Hydraulics

Mass

The quantitative measure of the amount of matter in a given body.

Weight (or Gravity Force)

The earth's gravitational pull upon a body. SI Unit: Newton, N.

Density

The mass of fluid contained in a unit volume.

Specific Weight

The weight of fluid which is contained in a unit volume.

Specific Gravity

The dimensionless ratio of the specific weight or density of a fluid to the specific weight or density of a standard fluid.

Specific Volume

The volume occupied by a unit mass of a fluid (the reciprocal of density).

Pressure

The force acting normal to an area divided by this area.

Intensity of Pressure

The force per unit area acting on a real or imaginary surface within a fluid. It acts equally in all directions at any point in a fluid.

Zero Absolute Pressure

The pressure that exists in a perfect vacuum, where no fluid is present.

Absolute Pressure

Any pressure measured above the zero absolute pressure.

Gage Pressure

Any pressure measured above or below the atmospheric pressure. It is often used to measure pressure relative to the atmospheric pressure.

Atmospheric Pressure

The pressure exerted by the atmosphere on every surface with which it comes in contact.

Manometer

A pressure measuring technique using tubes usually shaped in the form of U's and applying the principles of fluid statics.

Open Type Manometer

A manometer used for measuring gage pressures, using a base liquid. It is a system of bent tubes containing an atmospheric level in one of its end legs.

Differential Type Manometer

A manometer utilized in the measurement of pressure difference between two points in the system, and does not have any atmospheric level.

Eccentricity

The distance from the centroid to the center of pressure.

Depth of Center of Pressure

The vertical distance from the liquid surface to the center of pressure.

Center of Pressure

The point on a submerged surface where the resultant hydrostatic force acts.

Centroid

The geometric center of a submerged surface, used to calculate the average pressure acting on the surface.

Moment of Inertia

A geometric property of a cross-section used to determine the location of the center of pressure.

Dam

A structure built across a river or stream to hold back water.

Uses of Dams

Water Supply, Irrigation, Electrical Generation, Flood Control, Water Storage, Debris Control, Navigation and Recreation

Lagrangian Description – System Approach

A method of defining fluid flow by "tagging" each fluid particle and specifying its velocity and acceleration as a function of time as the particle moves from one position to the next. It is named after the Italian mathematician Joseph Lagrange.

Eulerian Description – Control Volume Approach

A method of describing the velocity of fluid particles within a system by considering a fixed point surrounded by a differential volume of space. The velocity of all particles that pass through this point or volume is measured at this point. It is named after the Swiss mathematician Leonard Euler.

Control Volume

The volume of space through which the particle flow is considered in the Eulerian description.

Control Surface

The boundary of the control volume.

Kinematics

A description of the position, velocity, and acceleration of a system of fluid particles.

System

Consists of a specific quantity of fluid that is enclosed within a region of space, apart from the fluid outside this region.

Surrounding

The fluid outside the region that encloses the system.

Laminar Flow

Flow where the lamina or thin layers of fluid are "layered" and are "orderly" and flows smoothly, following smooth streamlines.

Turbulent Flow

Flow where an increase in velocity or decrease in viscosity causes the layers to mix and follow erratic paths, which causes a high rate of mixing within the fluid.

Transitional Flow

Flow that happens between the two regimes in which regions of both laminar and turbulent flow coexist.

Continuity Equation (Principle)

The first basic equation of fluid motion, derived from the law of conservation of mass.

Momentum Equation (Principle)

The second fluid dynamic equation, derived from the 2nd Law of Newton. It states that "a mass acted upon by a force F is given an acceleration that is proportional to and in the same direction as F, and inversely proportional to M," known as the law of acceleration.

Energy Equation (Principle)

The third basic equation of fluid motion, derived from the Law of Conservation of Energy. It is concerned with the mechanics of internal energy changes and the velocity and pressure variations in fluid motion.

Bernoulli's Energy Theorem

In 1738, Daniel Bernoulli demonstrated that in any stream flowing steadily without friction, the total energy contained in a given mass is the same at every point in its path of flow.

Pump

A turbomachine used to transfer liquids from one point to another. It uses mechanical energy to increase the liquid's energy level or entropy, and consequently its pressure. Most pumps work on a basis of a rotational motion, though some use linear motion. The source of energy is usually a fuel engine or an electrical motor.

Turbine

A water machine that absorbs energy from the flow of water and converts it into mechanical work. By connecting an electric generator to the shaft of a turbine, mechanical work is converted into electrical energy.

Shaft

The rod along the central axis of the turbine that rotates around itself with the blades attached to it.

Blades

The parts attached to the turbine shaft that are usually shaped like flat blades or, in some cases, in the form of buckets. The geometry is designed so that the liquid can apply the rotation to the rotor in the same direction as the force applied to the blades.

Darcy-Weisbach Equation

An equation used to calculate the major pressure and head loss due to friction in ducts, pipes, or tubes. It is named after Henry Darcy and Julius Weisbach.

Head Loss

The loss of energy in a fluid due to friction as it flows through a pipe.

Friction Factor

A dimensionless coefficient used in the Darcy-Weisbach equation to account for the roughness of the pipe and the Reynolds number of the flow.

Manning's Equation

One of the most commonly used equations governing Open Channel Flow, introduced by Irish Engineer Robert Manning in 1889 as an alternative to the Chezy Equation. It is an empirical equation that applies to uniform flow in open channels and is a function of the channel velocity, flow area, and channel slope.