Ijciet 10 01_165

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International Journal of Civil Engineering and Technology (IJCIET)
Volume 10, Issue 01, January 2019, pp. 1781–1791, Article ID: IJCIET_10_01_165
Available online at http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=10&IType=1
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
©IAEME Publication Scopus Indexed
NUMERICAL SIMULATION AND RESPONSE
STUDY OF VERTICAL CYLINDER UNDER
BREAKING WAVES
Muthu Subramanian S
MS Scholar, Dept. of Civil Engineering, NIT, Tiruchirappalli, Tamil Nadu, India
R Manjula
Assistant Professor, Dept. of Civil Engineering, NIT, Tiruchirappalli, Tamil Nadu, India
ABSTRACT
Offshore structures are continuously exposed to extremely varying aerodynamic
and hydrodynamic loads. The storm waves and breaking waves may cause significant
impact on coastal and offshore structures such as vertical sea wall, wind turbines,
LNG carriers and submarine pipelines etc. The prediction of the breaking wave
impact pressure is the important aspect in the design of those structures. The breaking
wave forces produce the highest hydrodynamic loads on substructures in shallow
water, predominantly plunging breaking waves. Owing to the complex and transient
nature of the impact forces it requires more details concerning the physics of breaking
waves and nature of wave interaction with those structures.
In this paper, A Piston-type wave generator was incorporated in the
computational domain to generate waves. Flow 3D was used for simulating 3D
numerical wave tank. The desired breaking waves are simulated using the concept of
wave focusing using Flow 3D solver. These waves are made to impinge on the elastic
circular cylinders of different materials such as PVC, timber and concrete by varying
the support conditions such as cantilever, both ends fixed, inclined support with 30º
inclination. The hydrodynamic response and the structural response are analysed and
validated with the experimental literatures. The maximum impact pressure transpired
on the cylinder due to plunging wave impact from numerical simulation is found to be
eight times of the non-breaking waves.
Key words: Breaking wave, Flow 3D solver, Fluid Structure Interaction, Numerical
model, Wave Impact force.
Cite this Article: Muthu Subramanian S, R Manjula, Numerical Simulation and
Response Study of Vertical Cylinder Under Breaking Waves, International Journal of
Civil Engineering and Technology (IJCIET) 10(1), 2019, pp. 1781–1791.
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=10&IType=1

Numerical Simulation and Response Study of Vertical Cylinder Under Breaking Waves
1. INTRODCUTION
When a wave travels in water, the wave crest rises with a sharper front and thus the thrust of
the wave front increases and in particular, the slope of the wave front rises till the wave
breaks. Hence the wave front becomes more or less vertical during the breaking point for
plunging breaker. Also the velocity is more in the crest than the rest part of the wave. Hence
the wave impact mainly hangs on the shape of the wave front and the speed at the time of
breaking. Breaking waves and their impact on fixed and floating structures, like production &
offloading platforms, coastal protection systems and offshore wind farms, have been focused
for the past few decades that could only be studied with experimental methods.
Experimental studies have given a substantial level of contribution to the current
information of wave breaking forces on slender cylinders and the associated flow features
around them (e.g. Goda et al. (1966) [1]; Sawaragi and Nochino (1984) [2]; Wienke and
Oumeraci (2004)) [3]. Even though the experimental methods are more predominant in
studying the breaking wave impact on structures, the analysis of various parameters involves
huge manpower, measurement, space, time and cost. With the advent of new technology, the
numerical method is gaining importance in studying the breaking waves and its impact
Numerical modelling of breaking waves and the interaction with offshore structures are
subjected to noteworthy uncertainties since the fundamental physical processes are still not
fully understood. The evolution of breaking waves and their interaction with structures can be
modelled numerically with computational fluid dynamics (CFD) models based on the Navier-
Stokes equations. A number of numerical investigations have been attempted to model
breaking waves and the related flow characteristics in shallow waters. Numerical studies have
been carried out to examine the interaction between breaking waves and structures. A class of
non-iterative methods for solving the Poisson equation on regular grids in near-optimal time
is developed in the 1960s and 1970s.
There are rapid developments in the field of Krylov subspace methods for non-symmetric
linear systems (Young, van der Vorst), preconditioning, multilevel algorithms, and large-scale
Eigen value solvers in the 1980s and 1990s. Park et al., 2001[7] developed a numerical wave
tank technique for the purpose of motion simulation regarding offshore structures in offshore
environments, especially to derive the characteristics and accuracy with respect to a numerical
wave simulation. In other studies, numerical simulation of wave run-up around a circular
column in regular waves was carried out by Yang et al., 2015 [8]. There are not enough
studies to show the effect of structural response due to various support conditions along with
various material properties. The present paper deals with developing a numerical model for
simulating breaking waves and its impact on cylinders by varying materials and support
conditions.
2. NUMERICAL APPROACH
Computational Fluid Dynamics (CFD) methods are widely applied across a range of
industries to examine fluid. CFD can be used to predict the dynamic and structural response
of the platform during wave impact. Navier Stokes equation (NSE) solver is used to model the
flow in order to capture the forces exerted by the fluid. Two dimensional, hydrostatic models
which are used to study the horizontal velocities and the water surface elevations are
calculated by the mass conservation equation. These models work well for the determination
of structural response in breaking waves. A Navier-Stokes approach is more suitable for these
problems as it includes the vertical variation of the velocity/acceleration and it helps to
estimate the forces applied by the flow on any structure in the path of the flow (Ashwin
Lohithakshan Parambath, Dec-2010 [5]). Hence Flow 3D Solver is used to generate the
numerical model in line with the experimental model and the output obtained are compared

