• Journal of Korean Ophthalmic Optics Society
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• v.21 no.2
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• pp.99-108
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• 2016

Purpose: The present study was aimed to compare the tear volume and distribution by corneal eccentricity when fitted with spherical and aspherical RGP lenses. Methods: Spherical and aspherical RGP lenses were fitted in best alignment on a total of 77 subjects (136 eyes) in their twenties and thirties without any ocular disease or ocular surgery experience. The tear volume was analyzed by estimating the concentration of tear stained with fluorescein in the center of RGP lens as well as at the mid-peripheral and peripheral areas, and the difference of tear distributions was analyzed according to corneal eccentricity. Results: Tear distribution from the center to the peripheral area was not significantly different when spherical RGP lenses were fitted on the corneal eccentricities of e < 0.38 and $0.68{\leq}e$, indicating the relatively even tear distribution compared with other corneal eccentricity. In the case of aspherical RGP lenses, the difference of tear distribution between the central and peripheral areas was smaller than spherical RGP lenses. The significant difference of tear distribution according to RGP lens design was observed in the corneal eccentricity of 0.48 < e < 0.68. In other words, more even tear distribution was shown when aspherical RGP lenses were fitted on the cornea with eccentricity of $0.48{\leq}e<0.68$ and spherical RGP lenses were fitted on the cornea with eccentricity $0.68{\leq}e$. Furthermore, tear volume in the mid-peripheral area increased with higher corneal eccentricity. Conclusions: The results suggest that the appropriate selection of RGP lens design according to corneal eccentricity is necessary since tear volume and distribution by the regions of spherical and aspherical lenses are affected by corneal eccentricity.

• 제어로봇시스템학회:학술대회논문집
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• 1991.10a
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• pp.243-247
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• 1991

A roll eccentricity controller for a tandem cold rolling process is designed to attenuate the outlet thickness deviation due to roll eccentricity. In order to design the controller, the excess stability margin is maximized by solving a standard H.inf. optimization problem under the requirement that ensure disturbance rejection for a class of disturbance. Robust performance of the proposed controller is checked by a computer simulation.

• Journal of the Korean Society of Hazard Mitigation
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• v.4 no.4 s.15
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• pp.63-71
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• 2004

The centroid of rail doesn't coincide with the centroid of stringer on target truss bridge. If there is no eccentricity on the bridge, bending stress works only. But in the real design and execution, not only bending stress works but also torsional stress does because of it's eccentricity. So this study evaluates how much the torsional stress by eccentricity effects joint members on the bridge. We investigate the possibility to control torsional stress if we model longitudinal bracing between stringers.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.1
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• pp.59-72
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• 1998

This experimental study was carried out to investigate the characteristics of the in-cylinder eccentricity swirl flow generated by a 4 valve cylinder head with a tangential and a helical intake port. the measurements of the in-cylinder velocity field have been made by a two-channel LDA system. The mean flow coefficient(Cf(meam)), swirl ratio(Rs) and mass flowrate with valve eccentricity ratios and an intake port partition between the two intake ports were measured in the steady flow test fig using the ISM(impulse swirl meter). The experimental results indicated that the mass flowrate through the tangential intake port was 19% and 7.7% more than that of the helical intake port in case of with and without intake port partition respectively. There was a tendency to be a single rotation flow in swirl flow fields formed by a 4 valve cylinder head because of the interaction between the two intake ports. As the intake port partition was not set between flow coefficient(Cf(mean)) was 7.35%.

• Journal of Astronomy and Space Sciences
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• v.37 no.1
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• pp.1-9
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• 2020

Frozen orbit is an attractive option for orbital design owing to its characteristics (its argument of pericenter and eccentricity are kept constant on an average). Solar sails are attractive solutions for massive and expensive missions. However, the solar radiation pressure effect represents an additional force on the solar sail that may greatly affect its orbital behavior in the long run. Thus, this force must be included as a perturbation force in the dynamical model for more accuracy. This study shows the calculations of initial conditions for a lunar solar sail frozen orbit. The disturbing function of the problem was developed to include the lunar gravitational field that is characterized by uneven mass distribution, third body perturbation, and the effect of solar radiation. An averaging technique was used to reduce the dynamical problem to a long period system. Lagrange planetary equations were utilized to formulate the rate of change of the argument of pericenter and eccentricity. Using the reduced system, frozen orbits for the Moon sail orbiter were constructed. The resulting frozen orbits are shown by two 3Dsurface (semi-major, eccentricity, inclination) figures. To simplify the analysis, we showed inclination-eccentricity contours for different values of semi-major axis, argument of pericenter, and values of sail lightness number.

