• Journal of the Korean Society of Marine Environment & Safety
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• v.30 no.1
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• pp.127-134
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• 2024

With the growth of offshore wind power generation market, the corresponding installation vessel market is also growing. It is anticipated that approximately 100 installation vessels will be required in the of shore wind power generation market by 2030. With a price range of 300 to 400 billion Korean won per vessel, this represents a high-value market compared to merchant vessels. Particularly, the demand for large installation vessels with a capacity of 11 MW or more is increasing. The rapid growth of the offshore wind power generation market in the Asia-Pacific region, centered around China, has led to several discussions on orders for operational installation vessels in this region. The seabed geology in the Asia-Pacific region is dominated by clay layers with low bearing capacity. Owing to these characteristics, during vessel operations, significant spudcan and leg penetration depths occur as the installation vessel rises and descends above the water surface. In this study, using penetration variables ranging from 3 to 21 m, the unique vibration period, structural safety of the legs, and conductivity safety index were assessed based on penetration depths. As the penetration depth increases, the natural vibration period and the moment length of the leg become shorter, increasing the margin of structural strength. It is safe against overturning moment at all angles of incidence, and the maximum value occurs at 270 degrees. The conditions reviewed through this study can be used as crucial data to determine the operation of the legs according to the penetration depth when developing operating procedures for WTIV in soft soil. In conclusion, accurately determining the safety of the leg structure according to the penetration depth is directly related to the safety of the WTIV.

• Korean Journal of Ichthyology
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• v.22 no.2
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• pp.90-95
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• 2010

Blue devil (Pomacentrus caeruleus, also called Chrysiptera cyanea) is widespread in the Indo-Pacific Ocean and very popular all over the world as an aquarium fish because it is so easy to keep in a marine aquarium. However, tank-breeding techniques are not completely known. In this study, we reared blue devil and investigated its spawning ecology, as a necessary precursor for successful artificial-tank breeding. We investigated the spawning volume according to time with two types of calendars: solar and lunar. Rearing conditions were set at 30 ppt salinity, $27^{\circ}C$ water temperature, in two aquariums with water volumes of 80 and 125 L. We successfully bred P. caeruleus in this artificial-tank system. The aquarium fish formed a spawning harem with one male and more than two females. We harvested about 113,580 eggs in 44 spawning episodes by two spawning harems during the 11-month period from December to October. They showed a peak season of spawning volume and time in May and June. We confirmed the two peak points in spawning volumes and times, which coincided with the first quarter and last (third) quarter of the lunar phases of the moon.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.6
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• pp.559-567
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• 2012

A level set based topological shape optimization method for nonlinear structure considering hyper-elastic problems is developed. To relieve significant convergence difficulty in topology optimization of nonlinear structure due to inaccurate tangent stiffness which comes from material penalization of whole domain, explicit boundary for exact tangent stiffness is used by taking advantage of level set function for arbitrary boundary shape. For given arbitrary boundary which is represented by level set function, a Delaunay triangulation scheme is used for current structure discretization instead of using implicit fixed grid. The required velocity field in the actual domain to update the level set equation is determined from the descent direction of Lagrangian derived from optimality conditions. The velocity field outside the actual domain is determined through a velocity extension scheme based on the method suggested by Adalsteinsson and Sethian(1999). The topological derivatives are incorporated into the level set based framework to enable to create holes whenever and wherever necessary during the optimization.

• Journal of the Korean Society of Marine Environment & Safety
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• v.19 no.2
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• pp.225-231
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• 2013

Liquefied gas carriers generally transport cargoes of flammable or toxic nature. Since these cargoes may cause an explosion, fire or human casualty, the accommodation spaces, service spaces and control stations of liquefied gas carriers should be so located as to avoid ingress of gas. For this reason, the paragraph 8.2.9 of IGC Code in IMO requires that the height of vent exits should be not less than B/3 or 6 m whichever is greater, above the weather deck and 6 m above the working area and the fore and aft gangway to prevent any concentration of cargo vapor or gas at such spaces. Besides as known, the LNG market has been growing continually, which has led to LNG carriers becoming larger in size. Under this trend, the height of a vent will have to be raised considerably since the height of a vent pipe is generally decided by a breadth of a corresponding vessel. Accordingly, we have initiated an examination to find an alternative method which can be used to determine the safe height of vent masts, instead of the current rule requirement. This paper describes the dispersion characteristics of boil-off gas spouted from a vent mast under cargo tank cool-down conditions in the membrane type LNG carriers.

• Journal of the Korean Society of Marine Environment & Safety
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• v.19 no.2
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• pp.138-144
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• 2013

Large and small marine accidents which are related to vessel's navigation are happening continuously and these maritime accidents have caused loss of lives and properties, and serious maritime environmental pollution damage. It is also true that maritime pollution damage is increasing due to these accidents, probability of growth of seaborne volume and complicated maritime traffic environment. Korea, recently, is developing an evaluation index which can assess sea risk through the evaluation of maritime traffic environment and provide danger and general information with relation to maritime traffic environment on target sea area to evaluate maritime traffic safety. In this paper, we intend to confirm the validity of maritime traffic safety on the basis of vessel navigator's risk consciousness and various sailing conditions by using the ship handling simulator. To confirm the validity of sailing vessel's maritime traffic safety, we use analysis of variance. By using analysis of variance, we analyze vessel navigator's characteristics, distance, speed and encounter type between vessels. Through multiple comparison of each factor's risk difference, we can confirm the change of numerical value of risk difference in statistical aspect.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.9
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• pp.480-485
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• 2017

