• Bulletin of the Society of Naval Architects of Korea
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• v.26 no.4
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• pp.44-56
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• 1989

Recently the residual strength of damaged tubulars under axial compression has extensively been investigated. However, in spite of the possibility of damage onto underwater members of offshore structures as results of collisions, dropped objects and other accidental impacts occurring in service or during fabrication or installation, no research works on the structural behaviour of damaged tubulars under combined loadings including hydrostatic pressure have been reported in the literature. In this paper, a numerical method has been proposed to estimate the residual strength of damaged tubulars under combined loadings, and then the proposed method has been substantiated with corresponding test data. A simple design equation has been derived based upon the results of the parametric study using the proposed method. The accuracy of the predictions using the derived equation is found to be a 10.1% COV(Coefficient of Variation) together with an 1. 037 mean comparing with the test data.

• Journal of the Korean Society of Marine Environment & Safety
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• v.21 no.2
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• pp.215-222
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• 2015

To improve the ocean waves of the ship maneuvering simulator, we study and summarize the visualization elements of the ocean waves and the overall direction of their implementation in detail. We categorize the visualization elements of the ocean waves into five groups, including wave surface, wave breaking, interaction, lighting effects, and underwater. We also analyze the design and implementation issues of the visualization of the ocean waves for ship maneuvering simulator with respect to realistic and real-time ocean visualization, ship dynamics, and application purposes. Through the analysis, we have found that the realistic visualization of ocean waves plays an important role in the generation of immersiveness, more accurate ship motion, and the various and controllable simulation scenarios for the ship maneuvering simulator. Additionally, we have confirmed that there are many visualization elements, methods, and limitations to be considered for the visualization of the ocean waves for ship maneuvering simulator, and we have concluded that the systematic design is required before implementation.

• Journal of the Korean Society for Marine Environment & Energy
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• v.13 no.4
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• pp.241-248
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• 2010

This paper deals with the performance analysis and design of the Darrieus-type vertical axis turbine to evaluate the effect of key design parameters such as number of blade, blade chord, pitch and camber. The commercial CFD software FLUENT was employed as an unsteady Reynolds-Averaged Navier-Stokes (RANS) solver with k-e turbulent model. Grid system was modelled by GAMBIT. Basic numerical methodology of the present study is appeared in Jung et al. (2009). Two-dimensional analysis was mostly adopted to avoid the barrier of massive calculation required for parametric study. It was found that the highly efficient turbine model could be designed through the optimization of design parametrrs.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.6
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• pp.83-88
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• 2010

In this paper, to propose a valid method solving a problem relevant to grounding from actual field data, the experimental results relevant to touch and step voltages and surface potential profiles measured around the real-sized and small-sized grounding electrode models were described. The ground surface potential profiles and dangerous voltages around the concrete pedestals employed in street facilities such as street lamps, traffic signal lamp and controllers as a case study were measured and discussed. The hemispherical cell with a diameter of 1,160[mm] was employed to simulate uniform soil. As a result, the results measured with the small-sized model were in reasonably agreement with the data obtained from the real-sized installation. It was found that the small-sized model test could be employed as a useful means evaluating the dangerous voltages around grounding electrodes installed at the inaccessible areas such as mountains, underground, underwater, and so on.

• Journal of Navigation and Port Research
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• v.41 no.1
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• pp.1-8
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• 2017

The estimation of non-linear ship motion is one of the most important issues in recent studies of ship stability. In this paper, bispectral analysis and bicoherence analysis were introduced in order to analyze the non-linear ship motion. In addition to the previously observed non-linear pitching motion in following seas, this study observed the non-linear phase coupling of pitching motion in following & quartering seas, and starboard beam seas. By comparing phase coupling between each frequency quantitatively via the bicoherence analysis, it was confirmed that non-linear phase coupling was much stronger in frequency regions other than the peak frequencies of a power spectrum. Furthermore, it was found out that the results of bicoherence calculation were analagous to each other, although the different normalization methods were applied.

• Journal of The Korean Society of Integrative Medicine
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• v.4 no.3
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• pp.39-47
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• 2016

PURPOSE : This study attempts to find the effects of water perturbation exercise performed on stroke patients in their physiological cost index and gait ability tests. METHOD : The subjects were 30 stroke patients, water perturbation exercise group was performed 3 day per week, for 40 minutes a day, for a period of eight weeks. The physiological cost index and gait of all subjects were assessed by using the polar, 6 Minute Walk Test (6MWT), and 10 meter Walk Test(10mWT) at pre training and post training. Paired t-test was used to analyze change before and after intervention in group. Pearson's correlation was used to analyze correlation of all variables. RESULT : Water perturbation exercise group showed increased physiological cost index. Water perturbation exercise increased gait ability, showing a significant difference. Showing the correlation between the relatively high amount between physiological cost index and 6 minutes walking test. CONCLUSION : From the result of the study, we found that water perturbation exercise was effective in improving physiological cost index and gait ability. The patient is considered to be used by itself to involve the treatment and the risk of falling from the lowered state into the treatment method for the intensive treatment of stroke patients to be useful in improving the cardiovascular system and ability to walk. Through underwater training for stroke patients in the future on the basis of this study it is considered to require additional clinical studies on the impact on daily living and quality of life of stroke patients.

