• The Transactions of the Korean Institute of Electrical Engineers D
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• v.53 no.3
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• pp.173-181
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• 2004

In normal robot control systems without any actuator failures, it is assumed that actuator torque coefficients applied at each joint have normally 1's all the time. However, it is more practical that actuator torque coefficients applied at each joint are nonlinear time-varying. In other words, it has to be considered that actuators equipped at joints may fail due to hardware or software faults. In this work, actuator torque coefficients are assumed to have non-zero values at all joints. In the case of an actuator torque coefficient which has a zero value at a joint, it means the complete loss of torque on the joint. This paper doesn't deal with the case. As factors of performance degradation of robots, both actuator failures and uncertainties are considered in this paper at the same time. This paper proposes a robust adaptive fault-tolerant control scheme to maintain the required performance and achieve task completion for robot manipulators with performance degradation due to actuator failures and uncertainties. Simulation results are shown to verify the fault tolerance and robustness of the Proposed control scheme.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.4
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• pp.297-303
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• 2006

Friction and heat transfer coefficients were measured inside the corrugated tube using water as the working fluid. The test is performed for 16 tubes which outer diameter of tubes are 12.7 mm. These specifications are 4 indentation depths and 4 indentation pitches, respectively. The range of the water velocity inside the tube is from 0.5 to 3.0 m/s (8,500

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.4
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• pp.281-289
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• 2016

Accurate prediction of the trajectory and time of a time-varying mass parachute system remains essential in the mission requiring a precision airdrop to the ground. In this study, we investigate the altitude-varying behavior of a cross-type parachute system designed to deliver a time-varying mass object like flare. The dynamics of the descending parachute system was analyzed based on the Runge-Kutta method of the ordinary differential system. The drag coefficients of the cross-type parachute and flare were calculated by a CFD code based on the incompressible Navier-Stokes equation. Finally, by using a simplified gust wind model in troposphere, the combined effects of gust wind and time-varying mass were examined in detail.

• Steel and Composite Structures
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• v.16 no.4
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• pp.375-387
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• 2014

The purpose of this paper is to propose a method for evaluation of varying stiffness coefficients of tailored conical shells (TCS). Furthermore, a comparison between buckling loads of these shells under axial load with the different fiber path is performed. A circular truncated conical shell subjected to axial compression is taken into account. Three different theoretical path containing geodesic path, constant curvature path and constant angle path has been considered to describe the angle variation along the cone length, along cone generator of a conical shell are offered. In the TCS with the arbitrary fiber path, the thickness and the ply orientation are assumed to be functions of the shell coordinates and influencing stiffness coefficients of the structure. The stiffness coefficients and the buckling loads of shells are calculated basing on classical shells theory (CST) and using finite-element analysis (FEA) software. The obtained results for TCS with arbitrary fiber path, thickness and ply orientation are derived as functions of shell longitudinal coordinate and influencing stiffness coefficients of structures. Furthermore, the buckling loads based on fiber path and ply orientation at the start of tailored fiber get to be different. The extent of difference for tailored fiber with start angle lower than 20 degrees is not significant. The results in this paper show that using tailored fiber placement could be applied for producing conical shells in order to have greater buckling strengths and lower weight. This work demonstrates the use of fiber path definitions for calculated stiffness coefficients and buckling loads of conical shells.

• Structural Engineering and Mechanics
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• v.58 no.6
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• pp.1001-1020
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• 2016

The study is to investigate the free vibration of antisymmetric angle-ply conical shells having non-uniform sinusoidal thickness variation. The arbitrarily varying thickness is considered in the axial direction of the shell. The vibrational behavior of shear deformable conical shells is analyzed for three different support conditions. The coupled differential equations in terms displacement and rotational functions are obtained. These displacement and rotational functions are invariantly approximated using cubic spline. A generalized eigenvalue problem is obtained and solved numerically for an eigenfrequency parameter and an associated eigenvector of spline coefficients. The vibration characteristic of the shells is examined for cone angle, aspect ratio, sinusoidal thickness variation, layer number, stacking sequence, and boundary conditions.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.482-483
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• 2008

This paper compares particle swarm optimization techniques for PV allocation planning problem in power systems. PV allocation planning problem is formulated as a mixed-integer nonlinear problem. Five variants of PSO techniques are investigated for the applicability on the PV allocation problem. Namely, PSO with constant inertia weight approach (PSO-CIW), PSO with time varying inertia weight (PSO-TVIW), PSO with random inertia weight (PSO-RIW), PSO with constriction factor (PSO-CF) and PSO with time varying acceleration coefficients (PSO-TVAC).

• Steel and Composite Structures
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• v.34 no.6
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• pp.795-802
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• 2020

The subject of the paper is a circular plate with symmetrically thickness-wise varying mechanical properties. The plate is simply supported and carries a concentrated force located in its centre. The axisymmetric bending problem of the plate with consideration of the shear effect is analytically and numerically studied. A nonlinear function of deformation of the straight line normal to the plate neutral surface is assumed. Two differential equations of equilibrium based on the principle of stationary potential energy are obtained. The system of equations is analytically solved and the maximum deflections and shear coefficients for example plates are derived. Moreover, the maximum deflections of the plates are calculated numerically (FEM), for comparison with the analytical results.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.5
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• pp.762-772
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• 2004

Fatigue life of a Piston for large liquid Petroleum liquid injection(LPLi) bus engines is analyzed considering effects of cooling condition parameters : temperature of cooling water, and heat transfer coefficients at oil gallery and bottom surface of piston head. Temperature of the piston is analyzed with varying cooling conditions Stresses of the piston from two load cases of pressure loading. and pressure and thermal loading are analyzed Fatigue life under repeated peak pressure and thermal cycle is analyzed by the strain-life theory. For the two load cases, required loading cycles for engine life are defined, and loading cycles to failure and partial damages are calculated. Based on the resulting accumulated fatigue usage factors, endurance of the piston is evaluated and effects of varying cooling condition Parameters are discussed.

• Transactions of the Korean Society of Automotive Engineers
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• v.21 no.1
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• pp.78-85
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• 2013

This paper presents the sliding mode control methods for anti-lock brake system (ABS) with the friction force observer. Using a simplified quarter car model, the sliding mode controller for ABS is designed to track the desired wheel slip ratio. Here, new method to find the desired wheel slip ratio which produces the maximum friction force between road and tire is suggested. The desired wheel slip ratio is varying according road and tire conditions to produce maximum friction force. In order to find optimum desired wheel slip ratio, the sliding mode observer for friction force is used. The proposed sliding mode controller with observer is evaluated in simulation, and the control design is shown to have high performance on roads with constant and varying adhesion coefficients.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.10 s.241
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• pp.1321-1328
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• 2005

Based upon the Floquet theory, the complex modal solution for general rotor systems with periodically time-varying parameters is newly derived. The complete modal response can be obtained from the orthonormality condition between the time-variant eigenvectors and the corresponding adjoint vectors. The harmonic solutions such as the response and directional special a patterns are then derived in terms of harmonic modes whose coefficients are obtained from the modal analysis. The stability analysis by the Floquet's transition matrix and the eigen-analysis is also performed.