• Journal of the Society of Naval Architects of Korea
• /
• v.55 no.4
• /
• pp.297-305
• /
• 2018

In a shipyard, block lifting is an important process in the production of ships and offshore structures. Block lifting is a sensitive process because lifting blocks have to be erected with exact positions and orientations. If we use a numerical method for the process, it is important to find tensions of wires and positions of equalizers to maintain the initial equilibrium position of the block. At this time, equations of motion of the block should be solved to calculate the initial equilibrium position of the block. Because the solving technique changes according to the number of equalizers, a suitable equation for the corresponding problem is required. In this study, three types of equations are proposed to find the initial equilibrium position of the block according to the number of equalizers. The Newton-Raphson's method is used to solve nonlinear simultaneous equations and the optimization method is used to determine the appropriate solution to the undetermined problem. To evaluate the applicability of the proposed methods, the dynamic simulations are performed using the tensions calculated from the proposed methods, and the results are discussed. The results show that the proposed methods can be effectively used to determine initial equilibrium position of the block for the block lifting.

• 한국전산유체공학회:학술대회논문집
• /
• 2011.05a
• /
• pp.504-507
• /
• 2011

The inertial migration of a two-dimensional elastic capsule in a channel flow was studied over the Reynolds number range $1{\leq}Re{\leq}100$. The lateral migration velocity, slip velocity, and the deformation and inclination angle of the capsule were investigated by varying the lateral position, Reynolds number, capsule-to-channel size ratio(${\lambda}$), membrane stretching coefficient(${\Phi}$), and membrane bending coefficient(${\gamma}$). During the initial transient motion, the lateral migration velocity increased with increasing Re and ${\lambda}$ but decreased with increases in ${\Phi}$, ${\gamma}$ and the lateral distance from the wall. The initial behavior of the capsule was influenced by variation in the initial lateral position ($y_0$), but the equilibrium position of the capsule was not affected by such variation. The balance between the wall effect and the shear gradient effect determined the equilibrium position. As Re increased, the equilibrium position initially shifted closer to the wall and then moved towards the channel center. A peak in the equilibrium position was observed near Re=30 for ${\gamma}=0.1$, and the peak shifted to higher Re as ${\gamma}$ increased. Depending on the lateral migration velocity, the equilibrium position moved toward the centerline for larger ${\gamma}$ but moved toward the wall for larger ${\Phi}$ and ${\gamma}$.

• Journal of Ocean Engineering and Technology
• /
• v.9 no.2
• /
• pp.53-60
• /
• 1995

A multi-leg spread mooring system for floating offshore structures is important, but the multi-leg static analysis is complicated due to the nonlinear behavior of each line and the effect of current which affects each line differently. The pretensioned position of the multi-leg mooring system obtained from the static equilibrium condition changes into a different position due to external loads and current. In this paper, the new position and the static tension at each line are caculated. The relation between the initial static equilibrium position and the new position due to the external loads is expressed in terms of the Taylor's series expansion. The Runge-Kutta $4^{th}$ method is employed in analyzing the 3-dimensional static cable nonlinear equations.

• The Bulletin of The Korean Astronomical Society
• /
• v.35 no.2
• /
• pp.48.2-48.2
• /
• 2010

Quiescent filaments are bigger, more stable, and longer lived than active region filaments. So, the shape of a quiescent filament changes little during its lifetime and a fast motion of plasma rarely occurs. But when it is dynamically influenced by external phenomena, a rapid motion of plasma may temporarily occur. By analyzing the motion of plasma we can infer some of the magnetic structure permeating such an excited quiescent filament. We analyzed the H$\alpha$ images of a quiescent filament in the northern hemisphere that was observed at Big Bear Solar Observatory on 2004 August 2, and found that: 1) the filament was excited by a flare that occurred in a remote active region located in the southern hemisphere, 2) By this excitation, a part of the filament moved vertically upward and horizontally out of main body, and then it stayed there without much motion. Then after it moved vertically downward and horizontally to the main body, 3) the final position of plasma, however, was not the same as the initial position, being about 14Mm above it. We suggest that the filament was initially in a more or less static equilibrium. The excitation of the filament broke the initial equilibrium, and then brought about a new one that is different from the original one. Since the filament should have magnetic field, it is likely that both the equilibria may have been maintained by diplike magnetic structures. Furthermore, the transition from one equilibrium to another as we inferred should have accompanied a permanent change of magnetic configuration as well.

• 제어로봇시스템학회:학술대회논문집
• /
• 1997.10a
• /
• pp.207-210
• /
• 1997

In this paper, a hierarchical fuzzy controller for stabilization of the inverted pendulum system is proposed. The facility of this hierarchical fuzzy controller which has a swing-up control mode and a stabilization one, moves a pendulum in an initial natural stable equilibrium point and a cart in arbitrary position to an unstable equilibrium point and a center of rail. Specially, the virtual equilibrium point (.PHI.$_{VEq}$ ) which describes functionally considers the interactive dynamics between a position of cart and a angle of inverted pendulum is introduced. And comparing with the convention optimal controller, the proposed hierarchical fuzzy inference made substantially the inverted pendulum system robust and stable.e.

