• 제어로봇시스템학회:학술대회논문집
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• 1986.10a
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• pp.251-255
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• 1986

Some missiles using canards as control device adopt rollerons to reduce roll motion due to aerodynamically induced rolling moment. This paper presents equations of motion of these missiles including the gyroscopic effect of rolleron rotors. Some linearized analysis results and simulation results are shown to coincide, thus some characteristic motions of missiles and rollerons can be seen.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2006.10a
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• pp.134-143
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• 2006

Out of all types of motions the critical motions leading to capsize is roll. The dynamic amplification in case of roll motion may be large for ships as roll natural frequency generally falls within the frequency range of wave energy spectrum typical used for estimation of motion spectrum. Roll motion is highly non-linear in nature. Den are various representations of non-linear damping and restoring available in literature. In this paper an uncoupled non-linear roll equations with three representation of damping and cubic restoring term is solved using a perturbation technique. Damping moment representations are linear plus quadratic velocity damping, angle dependant damping and linear plus cubic velocity dependant damping. Numerical value of linear damping coefficient is almost same for all types but non-linear damping is different. Linear and non-linear damping coefficients are obtained form free roll decay tests. External rolling moment is assumed as deterministic with sinusoidal form. Maximum roll amplitude of non-linear roll equation with various representations of damping is calculated using analytical procedure and compared with experimental results, which are obtained form forced tests in regular waves by varying frequency with three wave heights. Experiments indicate influence of non-linearity at resonance frequency. Both experiment and analytical results indicates increase in maximum roll amplitude with wave slope at resonance. Analytical results are compared with experiment results which indicate maximum roll amplitude analytically obtained with angle dependent and cubic velocity damping are equal and difference from experiments with these damping are less compared to non-linear equation with quadratic velocity damping.

• Ocean Systems Engineering
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• v.2 no.4
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• pp.239-255
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• 2012

Analysis of ship parametric roll has generally been restricted to simple analytical models and sophisticated time domain simulations. Simple analytical models do not capture all the critical dynamics while time-domain simulations are often time consuming to implement. The model presented in this paper captures the essential dynamics of the system without over simplification. This work incorporates various important aspects of the system and assesses the significance of including or ignoring these aspects. Special consideration is given to the fact that a hull form asymmetric about the design waterline would not lead to a perfectly harmonic variation in metacentric height. Many of the previous works on parametric roll make the assumption of linearized and harmonic behaviour of the time-varying restoring arm or metacentric height. This assumption enables modelling the roll motion as a Mathieu equation. This paper provides a critical assessment of this assumption and suggests modelling the roll motion as a Hills equation. Also the effects of non-linear damping are included to evaluate its effect on the bounded parametric roll amplitude in a simplified manner.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.5
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• pp.420-427
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• 2008

For simulation of a fin unfolding motion for the various aerodynamic conditions, equations and moments applying to the unfolding fin were modelled. Aerodynamic roll moment consists of the static roll moment and the damping moment, which were obtained through wind tunnel tests and numerical analyses respectively. Panel method was used to compute the roll damping coefficient with deflected fin, whose angle was equivalent to angle of attack due to the deployment motion. Roll damping coefficient is a function of angle of attack, sideslip angle, and deployment angle but not of angular velocity of deployment. Simulation with aerodynamic damping model gave more similar deployment time compared to fin deployment test results.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2018.05a
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• pp.41-42
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• 2018

This study is about the prediction of ship's roll motion characteristic which has been used for evaluating ship's seakeeping performance. In order to obtain the ship's roll RAO during voyage, this paper utilized machine learning-based surrogate model. By comparing the prediction result data of surrogate model with test data, we suggest the best approximation technique and data sampling interval of the surrogate model appropriate for predicting the ships' roll motion characteristic.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.47 no.1
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• pp.37-45
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• 2011

Reduction of ship's rolling is the most important performance requirement for improving the safety of the crew on board and preventing damage to cargo as well as improving the comfort of the ride. It is a common experience for mariners, to see that steering with a rudder generally induces rolling of the ship, though the original aim of the rudder is to keep the ship's heading to the required course. At the first stage, when a rudder is steered, usually a ship heels in an inward direction, due to the roll moment acting on the rudder. At the next stage in steering, the main heel may change to an outward. This coupling between rudder and roll motion has become an attractive problem from the point of view of roll stabilization using the rudder, because it is a natural in sight that if the rudder action is skillfully related to the change of roll as well as to the course deviation, the roll can be reduced to a certain degree. The main aim of this paper is to discuss the results of the actual full-scale sea trials carried out on steer gear No.1 and No.1 2, the individual quartermaster and to make clear their statistical properties, using the actual data which included measurement of roll angle, roll rate and the comparative tests were carried out immediately after each other, in order to minimize any statistical variation in sea conditions. It can be concluded that the steer gear No. 1 2 reduced the roll motion on average by about 21% in comparison with the No.1 and confirmed the some difference as per a ability of quarter-master's maneuver.

• Ocean Systems Engineering
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• v.7 no.1
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• pp.53-74
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• 2017

Ship shaped FPSO (Floating Production, Storage and Offloading) units are the most commonly used floating production units to extract hydrocarbons from reservoirs under the seabed. These structures are usually much larger than general cargo ships and have their natural frequency outside the wave frequency range. This results in the response to first order wave forces acting on the hull to be negligible. However, second order difference frequency forces start to significantly impact the motions of the structure. When the difference frequency between wave components matches the roll natural frequency, the structure experiences a significant roll motion which is also termed as second order roll. This paper describes the theory and numerical implementation behind the calculation of second order forces and motions of any general floating structure subjected to waves. The numerical implementation is validated in zero speed case against the commercial code OrcaFlex. The paper also describes in detail the popular approximations used to simplify the computation of second order forces and provides a discussion on the limitations of each approximation.

• Journal of Power System Engineering
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• v.13 no.1
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• pp.26-32
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• 2009

This study is about roll characteristics evaluation to show the advantage of using MR(magneto-rheological) dampers for steering of a SUV(sports utility vehicle). Roll characteristics is very important to observe the roll-propensity of the SUV. ADAMS/Car program was used to simulate the basic steering motion, using 63 D.O.F. vehicle model. Sky-Hook and Ground-Hook control algorithms were used as a semi-active suspension system controller. The roll characteristics from the steering motion were compared between the simulation results from the semi-active suspension system and the passive suspension system.

• Journal of the Society of Naval Architects of Korea
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• v.59 no.6
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• pp.338-344
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• 2022

Roll moment usually is ignored when analyzing the maneuverability of surface ships. However, it is well known that the influence of roll moment on maneuverability is significant for ships with small metacentric height such as container ships, passenger ships, etc. In this study, a pure roll test is performed to determine the hydrodynamic derivatives with respect to roll motion as added mass and damping. The target ship is an autonomous surface ship designed to carry containers with a small drift and large freeboard. The commercial code of STAR CCM+ software is applied as a specialized tool in naval hydrodynamic based on RANS equation for simulating the pure roll of the ship. The numerical uncertainty analysis is conducted to verify the numerical accuracy. By distinguishing the in-phase and out-of-phase from hydrodynamic forces and moments due to roll motion, added mass derivatives and damping derivatives relative to roll angular velocity are obtained.

• 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.