Transcript Structural Analysis of Ship Collision and Grounding

Efficient Prediction of Dynamic Response for Flexible and
Multi-body Marine Structures
Reza Taghipour , Professor Torgeir Moan

The objective is to establish
models that enable efficient and
robust analysis of wave-induced
motion and structural response for
novel marine structures.

The focus is mainly on flexible and
multi-body marine structures with
applications in Very Large Floating
Structures,
Wave
Energy
Converters, Aquaculture Structures
and Oil and Gas industry.
Wave induced structural Analysis Results for the FO3 Platform by interfacing WAMIT and ABAQUS.
Comparison between the measurements (by Malenica et. Al.) and simulated (in an efficient manner)
transient response of a flexible barge when it is released from a displaced condition shown in the left figure.
Structural Analysis of Ship Collision and Grounding
Ph.D candidate Lin Hong, Prof. Jørgen Amdahl
Deck
Stringer
Bottom
floor
Longitudinal girder
Transverse frame or
bulkhead
 A brief overview of the ongoing
project – ScenaRisC&G:
Scenario-based Approach to Risk
Analysis of Ship Collision and
Grounding.
 As the process of collision and
grounding can be decoupled into
external dynamics and internal
mechanics, the focus here is
placed on internal mechanics.
Existing methods are summarized,
and the aim is to develop a fast
estimation tool with relative
accuracy. Therefore, simplified
analytical method is adopted.
Various types of web girders in a double hull ship midsection
 Simplified analytical methods for web girders in collision and grounding are developed.
Two different deformation patterns have been identified, namely local denting and
sliding deformation. Both the crushing force and the energy dissipation capacity are
derived and verified by experiments or finite element simulations.
 Further work: develop simple tools for fast and reliable assessment of the outcome of
accidental collision and grounding events which can be incorporated into decision
support tools for crisis handling in emergency situations, e.g. for tankers in disabled
conditions.
Safety level in marine operations – Sea transport
Asle Natskår. Supervisor: Prof. Torgeir Moan, Co-supervisor: Per Øystein Alvær, DNV
 Investigate the safety level
inherent in marine operations
designed according to
recognized rules.
 The project focus on safety
level including the effect of
human errors.
Load-out / Load-in operation
Sea transport (picture by Umoe)
 Sea transport on ship or barge.
What is the safety level
incorporated in simplified
motion criteria?
A Specialized FEM Prototype for Structural Analysis of a
Floating Fish Cage
Paul Thomassen, Prof. Bernt Leira
Laboratory measurements (From Sumer, B.M.)
 Escape of fish due to structural
collapse is a serious problem for
the 20 billion NOK Norwegian
fish farming industry
 Trial-and-error has been the
dominating design method rather
than scientifically based
structural analysis and design.
 Why? A slender, floating
structure is unusual, i.e. methods,
results, and tools from related
areas of engineering cannot be
adopted directly.
 Approach:
 Investigate the hydrodynamic
model.
 Investigate structural
characteristics.
 Focus on fatigue design of fish
cages in steel.
 Implement a dynamic, nonlinear
time domain analysis in
irregular waves.
 Develop a specialized FEM
prototype based on an objectoriented FEM framework.
Over: Screendunp of the base case structure. Under: grafical user interface of the prototype.
Frequency-domain Fatigue Analysis of Wide-band Processes
Dr. Zhen Gao; Prof. Torgeir Moan
 The objective is to develop a
frequency-domain method for
fatigue analysis of random
processes with a general wideband power spectral density
function.
 First, the method for bimodal
Gaussian fatigue analysis is
introduced, using the envelope
of narrow-band processes.
 This method is then
generalized to Gaussian
processes with three or more
modes.
 Finally, for a general wideband process, a method is
developed by dividing the
spectrum into three segments
and calculating the fatigue
damage as the same as for an
ideal trimodal process.
Vertical Wave Loads on Platform Decks
RAVI KOTA (Supervisors: Prof. Torgeir Moan & Prof. Odd Faltinsen)
•
Objective: To study global, vertical wave loads on
platform decks in an irregular sea.
•
Method of Analysis:
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z
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 0
 0
[+c(t),0]

 VR
z
[-c(t),0]
x
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Froude-Krylov Force
Added-Mass Force
Slam Force
TOTAL FORCE
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Key results sought:
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20
0
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Force in N
-20
-40
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-60
2-D Slamming Model (von Kármán) applied to
linear, incident Gaussian sea-state for fixed, rigid
deck,
Extend to 3-D including Diffraction and platform
motions,
Time-domain simulation of forces and postprocess for statistics,
Compare against analytical Gaussian formulation.
