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Human Movement in Fluids

Human Movement in Fluids. Gases (air) & liquids are considered to be fluids! Pressure on the objects in these fluids Hydrostatic pressure Blanket analogy Relative velocity Velocity of the object in relation to the fluid around it Wind assisted runs, swimming in a flume, wave pools, etc.

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Human Movement in Fluids

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  1. Human Movement in Fluids • Gases (air) & liquids are considered to be fluids! • Pressure on the objects in these fluids • Hydrostatic pressure • Blanket analogy • Relative velocity • Velocity of the object in relation to the fluid around it • Wind assisted runs, swimming in a flume, wave pools, etc. • Flow dynamics • Laminar flow (Fig. 8.7) • Turbulent flow (Fig. 8.7) • Fluid properties • Density of the fluid • Specific weight • Viscosity • Atmospheric pressure & temperature

  2. Buoyancy • Force due to immersion • Archimedes principle • Magnitude of the buoyant force equals the weight of the fluid displaced by the object Fb = Vd • Center of buoyancy or Center of Volume • Fig. 8.2 • External buoyancy factors • Fluid temperature • Fluid density (ie. salt water) • Buoyancy can affect drag!

  3. Drag • Drag force acting on a body in relative motion with respect to a fluid! FD = ½ CD Ap v2 • FD is the Drag force • CD is the Coefficient of drag •  is Fluid density • Ap is the Surface area perpendicular to the flow • v2 is the Relative velocity of the object in relation to the fluid flow • Theoretical Square Law • Drag increases approximately with the square of velocity when relative velocity is low! • If a cyclist doubles their speed and other factors remain constant, the drag force opposing them increases fourfold! Higher velocity, increased drag!

  4. Forms of Drag • Surface drag or skin friction or viscous drag • Effects the boundary layer around the object • Form drag or shape drag • Pressure gradient from the front to the rear of the object • Highest form of drag • Equipment design • Wave drag • Interaction between the water and air and then on the object • Thrashing in the water causes “wave drag”

  5. Lift Force • Lift • Force acting on a body that in a direction that is perpendicular to the fluid flow • This force can act in any direction • Hand out the window on a highway! • Being dragged through the water! • Factors affecting Lift • Coefficient of lift • Fluid density • Projected surface area • Relative velocity of the object to the fluid FL = 1/2 CLApv2

  6. Factors Affecting Lift • Coefficient of Lift • Unitless value that is an index of a body’s ability to generate lift • Table 15-2 (Hall text: Page 525) • Factors Affecting the Magnitudes of Fluid Forces • Buoyant force • Skin friction • Form drag • Wave drag • Lift force

  7. Foil Shape • Foil • Shape of an object conducive to generating lift • Figure 8.12 • Bernoulli’s principle • Inverse relationship between relative velocity of the object and the relative pressure in a fluid flow!

  8. Angle of Attack • Angle of orientation of the projectile with respect to the fluid flow! • Alpha () affects horizontal displacement • Examples • Frisbee shape • Vortec footballs • Swirl footballs • Whoosh • Figure 15-13 (Hall text: Page 527)

  9. Lift/Drag Ratio • An optimum angle of attack for maximizing horizontal displacement occurs at the maximum lift/drag ratio! • Figure 8.10 & 8.11

  10. Magnus Effect • Magnus force is the lift force directed from the high pressure region to the low pressure region! • Figure 8.13 • Figure 15-16 (Hall text)

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