• Earthquakes and Structures
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• v.9 no.2
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• pp.391-413
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• 2015

Damage of torsionally coupled buildings situated on soil sites has been reported in literature, however no site-specific studies are available for torsionally coupled buildings having site characteristics as a parameter. Effect of torsion is being accounted in seismic codes by the provision of design eccentricity where the dynamic to static eccentricity ratio is a parameter. In this paper, a methodology to determine dynamic to static eccentricity ratio of torsionally coupled buildings has been demonstrated for Delhi region for two torsionally coupled buildings on three soil sites. The variations of average and standard deviations of frame shears for stiff and flexible edges are studied for four eccentricity ratios for the two buildings for the three sites. From the limited studies made, it is observed that the dynamic to static eccentricity ratios observed for site-specific earthquakes are different from Indian seismic code specified value, hence a proposal is made to include a comment in Indian seismic code. Methodology proposed in this paper can be adopted for any region, for the estimation of dynamic to static eccentricity ratio for site specific earthquake.

• Journal of Electrical Engineering and Technology
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• v.9 no.5
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• pp.1623-1631
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• 2014

Eccentricity faults more or less exist in all rotating electrical machines. This paper establishes a more precise model of dynamic eccentricity (DE) in electrical machines named as curved dynamic eccentricity. It is a kind of axial unequal eccentricity which has not been investigated in detail so far but occurs in large electrical machines. The inductances of a large three-phase squirrel-cage induction machine (SCIM) under different levels of curved DE conditions are evaluated using winding function approach (WFA). These inductances include the stator self and mutual inductances, rotor self and mutual inductances, and mutual inductances between stator phases and rotor loops. A comparison is made between the calculation results under curved DE and the corresponding pure DE conditions. It indicates that the eccentricity condition will be more terrible than the monitored eccentricity based on the conventional pure DE model.

• 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.

• KSTLE International Journal
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• v.1 no.1
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• pp.59-62
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• 2000

This paper deals with an experimental study on the dynamic response of an elastomeric oil seal when the interferences between shaft and lip as well as the dynamic eccentricities are present. The dynamic response of seal lip in oil seals was observed with the aid of an image processing apparatus. The temperature of the seal lip edge, friction torque and the dynamic sealing gap between shaft and lip are measured at different conditions of the initial interference and the shaft eccentricity, The data were simultaneously measured under dynamic conditions. Experimental results show that, as the shaft speed is increased, S/e$_{d}$ has nearly reached a constant asymptotic value fur a certain range of shaft speeds. The results indicate that the gap separation between shaft and lip is provided due to the shaft eccentricity because the seal lip cannot follow quickly the radial displacements with increasing shaft speed.d.

• Journal of Electrical Engineering and Technology
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• v.9 no.1
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• pp.106-113
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• 2014

Rotor eccentricity is one of the major factors that directly influence the security of horizontal electrical machines, and the critical speed of the shaft has a close relationship with vibration. This paper deals with the influence of thermal expansion on the rotor eccentricity and critical speed in large dry submersible motors. The dynamic eccentricity (where the rotor is still turning around the stator bore centre but not its own centre) and critical speed of a three-phase squirrel-cage submersible induction motor are calculated via hybrid analytical/finite element method. Then the influence of thermal expansion is investigated by simulation. It is predicted from the study that the thermal expansion of the rotor and stator gives rise to a significant air-gap length decrement and an inconspicuous slower critical speed. The results show that the thermal expansion should be considered as an impact factor when designing the air gap length.

• Proceedings of the KIPE Conference
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• 2008.10a
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• pp.85-87
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• 2008

This paper presents dynamic characteristics in Switched Reluctance Motor (SRM) with rotor eccentricity and proposes the reduction method of rotor eccentricity effects by the different winding connections. These characteristics investigations are computed by 2D transient magnetic FEM analysis coupled with external circuits. The radial and unbalance magnetic force in the stator, which is the main exciting force of the vibration, is calculated using Maxwell stress method and compared with the performance characteristics according to the serial and parallel connections of windings. The influence of winding method counteracting unbalance forces on the rotor vibration behavior is estimated by the current waveforms of the paralleled paths under rotor eccentricity.

• Earthquakes and Structures
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• v.23 no.3
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• pp.283-295
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• 2022

Seismic design codes permit the use of Equivalent Static Analysis of buildings considering torsional eccentricity e with dynamic amplification factors on structural eccentricity and some accidental eccentricity. Estimation of e in buildings is not addressed in codes. This paper presents a simple approximate method to estimate e in RC Moment Frame and RC Structural Wall buildings, which required no detailed structural analysis. The method is validated by 3D analysis (using commercial structural analysis software) of a spectrum of building. Results show that dynamic amplification factor should be applied on torsional eccentricity when performing Response Spectrum Analysis also. Also, irregular or mixed modes of oscillation arise in torsionally unsymmetrical buildings owing to poor geometric distribution of mass and stiffness in plan, which is captured by the mass participation ratio. These irregular modes can be avoided in buildings of any plan geometry by limiting the two critical parameters (normalised torsional eccentricity e/B and Natural Period Ratio 𝜏 =T_𝜃/T, where B is building lateral dimension, T_𝜃 uncoupled torsional natural period and T uncoupled translational natural period). Suggestions are made for new building code provisions.

• Earthquakes and Structures
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• v.20 no.3
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• pp.239-260
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• 2021

Torsional response of buildings is attributed to poor structural configurations in plan, which arises due to two factors - torsional eccentricity and torsional flexibility. Usually, building codes address effects due to the former. This study examines both of these effects. Buildings with torsional eccentricity (e.g., those with large eccentricity) and with torsional flexibility (those with torsional mode as a fundamental mode) demand large deformations of vertical elements resisting lateral loads, especially those along the building perimeter in plan. Lateral-torsional responses are studied of unsymmetrical buildings through elastic and inelastic analyses using idealised single-storey building models (with two degrees of freedom). Displacement demands on vertical elements distributed in plan are non-uniform and sensitive to characteristics of both structure and earthquake ground motion. Limits are proposed to mitigate lateral-torsional effects, which guides in proportioning vertical elements and restricts amplification of lateral displacement in them and to avoid torsional mode as the first mode. Nonlinear static and dynamic analyses of multi-storey buildings are used to validate the limits proposed.

• 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.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.12
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• pp.2230-2235
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• 2011

The purpose of this paper is to provide the unbalanced magnetic force and vibration mode comparison between two large interior permanent magnet machines(IPM) with different pole-slot combination considering stator and rotor eccentricity. Due to the punching tolerance, the mixed eccentricity of air-gap is inevitable. It will generate the asymmetric magnetic flux density in air-gap, which makes the unbalanced magnetic pull and vibration. The study is focused on the unbalanced magnetic force and their harmonic components according to eccentricity conditions such as static, dynamic and mixed. When the high vibration is produced especially resonance, the obtained results provide clues what eccentricity condition occurs in the machine.