Passive, Semi-Active and Active Vibration Control Systems for ...

Passive, Semi-Active and Active
Vibration Control Systems for Offshore
Platform Steel Jacket Structures
OU Jinping
WU Bin XIAO Yiqing DUAN Zhongdong et al
Harbin Institute of Technology
P.R. China

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Background

�More than 5000 steel offshore
structures in the world
100 in China
�Main dynamic excitations:
wind, wave, ice and earthquake
�Vibration amplitude reduced 15%
the life of structure enhance double

�mail control loads in Bohai Ocean of
China
Ice force and Earthquake
Seismic fortified intensity:8 degree
�2 platforms collapsed by ice
in China (1969,1977)
2 collapsed in USA (1964)

•It is urgent to have an effective scheme to
control ice-induced and earthquake-induced
vibration of offshore structures
for ocean oil development
Some effective control schemes
for buildings may not work for
offshore structures since
underwater and corrosion

I. Damping brace control
systems(DBS)
II. Passive and semi-active
damping isolation systems(DIS)
III. AMD control systems

JZ20-2MUQ
1:10 Model
Placement of
Damper
Õ³ ÖÍ º ÄÄÜ
Æ÷¼° б³ Å

• Passive Vibration Control
with Viscous or Visoelastic Dampers

1.1 Design and Tests of Viscous Dampers
1) Configurations of viscous dampers
(a) With a gap
(b) With holes

2) Tests of scale dampers with a gap
i) Damping media:
¼ôÓ¦Á¦(Pa)
Fluid with
power law
20
16
12
8
4
0
0 1 2 3
¼ôÓ¦±äËÙÂÊ(1/s)
Silicon oil 7000
τ = kγ&
m
Tested curves of the media
under low shear velocity

Configuration Parameters of dampers
Damper 1
D = 40 mm 0 39.
2 = D mm
l = 39 mm d = 20 mm
Damper 2
D = 80 mm 0 79 = D mm
l = 40 mm d = 45 mm

×èÄáÁ¦(KN)
6
3
0
-3
-6
Tested damping forces
•Damper 1
-6 -4 -2 0 2 4 6
λÒÆ(mm)
×èÄáÁ¦(KN)
9
6
3
0
-3
-6
-9
-6 -4 -2 0 2 4 6
λÒÆ(mm)
Case a3 Case a4

×èÄáÁ¦(KN)
12
8
4
0
-4
-8
•Damper 2
-12
-6 -4 -2 0 2 4 6
λÒÆ(mm)
×èÄáÁ¦(KN)
-12 -8 -4 0 4 8 12
Case b3 Case b4
6
3
0
-3
-6
λÒÆ(mm)

2) Damping
media:
Bingham
fluid
Configuration parameters of damper
D =100 mm
d =40 mm
D0 =96 mm
l =40 mm
h =2 mm
Bingham fluid
τ τ = η & γ
− 0
p

×èÄáÁ¦(kN)
×èÄáÁ¦(kN)
Tested damping force
6
4
2
0
-2
-4
-6
-10 -5 0 5 10
λÒÆ(mm)
f=0.5Hz, A=10mm
6
4
2
0
-2
-4
-6
-10 -5 0 5 10
λÒÆ(mm)
f=1Hz, A=10mm
×èÄáÁ¦(kN)
×èÄáÁ¦(kN)
6
4
2
0
-2
-4
-6
-6 -4 -2 0 2 4 6
6
4
2
0
-2
-4
-6
λÒÆ(mm)
f=1Hz, A=5mm
-6 -4 -2 0 2 4 6
λÒÆ(mm)
f=2Hz, A=5mm

3) Tests of full scale damper with Bingham fluid
The configuration of damper
Configuration parameters of damper
D =200 mm
d =100 mm
D0 =196 mm
l =200 mm
h =2 mm

×èÄáÁ¦(kN)
400
300
200
100
0
-100
-200
-300
-400
Tested results f=1 Hz
-9 -6 -3 0 3 6 9
λÒÆ(mm)
A=8.71mm
×èÄáÁ¦(kN)
400
300
200
100
0
-100
-200
-300
-400
-12 -8 -4 0 4 8 12
λÒÆ(mm)
A=12.80mm

1.3 The Tested Responses of Offshore Structures
with / without Viscous Dampers El Centro
Maximum Displacement
and Maximum Acceleration
Reduction ratio: 42%

2. Smart Vibration Control
with MR Dampers

Type A (carrier fluid’s viscosity is 70 centistoke)
Yi el d st r ess£¨ kPa£©
40
35
30
25
20
15
10
5
0
1. Magnetorheological Fluid
and Smart Damper
1) Properties of MR fluid
0 0.1 0.2 0.3 0.4
Magnet i c i nduct i on£¨ T£©

Type B (carrier fluid’s viscosity is 2000
centistoke)
Yi el d st r ess£¨ kPa£©
40
35
30
25
20
15
10
5
0
0 0.1 0.2 0.3 0.4
Magnet i c i nduct i on£¨ T£©

40
35
30
25
20
15
10
5
0
0 0. 1 0. 2 0. 3 0. 4
Yi el d st r ess£¨ kPa£© •Property comparison of MR fluid
Magnet i c i nduct i on£¨ T£©
Type A ( OU,et al, 1998) Lord Ltd. (1995)

2) MR damper
Table 4 Parameters for MR damper
h(mm) D(mm) d(mm) L(mm)
2 100 40 40
The schematic

