DETERMINATION OF DRAG AND LIFT RELATED COEFFICIENTS OF AN AUV USING COMPUTATIONAL AND EXPERIMENTAL FLUID DYNAMICS METHODS

Determination of hydrodynamic coefficients is a vital part of predicting the dynamic behavior of an Autonomous Underwater Vehicle (AUV). The aim of the present study was to determine the drag and lift related hydrodynamic coefficients of a research AUV, using Computational and Experimental Fluid Dynamics methods. Experimental tests were carried out at AUV speed of 1.5 m s-1 for two general cases: I. AUV without control surfaces (Hull) at various angles of attack in order to calculate Hull related hydrodynamic coefficients and II. AUV with control surfaces at zero angle of attack but in different stern angles to calculate hydrodynamic coefficients related to control surfaces. All the experiments carried out in a towing tank were also simulated by a commercial computational fluid dynamics (CFD) code. The hydrodynamic coefficients obtained from the numerical simulations were in close agreement with those obtained from the experiments.

And…Action! Setting the Scene for Accurate Visual CFD Comparisons Using Ray Tracing

Increased graphical capabilities of contemporary computer hardware make ray tracing possible for a much wider range of applications. In science, and numerical fluid mechanics in particular, visual inspections still play a key role in both understanding flows, predicted by computational fluid dynamics, exhibiting features observable in real-life, such as interfaces or smoke, and when comparing such flows against experimental observations. Usually, little attention is paid to the visualisation itself, unless when the render is used solely for its eye-catching appearance. In this work, we argue that the use of ray tracing software can help make comparisons between computational and experimental fluid dynamics more robust and meaningful, and that, in some cases, it is even a necessity. Several visualisation problems which can be overcome through application of this methodology are discussed, and the use of ray tracing is exemplified for several common test cases in the maritime field. Using these examples the benefits of ray tracing are shown, and it is concluded that ray tracing can improve the reliability of scientific visual comparisons.

Vortex Shedding Suppression: A Review on Modified Bluff Bodies

Vortex shedding phenomenon behind bluff bodies and its destructive unsteady wake can be controlled by employing active and passive flow control methods. In this quest, researchers employed experimental fluid dynamics (EFD), computational fluid dynamics (CFD) and an analytical approach to investigate such phenomena to reach a desired outcome. This study reviews the available literature on the flow control of vortex shedding behind bluff bodies and its destructive wake through the modification of the geometry of the bluff body. Various modifications on the bluff body geometries namely perforated bluff bodies, permeable and porous mesh, corner modification and wavy cylinder have been reviewed. The effectiveness of these methods has been discussed in terms of drag variation, wake structure modifications and Strouhal number alteration.

CFD Simulations of Self-Propulsion and Turning Circle Maneuver up to 90º of Ship in Waves

In the present work, a Reynolds-Averaged Navier-Stokes (RANS)-overset method is used to numerically investigate self-propulsion and turning circle maneuver in waves for a container ship. A computational fluid dynamics (CFD) solver naoe-FOAM-SJTU is used for the numerical computations of the fully appended Duisburg Test Case ship model. Overset grids are used to handle the motions of the ship hull appended with the propeller and the rudder. Open source toolbox waves2Foam is used to prevent wave reflection in the computational domain. The current numerical method is validated by comparing the ship speed in the self-propulsion case between CFD and Experimental Fluid Dynamics (EFD). Predicted ship 6-DOF motions, hydrodynamic forces, free surfaces, and inflow of the propeller are presented. The propulsion characteristic is mainly studied. Assuming the thrust identification method works even in unsteady conditions, the wake fraction and propulsion efficiency are discussed. The effect of orbital motion of water particle and ship motion on the propulsion performance are identified. In conclusion, the present RANS-overset method is a reliable approach to directly simulate self-propulsion and turning circle maneuver in waves.

The Fluids Rap: It’s All About Flow

Most of the currently-enrolled undergraduate engineering students grew up with exposure to social media websites like Facebook and Youtube. Making sure that students are not distracted by their mobile devices in class has become more challenging, and one way to address the issue is to present engineering in a more entertaining and engaging way. A rap song about fluid mechanics was created by the author for entrainment, outreach, and education purposes. The song covers the fundamentals of fluid mechanics and mentions some theoretical basics, as well as some of the most widely used computational fluid dynamics and experimental fluid dynamics techniques. The song was written with the intention to be entertaining and educational — the goal was that someone with no prior fluid mechanics background will be able to understand it after spending 10–20 minutes reading through the lyrics explanations. A music video was produced for the song. The video production was sponsored by the American Society of Mechanical Engineers and includes visuals of experimental facilities and equipment. The paper provides the background of the project, marketing plans, some of the lessons learned, the lyrics, and the explanations of the lyrics.