Design Wind Power Turbine - Hybrid Anisotropic Materials for Wind Power Turbine Blades - page 47

The.leading.and.trailing.edges.that.are.unsupported.by.inner.webs.include.
a.carbon.iber,.which.stiffness.is.two.times.more.than.glass.ibers.

2.10.2 Stiffness Calculation

The.stiffness.of.the.composite.is.controlled.and.calculated.according.to: 5

. E c. =.h.V f .E f. +.V m E m . (2.49)

where
E c. is.the.stiffness.of.composite
..h.is.the.orientation.factor.for.the.ibers
V f. is.the.iber.volume.fraction
E f. is.a.modulus.of.elasticity.for.iber
V m. is.the.matrix.volume.fraction
E m. is.a.modulus.of.elasticity.for.matrix

The.orientation.factor.is.equal.to.1.for.aligned.parallel.ibers.loaded.along.
the.iber.direction..For.the.randomly.oriented.iber.assembly,.the.orientation.
factor.equals.one-third. 5 .The.ibers.are.normally.the.dominant.contributor.to.
the.composite.properties..In.case.of.wind.turbine.blade,.stiffness.calculated.
as.combination.shell.stiffness.and.core.stiffness:

. E c. =.E sh .+.E cor . (2.50)

We.reduce.thickness.of.the.shell.by.increasing.the.stiffness.of.core.material.

2.10.3 Skin Thickness Calculation of Blades

Skin. thickness. of. power. turbine. blades. can. be. predicted. if. we. know. the.
stresses.acting.under.bending.moments.Mz,.My,.and.Mx.are.rotating—tor-
sion.moment.relative.to.axis.x.
Varying.the.angle.of.twist.(+15 °. +45 ° /-15 ° .-45 ° ),.blades.create.some.problems..
However,. relations. between. normal. and. shear. stresses. can. be. selected. as.
boundary. conditions. and. strength. criteria. can. be. designed. as. polynomial.
forth.order,.such.as:

2

- ( (

σ σ ) + σ σ

. (2.51)

ik ik ik ik 1/2

a σ σ ) = 0

.

ikem ik ik

2

where:
δ ik .=.0.if.i¹k

This.criterion.can.be.used.separately.for.tensile.and.compressive.loads. 21