hydrodynamics::ScreenMF2022 Struct Reference

#include <ScreenMF2022.h>

Static Public Member Functions
static constexpr bool	InValidSolidityRange (double solidity)

Static Public Attributes
static constexpr bool	acceptsAtPanel = false
	MF2022's coefficients include the panel's own induction.
static constexpr double	kMinValidSolidity = 0.18
	Lower end of the Eq. 10 fit, MF2022 p. 5.
static constexpr double	kMaxValidSolidity = 0.36
	Upper end of the Eq. 10 fit, MF2022 p. 5.

Detailed Description

MF2022 Eq. 10 panel coefficients, with an Eq. 14 (KF2012) angle dependence fitted to them.

MF2022 Eq. 10 (p. 5) gives, for Rn = 2000 and a measured solidity Snm in [0.18, 0.36],

• CD(0°) = 1.782 Sn² + 1.057 Sn − 0.053
• CD(45°) = 1.165 Sn − 0.0919
• CL(45°) = 1.693 Sn² − 0.217 Sn + 0.022

with CD and CL on the area of the netting rectangle and the free-stream speed U (MF2022 Eq. 3, p. 4). Drag is along the flow, lift across it (p. 4).

Angle dependence, θ the angle between U and the panel normal, folded into [0, π/2]:

• C_D(θ) = CD0 ((1 − a3) cos θ + a3 cos 3θ). a3 is fitted exactly, per solidity, so that C_D(45°) is the Eq. 10 value: a3 = (1 − √2 CD45/CD0)/2. It is 0.068 for N19a (Sn = 0.193) and 0.086 for N36a (Sn = 0.364); the plan's 0.07 is the N19a value. C_D is zero at θ = 90°: the form has no skin-friction drag along the panel.
• C_L(θ) = CL45 (b2 sin 2θ + b4 sin 4θ) with b2 = 1 and b4 = 0. MF2022 measured lift at 45° only, so it cannot fix b4.

The force is F = ½ ρ A |U|² (C_D Û + C_L L̂), with L̂ = normalize((Û × n̂) × Û) and n̂ flipped into the half-space of U (KF2012 Eq. 20). With c = Û·n̂ unflipped this is C_L L̂ = 2 CL45 (c n̂ − c² Û), which needs neither a sign nor a division by sin θ.

In-plane twine friction (MARE-0111): when the netting has bar directions, the law adds the tangential skin-friction term of TwineCrossFlow, twine_friction::EvaluateTwineFriction (TwineFriction.h), so it is not zero for flow along the panel. The term is zero at θ = 0 and without bar data; at 45° it raises C_D by about 1 % above Eq. 10 (MF2022's measured drag already contains the friction). drag, lift, momentumDeficit and localCd include it.

Reynolds number: Rn = |U| t / ν (MF2022 Eq. 4, p. 4). The Eq. 10 coefficients do not depend on it; they are the Rn = 2000 fit, so the law does not reproduce the rise of the coefficients at lower Rn that MF2022 report (p. 5). Rn is reported in PanelLoad::reynolds only, and is never clamped.

MF2022 derived the coefficients against the free stream, with the panel's own induction in them, so the law rejects FlowReference::AtPanel (acceptsAtPanel). Evaluate does not check the reference; the setup code does, through Accepts.

Solidity: Eq. 10 was fitted for 0.18 <= Sn <= 0.36. Outside that range the polynomials are extrapolated, and the setup code warns through InValidSolidityRange. CD(45°) is negative below its root Sn = 0.0919/1.165 = 0.0788841 and CD(0°) below its root (−1.057 + √(1.057² + 4·1.782·0.053))/(2·1.782) = 0.0464970; CL(45°) has no real root. Below Sn = 0.1005001 the fitted a3 exceeds 1/4, and C_D(θ) = CD0 cos θ (1 − 4 a3 + 4 a3 cos² θ) is negative over part of 45° < θ < 90°. Evaluate clamps Sn into [kMinSolidity, 0.5], kMinSolidity being the Sn where a3 = 1/4, so the clamp goes only as far as C_D(θ) >= 0 at every θ needs (owner answers to Q5 and QG1, MARE-0130), and sets flag bit 0 when it clamps.

Member Function Documentation

InValidSolidityRange()

static constexpr bool hydrodynamics::ScreenMF2022::InValidSolidityRange ( double  solidity )

inlinestaticconstexpr

Whether a solidity lies in the range MF2022 fitted Eq. 10 for.

Parameters

solidity

The panel solidity, dimensionless.

Returns

True for 0.18 <= solidity <= 0.36.

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The documentation for this struct was generated from the following file:

• webfhsim/reloadrepos/fhsim_marine_elements/src/hydrodynamics/ScreenMF2022.h