Mun-Keun Ha

A Direct Assessment Approach for Structural Strength Evaluation of Cargo Containment System Under Sloshing Inside LNGC Tanks Based on Fluid Structure Interaction

The sloshing phenomenon is one of the most important and challenging issues for the design of cargo containment systems of LNG carriers and is being studied by various research groups in many countries. In this paper, a direct assessment approach based on fluid structure interaction is proposed to assess the structural safety of cargo containment systems against extreme sloshing loads. In the course of developing the methodology, two technical issues are mainly dealt with; (1) how to efficiently apply a numerical method for sloshing phenomena and (2) how to verify the structural safety criteria of cargo containment system against sloshing. The developed methodology is applied to a membrane-type cargo containment system of a large LNG carrier built in Samsung Shipyard.Copyright

Analysis of Full-Scale Hull Girder Loads of a Container Carrier and Its Simulation Using a Nonlinear Seakeeping Program

ABS, SHI, and OOCL have been conducting a project on full-scale measurement of hull stress of a container carrier since 2006. A Hull Stress Monitoring System (HSMS) was installed on an 8063 TEU container carrier recording hull girder loads and other navigation data. Vibratory responses of the hull girder were recorded at certain conditions, such as in the limited fetch storm waves in the Mediterranean Sea. The recorded data has been analyzed to determine the level of vibratory responses and the conditions in which they occurred. Since the vibratory response is superposed to the wave frequency component of the hull girder loads, it also affects the statistics of the maximum hull girder loads in waves. The effects of the vibratory responses in the long-term have been investigated for the dynamic Vertical Bending Moment (VBM) and bow acceleration. While the full-scale measurement provides valuable data for what actually happened in real vessel operations, the actual conditions can not be controlled, such as the wave environments or loading conditions. Hence, numerical calculation results are also desirable to investigate the vibratory responses under controlled conditions taking into account the elastic hull girder properties under exact conditions for validation purposes. ABS has been applying a time domain nonlinear wave/body interaction analysis program, NLOAD3D, for the assessment of the structural responses of vessels in large waves. The NLOAD3D program has been further developed to incorporate an elastic beam model to reproduce vibratory hull girder responses, with the simulations being carried out on motions and moments for selected notable events recorded during the voyages. Comparisons of the simulation and the measurement are presented.Copyright

Development of 115K Tanker Design Adopted Ice Class 1A

There are very few numbers of 115K FPP (Fixed Pitch Propulsion) Tankers for the Baltic ice class IA because the minimum power requirement of FMA (Finish- Swedish Maritime Association) needs quite large engine power and the 40 m Beam is out of calculation range of FMA minimum power requirements. The shipyard has no choice except to increase the engine power to satisfy FMA minimum power requirement Rule. And the operation cost, efficiency of hullform and its building cost are not good from the ship owners` point of view To solve this problem, the experience of ice breaking tanker development and the ice tank test results were adopted. The main idea to reduce the ice resistance is by reducing waterline angle at design load waterline. The reason behind the main idea is to reduce the ice-clearing force. Two hull forms were developed to satisfy Baltic Ice class IA. Two ice tank tests and one towing tank test was performed at MARC (Kvaener-Masa Arctic Research Center) and SSMB (Samsung Ship Model Basin) facilities, respectively. The purpose of these tests was to verify the performance in ice and open water respectively The hull form 2 shows less speed loss compared to Hull form 1 in open water operation but hull form 2 shows very good ice clearing ability. finally the Hull Form 2 satisfying Baltic ice class IA. The merit of this hull form is to use the same engine capacity and no major design changes in hull form and other related designs But the hull structure has to be changed according to the ice class grade. The difference in two hull form development methods, ice model test methods and analysis methods of ice model test will be described in this paper.

Research of Design Improvement regarding Foundation Technologies for Floating LNG

Typical technical issues associated with Floating LNG (FLNG: FSRU and LNG FPSO) design are categorized in terms of global performance evaluation. Although many proven technologies developed through LNG carrier and oil FPSO projects are available for FLNG design, we are still faced with several technical challenges to clear for successful FLNG projects. In this paper, some of the challenges encountered during development of the floating LNG facility (i.e. LNG FPSO and FSRU) will be reviewed together with their investigated solution. At the same time, research of design improvement including new LNG-related technologies such as combined containment system will be presented to overcome the unrevealed challenges for the FLNG development.

