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Showing posts with the label Marine Engineering

Airfoil

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An airfoil is the cross-section of a wing, blade, rudder or foil, shaped to produce lift with as little drag as possible. The same theory applies in air and in water, from aircraft wings and wind turbine blades to ship rudders, keels and hydrofoils. This post covers the fundamentals, the key equations, a worked wing example and the checks that keep airfoil estimates useful in design. Aircraft model in the NASA Ames 40x80 ft wind tunnel. Photo: NASA Ames Research Center / NASA , Public domain via Wikimedia Commons Airfoil Fundamentals A flowing fluid creates lift on an airfoil because the pressure on the lower surface is higher than on the upper surface. Equivalently, the airfoil generates circulation around itself. The sharp trailing edge fixes the flow there (the Kutta condition), which sets the amount of circulation and therefore the lift. Term Meaning Chord (c) Straight-line distance from leading edge to trailing edge Camber Curvature of the mean line, which gives lift at ...
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Marine Engineering and Naval Architecture: Stability, Loads and Design Workflow

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A vessel or floating structure has to float upright, move through water efficiently, survive the sea and satisfy a class society before it can sail. Each of those requirements is a naval architecture problem, and they interact. This post explains the core calculations and the design workflow behind marine engineering and naval architecture services, from stability to class approval. Underwater hull form of the SS Great Britain in dry dock. Photo: Nortix08 , CC BY-SA 4.0 via Wikimedia Commons Intact Stability and GM Intact stability describes a vessel's ability to return upright after a heel disturbance. The starting measure is the metacentric height, GM = KM − KG , where KM = KB + BM and BM = I / ∇ (waterplane second moment of area divided by displaced volume). The GZ curve then shows the righting lever across all heel angles. Its shape matters more than GM alone. Worked example. A box barge is 40 m long, 10 m wide, floats at a 2 m draft and has KG = 3.0 m. Displaced volume ∇...
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