Supertype for an object that recieves a noise prediction when combined with an acoustic analogy source; computational equivalent of a microphone.

(obs::AcousticObserver)(t)

Calculate the position of the acoustic observer at time t.

CompactSourceElement(ρ0, c0, r, θ, Δr, Λ, fn, fc, τ)

Construct a source element to be used with the compact form of Farassat's formulation 1A.

Arguments

• ρ0: Ambient air density (kg/m^3)
• c0: Ambient speed of sound (m/s)
• r: radial coordinate of the element in the blade-fixed coordinate system (m)
• θ: angular offest of the element in the blade-fixed coordinate system (rad)
• Δr: length of the element (m)
• Λ: cross-sectional area of the element (m^2)
• fn: normal load per unit span on the fluid (N/m)
• fr: radial load on the fluid (N/m)
• fc: circumferential load on the fluid (N/m)
• τ: source time (s)

CompactSourceElement(rotor::CCBlade.Rotor, section::CCBlade.Section, op::CCBlade.OperatingPoint, out::CCBlade.Outputs, θ, Δr, area_per_chord2, τ)

Construct a source element to be used with the compact form of Farassat's formulation 1A from CCBlade objects.

The source element's position is calculated from section.r, rotor.precone, and the θ argument using

    sθ, cθ = sincos(θ)
    spc, cpc = sincos(precone)
    y0dot = [r*spc, r*cpc*cθ, r*cpc*sθ]

where y0dot is the position of the source element.

Arguments

• rotor::CCBlade.Rotor: CCBlade rotor object, needed for the precone angle.precone.
• section::CCBlade.Section: CCBlade section object, needed for the radial location and chord length of the element.
• op::CCBlade.OperatingPoint: CCBlade operating point, needed for atmospheric properties.
• out::CCBlade.Outputs: CCBlade outputs object, needed for the loading.
• θ: polar coordinate of the element, in radians.
• Δr: length of the element.
• area_per_chord2: cross-sectional area divided by the chord squared of the element.
• τ: source time of the element.

ConstVelocityAcousticObserver(t0, x0, v)

Construct an acoustic observer moving with a constant velocity v, located at x0 at time t0.

Output of the F1A calculation: the acoustic pressure value at time t, broken into monopole component p_m and dipole component p_d.

F1APressureTimeHistory(apth::AbstractArray{<:F1AOutput}, period::AbstractFloat, n::Integer, axis::Integer=1)

Construct an F1APressureTimeHistory struct suitable for containing an acoustic prediction from an array of F1AOutput struct.

The elapsed time and length of the returned F1APressureTimeHistory will be period and n, respectively. axis indicates which axis the apth structs time varies. (period, n, axis are passed to common_obs_time.)

F1APressureTimeHistory([T=Float64,] n, dt, t0)

Construct an F1APressureTimeHistory struct suitable for containing an acoustic prediction of length n, starting at time t0 with time step dt.

StationaryAcousticObserver(x)

Construct an acoustic observer that does not move with position x (m).

(trans::KinematicTransformation)(se::CompactSourceElement)

Transform the position and forces of a source element according to the coordinate system transformation trans.

adv_time(se::CompactSourceElement, obs::AcousticObserver)

Calculate the time an acoustic wave emmited by source se at time se.τ is recieved by observer obs.

combine(apth::AbstractArray{<:F1AOutput}, period::AbstractFloat, n::Integer, axis=1; f_interp=akima)

Combine the acoustic pressures of multiple sources (apth) into a single acoustic pressure time history on a time grid of size n extending over time length period.

combine!(apth_out::F1APressureTimeHistory, apth::AbstractArray{<:F1AOutput}, axis; f_interp=akima)

Combine the acoustic pressures of multiple sources (apth) into a single acoustic pressure time history apth_out.

The input acoustic pressures apth are interpolated onto the time grid returned by time(apth_out). The interpolation is performed by the function f_intep(xpt, ypt, x), where xpt and ytp are the input grid and function values, respectively, and x is the output grid.

common_obs_time(apth::AbstractArray{<:F1AOutput}, period, n, axis=1)

Return a suitable time range for the collection of F1A acoustic pressures in apth.

The time range will begin near the latest start time of the acoustic pressures in apth, and be an AbstractVector (really a StepRangeLen) of size n and of time length period. axis indicates which axis of apth the time for a source varies.

endpoints(se::CompactSourceElement)

Return the Tuple containing the endpoint locations of the compact source element se.

f1a(se::CompactSourceElement, obs::AcousticObserver, t_obs)

Calculate the acoustic pressure emitted by source element se and recieved by observer obs at time t_obs, returning an F1AOutput object.

The correct value for t_obs can be found using adv_time.

f1a(se::CompactSourceElement, obs::AcousticObserver)

Calculate the acoustic pressure emitted by source element se and recieved by observer obs, returning an F1AOutput object.

get_ccblade_dradii(rotor::CCBlade.Rotor, sections::Vector{CCBlade.Section})

Construct and return a Vector of the lengths of each CCBlade section.

get_dradii(radii, Rhub, Rtip)

Compute the spacing between blade elements given the radial locations of the element midpoints in radii and the hub and tip radius in Rhub and Rtip, respectively.

Assume the interfaces between elements are midway between adjacent element's midpoints.

source_elements_ccblade(rotor::CCBlade.Rotor, sections::Vector{CCBlade.Section}, ops::Vector{CCBlade.OperatingPoint}, outputs::Vector{CCBlade.Outputs}, area_per_chord2::Vector{AbstractFloat}, period, num_src_times)

Construct and return an array of CompactSourceElement objects from CCBlade structs.

Arguments

• rotor: CCBlade rotor object.precone).
• sections: Vector of CCBlade section object.
• ops: Vector of CCBlade operating point.
• outputs::Vector of CCBlade output objects.
• area_per_chord2: cross-sectional area divided by the chord squared of the element at each CCBlade.section. Should be a Vector{AbstractFloat}, same length as sections, ops, outputs.
• period: length of the source time over which the returned source elements will evaluated.
• num_src_times: number of source times.

to_paraview_collection(name::AbstractString, ses::AbstractArray{<:CompactSourceElement}, axis::Integer=1)

Construct and write out a ParaView collection data file (.pvd) object for an array of CompactSourceElement with name name.pvd (i.e., the name argument should not contain a file extension).

axis indicates the axis of ses over which the source time for the source elements in ses vary. One VTK PolyData (.vtp) file will be written for each valid index along axis.

Returns a list of filenames written out by WriteVTK.jl.

to_vtp(name::AbstractString, ses::AbstractArray{<:CompactSourceElement})

Construct and return a VTK polygonal (.vtp) data file object for an array of CompactSourceElement with name name.vtp (i.e., the name argument should not contain a file extension).