Daisy Chain - A method of propagating signals along a bus in which the devices are connected in series and the signal
passed from one device to the next.
Daltons Law - The total pressure of a mixture of gases is equal to the sum of the partial pressures of the constituent gases.
Damping - The reduction of response at the resonant frequency through the use of a damping media such as oil.
Damping Pad - Material applied to add damping to another material to reduce structural vibrations. This layer may be
constrained or unconstrained.
Darcy's Law - An empirical equation developed to compute the quantity of water flowing through an aquifer.
dB - Decibel, unit for measurement of sound intensity
DC - Direct Current. An electric current flowing in one direction only and substantially constant in value.
Dead Centre - A centre that does not rotate.
Deasphalting - Process of removing asphaltic materials from reduced crude using liquid propane to dissolve nonasphaltic
Deburr - To remove sharp edges.
Decalescence - A decrease in temperature that occurs while heating metal through a range in which change in structure
Decarburization - The loss of carbon from the surface of a ferrous alloy.
Decibel - The human ear responds logarithmically and it is convenient to deal in logarithmic units in audio systems.
Deep Etching - Severe etching of a metallic surface for examination.
Defect Structure - Relating to the kinds and concentrations of vacancies and interstitials in a ceramic compound.
Deflection - The distance a beam or structure deforms under loading
Degas - Removing air from a liquid, usually by ultrasonic or vacuum methods.
Degrees of Freedom - The number of degrees-of-freedom of a mechanical system is equal to the minimum number of
independent co-ordinates required to define completely the positions of all parts of the system at any instant of time.
Dehydrator - A separator that removes water from the system fluid.
Deionization Potential - The potential at which ionization of the gas within a gas-filled tube ceases and conduction stops
Delamination - Occurs when a composite material formed from a number of layers is stressed, thermally or otherwise, such
that the layers begin to separate.
Delayed Coking - A coking process that raises the temperature of the heavy oil residue to nearly 1000° and leaves the oil in
a large drum to gradually crack the large molecules into light oil components (see Coking).
Delimiter - A character used to indicate the beginning and end of a character string
Delta Iron - An allotropic form of iron stable above 1400°C.
Demodulator - A circuit used in servo-systems to convert an AC signal to a DC signal
Dendrite - A crystal that has a tree-like branching pattern.
Denitrification - The anoxic biological conversion of nitrate to nitrogen gas. It occurs naturally in surface waters low in
oxygen, and it can be engineered in wastewater treatment systems.
Density - The mass or quantity of a substance per unit volume.
Deoxygenation - The consumption of oxygen by the different aquatic organisms as they oxidized materials in the aquatic
Depth Gauge - A tool used in measuring the depth of holes or recesses.
Depth Micrometer - A micrometer in which the spindle projects through a flat accurately machined bar.
Design-Build - A system of contracting under which one entity performs both architecture/engineering and construction under
one single contract.
Design Limit - The operational limit of a product, beyond which it not required to function properly.
Dewatering - Process of removing excess moisture from biosolids
Dewaxing - Removal of wax from petroleum products by solvent absorption, chilling and filtering.
Dial Indicator Gauge - Used to measure shaft runout or deviation from a nominal position.
Diesel Engine - An internal-combustion engine in which the fuel is injected into the cylinder near the end of the compression
stroke and is ignited by the heat of the compressed air in the cylinder.
Diesel Particulate Filter - A device which physically captures diesel particulates preventing their discharge from the tailpipe.
Diffusion - The scattering of reflected light waves from an object, such as white paper
Digitize - To convert an analog signal into a digital signal carrying equivalent information.
DIN - Deutsche Industrial Norm, a set of technical, scientific and dimensional standards developed in Germany.
Diode - A two-terminal device that rectifies signals (passes current in only one direction)
Dip Brazing - A brazing process in which bonding is produced by heating in a molten chemical or metal bath.
Dipstick - The metal rod that passes into the oil sump it is used to determine the quantity of oil in the engine.
Direct Quenching - Quenching carburized parts directly from the carburizing operation.
