OMAE2014 - 23661 Experimental Assessment of The Behaviour Of A Pipe Vibration Damper Underwater

1 Copyright © 2014 by ASME
Proceedings of the ASME 2014 33
rd
International Conference on Ocean, Offshore and Arctic Engineering
OMAE 2014
June 8-13, 2014, San Francisco, California, USA
23661
EXPERIMENTAL ASSESSMENT OF THE BEHAVIOUR OF A
PIPE VIBRATION DAMPER UNDERWATER
Sergio N. Bordalo
U. of Campinas
Campinas, São Paulo, Brazil
Celso K. Morooka
U. of Campinas
Luan G. Tochetto
U. of Campinas
Renato Pavanello
U. of Campinas
Gangbing Song
U. Houston
Houston, Texas, USA
John C. Bartos
Cameron
Houston, Texas, USA
ABSTRACT
Submarine petroleum pipelines, risers and jumpers suffer
static and dynamic loads due to sea currents and waves, due to
the displacements of the floating production units and due to the
internal flow, among other causes. Mitigating the oscillations
caused by such excitations is critical to the reliability and
fatigue of those underwater bodies. The Pounding Tuned Mass
Damper (PTMD) is one device that may be employed to absorb
and dissipate vibrations. These devices have long been used for
mechanical systems operating in the atmosphere, but are new
for underwater applications. This paper presents a study of the
behaviour of a PTMD working underwater.
A small scale laboratory apparatus was built to assess the
effect of the absorber on the oscillation of a pipe submerged in
a water tank. The PTMD was attached to a test pipe section
mounted on an elastic suspension harness. The PTMD model is
a lumped mass-spring attachment similar to a tuned mass
dumper (TMD) suppressor, but with the addition of a pounding
layer, which limits the motion of the PTMD mass, dissipating
the energy of the oscillating pipe through the impact of the
PTMD mass against that layer. Free and forced oscillation
experiments were executed in air and in water, with and without
the oscillation absorber, to determine the effectiveness of the
PTMD. The tests were run on a range of excitation frequencies
and the amplification factors were obtained for each case.
The data show a remarkable influence of the surrounding
media on the dynamics of the pipe-absorber system, therefore
the interaction with the water must be taken into consideration
in the design of the system. Although the results are only a
preliminary step on the development of a device applicable to
an actual petroleum submarine pipeline, it was observed that the
PTMD does indeed suppress the vibrations, but it must be
properly configured to achieve an optimum performance. The
data gathered from this work will also be useful in the
improvement of a numerical model of the pipe-PTMD system
for use in a computer simulator.
INTRODUCTION
Petroleum production in Brazil takes place under very
deep waters for most of the larger offshore fields in that
country. Therefore, the forces on submarine structures,
pipelines, risers and long free spam lines are considerable.
These bodies suffer different kind of forces – from sea currents,
from the movement of the floating production or drilling vessel
etc; incurring in vibration of the pipelines, depending on their
geometry. One of the major concerns of the petroleum industry
is the life time of these submarine systems subjected to all of
the existing loads. Consequently, devices capable of minimizing
the oscillations of the submarine pipelines have been studied for
a long time in the petroleum industry.
Some of those devices modify the flow surrounding the
pipe, altering its behavior and diminishing the amplitude of the
oscillations (Bearman, 1984; Blevins, 2001; Williamsom et al,
2004; Ding et al, 2004). Another method is the use of dynamic
vibration absorbers. The TMD (tuned mass damper) is a well
known absorber (Den Hartog, 1984), which consists of a
secondary mass-spring combination added to the primary mass-
spring body to prevent this last one from vibrating. The stiffness
and mass of the absorber are tuned to minimize the primary
body displacements, when within the range of the natural
frequency of the primary body, guaranteeing the integrity of the
overall system.
The PTMD (Pounding Tuned Mass Damper), on the
other hand, consists of a TMD absorber, but with the addition of
an impact viscoelastic layer, limiting the motion of the
secondary body. As the energy of the primary body is
transferred to the secondary one, it is dissipated efficiently as
the absorber strikes the viscoelastic layer (Ekwaro-Osire et al,
2006; Mikhlin and Reshetnikova, 2006; Karayannis et al, 2008;