3) Damping properties
a Amplitude=1.5cm
frequency=0.25Hz
b Amplitude=1.5cm
frequency=0.5Hz

a Amplitude=1.5cm
frequency=0.25Hz
b Amplitude=1.5cm
frequency=0.5Hz

2. Numerical Analysis of Smart Vibration
Control of JZ20-2MUQ Platform Structures
1) Passive-Off and Passive-On
Passive -Off
Under ice force of 1 year return Under El Centro earthquake (190 gal)

2) Fuzzy Control Rules for Offshore Structure
NB NM NS ZE PS PM PB
NB PB PB NS NM NB NB NB
NM PB PB ZE NS NM NB NB
NS PB PB PS NS NS NB NB
ZE PB PB PS ZE NS NB NB
PS PB PB PS PS NS NB NB
PM PB PB PM PS ZE NB NB
PB PB PB PB PM PS NB NB
⎧Fmin
F ⋅ FMR
≤ 0 or F < Fmin
⎪
Fcoul = ⎨Fmax
F ⋅ FMR
> 0 and F > Fmax
⎪
⎩F
ÆäËûÇé¿ö

3) Numerical results
�El-Centro earthquake

• Damping Force under Fuzzy Control Rules
Damping force versus displacement Damping force versus velocity

• Displacement response under Ice Force
Under the crushed ice force of 1 year return

Under the bended ice force of 1 year return

�Control effectiveness
• Under earthquke
– 23 30
• Under ice force
– 33 47 for light ice
– 30 50 for heavy ice

3. Shaking Table Tests of Smart Vibration
Control of Scale Model Platform
Structures
Control strategy
–PassiveOff –PassiveOn – Semi-active fuzzy control

•Control rules
¿ØÖÆÐźÅ(V)
4
2
0
15
10
ËÙÈ
5
0
0
5
λ Ò Æ
10
15

Tested Results
� Passive Off Passive On Semi-active
fuzzy control have the same results:
0.6 - 37

The reason:
Damping force versus displacement and
velocity
×èÄáÁ¦£ ¨ Ö£ ©
1.5
1
0.5
¼ÓÔØËÙ È 1cm/s
0 A
2 A
0
0 1 2 3 4 5
Î »ÒÆ£¨cm£ ©

II. Passive and semi-active
damping isolation systems(DIS)

Passive and semi-active damping
isolation systems(DIS)
¸ô Õð×èÄá Æ÷

Damping isolation mechanism
� Traditional isolation increase or reduce the
fundamental period and avoid the predominant
period of excitation, and then suppress the
vibration of structure.
� Damping isolation lay a flexible layer to make
the dampers dissipate vibration energy as much
as possible, and then suppress the vibration of
structure

� The local damping coefficient can be
transferred into the damping ratio of
whole structure, then suppress the
vibration of structure
m2
m1
MX&& + CX&+ KX = F() t
m >>
2
m
⎡ c1 +c2 -c2 ⎢
⎣ -c2 c2 1
⎤
⎥
⎦
c ξ
2

Relationship of damping coefficient c 2 in isolation
layer and damping ratio ξ 1 of structure
ξ 1
0. 5
0. 4
0. 3
0. 2
0. 1
k 2 =0. 3k 1
k 2 =0. 5k 1
0. 0
1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
c 2 (kN s/m)

• Control Effectiveness with viscous dampers
(Numerical results)
• Under ice force
Relative displacement of isolated layer: 30mm
Reduction ratio:
Displacement 30%
Acceleration 50%
2. Under earthquake (190gal)
Relative displacement of isolated layer: 50mm
Reduction ratio:
Displacement 35%
Acceleration 30%

•Control Effectiveness with MR dampers
(Numerical results)
Under Taft earthquake (190 gal)
Case Relative
displacement
of damping
layer (cm)
Without
control
Max. displ. of
jacket
structure (cm)
Max. accel. of
jacket
structure
(cm/s 2 )
6.63 198.90
Passive off 3.32 1.11 64.20
Passive on 1.72 1.32 129.98
Semi-active 1.68 1.27 105.28

III. AMD control systems

3.1 Numerical Analysis
• Main Parameters of AMD Systems
for the Vibration Control of JZ20-2MUQ
Platform In Baihai Ocean
Mass: 100 t mass ratio: 4%
Maximum control force: 120 t
Maximum displacement of the mass :0.8 m

EL+39.750
EL+16.5000
EL-23.500
AMD Without
control
� Under earthquake
– Elcentro with Max
Acce. 220gal
� Control effectiveness
– Disp. 46.8%
– Acce. 31.4%

EL+39.750
EL+16.5000
EL-23.500
AMD Without
control
• Under ice force
– Crushed ice force
40cm
• Control
effectiveness
– Disp. 33%
–Acce. 44%

3.2 Tests of 1:10 Model with AMD
Control algorithm
� LQG with acceleration feedback
� Controller
� Single input acceleration of deck
� Single output voltage of actuator

Acceleration gal
Displacement mm
Under Taft Earthquake (190 gal)
5
0
-5
0 2 4 6 8 10 12
500
0
-500
0 2 4 6 8 10 12
(sec)

•Control effectiveness
(Tested results)
� Input earthquake
� El Centro 300gal Taft 250gal
Tianjing 120gal
� Reduction ratio of disp. 17 47 45
� Reduction ratio of accel. -6 52 38
� Actuator
� Max disp. 13.8mm 6.1mm 7.9mm
� Max. force 1.93 kN 1.20kN 1.22kN

Conclusions
Recommended control schemes
for offshore structures:
• Passive and semi-active damping
isolation systems(DIS)
•AMD control systems