General information
In irregular seas a moored ship may show low frequency motions in the horizontal plane (surge, sway, yaw). These are caused by the low frequency wave drift forces. These second order wave forces are much smaller than the first order wave loads (which cause the wave frequency motions). However, since the wave drift forces are slowly varying, they may excite the moored ship at its natural surge, sway or yaw periods, resulting in large motions.
In irregular seas a moored ship may show low frequency motions in the horizontal plane (surge, sway, yaw). These are caused by the low frequency wave drift forces. These second order wave forces are much smaller than the first order wave loads (which cause the wave frequency motions). However, since the wave drift forces are slowly varying, they may excite the moored ship at its natural surge, sway or yaw periods, resulting in large motions.
Services & Activities
The Offshore Department has ample experience in the analyses, model testing and simulation of low frequency motions. The research on this topic started with the analysis of the behaviour of moored tankers in irregular waves in the late 70s and early 80s. Later research focussed on the effects of current on the wave drift forces and on coupled mooring analysis, taking into account the interaction between low frequency motions and dynamic mooring loads. At present, great effort is taken in understanding phenomena typcial for side-by-side moored vessels and shallow water. Also the low frequency motions of structures other than tankers, such as semi-submersibles, is being investigated. Small water plane area floaters such as semi-submersibles and spars may show not only horizontal low frequency motions, but also vertical (roll and pitch) as a result of their long roll and pitch natural periods.
The Trials and Monitoring Department can be involved in full-scale measurement of low frequency motions.
The Offshore Department has ample experience in the analyses, model testing and simulation of low frequency motions. The research on this topic started with the analysis of the behaviour of moored tankers in irregular waves in the late 70s and early 80s. Later research focussed on the effects of current on the wave drift forces and on coupled mooring analysis, taking into account the interaction between low frequency motions and dynamic mooring loads. At present, great effort is taken in understanding phenomena typcial for side-by-side moored vessels and shallow water. Also the low frequency motions of structures other than tankers, such as semi-submersibles, is being investigated. Small water plane area floaters such as semi-submersibles and spars may show not only horizontal low frequency motions, but also vertical (roll and pitch) as a result of their long roll and pitch natural periods.
The Trials and Monitoring Department can be involved in full-scale measurement of low frequency motions.
Facilities & Tools
Low frequency motions are investigated in the following MARIN facilities :
Low frequency motions are investigated in the following MARIN facilities :
- Offshore Basin: DP model tests in combined current, waves and wind
- Shallow Water Basin
The following tools are used to study low frequency motion issues :
DIFFRAC: 3-D potential theory including wave diffraction
DRIFTP/DBDRIFT: Second order wave excited (drift) forces
LIFSIM/LIFMOT: Analysis of multi body dyamics and lift operations
TERMSIM: Assessment of dynamic line and fender loads for moored tankers
DYNFLOAT: Assessment of dynamic mooring system loads and tanker motions
DRIFTP/DBDRIFT: Second order wave excited (drift) forces
LIFSIM/LIFMOT: Analysis of multi body dyamics and lift operations
TERMSIM: Assessment of dynamic line and fender loads for moored tankers
DYNFLOAT: Assessment of dynamic mooring system loads and tanker motions
Software Sales
Some software tools are available for commercial use outside MARIN. A complete overview of these software tools for sale can be found under Software Sales.
Some software tools are available for commercial use outside MARIN. A complete overview of these software tools for sale can be found under Software Sales.
Experience record
The list below gives a review of projects carried out at MARIN in which the low frequency motions were asessed :
The list below gives a review of projects carried out at MARIN in which the low frequency motions were asessed :
- Akpo FPSO (TOTAL/Saipem) 2005
- Deepstar theme structures model tests (Deepstar) 2001
- Millenium ExD semi submersible (Friede & Goldman / Sante Fe Corporation) 2001
- Shell floating LNG development: side-by-side offloading tests (Shell) 2000
- Jotun FPSO (Esso/Bluewater/Kvaerner) 1997
The following Joint Industry Projects (JIPs) are focussed on low frequency motions :
- HAWAI
- SHUTTLE
- DYNFLOAT
- TERMSIM II
- DIFFRAC
Most recent papers on low frequency motions presented by MARIN
(complete overview of papers can be found under Publications)
(complete overview of papers can be found under Publications)
Cruise ship seakeeping and passenger comfort
R.P. Dallinga and J.E. Bos, HPAS 2010, 2010
The Effect of Wave Directionality on Low Frequency Motions and Mooring Forces
Olaf Waals (MARIN), OMAE Conference, Honolulu, 2009
On the Application of Advanced Wave Analysis in Shallow Water Model Testing (Wave Splitting)
Olaf Waals (MARIN), OMAE Conference, Honolulu, 2009
Motions and Mooring Loads of an LNG-Carrier Moored at a Jetty in a Complex Bathymetry
Otto Weiler (Deltares), Hans Cozijn (MARIN), Bas Wijdeven (Deltares), Stephane Le-Guennec (Total) and Francois Fontaliran (Yemen, OMAE Conference, Honolulu, 2009
Time Domain Analysis for DP Simulations
Jorrit-Jan Serraris (MARIN), OMAE Conference, Honolulu, 2009
R.P. Dallinga and J.E. Bos, HPAS 2010, 2010
The Effect of Wave Directionality on Low Frequency Motions and Mooring Forces
Olaf Waals (MARIN), OMAE Conference, Honolulu, 2009
On the Application of Advanced Wave Analysis in Shallow Water Model Testing (Wave Splitting)
Olaf Waals (MARIN), OMAE Conference, Honolulu, 2009
Motions and Mooring Loads of an LNG-Carrier Moored at a Jetty in a Complex Bathymetry
Otto Weiler (Deltares), Hans Cozijn (MARIN), Bas Wijdeven (Deltares), Stephane Le-Guennec (Total) and Francois Fontaliran (Yemen, OMAE Conference, Honolulu, 2009
Time Domain Analysis for DP Simulations
Jorrit-Jan Serraris (MARIN), OMAE Conference, Honolulu, 2009
Most recent low frequency motion articles written for MARIN Report
(complete overview of articles can be found under Publications)
(complete overview of articles can be found under Publications)
Pulling together in ROPES JIP
Henk van den Boom, MARIN Report, 2010
Measuring success
MARIN Report, 2009
Oasis of the Seas
Giedo Loeff, Jaap van Heerd & Reint Dallinga, MARIN report, 2009
Henk van den Boom, MARIN Report, 2010
Measuring success
MARIN Report, 2009
Oasis of the Seas
Giedo Loeff, Jaap van Heerd & Reint Dallinga, MARIN report, 2009
Contact
For more information on how MARIN can help your organisation with low frequency motions, please contact the Offshore Department, Manoeuvring Department or the Trials and Monitoring Department.
For more information on how MARIN can help your organisation with low frequency motions, please contact the Offshore Department, Manoeuvring Department or the Trials and Monitoring Department.