and Polukoshko et al, 2010). Figure 1 illustrates the TMD and
PTMD systems.
The focus of the present project is the dynamic response
analysis of a submarine jumper with the attachment of a PTMD,
in air and underwater. A scaled down pipe model was used in a
water tank and a small scale PTMD was attached to the pipe.
The test body was excited in a range of frequencies while its
motion was captured by a video camera.
Figure 1 –TMD absorber (left) and the PTMD (right).
EXPERIMENTAL SETUP
The present work was conducted in a small scale water
tank (Figure 2) at UNICAMP. A prototype submarine jumper is
the base case for the current work. Its dynamic characteristics,
stiffness, mass and geometry were used for the idealization of
the scaled down model (Bordalo, 2013). Figure 3 depicts the
geometric characteristics of the prototype.
Figure 2 - Water tank used in the project.
The small scale of the test model and how it may affect
the representation of the real scale system played an important
role in the design of the apparatus. The smaller the scale, the
most difficult is the representation of the interplay of different
phenomena, such as elasticity, dynamics, and hydrodynamic
forces. Ideally, all the relevant dimensionless parameters should
be observed in order to guarantee full similarity between the
small model and the field prototype. However, this proves to be
nearly unattainable and impractical, so some workable
compromise was sought.
Figure 3 - Prototype jumper geometric characteristics.
As a result of the previous considerations, a cylindrical
pipe section, at half scale, with adjusted mass and springs, was
built to simulate the stiffness and dynamic behavior of the
prototype jumper, as shown in Figure 4.
Figure 4 - Representative scheme of the apparatus.
The apparatus consists of a metallic structure supporting
the springs, which are responsible for providing the horizontal
and vertical translation of the test body. The springs are
positioned above the water level to prevent interference with the
behavior of the test pipe inside the water (Figure 5.a).
The mass of the cylindrical pipe section and the
equivalent stiffness of the springs were adjusted by a computer
simulation, regarding the dynamic behavior of the real
prototype jumper in both vertical and horizontal directions.
The test body is a stainless steel pipe section with
1125 mm length, diameter of 73.5 mm and 11.1 kg of mass. All
the springs are pre-tensioned, enabling a maximum amplitude of
one diameter in both vertical and horizontal directions. The
springs were tested to check their linearity and to evaluate their
stiffness. The characteristics of the system are given in Table 1.
The excitation system (Figure 5.b) is driven by an
electric motor, of which the rotation speed () is controlled by a
variable frequency drive. The circular motion is converted by a
mechanism into an alternate sinusoidal type linear movement