A probability distribution for maximum/minimum
vertical force, and its duration
Characterize the response of a floating structure to
deck loads and duration.
Comparison against experimental data
-80
Wave Period = 1.25 s
Wave Ampl. = 0.06 m
Deck Height = 0.04 m
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-120
-140
0
0.1
0.2
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Time in sec
0.5
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Possible extensions:
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2nd-order wave models – simulation vs. analytical
approach.
Effect of Reynolds Number on Forced VIV Oscillations
Jamison L. Szwalek, Carl M. Larsen
Experimental Set-up
 Objective: determine effect of Re
on hydrodynamic coefficients for
vortex-induced vibrations
 Goal: use data to incorporate Re
effects into VIV prediction codes
Cylinder
Transducers
and optical
encoders
 Perform: experiments with five
Re, ranging from 4,600 to
46,000. Examine peak response
region.
IL Test Matrix.
Front View
Side View
Hydrodynamic Force Identification from VIV Experiment with Slender Beams
Jie Wu, Prof. Carl M. Larsen, Halvor Lie
Total hydrodynamic force contour
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11
10
 The objective is to identify
hydrodynamic forces from
response measurement and
construct a force model.
6
9
4
Riser length (m)
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7
2
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 Identification methods based on
Kalman filtering and constrained
optimization.
0
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-2
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-4
2
-6
1
 Validation of the methods by
numerical simulations.
Laboratory measurements (From Sumer, B.M.)
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Time step
Lift force coefficient
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400
-8
Added mass coefficient
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12
10
Ca
A/D
fh
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Gopal.
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Gopal.
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Riser length (m)
Riser length (m)
8
CL
A/D
fh
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4
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2
2
0
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-2.5
-2
-1.5
-1
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Lift Force Coefficient and Amplitude Ratio and Nondimensional frequency
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0
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2.5
Added Mass Coefficient, Amplitude Ratio and Nondimensional frequency
 Application to the rotating rig
test. L: 11.34 m, Do: 0.02 m
 Undergoing research on
Hanøytangen test. L: 90 m, Do:
0.03 m
Valve condition and performance monitoring
Erlend Meland, Prof. Magnus Rasmussen
 Tail IO introduction
 The objective is to develop valve
condition monitoring methodologies
which can detect leakages more
accurately for critical valves.
 MARINTEK’s CORD project, results
post analysis.
 New laboratory tests: Alternative
valves and measurements, inflicted
damage, frequency spectrum analysis
of ultrasound.
The Tail IO project
Modelling Ship Traffic From AIS Data
Karl Gunnar Aarsæther, Prof Torgeir Moan
 The introduction of the
Automatic Identification System
(AIS) has, as a secondary effect,
enabled mass collection of
quantitative data of ship traffic in
an area
 Extraction of geometric traffic
features, density and
quantification of variability in
the traffic pattern
Automatic Identification System Track-Lines
 The data available from the AIS
system will be presented along
with methods for data separation
and transformation into a
geometric and statistical model
for ship traffic in an example
area.
Extracted Track Features
Numerical Simulation of Scour around a Marine Pipeline
Muk Chen Ong, Dr. Torbjørn Utnes, Dr. Lars Erik Holmedal, Prof. Dag Myrhaug,
Prof. Bjørnar Pettersen
 The objective is to develop a
robust numerical model which is
able to predict 2-D pipeline scour
under the effect of current and
waves respectively, and possibly,
the effect of combined wave and
current.
Laboratory measurements (From Sumer, B.M.)
 Validation of a standard high
Reynolds number k-e model for
rough turbulent oscillatory flows
with suspended sediments is
presented.
 Numerical work using RANS
with a standard high Reynolds
number k-e model on flows
around a smooth circular
cylinder at high Re of 1x106 ~
3.6x106, which are beyond the
supercritical flow regime, is
presented.
