• 대한기계학회논문집A
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• 제29권2호
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• pp.239-246
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• 2005

A rotor dynamic analysis is implemented to confirm the vibration stability of the high speed centrifugal chiller coupled with gear system. As the rotating speed of the centrifugal chiller under investigation is increased up to 17605rpm at the pinion rotating part, the bearing instability is getting higher and, furthermore, the rotor-bearing system might experience a few critical speed which lead to system failure due to the excessive vibration. In this study, considering the loading capacity and stability conditions, offset journal bearings are adopted for the pinion rotating system and general cylindrical bearings are used for motor part. From the modal analysis, the system is found to be stable as the critical damping ratio which shows the damping characteristics of the system are positive over all operating ranges, and in addition, the synchronous rotating frequency does not come across with any whirl natural frequency. From these results the authors confirm the vibration stability of the rotor-bearing system suggested in this study.

• 한국소음진동공학회논문집
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• 제21권8호
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• pp.752-760
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• 2011

In tilting pad bearing design process, the selection of the proper configuration type of either a load-between-pad(LBP) or load-on-pad(LOP) as well as preload and pivot offset conditions is to be carefully considered. Also the bearing needs to be designed in order to be suited for the rotor-bearing system and operating condition. In this paper, it is observed that the dynamic characteristics in a five pad tilting pad bearing for the LBP and the LOP configurations are influenced by the variation of preload and pivot offset. In this context, rotor dynamic analysis of the 5 MW industrial gas turbine supported by the tilting pad bearing at the front and roller bearing at the rear is carried out based on the dynamic coefficients of the tilting pad bearing investigated. The result shows that two rigid body critical modes experience various changes according to the influence of the tilting pad bearing uniquely applied to one side of this machine. Mainly, the second critical speed, the rigid body mode of conical shape with high whirling in the tilting pad bearing, is significantly changed by preload and pivot offset regardless of the LBP and LOP configurations. And, the first critical mode, the rigid body mode of conical shape with high whirling in the roller bearing, is sensitively affected by preload applied to the LOP configuration and by its asymmetric dynamic properties.

• 한국산학기술학회논문지
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• 제4권3호
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• pp.193-198
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• 2003

증속기어장치를 이용한 고속회전 터보냉동기 시스템에 대한 회전체 동역학 설계 및 해석을 수행하였다. 특히 피동축의 회전수가 17,605 rpm가지 상승하여 회전체 안정성에 문제가 될 것으로 예측하여 특수베어링의 일종인 Offset베어링을 적용하였고, 구동축의 베어링은 단순베어링인 진원형 베어링을 적용하였다. 모드해석결과 회전체 시스템의 고유진동수가 어떠한 가진성분과 교차하지 않는 것이 확인 되었고, 전 운전영역에 걸쳐 감쇠값이 양의 값을 갖는 것을 알 수 있었으며 설계된 회전체 시스템이 정격운전 상태에서 충분한 안정성을 갖고 작동할 수 있음을 확인하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제33권1호
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• pp.28-36
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• 2009

In this paper, based on the measured data of hull deflection, an approximated hull deflection curve is drawn using reverse analyzed hull deflection data and the estimation method for flexibility analysis of shaft alignment is proposed by use of the approximate hull deflection curve. Generally an offset value of after stern tube bearing is a datum point with an fore stern tube bearing however the shaft alignment has a tendency which is able to get higher flexibility if the shafting system has the deflection value from after stern tube bearing as reference to bottom direction according to results of on this study. By applying this result of study, the shaft alignment for next similar ships will be able to estimate how to follow the hull deflection and how to be influenced by hull deflection at shaft alignment analysis state using the approximated hull deflection curve.

• 한국유체기계학회 논문집
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• 제17권4호
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• pp.70-75
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• 2014

In this paper a analysis method is presented to obtain the steady state dynamic response from the finite element based equations of a rotor-bearing system with initial deflection. The method has been applied to analyze the dynamic response of the two-shaft rotor-bearing system with rigid coupling offset in a heavy duty gas turbine-generator. Bumps in the dynamic response of each rotor system have been observed at each critical speed due to the effect of initial deflection for rigid coupling offset. And, the dynamic responses have been shown to reduce for operating condition changes from cold to hot.

