• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.05a
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• pp.692-695
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• 2000

This paper is concerned with Accuracy Design of LM Guide System in Machine Tools. Elastic deformation of bearing is calculated by Hertz contact theory and motion error of LM block is analyzed. A new algorithm using block stiffness is proposed fur the analysis of motion accuracy of the table. The best advantage of this algorithm is fast analysis speed because it isn't necessary iteration processes for satisfying equilibrium equation of the table. Motion errors of the table analyzed under artificial form error of rail theoretically and experimentally. Only one of two rails is bent by putting a thickness gauge into horizontal direction. This form error of rail is measured by gap sensor against the other rail. Then, motion errors of the table are predicted by proposed new algorithm theoretically and measured by laser interferometer. Measurements are carried out by changing the preload and thickness. The results show that the table motion errors are reduced from 1/2 to 1/60 times than form error of rail according to its height and width. And the effect of preloading is almost negligible.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.5 s.110
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• pp.441-451
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• 2006

It is known that ball bearings mounted in housing or on shaft are playing a key role to keep it running smoothly. The roundness of a housing bore on which bearing outer ring is mounted with interference has directly affected the running accuracy of bearing. The running accuracy of bearing, therefore, can extend the significant influence to the rotating machinery as well. In this paper, bearing's vibration and fatigue life considering raceway roundness of ball bearing before and after mounted in housing bore are theoretically estimated. To perform analysis, a simple three degrees of freedom model was proposed and then Newton-Raphson iterative method was introduced to be utilized in the analysis. The results show that the vibration magnitude of ball bearing fitted into housing unit is appeared considerably larger than the one of its pre-assembling. And theoretical $L_{10}$ life which ninety percent of the bearing population will endure decreased in about fifty percent.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.112-118
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• 2005

Ball bearings which were fitted between housing and shaft play an important role in rotating shaft system smoothly, Therefore bearing's running accuracy has significant influence on that of rotating machinery. Manufacturing accuracy of bearings as well as that of shaft and housing is main factor to affect bearing running accuracy In this paper, bearing's vibration and fatigue life considering raceway roundness of ball bearing before and after being fitted into housing are theoretically estimated. To perform analysis, a simple three degrees of freedom model was proposed and then these analysis was conducted utilizing the Newton-Raphson iterative method. The results show that vibration magnitude of ball bearing fitted into housing is considerably larger than before assembly, and bearing's theoretical L$_{10}$ fatigue life that ninety percent of the bearing population will endure decreased in about fifty percent.

• Structural Engineering and Mechanics
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• v.57 no.1
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• pp.141-159
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• 2016

Bearing joint dynamic parameter identification is crucial in modeling the high speed spindles for machining centers used to predict the stability and natural frequencies of high speed spindles. In this paper, a hybrid method is proposed to identify the dynamic stiffness of bearing joint for the high speed spindles. The hybrid method refers to the analytical approach and experimental method. The support stiffness of spindle shaft can be obtained by adopting receptance coupling substructure analysis method, which consists of series connected bearing and joint stiffness. The bearing stiffness is calculated based on the Hertz contact theory. According to the proposed series stiffness equation, the stiffness of bearing joint can be separated from the composite stiffness. Then, one can obtain the bearing joint stiffness fitting formulas and its variation law under different preload. An experimental set-up with variable preload spindle is developed and the experiment is provided for the validation of presented bearing joint stiffness identification method. The results show that the bearing joint significantly cuts down the support stiffness of the spindles, which can seriously affects the dynamic characteristic of the high speed spindles.

• Journal of the Society of Naval Architects of Korea
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• v.43 no.4 s.148
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• pp.512-520
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• 2006

The effects of flexibilities of supporting structures on shaft alignment are growing as ship sizes are Increasing mainly for container carrier and LNG carrier. But, most of classification societies not only do not suggest any quantitative guidelines about the flexibilities but also do not have shaft alignment design program considering the flexibility of supporting structures. A newly developed program, which is based on innovative shaft alignment technologies including nonlinear elastic multi-support bearing concept and hull deflection database approach, has S basic modules : 1)fully automated finite element generation module, 2) hull deflection database and it's mapping module on bearings, 3) squeezing and oil film pressure calculation module, 4) optimization module and 5) gap & sag calculation module. First module can generate finite element model including shafts, bearings, bearing seats, hull and engine housing without any misalignment of nodes. Hull deflection database module has built-in absolute deflection data for various ship types, sizes and loading conditions and imposes the transformed relative deflection data on shafting system. The squeezing of lining material and oil film pressures, which are relatively solved by Hertz contact theory and built-in hydrodynamic engine, can be calculated and visualized by pressure calculation module. One of the most representative capabilities is an optimization module based on both DOE and Hooke-Jeeves algorithm.