• Proceedings of the KIEE Conference
• /
• 1997.11a
• /
• pp.83-85
• /
• 1997

In this paper, a self-tunning fuzzy inference technique for stabilization of the inverted pendulum system is proposed. The facility of this self-tunning fuzzy controller which has swing-up control mode and a stabilization one, moves a pendulum in an initial natural stable equilibrium point and a cart in arbitrary position, to an unstable equilibrium point and a center of rail. Specially, the virtual equilibrium point(${\phi}_{VEq}$) which describes functionally considers the interactive dynamics between a position of cart and a angle of inverted pendulum is introduced. And comparing with the convention optimal controller, the proposed self-tunning fuzzy inference structure made substantially the inverted pendulum system robust and stable.

• Proceedings of the Korean Institute of Intelligent Systems Conference
• /
• 1998.10a
• /
• pp.304-309
• /
• 1998

In this paper, a fuzzy controller for stabilization of the inverted pendulum system is propose. The facility of this fuzzy controller which has a swing-up control mode and a stabilization one, moves a pendulum in an initial natural stable equilibrium point and a cart in arbitary position, to an unstable equilibrium point and a center of rail. Specially, the virtual equilibrium point ($\Phi$veq) which describes functionally considers the interactive dynamics between a position of cart and a angle of inverted pendulum is introduced. And comparing with the convention optimal controller, the proposed hierarchical fuzzy inference structur made substantially the inverted pendulum system robust and stable.

• Journal of Advanced Marine Engineering and Technology
• /
• v.21 no.4
• /
• pp.393-403
• /
• 1997

In this paper, we proposed an optimal identification method of identifying the membership func¬tions and the fuzzy rules for the stabilization controller of the nonlinear system by RVEGA( Real Variable Elitist Genetic Algo rithm l. Although fuzzy logic controllers have been successfully applied to industrial plants, most of them have been relied heavily on expert's empirical knowl¬edge. So it is very difficult to determine the linguistic state space partitions and parameters of the membership functions and to extract the control rules. Most of conventional approaches have the drastic defects of trapping to a local minima. However, the proposed RVEGA which is similiar to the processes of natural evolution can optimize simulta¬neously the fuzzy rules and the parameters of membership functions. The validity of the RVEGA - based fuzzy controller was proved through applications to the stabi¬lization problems of an inverted pendulum system with highly nonlinear dynamics. The proposed RVEGA - based fuzzy controller has a swing -. up control mode(swing - up controller) and a stabi¬lization one(stabilization controller), moves a pendulum in an initial stable equilibrium point and a cart in an arbitrary position, to an unstable equilibrium point and a center of the rail. The stabi¬lization controller is composed of a hierarchical fuzzy inference structure; that is, the lower level inference for the virtual equilibrium point and the higher level one for position control of the cart according to the firstly inferred virtual equilibrium point. The experimental apparatus was imple¬mented by a DT -- 2801 board with AID, D/A converters and a PC - 586 microprocessor.

• Journal of Advanced Marine Engineering and Technology
• /
• v.27 no.4
• /
• pp.526-534
• /
• 2003

Motions of animals and gymnasts in the air as well as free flying space robots without thruster are subject to nonholonomic constraints generated by the law of conservation of angular momentum. The interest in nonholonomic control problems is motivated by the fact that such systems can not stabilized to its equilibrium points by the smooth control input. The purpose of this paper is to derive analytical posture control laws for free flying objects in the air. We propose a control method using bang-bang control for trajectory planning of a 3 link mechanical system with initial angular momentum. We reduce the DOF (degrees of freedom) of control object in the first control phase and determine the control inputs to steer the reduced order system from its initial position to its desired position. Computer simulation for a motion planning of an athlete approximated by 3 link is presented to illustrate the effectiveness of the Proposed control scheme.

• Proceedings of the KSME Conference
• /
• 2007.05a
• /
• pp.985-990
• /
• 2007

This paper presents a novel control algorithm for position control of pneumatic cylinder. Generally, it is difficult to control the pneumatic servo system, due to nonlinearities such as air compressibility, the opening area of the valve, and frictional force between the cylinder and the piston. Especially, it is of significant importance for the control consisten-cy to return the cylinder pressures at equilibrium point to the initial states, still with guaranteeing the continuity of the pressures. For this purpose, the proposed control algorithm makes pressures of both cylinder chambers identical in magnitude but different in direction. The effectiveness and practicability of the control algorithm for the precise position control of the pneumatic cylinder are verified through the simulation study.