• Journal of Korean Society of Steel Construction
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• v.29 no.6
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• pp.401-410
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• 2017

This study deals with dynamic instability of a tendon moored submerged floating tunnel (SFT) due to tendon slack. In general, environmental loadings such as wave and current govern SFT design. Especially, the wave force, whose amplitude and direction continuously change, directly induces the dynamic behavior of the SFT. The motion of the floating tube, induced by the wave force, leads dynamic response of the attached tendons and the dynamic change of internal forces of the tendons significantly affects to the fatigue design as well as the structural strength design. When the severe motion of the SFT occurs due to significant waves, tendons might lose their tension and slack so that the floating tube can be transiently instable. In this study, the characteristics of dynamic instability of the SFT due to tendon slack are investigated performing hydrodynamic analysis. In addition, the effects of draft, buoyancy-weight ratio, and tendon inclination on tendon slack and dynamic instability behavior are analytically investigated.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.5
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• pp.1887-1895
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• 2013

In this study, physical experiments were performed in a two-dimensional wave flume to investigate the hydraulic and structural performance of a SFT model. The experiments were made by generating regular waves of different heights and periods under various conditions of buoyancy to weight ratio (BWR) and water depth as well. Through the analysis of the experimental data, it was clarified that the sway and heave motions of the tunnel body linearly increased with wave height and period. In contrast, the roll motion was rather insignificant unless wave height and period were comparatively large as the design wave. Similarly proportional relationship with respect to wave height and period was obtained in case of the maximum tensile force acting on the tension legs and the wave loads on the tunnel body. Regarding the change of water depth or BWR conditions, generally decreasing trend was obtained according to increase of water depth but decrease of BWR for both of the magnitudes of structural behaviors or wave loadings on the SFT structure.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.38 no.5
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• pp.316-322
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• 2005

In order to develop a floating breakwater, which can efficiently control long period waves, vertical plates are attached in pontoon. Wave control and dynamic behaviors of the newly developed vertical plates type are verified from numerical analysis and hydraulic experiment. As a result, for the wave control and energy dissipation, the newly developed vertical plates type is more efficient than the conventional pontoon type. For the floating body motion, the wave transmission, depending on incident wave period, is decreased at the natural frequency. Dimensionless drift distance has similar trend of the reflection rate of wave transformation near natural frequency except maximum and minimum values. Dimensionless maximum tension is 17 percent of the weight of floating breakwater in case of the conventional pontoon type and 18 percent or 14 percent in case of the newly developed vertical plates type. Thus, it is shown that the wave control is improved by the vertical plates type. In addition, by adjusting the interval of the front and back vertical plate, we would control proper wave control.

• Korean Journal of Applied Biomechanics
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• v.13 no.1
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• pp.95-108
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• 2003

The purposes of this study were to analyze the muscle activities and the characteristics of muscle recruiting patterns of upper trunk for Ssirum dutguri technique using three top-ranked elite Ssirum players. The EMG technique was used to record muscle activities of both right and left sides of latissimus dorsi, biceps brachii, and erector spinae. Six surface electrodes were placed on the surface of the selected muscles and one ground electrode was also attached on the back of neck(C7). One video camera was also used to record the Ssirum motion to define 4 events and 3 phases for further analysis. The raw EMG data were filtered with band pass filter (50-400 Hz) to remove artifacts and then low pass filtered (4 Hz) to find the linear envelope which resemble muscle tension curve. This filtered EMG data were normalized to MVIC for the purpose of comparion between the subjects. The results were indicated that each subject with different physical characteristics showed very different muscle activity patterns. Although Ssirum dutguri is considered as foot technique the player grasped opponent's satba(belt) with both hands when they play. Because of this reason, activities of upper trunk muscles were relatively high. However, direct comparison between upper and lower body muscles was not possible due to the lack of the data in present study. Interestingly, all threes subjects showed that erector spinae muscle activity was comparatively higher than those of latissimus dorsi and biceps brachii. This implies to reinforce back muscle as a routine of training to improve performance or to prevent back injury.

• Journal of Korean Society of Steel Construction
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• v.29 no.1
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• pp.49-60
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• 2017

As well as the strength check, fatigue life check is also mainly required for designing mooring lines of the floating structures. In general, forces which induce dynamic structural response significantly affect to fatigue design of the mooring lines. So, waves are mainly considered as the governing loading for fatigue design of the mooring lines. In this study, characteristics of the fatigue damage of the mooring lines for submerged floating tunnels (SFT) under irregular waves are investigated. For this study time domain hydrodynamic analysis is used to obtain motion of the tunnel and tension and stresses of the mooring lines under the specific environmental conditions. Also, the Rainflow-counting method, the Palmgren-Miner's rule, and S-N curves for floating offshore structures presented by DNV recommendation is applied to calculate the fatigue damage due to the fluctuating stresses. Referring to the design plactice of the tendon pipes for TLP (tension-leg platform), which is very similar structural system to SFT, it is assumed that a 100 year return period wave attacks the SFT systems during 48 hours and the fatigue damages due to the environmental loading are calculated. Following the analysis sequence, the effects of the tunnel draft, spacing and initial inclination angle of the mooring lines on the fatigue damage under the specific environmental loadings are investigated.

