• 한국항해학회지
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• 제10권2호
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• pp.83-96
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• 1986

In the restricted sea way such as fair way in harbor, narrow channel etc, the safe ship-handling is a very important problem, which is greatly related with turning ability of ships. It is of great importance that ship-handlers can grasp the position of pivoting point varying with time increase at any moment for relevant steering activities. Mean while, in advanced ship-building countries they study and investigated pivoting point related with turning characteristics, hut their main interest lies in ship design, not in safe ship controlling and maneuvering. In this regards it is the purpose of this paper to provide ship-handlers better under standing of pivoting point location together with turning characteristics and then to help them in safe ship-handling by presenting fact that pivoting points vary according to configuration of ships. The author calculated the variation of pivoting point as per time increase for various type of vessels, based on the hydrodynamic derivatives obtained at test of Davidson Laboratory of Stevens Institutes of Technology , New Jersey, U.S.A. The results were classified and investigated according to the magnitude of block coefficient , length-beam ratio, length-draft ratio, rudder area ratio ete, and undermentioned results were obtained. (1) The trajectory of pivoting point due to variation of rudder angle are all the same at any time, though the magenitude of turning circle are changed variously. (2) The moving of pivoting point is affected by the magnitude of block coefficient, length-beam ratio, length-draft ratio, however the effect by rudder area ratio might be disregarded. (3) In controlling and maneuvering of vessels in harbor, ship-handlers might regard that the pivoting point would be placed on 0.2~0.3L forward from center of gravity at initial stage. (4) The pivoting point of VLCC or container feeder vessels which have block coefficient more than 0.8 and length-beam ratio less than 6.5 are located on or over bow in the steady turning. (5) When a vessel intends to avoid some floating obstruction such as buoy forward around her eourse, the ship-handler might consider that the pivoting point would be close by bow in ballast condition and cloase by center of gravity in full-loaded condition.

• Journal of Biosystems Engineering
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• 제3권2호
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• pp.35-61
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• 1978

동력경운깅가 일반 경사지에서 견인주행하는 경우 견인주행성능과 주행특성을 구명하기 위하여 토양의 종류 및 상태는 일정하게 하고 지면의 기하학적 조건과 견인주행속도 및 견인하중을 변수로 하여 외부동력전달계의 시점인 좌우차륜과 토양간에 발생하는 차륜구동력 및 굴름정항과 Engine에서 구동륜까지 내부전달계를 통하여 전달된 동력의 이론치와 실험치와의 부합여부를 검정하고 부가적으로 동력경운기가 경사지기계화의 동력기로써의 가능성여부와 문제점을 찾으려한다.

• Journal of Biosystems Engineering
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• 제3권2호
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• pp.34-34
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• 1978

동력경운깅가 일반 경사지에서 견인주행하는 경우 견인주행성능과 주행특성을 구명하기 위하여 토양의 종류 및 상태는 일정하게 하고 지면의 기하학적 조건과 견인주행속도 및 견인하중을 변수로 하여 외부동력전달계의 시점인 좌우차륜과 토양간에 발생하는 차륜구동력 및 굴름정항과 Engine에서 구동륜까지 내부전달계를 통하여 전달된 동력의 이론치와 실험치와의 부합여부를 검정하고 부가적으로 동력경운기가 경사지기계화의 동력기로써의 가능성여부와 문제점을 찾으려한다.

• 한국항해학회지
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• 제24권3호
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• pp.123-132
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• 2000

In order to improve the ship maneuverability, It is important to estimate precisely the hydrodynamic coefficients of added mass forces acting on a ship especially in shallow waters, and simple methods for predicting such hydrodynamic forces Is also very desirable. In the previous paper using 3-Dimension potential flow theory, it has been demonstrated that potential calculation is available to estimate added mass coefficients. The present work is aimed at the suggestion of the simplified formulas for predicting the translation and lateral motion of added mass coefficients in shallow water. So, 3-D potential flow theory is also used to calculate the added mass coefficients in deep and shallow waters for Series 60 model which has 5 different kinds of block coefficients (0.6-0.8), SR196 model and T/S HANNARA. After some series computation, simplified formulas for Predicting the added mass force in shallow waters is suggested based on the computation results of Series 60 model. The formulas consist of the combination of principal dimensions and the water depth; d/B, Cb, d/H. The predicted results are compared with the Computation results for SR196 model and T/S HANNARA. The precision of predicted results by simplified formulas are good enough for the practical use. (d/B : draft-Breadth ratio, d/H draft-Water depth ratio, Cb : Block coefficients).

• Current Research on Agriculture and Life Sciences
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• 제4권
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• pp.95-101
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• 1986

진동경운(振動耕耘)에 있어서 경운저항(耕耘抵抗) 및 동력(動力)을 최소(最小)로 하는 Computer에 의한 자동제어(自動制御) 시스템의 개발(開發)을 목적(目的)으로 3가지 Mode의 제어(制御) program을 작성(作成)하여 실험(實驗)과 Simulation을 통(通)하여 각 Mode의 제어성능(制御性能)을 조사(調査)하였다. 진동속도비(振動速度比)를 일정(一定)(1.5)하게 한 경우 3가지 Mode 모두 동일(同一) 진동조건(振動條件)에 수렴하였다. 그러나 흙의 전단주파수(剪斷周波數)에 Blade의 진동수(振動數)를 match 시키는 방법 즉 흙의 전단주파수(剪斷周波數)의 2배의 진동수(振動數)로 Blade를 진동(振動)시키는 제어(制御) Mode가 수렴 시간이 짧고, 견인저항 및 동력의 최적치(最適値)에 가장 가까웠다. 또 경심(耕深) 및 토양수분(土壤水分)의 변화(變化)와 같은 외란(外亂)에 대한 견인저항 감소율의 변동(變動)은 10%이하(以下)로 적었다. 이상(以上)과 같이 흙의 전단주파수(剪斷周波數)에 Blade의 진동수(振動數)를 match 시키는 제어(制御) Mode의 제어성능(制御性能)이 가장 우수함을 알았다.