z(t) which is transferred to the test body by a soft spring. An
eccentric peg in a disc attached to the motor shaft provides
various excitation amplitudes. The vibration absorber is
attached to the test body as depicted in Figure 6.
(a) (b)
Figure 5 – (a) Spring mounted test body inside the water
tank; (b) excitation system diagram.
Table 1 - Spring system and test body characteristics.
Spring System – Equivalent Stiffness
Vertical 4.87 kN/m
Horizontal 2.51 kN/m
Test Body
Mass 11.1 kg
Length 1125 mm
Diameter 73.5 mm
Figure 6 – PTMD absorber attached to the test body.
The natural frequencies in both directions were obtained
from accelerometers. An image acquisition system was used to
gather the displacement of the test body under variable
excitation frequencies (Bordalo, 2013). One end section of the
test body was painted black with a circular red target of known
diameter at its center. With appropriate lighting and contrast, a
video was recorded at each frequency of interest by a high
speed camera. Image processing software was employed to
measure the coordinates of the target center on each video
frame, allowing the plotting of displacement versus time. Three
thousand images were acquired, with the duration of 10 seconds
at frame rate of 300 Hz on each test. Figure 7 shows the setup
for the optical acquisition. The image processing is shown in
Figure 8, starting from the raw video frame up to the cleaned
image.
Figure 7 - Optical target for the displacement acquisition.
Figure 8 – Image processing sequence (left to right).
EXPERIMENTAL RESULTS
Free oscillation tests without the PTMD on air and
underwater were conducted to characterize the dynamic
behavior of the experimental model. Comparing these with tests
with the PTMD allowed the observation of the effect of the
PTMD. Assessment of the structural and fluid viscous damping
was made possible from the decay rates. An initial displacement
was given to the test body in the vertical direction and then it
was released. Multiple tests were performed for each
experimental condition of interest, assuring its validation. Once
the free natural frequencies of the system in air and underwater
became known, then forced oscillation tests were performed in
a range of excitation frequencies around the natural values.
Driven oscillation tests were done to establish the amplitude-
frequency response curve of the system with and without the
PTMD, in air and under water.
Tests without the PTMD
Free oscillation in Air and in Water
The natural frequency in air was estimated at 3.6 Hz,
while the logarithm decay was 0.57 which means that the
damping factor was  = 0.091. When submerged in water, the
natural frequency was estimated at 3.0 Hz, while the logarithm
decay was 0.64 which means that the damping factor was  =
0.102.
zo(t)


0 1 2 3 4 5 6 7 8 9 10
40
50
60
70
80
90
100
Time (s)
VerticalDisplacement(mm)
Data
0 1 2 3 4 5 6 7 8 9 10
40
50
60
70
80
90
100
Time (s)
Data
Figure 9 – Free oscillation in air (top) and water (bottom), without the PTMD.
2.5 3 3.5 4 4.5 5 5.5
0
5
10
15
20
25
30
35
40
Frequency of Excitation (Hz)
VerticalAmplitude(mm)
Data
Excitation
2 2.5 3 3.5 4 4.5
0
5
10
15
20
25
30
35
40
Data
Excitation
Figure 10 – Forced oscillation in air (top) and water (bottom), without the PTMD.

0 1 2 3 4 5 6 7 8 9 10
40
50
60
70
80
90
100
Time (s)
Data
0 1 2 3 4 5 6 7 8 9 10
40
50
60
70
80
90
100
Time (s)
Data
Figure 11 – Free oscillation in air (top) and water (bottom), with the PTMD.
2 2.5 3 3.5 4 4.5 5 5.5
0
5
10
15
20
25
30
35
40
Data
Excitation
2 2.5 3 3.5 4 4.5 5
0
5
10
15
20
25
30
35
40
Data
Excitation
Figure 12 – Forced oscillation in air (top) and water (bottom), with the PTMD.

