• Journal of Ship and Ocean Technology
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• v.11 no.3
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• pp.1-13
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• 2007

A semi-submersible drilling rig is regarded as one of the typical offshore structures operated in the field with moderate environments such as the Gulf of Mexico, Brazil, and West Africa. Its typical roll and pitch natural periods are around 30 seconds, which avoids prevailing regions of the wave energy spectrum, and their responses in waves are quite acceptable for common operation conditions. But large roll and pitch motions can be induced by wave difference frequency energy spectrum if the metacentric heights of a semi-submersible decrease to small values in some loading conditions, and it is because the roll and pitch natural periods increase and approach to the region where the spectral density of the low frequency wave drift moment has significant value. This paper describes the low frequency roll motion of a semi-submersible that are excited by the wave 2nd order difference frequency energy by a series of model experiments. From the model tests with several different initial metacentric heights (GM), it was observed that a semi-submersible can experience large roll motion due to the wave group spectrum.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.04a
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• pp.65-71
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• 2009

The process of cold rolling is becoming more severe with the increase in the production of high tensile steel strip as a result of increased demand. Consequently, there is a need to develop work roll materials with better resistance to wear and roll failure. DOOSAN has developed an improved in-house 5%Cr alloy, New HSR1, with properties superior to the existing in- house 5%Cr alloy, Old HSR1. Test alloys were designed with controlled amounts of Si and Mn based on Old HSR1 and an optimum alloy was chosen based on thermal shock tests. A prototype work roll was manufactured with New HSR1, and properties of test specimens were evaluated. The results indicated that New HSR1 has better properties than Old HSR1. After application of New HSR1 work rolls, productivity increased due to advanced resistance to wear and roll failure.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.08a
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• pp.216-222
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• 2004

The caster roll shells have the good thermal conductivity and the low thermal expansion and have to exhibit high enough strength and good ductility at temperature up to $600^{\circ}C$. Thermal stress in particular is very high due to the contact with the liquid aluminium. The main stresses are of thermal origin, which bring a plastic fatigue on surface. This paper will represent one survey about the investigation of the failure of roll shells for continuous casters and an analysis using the simulation of the temperature distribution and the state of stress during hot rolling. Moreover, there will be a discussion on the roll shell of Mod. HAR 5 which is developed by heat treatment process. Mod. HAR 5 has advantages of high strength, high toughness and increased thermal stress resistance while maintaining the same productivity as the conventional roll.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.05a
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• pp.30-35
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• 2004

Several roll motion reduction devices are reviewed and suggested for the application in FPSO. The firstly suggested solution is the shape of the bilge. The next is a bilge keel. The last suggestion is the ART (anti-rolling tank). Typical U-tube type ART is designed for a FPSO and examined extensively by model experiment. The model section was made of transparent acryl. Free decay test, forced oscillation test and wave test were carried out at a two-dimensional wave flume. U-tube type ART is effective only when the natural periods of ART and ship are same. Therefore, the divided U-tube type ART with split plate is suggested for the reduction of the roll motion of a FPSO over the wide range of the roll period.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2011.06a
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• pp.759-760
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• 2011

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.04a
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• pp.62-64
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• 2009

Control of back-up roll deformation and wear profile in plate rolling is important not only for enhancement of the structural precision of mill, but also for improving the yield and rolling operation. in the heavy plate mill, there have been strong demands for upgrading back up roll operation technology. In order to satisfy these demands, it is essential to develop the backup roll deformation analysis models and wear profile prediction models. This paper gives a general description of the backup roll deformation and wear model, simulation result for deformation analysis and wear profile.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.08a
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• pp.207-215
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• 2004

There are various characteristics called for in work roll and intermediate rolls for cold rolling mills. Among these characteristics, the two main requirements are to ensure the quality of the rolled products and to reduce roll cost. To achieve these needs, resistance to wear, to thermal shock and to contact fatigue are especially important. This paper describes that new material(named DSR1) for intermediate rolls which greatly increases rolling campaign and improves resistance to wear has been developed. DSR1 was successfully manufactured and has been used in the cold rolling mill. It showed that Trial product was homogenous in hardness distribution and sufficient usable diameter. Also in service test, trial product is much more excellent rolling performance than conventional $5\%Cr$.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.11a
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• pp.188-192
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• 2004

A Numerical analysis method is developed in order to compute the flaw and wave field for 2-dimensional floating body in the free roll motion with 3 degrees of freedom. Navier-Stokes and continuity equations are gaverning equations in tire present study. Finite Difference method is introduced to discretize the governing equation. The free surface is traced by the interface tracking method and the grid system is fitted to boundaries including free surface and body surface, which is moving in the flow field. The numerical scheme is based on Maker and Cell method. For the sake of validation of the numerical method, the computed roll decay factors according to tire midship section shapes are compared with measured results. The numerical results are discussed in order to understand the effect of midship section shape on roll motion.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.05a
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• pp.565-566
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• 2012

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.10a
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• pp.169-173
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• 2001

This study presents the results of decoupling of free decay roll test data by discrete wavelet transform. Free roll decay test was performed to decide the coefficients of damping terms in equation of motion. During the experiment, a slight yaw motion was found while the model was in the free roll decay motion. Discrete wavelet transform was applied to the signal to extract the pure roll motion. The results were compared to those of the Fourier transform. DWT was able to decouple the two signals efficiently while the Fourier transform was not.