• 한국섬유공학회:학술대회논문집
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• 한국섬유공학회 1987년도 학술발표초록집
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• pp.34-34
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• 1987

Investigation has been carried out on the physical properties of several cotton rovings in various drafting conditions, such as twist, draft ratio and roller gauge. Drafting force and tensile strength were measured and analyzed by the statistical method like 3 factorial design. The correlations between drafting force and tensile strength were also examined. It was known that all factors effected on the drafting force and tensile strength of rovings. But the linear and quadratic effect of factors were found different results.

• Fibers and Polymers
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• 제7권4호
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• pp.424-431
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• 2006

Roll drafting, a mechanical operation attenuating fiber bundles to an appropriate thickness, is an important operation unit for manufacturing staple yams. It influences not only the linear density regularity of the slivers or staple yams that are produced, but also the quality of the textile product and the efficiency of the thereafter processes. In this research, the dynamic states of the fiber bundle in the roll drafting zone were analyzed by simulation, based on the mathematical model that describes the dynamic behavior of the flowing bundle. The state variables are the linear density and velocity of the fiber bundles and we simulated the dynamics states of the bundle flow, e.g., the profiles of the linear density and velocity in the draft zone for various values of the model parameters and boundary conditions, including the initial conditions to obtain their influence on the dynamic state. Results showed that the mean velocity profile of the fiber bundle was strongly influenced by draft ratio and process speed, while the input sliver linear density has hardly affected the process dynamics. Velocity variance of individual fibers that could be supposed to be a disturbing factor in drafting was also influenced by the process speed. But the major disturbance occurred due to the velocity slope discontinuity at the front roll, which was strongly influenced by the process speed. Thickness of input sliver didn't play any important role in the process dynamics.

• 공학교육연구
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• 제20권4호
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• pp.21-27
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• 2017

The purpose of this study is to provide basic data and guideline to STEM(Science, Technology, Engineering, Mathematics) educators who prepare engineering education in elementary and secondary school. For this, this study develops a composition model for engineering education program of elementary and secondary school. To do this, a literature research, experts interview and Delphi survey were conducted. Through the literature research, we extracted the components of model for engineering education program of elementary and secondary school and then made a first draft of the model. The draft was revised by experts while Delphi survey was used to validate the model based on Delphi panels' opinions. The panels for the Delphi survey consisted of 51 experts in the STEM education field. The survey was conducted three different times and importance survey was included in the third stage. The conclusions of this study were as follows: First, the model consist of definition, 4 directions, 4 characteristics, 3 educational goals according to school level, educational contents area and element, teaching and learning method and evaluation method. The educational contents area and element consist of 2 major areas, 7 areas and 18 elements. Second, all components of the developed model were valid in most of the statistics such as mean, standard deviation, the degree of consensus and convergence, and CVR(Content Validity Ratio). Third, importance for education contents area and element according to the school level are analyzed.

• International Journal of Naval Architecture and Ocean Engineering
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• 제7권5호
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• pp.906-919
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• 2015

The Deep Draft Semi-Submersible (DDS) concepts are known for their favourable vertical motion performance. However, the DDS may experience critical Vortex-Induced Motion (VIM) stemming from the fluctuating forces on the columns. In order to investigate the current-induced excitation forces of VIM, an experimental study of flow characteristics around four square-section cylinders in a square configuration is presented. A number of column spacing ratios and array attack angles were considered to investigate the parametric influences. The results comprise flow patterns, drag and lift forces, as well as Strouhal numbers. It is shown that both the drag and lift forces acting on the cylinders are slightly different between the various L/D values, and the fluctuating forces peak at L/D = 4.14. The lift force of downstream cylinders reaches its maximum at around ${\alpha}=15^{\circ}$. Furthermore, the flow around circular-section-cylinder arrays is also discussed in comparison with that of square cylinders.

• 대한조선학회지
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• 제12권2호
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• pp.3-12
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• 1975

As for two dimensional added mass coefficients for straight framed hull forms in a free surface of an ideal fluid, theoretical calculations by F.M. Lewis, vertical, K. Wendel, J.H. Hwang, and etc. are available; vertical modes of rectangular and triangle sections by Lewis, vertical, horizontal and torsional models of rectangular and triangle section by Wendel, and systematical calculations for vertical modes of single chine forms by Hwang. In this paper, employing the conformal transformation by which a unit circle and its exterior region can conformally mapped to a polygon and its exterior region, the author calculated two dimensional added inertia coefficients systematically for straight framed sections with single chine in horizontal and torsional modes of vibrations. As the results, it was found that sloping side angle is an important factor measuring the magnitude of two dimensional added inertia coefficient for a set of given values of the sectional area coefficient and the beam-draft ratio. To grasp it cleary in physical sense, pressure distributions are investigated for some typical section contours. The numerical results are presented graphically in the form of two dimensional added sectional area coefficients with beam-draft ratios and sloping side angles as parameters, so that the data may conveniently utilized for estimation of the added inertia coefficients based on a three parameter technique.