• 수산해양교육연구
• /
• 제29권2호
• /
• pp.415-421
• /
• 2017

This study is aiming to find one of working conditions for loading and unloading a large ship at game port. Firstly, for dynamic analysis of the moored ships, the motion characteristics of ship according to loading condition are figured out. The motion characteristics of ship is related to environmental factors such as current, wind, mooring line, fender and etc. As a result, it is ascertained through numerical simulation using the AQUA MARINE developed by ANSYS INC. This study might contribute to make a new method of mooring stability of target ship.

• 한국군사과학기술학회지
• /
• 제5권2호
• /
• pp.37-49
• /
• 2002

In this paper, flyout stability of missile that is launched in inclined launcher using sabots is analyzed. To include missile bending motion during flyout, FEA model of missile is converted into eight concentrated mass and equivalent stiffness matrix. Six d.o.f ship motion that have influence on flyout stability is modeled and missile firing time is modeled as probability variable to take arbitrary ship attitude into account. Gap between missile and sabot is modeled as normal distribution probability variable and Monte Carlo simulation is performed. As results, the coriolis acceleration effects by ship motion are analyed and statistical results of missile pitch rate are shown.

• 수산해양기술연구
• /
• 제35권2호
• /
• pp.147-155
• /
• 1999

본 연구에서는 8톤급 어선의 복원력 분석이 이루어졌다. 복원력 분석은 안정성과 관련이 있어, 선박의 기본설계시 중요한 항목중 하나이고, 각국 선급에서 규정을 준수하도록 하고 있다. 파랑중 어선의 전복현상은 파랑 및 바람에 의한 외력과 파랑중 선박의 브로우칭 (broaching) 현상과 복원력 변화가 어우러져 발생한다. 본 연구에서는 전복 -현상에 대한 분석을 하기 전에 필요한 파랑중복원력 분석이 수행되었다. 파도와의 만남 주파수가 0이 되는 선속과 파장의 관계가 구해졌다. 본 연구에서 택한 어선의 경우 선박의 길이와 비슷한 파장을 가지는 파도와 같은 방향으로 가면 만남 주파수가 작아짐 을 알 수 가 있었다. 이런 경우 위험한 상황이 발생할 가능성이 있다. 복원팔의 계산 결과 파정에 선박이 위치하고 있을 때, 복원력 감소가 상당히 발생하였음을 알 수가 있었다 파정에 오래 머물지 않도록 하는 운항 지침이 있어야 하겠다 전체적으로 본 연구에서 택한 어선을 대형 화물선보다 복원력 변에서는 유리한 것으로 판단되는데, 선체가 작아 상대적 으로 높은 파도를 만날 가능성이 많다. 앞 절에서 여러 가지 경우에 대한 계산 결과를 보았다. 김윤수(1994)는 대형화물선에 대하여 복원력 변화를 계산하였는데, 파도에 의한 복원력변화가 심하였다. 위의 그립을 보면 H/Lw=0.025에서 GZ 곡선의 최대 값이 1/2 이하로 줄어듦을 알 수 있다. 그러나 본 어선의 결과인 Fig. 6 과 7을 보면 변화가 대형화물선과 비교하며 작음을 알 수 있다. 이 것의 원인은 중앙단면의 형상 때문인 것으로 판단된다. 대형화물선의 경우 방형 비척계수 (뚱뚱함을 나타내는 계수)가 큰데 반하여, 본 어선은 방형 비척계수가 작고 측면에 차인을 두어 부력중심의 변화가 커서 복원력이 많이 작아지지 않는 것으로 판단된다. 앞으로 파도와 비슷한 속도와 방향으로 항주하는 어선의 동역학적인 안정성에 대한 분석이 이루어져야 하겠다.

• International Journal of Naval Architecture and Ocean Engineering
• /
• 제13권1호
• /
• pp.746-757
• /
• 2021

To investigate the mechanism of friction-induced vibration and noise of ship water lubricated stern bearings, a two-degree-of-freedom (2-DOF) nonlinear self-excited vibration model is established. The novelty of this work lies in the detailed analysis of influence of different parameters on the stability and nonlinear vibration characteristics of the system, which provides a theoretical basis for the various friction vibration and noise phenomenon and has a very important directive meaning for low noise design of water lubricated stern bearings. The results reveal that the change of any parameter, such as rotating speed of shaft, contact pressure, friction coefficient, system damping and stiffness, has an important influence on the stability and nonlinear response of the system. The vibration amplitudes of the system increase as (a) rotating speed of shaft, contact pressure, and the ratio of static friction coefficient to dynamic friction coefficient increase and (b) the transmission damping between motor and shaft decreases. The frequency spectrum of the system is modulated by the first mode natural frequency, which is continuous multi-harmonics of the first mode natural frequency. The response of the system presents a quasi-periodic motion.

• 대한조선학회논문집
• /
• 제40권6호
• /
• pp.30-36
• /
• 2003

To improve survivability of damaged ship, assessment of stability and structural safety, and behavior analysis in wave is required. Prediction of sinking time, damage stability and structural strength considering progressive flooding and dynamic force in wave is very important. To do it, a geometric model which can be express damaged ship is prepared. This paper described the geometric modeler for survivability assessment of damaged ship. The modeler is developed based on 3-D geometric modeling kernel, ACIS. The hull form and compartment definition is available fundamentally. And requirement for modeler contains data generation and interface for hydrostatic calculation, behavior analysis, and longitudinal strength analysis and so on. To easy access modeling system by conventional user such as crew, user interface is developing.

