טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentGafter Roy
SubjectDelta type VLFS for open sea
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Nitai Drimer
Full Thesis textFull thesis text - English Version


Abstract

The field of Very Large Floating Structures (VLFS) deals with the research and design of maritime structures of extreme dimensions, long life-span, and exceptional costs.  VLFS are traditionally classified into two categories: The Pontoon  and the Semi-Submersible.  The Pontoon type is characterized by a rectangular box hull, of large length-to-depth ratio, which makes this structure vulnerable to longitudinal-bending and hydro-elastic effects, therefore limited to relatively sheltered waters.  The Semi-Submersible type is composed of submerged hulls, and column tubes that hold

 the deck structure above the level of wave-crests.  Its small intersection area with the water surface makes it suitable to severe wave conditions, typical to open ocean.  However, semi-submersible VLFS does not exist yet. 

Our study presents a new concept - the Delta type VLFS, designed to provide stability, broad storage and operational area, and an integrated sheltered basin allowing accessibility in most weather conditions.

Our hydrodynamic study of the Delta- type VLFS included three stages: an initial study, a parametric study and a mooring study.  The initial study included the specification of initial parameters, setup of a model for wave-structure interaction and studying its motion-response and wave agitation by linear analysis.  Since the results showed low motion response to regular incident waves and significant reduction of the wave height in the basin, a comprehensive parametric study was justified.  This parametric study is the central part of this thesis. 

In order to keep constant operational space, the deck area, basin area and the hull depth were held constant, and six geometric configurations were modeled by varying the head angle and adjusting its associated dimensions to keep the operational constraints.  Two configurations of the six were preliminarily eliminated due to operability and construction considerations, and the hydrodynamic analysis focused on the remaining four.  Motion response, comfort and operability aspects, were studied at regular and real sea conditions.

The results of the parametric study were favorable for the configurations of narrow head-angles.  The best suited geometric configuration was chosen for studying the moored structure under extreme weather conditions at the East Mediterranean Sea.

As the results of the parametric analysis showed that the optimal orientation of the structure is head-on the incoming waves, a Single Point Mooring (SPM) system, which enables the rotation of the structure about the connection point at the bow, was preliminarily designed for the mooring analysis.  A time domain simulation was carried out to analyze the motion of the moored structure, as well as the loads applied to the mooring lines.  The analysis showed that the mooring system maintained the structure in its optimal position. As the preliminary design of the mooring system was comprised of commercially available components, our results indicate that the mooring of our Delta VLFS is indeed practical at the site of the study.

The obtained results of this research are promising from all the hydrodynamic aspects: motion related to comfort, efficiency of the basin, and mooring of the VLFS; hence justify the suggested future stage of the study - the structural aspects.