The surrounding fluid media caused the natural
frequency to decrease, which is likely due to the added inertia
of the displaced water mass; on the other hand, the damping
increased, probably due to viscous dissipation (Figure 9).
Forced oscillation in Air and in Water
In air, the amplitude peak is, consistently, close to the
natural frequency of 3.6 Hz observed in the free oscillation test.
The maximum measured amplitude was 36 mm at 3.55 Hz,
which is approximately 1/2 of the diameter of the test pipe. This
value is quite larger than the static displacement. When the
body is submerged, the natural frequency was estimated at
3.1 Hz, which is close to the free oscillation result. So, again,
one notices the effect of the added inertia of the water on the
natural frequency. The maximum registered amplitude was
20 mm, approximately 1/4 of the diameter of the test pipe,
which is half the maximum observed amplitude of the dry tests,
pointing to the dissipation of energy in the water (Figure 10).
Tests with the PTMD
Free oscillation in Air and in Water
The decay plot shows irregularities in the variations of
amplitude that are probably due to distortions caused by the
shocks of the PTMD against its bumper. In air, two eigenvalues
are determined in the frequency domain, which is justified by
the two-degrees of freedom of the two coupled masses. These
natural frequencies were 3.4 Hz and 5.4 Hz. The logarithm
decay was 0.76 which means that the damping factor was  =
0.12. In water, the two-mass system also displays two
eigenvalues, in this case close to 3.0 Hz and 4.8 Hz. The
logarithm decay was 0.76 which means that the damping factor
was  = 0.12.
The eigenvalues in water are lower than the ones for the
dry test, very likely because of the added inertia of the water
(Figure 11).
Forced oscillation in Air and in Water
Two amplitude peaks occurred in the tests in air, as
expected for a system with two-degrees of freedom; the bigger
one was 27 mm close to 3.5 Hz and the smaller was only 4 mm
close to 4.2 Hz. The first peak is very close to the first
eigenvalue of the free decay test. Again, under water, two
amplitude peaks appear; one close to 3.0 Hz of 14 mm and the
other close to 3.8 Hz of 3 mm. The eigenvalues here are lower
than the ones in the case of the dry test, which is consistent with
the concept of added inertia of the displaced water mass. The
amplitude peaks are smaller than those observed in the dry test,
which may be due to the dissipation of energy in the
surrounding fluid (Figure 12).
Summary
In the case of free oscillation decay, the main effect of
the water is to increase the global inertia of the system with an
impact on decreasing the natural frequency. The water has also
an effect on the dissipation of energy, as noticed by the increase
of the log decay and damping factor. The effect of the PTMD is
to modify the system changing its natural frequency into two
modes of natural frequencies – one below and one above the
frequency of the one mode system. The lower frequency shows
the larger amplitude, while the higher frequency shows the
shorter amplitude, in terms of Fourier analysis. The PTMD also,
and very importantly, increases the dissipation of energy, as
seen by the increase in the log decay and damping factor.
2 2.5 3 3.5 4 4.5 5 5.5
0
5
10
15
20
25
30
35
40
Dry
Water
Excitation
Figure 13 – Forced oscillation without the PTMD;
effect of water
2 2.5 3 3.5 4 4.5 5 5.5
0
5
10
15
20
25
30
35
40
Dry
Water
Excitation
Figure 14 – Forced oscillation with the PTMD;
effect of water
In the case of driven oscillations, the main effect of the
water is again to increase the global inertia of the system
decreasing the natural frequency (Figures 13 and 14 compile the
data in a single plot). The water has also an effect on the peak
amplitudes, which are reduced when the test body is submerged,
due to the dissipation of energy in the surrounding media.
The effect of the PTMD is again to modify the system
changing its natural frequency into two modes of natural
frequencies – one below and one above the frequency of the one
mode system (Figures 15 and 16 compile the data in a single
plot). The alteration of the frequency may vary depending on
the parameters of the system, such as the mass ratio between the
main body and the PTMD. In the present case, the alteration of
the first frequency was small, even though it was noticeable.
The lower frequency shows the larger peak, while the higher

