University of Twente Student Theses


Spherical body orientation extraction and Rayleigh-Bénard convection

Neut, M.W.M. (2014) Spherical body orientation extraction and Rayleigh-Bénard convection.

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Abstract:This thesis reports the work performed for obtaining a master’s degree at the Twente University. It consists of two main parts. In the first part, a novel method for obtaining the absolute orientation of a spherical object is developed. The method is based on painting a specific pattern onto the surface of a sphere and minimizing a cost function based on the difference between a image recording of the physical sphere and a digital reference pattern. Contrary to existing methods that use brute-force comparisons and select the best fitting image from a reference database, the method introduced herein uses a minimization algorithm that does not require databases or calibration. Instead, it employs a specifically designed pattern that is painted on the surface of a sphere using a 3D-printed stencil, while the digital counterpart is a simple piece-wise constant boolean function. It is shown in chapter 3 that the resulting performance exceeds existing methods by at least one order of magnitude in both computation speed and accuracy and allows sub-degree real-time analysis of the absolute orientation of a spere. For the second part of this work, Rayleigh-Bénard (RB) convection is studied both experimentally and numerically. Experimentally, a quasi-twodimensional RB convection setup is designed and built for both research and demonstrative purposes. As demonstration, shadowgraphy allows visualization of the complex dynamics of rising and falling thermal plumes inside a convection cell. The setup is proven very succesful in showcasing thermal convection with a table-top experiment. It is expected that the setup continues to be used for such demonstrations and provide insight into the field of fluid physics to the general public. In addition to Rayleigh- 3 PART Bénard experiments, the setup can be used for boiling experiments with only minor modifications. Also, a relatively novel technique called background-oriented schlieren [17] is elaborated and applied to the setup. This method allows resolving the temperature field of the thermal convection cell. The temperature field can be used for statistical analysis on the dynamics of the system. We hypothesized that with the conservation laws that govern these dynamics, the velocity field can be resolved from the temperature field (if known with sufficient spatial and temporal resolution). Unfortunately, however, we prove in section 6.5 that it is mathematically impossible to uniquely recover the velocity field from the temperature field. Finally, a novel direct numerical simulation code is used to study the influence of strong geometric confinement on heat transport in RB convection. It was recently shown [16] that heat transport enhancement is observed for moderate confinement, despite an overall decrease in flow velocity due to increased viscous drag from the sidewalls. In this thesis, we study a larger range of aspect ratio’s and show that heat transport does increase for moderate confinement, but peaks and decreases for very strong confinement. In addition, the code is used for design of the experimental setup.
Item Type:Essay (Master)
Faculty:TNW: Science and Technology
Subject:33 physics
Programme:Applied Physics MSc (60436)
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