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Publication Abstracts FEM, BEM & FVM and Design Optimization COTech403: Boundary
element method solution for large scale cathodic protection problems D
Rodopoulos1,
T
Gortsas1,
S
V Tsinopoulos2
and D
Polyzos1* Abstract.
Cathodic
protection techniques are widely used for avoiding corrosion
sequences in offshore structures. The Boundary Element Method (BEM)
is an ideal method for solving such problems because requires only
the meshing of the boundary and not the whole domain of the
electrolyte as the Finite Element Method does. This advantage becomes
more pronounced in cathodic protection systems since electrochemical
reactions occur mainly on the surface of the metallic structure. The
present work aims to solve numerically a cathodic protection problem
for a large offshore platform. The solution of that large-scale
problem is accomplished by means of “PITHIA Software” a BEM
package enhanced by Hierarchical Matrices (HM) and Adaptive Cross
Approximation (ACA) techniques that accelerate drastically the
computations and reduce memory requirements. The nonlinear
polarization curve for steel in sea-water is employed as boundary
condition for the under protection metallic surfaces and the
potential as well as the current density at all the surface of the
platform are effectively evaluated and presented. Keywords.
Adaptive
cross approximation technique, BEM, Boundary element method, Cathodic
protection, Hierarchical Matrices, Large scale problems. COTech404: Finite
element simulation of long wave impact on floating breakwaters with
variable stiffness T K Papathanasiou1*,
A
Karperaki2
and
K
A Belibassakis3
Abstract.
The
hydroelastic response of flexible, floating breakwaters is a subject
of interest for coastal engineering applications. In this study, a
higher order hydroelastic finite element is applied to the simulation
of floating breakwaters of variable stiffness undergoing long wave
impact. The main aim is the evaluation of breakwater efficiency in
terms of transmitted and reflected wave characteristics. It is
established that, for the wave-lengths examined, the maximum
amplitude and wave-length of the transmitted pulse are strongly
dependent on the breakwater stiffness. Finally it is shown that for
case of a periodic stiffness profile the transmitted energy is
minimised when the modulation wavelength is comparable to the
wavelength of the incoming excitation. Keywords—Hydroelasticity,
Long Waves, Floating Breakwaters, VLFS, Finite Elements, Wave
Reflection. COTech405:
An
efficient structural finite element for inextensible flexible risers T
K Papathanasiou1,
S Markolefas2,
P Khazaeinejad1
and H Bahai1 Abstract.
A core part of all numerical models used for flexible riser analysis
is the structural component representing the main body of the riser
as a slender beam. Loads acting on this structural element are
self-weight, buoyant and hydrodynamic forces, internal pressure and
others. A structural finite element for an inextensible riser with a
point-wise enforcement of the inextensibility constrain is presented.
In particular, the inextensibility constraint is applied only at the
nodes of the meshed arc length parameter. Among the virtues of the
proposed approach is the flexibility in the application of boundary
conditions and the easy incorporation of dissipative forces. Several
attributes of the proposed finite element scheme are analysed and
computation times for the solution of some simplified examples are
discussed. Future developments aim at the appropriate implementation
of material and geometric parameters for the beam model, i.e.
flexural and torsional rigidity. Keywords.
Flexible
risers, Structural elements, Inextensible beams, Finite elements. S
P Zaoutsos and M C Zilidou Laboratory
of Advanced Materials and Constructions, Department of
Mechanical Engineering Technological Educational Institute of
Thessaly, Ring Road Larissas-Trikalon, Larissa, Greece. Abstract.
In the current study dynamic mechanical
analysis (DMA) is performed in CFRPs that have been exposed for
certain periods of time to extreme low temperatures. Through
experimental data arising from respective DMA tests the influence of
low temperature exposure (-40 oC) on the dynamic
mechanical properties is studied. DMA tests were conducted in CFRP
specimens in three point bending mode at both frequency and thermal
scans in order to determine the viscoelastic response of the material
in low temperatures. All experimental tests were run both for aged
and pristine materials for comparison purposes. The results occurred
reveal that there is deterioration both on Tg
and storage modulus values while there is also a moderate increase in
the damping ability of the tested material as expressed by the factor
tanδ
as the period of exposure to low temperature increases. Keywords: Carbon
Fiber Reinforced Polymers (CFRPs),
Dynamic Mechanical Properties, Storage Modulus, Loss Modulus, Time-Temperature
Superposition Principle (TTSP). COTech407:
Numerical
Assessment of Wind Turbine Blade Damage Due to Contact/Impact with
Tower During Installation a,bAmrit
Shankar Verma,
dNils Petter Vedvik, a,b,cZhen Gao Abstract.
