• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.6
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• pp.463-469
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• 2004

In order to improve the instability of journal bearings, the leaf spring dampers (LSD) are introduced. The effects of LSD on the stability of journal bearings are investigated theoretically The stability of the journal bearing with LSD are compared with the results of the journal bearing without LSD. And the effects of the asymmetry of the stiffness of the leaf spring damper on the stability of rotors are also investigated.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.100-106
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• 2003

In order to improve the instability of a plane journal bearing, the leaf spring dampers (LSD) are introduced. The effects of LSD on the stability of a plane journal bearing are investigated theoretically. The stability of a plane journal bearing with LSD are compared with the results of a plane journal bearing without LSD. And the effects of the asymmetry of the stiffness of the leaf spring damper on the stability of rotors are also investigated.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.1
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• pp.40-46
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• 2011

This paper is to investigate the effects of the asymmetrical support stiffness on the stability of a supercritical driveshaft with asymmetrical shaft stiffness and anisotropic bearings. The equations of motion is derived for a system including a rigid disk, a massless flexible asymmetric shaft, anisotropic bearings and a support beam. The Floquet theory is applied to perform the stability analysis with the variation of the support stiffness, the shaft asymmetry, the shaft damping and the shaft speed. The results show that the asymmetric support stiffness is closely related to the stability caused by primary resonance as well as the supercritical operation. First, the stiffness variation can stabilize the system around primary resonance by weakening the parametric resonance from the shaft asymmetry. Second, it also improve the stability characteristics at a supercritical operation when the support stiffness is not so high relative to the shaft stiffness.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.545-548
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• 2002

Turbines have been known to be particularly susceptible to flow-induced self-excited vibration. In such vibrations, direct damping and cross stiffness effects of aerodynamic forces determine rotordynamic stability. In axial turbines with eccentric shrouded rotors, the non-uniform sealing gap causes azimuthal non-uniformities in the seal gland pressure and the turbine torque which destabilize the rotor system. Previously, research efforts focused solely on either the seal flow or the unshrouded turbine passge flow. Recently, a model for flow in a turbine with a statically offset shrouded rotor has been developed and some stiffness predictions have been obtained. The model couples the seal flow to the passage flow and uses a small perturbation approach to determine nonaxiymmetric flow conditions. The model uses basic conservation laws. Input parameters include aerodynamic parameters (e.g. flow coefficient, reaction, and work coefficient); geometric parameters (e.g. sealing gap, depth of seal gland, seal pitch, annulus height); and a prescribed rotor offset. Thus, aerodynamic stiffness predictions have been obtained. However, aerodynamic damping (i.e. unsteady aerodynamic) effects caused by a whirling turbine has not yet been examined. Therefore, this paper presents a new unsteady model to predict the unsteady flow field due to a whirling shrouded rotor in turbines. From unsteady perturbations in velocity and pressure at various whirling frequencies, not only stiffness but also damping effects of aerodynamic forces can be obtained. Furthermore, relative contributions of seal gland pressure asymmetry and turbine torque asymmetry are presented.

• Journal of the Korean Society of Safety
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• v.37 no.6
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• pp.60-70
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• 2022

This paper proposes an optimal design method of a seismic reinforcement system for the seismic performance of adjacent asymmetric-stiffness structures with viscous dampers. The first method considers plan asymmetry for efficient seismic reinforcement, and evaluates the seismic performance of optimal design applied to two cases of modeling: adjacent stiffness-asymmetric structures and adjacent stiffness-symmetric structures. The second method considers the response of asymmetric structures to derive the optimal objective function, and evaluates seismic efficiency of the objective function applied to two cases of responses: horizontal displacement and torsion. Numerical analyses are conducted on 7- and 10-story structures with a uni-asymmetric-stiffness plan using six cases of historic earthquakes, normalized to 0.4g. The results indicate that the seismic performance is excellent as modeled by adjacent asymmetric-stiffness structures and how much horizontal displacement is applied as the objective function.

