Chun-Ki Lee

Hydrodynamic forces between vessels and safe maneuvering under wind-effect in confined waters

It is well known that the ship maneuvering motion is greatly affected by hydrodynamic forces and moments acting between two ships passing too close to each other in confined waters, such as in a harbor or narrow channel. This hydrodynamic forces and moments can be assumed to be the functions of the longitudinal and transverse distance along with their speeds. The aim of the present research is to develop a guideline of ship velocity and safe distance between ships to avoid the influence of the hydrodynamic forces and moments and to navigate ships safely in confined waters. From the perspective of marine safety, considering the interaction and wind effect as a parameter, an overtaking and overtaken vessel navigating too close to each other under the condition of wind direction from 80° to 150° should be cautioned with high alert, regardless of ship types. Also, regardless of the ship-velocity ratio and ship types, an overtaking and overtaken vessel can be maneuvered safely without deviating from the original course under the following conditions; the transverse distance between two vessels is approximately kept at 1.0 times of ship length and 5 through 10 degrees of range in maximum rudder angle.

Assessment of Safe Navigation Including the Effect of Ship-Ship Interaction in Restricted Waterways

This paper is mainly concerned with the assessment of safe navigation between ships moving each other in restricted waterways. The numerical simulation of manoeuvring motion was conducted parametrically to propose an appropriate safe speed and distance, which is required to avoid sea accident under the different conditions, such as ship-velocity ratios, ship-length ratios, separation and stagger between ships. As for the calculation parameters, the ratios of velocity difference between two ships were considered as 0.6, 1.2, 1.5 and the ones of ship-length difference were regarded were regarded as 0.5, 1.0, 1.18. From the inspection of this investigation, it indicates the following result. Firstly, the separation between ships is more needed for the small vessel, compared to the large vessel. Secondly, the lateral distance between ships is necessarily required for the velocity ration of 1.2, compared to the cases of 0.6 and 1.5. The manoeuvring characteristics based on this investigation will be very useful for keeping the safety of navigation from the practical point of ships design and traffic control in confined water.

An Experimental Study on Ship-Bank Hydrodynamic Interaction Forces

This paper is mainly concerned with the ship-bank interaction by model test. The experiments for the characteristics of hydrodynamic interaction forces and moments between vessel and bank with a mound were carried out in the seakeeping and maneuvering basin. A series of tests were carried out with ship model in parallel course along a vertical sidewall with a mound with varying lateral spacing between model ship and sidewall, length of sidewall and water depth. From the experimental results, it indicated that the hydrodynamic interaction effects increase as length of sidewall with a mound increases. Furthermore, for lateral spacing less than about 0.2L between vessel and bank, it can be concluded that the bank effects increase largely as the lateral spacing between vessel and bank decreases. However, for spacing between vessel and bank more than about 0.3L, the interaction effects increase slowly as lateral spacing decreases. Also, for the water depth to draft ratio(h/d) less than about 1.5, the hydrodynamic interaction effects increase dramatically as h/d decreases.

Hydrodynamic Interaction Effects Between Vessels in Confined Waters

The hydrodynamic interaction effects between the multi-bodies can not be neglected when vessels are close to each other in congested and confined waters, such as in a harbour or narrow channel. Increase in speed and size of modern vessels make it necessary to consider this interaction effects when designing harbours and navigation channels. In this research, the hydrodynamic interaction effects of the spacing between vessels and water depth along with ship`s velocity are summarized and discussed. The goal of this research is to propose a guideline of appropriate speed and distance between passing and moored vessels to avoid the influence of hydrodynamic forces and to navigate safely in confined sea areas.

The Assessment of Safe Navigation Regarding Hydrodynamic forces between Ships in Restricted Waterways

This paper is primarily focused on the safe navigation between overtaking and overtaken vessels in restricted waterways under the external forces, such as wind and current. The maneuvering simulation between two ships was conducted to find an appropriate safe speed and distance, which is required to avoid collision. From the viewpoint of marine safety, a greater transverse distance between two ships is more needed for the smaller vessel. Regardless of external forces, the smaller vessel will get a greater effect of hydrodynamic forces than the bigger one. In the case of close navigation between ships under the forces of wind and current, the vessel moving at a lower speed is potentially hazardous because the rudder force of the lower speed vessel is not sufficient for steady-state course-keeping, compared to that of the higher speed vessel.