The
use of floating crane vessel for installation of offshore wind
turbine blades presents a great challenge in terms of its random
motions and is likely to increase the probability of the blade
hitting the preassembled tower during lifting operation. To evaluate
the consequences of such scenarios and to determine the allowable
motions or sea states for such operations, it is very important to
understand the damage development in the blade due to impact. The
present paper employs the application of high fidelity finite element
method to investigate the damage behavior in the blade when the
leading edge of the blade hits the tower. A nonlinear time domain
structural analysis using ABAQUS was conducted on the DTU 10 MW
reference blade model which is based on shell elements. Damage
assessment along with the nature of evolution of various energies is
examined and presented for two different impact velocities with
modified layup stacking sequence at the contact region. Keywords.
Contact/impact
behavior; Finite element method; Installation; Offshore wind turbine
blade; Progressive failure analysis; Glass fibre reinforced plastic
(GFRP) COTech408:
A
case study on topology optimized design for additive manufacturing
A
W Gebisa*, H G Lemu Keywords—
Additive
manufacturing, freedom design and manufacturing, material
distribution, topology optimization. COTech409:
A
Review of Fatigue Crack Propagation Modelling Techniques Using FEM
and XFEM Kristen
Rege, Hirpa G. Lemu Abstract.
Fatigue
is one of the main causes of failures in mechanical and structural
systems. Offshore installations, in particular, are susceptible to
fatigue failure due to their exposure to the combination of wind
loads, wave loads and currents. In order to assess the safety of the
components of these installations, the expected lifetime of the
component needs to be estimated. The fatigue life is the sum of the
number of loading cycles required for a fatigue crack to initiate,
and the number of cycles required for the crack to propagate before
sudden fracture occurs. Since analytical determination of the fatigue
crack propagation life in real geometries is rarely viable, crack
propagation problems are normally solved using some computational
method. In this review the use of the finite element method (FEM) and
the extended finite element method (XFEM) to model fatigue crack
propagation is discussed. The basic techniques are presented,
together with some of the recent developments. Keywords.
Crack growth, Crack propagation, Extended finite element method,
Fatigue, Finite element method, Fracture mechanics COTech410:
Experimental
and Numerical Study of Bondura® 6.6 PIN Joints aImad Berkani,
bØyvind Karlsen*,
aHirpa G. Lemu Abstract:
Pin
joints are widely used in heavy-duty machinery such as aircrafts,
cranes and offshore drilling equipment to transfer multi-dimensional
shear forces. Their strength and service life depend on the clamping
force in the contact region that is provided by interference fits.
Though the interference fits provide full contact at the pin-hole
interface under pretension loads, the contact interface reduces when
the pin is subjected to an external load and hence a smaller contact
surface leads to dramatic increase of the contact stress. The PIN
joint of Bondura® Technology, investigated in this study, is an
innovative solution intended to reduce the slack at the contact
surface of the pin joint of heavy-duty machinery by using tapered
sleeves on each end of the PIN. The study is aimed to better
understand the contact pressure build-up and stress distribution in
the supporting contact surface under pre-loading of the joint and the
influence of temperature difference between part assembly and
operation conditions. Numerical simulation using finite element
method and diverse experimental tests were conducted. The numerical
simulation and the test results show good conformance, particularly
the tests conducted with lubricated joints.
Keywords. Bolt preload, Bondura® Technology, Interference fit, Numerical simulation, Pin joint. COTech411:
Recursive
thoughts on the simulation of the flexible multibody dynamics of
slender offshore structures
J
Schilder*, M Ellenbroek, and A de Boer Abstract.
In this work, the floating frame of reference formulation is used to
create a flexible multibody model of slender offshore structures such
as pipelines and risers. It is shown that due to the chain-like
topology of the considered structures, the equation of motion can be
expressed in terms of absolute interface coordinates. In the
presented form, kinematic constraint equations are satisfied
explicitly and the Lagrange multipliers are eliminated from the
equations. Hence, the structures can be conveniently coupled to
finite element or multibody models of for example seabed and vessel.