Muthu Subramanian S, R Manjula
with the experimental results. The governing equations for the flow of an incompressible,
Newtonian fluid in a domain, is given by V. u=0 and the equation of momentum conservation
given by
(∂u/∂t) + (V.u) u= (Vp/ρ) + (vV2
+G)
where, u (x, t) is the velocity vector of the flow at any point x, at time t, p is the pressure,
ρ is the density of the fluid, v is the kinematic viscosity and G is the acceleration due to
gravity vector.
3. FLOW-3D APPROACH
The above mentioned equations are applied in FLOW-3D, which is a CFD solver that is
capable of solving a wide variety of physical flows. Some of the significant features of
FLOW-3D are FAVOR method, Computational grid and geometry are independent, can
handle internal, external and free surface flows, can handle one, two and three dimensional
flows,
It can solve transient flows which are in viscid, viscous, laminar and turbulent, Can track
fluid interfaces using the VOF method, Can track sharp fluid interfaces, Has implicit and
explicit modelling options, Can handle many different types of fluid boundaries such as rigid
wall, continuative, periodic, outflow, hydrostatic pressure, etc., Provisions for changing some
of flow properties at runtime using the restart option.
4. METHODOLOGY
Figure 1 Methodology Flow Chart

5. NUMERICAL WAVE TANK
Figure 2 Numerical Wave Tank
The numerical wave tank of size 30m long wave flume with 2m wide and 1.8m deep
under breaking wave impact was chosen from the literature (Manjula et al, 2013). Piston wave
type wave paddle is used at one end and wave absorber is other end is developed in the
numerical model. Still water level is taken as 0.8m from the bottom.
The three type of cylinder such as PVC of size 160mm diameter and 5.5mm thickness,
Timber and Concrete of thickness 160mm is used as cylinder models. Both regular waves
and breaking waves impact on the vertical cylinder is studied using the Flow3D solver. The
Young’s modulus and density of PVC, Timber and Concrete materials are tabulated below.
The methodology flowchart is shown in Fig.1
Table 1 Material Properties
Material
Young’s Modulus
(Mpa)
Density (kg/m3)
PVC 661 1600
Timber 12500 630
Concrete 17000 2400
6. NUMERICAL SIMULATION OF BREAKING WAVE
The numerical wave tank is created using Flow 3D solver. The mesh size was given as exactly
as the size of experimental tank. The mesh can either be defined by total number of cells or
cell size. Here the mesh is defined by the size of the cells. Three mesh blocks were created for
defining the flume. One is from 0 to 7m with the size of cell as 0.1m and the second mesh is
from 7 to 9m with the size of cell as 0.005m and the third mesh block from 9 to 30m with the
size as 0.1m again. Since the vertical cylinder Is located at 8.2m from the wave paddle, the
particular area is defined with the fine mesh. Other specific blocks are defined as coarser
mesh as explained earlier.
The vertical cylinder was created using the Geometry available in the solver. The
Boundary conditions are defined. Here, from –y is considered as fluid inflow and +y is
considered as fluid outflow. Other boundaries like x and z are considered as wall. For fluid
inflow, the –y input in boundary condition the wave option is selected.

