• Journal of the Korean Society for Nondestructive Testing
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• v.14 no.2
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• pp.122-131
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• 1994

Journal bearings in the rotating machineries are vulnerable to the contamination or the insufficient supply of lubricating oil, which is likely to be the cause of unexpected shutdown or malfunction of these systems. Various destructive and nondestructive testing methods had been used for the reduction of maintenance cost and the operational safety problems due to the accidents related to bearing damages. In this experimental approach, acoustic emission monitoring is employed to the detection of incipient failure caused by intervention of foreign particles most probable in the journal bearing systems. Experimental schedules for the intervention of foreign particles was composed to be more quantitative and systematic than last study in consideration of minimum oil film thickness and particle size. The experiment was conducted under such designed conditions as inserting alumina particles to the lubrication layer in the simulated journal bearing system. Several parameters such as AE rms level, waveform, AE energy distribution and other AE event parameters are used for analysis and characterization of damage source. The results showed that the history of damage was well correlated with the changes of AE rms level and the type of damage source signal can be verified using other informations such as waveform, distributions of AE parameters etc.

• Journal of the Korean Society for Railway
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• v.16 no.1
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• pp.7-13
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• 2013

A scaled version of a roller rig is developed to demonstrate the dynamic characteristics of a railway vehicle for academic purposes. This rig is designed based on Jaschinski's similarity law. It is scaled to 1/10 of actual size and allows 9-DOF motion to examine the up and down vibration of a train set. The test rig consists of three sub-hardware components: (i) a driving roller mechanism with a three-phase AC motor and an inverter, (ii) a bogie structure with first and second suspensions, and (iii) the vehicle body. The motor of the rig is capable of 3,600rpm, allowing the test to simulate a vehicle up to a maximum speed of 400Km/hr. Because bearings and joints are properly connected to the sub-structures, various motion analyses, such as a lateral, pitching, and yawing motion, are allowed. The slip motion between the rail and the wheel set is also monitored by several sensors mounted in the rig. After the construction of the hardware, an experiment is conducted to obtain the natural frequencies of the dynamic behavior of the specimen. First, the test rig is run and data are collected from six sets of accelerometers. Then, a numerical analysis of the model based on the ADAMS program is derived. Finally, the measurement data of the first three fundamental frequencies are compared to the analytical result and the validation of the test rig is conducted. The results show that the developed roller rig provides good accuracy in simulating the dynamic behavior of the vehicle motion. Although the roller rig designed in this paper is intended for academia, it can easily be implemented as part of a dynamic experiment of a bogie and a vehicle body for a high-speed train as part of the research efforts in this area.

• Journal of Korean Medical classics
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• v.11 no.1
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• pp.224-307
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• 1998

The above study is based upon the Theory of Five Woon(Reasons) and Six Qi(Climates), namely Five dynamic Yin and Yang, the principle of five-six combination, the rules of ten periodically changing Woon and twelve periodically changing Qi, and its reference to the main chapters of the theory by several experts. After careful, comprehensive research and study, the followings are concluded. 1. The Theory of Five Woon and Six Qi controls all of the physical phenomena of the universe, yet it originates from Essence of the Sky that is replete and in constant motion within the abysmal expanse of the universe. So it is natural to claim that it is the Essence of the universe that is the source of the variety of phenomena in nature. 2. There is order of dynamics in the Essence and it is Yin Yang Five Movement and expressed by Five Woon and Six Qi. Therefore the Five Woon and Six Qi, which is the climatic changes of nature, is the basis and condition for all of the natural, physical occurrences including the organic phenomena of human beings. 3. Since the Sky embodied the number Five, and the Earth the number Six, Qi of the Sky itself is consequently Five Woon and Qi of the Earth itself is Six Qi. 4. In Sixty Repetition Intervals (Yuk Sip Kap Ja), the Sky took the number Six, designating the six times repetition of the ten Intervals of the Sky and the Earth chose the number Five, symbolizing five times recurrence of the twelve Intervals of the Earth. Though the number for the Sky is Five and the number for the Earth is Six, the two combine and interact in order for the Sky to exploit the number Six and for the Earth to use the number Five. This interplay implies the relationship of operation and principle of Yin in Yang and Yang in Yin. 5. There seems to be clear and intimate association between five dynamics, five bearings and five Qi' in nature and five organs, five stamina, and five emotions in physiological activities of human beings. Such an correlation apparently demonstrates the idea of climatic changes of the universe in balance among human beings, the Sky, and the Earth. 6. Because nature is of an endlessly dynamic organism itself, to have changes must mear there being movements. Thus the climatic changes in nature are the subsequent consummation of the interaction in mutual balance and unbalance of the rise and fall of the Five Woon and Six Qi. 7. The interpretation, by Chang Ji Chong of "Yin and Yang of the Sky are for birth and growth and Yin and Yang of the Earth for demise and interment" as an explanation that the first half is mainly for life and the second half for death, appears to be correct by his view that there is balance and harmony between the long and short and the strong and weak. 8. In addition to Three Yang and Three Yin, as attributes of the Intervals of the Sky and the twelve Intervals of the Earth, Five Woon and Six Qi are utilized in the annual observation of the perpetual changes of climates.