The chain-like topology enables the efficient use of recursive
solution procedures for both transient dynamic analysis and
equilibrium analysis. For this, the transfer matrix method is used.
In order to improve the convergence of the equilibrium analysis, the
analytical solution of a ideal catenary is used as an initial
configuration, reducing the number of required iterations. Keywords. Catenary theory, Flexible multibody dynamics, Floating frame of reference, Interface coordinates, Pipe-laying, Recursive solution procedures, Transfer matrix method. COTech412:
A nonlinear
dynamic corotational finite element model for submerged pipes F H de Vries1*,
H J M Geijselaers1,
A H van den Boogaard1,
A Huisman2 Abstract.
A three dimensional finite element model is built to compute the
motions of a pipe that is being laid on the seabed. This process is
geometrically nonlinear, therefore co-rotational beam elements are
used. The pipe is subject to static and dynamic forces. Static forces
are due to gravity, current and buoyancy. The dynamic forces exerted
by the water are incorporated using Morison’s equation. The dynamic
motions are computed using implicit time integration. For this the
Hilber-Hughes-Taylor method is selected. The Newton-Raphson iteration
scheme is used to solve the equations in every time step. During
laying, the pipe is connected to the pipe laying vessel, which is
subject to wave motion. Response amplitude operators are used to
determine the motions of the ship and thus the motions of the top end
of the pipe. Keywords—
Buoyancy,
Co-rotational, FEM, Hilber-Hughes-Taylor, Morison, Nonlinear, Three
dimensional COTech413:
Application
of Foam-extend on Turbulent Fluid-Structure Interaction
Kristen
Rege*, Bjørn H. Hjertager Abstract.
Turbulent
flow around flexible structures is likely to induce structural
vibrations which may eventually lead to fatigue failure. In order to
assess the fatigue life of these structures, it is necessary to take
the action of the flow on the structure into account, but also the
influence of the vibrating structure on the fluid flow. This is
achieved by performing fluid-structure interaction (FSI) simulations.
In this work, we have investigated the capability of a FSI toolkit
for the finite volume computational fluid dynamics software
foam-extend to simulate turbulence-induced vibrations of a flexible
structure. A large-eddy simulation (LES) turbulence model has been
implemented to a basic FSI problem of a flexible wall which is placed
in a confined, turbulent flow. This problem was simulated for 2.32
seconds. This short simulation required over 200 computation hours,
using 20 processor cores. Thereby, it has been shown that the
simulation of FSI with LES is possible, but also computationally
demanding. In order to make turbulent FSI simulations with
foam-extend more applicable, more sophisticated turbulence models
and/or faster FSI iteration schemes should be applied.
Keywords.
Computational
fluid dynamics, Finite volume method, Fluid-structure interaction,
Large eddy simulation COTech414:
Evaluating stress
analysis and failure criteria for offshore structures for Pechora Sea
conditions
S
Nesic1,
Y
Donskoy2
and A
Zolotukhin2,3,4 Abstract.
Development of Arctic hydrocarbon resources has faced many challenges
due to sensitive environmental conditions including low temperatures,
ice cover and terrestrial permafrost and extreme seasonal variation
in sunlight. Russian offshore field development in Arctic region is
usually associated with annual ice cover, which can cause serious
damage on the offshore platforms. The Pechora Sea has claimed as one
of the most perspective oil and gas region of the Russian Arctic with
seven discovered oil and gas fields and several dozens of structures.
Our rough assessment, based on in-place hydrocarbon volumes and
recovery factor evaluation concept, indicates that Pechora Sea alone
has in-place volumes amounting to ca. 20 billion Barrel of Oil
Equivalent (BOE). This quantity is enough to secure produced volumes
by 2040 exceeding 3 billion BOE that indicates huge resource
potential of the region. The environmental conditions are primarily
function of water dynamics and ice cover. The sea is covered by the
ice for greatest part of the year. In this article, the ice load
simulations were performed using explicit dynamic analysis system in
ANSYS software to determine best shape and size of an offshore
platform for the Pechora Sea ice conditions. Different gravity based
structures (GBS) were analyzed: artificial island, hollow cylindrical
and conical concrete structures and four-leg GBS. Relationships
between the stress, deformations and time were analyzed and important
observations from the simulation results were a basis for selecting
the most preferable structures. Keywords.
Ice
loading, Pechora Sea, Arctic, Offshore structures, Ice load
simulation
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