• Structural Engineering and Mechanics
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• 제38권3호
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• pp.361-384
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• 2011

Earlier studies on hollow-circular rubber bearings, all of which are conducted for steel-reinforced bearings, indicate that the hole presence not only decreases the compression modulus of the bearing but also increases the maximum shear strain developing in the bearing due to compression, both of which are basic design parameters also for fiber-reinforced rubber bearings. This paper presents analytical solutions to the compression problem of hollow-circular fiber-reinforced rubber bearings. The problem is handled using the most-recent formulation of the "pressure method". The analytical solutions are, then, used to investigate the effects of reinforcement flexibility and hole presence on bearing's compression modulus and maximum shear strain in the bearing in view of four key parameters: (i) reinforcement extensibility, (ii) hole size, (iii) bearing's shape factor and (iv) rubber compressibility. It is shown that the compression stiffness of a hollow-circular fiber-reinforced bearing may decrease considerably as reinforcement flexibility and/or hole size increases particularly if the shape factor of the bearing is high and rubber compressibility is not negligible. Numerical studies also show that the existence of even a very small hole can increase the maximum shear strain in the bearing significantly, which has to be considered in the design of such annular bearings.

• The Journal of Korean Physical Therapy
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• 제26권4호
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• pp.226-233
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• 2014

Purpose: This study was conducted in order to investigate the exercise limit that may occur depending on changes in postural alignment by examining the significance of postural alignment changes, foot pressure, and balance of patients with stroke. Methods: In this study, 50 patients diagnosed with a stroke were selected as subjects. Imbalance of postural alignment of the trunk, pelvic tilt of trunk rotation of the body, angle of kyphotic curving of the thoracic, and angle of lordotic curving of the lumbar vertebra were measured. Foot pressure was examined by measuring average pressure and weight bearing. Balance was examined by measuring the center of pressure and limit of stability. Results: The significance of postural alignment, foot pressure, and weight bearing of the non-paretic side was examined. In addition, the significance between postural alignment and balance was examined. Conclusion: It is thought that limits of foot pressure and balance in the standing position can be caused by postural alignment. Thus, both a therapeutic intervention program and postural alignment training should be provided together in order to improve the function of patients with stroke.

• Tribology and Lubricants
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• 제29권4호
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• pp.228-234
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• 2013

This paper presents analysis of elastohydrodynamic lubrication (EHL) of ball bearings, in which surface roughness is considered. A lot of time is required to obtain a solution in the case of EHL analysis where surface roughness is considered, because the analysis requires a variety of analytic nodes. To save time, we use the full approximation scheme (FAS) among multilevel methods. We analyze the results of EHL and contact analyses in terms of pressure. We also compare the results for smooth and rough surfaces with respect to film thickness. We confirm that the film pressure decreases as compared to contact pressure because of the presence of lubricants between the ball and the raceway. Furthermore, in the case when surface roughness is considered, the film pressure increases because of contact asperities. Therefore, surface roughness should be considered when designing ball bearings.

• 한국지반공학회논문집
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• 제20권2호
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• pp.115-124
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• 2004

조립토 다짐말뚝(granular compaction pile)공법은 비교적 강성이 크고 압축성이 작은 자갈, 쇄석 및 모래 등의 조립질 재료를 사용하여 연약한 지반에 말뚝을 조성하는 공법으로, 기초지반의 지지력 증가, 침하량 감소 및 압밀배수 촉진 등에 의한 지반개량 효과 뿐만 아니라, 사질토 지반에 적용시 지진에 의한 액상화 방지효과도 큰 공법으로 알려져 있으나 국내에서는 아직까지 널리 사용되지 않고 있다. 일반적으로 조립토 다짐말뚝은 Piled-raft system으로 시공되므로, 이 때 조립토 다짐말뚝의 극한지지력에 대한 평가는 팽창파괴 중심부의 깊이에 따라 달라지게 된다. 또한 조립토 다짐말뚝과 주변지반과의 하중분담에 대한 영향 및 지반내에서 조립토 다짐말뚝에 작용하는 구속응력의 변화를 적절하게 고려하여 조립토 다짐말뚝의 극한지지력이 결정되어야 한다. 본 연구에서는, 김 등(1998)에 의하여 연구되었면 조립토 다짐말뚝의 극한지지력 평가에 대한 해석기법을 토대로, 단일 말뚝에 대하여 상재하중의 크기, 재하면적의 크기 및 파괴깊이에 따른 수평구속응력의 변화를 고려하여 극한지지력을산정하기 위한 기법을 부시네스크 식을 이용하여 제안하였다. 또한 제안된 조립토 다짐말뚝의 극한지지력 평가 기법의 타당성을 실내모형 실험 및 수치해석 프로그램인 PFC-2D 프로그램을 이용한 수치해석 결과와의 비교, 분석을 통해 검증하였다.