• Structural Engineering and Mechanics
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• v.13 no.6
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• pp.671-694
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• 2002

This paper presents theoretical investigation on the cross correlation between torsional vibration ($u_{\theta}$) and translation vibration ($u_x$) of asymmetrical structure under white noise excitation. The formula reveals that the cross correlation coefficient (${\rho}$) is a function of uncoupled frequency ratio (${\Omega}={\omega}_{\theta}/{\omega}_x$), eccentricity, and damping ratio (${\xi}$). Simulations involving acceleration records from fifteen different earthquakes show correlation coefficients results similar to the theoretical correlation coefficients. The uncoupled frequency ratio is the dominating parameter to ${\rho}$; generally, ${\rho}$ is positive for ${\omega}_{\theta}/{\omega}_x$ > 1.0, negative for ${\omega}_{\theta}/{\omega}_x$ < 1.0, and close to zero for ${\omega}_{\theta}/{\omega}_x$ = 1.0. When the eccentricity or damping ratio increases, ${\rho}$ increases moderately for small ${\Omega}$ (< 1.0) only. The relation among $u_x$, $u_{\theta}$ and corner displacement are best presented by ${\rho}$; a simple way to hand-calculate the theoretical dynamic corner displacements from $u_x$, $u_{\theta}$ and ${\rho}$ is proposed as an alternative to dynamic analysis.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.748-752
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• 2004

Fluid dynamic bearings (FDBs) have been replacing ball bearings of the HDD spindle motor very rapidly. But there are several demerits of HDB, such as high friction torque, variable viscosity of the fluid lubricant depending on operating temperature, low stiffness, and etc. Eccentricity is one of the major parameters which affects the static and dynamic characteristics. As the static eccentricity is larger, the stiffness and the damping coefficients become bigger. But friction torque is relatively unaffected by the static eccentricity. This research proposes a new type of journal bearing with asymmetric journal grooves which results in better dynamic characteristics. The static and dynamic characteristics of the new journal bearing are investigated by solving the Reynolds' equation with FEM, and the transient analysis is performed to predict the dynamic behavior of rotor by solving the equations of motion of a HDD spindle system with Runge-Kutta method. The result shows that the proposed Journal bearings have much bigger stiffness and damping coefficients compared with the conventional symmetric ones. And consequently, it has smaller whirl radius and tilting angle.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.11 no.9
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• pp.454-461
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• 2001

Acoustic noise and vibration of a BLDC motor is a coupled phenomenon between mechanical characteristics and electromagnetic origins through the motor air-gap. When a relative misalignment of rotor in the air-gap center exists on the assemblage, it is considered to influence the motor system characteristics. In this paper, the back electro motive force(BEMF) is analyzed by Finite Element Method(FEM) and verified by experiments for the SPM and IPM type motors. For magnetic field analysis, a FEM is used to account for the magnetic saturation. Using these results, the FEM is made to determine the appropriate electromagnetic field analysis in BLDC motors with rotor eccentricity ratio. A radial magnetic imbalance force of BLDC motor with rotor eccentricity is analyzed. Results demonstrate that the imbalance force is increased according to the degree of misalignment. An IPM motor, mostly chosen to realize high-speed operation, shows a worse effect on magnetic unbalanced forces and dynamic responses compared with SPM motor due to magnetic saturation when the rotor eccentricity exists.

• Wind and Structures
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• v.6 no.1
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• pp.23-40
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• 2003

The steady state response of a torsionally coupled system with tuned mass dampers (TMDs) to external wind-induced harmonic excitation is presented. The torsionally coupled system is considered as one-way eccentric system. The eccentricity considered in the system is accidental eccentricity only. The performance of single tuned mass damper (TMD) optimally designed without considering the torsion is investigated for the torsionally coupled system and found that the effectiveness of a single TMD is significantly reduced due to torsion in the system. However, the design of TMD system without considering the torsion is only justified for torsionally stiff systems. Further, the optimum parameters of a single TMD considering the accidental eccentricity are obtained using numerical searching technique for different values of uncoupled torsional to lateral frequency ratio and aspect ratio of the system. The optimally designed single TMD system is found to be less effective for torsionally coupled system in comparison to uncoupled system. This is due to the fact that a torsionally coupled system has two natural frequencies of vibration, as a result, at least two TMDs are required which can control both lateral and torsional response of the system. The optimum damper parameters of different alternate arrangements such as (i) two identical TMDs placed at opposite corners, (ii) two independent TMDs and (iii) four TMDs are evaluated for minimum response of the system. The comparative performance of the above TMDs arrangements is also studied for both torsionally coupled and uncoupled systems. It is found that four TMDs arrangement is quite effective solution for vibration control of torsionally coupled system.

• Structural Engineering and Mechanics
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• v.39 no.2
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• pp.207-221
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• 2011

This paper aims to study the behavior of short reinforced concrete columns confined with external glass Fiber Reinforced Polymers (GFRP) sheets under eccentric loads. The experimental part of the study was achieved by testing 9 specimens under eccentric compression. Three eccentricity ratios corresponding to e/t = 0, 0.10, 0.50 in one direction of the column were used. Specimens were divided into three groups. The first group was the control one without confinement. The second group was fully wrapped with GFRP laminates before loading. The third group was wrapped under loading after reaching 75% of failure loads of the control specimens. The third group was investigated in order to represent the practical case of strengthening a loaded column with FRP laminates. All specimens were loaded until failure. The results show that GFRP laminates enhances both failure load and ductility response of eccentrically loaded column. Moreover, the study also illustrates the effect of confinement on the first crack load, lateral deformation, strain in reinforcement and failure pattern. Based on the analysis of the experimental results, a simple model has been proposed to predict the improvement of load carrying capacity under different eccentricity ratios. The predicted equation takes into consideration the eccentricity to cross section depth ratio, the ultimate strength of GFRP, the thickness of wrapping laminate, and the time of wrapping (before loading and under loading). A good correlation was obtained between experimental and analytical results.