• Journal of the Korean Society of Marine Environment & Safety
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• v.20 no.1
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• pp.42-48
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• 2014

Seasickness not only makes persons on board vessels to vomit but also causes vertigo, headache, sleepiness, fatigue, lethargy and other discomforts. This ailment leads to disturbance of biorhythm and decline of perception which would eventually cause reduction of situational awareness among ship's operators that leads to marine accident. This study is about the sensitivity of people onboard ships to seasickness and focused on deck or navigation officer cadets(apprentice officers) and engine officer cadets(apprentice engineers) who have no previous experiences on board. It is conducted by using motion sensor that can measure ship's X, Y, Z-axis motions and through the questionnaire survey, and evaluated each students' degree of seasickness symptoms. Through this study, in same circumstance, we have known that there are different degrees of motion sickness for wheel house worker and engine room worker, It also confirmed that seasickness have high relationship with degree of hull motion and also, with cycle of hull motion. In addition, we have confirmed that Z-axis hull movement has higher relationship with seasickness than X-axis and Y-axis hull movements. This study aims to initiate additional researches about X-axis and Y-axis of the ship's motion which it expects to greatly enhance safety of wheelhouse and engine room personnel, ship's livability and comfortable sailing.

• Journal of the Korean Society of Marine Environment & Safety
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• v.21 no.5
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• pp.538-542
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• 2015

The transverse moment of inertia is an indispensable factor in analyzing the roll motion characteristics of ships and the calculating method needs to be based on the more reasonable theories when deciding the value as the results and reliability of analysis could be much affected by the correctness. However, the mass distribution and shape of hulls are quite complicated and give much difficulties in case of calculating the value directly from the ship design data, furthermore even acquiring the detailed design data for calculation is almost impossible. Therefore some simpler ways are practically adopted in the assumption that the gyradius of roll moment can be decided by a given ratio and hull width. It is well known that the responses of the free roll decay are varied according to the value of roll moment in view of roll period and amplitude decay ratio, so that the general formula to get the moment value can be derived also from the observation of roll decay responses. This study presents how the roll period and decay ratio are interrelated each other from the roll motion characteristics with suggesting a general formula to be able to calculate roll moment from it. Finally, the obtained general formula has been applied to a ship data to check the resultant characteristics through analyzing graphs and showed that the roll moment becomes more accurate when rolling period and decay ratio are considered together in calculation.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.3
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• pp.125-130
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• 1992

A digital 6-dof motion measuring system is developed using 7 accelerometers following Miles'[1] method. A snoic wave height gauge is also developed to measure the relative wave height at the foremost end of the ship. By combining the time series of both 6-dof motions and relative wave height, we can estimate the time series of real sea wave. Results of model tests shows the validity of the developed system.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.9 no.1
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• pp.24-34
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• 1997

To find the causes of the downtime problems in Pohang New Harbor, extensive field measurements of short- and long-period waves for 1.5 months and their analyses were made taking into account of wind and downtime records. Measured wave height ratios inside the harbor are appeared to be slightly larger than predicted ones using numerical methods in the previous studies. It is shown that the major causes of the downtime are the wind wave (or swell) higher than loading criteria and also swell with even smaller wave height but longer period(more than 10 sec). Waves of long-period components[0(min)] were recorded as 20 cm high in case of dominant seiche phenomena but they might not be related with the downtime problems.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.13 no.2
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• pp.122-138
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• 2001

It is well known that whcn waves propagating on a shallow water suddenly encounter a much deeper water they do not propagate further but are reflected. If we apply this phenomenon to a harbor by making the harbor depth much greater than outside, we could improve the harbor tranquillity by making the waves impinging into the harbor be reflected at the harbor entrance. In the present paper, first we apply the numerical models based' on the mild-slope equation and extended mild-slope equation to calculate the long wave resonances in a rectangular harbor with a very large depth discontinuity at its entrance to find that the difference between the models is almost negligible. By applying the numerical model to a realistic model harbor whose inside is entirely dredged, it is found that the effect of dredging is insignificant when the inside depth is twice the outside one but tripled inside depth significantly reduces the long waves of period of one to five minutes whieh may exert a bad influence on ship motion. Moreover, even when only a portion of the harbor basin is dredged, the cffect of dredging in the dredged area is found to be comparable to that of entire dredging, showing that the dredging of harbor basin can be a countenncasure for harbor resonance.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.38 no.3
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• pp.226-233
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• 2002

