Wave amplitude

   Triangle (ETS) height

   Absorption coefficient

   Particle acceleration

   Width

   Threshold or given value of the surface elevation

   Threshold or given value of a wave crest height

   Triangle (ETS) base

   Wave propagation speed

   Height of a wave crest

   Energy-flux/energy factor

   Diffraction coefficient

   Refraction coefficient

   Shoaling coefficient

   Drag coefficient

   Inertia coefficient

   Group velocity

   Propagation speed of the reflected wave energy

   Water depth

   Diameter

   Directional distribution

   Persistence above a fixed threshold

   Mean wave energy per unit surface

   Dimensionless frequency spectrum

   Frequency spectrum (omnidirectional spectrum)

   Electrical power

   Frequency

   General function

   General function

   Function in the diffraction theory

   Force per unit length

   Force, or force per unit length

   Phase-speed reduction factor

   Acceleration due to gravity

   Function in the diffraction theory

   Threshold or given value of the significant wave height

   Energy per unit weight at various locations of a converter

   Wave height

   Significant wave height

   Significant wave height on deep water

   Wave number

   Exponent in the gas law

   Constant

   Head loss factor

   Parameters regression base height of ETS

   Parameters distribution wave heights in a sea state

   Parameter relationship between T_p and H_s for wind seas

   Keleugan–Carpenter number

   Normalizing factor directional distribution

   Lifetime of a structure

   Wavelength

   Wavelength on deep water

   Wavelength relevant to wave period T_p

   Wavelength, on deep water, relevant to wave period T_p

   jth spectral moment (with angular frequencies)

   Variance of the surface elevation of a sea state

   Determinant of a covariance matrix

   Moment of a force

   Air mass

   i,j cofactor of a covariance matrix

   Width parameter of the directional distribution at the peak frequency

   Pressure

   Probability density function

   Probability of exceedance

   Probability

   Absolute pressure air

   Flow rate per unit length

   Polar coordinate

   Radius

   Return period

   Resonance coefficient

   Local propagation axis

   Directional spectrum

   Time

   Special time instant

   Wave period

   Time lag

   Lag of the absolute minimum of the autocovariance

   Peak period

   Period of a very large wave

   Mean wave period

   Dummy variable

   Current velocity

   Wind speed at an elevation of 10 m above the mean sea surface

   Velocity in the vertical duct of a U-OWC

   Parameter of the Weibull 2-parameter distribution

   Particle velocity

   Dummy variable

   Dimensionless frequency (=ω/ω_p)

   Parameter of the Weibull 2-parameter distribution

   Dummy variable

   Horizontal coordinate axis

   Fixed value of x

   Space lag

   Horizontal coordinate axis

   Fixed value of y

   Space lag

   Fetch

   Vertical coordinate axis with origin at the still water level

   Angle between x-axis and direction of wave advance

   Quotient between wave height and RMS surface elevation of a sea state

   Energy scale parameter JONSWAP spectrum (α in the original paper)

   Dimensionless wave height with a universal distribution

   Polar coordinate

   Ratio between the wave height at a U-OWC and the wave height at a vertical breakwater

   Specific weight of water

   Wave pressure

   Angular frequency resolution

   Phase angle

   Vertical coordinate axis with origin at the seabed

   Surface elevation (assumed to have a zero mean)

   Angle between the y-axis and the direction of wave advance

   Angle of the dominant direction

   Sea bottom slope

   Chinematic viscosity

   Dummy variable whose domain is (0,1)

   Ratio between crest height and wave height

   Height of the air pocket of a U-OWC

   Water density

   RMS surface elevation of a sea state

   Time lag between crest and trough

   Ratio between a time lag T and peak period T_p

   Time lag covariance pressure-discharge in a converter

   Velocity potential

   Cross-covariance of surface elevation and velocity potential

   Mean energy flux per unit length

   Ratio between c_R and c_G

   Shape parameter JONSWAP spectrum (γ in the original paper)

   Shape parameter JONSWAP spectrum (σ in the original paper)

   Autocovariance function

   Narrow bandedness parameter (= absolute value of the ratio between the minimum and the maximum of the autocovariance function)

   Cross-covariance of surface elevation

   Cross-correlation of surface elevation

   Angular frequency

   Dominant angular frequency of the spectrum

   Time average of function f(t)

   Time derivative of function f(t)