• Tribology and Lubricants
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• v.28 no.6
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• pp.265-271
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• 2012

In the preceding Part I study, for improving the unbalance response vibration of a large PRT motor-generator rotor fundamentally by design, a series of design analyses were carried out for bearing improvement by retrofitting from original plain partial journal bearings, applied for operation at a rated speed of 1,800 rpm, to final tilting pad journal bearings. To satisfy evenly key basic lubrication performances such as the minimum lift-off speed and maximum oil-film temperature, a design solution of 5-pad tilting pad journal bearings and maximizing the direct stiffness by about two times has been achieved. In this Part II study, a detailed rotordynamic analysis of the large PRT motor-generator rotor-bearing system will be performed, applying both the original plain partial journal bearings and the retrofitted tilting pad journal bearings, to confirm the effect of rotordynamic vibration improvement after retrofitting. The results show that the rotor unbalance response vibrations with the tilting pad journal bearings are greatly reduced by as much as about one ninth of those with the plain partial journal bearings. In addition, for the tilting pad journal bearings there exist no critical speed up to the rated speed and just one instance of a concerned critical speed around the rated speed, whereas for the plain partial journal bearings there exist one instance of a critical speed up to the rated speed and two instances of concerned critical speeds around the rated speed.

• Journal of the Korean Institute of Navigation
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• v.13 no.3
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• pp.21-36
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• 1989

The submarine played an active part in military operation during the last of nineteenth century. Today, as an aid to science and technology and technology m the submarine is being utilized in the fields of deep sea investigation and sight-seeing as well as military activities. When the stability and the maneuverability of a submarine is studied, the problems arise on the vertical plane as well as the horizontal plane. However, the horizontal plane has been dealt with in the study of surface vessels. The author attempts to look into the hydrodynamic directional stability at high speeds (above 10knots) on the vertical plane, and to clarify the submarine's depth-rate as related to the factors that affect it : the distance from the center of buoyancy to the center of gravity, the speed of the submarine, and the position and the area ratio of hydroplane. In this study, the author considered the two groups of dimensionless derivatives of submarine. It is confirmed that the depth-rate of a submarine is decreased when the length, of BG is increased under the continuous submerging status. But the depth-rate is increased when the area ratio of hydroplane is enlarged. It is also confirmed that a submarine has only one critical speed in accordance with the shape of its hull, but unconcerned with its speeds.

• Proceedings of the KIEE Conference
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• 1996.07a
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• pp.190-192
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• 1996

This paper is a study on the rotating type of superconducting power supply(R.S.P.S.) with superconducting excitation coils. In this paper, a new idea of excitation coil is introduced to control the pole-flux in air gap. We manufactured the R.S.P.S. by using superconducting excitation coils and measured the charging current of superconducting load with respect to rotational speeds and excitational current. Through this experiment, 425A of maximum current was obtained a few minutes. It turned out that the charging rate of load current is proportional to rotational speeds and excitational current. Furthermore, it is found that it's possible to generate the charge current of thousands of amperes by using wires of larger critical current.

• Composites Research
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• v.18 no.4
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• pp.8-13
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• 2005

Rotating circular disks are widely used in data storage devices as well as in traditional industrial machines. Faster rotating speed is required in data storage devices for higher data transfer rate. In this Paper an application of composite materials to CD is proposed to increase critical speeds and the strength analysis was performed. A differential equation of displacement is derived for the analytic stress distribution of rotating polar orthotropic disk. The stress distributions for typical GFRP and CFRP disks and the maximum allowable speeds subjected to a constraint of tensile strength are presented in addition to polycarbonate disk. The results show that the application of CFRP to rotating disk can increase the maximum allowable rotating speed but this may not be applicable to GFRP disk.

• Wind and Structures
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• v.9 no.3
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• pp.217-230
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• 2006

This paper describes a procedure to develop fragility curves for woodframe structures subjected to lateral wind loads. The fragilities are cast in terms of horizontal displacement criteria (maximum drift at the top of the shearwalls). The procedure is illustrated through the development of fragility curves for one and two-story residential woodframe buildings in high wind regions. The structures were analyzed using a monotonic pushover analysis to develop the relationship between displacement and base shear. The base shear values were then transformed to equivalent nominal wind speeds using information on the geometry of the baseline buildings and the wind load equations (and associated parameters) in ASCE 7-02. Displacement vs. equivalent nominal wind speed curves were used to determine the critical wind direction, and Monte Carlo simulation was used along with wind load parameter statistics provided by Ellingwood and Tekie (1999) to construct displacement vs. wind speed curves. Wind speeds corresponding to a presumed limit displacement were used to construct fragility curves. Since the fragilities were fit well using a lognormal CDF and had similar logarithmic standard deviations (${\xi}$), a quick analysis to develop approximate fragilities is possible, and this also is illustrated. Finally, a compound fragility curve, defined as a weighted combination of individual fragilities, is developed.

