December 2005
Table of Contents:

Greek Section

Canadian Atlantic Section

Greek Section
by Nikos Dionissopoulos

October 13, 2005

On October 13th, 2005 the first technical meeting of the Greek Section for the 2005-2006 season was held in the presence of more than 80 members and students, during which Mr. H.C.Kim, Executive Vice President and Head of Engineering and Technology Division and Mr. Y.B.Lee, Research Engineer, both of DAEWOO Shipbuilding & Marine Engineering Co. presented their paper on “ Recent Evolution of LNG Carriers”.

The need for alternative and more environment-friendly energy sources to oil has been stimulating the LNG industry at all stages of production, transportation and distribution. In transportation, innovational developments of LNG carriers are dazzling. During the last five years, their cargo capacity increased rapidly up to 250,000 m3 based on membrane types. DAEWOO developed diverse LNG carriers to meet the surge in the new LNG market and has successfully launched new concept vessels, the LNG RV that can supply local consumers at land with re-gasified natural gas on-board. This type of vessels can significantly affect the value chain of natural gas and, therefore, it is advantageous over conventional LNG carriers.

In the presentation, the overall design concept of large LNG carriers and LNG RV were introduced and some core design issues for large LNG carrier were discussed including optimum hull form development, sloshing assessment of large cargo tanks, structural strength assessment, vibration aspects concerning the accommodation and pump tower and a comparison of cargo containment systems.

For all the above topics very useful research and development measurements were presented, which impressed the audience.

In connection with the hull form development, data were presented that included the advantages of the twin skeg & twin screw versus the single screw LNG designs, in terms of propulsion, maneuvering and seakeeping performance. Figures with comparative measurements were given.

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Canadian Atlantic Section
by Dusty Miller

October 19, 2005

The Canadian Atlantic local section meeting, held on October 19th, was addressed by Dr. Robert Dow, of Martec Ltd., on “Structures, Benefits and Issues with Trimaran Hull Forms”. This presentation was based on the work conducted by MOD on the Royal Navy vessel “Triton”. This full scale test bed vessel is 97.8 m Loa x 22.5 m beam x 1300 tonnes displacement, and the vessel’s test program was extensive and intensive, in particular regarding operations in rough weather and waves to seek experience and record the extreme loading of the vessel’s structure.

Initially the vessel’s structural design was developed in two parallel streams, by a Vosper/DNV team and a UK MOD team. This allowed the two teams from two different bases, to consistently compare their results and allowed continuous refinement of the loading patterns to be used and resulting structures. Both global and more detailed FE models were employed during the design of RV "Triton". The most detailed global model utilized 263163 elements and was used to obtain calibration factors between measured strains and loads. Parallel investigations were also made using a large segmented model (6 segments in the length) in the wave tank in both regular and irregular waves.

After construction of the vessel was completed, the vessel was dry docked at Rosyth Royal Dockyard where it was subjected to testing of the structure by the application of known loads by hydraulic jacks. These tests allowed calibration factors between the measured strains and the applied load, to be determined and the FE model thus to be calibrated. The rough weather full-scale sea trials were conducted between Scotland and Iceland, in both deep, off the continental shelf water and shallow water. Tests were regularly conducted in Sea States up to 8, and some limited results were obtained in Sea State 9 The vessel instrumentation system had 201 structural channels and about 12 Gbytes of data per day were collected. The results from the FE model calibration allowed the conversion of the strain measurements from the rough water full scale sea trials into loads, which were then used to predict the extreme design loads. Local pressures of 337 kPa (54.7 psi) were recorded on the front face of the midship cross structure to the outrigger. This pressure considerably exceeded the elastic limit of the structure, which was evidenced by the permanent deflection of the plating, which occurred.

The conclusions of the test program were very positive and concluded that the vessel exceeded the performance design predictions, that the structural arrangements were more than adequate (some areas were clearly over designed and could still be lightened), and that there were no inherent problems as a result of the vessel being a trimaran. The testing program continues.

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