frequency shows the shorter peak. The PTMD has a significant
impact in decreasing the peak amplitudes.
2 2.5 3 3.5 4 4.5 5 5.5
0
5
10
15
20
25
30
35
40
Without PTMD
With PTMD
Excitation
Figure 15 – Forced oscillation in Air – effect of the PTMD
2 2.5 3 3.5 4 4.5 5
0
5
10
15
20
25
30
35
40
Frequency of Excitaiton (Hz)
Without PTMD
With PTMD
Excitation
Figure 16 – Forced oscillation in Water – effect of the PTMD
It is expected that adjusting the mass ratio will produce a
frequency shift in the amplitude-frequency curve, that would
cause the “valley” between the two natural frequencies peaks to
be located around the undesirable frequency of a forcing load,
thus avoiding magnification of forced displacements.
CONCLUSIONS
The present work introduces an apparatus to study the
dynamics of the coupling of submerged pipes to PTMD
devices. Concurrently, preliminary results of the experiments on
a scaled down model became the starting point for the study of
applications of PTMDs to submarine pipelines in offshore
petroleum fields.
As observed from the present results, the effect of the
water is twofold: it lowers the natural frequency due to the
additional inertia of the surrounding medium (which the fluid
dynamicists call the “added mass” effect); and it dissipates more
energy than the air due to its greater viscosity, thus increasing
the damping factor, leading to a lower amplitude peak. The
PTMD device diminishes the response amplitudes near the
natural frequency of the primary body, and tends to pull the
amplitude peak towards the lower frequencies, while at the
same time diminishing the amplitude peak magnitude. Further
adjustments of the mass, spring and impact gap of the PTMD
should provide even lower amplitudes around the natural
frequency of the primary body. Once this technique is mastered,
an optimum PTMD can be designed to fit the purpose of any
jumper or pipe project.
Since the surrounding water has a remarkable effect on
the pipe oscillation, underwater conditions should be taken into
account in the design of PTMDs. Also, it must be emphasized
that the PTMD can be effective underwater as well as in air, but
it must be properly adjusted to function as well as desired;
therefore a better understanding of the PTMD effect will require
an exploration of its parameters (mass ratio, impact gap etc) in
future works. These future experiments must take place under
water, due to the importance of the surrounding fluid. Such
work will be needed if one wishes to develop computation
models to simulate the PTMD-pipe dynamics including the
adequate representation of the interaction of the submerged pipe
and the water.
ACKNOWLEDGMENTS
The authors would like to thank Cameron do Brasil for
financial support to this research project, and to acknowledge
the continuous support of the Brazilian National Petroleum
Agency, Petrobras and CNPq to our laboratory, researchers and
students in the course of this work. Also, many thanks are due to
Dr. Song for sharing his valuable experience on the viscoelastic
PTMD.
NOMENCLATURE
a amplitude, mm.
d diameter, mm.
f frequency, Hz.
k spring stiffness, kN/m.
L length, mm.
m mass, kg.
 rotation speed, rad/s.
 damping factor.
PTMD pouding tuned mass damper
TMD tuned mass damper
REFERENCES
BEARMAN, P.W. Vortex shedding from oscillating bluff
bodies. Annual Review of Fluid Mechanics, 16:195–222, 1984.
BLEVINS, R.D. Flow-induced vibration. Second ed.,
Krieger Pub. Co., Florida, 2001.
BORDALO, S.N., TOCHETTO, L.G., MOROOKA, C.K.,
PAVANELLO, R., SONG, G., Experimental Study of a PTMD
Vibration Absorber on a Scaled Down Submarine Jumper
Model, Rio Pipeline 2013, IBP, Rio de Janeiro, Brazil, Sept.
24-26, 2013.

DEN HARTOG, J. Mechanical vibrations. Dover
publications, 1984.
DING, Z., BALASUBRAMANIAN, S., LOKKEN, R. and
YUNG, T. Lift and damping characteristics of bare and straked
cylinders at riser scale Reynolds numbers. Offshore Technology
Conference, 2004.
EKWARO-OSIRE, S., OZERDIM, C. and KHANDAKER,
M. Effect of attachment conﬁguration on impact vibration
absorbers. Experimental Mechanics, Vol. 46, n. 6, 669–681,
2006.
KARAYANNIS, I., VAKAKIS, A. and GEORGIADES, F.
Vibro-impact attachments as shock absorbers. Proceedings of
the Institution of Mechanical Engineers, Part C: Journal of
Mech. Eng. Science, Vol. 222, n. 10, 1899–1908, 2008.
MIKHLIN, Y. and RESHETNIKOVA, S. Dynamical
interaction of an elastic system and a vibroimpact absorber.
Mathematical Problems in Engineering, Vol. 2006, 2006.
POLUKOSHKO, S.; BOYKO, A.; KONONOVA, O.;
SOKOLOVA, S. e JEVSTIGNEJEV, V. Impact vibration
absorber of pendulum type. Proceedings of the7th International
DAAAM Baltic Conf. of Industrial Engineering, 2010.
WILLIAMSOM, C.H.K,, GOVARDHAN, R. Vortex-
induced vibrations. Annual Review of Fluid Mechanics,
36:413–55, 2004.

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