• Journal of Korean Society of Steel Construction
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• v.24 no.3
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• pp.325-336
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• 2012

Smart base isolation systems developed for structures in high seismic regions cannot be directly applied to structures in regions of low-to-moderate seismicity, such as Korea. Therefore, the problems that occur by applying the smart base isolation system for high seismic regions to the structures in regions of low-to-moderate seismicity have been investigated in this study. To this end, a five-story building is used as an example, and an MR damper and low damping elastomeric bearings were used to compose a smart base isolation system. Artificial earthquakes are simulated for ground motions in regions of high and low-to-moderate seismicity. Based on numerical simulation results, the MR damper capacity that can provide good control is quite different among regions of high and low-to-moderate seismicity. Moreover, it is noted that the properties of a smart base isolation system for the regions of low-to-moderate seismicity should be carefully designed because the base isolation effects of the smart base isolation system for high seismic regions deteriorate when it is applied to the structures in regions of low-to-moderate seismicity.

• Journal of Ocean Engineering and Technology
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• v.3 no.2
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• pp.138-144
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• 1989

It has been very important in various industry fields to improve the fatigue strength characteristics of bearings such as bearing life, fatigue limit, etc., because such poor properties could result in shortening the machinery life as well as in decreasing the accuracy. However, no successful heat treatment criterion seems to be available at present. In this study, the effect of the $170^{\circ}C\times120min$ tempering cycles repeated after $380^{\circ}C\times80min$ oil quenching for $800^{\circ}C$ spheroidizing-annealed bearing steel (STB2) as base metal on the $120^{\circ}C$ high temperature rotary bending fatigue strength characteristics were investigated, including the effects on hardness, Charpy impact value and micro-structure, in order to seek for the best heat treatment condition finally. The important results obtained are as follows : 1) The optimal cycle of tempering so that the fatigue strength .sigma. could become the highest was the 4th cycle. And it is confirmed that this $\sigma_{F}$ is about 6 times more increased than that of base metal, and about 1.3 times more increased than the case of the 1 cycle tempered. 2) As a result of the investigation for the effects of tempering cycles on hardness, the hardness at the tempering number of 2 thru 5 cyles was not decreased severely ; only about 10% decrease from those of the quenched and 1 cycle tempered case. Such hardness is equivalent to $H_{R}$/C61-62 with no bad effect on anti-abrasion of bearing steel. 3) In the case of 2 thru 5 cycle tempering as well as 1 cycle tempering, the impact value was not so improved comparing with the case of quenching, but an increase of 5 to 10% could be expected at least. 4) It was experimentally confirmed that the control of the mechanical properties improvement such as fatigue strength and fatigue life for bearing steels could be possible by the number of tempering cycles.

• Journal of Ocean Engineering and Technology
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• v.3 no.2
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• pp.638-638
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• 1989

It has been very important in various industry fields to improve the fatigue strength characteristics of bearings such as bearing life, fatigue limit, etc., because such poor properties could result in shortening the machinery life as well as in decreasing the accuracy. However, no successful heat treatment criterion seems to be available at present. In this study, the effect of the $170^{\circ}C\times120min$ tempering cycles repeated after $380^{\circ}C\times80min$ oil quenching for $800^{\circ}C$ spheroidizing-annealed bearing steel (STB2) as base metal on the $120^{\circ}C$ high temperature rotary bending fatigue strength characteristics were investigated, including the effects on hardness, Charpy impact value and micro-structure, in order to seek for the best heat treatment condition finally. The important results obtained are as follows : 1) The optimal cycle of tempering so that the fatigue strength .sigma. could become the highest was the 4th cycle. And it is confirmed that this $\sigma_{F}$ is about 6 times more increased than that of base metal, and about 1.3 times more increased than the case of the 1 cycle tempered. 2) As a result of the investigation for the effects of tempering cycles on hardness, the hardness at the tempering number of 2 thru 5 cyles was not decreased severely ; only about 10% decrease from those of the quenched and 1 cycle tempered case. Such hardness is equivalent to $H_{R}$/C61-62 with no bad effect on anti-abrasion of bearing steel. 3) In the case of 2 thru 5 cycle tempering as well as 1 cycle tempering, the impact value was not so improved comparing with the case of quenching, but an increase of 5 to 10% could be expected at least. 4) It was experimentally confirmed that the control of the mechanical properties improvement such as fatigue strength and fatigue life for bearing steels could be possible by the number of tempering cycles.

