• Tribology and Lubricants
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• v.20 no.4
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• pp.190-196
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• 2004

The effect of tangential loading on the subsurface stress field has been investigated numerically. As tangential load increases, the subsurface stress field expands more widely to the direction of the tangential load. Places of the maximum shear stress and the maximum effective stress are getting closer to the surface with the increasing tangential load. The tangential load in an elasto-hydrodynamic lubrication condition is so low that it does not affect the subsurface stress field.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2004.11a
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• pp.261-268
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• 2004

For cam and roller-follower contacting surfaces, the effect of tangential loading on the subsurface stress field at an elaso-hydrodynamic lubrication condition has been studied numerically. As tangential load increases, the subsurface stress field extended more widely to the direction of the tangential load. The positions of the maximum shear stress and the maximum effective stress are getting closer to the surface with the increasing tangential load. The tangential load at the elasto-hydrodynamic lubrication condition is of little consequence to the subsurface stress field.

• Tribology and Lubricants
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• v.10 no.2
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• pp.43-50
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• 1994

The hydrodynamic bearing is accepted in many rotating systems because it has a large load carrying capacity. But the anisotropic pressure distribution of the bearing can arise the unstable vibration phenomenon over a certain speed. The magnetic bearing is an active element so that the unstable phenomenon of the hydrodynamic bearing, which is induced by the anisotropic support pressure of the oil film, can be controlled if the control algorithm and the controller gains are chosen appropriately. In this study, we investigate the stabilization method of the hydrodynamic bearing system composing the hybrid bearing which is the single unit of hydrodynamic bearing and magnetic bearing. The load carrying conditions of the hybrid bearing is modelled by the sum of the stiffness and damping coefficients of the hydrodynamic and the magnetic bearings in each direction. The dynamics of the rotor is analyzed by the Finite Element Method and the stability limit is determined by the eigenvalues of the hybrid bearings and shaft system. The eigenvalue study of the system shows that the stability limit of the hybrid bearing is increased compared to that of the hydrodynamic bearing. A Small increment of the stiffness and damping coefficient of the hybrid bearings by the magnetic actuators can increase the stability limit of the system. In this paper we tried to show the design references of the hybrid bearings by using the nondimensional bearing parameters. The analysis results show the possibilities of the stability limit increment of the hydrodynamic bearing system by combining the magnetic bearing.

• Tribology and Lubricants
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• v.15 no.3
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• pp.248-256
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• 1999

Many tribological components in automobile engine undergo high load and sliding speed with thin film thickness. The lubrication characteristics of the components are regarded as ether hydrodynamic lubrication or boundary lubrication, whereas in a working cycle they actually have both characteristics. Many modem engine lubricants have various additives for better performance which make boundary film formation even under hydrodynamic lubrication regime. Conventional Reynolds equation with the viewpoints of continuum mechanics concerns only bulk viscosity of lubricant, which means that its simulation does not give insights on boundary lubrication characteristics. However, many additives of modern engine lubricant provide mixed modes of boundary lubrication characteristics and hydrodynamic lubrication. Especially, high molecular weight polymeric viscosity index improvers form boundary film on the solid surface and cause non-Newtonian fluid effect of shear thinning. This study has performed the investigation about journal bearing system with the mixed concepts of boundary lubrication and hydrodynamic lubrication which happen concurrently in many engine components under the condition of viscosity index improver added.

• Nuclear Engineering and Technology
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• v.52 no.3
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• pp.654-659
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• 2020

The reliability of the spent fuel pool instrument is very important for the security of nuclear power plant, especially during the earthquake. The effect of the fluid force on the vibration characteristics of the flexible tube of the spent fuel pool instrument needs comprehensive analysis. In this paper, based on the potential flow theory, the hydrodynamic pressures acting on the flexible tube were obtained. A mathematical model of a flexible tube was constructed to obtain the dynamic response considering the effects of seismic load and fluid force, and a computer code was written. Based on the mathematical model and computer code, the maximum stresses of the flexible tube in both safe shutdown earthquake and operating basis earthquake events on the spent fuel pool with three typical water levels were calculated, respectively. The results show that the fluid force has an obvious effect on the stress and strain of the flexible tube in both safe shutdown earthquake and operating basis earthquake events.