Turbulent kinetic energy field at Re = 3.6 x106
Hydroelastic slamming including air pocket
Bjørn Chr. Abrahamsen Supervisors: Odd Faltinsen and Torgeir Moan
 The objective is to investigate
slamming loads inside tanks
when the free surface captures an
air pocket (figure 1). The
compressibility of the air causes
an oscillatory pressure in time
with small spatial variation (
figure 2)
Figure 1: Experiments by Rognebakke and Allers
 When these pressure oscillations
governs the flow physics, scaling
laws are affected. In addition the
oscillatory pressure can cause
important hydroelastic effects on
the tank structure. These are the
two main aspects of this project.
 A theoretical model of this
phenomena is planned using a
combination of the boundary
element method BEM and an
analytical method. For the
hydroelastic problem a
combination of BEM and the
finite element method FEM is
planned.
Figure 2: Pressure-time history (Faltinsen and Rognebakke)
LNG Carrier by offshore terminal in shallow water
Trygve Kristiansen, Prof. Odd M. Faltinsen
 The objective is to investigate
features associated with the
operation of an LNG carrier by
an offshore terminal subject to
incoming waves
 Work: 2D fully nonlinear
numerical wavetank based on
BEM. Model tests in a wave
flume.
Model testing of ship by terminal in shallow water subject to waves
 The resonant piston mode
behavior of the fluid between
the ship and terminal has
primarily been investigated.
 Vortex shedding found to
cause the discrepancy
between linear theory and
measurements
Left: Piston mode amplitude relative to forced heave amplitude. Results from simulations
with and without vortex separation by an inviscid vortex tracking method compared to
linear theory and experimental data. Right: Snapshot from wavetank simulation with
vortex.
Direct Numerical Simulation of Back-ward Facing Step Couette Flow
George El Khoury, Mustafa Barri, Prof. Helge I. Andersson, Prof. Bjørnar Pettersen
•
•
Separation and reattachment of turbulent flows occur in many practical engineering
applications, both in internal flow systems such as combustors and channels with sudden
expansion, and in external flows such as around airfoils.
In the present study , turbulent flow over a back-ward facing step is studied by direct numerical
simulation of Navier Stokes equation at a Reynolds number 1300 based on half channel height
at the input
Applications of a BEM to strongly nonlinear wave-body
interaction problems
Hui Sun and Prof. Odd M. Faltinsen
t = 0.15 s
t = 0.15 s
t = 0.12 s
t = 0.12 s
t = 0.10 s
t = 0.10 s
t = 0.09 s
t = 0.09 s
t = 0.08 s
t = 0.08 s
t = 0.05 s
-0.2
-0.1
t = 0.05 s
0.0
0.1
0.2
0.3
0.4
y (m)
Water entry of a bow-flare ship section with heel angle
 A 2D Boundary Element Method is
developed to study the strongly
nonlinear wave-body interaction
problem. Two applications are
presented.
 The first one is the asymmetric water
entry of a bow-flare ship section with
heel angle. Non-viscous flow
separation from knuckles or from the
leeward surface can be simulated.
 The second application is to use the
2D BEM together with a 2D+t
method to study the vertical loads on
a planing vessel in heave or pitch
motions. Then a linear stability theory
is applied to predict the inception of
porpoising instability.
Porposing instability analysis of a planing vessel
Dynamic loads on marine propellers due to intermittent ventilation
Andrea Califano, Prof. Sverre Steen, Prof. Knut Minsaas
h = 0.261 m
1
Duncan (1983)
0.01
cavitation tunnel
0.9
Landrini et al. (1999)
CFD
0.8
0.005
AKPA 5.2
3fineBL-rkeEWT
0.7
2fineBL-MU5e-7
0.6
0
y
10 KQ
0.5
KT
h
-0.5
0
0.5
1
1.5
fineBL-inv
0.4
-0.005
fineBL-rkeEWT
0.3
coarseBL-inv
-0.01
0.2
coarseBL-rkeSWF
0.1
NACA0012-a5°
-0.015
0
0
0.1
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0.7
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0.9
1
J
Propeller open water diagrams
Koushan K., Dynamics of ventilated
propeller blade loading on thrusters
World Maritime Technology
Conference - WMTC'06, 2006
2fineBL-rkeEWT
1.1
1.2
1.3
x
Steady waves past a 2D hydrofoil
 The main objective is to develop a CFD model capable to
calculate the extent of propeller ventilation and the resulting
forces acting on it.
 A short description of the activities carried out within the
Rolls-Royce University Technology Center is outlined.
 The validation and verification CFD activities against the
propeller open water tests and the steady breaking waves over
a 2D hydrofoil are presented.