less than 0.2 PSI over five runs. / Thesis / Master of Applied Science (MASc) / During the sand casting of aluminium and magnesium rapid cooling will greatly improve the material properties. By containing the liquid metal in a water soluble sand mould, and spraying it with water; the desired part shape and rapid cooling can be achieved. Removing the mould requires a powerful high flow rate jet. During the solidification of the metal, the flow rate must be reduced or the part would be demolished. This necessitated the development of a high speed, high flow rate controller to adjust the flow rate to remove the sand but not damage the part, and to maintain a smooth continuous cooling rate. The hydraulic system being controlled consists of three electronic valves connected to six spray nozzles. Several controllers are developed and compared experimentally. The best controller is shown to provide a quick and precise response.