• Journal of the Korea Society for Simulation
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• v.23 no.4
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• pp.41-49
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• 2014

Detection and processing techniques for small objects on seabed by the active synthetic aperture sonar can be increased the detection performance because it can be used by short sensor array in small unmanned underwater systems that are spatially constrained. But the limited conditions on constant speed and straight movement of the platform cause a large error in the number of external environmental factors and exact phase synthesis process. In this study, analyzed the applicability of active synthetic aperture processing that is mounted on such a system, and compared detection resolution change in accordance with the phase difference mismatch caused by the along track disturbance. Various simulations were performed as a coherently focus processing model by adding along track disturbance mismatched parameter on the configuring simulator. As the result, detection performance of active synthetic processing for small objects on seabed was found a number of changes by the phase difference mismatch errors according to track disturbances and S/N ratio variations.

• Ocean Systems Engineering
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• v.6 no.4
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• pp.377-400
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• 2016

Dropped objects are among the top ten causes of fatalities and serious injuries in the oil and gas industry (DORIS, 2016). Objects may accidentally fall down from platforms or vessels during lifting or any other offshore operation. Proper planning of lifting operations requires the knowledge of the risk-free zone on the sea bed to protect underwater structures and equipment. To this end a three-dimensional (3D) theory of dynamic motion of dropped cylindrical object is expanded to also consider ocean currents. The expanded theory is integrated into the authors' Dropped Objects Simulator (DROBS). DROBS is utilized to simulate the trajectories of dropped cylinders falling through uniform currents originating from different directions (incoming angle at $0^{\circ}$, $90^{\circ}$, $180^{\circ}$, and $270^{\circ}$). It is found that trajectories and landing points of dropped cylinders are greatly influenced by the direction of current. The initial conditions after the cylinders have fallen into the water are treated as random variables. It is assumed that the corresponding parameters orientation angle, translational velocity, and rotational velocity follow normal distributions. The paper presents results of DROBS simulations for the case of a dropped cylinder with initial drop angle at $60^{\circ}$ through air-water columns without current. Then the Monte Carlo simulations are used for predicting the landing point distributions of dropped cylinders with varying drop angles under current. The resulting landing point distribution plots may be used to identify risk free zones for offshore lifting operations.

• Ocean and Polar Research
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• v.28 no.3
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• pp.225-236
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• 2006

Seagrass meadows are considered as critical habitats for a wide variety of marine organisms in coastal and estuarine ecosystems. In many cases, studies on the spatial/temporal distribution of seagrass have depended on direct observations using SCUBA diving. As an alternative method fur studying seagrass distribution, an application of hydroacoustic technique has been assessed for mapping seagrass distribution in Dongdae Bay, on the south coast of Korea, in September 2005. Data were collected using high frequency transducer (420 kHz split-beam), which was installed with towed body system. The system was linked to DGPS to make goo-referenced data. Additionally, in situ seagrass distribution has been observed using underwater cameras and SCUBA diving at four stations in order to compare with acoustic data. Acoustic survey was conducted along 23 transects with 3-4 blot ship speed. Seagrass beds were vertically limited to depths less than 3.5m and seagrass height ranged between 55 and 90cm at the study sites. Dense seagmss beds were mainly found at the entrance of the bay and at a flat area around the center of the bay. Although the study area was a relatively small, the vertical and spatial distributions of the seagrass were highly variable with bathymetry and region. Considering dominant species, Zostera marina L., preliminary estimation of seagrass biomass with acoustic and direct sampling data was approximately $56.55g/m^2$, and total biomass of 104 tones (coefficient variation: 25.77%) was estimated at the study area. Hydroacoustic method provided valuable information to understand distribution pattern and to estimate seagrass biomass.

• Journal of the Korean Society of Clothing and Textiles
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• v.35 no.9
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• pp.1039-1048
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• 2011

This research develops a basic design structure for scuba diving wetsuits suitable for the shape of Korean men in their 30's as well as enhances the reduction rate for underwater activity. The clothing pressure and fitness tests were performed using four different types of body suits. The usable data of the tests were coded for further statistical analysis that includes one way-ANOVA test and S-N-K Multiple Range Test by using SPSSWIN 17.0. An analysis of the results shows: (1) The results of the clothing pressure test (using a dummy) indicated that the larger the reduction rate, the stronger the clothing pressure gets (with an exception on the knee area). It has great impact on clothing pressure with regards to the different body parts. The different reduction rates should be applied to body parts accordingly. (2) In the case of test subjects, the overall mean values of the clothing pressure were lower than the ones with the dummy (attributable to the cushion function of body skin and muscle as well as the high stretch of the fabric). (3) In evaluating the subjective fit test of four types of body suits, a statistically significant difference was found in the relation between pattern reduction rates and all parts of the body. It was revealed that the reduction rate of 'B' pattern (X: 4%, Y: 3%) was the most suitable pattern and the 'B' pattern scored highest in the motion functional fit test performed by a test subject.