The main reason for the heat induced accidents occurring at the after stern tube journal bearing is the excessive local pressure caused by the deflection of the propulsion shaft due to the propeller loads. It is expected that the contact area could beenlarged and the local pressure reduced accordingly by using a lining material having alow Young's modulus instead of the existing white metal. The purpose of this work is to investigate the characteristics of the pressure distribution and determine the allowable pressure value in the case where bearing products made of materials having a low Young's modulus are used. In this study, the propeller loads, heat effect, and hull deflection are considered in the evaluation of the local pressure of the ship propulsion shaft. Also, the Hertzian contact condition was applied. From the analysis results in the case where a lining material with a low Young's modulus was used, it was found that a robust design could be achieved and the local pressure could be reduced effectively independent of the load conditions. It will be possible to producenew products made of materials having a low Young's modulus if the manufacturer confirms the performance specifications drawn by this study.

• Journal of the Korean Society of Marine Environment & Safety
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• v.21 no.1
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• pp.47-56
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• 2015

Under the conditions of invested actual changes of heeling angles during MV Sewol's sinking, this study proposes passengers' evacuation scenarios, which are based on the assumption of normal orders of evacuation being given to the passengers, and evaluates using a marine-specialized human evacuation simulation tool. As results, when the heeling angle is set as 0 degree or 30 degree, it is found out that almost every passengers can success to evacuate to the musterstations, even though the evacuation times are different depending on the scenarios and the walking speeds. Meanwhile, when the heeling angle is varied as the Sewol incident, 3.1 %(Scenario Sc-Va which set chutes on port side as evacuation routes), 11.1 %(Sc-Vb, every open decks of port side as evacuation routes) and 20.0 %(Sc-Vc, every open decks of port and AFT sides as evacuation routes) among 476 passengers can successfully reach to the musterstations from their cabins with the condition of average walking speed as 2.04 m/s on flat. And only 0.8 %(Sc-Va), 3.8 %(Sc-Vb) and 10.7 %(Sc-Vc) can success to evacuate with the condition of average walking speed as 1.48 m/s on flat.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.6
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• pp.620-625
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• 2015

In an effort to reduce the onset of global warming, the International Maritime Organization Marine Environment Protection Committee (IMO MEPC) proposed the reduction in ship speeds as a way of lowering the proportion of carbon dioxide ($CO_2$) in the Green House Gas emissions from ships. To minimize fuel costs, shipping companies have already been performing slow steaming for their own fleets. Specifically, the slow steaming approach has been adopted for most ocean-going container lines. In addition, because of the increased marine fuel cost that is required to enable increased capacity, there is an urgent need for more advanced fuel-saving technologies. Therefore, in this present study, we propose a fuel-cost reduction method that can improve the performance of diesel engines. We introduce a predetermined amount (0.025% of the amount of fuel used) of fuel additive (oil-soluble calcium-based organometallic compound). For improved experimental accuracy, as the test subjects, we utilize a large two-stroke diesel engine installed in land plants. The loads of the test engine were classified as low, medium, and high (50, 75, and 100%, respectively). We compare the engine performance parameters (power output, fuel consumption rate, p-max, and exhaust temperature) before and after the addition of fuel additives. Our experimental results, confirmed that we can realize fuel-cost savings of at least 2% by adding the fuel additive in low load conditions (50%). Likewise, the maximum combustion pressure was found to have increased. On the other hand, we observed that there was a reduction in the exhaust temperature.

• Journal of the Korean Geosynthetics Society
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• v.14 no.2
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• pp.89-94
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• 2015

In this study, the mixed soil with an optimum mixed ratio was suggested in order to recycle the powdered sludge of basalt in Jeju Island as the impermeable liner materials. As the results of soil laboratory tests, the grain size of the powdered sludge of basalt is less than 0.1mm and the powdered sludge was classified into ML or CL category in accordance with the Unified Soil Classification System (USCS). Also, the grain size of natural soils is ranged from 0.1 mm to 10 mm and the soils were classified into SW category in USCS. To select the optimum mixed ratio of powdered sludge, the variable permeability test was performed to various mixed soils with different powdered sludge amount under both optimum compaction and field conditions. As the results of permeability tests, the coefficient of permeability of mixed soils was decreased with increasing the mixed ratio of powdered sludge, and the mixed soil with mixed ratio of 60% has the minimum coefficient of permeability. Therefore, the optimum mixed ratio of powdered sludge is 60% for recycling the powdered sludge of basalt as the impermeable liner materials.

• Journal of the Korean Geotechnical Society
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• v.21 no.4
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• pp.99-114
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• 2005

In Part I of this paper, a conceptual approach of the stress path method was newly proposed for a rational estimation of settlements of saturated clay deposits. A detailed procedure for effective evaluation and use of settlement-related characteristic deformation behaviors was developed in order to provide practicality to the new approach. In this Part II, on the basis of the results of Part 1, the concept of the new approach was embodied in the form of a detailed settlement estimation procedure. The applicability and usefulness of the new procedure were strongly supported by various application examples. In addition, possible errors of other conventional settlement estimation methods were investigated by comparing with the new procedure. Because of its flexible applicability for wide range of field conditions, the new procedure will have great usefulness in the practical side. For example, a reasonable foundation design based on allowable settlement criteria can be easily performed and modification of design factors can be readily reflected even during the subsequent construction stage. Especially, the new procedure will be of great use for preliminary work in a large scale construction site where various structures are planned to be constructed on a nearly identical ground condition.