Numerical analysis for hydrodynamic interaction effects between vessel and semi-circle bank wall

Abstract The hydrodynamic interaction forces and moments induced by the vicinity of bank on a passing vessel are known as wall effects. In this paper, the characteristics of interaction acting on a passing vessel in the proximity of a semi-circle bank wall are described and illustrated, and the effects of ship velocity, water depth and the lateral distance between vessel and semi-circle bank wall are discussed. For spacing between ship and semi-circle bank wall (SP) less than about 0.2 L and depth to ship’s draft ratio (h/d) less than around 2.0, the ship-bank interaction effects increase steeply as h/d decreases. However, for spacing between ship and semi-circle bank wall (SP) more than about 0.3 L, the ship-bank interaction effects increase slowly as h/d decreases, regardless of the water depth. Also, for spacing between ship and semi-circle bank wall (SP) less than about 0.2 L, the hydrodynamic interaction effects acting on large vessel increase largely as ship velocity increases. In the meantime, for spacing between ship and semi-circle bank wall (SP) more than 0.3 L, the interaction effects increase slowly as ship velocity increases.

A Study on the Hydrodynamic Force Acting on a Large Vessel in the Proximity of Breakwater

It is well known that the hydrodynamic forces and moments induced by the proximity of bank in confined waters, such as in a harbour or narrow channel affect ship`s maneuvering motion. In this paper, the calculation method based on the slender body theory for estimation of the hydrodynamic force between ship and breakwater is applied, and also, the characteristic features of hydrodynamic force acting on a large vessel in the proximity of a breakwater are described and illustrated. Furthermore, the effects of water depth and the lateral spacing between ship and breakwater are summarized and discussed.

A Study on the Method of Safe Shiphandling in Violently Rough Sea by Typoon or Hurricane

The object of this study is to develop the method of safe conducting of a vessel through stormy sea when we encounter typoon or hurricane on ocean. The scope of investigation in this paper will be limited to safe maneuvering related only with rolling motions of a vessel. The processes of investigations are as follows; Firstly, we decide a CPA(Closest Point of Approach) with the center of the storm and decide significant wave height() by SMB method and then calculate wave height of the highest of 1000 waves() and other data. Secondly, we make mathematical model of rolling motions of the vessel on the stormy sea and calculate the biggest rolling angle of the vessel and etc. Thirdly, we decide the most safe maneuvering method to ride out the stormy sea. By the above mentioned method we are able to calculate the status of the stormy sea and ships motions to be encountered and ride out safely through violently rough sea.

A Study on the Safe Manoeuvring of Ships Navigating in Shallow Water under Strong Environmental Forces

*Research Professor, Underwater Vehicle Research Center, Korea Maritime University요 약 :이 연구는 천수역에서 강한 바람과 조류하에 근접 항행중인 두 선박간의 상호유체력이 선박조종운동에 미치는 영향에 대해서 다룬다. 천수역에서 추월 및 피추월관계에 있는 대형선박의 조종운동은 바람 , 조류 및 두 선박간의 상호유체력으로 인하여 상당히 복잡해진다. 이 연구의 목적은 안전항행을 위하여 천수역에서 강한 바람 및 조류하에 근접 항행중인 두 대형선박에게 요구되어지는 두 선박간의 속도에 따른 안전항과거리에 대해서 검토, 고찰하고자 한다. 핵심용어 : 선박조종운동, 두 선박간의 상호유체력(간섭력), 안전항과거리, 천수역, 외력 Abstract :This paper focuses on the effects of hydrodynamic forces between overtaking and overtaken vessels moving under the influences of external forces, such as strong wind and current in shallow water, in which condition the ship handling may become very complex. The purpose of this paper is to develop a guideline for safe conducting distance between two ships according to the velocity and the significance of external disturbances.Key words :Ship handling, Hydrodynamic force, Safe conducting distance, Shallow water, Wind, Current* leeck@hhu.ac.kr 051)410-4709

Characteristics on the rolling response of a small fishing boat according to the waves and the ship's speed

Marine casualties of vessel are serious problems on social and national aspects, because it results in sacrifice of lives, a great lose of properties and marine pollution. According to recent statistics of marine casualties of vessel, fishing boats are more likely to be ended in the casualty, and especially, small fishing boats cause much more accidents than any other big vessels. Most of marine casualties were caused by the human factors such as poor watch keeping, inadequate manoeuvering and negligent action for engine, etc. This study is intended to provide navigator of small fishing boat with a specific information of necessary to assist both the manoeuvering and the avoidance of capsizing. The manoeuvering characteristics of ship can be adequately judged by the results of typical ship trials manoeuvres. For this purpose, the author measured the roll responses of a small fishing boat in waves using the real sea experimental measuring system, and analyzed the experimental data by the statistical and spectral analyzing methods to get the characteristics of the roll motion responses of the small boat through the wave directions and the ship`s speed.