Where does roughness collide?

In open-channel and pipe hydraulics, roughness describes how strongly the wetted boundary resists the fluid moving over it, lumping the drag of grains, ripples, and irregularities into a single resistance that sets how fast water flows for a given slope and depth. Chow's Open-Channel Hydraulics presents this through coefficients such as Manning's n and the equivalent sand-grain roughness height, calibrated for surfaces from smooth concrete to weedy natural streams. The referent is a flow-resistance parameter of a boundary, estimated from the channel material and condition, and distinct from the ride quality of a road or the finish of a machined part.[1]

Unit

A resistance coefficient such as Manning's n or an equivalent roughness height (mm)

Recovery means

Not applicable

Measured by

Back-calculated from measured discharge, slope, and geometry, or estimated from tables keyed to boundary material and channel condition

In manufacturing and surface metrology, roughness is the fine-scale, short-wavelength irregularity of a solid surface left by the machining or finishing process, separated from longer-wavelength waviness and form. Thomas's Rough Surfaces sets out how such surfaces are measured by stylus and optical profilometry and summarised by parameters such as the arithmetic mean deviation Ra and the root-mean-square Rq. The referent is the texture of a part's surface at the micrometre scale, which governs friction, sealing, wear, and fatigue of components, and is a different thing from the resistance a channel offers to flow or the unevenness of a road felt by a vehicle.[2]

Unit

Height-deviation parameters such as Ra or Rq, in micrometres

Recovery means

Not applicable

Measured by

Quantified from a measured surface profile by stylus or optical instruments, reporting amplitude parameters like Ra and Rq over a defined sampling length

In pavement engineering, roughness is the longitudinal unevenness of the road profile that a travelling vehicle experiences as vertical motion, and it is the leading indicator of ride quality and of the pavement's condition over its life. Múčka's International Roughness Index specifications around the world reviews how agencies quantify it through the International Roughness Index (IRI), a quarter-car model that accumulates simulated suspension travel per unit length from a measured elevation profile. The referent is the ride-relevant unevenness of a road surface at wavelengths of metres, not the micrometre finish of a part nor the flow resistance of a channel.[3]

Unit

International Roughness Index, in m/km (or mm/m) of accumulated suspension travel

Recovery means

Roughness is reduced by resurfacing or overlay; pavements do not smooth themselves, and roughness grows as distress accumulates

Measured by

Computed as IRI by running a standardised quarter-car model over a measured longitudinal profile collected by a profilometer or inertial profiler

In psychoacoustics, roughness refers to the harshness heard when partials of two tones fall within a critical band and beat, the basis of sensory dissonance. This meaning comes from Plomp (1965) in The Journal of the Acoustical Society of America.[4]

Unit

Recovery means

Measured by