Figure 3 Mesh Blocks for Wave Tank
Figure 4 Numerical model of Wave Tank in Solver
For generating regular wave, linear wave option is selected with wave amplitude as 0.2m
and 1.5s wave period as the inflow condition. Outflow condition is selected for +y boundary
condition. In Outflow, the wave absorbing layer is enabled to absorb the generated waves so
that the wave will not propagate to and forth inside the tank. The fluid initialisation command
is given to maintain the depth of fluid as 0.8m as similar to the literature. Water is selected as
Fluid 1 for the generation of waves. Gravity and Non inertial reference, -9.81m/s is given
under the z axis to enable the flow of the fluid. Similarly, viscosity and turbulence condition
is initialised. Also the Density evaluation condition is enabled for fluid structure interaction.
The required output parameters were selected like, Pressure, Fluid velocity, Distance travelled
by fluid etc. The model was simulated and ran with selected input and boundary conditions.
For generating breaking wave, a wave paddle is used as similar to the experimental model.
The wave paddle time history is given as the input for strong plunging and moderate plunging
wave which was taken from the literature study (Manjula et al).

Figure 5 Breaking Wave striking vertical cylinder in cylinder view
Figure 6 Wave generation shown in 3D
7. RESULTS AND DISCUSSIONS
7.1. PVC with Cantilever Fixed at Top Support
The pressure variation was observed with a fine mesh of size 5mm in Numerical simulation.
The numerical tank was made up of mesh size 100 mm. The run time for the solver is
approximately 36 hours
Figure 7 Pressure Values for Strong Plunging Breaking waves measured @0.8m height

Figure 8 Wave height results for Strong Plunging Breaking waves measured @0.8m height
The maximum pressure exerted on vertical cylinder is found to be 46700 Pa at 11.3
seconds from literature. In Numerical simulation, the pressure is found to be 49900 Pa at 11.7
seconds. The difference is 6% and hence numerical model is able to simulate breaking waves
at higher accuracy. The wave height in strong plunging incident for literature is found to be 29
cm whereas in numerical it found to be 32 cm
Figure 9 Deflection observed in Strong Plunging Breaking waves measured @0.8m height.
Figure 10 Deflection Profile under Strong plunging waves hitting the cylinder compared with Manjula
et al 2013

The deflection of vertical cylinder in strong plunging incident for numerical simulation is
found as 2.5x10-5
m (shown in Fig.9) which is matching with literature results. The impact
force for P1 (strong plunging breaking wave) is taken as 8412N and P4 (moderate plunging
breaking wave) event is 6300N taken directly from literature for computation of results. Fig.
10 and Fig. 11 shows the comparison of deflection normalised with impact force and plotted
against the length of the cylinder for both numerical and literature results.
The pattern is matching with literature results when z/Hb is > 0 in P1 event and when
z/Hb is < 0 for P4 event. As it is a cantilever support, the deflection at the free end is higher.
Even though the impact force transpired on the cylinder for P4 is about 0.8 times that of P1
event, the maximum deflection observed P4 event in the impact zone is larger than that of P1
event. Thus, the cylinder yields more under moderate plunging which imparts larger impulse
compared to a severe plunging event.
Figure 11 Deflection Profile under Moderate plunging waves hitting the cylinder compared with
Manjula et al 2013
Figure 12 Deflection response of the cylinder under Strong and moderate plunging waves Compared
with literature
The variation of deflection normalised with impact force and plotted against the wave
steepness parameter is shown in the Fig. 12 for the strong plunging (P1) and moderate
plunging (P4) occurrences. The wave steepness parameter is 0.5773 for P1 and 0.5451 for P4
event which is taken directly from literature for the computation of results. The deflection