• Journal of the Society of Naval Architects of Korea
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• v.42 no.3
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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.

• Journal of the Society of Naval Architects of Korea
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• v.42 no.5 s.143
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• pp.479-486
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• 2005

The final goal of shift alignment design is that the bearing reaction forces or mean pressures are within design boundaries for various service conditions of a ship. However, it is found that calculated bearing load can be substantially variable according to the locations of the effective support points of after sterntube bearing which are determined by simple calculation or assumption suggested by classification societies. A new analysis method for shaft alignment calculation is introduced in order to resolve these problems. Key concept of the new method is featured by adopting both nonlinear elastic and multi-support elements to simulate a bearing support Hertz contact theory is basically applied for nonlinear elastic stiffness calculation instead of the projected area method suggested by most of classification societies. Three loading conditions according to the bearing offset and the hydrodynamic moment and twelve models according to the locations of the effective support points of sterntube bearings are prepared to carry out quantitative verifications for an actual shafting system of 8000 TEU class container vessel. It is found that there is relatively large difference between assumed and calculated effective support points.

• Journal of the Society of Naval Architects of Korea
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• v.57 no.1
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• pp.23-34
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• 2020

This paper covers the development of prediction techniques for ice load on ice-breakers operating in continuous ice-breaking under level ice conditions using particle-based continuum mechanics. Ice is assumed to be a linear elastic material until the fracture occurs. The maximum normal stress theory is used for the criterion of fracture. The location of the crack can be expressed using a local scalar function consisting of the gradient of the first principal stress and the corresponding eigen-vector. This expression is used to determine the relative position of particle pair to the new crack. The Hertz contact model is introduced to consider the collisions between ice fragments and the collisions between hull and ice fragments. In order to verify the developed technique, the simulation results for the three-point bending problems of ice-specimen and the continuous ice-breaking problem around a wedge-type model ship with bow angle of 20° are compared with the experimental results carrying out at Korea Research Institute of Ships and Ocean Engineering (KRISO).

• Journal of the Society of Naval Architects of Korea
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• v.58 no.2
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• pp.84-89
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• 2021

Recently, shipyards are making many efforts to reduce the number of the mounted blocks by increasing the block size. This is to improve productivity and reduce related costs by minimizing block movement and shortening the building period. However, as the blocks become larger, the weight increases considerably. If the target block has a damage due to an unexpected accident during block lifting, it may seriously cause a problem of the reusability of the block. In this study, a large-sized block of the offshore structure weighing 480 tons was lifting with a total of seven sling belts, and one sling belt was broken while it was moving, resulting in a situation in which a part of the edge of the block collided with the ground. The aim of this paper is to verify the structural integrity of the block that directly collides with the ground in the form of free fall due to the sling breakage. Considering that the hook loads acting on several sling belts holding the block are redistributed when a sling belt is broken, the hook loads were recalculated at the angle just before the sling breakage. These loads were used to check the safety of the sling belts. In addition, FE analysis was performed by calculating the amount of impact from the free fall condition, obtaining the impact area by using Hertz's contact theory, and then applying the impact load to the area.

• Tribology and Lubricants
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• v.35 no.3
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• pp.158-168
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• 2019

This paper presents the investigation of two types of rotordynamic modeling issues for 2.2 kW-class, rated speed of 1,800 rpm, squirrel-cage type induction motors. These issues include the lamination structure of rotor cores, and the radial clearance of ball bearings that support the shaft of the motor. Firstly, we focus on identifying the effects of rotor core lamination on the rotordynamic analysis via a 2D prediction model. The influence of lamination is considered as the change in the elastic modulus of the rotor core, which is determined by a modification factor ranging from 0 to 1.0. The analysis results show that the unbalanced response of the rotor-bearing system significantly varies depending on the value of the modification factor. Through modal testing of the system, the modification factor of 0.079 is proven to be appropriate to consider the effects of lamination. Next, we investigate the influence of ball bearing clearance on the rotordynamic analysis by establishing a bearing analysis model based on Hertz's contact theory. The analysis results indicate that negative clearance greatly changes the bearing static behavior. Rotordynamic analysis using predicted bearing stiffness with various clearances from -0.005 mm to 0.010 mm reveals that variations in clearance result in a slight difference in the displacement of the system up to 18.18. Thus, considering lamination in rotordynamic analysis is necessary as it can cause serious analysis errors in unbalanced response. However, considering the effect of the bearing clearance is optional because of its relatively weak impact.