• Structural Engineering and Mechanics
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• v.2 no.2
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• pp.211-225
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• 1994

Responses of asymmetrical multistorey buildings to earthquakes are obtained by quasi-static code approach and real time dynamic analysis, using two different structural models. In the first model, all vertical members are assumed to be restrained at the slab levels and hence their end rotations, about horizontal axes, are taken as zero. In the second model this restriction is removed and the rotation is assumed to be proportional to the lateral stiffness of the member. A simple microcomputer based procedure is used in the analyses, by both models. Numerical examples are presented where results obtained from both the models are given. Effects of modelling on the response of three buildings, each with a different type and degree of asymmetry, are studied. Results for deflections and shear forces are presented and the effects of the type of model on the response are discussed.

• Journal of Mechanical Science and Technology
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• v.14 no.6
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• pp.590-596
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• 2000

Cause of excessive vibration with twice the rotational speed of a two-pole generator rotor for the fossil power plants was investigated. The two-pole generator rotor, treated as a typically asymmetric rotor in vibration analysis, produces asynchronous vibration with twice the rotational speed, sub-harmonic critical speeds, and potentially unstable operating zones due to its own inertia and/or stiffness asymmetry. This paper introduces a practical balancing procedure, and presents the results of the investigation on sources of the excessive vibration based on the experimental vibration data of the asymmetric two-pole rotor in balancing.

• Journal of Korean Society of Steel Construction
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• v.28 no.1
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• pp.43-52
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• 2016

A numerical study on required stiffness of the longitudinal stiffener in the webs stiffened with flat plate at one-side of the web was conducted. The longitudinal stiffeners are commonly placed around 0.2D, i.e., 1/5 the web depth due to fabrication convenience although most plate girders for bridges are unsymmetric section. Considering asymmetry of section, aspect ratio of web and the rigidity ratio of longitudinal stiffener(${\gamma}^*$), eigenvalue analysis were performed to evaluate the buckling strength for the webs with a stiffener located at 0.16D~0.24D. Based on the parametric analysis, the required stiffness of the longitudinal stiffener to satisfy the buckling strength specified in AASHTO LRFD specifications was presented.

• Journal of KSNVE
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• v.9 no.4
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• pp.835-840
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• 1999

Cause of excessive vibration signals with twice the rotational speed of a 2-pole generator rotor in balancing for fossil power plants was investigated. The 2-pole generator rotor is treated as a typically asymmetric rotor in vibration analysis, and produces asynchronous vibration with twice the rotational speed for its own inertia and stiffness asymmetry. This paper introduces practical balancing procedure and experimental vibration data of the asymmetric 2-pole rotor in balancing, and presents the results of investigation into sources of the excessive vibration signals.

• Earthquakes and Structures
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• v.13 no.5
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• pp.485-496
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• 2017

The behavior of 8 steel reinforced high-strength concrete (SRHSC) columns, which comprised of four identical columns with cross-shaped steel and other four identical columns with square steel tube, was investigated experimentally under cyclic uniaxial and biaxial loading independently. The influence of steel configuration and loading path on the global behavior of SRHSC columns in terms of failure process, hysteretic characteristics, stiffness degradation and ductility were investigated and discussed, as well as stress level of the longitudinal and transverse reinforcing bars and steel. The research results indicate that with a same steel ratio deformation capacity of steel reinforced concrete columns with a square steel tube is better than the one with a cross-shaped steel. Loading path affects hysteretic characteristics of the specimens significantly. Under asymmetrical loading path, hysteretic characteristics of the specimens are also asymmetry. Compared with specimens under unidirectional loading, specimens subjected to bidirectional loading have poor carrying capacity, fast stiffness degradation, small yielding displacement, poor ductility and small ultimate failure drift. It also demonstrates that loading paths affect the deformation capacity or deformation performance significantly. Longitudinal reinforcement yielding occurs before the peak load is attained, while steel yielding occurs at the peak load. During later displacement loading, strain of longitudinal and transverse reinforcing bars and steel of specimens under biaxial loading increased faster than those of specimens subjected to unidirectional loading. Therefore, the bidirectional loading path has great influence on the seismic performance such as carrying capacity and deformation performance, which should be paid more attentions in structure design.