Efficient Prediction of Dynamic Response for Flexible and Multi-body Marine Structures Reza Taghipour , Professor Torgeir Moan

1
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.
2
Structural Analysis of Ship Collision and
Grounding Ph.D candidate Lin Hong, Prof. Jørgen
Amdahl

• A brief overview of the ongoing project
  ScenaRisCG 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.

3
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.
• Sea transport on ship or barge. What is the
  safety level incorporated in simplified motion
  criteria?

Load-out / Load-in operation
Sea transport (picture by Umoe)
4
A Specialized FEM Prototype for Structural
Analysis of a Floating Fish Cage Paul Thomassen,
Prof. Bernt Leira

• 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
  object-oriented FEM framework.

Laboratory measurements (From Sumer, B.M.)
Over Screendunp of the base case structure.
Under grafical user interface of the prototype.
5
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 wide-band 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 wide-band 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.

6
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
• 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 post-process
  for statistics,
• Compare against analytical Gaussian formulation.
• Key results sought
• 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
• Possible extensions
• 2nd-order wave models simulation vs. analytical
  approach.

7
Effect of Reynolds Number on Forced VIV
OscillationsJamison 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
• Perform experiments with five Re, ranging from
  4,600 to 46,000. Examine peak response region.

Transducers and optical encoders
Cylinder
IL Test Matrix.
Front View
Side View
8
Hydrodynamic Force Identification from VIV
Experiment with Slender Beams Jie Wu, Prof. Carl
M. Larsen, Halvor Lie

• The objective is to identify hydrodynamic forces
  from response measurement and construct a force
  model.
• Identification methods based on Kalman filtering
  and constrained optimization.
• Validation of the methods by numerical
  simulations.
• 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

Laboratory measurements (From Sumer, B.M.)
9
Valve condition and performance monitoringErlend
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.
• MARINTEKs CORD project, results post analysis.
• New laboratory tests Alternative valves and
  measurements, inflicted damage, frequency
  spectrum analysis of ultrasound.

The Tail IO project
10
Modelling Ship Traffic From AIS DataKarl 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
• 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.

Automatic Identification System Track-Lines
Extracted Track Features
11
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.
• 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.

Laboratory measurements (From Sumer, B.M.)
Turbulent kinetic energy field at Re 3.6 x106
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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)
• 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 1 Experiments by Rognebakke and Allers
Figure 2 Pressure-time history (Faltinsen and
Rognebakke)
13
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.
• 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

Model testing of ship by terminal in shallow
water subject to waves
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.
14
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

15
Applications of a BEM to strongly nonlinear
wave-body interaction problems Hui Sun and Prof.
Odd M. Faltinsen

• 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 2Dt 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.

Water entry of a bow-flare ship section with heel
angle
Porposing instability analysis of a planing vessel
16
Dynamic loads on marine propellers due to
intermittent ventilation Andrea Califano, Prof.
Sverre Steen, Prof. Knut Minsaas
Steady waves past a 2D hydrofoil
Propeller open water diagrams

• 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.

Koushan K., Dynamics of ventilated propeller
blade loading on thrusters World Maritime
Technology Conference - WMTC'06, 2006