usually determined by a spectral factorization method (Daubechies, 1992)。
Similar to a discrete Fourier transform method, the discrete wavelet transform requires an extension of the
sponses arising at the point of installation of the meas- uring devices。 By decomposing the vertical bending
data series S0, S1, …, S
2n 1
with a constant interval step
moment time history into low frequency and high fre-
into a periodic data set of
2n1 entries, i。e。 S0, S1, …,
quency components, impact occurrence is easily de- tected, and impact characteristics (i。e。 maximum value, duration, decay behaviour, etc) exhibited by the fluid- structure interaction system and transient force deter- mined。 This information can be used in the generation
S ,S , 。。。, S 。 To achieve a small edge effect
2 1 2 2 1
due to this extension, a mirror extension or cubic spline extension method is usually adopted (Nievergelt, 1999)。
Once the family of wavelets is chosen and the data se-
of empirical formulae to describe transient impact forces acting on ships travelling in severe waves。
ries S0, S1,…, S
2 1
, with a constant interval step, are
extended into a periodic data set of 2n+1, the signals can
be expressed approximately by the scaling function
~ 2n11
are localized both in frequency (by compression in the
form ofx ) and in space (by shifting a distance of N-
Wavelet decomposition works in a similar manner to a
Due to the periodic property of the extended signal
windowed Fourier transform, where the window is sim-
series, the series of coefficients a0 , a1, 。。。,a n11
are also
ply a wave base that is compactly supported within
x
a periodic data set。 Substituting Eq。 3 into Eq。 5, we find that the signal expression is replaced by an equiva- lent combination of 2n slower level scaling functions
( x j) and of 2n slower level wavelet functions
( N 1 j) [N 1, N] 。 However, an advantage
2m
of wavelet transforms over the windowed Fourier trans- form is that the windows vary between the different frequency levels (Daubechies, 1992)。 From Eq。 7,
~changes in the function f (x) at each frequency level are
( x j) , in the form2
determined by the values of c nm
A larger value of c j
at a higher level n-m implies
signal discontinuities or transient oscillations at the location。
Extreme wave load test of a flexible ship model
ABS702 material was used to build a 3。6m self-
propelled flexible model of the S175 container ship。
The thickness of plastic plate for the hull is 2mm, and
for bulkhead, keel and deck girder 4mm。 Twenty-one 极端波浪载荷实验船模的小波分析英文文献和中文翻译(3):http://www.youerw.com/fanyi/lunwen_94996.html