• 한국해양공학회지
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• 제15권4호
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• pp.8-13
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• 2001

It is important to estimate exactly wave forces acting on various types of offshore structures under the severe environmental conditions in the ocean site. This paper presents an easy experimental method which deals with transient waves. The proposed scheme made it possible to generate breaking waves at any position in the wave tank by changing the maximum slope of the component waves. The theoretical and experimental methods were investigated by generating concentrated waves which acted on a single and multiple cylinders. The waves forces increased rapidly when the models encountered breaking waves. The theoretical results underestimates the forces due to breaking waves. Therefore, the effects due to breaking waves should be considered carefully in the design process of a structure under the influence of breaking waves.

• 한국해양공학회지
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• 제10권3호
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• pp.62-73
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• 1996

Numerical simulation is made of the three-dimensional wave breaking motion about a part of a floating offshore structure containing a circular cylinder mounted vertically onto a lower hull in regular periodic gravity wave generated by a numerical wave maker. TUMMAC-VIII finite-difference method is newly developed for such a problem. By use of density-function technique the three-dimensional wave breaking motion is approximately implenented in the framework of rectangular grid system. A porosity technique is devised for the implementation of the no-slip bydy boundary conditions. The generation of breaking waves by the interaction of incident waves with the structure is well simulated and interesting features of breaking waves are revealed with containing degree of quantitative and qualitative accuracy.

• 한국기계가공학회지
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• 제4권2호
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• pp.3-9
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• 2005

In this study, the chip breaking characteristics of S, PbS and BiS free machining steels have been assessed. PbS free machining steel shows the lowest value of chip thickness ($t_c$) under the same cutting conditions. SM10C steel has the largest value of the chip cross-section area ratio ($R_{CA}$). As the feed rate becomes larger the chip breaking cycle time ($T_B$) decreases and the chip breaking index ($C_B$) increases. The properly controlled-C type chip has been obtained with the value of $C_B$ between 0.05 and 0.2. Free machining steel, PbS produces the properly controlled-C type chip in a wider feed rate range than other steels.

• 비파괴검사학회지
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• 제25권3호
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• pp.215-221
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• 2005

It is required to evaluate nondestructively depth of surface-breaking cracks in structures. In this paper, the self-compensated technique by laser-based ultrasound is used to measure the depth of surface-breaking defect. Optical generation of ultrasound produces a well defined pulse with reliable frequency content. It is broad banded and suitable for measurement of attenuation and scattering over a wide frequency range. The self-calibrated signal transmission data of surface wave shows good sensitivity as a practical tool far assessment of surface-breaking defect depth. It is suggested that the relationship between the signal transmission and crack depth can be used to predict the surface-breaking crack depths in structures.

• 한국해안해양공학회지
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• 제2권2호
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• pp.96-103
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• 1990

A local Iribarren number is suggested for the universal use of breaker type classification, which relates the bed slope to the wave steepness, both being given from the breaking point. The existing Iribarren number uses the wave length at an offshore point, while the local Iribarren number uses the wave length at the breaking point so that it can imply any influences due to current interaction and diffraction. The modified form of Miche's breaking criterion includes 고 breaking parameter which may be related to the local Iribarren number. Using the modifiedform of Miche's criterion with the local Iribarren number, the inclusion of Doppler effect seems to describe well the wave breaking mechanism in a current-interacted flow on a sloping beach without any additional effects implemented.

• 한국정밀공학회지
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• 제11권6호
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• pp.179-184
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• 1994

In this study a nondimensional parameter, feed/land length(F/L) was introduced, and using this parameter, cutting performance and chip breaking characteristics of the groove and the land angle type chip formers were assessed. Specific cutting energy consumed and shape of broken chip with its breaking cycle time were appraised to find out the ranges of F/L value where efficient cutting and effective chip breaking could be achieved. C type chip was found out to be the most preferable in terms of cutting efficiency.

• 대한조선학회논문집
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• 제55권4호
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• pp.306-312
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• 2018

To navigate in ice-covered waters, the ice-breaking process is required. The ice-breaking mode depends on material properties of sea ice and ice conditions. The ice-breaking mode is classified into ramming and continuous ice-breaking. The ramming is effective on large ice features, such as thick ice ridge and icebergs, and the continuous ice-breaking is on level ice. In general, the impact time duration of crushing or bending on ice sheets is from 0.2 to 1.0 second. However, impact duration in ramming will be increased. The Korean ice-breaking research vessel ARAON conducted her research voyage in the Antarctic sea during the winter of 2012. The IBRV ARAON measured strain in ramming and continuous ice-breaking. Strain gauge signals were recorded during the planned ice-breaking performance and the unplanned ice transits in heavy ice conditions. The aim of this study is to investigate the ice load signals measured in ramming processes under the heavy ice condition. Based on the time history of the signals, a raising time, a half-decaying time and time duration were investigated and compared with the previous study which was suggested the five profiles of the ice load signals.

• 한국기계가공학회지
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• 제3권2호
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• pp.25-31
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• 2004

Machinability in metal cutting processes depends on cutting input conditions such as cutting velocity, feed rate, depth of cut, types of work material and tool shape factors. In this study, to assess chip breaking characteristics of a turning process, an equivalent oblique cutting system to this has been established. And the equivalent effective rake angle was determined using side rake angle, back rake angle and side cutting edge angle of the tool. A non-dimensional parameter, Chip breaking index(CB), was used to assess Chip breaking characteristics of chip in conjunction with the equivalent effective rake angle. In case of positive rake angles of the equivalent effective rake, the back rake angle has little effect on the chip breaking characteristics however, in case of negative ones, the side rake angle has some effect on Chip breaking characteristics.

• 대기
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• 제17권3호
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• pp.231-240
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• 2007

The flow regimes of continuously stratified flow over a double mountain and the effects of a double mountain on wave breaking, upstream blocking, and severe downslope windstorms are investigated using a mesoscale numerical model (ARPS). According to the occurrence or non-occurrence of wave breaking and upstream blocking, three different flow regimes are identified over a double mountain. Higher critical Froude numbers are required for wave breaking and upstream blocking initiation for a double mountain than for an isolated mountain. This means that the nonlinearity and blocking effect for a double mountain is larger than that for an isolated mountain. As the separation distance between two mountains decreases, the degree of flow nonlinearity increases, while the blocking effect decreases. A rapid increase of the surface horizontal velocity downwind of each mountain near the critical mountain height for wave breaking initiation indicates that severe downslope windstorms are enhanced by wave breaking. For the flow with wave breaking, the numerically calculated surface drag is much larger than theoretically calculated one because the region with the maximum negative perturbation pressure moves from the top to the downwind slope of each mountain as the internal jump propagating downwind occurs.

• 한국레이저가공학회지
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• 제9권1호
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• pp.9-16
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• 2006

Glass is one of brittle materials. Generally, brittle material is weak for tensile stress but strong for compression stress. Laser breaking of glass used this brittle characteristics. Laser breaking of glass was simulated to optimize breaking condition by using commercial FEM code MARC which is applicable to thermo-mechanical coupling analysis. Various shapes of heat sources were applied to the analysis and the distance between heating and cooling source were varied for each simulation. The shapes of heat sources were circle, single and double ellipse and the distance was varied from 0mm to 30mm. Moving heat sources were designed on the basis of experimental condition. As a result, double elliptic shape of heat source was the most suitable among them in laser breaking of glass. And it should be useful to determine optimal condition of laser breaking for glass.