• Journal of the Korean Wood Science and Technology
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• 제50권4호
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• pp.237-245
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• 2022

This study examined the structural performance of experimental parallel strand lumber (PSL) from a Larch veneer strand. The prototype of PSL from a Larch veneer strand was manufactured in the experimental laboratory and tested. The bending and dowel bearing strength were determined from the modulus of elasticity (MOE), modulus of rupture (MOR), and dowel bearing strength based on a 5% offset yield load. The test results indicated that the average MOR of PSL was higher than that of 2 × 4 dimension lumber, and the average MOE of PSL was lower than that of 2 × 4 dimension lumber. A linear relationship was observed between the MOR and MOE. The allowable bending stress of PSL was derived as specified in ASTM D2915 and compared with other research. The dowel bearing strength of PSL in parallel to the grain was approximately double that perpendicular to the grain of PSL. A comparison of several theoretical calculations based on each national code for the dowel bearing strength was conducted, and some theoretical equations produced results closer to the experimental results when it was parallel to the grain, but the difference was higher in the case perpendicular to the grain. The test results showed that PSL made with Japanese larch veneer strands appeared to be suitable for a raw material of structural composite lumber (SCL) appeared to be used as a raw material for SCL.

• 한국지반공학회논문집
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• 제16권1호
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• pp.107-116
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• 2000

4개 현장에 실물크기의 강관말뚝과 PC 및 PHC 말뚝의 축방향에 대한 지지거동을 알아보기 위하여, 강관말뚝에 스트레인게이지를 부착하고 항타시 계측기 손상여부를 조사하면서 동재하시험을 수행하였다. 아울러 동일한 말뚝에 대하여 2일과 7일 경과후에 정재하시험을 실시하여 하중-침하량 거동과 주면 및 선단지지력을 분리 측정하였다. 그 결과, CAPWAP 해석에 Davisson방법을 적용하여 구한 강관말뚝의 허용지지력은 정재하시험에서 구한 허용지지력 보다 약 2~33%정도 크게 나타났다. 그리고 정재하시험 결과에서 구한 산술평균한 허용지지력은 CAPWAP해석에서 Davisson's offset방법으로 구한 허용지지력보다 극한지지력에 FS=2.5를 적용하여 구한 허용지지력에 더 근접하는 경향을 보였다. 또한, 단위면적당 주면지지력은 깊이가 증가함에 따라 증가하였고, 말뚝선단부 1~2m 이내에서 발휘되는 비율이 상당히 큰 것으로 나타났다.

• Journal of Advanced Marine Engineering and Technology
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• 제40권3호
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• pp.191-197
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• 2016

선박이 고출력화, 대형화 됨에 따라 추진축의 강성은 증가한 반면에 선체는 고장력 후판을 사용하므로 이전의 선체보다 훨씬 더 쉽게 변형되는 실정이다. 흘수변화에 따른 선체변형은 축계를 구성하는 각각의 베어링 옵셋 및 반력에 연쇄적인 영향을 미치게 된다. 이는 기존의 선박보다 더욱 정교한 축계정렬이 요구됨을 의미한다. 본 연구에서는 최근 친환경 고효율 선박으로 등장한 5만 DWT급 석유화학제품운반선을 대상으로 선박의 흘수 변화에 따른 선미부 구조해석을 실시하고 구조해석으로부터 얻어진 축계의 상대변위를 이용하여 축계정렬 해석을 수행하였다. 구조해석은 선박의 통상 운항조건에서 최대 흘수 변화를 고려한 2개 조건에서 수행하였다. 이를 바탕으로 선체변형에 따른 베어링 옵셋 변화가 축계정렬에 미치는 영향을 검토하였다.

• Tribology and Lubricants
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• 제16권4호
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• pp.247-252
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• 2000

As the demand for higher areal recording densities requires a lower flying height of the slider, the variation of the flying height of the slider during drive operation becomes of great concern. The variation of the flying height is closely related with the slider design parameters such as air bearing shape, cavity depth, shallow step depth, crown, camber, pitch offset, roll offset, gram load, and so on. The objective of this work is to optimize the cavity depth and the shallow step depth, which are the control factors in air bearing design, using Robust Design method. It was found that the shallow step depth was statistically significant in affecting the variation of flying height, therefore the level of the shallow step depth should be chosen to minimize the variation of flying height.

• 대한조선학회논문집
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• 제42권5호
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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.