• 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.

• Tribology and Lubricants
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• 제17권1호
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• pp.64-71
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• 2001

This paper presents dynamic responses of disk flutter and bump in HDD slider. The slider is modeled for three degree-of-freedom systems, which are capable of lifting, pitching, and rolling motions. In numerical analysis, loads from air pressure, preload and static moments from the slider, and stiffness and damping coefficients of the suspension are considered for investigating the dynamic characteristics analysis. The numerical results are presented as functions of typical parameters such as a disk velocity, stiffness and damping coefficients of the suspension, and skew angle.

• 한국생산제조학회지
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• 제9권4호
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• pp.99-107
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• 2000

In this study, a static and dynamic characteristics analysis system for machine tool spindle systems with 3 lobe sliding bearing is developed based on Timoshenko theory, finite element method and windows programming techniques. And the characteristics value of 3 lobe sliding bearing such as eccentricity ratio, attitude angle, friction coefficient , stiffness coefficients, damping coefficients and so on, are determined by using the thermal equilibrium conditions of spindle systems. Since the developed system has various analysis modules related to static deformation analysis, modal analysis, frequency responses analysis and so on, it can be utilized to perform systematically the design an devaluation process of spindle systems with 3 lobe sliding bearing under windows GUI environment.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2001년도 제33회 춘계학술대회 개최
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• pp.224-230
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• 2001

A numerical analysis for the gas lubricated flexure-pivot tilting pad journal bearing has been accomplished. The film pressure are obtained by Newton-Raphson method and the dynamic coefficients are evaluated by the pad assembly method. The effects of the pivot position of the pad on the static and dynamic characteristics are presented for three pads journal bearing with LBP. The optimum pivot positions for the static performance is different from that of the dynamic performance.

• Tribology and Lubricants
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• 제10권1호
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• pp.46-55
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• 1994

The static and dynamic analysis of air lubricatied tilting pad journal bearing which considers tilting effect of each pad, preload but which neglects pad inertia effect and deflection are performed. A direct numerical method is used in evaluating the static characteristics such as load carrying capacity, friction force and small peturbation method is used for calculation of dynamic characteristics. Stiffness and damping coefficients are compared with the variation of the preload. And these coefficients are slightly decreased with increased compressibility number under the constant bearing load carrying capacity.

• Journal of Power Electronics
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• 제18권3호
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• pp.944-953
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• 2018

This paper proposes an analysis method based on the magnitude-phase dynamic theory for isolated power systems with static synchronous compensators (STATCOMs). The stability margin of an isolated power system is greatly reduced when a load is connected, due to the disadvantageous features of the self-excited induction generators (SEIGs). To analyze the control process for system stability and to grasp the dynamic characteristics in different timescales, the relationships between the active/reactive components and the phase/magnitude of the STATCOM output voltage are derived in the natural reference frame based on the magnitude/phase dynamic theory. Then STATCOM equivalent mechanical models in both the voltage time scale and the current time scale are built. The proportional coefficients and the integral coefficients of the control process are converted into damping coefficients, inertia coefficients and stiffness coefficients so that analyzing its controls, dynamic response characteristics as well as impacts on the system operations are easier. The effectiveness of the proposed analysis method is verified by simulation and experimental results.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 추계학술대회논문집
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• pp.407-413
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• 2008

This paper investigates the dynamics of a HDD spindle system due to the change of FDBs. Flying height of the HDD spindle system is determined through the static analysis of the FDBs, and the stiffness and damping coefficients are calculated through the dynamic analysis of the FDBs. Free vibration characteristics and shock response of the HDD spindle system are analyzed by using the finite element method and the mode superposition method. Experimental modal test is also performed to verify the accuracy of the proposed method. This research shows that the stiffness coefficients of journal heating mostly affect the rocking frequencies because their magnitude are within the range of the stiffness of supporting structure. It also shows that the damping coefficients of thrust bearing mostly affect the axial frequency because the stiffness of thrust bearing is much smaller that that of supporting structure.

• 한국도로학회논문집
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• 제19권1호
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• pp.73-80
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• 2017

PURPOSES : This paper presents a comparison study between dynamic and static analyses of falling weight deflectometer (FWD) testing, which is a test used for evaluating layered material stiffness. METHODS: In this study, a forward model, based on nonlinear subgrade models, was developed via finite element analysis using ABAQUS. The subgrade material coefficients from granular and fine-grained soils were used to represent strong and weak subgrade stiffnesses, respectively. Furthermore, the nonlinearity in the analysis of multi-load FWD deflection measured from intact PCC slab was investigated using the deflection data obtained in this study. This pavement has a 14-inch-thick PCC slab over fine-grained soil. RESULTS: From case studies related to the nonlinearity of FWD analysis measured from intact PCC slab, a nonlinear subgrade model-based comparison study between the static and dynamic analyses of nondestructive FWD tests was shown to be effectively performed; this was achieved by investigating the primary difference in pavement responses between the static and dynamic analyses as based on the nonlinearity of soil model as well as the multi-load FWD deflection. CONCLUSIONS : In conclusion, a comparison between dynamic and static FEM analyses was conducted, as based on the FEM analysis performed on various pavement structures, in order to investigate the significance of the differences in pavement responses between the static and dynamic analyses.

• International Journal of Railway
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• 제7권2호
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• pp.46-56
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• 2014

The superstructure of the railway track undertakes the forces that develop during train passage and distributes them towards its seating. The track panel plays a key role in terms of load distribution, while at the same time it maintains the geometrical distance between the rails. The substructure and ballast undergo residual deformations under high stresses that contribute to the deterioration of the so-called geometry of the track. The track stiffness is the primary contributing factor to the amount of the stresses that develop on the substructure and is directly influenced by the fastening resilience. Four methods from the international literature are used in this paper to calculate the loads and stresses on the track substructure and the results are compared and discussed. A parametric investigation of the stresses that develop on the substructure of different types of railway tracks (i.e. balastless vs ballasted) is performed and the results are presented as a function of the total static track stiffness.

• 전산구조공학
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• 제8권2호
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• pp.103-113
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• 1995

고무 재질로 이루어진 차량 구조물의 연결요소에 대한 등가 강성계수는 차량 시스템 동역학 특성에 매우 민감하게 영향을 주므로 이에 대한 신뢰성있는 해석이 요구된다. 본 논문에서는, 고무의 역학 모델을 정하중 하에서는 유한 변형 및 Hook 모델로 그리고 동하중 하에서는 Voigt 모델로 가정하여, 연결요소의 등가 정-동강성계수를 유한요소법으로 해석하고자 한다. 실제 차량에 사용되고 있는 동일 모양의 방진고무들을 실험 평가한 결과 강성계수값들의 분산 정도가 심함을 알 수 있었다. 유한요소 해석에 필요한 고무 재질의 물성치의 신뢰성을 높이기 위하여 제품의 특정 방향 정특성 실험 데이타로부터 역으로 재질의 물성치를 규명하였다. 그 물성치로부터 원하는 방향에서의 강성계수를 산출하여 실험치와 비교하여 효용성을 보였다.