• 대한조선학회논문집
• /
• 제43권1호
• /
• pp.1-14
• /
• 2006

To improve maritime safety, it is very important not only to make safer design and operation but also to do proper response in case of maritime casualty. The large-scaled casualties will be caused by loss of structural strength and stability due to the progressive flooding and enlargement of damage by the effect of waves and wind. To prevent foundering and structural failure, the prediction of ship motion behavior of damaged ship in wave is necessary. This paper describes the motion behavior of damaged ship in waves through theoretical and experimental studies. A time domain theoretical model of damaged ship motions and accidental flooding, which can be applied to any type of ship or arrangement and considers the effects of flooding of compartments, has been developed. The model tests have been carried out in regular and irregular waves with different wave heights and directions in ship motion basin. Those were performed for three different damaged conditions such as engine room bottom damage, side shell damage and bow visor damage of a Ro-Ro ship. Comparison of theoretical and experimental results was performed.

• Structural Engineering and Mechanics
• /
• 제43권5호
• /
• pp.679-690
• /
• 2012

A new concept sea-floating port called mobile harbor has been introduced, in order to resolve the limitation of current above-ground port facilities against the continuous growth of worldwide marine transportation. One of important subjects in the design of a mobile harbor is to secure the dynamic stability against wave-induced excitation, because a relatively large-scale heavy crane system installed at the top of mobile harbor should load/unload containers at sea under the sea state up to level 3. In this context, this paper addresses a two-step sequential analytical-numerical method for analyzing the structural dynamic response of the mobile harbor crane system to the wave-induced rolling excitation. The rigid ship motion of mobile harbor by wave is analytically solved, and the flexible dynamic response of the crane system by the rigid ship motion is analyzed by the finite element method. The hydrodynamic effect between sea water and mobile harbor is reflected by means of the added moment of inertia.

• International Journal of Control, Automation, and Systems
• /
• 제4권2호
• /
• pp.255-270
• /
• 2006

In this paper, a design method of nonlinear autopilot for ship-to-ship missiles is proposed. Ship-to-ship missiles have strongly coupled dynamics through roll, yaw, and pitch channel in comparison with general STT type missiles. Thus it becomes difficult to employ previous control design method directly since we should find three different solutions for each control fin deflection and should verify the stability for more complicated dynamics. In this study, we first propose a control loop structure for roll, yaw, and pitch autopilot which can determine the required angles of all three control fins. For yaw and pitch autopilot design, missile model is reduced to a minimum phase model by applying a singular perturbation like technique to the yaw and pitch dynamics. Based on this model, a multi-input multi-output (MIMO) nonlinear autopilot is designed. And the stability is analyzed considering roll influences on dynamic couplings of yaw and pitch channel as well as the aerodynamic couplings. Some additional issues on the autopilot implementation for these coupled missile dynamics are discussed. Lastly, 6-DOF (degree of freedom) numerical simulation results are presented to verify the proposed method.

• 한국항해학회지
• /
• 제16권3호
• /
• pp.33-41
• /
• 1992

Handling performance of a vessel is greatly related with her steering characteristics which consist of two kinds of motion characteristics ; namely course stability and turning ability. The correct prediction of the qualities, especially the steering characteristics is as much important in ship handling as in ship design. It is the purpose of this paper to provide ships handlers better understanding of steering characteristics and then to help them in safe controlling and maneuvering of vessels presenting distinct inherent steering characteristic difference that lies between a fine-form vessel and full-form vessel. The authors calculated dynamic course stabilities of two kinds of ideal models, one of which represents a fine-form ship and the other a full-form ship, based on hydrodynamic data of forces and moments obtained by model tests in maneuvering tanks. The result of calculations indicated that a ship of full-form configuration has inhernet course instability. Though significant nonlinearties affect ship montions in maneuvers, application of linear theory is sufficient for prediction of the maneuvering characteristics of vessels on calm waters for handling reference.

• International Journal of Aeronautical and Space Sciences
• /
• 제12권1호
• /
• pp.78-83
• /
• 2011

Traditional autopilot design requires an accurate aerodynamic model and relies on a gain schedule to account for system nonlinearities. This paper presents the control architecture applied to a dynamic model inversion at a single flight condition with an on-line neural network (NN) in order to regulate errors caused by approximate inversion. This eliminates the need for an extensive design process and accurate aerodynamic data. The simulation results using a developed full nonlinear 6 degree of freedom model are presented. This paper also presents the stability evaluation for control systems to which NNs were applied. Although feedback can accommodate uncertainty to meet system performance specifications, uncertainty can also affect the stability of the control system. The importance of robustness has long been recognized and stability margins were developed to quantify it. However, the traditional stability margin techniques based on linear control theory can not be applied to control systems upon which a representative non-linear control method, such as NNs, has been applied. This paper presents an alternative stability margin technique for NNs applied to control systems based on the system responses to an inserted gain multiplier or time delay element.