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Making the Case for Unmanned and Autonomous Ships
Published in R. Glenn Wright, Unmanned and Autonomous Ships, 2020
Current designs for ship propulsion using internal combustion engines and inefficient drive trains are giving way to electric propulsion fueled with energy stored in batteries as well as other marine engines that rely on liquid natural gas, hydrogen fuel cells, wind power and hybrid propulsion methods comprised of two or more methods. Norway’s fully electric and autonomous container ship Yara Birkeland is the first zero-emissions MASS at the point of operation as the power generation needed to charge its batteries is accomplished elsewhere. Reductions in fuel consumption are also anticipated due to more hydrostatically and wind-efficient MASS designs that may be streamlined without having concerns for operator visibility.
Fundamentals of Fluid Mechanics
Published in Ethirajan Rathakrishnan, Instrumentation, Measurements, and Experiments in Fluids, 2016
For bluff bodies the pressure drag is many times larger than the skin friction drag and for streamlined bodies the condition is the reverse. In the case of streamlined bodies like aerofoil the designer aims at keeping the skin friction drag as low as possible. Maintaining laminar boundary layer conditions all along the surface is the most suitable arrangement. Though such aerofoils have been designed, they have many limitations. Even small surface roughness and disturbances make the flow turbulent, which spoils the purpose. In addition, there is a tendency for the flow to separate even at small angles of attack, which severely restricts the use of such aerofoils.
Random Vibration: Probabilistic Forces
Published in Haym Benaroya, Mark Nagurka, Seon Han, Mechanical Vibration, 2017
Haym Benaroya, Mark Nagurka, Seon Han
All structures must be designed to withstand wind forces. One can classify structures subjected to wind as either streamlined or bluff bodies. Streamlined structures, such as wings, have a high aspect ratio (ratio of one dimension to another) and are optimally shaped so a streamline can naturally flow around them. They are designed so that the interaction of their shape with the wind results in a desirable configuration of forces. Bluff bodies, such as tall buildings or offshore drilling platforms, are generally of low aspect ratio and may have corners or sharp edges. They are designed more for strength than for fitting within the streamlines.
Aerodynamic investigation of the inrun position in Ski jumping
Published in Sports Biomechanics, 2021
A large group difference in inrun position between the WC and COC athletes was also observed. The average difference in CDA between the groups in the preferred position was 0.016 m2 (~15.5%), which would give a speed difference of 0.6–1.3 kmh−1, and almost 0.01 m2 (~10.8%) for the best tested position, which corresponds to a speed difference of around 0.4–0.8 kmh−1. The only significant difference in body position between the groups was the trunk angle. For the preferred position, variations in thigh and leg angle were observed but there were no significant differences between the groups due to a large variation within the COC group. The difference in trunk angle between the groups was ~3° both for the preferred and best tested position. A ~3° larger trunk angle would increase the frontal area, thus increase the CDA. In other sports where aerodynamic forces play a big role like cycling, alpine skiing and speed skating, the athletes try to maintain a streamlined shape, like a water drop or airfoil, to reduce the drag. A streamlined shape will cause a later flow separation, which will reduce drag coefficient. This will also apply for a ski jumper in an inrun position, and a 0° will give a more streamlined positioning of the torso. Hence, a higher trunk angle will increase both the drag coefficient (CD) and the frontal area (A). From a biomechanical point of view, a 0° could also move the centre of mass closer to the centre of application of the drag force, which again could make it easier to maintain balance.