• Earthquakes and Structures
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• 제8권2호
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• pp.423-442
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• 2015

The effects of accidental eccentricity on the seismic response of four-storey steel buildings laterally stabilized by buckling restrained braced frames are studied. The structures have a square, symmetrical footprint, without inherent eccentricity between the center of lateral resistance (CR) and the center of mass (CM). The position of the bracing bents in the buildings was varied to obtain three different levels of torsional sensitivity: low, intermediate and high. The structures were designed in accordance with the seismic design provisions of the 2010 National Building Code of Canada (NBCC). Three different analysis methods were used to account for accidental eccentricity in design: (1) Equivalent Static Procedure with static in-plane torsional moments assuming a mass eccentricity of 10% of the building dimension (ESP); (2) Response Spectrum Analysis with static torsional moments based on 10% of the building dimension (RSA-10); and (3) Response Spectrum Analysis with the CM being displaced by 5% of the building dimension (RSA-5). Time history analyses were performed under a set of eleven two-component historical records. The analyses showed that the ESP and RSA-10 methods can give appropriate results for all three levels of torsional sensitivity. When using the RSA-5 method, adequate performance was also achieved for the low and intermediate torsional sensitivity cases, but the method led to excessive displacements (5-10% storey drifts), near collapse state, for the highly torsionally sensitive structures. These results support the current provisions of NBCC 2010.

• Journal of Mechanical Science and Technology
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• 제20권2호
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• pp.177-184
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• 2006

An orbital design method of the formation initialization based on the relative orbital element method is presented. It firstly constructed the relative motion equation of the satellite formation flying in terms of the leader and followers' orbital elements. Then the equation was simplified when the orbit eccentricity of the leader satellite was small. And according to the satellites' mission, a general design method for the relative trajectory was proposed. The advantage of this method is that one can get a very simple analytical formula of each follower satellite's orbital elements when the orbital eccentricity of the leader satellite is zero. The simulation results show that the method is effective.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 춘계학술대회논문집
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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.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 B
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• pp.952-954
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• 2002

The effort for measuring the rotor vibration caused by the short of rotor winding or air-gap eccentricity has been carried on. This paper introduces on-line vibration monitoring technologies using search coils to measure flux for synchronous generators. A 3,300/6,600 (V), 150 [kW] synchronous generator is built, and search coils are designed and inserted in the wedges. Furthermore, air-gap eccentricity is analyzed by finite element method and compared with experiment tests. Induced voltages caused by different air-gap eccentricity on the search coils are compared as well.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 B
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• pp.706-708
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• 2002

Vibration, giving rise to acoustical noise, is an important index of motor performance. The unbalance force due to rotor eccentricity caused by manufacturing imprecision or bearing defects is one possible source of excitation to vibration. With the advent of new high-energy magnetic material together with high precision motor applications, magnetic sources of vibration are becoming more serious. This paper introduces two types of high-speed slotless permanent magnet (PM) machine for electro-mechanical battery and investigates unbalance force due to static eccentricity with finite element method.

• 소성∙가공
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• 제8권4호
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• pp.393-398
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• 1999

The plastic instable flow phenomenon happens in practical forming process, I. e. upsetting, backward extrusion, piercing, indentation. And also, it is difficult to control precisely the shape and dimensions of forming process. It is found that instabilities of the process are mainly connected with imperfections in the lubrication, billet eccentricity, inclined punch alignment. In view of the direct relationship between instable material flow and quality defects of the products and for better control of forming operation, we should necessarily find out their phenomena. In this study, we introduced the friction disturbance due to inclined punch angle. Analysis of upset forging is carried out using the rigid plastic FEM and slab method with eccentricity. Also, we considered the buckling parameters of billet with the large aspect ratio in upset forging.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 춘계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.188-190
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• 2006

This paper describes the effects of air gap eccentricity in induction machines. Asymmetric electro-magnetic force caused by the frictional worn bearing, rotor misalignment and unbalanced rotor etc. generates an asymmetrical operation, vibration and electro-magnetic noise. The need for detection of these rotor eccentricities has pushed the development of monitoring methods with increasing sensitivity and noise immunity. In this paper, we focus on investigating the asymmetrical operation considering of unbalanced magnetic force in squirrel-cage induction motor with 380 [V], 7.5 [kW], 4P, 1,768 [rpm]. The effects of the rotor eccentricity, magnetic force are investigated by finite element method (FEM).

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2001년도 춘계학술발표대회 논문집
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• pp.168-171
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• 2001

Due to intrinsic load eccentricity, severe peel stress concentration occurs at both ends of the single-lap joint. To avoid load eccentricity as well as the singular tensile peel stress in the joint interface, composite wavy-lap joint is proposed. In this paper, refined 3-D stress analysis of wavy-lap joint is performed by finite element method using parallel mutifrontal solver. Analysis results show that the singular tensile peel stress concentration is totally avoided in wavy-lap joint, and that loads are more evenly transferred over the length of the joint. Therefore, the strength of wavy-lap joint is significantly higher than that of conventional single-lap joint. And it is believed that even higher strengths can be obtained by optimizing the new design configuration.

• Steel and Composite Structures
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• 제27권3호
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• pp.285-295
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• 2018

In this paper, the bearing capacity of a non-eccentric and eccentric tubular, concrete-filled, steel bridge pier was studied through the finite element method. Firstly, to verify the validity of the numerical analysis, the finite element analysis of four steel tube columns with concrete in-fill was carried out under eccentric loading and horizontal cyclic loading. The analytical results were compared with experimental data. Secondly, the effects of the eccentricity of the vertical loading on the seismic performance of these eccentrically loaded steel tubular bridge piers were considered. According to the simulated results, with increasing eccentricity ratio, the bearing capacity on the eccentric side of a steel tubular bridge pier (with concrete in-fill) is greatly reduced, while the capacity on the opposite side is improved. Moreover, an empirical formula was proposed to describe the bearing capacity of such bridge piers under non-eccentric and eccentric load. This will provide theoretical evidence for the seismic design of the eccentrically loaded steel tubular bridge piers with concrete in-fill.

• Tribology and Lubricants
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• 제15권1호
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• pp.17-23
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• 1999

A Gerotor hydraulic motor is a planar mechanism consisting of a pair of rotors one of which encloses another rotor. The motion of the inner-rotor relative to the outer-rotor is produced by the pressure difference between the adjacent chambers. A design method of inner-rotor tooth profile using unit tangential vectors is presented in this work. Based on the relationships derived, the influence of the eccentricity of inner-rotor and the radius of circular arc tooth on the flow rate, torque and curvatures were investigated. It was shown that the flow rate and mean torque is proportional to eccentricity, but inversely proportional to the radius of circular arc teeth. Also, the maximum value of the equivalent curvature is increased as the eccentricity and the radius of circular arc teeth increased.