Nomenclature

PyFlange names follow the symbols of IEC 61400-6 Annex G (ref. [2]) where possible. This page maps the parameters and properties of the flange segment classes to the symbols of the standard.

Geometry

L-flangeT-flange

Cross-section of an L-flange segment (one bolt). The flange is on the inside of the tower.

Cross-section of a T-flange segment (one bolt pair). For T-flanges, a is measured from the bolt axis to the edge of the flange.

The drawings are schematic: proportions are not to scale, and the fillet radius r, washers and gap are not shown. Z is the shell force acting on the segment, positive in tension.

Flange segment parameters

PyFlange	IEC 61400-6	Unit	Description
a	a	m	L-flange: distance from the inner face of the flange to the bolt axis. T-flange: distance from the flange edge to the bolt axis.
b	b	m	Distance from the bolt axis to the center line of the shell.
s	s	m	Shell (tower wall) thickness.
s_ratio	–	–	Thickness of the lower shell divided by s. The mean thickness is used where the standard requires it.
t	t	m	Flange thickness.
R	R, D/2	m	Outer radius of the shell.
central_angle	–	rad	Angle of the segment: 2π / nbolts (L-flange) or 2π / npairs (T-flange). The segment width at the shell mid-surface is c = central_angle · (R − s/2).
r	r	m	Fillet radius between flange and shell.
Zg	Z1, Zdw	N	Shell force of the segment at rest (dead weight); negative for compression.
Fv	Fp,C (before losses)	N	Bolt preload before settlement and plastic losses.
PPL	ΔFpl / Fp	–	Plastic preload loss, as a fraction of Fv (ref. [2], eq. (24)).
DFT	DFTsbw	m	Coating thickness under the washers, for the settlement loss (ref. [2], eq. (28)).
settlement_factor	–	–	1.0, or 0.5 for tension tightening with re-tightening (ref. [2], 6.7.5.1.2).
Do	dB	m	Bolt hole diameter.
bolt, nut, washer	–	–	Bolt, nut and washer objects (pyflange.bolts). The washer outer diameter, or the nut bearing diameter without washer, is Dw.
gap.height	k, kdesign	m	Gap height.
gap.angle	αgap	rad	Gap angle. The gap length is Lgap = R · αgap.
gap.shape_factor	–	–	Scales the bolt force curve for gaps that are not sinusoidal (1.0 = sinusoidal).
tilt_angle	αincl	rad	Inclination of the flange contact surface (ref. [2], G.2.4).
E, G	E, G	Pa	Elastic and shear modulus of the flange. Poisson's ratio is derived as ν = E/(2G) − 1.
k_shell	kshell,ini	N/m/m	Initial shell stiffness; if None, eq. G.43 is used.

Results and intermediate quantities

PyFlange	IEC 61400-6	Description
bolt_axial_force(Z)	FS(Z)	Bolt axial force.
bolt_bending_moment(Z)	MS(Z)	Bolt bending moment.
bolt_preload	F'p,C	Preload after losses (ref. [2], eq. (23) without the COV term).
shell_force_at_rest, bolt_force_at_rest	Z1, FS,1	Point 1.
shell_force_at_tensile_ULS, bolt_force_at_tensile_ULS	Z2, FS,2	Point 2.
shell_force_at_small_displacement, bolt_force_at_small_displacement	Z3, FS,3	Point 3.
shell_force_at_closed_gap	Zclose	Point 4: shell force that closes the gap.
bolt_moment_at_rest, ..._at_tensile_ULS, ..._at_small_displacement	MS,1, MS,2, MS,3	Bolt moments at the points.
failure_mode(...)	Fu,A, Fu,B, Fu,D, Fu,E	Ultimate shell forces of the failure modes (ref. [2], G.1.2).

The JSON result files (pyflange determ) also report internal quantities, such as a_prime (a'), Z0 (Z₀), DZ_gap (ΔZ_gap), DZ_gap_inclination, DZ_gap_tot, stiffness_correction_factor (α_k), polynomial_initial_slope (χ_ini,mod), gap_k_fac (k_fac), gap_k_shell (k_shell,ini), gap_k_fl (k_fl), gap_stiffness_correction_factor (f_tot), a_star (a*) and I_tg (I_tg).

Fatigue

PyFlange	IEC 61400-6	Description
MarkovMatrix.range, .mean, .cycles	ΔM, Mmean, n	Load bins.
BoltFatigueCurve(diameter, DS_ref, gamma_M)	d, ΔσC, γM	Bolt S-N curve (ref. [2], 6.7.5.4).
BoltFatigueAnalysis.damage	D	Miner's sum.
BoltFatigueAnalysis.allowable_damage	Dallow	Allowable damage (1.0 in ref. [2]).
SMF	SMF	Stress multiplication factor (model uncertainty, ref. [5], 6.5).