How do hydrodynamics work?

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Hydrodynamics is the study of fluids in motion. The term fluid flow is also used. The concept of dynamic movement is inherent in the terminology of hydrokinetics that is likewise used as a description.

There are a number of principles that are important within the understanding of how hydrodynamics work. Viscosity is the basis of this notion. Viscosity refers to the density of the fluid; in this instance focusing on the fact that the liquid water is almost 1,000 times denser than air. The internal resistance that the fluid has in relation to flow, and thus the friction that arises, further defines the principle of viscosity. Fluids that are lighter tend to flow more easily, whereas those with a denser or higher viscosity demonstrate greater flow resistance. When the fluid flow is streamlined, fluid velocity and fluid viscosity are not too different, it is called laminar; when the resistance to flow is increased the fluid flow is entitled nonlaminar or turbulent.

Hydrodynamics takes into account the fluid viscosity, the resistance to flow, as well as the relationship to other structures and the effect this has. The concept of drag comes into play. What causes the drag resistance is studied and equally what enables lift. Objects moving within a fluid all experience a certain viscous drag as a result of the viscosity of the fluid.

Specialized engineering faculties focus on the study of marine hydrodynamics. The ocean as a significant resource is the subject of investigation, with its magnitude of potential energy. Fish are studied as phenomenal natural examples of propulsion through water. Marine hydrodynamics regard the way the fish are able to do so, how their shapes influence movement, what the drag forces are and how these are reduced. The effect of oceanic turbulence and the fish’s management of this is considered.

The above studies impact on the design of various ocean vessels such as naval and research vessels, ferries, container and cargo ships, and racing yachts. Marine hydrodynamics laboratories are set up to measure and evaluate the fluid flow principles and performance for propulsion devices. These include devices such as propellers, waterjets, hydrofoils and submersibles. The way ships are designed and the manner in which offshore platforms are created to withstand ocean currents, pressure, wave and wind force, form part of the range of oceanic engineering hydrodynamics. Offshore engineering deals particularly with offshore platforms whose design requires understanding of the hydrodynamic forces operating as per the surfaces and wave and wind force.

Ocean waves and the hydrodynamic forces on bodies, including concepts of wave theory, mass, wave force and viscous force on ships and vessels, are studied. Whether the ship moves in a linear or angular fashion has a relationship to the fluid flow.

The theory proposed by Swiss mathematician Bernoulli, in the 18th century, provides a formula thought to be crucial to hydrodynamics. The way the pressure of the fluid, the kinetic energy and potential energy interrelate was calculated by Bernoulli and bears relevance to the phenomenon of lift. The principle is formulated according to fluid pressure (P), fluid density (p), fluid velocity V), gravitational acceleration (g) and height (h) as:

P+1/2pV^2+gh=C

The lifting force is explained as occurring when the pressure above is lower than the pressure below. Bernoulli’s principle appears to apply only when there is no turbulence and the fluid flows in a steady motion.

Another theory propounded by his colleague, Euler, as a hydrodynamics equation to explain lifting force, is formulated as:

dP/dn=pV^2R

This describes the relationship between fluid pressure (P), normal vector to curved streamline (n), fluid density (p), fluid velocity (V) and radium of curvature of streamline (R).

A MIT (Massachusetts Institute of Technology) hydrodynamic experimental study gives an example of a sailboat experiencing lift. The combination of wind force and drag force in relation to the boat mass and acceleration is described. The lifting force is explained using Bernoulli’s principle and Euler’s equation.

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