Progress Reports: December 2005
Relative Motions of LNG Terminal and Carrier in Offloading Operation Including the Effects of Tank Sloshing
OBJECTIVE: The hydrodynamic interactions are very important to reliably assess the relative motions between LNG terminal and LNG carriers under certain wave-wind-current condition. The relative motions affect the design of offloading piping system, offloading operations, maximum loading on hawser/fenders, operable weather criteria (down-time prediction), and the sloshing of liquid cargo. In the conventional ship-motion analysis, the effects of inner free surface and its sloshing inside the liquid container have usually been ignored. However, recent experimental and numerical studies have shown that the coupling effect between liquid cargo sloshing and LNG ship motion is significant to both the impact on the cargo wall and the global performance of the system. The coupling effects become more important as the size of LNG tanks increases. In this project, we first develop numerical tools to analyze the offloading between LNG terminal and carrier and assess the global performance in various structural types, gap, yoke, mooring, hawser, fender, and weather conditions. Secondly, the numerical tools will further be extended to include coupling effects between liquid sloshing and vessel motions for various LNG filling conditions. This is of a great concern to the LNG FPSO/FSRU operation in the production site and offloading operation of LNG carriers close to LNG terminal.APPROACH: The vessel-mooring-riser coupled dynamics program WINPOST has been extended to analyze dual floating bodies connected by many elastic lines. Yoke, hawser, and fender modeling will further be added to this computer program. Then, various operational and weather conditions will be set for a series of operability and down-time analyses for the cases of particular interest to offshore industry. The WAMIT program will be used in analyzing the effect of tank sloshing on vessel motions. For this, both internal and external BVPs have to be set up and solved by using WAMIT and the results should be imported to WINPOST program for ensuing vessel-mooring coupled dynamic analysis in time domain. Our preliminary-study results on the effects of liquid sloshing on vessel motions are summarized in an ISOPE’05 paper.
DEPLOYMENT OF RESULTS: The numerical results will be refined and verified by comparing with future experimental results at OTRC. The analysis results will be published as OTRC report as well as journal and conference papers.
ANTICIPATED NUMBER OF PHASES: 2
PROJECT PLAN FOR PHASE 1 (2005 -2006):
Scope and Plan: The vessel-mooring-riser coupled dynamics program WINPOST for dual floating bodies will be used for relative motion analysis between LNG terminal and LNG carrier connected by offloading piping system, yoke, and hawsers. A fender modeling will be added to this computer program. The numerical results will be compared against available experimental results. Then, various structural types, operational, and weather conditions will be set for the case studies of particular interest to offshore industry. The coupling of liquid sloshing with ship motion will be formulated and numerically implemented.
Anticipated Results: The research results will be summarized in a final project report and journal papers.
PROJECT PLAN FOR PHASE 2 (2006 - 2007):
Scope of Work: The WAMIT program will be used in analyzing the effect of tank sloshing on vessel motions. For this, both internal and external BVPs have to be set up and solved by using WAMIT and the results should be imported to WINPOST program for ensuing vessel-mooring coupled dynamic analysis in time domain. First, the proposed scheme will be applied to a single LNG carrier with various fill ratios. The numerical results will be compared against available experimental results. Then, the same scheme will be extended to the interactions of LNG terminal and carrier including sloshing effects. The free-surface part of the liquid sloshing will be extended to nonlinear condition possibly with viscous effect.
Anticipated Results: The research results will be summarized in a final project report and journal papers.
PRINCIPAL INVESTIGATOR (S) & OTHERS INVOLVED IN PROJECT:
PI: M. H. Kim
Date: December, 2005
Project Name: Relative Motions of LNG Terminal and Carrier in Offloading Operation Including the Effects of Tank Sloshing
Project Number: 32518/1510L Industry Funded
Principal Investigators: M. H. Kim
Estimated Completion Date: Aug.2006 (1st Phase)
Project Description:
The hydrodynamic interactions and coupled dynamics are very important to reliably assess the relative motions between LNG terminal and LNG carriers under certain wave-wind-current condition. The relative motions affect the design of offloading piping system, offloading operations, maximum loading on hawser/fenders, operable weather criteria (down-time prediction), and the sloshing of liquid cargo. In the conventional ship-motion analysis, the effects of inner free surface and its sloshing inside the liquid container have usually been ignored. However, recent experimental and numerical studies have shown that the coupling effect between liquid cargo sloshing and LNG ship motion is significant to both the impact on the cargo wall and the global performance of the system. The coupling effects become more important as the size of LNG tanks increases. In this project, we first develop numerical tools to analyze the offloading between LNG terminal and carrier and assess the global performance in various structural types, gap, yoke, mooring, hawser, fender, and weather conditions. Secondly, the numerical tools will further be extended to include coupling effects between liquid sloshing and vessel motions for various LNG filling conditions. This is important to the LNG FPSO/FSRU operation in the production site and offloading operation of LNG carriers close to LNG terminal.Progress:
The vessel-mooring-riser coupled dynamics program WINPOST has been extended to analyze dual floating bodies connected by many elastic lines, hawsers, and fenders. It is seen that neglecting off-diagonal hydrodynamic interaction terms may lead to appreciable error in the case of side-by-side offloading operation. The hydrodynamics program is being extended to analyze the effect of tank sloshing on vessel motions. For this, both internal and external BVPs are set up in the frequency domain and the results are imported to the time-domain simulation program. Both linear potential 3D panel program and 3D Navier-Stokes CFD program are used for liquid sloshing and ship-motion simulations for comparison. The simulation methods will be extended to two bodies and multiple tanks. More systematic results will be obtained for a series of vessel, mooring, environmental and operating conditions.Reports & Publications:
Koo, B.J. and Kim, M.H., “Relative motion analysis of two floating platforms with mooring and hawser lines in side-by-side offloading operations”, J. of Applied Ocean Research (In Press)Kuriakose, V.P., “Floating terminal and LNG carrier interaction analysis for side-by-side offloading operation” M.S. Thesis, Texas A&M Univ., 2005