observed along the length of the cylinder shows that, though the impact force is less for P4
event, the rise time of wave is higher than P1 event and hence the deflection values observed
for moderate plunging is higher than strong plunging event.
The maximum deflection is around 0.25mm for P1 event and for P4 event, it is around
60mm. While, the value of deflection observed is 0.18mm for P1 event and 50mm for P4
event from the l results by Manjula et al 2013.While for P4 event, the average maximum
deflection of 42mm (35mm in experimental results) is observed throughout the impact zone
which is crucial for design.
10. RESPONSE BY VARYING SUPPORT CONDITIONS & MATERIAL
PROPERTIES
The numerical model is used to study the response of the cylinder under various support
conditions such as bottom fixed top free, inclined at 30º and fixed at both ends. The material
used is PVC of 160mm diameter and 5.5mm thickness. From Fig. 13, it is observed that the
deflection ratio for both ends supported cylinder is 0.3 times to that of cylinder supported at
top end and the inclined cylinder yields almost similar with the cylinder supported at top end.
The Both ends fixed support cylinder yield lesser when compared to the other two support
conditions. It is also interesting to note that the deflection of cylinder observed is not varying
much in the breaking zone.
Fig. 14 shows the structural response of cylinder studied with the different material
properties such as timber and concrete instead of PVC supported at top and bottom end free.
The deflection observed along the length of the cylinder is plotted and the results obtained
shows that the concrete cylinder yields less deflection than timber and PVC cylinder. The
timber deflects 0.9 times as that of PVC and concrete yields 0.79 times that of PVC. It is to be
noted that being a rigid material, the concrete cylinder yields lesser deflection when compared
to the other two different materials. Also in the breaking free zone there is not much variation
in the deflection of cylinder observed.
Fig.15 shows the maximum deflection plotted for cylinder with various support conditions
and different materials. The both end fixed support yield lesser when compared to the other
support conditions and other materials used.
Figure 13 Comparison of deflection for Strong Plunging Breaking waves while the cylinder is
Inclined supported, Bottom supported & both end supported

Figure 14 Comparison of deflection for Strong Plunging Breaking waves while a timber and concrete
cylinder is used
Figure 15 Maximum Deflection response of the cylinder under Strong plunging waves incidences for
different support conditions and different materials
10. CONCLUSIONS
It is found from the study that the numerical model for regular waves estimates the wave
height and pressure with 99 percentage accuracy when compared with the literature results.
This is motivating as it is commonly a difficult task to evaluate the forces exerted on objects
placed in a fluid under severe environmental conditions. Also, for breaking wave, in strong
plunging numerical model, the pressure observed is found to be 49900 Pa which is only 6%
more than the literature results. The maximum deflection for the P1 event is found to be 2.5e-
5
m at 0.8m height. The support conditions and the material properties are unaffected by strong
plunging breaking waves since there is not much variation in the deflection profile for both.

REFERENCES
[1] Goda, Y., Haranaka, S. and Kitahata, M., 1966. Study on impulsive breaking wave forces
on piles. Rep. Port Harbour Res. Inst., 6(5): l-30.
[2] Sawaragi, T. and Nochino, M., 1984. Impact forces of nearly breaking waves on a vertical
circular cylinder. Coastal Eng. Jpn., 37: 249-263.
[3] Wienke, W., Oumeraci, H., 2004. Breaking wave impact force on a vertical and inclined
slender pile theoretical and large scale model investigations, Coastal Eng. 52, 435-462[4]
Manjula, R., Sannasiraj, S.A., Palanichamy, K., 2013. Laboratory measurements of
breaking wave impact pressures on a slender cylindrical member, International Journal of
Ocean and Climate systems 4(3), 151-167.
[4] Ashwin Lohithakshan Parambath, Imapct of tsunamis on near shore wind power units,
Texas A&M University, Dec-2010
[5] R. Manjula, Response of Slender Vertical Cylinder Due to Breaking Wave Impact, India
Institute of Technology, Madras, Dec 2013
[6] Park, J.C., Kim, M.H., Miyata, H. Three-dimensional numerical wavetank simulation on
fully nonlinear wave-current-body interactions. 2001
[7] Yang, I.J., Lee, Y.G., Jeong, K.L. Numerical simulation of the freesurface around a
circular column in regular waves using modiﬁed marker-density method. Int. J. Nav.
Archit. Ocean Eng. 7, 610-625. 2015

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