• Economic and Environmental Geology
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• v.30 no.5
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• pp.459-467
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• 1997

In order to examine the primary trends and characteristics of geological lineaments along the southwestern boundary of Okcheon zone, we carried out the analysis of geological lineament trends over six selected sub-areas using Landsat-5 TM images and digital elevation model. The trends of lineaments is determined by a minimum variance method, and the resulting geological lineament map can be obtained through generalized Hough transform. We have corrected look direction biases reduces the interpretability of remotely sensed image. An approach of histogram modification is also adopted to extract drainage pattern specifically in alluvial plains. The lineament extracting method adopted in this study is very effective to analyze geological lineaments, and that helps estimate geological trends associated various with the tectonic events. In six sub-areas, the general trends of lineaments are characterized NW, NNW, NS-NNE, and NE directions. NW trends in Cretaceous volcanic rocks and Jurassic granite areas may represent tension joints that developed by rejuvenated end of the Early Cretaceous left-lateral strike-slip motion along the Honam Shear Zone, while NE and NS-NNE trends correspond to fault directions which are parallel to the above Shear Zone. NE and NW trends in Granitic Gneiss are parallel to the direction of schitosity, and NS-NNE and NE trends are interpreted the lineation by compressive force which acted by right-lateral strike-slip fault from late Triassic to Jurassic. And in foliated Granite, NE and NNE trends are coincided with directions of ductile foliation and Honam Shear Zone, and NW-NNW trends may be interpreted direction of another compressional foliation (Triassic to Early Jurassic) or end of the Early Cretaceous tensional joints. We interpreted NS-NNE direction lineation is related with the rejuvenated Chugaryung Fault System.

• Journal of Ocean Engineering and Technology
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• v.33 no.5
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• pp.400-410
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• 2019

In this study, the numerical code for the 3D nonlinear dynamic analysis of an SLWR (Steel Lazy Wave Riser) was developed using the lumped mass line model in a FORTRAN environment. Because the lumped mass line model is an explicit method, there is no matrix operation. Thus, the numerical algorithm is simple and fast. In the lumped mass line model, the equations of motion for the riser were derived by applying the various forces acting on each node of the line. The applied forces at the node of the riser consisted of the tension, shear force due to the bending moment, gravitational force, buoyancy force, riser/ground contact force, and hydrodynamic force based on the Morison equation. Time integration was carried out using a Runge-Kutta fourth-order method, which is known to be stable and accurate. To validate the accuracy of the developed numerical code, simulations using the commercial software OrcaFlex were carried out simultaneously and compared with the results of the developed numerical code. To understand the nonlinear dynamic characteristics of an SLWR, dynamic simulations of SLWRs excited at the hang-off point and of SLWRs in regular waves were carried out. From the results of these dynamic simulations, the displacements at the maximum bending moments at important points of the design, like the hang-off point, sagging point, hogging points, and touch-down point, were observed and analyzed.

• Journal of the Society of Naval Architects of Korea
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• v.30 no.3
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• pp.29-40
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• 1993

The fundamental characteristics of nonlinear free-surface waves generated by a shallowly submerged 3-dimensional hydrofoil are investigated. The fluid is assumed inviscid, incompressible and its motion irrotational. The surface tension on the free-surface is neglected. The hydrofoil is represented by a horseshoe vortex system whose shape is assumed fixed. Also the strengths of vortices are assumed given. The exact problem for the wave potential due to the horseshoe vortex system is formulated by the variational principle based on the classical Hamilton's principle. The localized finite element method is used in the numerical computations. In order to increase the numerical efficiency, an intermediate nonlinear-to-linear transition buffer subdomain for a smooth matching is introduced between the fully nonlinear computation subdomain and the truncated linear infinite subdomain. Also used is the modal analysis to reduce the computation tome drastically. The effect of inflow velocity, submergence depth of the hydrofoil and the shape of circulation distribution on the wave profiles are thoroughly examined. Especially it was possible to investigate the nonlinear influence of the free vortex on the free vortex. The nonlinear free-surface effect on the induced forces on the hydrofoil is also investigated.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.37 no.4
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• pp.285-295
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• 2001

This study describes the analysis on the dynamic characteristics of model as a fundamental studies for the horn fish Hemiramphus sajor surface pair trawl gear. The model experiments were carried out in a flume tank by using model net for the horn fish surface par trawl gear. The model net was made to the scale of 1/40 by scaling down two surfce par trawl boats of 6.67 and 9.98 ton used for sea experiment in the coast of Jeju Island. Dimensions of the model net were 1.2m for stretch length of net, 1.3m for float line, 1.0m for sinker line, 2.5g for floats, and 0.86g for sinkers. Experiments were conducted in the observation channel of a flume tank with experimental equipments used to change the distance between paired boats and towing velocity. Motion of model net during towing was recorded by two sets of digital camera which were placed in the top and side of the model net. The leading coordinate of net height and net mouth width was captured by the photograph analysis system. Through the experiment, we obtained the following results: 1. The relationship between the net hight(Nh) and towing velocity(Vt) during towing was found to be Nh=(2.39Db-$^{0.62})Vt^{0.56}$ and the relationship between the net mouth width (Nw) and towing velocity during towing was Nw=(0.96Db^{0.62})Vt^{0.11}$, where Db is the distance between paired boats. 2. The relationship between the net tension(Nt) and towing velocity during towing was found to be Nt=106.94Vt+1.43 and the model net becomes parallel to the water surface at the towing velocity larger than 1.5 Knot. 3. The relationship between the net opening area(Na) and towing velocity during towing was found to be Na=(2.28Db0.37)Vt.-0.45, and the relationship between the filtering volume(Fv) and towing velocity during towing was Fv=(69.9Db$^{0.37})Vt^{0.55}$. The net opening area and filtering volume reach maximum value at the distance of 25m between paired boats.