Browsing by Author "Bartolomeu, Tiago Correia"
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- Hydrodynamic Optimization of a torpedo-shaped hullPublication . Bartolomeu, Tiago Correia; Brojo, Francisco Miguel Ribeiro Proença; Figueiredo, Paulo de VasconcelosNowadays, it is not fully clear how the Ocean seabed can contribute to Earth ecosystems. However, several steps are being taken to completely understand Ocean’s seabed. Lately, many methods are being developed to explore the Oceans, although there is one method which fulfill the desired trade-off (between low operational costs and high quality data collection). This efficient method developed to explore the Ocean’s depth is known as submarine vehicles, and the most efficient of them, to explore and mapping, is certainly the Autonomous Underwater Vehicle (AUV). The increasing use of AUV’s is leading to a point in which its design parameters are crucial. Characteristics as high endurance, long operation time, high maneuverability and range are demanded at an early design stage; thus, it is essential to find an optimum hull shape design to improve these characteristics. This thesis presents the effect of hydrodynamic forces of axisymmetric underwater vehicles through the variation of the shape of a torpedo-shaped hull body. Furthermore, this thesis is intended to analyze, experimentally, the length-to-Diameter (D) ratios of nose (N) and tail (T), as well as its shapes, in order to find the optimum ratios and shape combinations for the minimization of Drag. The experimental tests were conducted in the towing tank of the University of Beira Interior (UBI). However, due to the Towing Tank dimensions, the development of a scaled model had to be made. A similarity between the scaled model and the full-scale prototype must be done to assume similar flow conditions. Several torpedo-shaped combinations were tested experimentally and further validated the numerical simulations. Moreover, parameters such as the pitch angles (or Angle of Attack (AoA)) [0 - 20°] and velocities [0.50 – 1 m/s] were investigated to understand their influence on the hydrodynamic Drag. The experimental setup is hereby fully described, showing the various procedures adopted until the data collection phase. A strain gauge system (load cell) was used to measure the Drag induced by the hull body. Experimental results demonstrate an optimum configuration for N/D = 0.8 (Elliptical shape) and T/D = 1.6 (Conical shape). From the experimental and numerical data, it could be seen that the Drag increases with the increase of velocity. Same occurrence happens for AoA, where Drag increases with higher AoA’s. Therefore, it can be concluded that the influence of AoA on Drag is higher for greater velocities. The experimental measurements have been used to validate results obtained from a Computational Fluid Dynamics (CFD) software that uses Reynolds Average Navier-Stokes (RANS) equations (ANSYSTM FLUENT). A mesh-independency study was made to investigate two turbulence models: Standard ?-e and ?-? SST models. Standard ?-e showed to be the most appropriate model to this study with a lower computational cost. Results between Experimental and Numerical methods showed a good agreement, considering the conditions mentioned.