• International Journal of Aeronautical and Space Sciences
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• v.16 no.1
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• pp.41-49
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• 2015

Analysis and test of hydrodynamic ram in welded metallic tanks containing water were performed to investigate the phenomena and to understand the effects on the resulting structural behavior. Arbitrary Lagrange-Euler coupling method was used for the analysis of the fluid-structure interaction occurring in the hydrodynamic ram, where the projectile, tank, and water are exchanging load, momentum, and energy during the traveling of the projectile through the water of the tank. For a better representation of the physical phenomena, modeling of the welded edges is added to the analysis to simulate the earlier weld line fracture and its influence on the resulting hydrodynamic ram behavior. Corresponding hydrodynamic tests were performed in a modified gas gun facility, and the following panel-based examinations of various parameters, such as displacement, velocity, stress, and energy, as well as hydrodynamic ram pressure show that the analysis and test are well correlated, and thus the results of the study reasonably explain the characteristics of the hydrodynamic ram. The methodology and procedures of the present study are applicable to the hydrodynamic ram assessment of airframe survivability design concepts.

• 한국방재학회:학술대회논문집
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• 2007.02a
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• pp.275-278
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• 2007

In case of having no consideration for pore pressure, we may underestimate earthquakes in seismic analysis of fill dam. because we can not consider hydrodynamic pressures induced by earthquakes. Nevertheless, there are few actual results on hydrodynamic pressures variation due to the principal variables of seismic analysis of fill dam. So, in this study we study earthquake-pore pressure interaction performing divers variable analysis, as considering Sesimic load-Pore Pressure.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.06a
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• pp.156-161
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• 1999

new bearing concept, the wave journal bearing, has been developed to improve the static and dynamic performances of an air-lubricated hydrodynamic journal bearing. This concept features waves on bearing surface. In this study, we present the solution of the compressible Reynolds equation valid for arbitrary Knudsen numbers. Straight wave journal bearing is investigated numerically. The performances of straight wave bearing are compared to the plain journal bearing over relatively wide range of bearing number and eccentricity. The wave journal bearing offers better stability than the plain journal bearing under a13 bearing numbers covered in this study. The bearing load and stability characteristics are dependent on the geometric parameters such as the amplitude and the starting point of the wave relative to the applied load. Under the condition of Knudsen number)0.01, we can not ignore the effect of slip for journal bearing.

• Tribology and Lubricants
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• v.25 no.5
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• pp.292-297
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• 2009

Air foil thrust bearings are the critical components available on high-efficiency turbomachinery which need an ability to endure the large axial force. Air foil bearings are self-acting hydrodynamic bearings that use ambient air as their lubricant. Since the air is squeezed by the edge of compliance-surface of bearing, hydrodynamic force is generated. In this study, we measured the air film thickness and obtained the minimum film thickness experimentally. To increase the maximum load capacity, compliance of sub-structure was controlled. From numerical analyses, it is seen that, if the air film thickness is distributed more uniformly by variable compliance, the thrust bearings can take more axial load.

• International Journal of Ocean System Engineering
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• v.3 no.4
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• pp.164-168
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• 2013

Tidal-current power is now recognized as a clean power resource. The turbine blade is the fundamental component of a tidal current power turbine. The kinetic energy available within a tidal current can be converted into rotational power by turbine blades. While in service, turbine blades are generally subjected to cyclic fatigue loading due to their rotation and the rotor-tower interaction. Predicting the fatigue life under a hydrodynamic fatigue load is very important to prevent blade failure while in service. To predict the fatigue life, hydrodynamic load data should be acquired. In this study, the vibration characteristics were analyzed based on three-dimensional unsteady simulations to obtain the cyclic fatigue load. Our results can be applied to the fatigue design of horizontal-axis tidal turbines.