Safety Assessment of Inner Hull Structure Affected by Cryogenic Temperature

The market of LNG (Liquefied Natural Gas) carrier is continuously in a prosperous condition, and a lot of LNG vessels are being built in many shipyards. Membrane-type MARK-III LNG CCS (Cargo Containment System) is used more and more in the construction of LNG carrier, and it has already taken considerable market share among the various LNG CCS products. This paper deals with a study on structural safety of LNG carrier whose inner hull structure is affected by cryogenic temperature of LNG. If the primary and secondary barriers are failed simultaneously, the inner hull structure comes to be in direct contact with LNG. It is well known that the cryogenic temperature exposes the inner hull structure to fatal risk of structural failure due to brittle fracture, but nevertheless it is quite difficult to find a precedent research which explains the degree of risk and severity with due consideration of the consequence caused by structural failure of inner hull. The heat transfer test has been performed using the specimen appropriate to realize test scenario while considering cryogenic liquid flow from primary and secondary barrier into inner hull structure, and at the same time, the specimen has been tested by applying proper deformation so as to examine the structural behavior of inner hull structure under cryogenic condition. The heat transfer analysis has been performed to simulate and verify the heat transfer test, and consequently it is possible to obtain actual distribution of temperature in the inner hull structure exposed to cryogenic temperature. The structural analysis has been performed to evaluate the damage of inner hull structure and as a result to assess overall decrease of hull girder strength of LNG carrier. Finally, consequence of the decrease of global strength has been discussed.© 2010 ASME

Winterization Techniques for Semi-Submersible Rig Operating in the Arctic Ocean

Samsung Heavy Industries (SHI) has been developed many useful design concepts and procedures for offshore platforms operating in cold regions. In comparison with normal platforms, winterization for outfitting systems can be considered as an essential difference in design process to guarantee safe operation in cold environments. This study selected a Semi-Submersible Drilling Floating Rig ordered by LLC Gazflot, and shows an effective design procedure and its performance of winterization. A dominant area for winterization should be derrick and drilling deck space that have large opening areas to transport drilling, subsea equipments, risers and which have many those equipments required minimum temperature of about minus 20 degree of Celsius to guarantee normal operation under the lowest operating ambient weather condition of minus 30 degree of Celsius. The possible optimum solutions were proposed by suggesting wind wall design with openings for ventilation and by finding locations and quantities of heaters and blowers considering local temperature and air change rate to satisfy hazardous guide. Those solutions were verified by CFD (Computational Fluid Dynamics) approaches with suitable boundary conditions.Copyright

Development and Evaluation of Optimal Routing System

To improve the safety and efficiency of trans-ocean voyage, authors developed a new onboard weather routing system (so called SORAS). The system utilizes weather forecasting data to evaluate seakeeping performance and to generate optimized route plan with respect to fuel consumption and sailing time. The system can provide decision support for navigator in real time. For this feature, onboard wave measurement system and hull stress monitoring system are integrated to provide real time wave information and actual hull stress and bow acceleration. The optimal route depends on not only weather condition but also ship’s propulsion performance. We performed a simulation study to determine the accuracy limit of mathematical model for propulsion performance. To evaluate the system, we compared calculation results with actual voyage data. The estimation results of speed reduction and fuel consumption showed good coincidence with measurement results. The wave bending moment was estimated on the forecasted wave condition. The results were compared with measured wave bending moment. For optimal route, it was confirmed that the efficiency of optimal route is superior to the efficiency of the actual route which planned by captains or officers, and the improvement of efficiency would be significant.Copyright

Hull Forms for Icebreaking Tankers

The optimum design for an icebreaking tanker will depend on the trade route and the cargo delivery requirements. For example, the hull shape of a ship that spends almost all of its time operating in heavy ice can be optimized for low speed icebreaking conditions. In contrast, a ship that spends a small portion of its time in light ice that has been previously broken and the rest of its time in open water can be optimized for different requirements. The challenge for the designer is complicated by the observation that many ship design features that enhance powering performance in ice are detrimental to open water performance. This paper presents predictions of ship resistance in pack ice, level ice and open water for four tanker designs, which include a conventional hull with no modification for ice at all and three designs proposed for operation in Arctic ice conditions. The predictions of ship performance are based on model experiments carried out in Canada and Korea. The resistance of the four hulls in open water, two concentrations of pack ice and two level ice thicknesses are compared and discussed. Information of this sort is essential for developing the optimum ship design for a particular shipping route, given known profiles of open water, pack ice and level ice.Copyright

ANALYSIS OF RINGING BY CONTINUOUS WAVELET TRANSFORM

This paper investigates the ringing phenomenon by using continuous wavelet transform (CWT). Experiments were conducted in a wave tank. Breaking waves were generated to understand the ringing phenomenon. The model tested was a surface piercing circular cylinder and the time series of the wave height and force on the cylinder was measured. An analysis was conducted using continuous wavelet transform. The scalograms of the time series of the wave height and those of the forces showed that high frequency components were generated at the onset of the breaking wave impact in the time domain. It was concluded that, ringing is a natural frequency response due to the breaking wave impact.