In the field of research of sea keeping quality, much development has been made in recent years using the method of calculation based on the strip theory. It is very important to investigate the hull response of a fishing vessel in waves to ensure the safe navigation and fishing operation in rough seas by preserving excellent sea keeping qualities. For this purpose, the author measured various responses of three fishing vessels in waves using real sea experimental measuring system and analyzed the experimental data The results obtained can be summarized as follow. 1. The amplitudes of pitching motion in the experiments appeared low values with more than one peak occasionally in following sea and quartering sea, and the band width of those was found to be wide relatively. 2. The amplitudes of rolling motion in the experiments appeared high values with only one peak in following sea and quartering sea regardless of ship's tonnage, and the band width of those was found to be narrow relatively. 3. The comparisions of theoretical results with those of experiments for the pitching motions and rolling motion in following sea and quartering sea show that the theoretical values are higher slightly than those of experiments in both directions and the period at which the peak appears in the calculations and the experiments has good agreement approximately 4. The calculated responses of two vessels under a assumed wave of 2.2m height and 5.0sec period showed that the response of pitching motion of ship-A are 2.2 times bigger than those of ship-C in following sea and quartering sea, and the response of rolling motion of ship-A is 4.2 times bigger than that of ship-C in quartering sea.

• Journal of Navigation and Port Research
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• v.30 no.6 s.112
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• pp.433-438
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• 2006

Recently, the earth scale disaster is occurring frequently. Under the effects of global warming, the weather has become unseasonable worldwide. Hence, the earth is experiencing unstable condition with many disasters such as storms and flood damages as well as earthquake. Therefore, it is necessary to consider what we am do to prevent disasters. Consequently, recent warnings indicate that there is a potential risk of massive earthquakes. Consideration of the effects of tsunami to the moored ship is very important. Operational problems such as moored ship motions sometimes become remarkable with large amplitude and long periods in harbor. Moored ship motions may cause the breakage of mooring systems such as mooring lines, fenders or quay. Large and long period moored ship motions are caused by resonant effects. In this paper, the moored ship motions within a harbor by the large-scale tsunami and the effects on the motions and mooring loads with resonant effects are investigated by numerical simulations.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.4
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• pp.132-145
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• 1992

A series of design, theoretical analysis and model test procedures is presented for the development of an axisymmetric stator-propeller system. A preswirl stator is located in front of a propeller in order to improve the propulsion efficiency by cancellation of the slip stream rotational velocity due to the propeller. Model test results show that propulsion efficiency gain due to the symmetric stator-propeller system is about 3% compared to the single propeller. This efficiency gain would increase for full scale application since the pressure drag coefficient of the stator would decrease due to increasement of turbulent intensity behind the hull wake and increasement of Reynolds number.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.14 no.2
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• pp.97-112
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• 1978

The rule 15, 16 and 17 of International Regulations for Preventing collisions at Sea direct actions to avoid collision when two power-driven vessels are crossing. But these rules do not present the safety minimum approaching distances outside which a give- way vessel deeps out of the way of a stand-on vessel. In this paper, the author analyzed the ship's collision avoiding actions from a viewpoint of ship kinematics as the method to calculate this distance. The author worked out mathematic formulas for calculating the safety minimum approaching distances outside which the give-way vessel takes the actions to avoid collisions in accordance with the cross angles of the crossing vessels' courses. Figuring out actually the values of maneuvering indices of the M. S. Koan Ack San (GT: 224tons), the training ship of the National Fisheries University of Busan and the M. S. Golden Clover (GT: 101, 235tons) of the Eastern Shipping Co., Ltd. through their Z test, the author applied these values to the calculating formulas and calculated the safety minimum approaching distances. The results of calculations are as follows; 1. The greatest distance is to be kept by the give-way vessel to avoid collision when the cross angle of courses is 90$^{\circ}$ or near it. In such case the safety minimum approaching distance of a small vessel must be more than 5 times of her own length and that of a large vessel more than 11 times of her own length. 2. Collision danger is greater when crossing angle is obtuse than in an acute angle, therefore greater distance is to be kept by the give-way vessel to avoid collision in the case of the obtuse angle. 3. The actions to be taken to avoid collisions by the give-way vessel in Rule 16 and by the stand-on vessel in Rule 17(a)(ii) of International Regulations for Preventing Collisions at Sea, must be done outside the above safety minimum approaching distance. When inevitably such actions are to be taken within the safety minimum approaching distance, they should be accompanied with engine motions.