• Journal of the Korean Geographical Society
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• v.50 no.1
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• pp.37-52
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• 2015

The purpose of this study is to elucidate the traits of the spatial orientation of urban residents. The analysis materials are the 110 rough maps which have been collected for the last ten years in Yeonsugu, Incheon metropolitan. The urbanites' spatial orientation are analysed from an aspect of the orientation elements and the orientation frames respectively. As a result, the urban dwellers make use of five elements - path, node, district, landmark, and language clue for their spatial orientation. Again the orientation frames of the urban people are investigated in terms of locating and directing in space. In regard to the former, they tend relatively to depend on horizontal axes based on broad streets and to prefer to position at the center on coordinate system. With reference to the latter, they show to be north-at-the-top directed tendency and to hold higher proportion of exocentric perspective than egocentric. Consequently urban residents tend to form spatial orientation with using five spatial elements, leaning horizontal axis, positioning themselves at the central part of coordinates, directing toward north-at-the-top through exocentric perspective.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.4
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• pp.737-752
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• 1992

Analysis of elasto-dynamic deformation of flexible linkage mechanism is conducted using the finite element method. The equations of motion of the system are derived from the static structural problem in which dynamic inertia, gravitational and driving forces are treated as external loads. Linear spring model is included in the formulation of equation of motions to represent the effects of deformation of elastic bearings of revolute joints on the system behavior. A computer program is constructed and applied to analyze a specific crank-lever 4-bar mechanism. The algorithm of the program is as follows. First, the natural frequencies and the mode shapes of the system are calculated by solving the eigenproblem of the mechanism system which can be considered as a static structure by assuming the input shaft (crank shaft) to be fixed at any given configuration of mechanism. And finally, the elasto-dynamic deformation of the whole system is obtained using mode superposition method for the case of constant input speed. The effect of geometric stiffness on the mechamism is included in the program with the axial forces of links obtained through the quasi-static displacement analysis. It is found that the geometric stiffness exerts an important effect upon the elasto-dynamic behavior of the flexible linkage mechanism. Elastic deformation of bearing lowers the natural frequencies of the system, resulting smaller elastic displacement at the mid-point of the links and bigger elestic displacement at the ends of the links than rigid bearing. The above investigation of flexible linkage mechanism shows that the effects of the elastic deformation of bearing on the mechanism should be considered to design the mechanism which satisfies more preciously the purpose and the condition of design.

• Journal of KSNVE
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• v.8 no.5
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• pp.964-973
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• 1998

In this paper we propose a levitation and imbalance compensation controller design methodology of magnetic bearing system. In order to achieve levitation and elimination of unbalance vibartion in some operation speed we use the discrete-time Q-parameterization control. When rotor speed p = 0 there are no rotor unbalance, with frequency equals to the rotational speed. So in order to make levitatiom we choose the Q-parameterization controller free parameter Q such that the controller has poles on the unit circle at z = 1. However, when rotor speed p $\neq$ 0 there exist sinusoidal disturbance forces, with frequency equals to the rotational speed. So in order to achieve asymptotic rejection of these disturbance forces, the Q-parameterization controller free parameter Q is chosen such that the controller has poles on the unit circle at z = $exp^{ipTs}$ for a certain speed of rotation p ( $T_s$ is the sampling period). First, we introduce the experimental setup employed in this research. Second, we give a mathematical model for the magnetic bearing in difference equation form. Third, we explain the proposed discrete-time Q-parameterization controller design methodology. The controller free parameter Q is assumed to be a proper stable transfer function. Fourth, we show that the controller free parameter which satisfies the design objectives can be obtained by simply solving a set of linear equations rather than solving a complicated optimization problem. Finally, several simulation and experimental results are obtained to evaluate the proposed controller. The results obtained show the effectiveness of the proposed controller in eliminating the unbalance vibrations at the design speed of rotation.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.6
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• pp.803-809
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• 2018

Generally, the gap-and-sag method is used in the shipbuilding stage before coupling the shafts to check whether they are installed at the same position as designed and derived from shaft alignment calculation. The primary installed propeller shaft becomes a reference point, the position of the remaining shafts are sequentially determined through the gap-and-sag value derived from the deflection and deflection angle at each shaft flange by own weight. If the reference point varies against the design value, it would have a series of effects on the installation of the remaining shafts. Moreover, after coupling the shafts, even if the bearing reaction forces derived from measurement are satisfied by the allowable limit range, consequently it might have an adverse effect on the stability of the shafting system by not being able to estimate the relative slope angle between the propeller shaft and the after-stern tube bearing. In this paper, to deal with above-mentioned phenomenon, the theoretical calculations related to designing an effective support point of the aft stern tube bearing and analysis by measurement is conducted through a case of open-up inspections. Based on this, a shaft installation guideline is proposed to minimize the misalignment related to preventing wiping damage of the after-stern tube bearing.