International Core Journal of Engineering 2020-26 | Page 54

III. F INITE ELEMENT MODEL
Fourier decomposition in the form of harmonics, which has
a high practical value in the study. First, the actual
settlement of the tank week is obtained from several
monitoring points arranged around the bottom of the tank. It
is a limited number of discrete data and can only partially
reflect the settlement of the tank foundation. Too many
monitoring points are not economical and practicality.
Therefore, the Fourier decomposition is carried out on the
basis of the measured settlement data of the limited tank
foundation, and the approximate settlement value of any
point on the bottom circle of the tank can be obtained, and
the accuracy is ensured. Secondly, the expression of
settlement harmonic obtained by Fourier decomposition is
very simple and convenient for application in research.
Furthermore, due to the complex influence of the settlement
of the tank on the structure of the storage tank, the influence
of the combined harmonic settlement on the storage tank
can be directly studied after the Fourier decomposition of
the settlement, and the effects of the individual harmonic
settlement on the storage tank can be studied separately, and
the results of the results are linearly stacked. The complete
storage tank structure can be obtained in response to [6] .
The finite element model of a full-scale storage tank is
established by using the structural dimension data of a
100000m 3 large external floating roof tank. The diameter of
the selected tanks is 80m, the storage tank height is 21.8m,
and the limit liquid level is 19.5m. The parameters of plate
steel used for each part of storage tank are shown in Table
III [7] .
T ABLE III P ARAMETERS OF TANK STEEL
Tank plate name
Bottom edge board
Bottom plate
First siding
Second siding
Third floor siding
Fourth floor siding
Fifth siding
Sixth siding
Seventh floor siding
In this paper, 24 horizontal observation points are
regularly arranged on the outside side of the 100000 m3
large external floating roof tank, and settlement detection is
carried out regularly. After the foundation has settled, the
settlement measured at each observation point is shown in
Table I [7] .
Eighth floor siding
Ninth siding
1 2 3 4 5 6
Settlement amount /mm 242 236 238 250 259 287
Measuring point number 7 8 9 10 11 12
425
Settlement amount /mm 306 336 362 392 418 Measuring point number 13 14 15 16 17 18
Settlement amount /mm 430 429 431 434 410 388
Measuring point number 19 20 21 22 23 24
Settlement amount /mm 347 297 268 249 249 237
20 - 490
12
32
27 -
2420
2420 235
490
490
21.5 2420 490
18.5 2420 490
15
12 2420
2420 490
490
12 2420 490
12 2380 345
12 2380 235
The first model: the tank and its accessories are
simulated by the shell element SHELL181, the foundation
soil is simulated by the solid element SOLID185, and the
tank bottom and the foundation soil are connected by the
common node.
T ABLE II D ATA OF HARMONIC SETTLEMENT
Settlement
amplitude /mm
330
106.1
-9.633
10.22
5.486
0.4133
-1.39
1.151
1.378
Yield
strength/MPa
The interaction between the tank accessories and the
foundation soil and the bottom of the tank will have a
complex effect on the structural response of the storage tank
under the condition of foundation settlement. Therefore,
three finite element models of full size storage tanks are
established in different ways to compare and analyze the
three models as described below.
The Fourier decomposition method is used to deal with
the measured settlement data in the table, and the
superposition combination of the first 8 order harmonic
settlement is taken as the measured settlement function,
which is used for the finite element modeling analysis. The
parameters of the harmonic settlement of each order are
shown in Table II.
Harmonic
order
0
1
2
3
4
5
6
7
8
Height
/mm
The density of plate steel used for storage tanks is
ρ=7850kg/m 3 , the modulus of elasticity is E 1 =2.06×10 11 Pa,
and Poisson's ratio is υ 1 =0.3. The elastic modulus of storage
tank foundation is E 2 =1.6h10 10 Pa, Poisson's ratio is υ 2 =0.3.
According to the above parameters, the finite element
analysis software ANSYS is used to take into account the
influence of the attachments of the anti-wind ring, the
reinforced ring and the corner steel, and the interaction
between the foundation soil and the bottom of the tank. The
finite element model of the tank is established, and the
operation of the storage tank under the foundation
settlement is simulated.
T ABLE I S ETTLEMENT DATA OF MEASURING POINTS
Measuring point number Thickness
/mm
Initial phase angle /rad
-
4.557
3.650
1.344
3.128
0.369
1.708
0.556
1.686
Second models: the storage tank and its accessories are
simulated by the solid element SOLID185, and the
foundation soil is simulated by the entity unit SOLID185,
and the tank bottom and the foundation soil are connected
by the common node.
Third models: the storage tank and its accessories are
simulated by the shell element SHELL181. The foundation
soil is simulated by the solid element SOLID185, and the
contact unit is set up between the bottom of the tank and the
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