Distributed Load - An external force which acts over a region of length, surface, or area: essentially any external force which
is not a concentrated force.
DOCSIS - Data Over Cable Service Interface Specification: A standard for delivering data over cable TV systems, typically for
subscriber Internet access services
Dividing Head - A machine tool holding fixture which positions the work for accurately space holes, slots, flutes and gear
teeth and for making geometric shapes
Doppler Effect - The apparent change in frequency or pitch when a sound source moves either toward or away from a
listener. In radar, the change in frequency of a received signal caused by the relative motion between the radar and the
Doppler Sonar - An acoustic instrument that measures the change in the acoustic frequency of the scattered sound or echo
from that of the transmitted pulse. The magnitude and direction of the shift in frequency is related to the relative motion of
the sensor and the scatterer.
Double Glazing - Two layers of glazing used to improve thermal and acoustic radiation.
Double Row Bearing - A bearing having two rows of rolling elements.
Double-Ended Spanner - A tool which has a hexagon ring at each end.
Dovetail Saw - A saw designed for cutting dovetail joints and other wood joints.
Dowel - A pin fitted or keyed in two adjacent parts to accurately align the parts when assembling them.
Down Feed - A seldom used method of feeding work into milling cutters.
Downforce - The opposite of aerodynamic lift, sometimes referred to as negative lift. The force caused by the air over the
wings to push the car into the ground, increasing grip and cornering speeds.
Downstream (oil industry) - The refining or process of crude oil into finished fuel products.
Drag - Resistance of a vehicle body to motion through the air. A smooth surface has less drag than a rough one.
Drag Coefficient - A dimensionless value that allows the comparison of drag incurred by different sized and different shaped
Drain Plug Spanner - A tool for removing and tightening drain plugs.
Drawing - A deformation technique used to fabricate metal wire and tubing.
Dressing - The act of removing the glaze and dulled abrasives from the face of a grinding wheel to make it clean and sharp.
Drill Bits - Normally made of hardened or high speed steel with two cutting edges on the conical end with two helical flutes
that act to move material away from the cutting edges.
Drill Chuck - A device used to grip drills and attach them to a rotating spindle.
Drill Gauge - A flat steel plate drilled with holes of various sizes, each marked with the correct size or number into which small
twist drills may be fitted to determine the size of their diameters.
Drill Jig - A jig that holds parts of a structure and by means of bushings, guides the drill so that the holes are properly located.
Drill Press - An upright power-driven machine for drilling holes in metal, wood, or other material.
Drive Fit - One of several classes of fits in which parts are assembled by pressing or forcing one part into another.
Dry Friction Damping - Coulomb damping is the dissipation of energy that occurs when a particle in a vibrating system is
resisted by a force whose magnitude is constant independent of displacement and velocity, and whose direction is opposite
to the direction of the velocity of the particle.
Dry Sump - A lubrication system in which the oil is pumped into the engine's sump under pressure and then pumped out
Dual Voting - Concept where two independent inputs are required before action, usually machine shutdown, is taken.
Duct - A pipe or closed conduit made of sheet metal, fibreglass board, or other suitable material used for conducting air to
and from an air handling unit.
Duct Acoustics - Ducts with acoustic waves propagating through them exist in many forms.
Ductile Fracture - A mode of fracture that is attended by extensive gross plastic deformation.
Ductility - A measure of a material′s ability to undergo appreciable plastic deformation before fracture.
Dwell - In an engine, the time allowed for current to build in the primary circuit of the ignition coil for each spark generation.
Dye Penetrant - Penetrant with dye added to make it more readily visible under normal lighting conditions.
Dynamic Equilibrium - Equilibrium which includes inertial forces.
Dynamic Friction - Resistance to relative movement of two bodies that are already in motion.
Dynamic Modulus - Ratio of stress to strain under vibratory conditions.
Dynamic viscosity - That molecular property of a fluid which enables it to support tangential stresses for a finite time and thus
to resist deformation.
Dynamometer - A device for determining the power of an engine.
Engineering Glossary, Engineering Dictionary D
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