• 대한조선학회논문집
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• 제42권3호
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• pp.259-267
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• 2005

The effects of hull flexibility on shaft alignment are growing as ship sizes are increased mainly for container carrier and LNG carrier. In order to consider hull flexibility on a propulsion shafting system, standardization of ship service conditions is necessary because hull deformation is continuously variable according to ship service conditions. How to summarize ship service conditions is suggested based on practically applicable four viewpoints : hull, engine, loading and sea status. Effects of the external forces acting on a ship propulsion shafting system are generally commented. Several design criteria regulated by classification societies are pointed at issue which seems to have Insufficient technical background. A qualitative verification is carried out to point out the invalidity of the assumption of effective supporting position. In this work, an elastic nonlinear multi-supporting bearing system is introduced as a key concept of the elastic shaft alignment. Hertz contact theory is proved to be more proper one than projected area method in calculation of the nonlinear elastic stiffness of the bearing, The squeezing and oil film pressure calculations in the long journal bearing like an after stern tube bearing are recognized as a necessary process for elastic shaft alignment design.

• Tribology and Lubricants
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• 제17권5호
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• pp.365-372
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• 2001

This paper has been presented the hydrodynamic effect by the journal speed, eccentricity and source positions in order to overcome the defects of air bearing such as low stiffness and damping coefficient. Choosing the two row source position of air bearing is different from existed investigations in the side of pressure distribution of air film because of the high speed of journal and the wedge effects by the eccentricity. These optimal chooses of the two row source positions enable us to improve the performance of the film reaction force and loading force as making the high speed spindle. In this paper, The pressure behavior in theory of air film according to the eccentricity of journal and the source positions analyzed. The results of investigated characteristics may be applied to precision devices like ultra-precision grinding machine and ultra high speed milling.

• KSTLE International Journal
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• 제4권2호
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• pp.66-72
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• 2003

This paper presents the hydrodynamic effect by the journal speed, eccentricity and source positions in order to overcome the defects of air bearing such as low stiffness and damping coefficient. Choosing the two row source position of air bearing is different from existing investigations in the side of pressure distribution of air film because of the high speed of journal and the wedge effects by the eccentricity. These optimal choices of the two row source positions enable us to improve the performance of the film reaction force and loading force as making the high-speed spindle. In this paper, The pressure behavior in theory of air film in high speed region of journal according to the eccentricity of journal and the source positions analyzed. The theoretical analysis has been identified by experiments. The results of investigated characteristics may be applied to precision devices like ultra-precision grinding machine and ultra high-speed milling.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.498-501
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• 2000

Air dynamic bearings are inherently unstable in dynamic behavior due to the varying angle of a force produced and the nonlinear characteristics of stiffness. In this study, such dynamic behavior is obtained and compared with experimental results. A body axis coordinate system is employed to avoid the change of a moment of inertia. FDM is used to calculate the pressure distribution on the bearing surface and then the force acting on the rotor was calculated by integrating the pressure distribution. By integrating accelerations which are calculated from the equations of motion using the 4th order Runge-Kutta method, the pose of the bearing at each time step is obtained.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.607-610
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• 2002

As machines become smaller and faster multileaf foil bearings are used to overcome the problems with heat, friction and wear Systems with foil bearings do not need a separate system for lubrication. These bearings are self acting and are therefore green systems. Until now, there have been many studies on the structural and dynamical performances. Therefore the object of the present study is to predict the flow and structural characteristics by using the Fluid/structure interaction method. The increase in RPM led to the increase in pressure, temperature difference, maximum velocity, Mach number, shear stress and torque. In the case of 90,000 RPM effects such as choking led to a non-lineararity in the system. Also the effect of eccentricity ratio was observed and showed that eccentricity increased the maximum pressure and the density difference while decreasing the shear stress and torque.

• Tribology and Lubricants
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• 제17권6호
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• pp.476-481
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• 2001

This paper has been presented the hydrodynamic effect by the journal speed, eccentricity and source positions in order to overcome the defects of air bearing such as low stiffness and damping coefficient. Choosing the two row source position of air bearing is different from existed investigations in the side of pressure distribution of air film because of the high speed of journal and the wedge effects by the eccentricity. These optimal chooses of the two row source positions enable us to improve the performance of the film reaction force and loading force as making the high speed spindle. In this paper, The pressure behavior in theory of air film according to the eccentricity of journal and the source positions analyzed. The theoretical analysis have been identified by experiments. The results of investigated characteristics may be applied to precision devices like ultra-precision grinding machine and ultra high speed milling.