• Wind and Structures
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• v.12 no.1
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• pp.1-19
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• 2009

In this paper, the airflow around an ideal thin plate (hereafter referred to as ITP) with various ratios of central slot is simulated by using the finite-difference-method (FDM)-based Arbitrary-Lagrangian-Eulerian descriptions for the rigid oscillating body. The numerical procedure employs the second-order projection scheme to decouple the governing equations, and the multigrid algorithm with three levels to improve the computational efficiency in evaluating of the pressure equation. The present CFD method is validated through comparing the computed flutter derivatives of the ITP without slot to Theodorsen analytical solutions. Then, the unsteady aerodynamics of the ITP with and without central slot is investigated. It is found that even a smaller ratio of central slot of the ITP has notable effects on pressure distributions of the downstream section, and the pressure distributions on the downstream section will further be significantly affected by the slot ratio and the reduced wind speeds. Continuous increase of $A_2^*$ with the increase of central slot may be the key feature of the slotted ITP. Finally, flutter analyses based on the flutter derivatives of the slotted ITP are performed, and moreover, flutter instabilities of a scaled sectional model of a twin-deck bridge with various ratios of deck slot are investigated. The results confirm that the central slot is effective to improve bridge flutter stabilities, and that the flutter critical wind speeds increase with the increase of slot ratio.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.3
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• pp.52-59
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• 2008

Most accident reconstruction or analysis depend on the coefficient of friction to estimate the vehicle speeds. Skid mark and coefficient of friction are usually utilized to calculate the velocity and behavior of vehicles. For a critical case such as traffic accident reconstruction, however, the initial velocity of the car should be calculated precisely. In this paper, emergency brake tests on ABS and Non-ABS brake system are conducted on the dry pavement asphalt road on speed 40, 60, 80 and 100 km/h respectively. The SWIFT sensor was established in the front wheel and rear wheel at driver side to measure the forces, moments and speeds of revolution of the tires. These tests results can be available to brake tests and accident reconstruction.

• International Journal of Railway
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• v.5 no.2
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• pp.93-101
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• 2012

Owing to the lightening of railway vehicles and increased operation speeds, the reduction of running safety in the presence of crosswind is becoming an important problem. In particular, the running safety tends to decrease when vehicles run on curved track. When a crosswind acts on a vehicle negotiating a curve from the outer side, flange climbing can occur. In this study, a full-vehicle model was constructed using the multi-body simulation software SIMPACK, and a simulation of a bogie vehicle with two-axle trucks negotiating a curve was carried out to examine the running safety under the condition where a crosswind acts on the vehicle from the outer side of the curve. As a result, it was verified that the derailment coefficient of the first wheelset becomes large in the exit transition curve and the coefficient of the third wheelset does in the entrance transition curve, and this trend becomes pronounced at low operation speeds in the presence of a stronger crosswind. It was also shown that the critical derailment coefficients obtained by modified Nadal's formula considering the effect of attack angle become close to the actual derailment coefficients at the timing that flange climbing occurs.

• Aerospace Engineering and Technology
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• v.6 no.2
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• pp.205-210
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• 2007

A LOX pump rotordynamic design was performed for a 75 ton thrust liquid rocket engine. Axial positions of an inducer, an impeller and bearings on a shaft are decided on the basis of the experience achieved by previously developed turbopump which has the similar layout. The result of pump hydraulic design was reflected in the present study to decide axial length of the inducer and impeller. A distance from the rear bearing to the impeller was considered as a design parameter for load distribution of the bearings. Asynchronous eigenvalue analysis was performed as a function of rotating speeds and bearing stiffness to investigate critical speed of the LOX pump. From the numerical analysis, it is found that the LOX pump with the proper bearing loads safely operates as a sub-critical rotor of which critical speed is high enough compared to the operating speed 11,000 rpm.

• Aerospace Engineering and Technology
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• v.6 no.1
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• pp.201-208
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• 2007

A fuel pump and turbine rotordynamic design is performed for a 75 ton thrust liquid rocket engine. A distance from the rear bearing to the turbine was considered as a design parameter for load distribution of the bearings. Asynchronous eigenvalue analysis was performed as a function of rotating speeds, turbine mass and bearing stiffness to investigate critical speed of the fuel pump and turbine. From the numerical analysis, it is found that the effect of the front bearing stiffness is negligible in the critical speed due to the large mass moment of inertia of the turbine. With the rear bearing stiffness over $2{\times}10^{8}N/m$ and the turbine mass below 20 kg, the critical speed of the fuel pump and turbine in long shaft case is at least 70 % higher than the operating speed 11,000 rpm.