• 대한조선학회 특별논문집
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• 대한조선학회 2009년도 특별논문집
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• pp.1-5
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• 2009

Recent growth in global economic situation has led dramatic increase in new buildings of large containerships. These increased new building orders have brought keen concerns of developing and improving the quality of design and increasing the productivity of the vessel in order to satisfy the ship Owner's various requirements. For the increment of productivity and quality of containership, the plastic type bearing pad of cargo hatch cover has been investigated intensively for years with the supplier of cargo hatch cover. The result of investigation showed that there are numbers of advantages for the Owner and Builder over the existing bronze bearing pads which are better corrosion resistance long life time, low friction coefficient, easy maintenance, easy installation, better production lead time and low maintenance cost.

• 한국공작기계학회논문집
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• 제16권2호
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• pp.1-7
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• 2007

Active magnetic bearing has been adopted to support the rotor by electomagnetic force without mechanical contact and lubrication process. A property of the control system for magnetic bearing is improved in accordance with making higher system gain. If the control system has integral part, an excessive overshoot response is shown by making higher integral gain. Therefore, this paper suggests a PID control system in order to eliminate the overshoot at the first stage and improve response characteristics to an impact disturbance at the status of levitation. The control gain was obtained by LQR design method which has the structure of I-PD control system in the state space. The PID control system containing prefilter has the same structure as the I-PD control system. Therefore, the PID control system adopted is able to be tuned by LQR design method. Finally, this paper shows the effect of the prefilter on the active magnetic bearing system through response experiments for levitation responses.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2006년도 추계 학술발표회
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• pp.574-584
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• 2006

Bi-directional loading test data are available to evaluate the design parameters which reflect the characteristics of a construction method and the variations of ground at the site where drilled shafts are installed. The method to obtain the design parameters of a real bridge by hi-directional loading test was introduced. The plans of multi-level testing and installation of measuring instruments should be made according to the rough estimation of axial bearing capacity, the length of pile, and the construction method. While the relationship between end bearing resistance and displacement was obtained directly from the hi-directional loading test, the relationship between unit side resistance and displacement was calculated through the measuring values. 1% displacement of pile diameter was adopted as the criteria of failure for ultimate resistance. As the settlement of pile head at the total ultimate bearing capacity obtained from these method was less than 1.5 % of pile diameter, this method was conservative to use in the field.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2004년도 춘계학술발표회
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• pp.552-560
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• 2004

Stone column is a soil improvement method and can be applicable for loose sand or weak cohesive soil. Since the lack of sand in Korea, stone column seems one of the most adaptable approach for poor ground as a soil improvement method. However, this method was not studied for practical application. In this paper, the most effective design parameters for the being capacity of stone column were studied. The parametric study of major design factors for single stone column was carried out under the bulging and general shear failure condition, respectively. Especially, a test result of single stone column by static load was compared with the bearing capacity values of suggested formulas. The analysis result showed that the ultimate bearing capacity by the formula was much less than the measured value by the static load test. Especially, the result of the parametric study under general shear failure condition showed that the bearing capacity has apparent difference between each suggested formulas with the variation of the major design parameters. Therefore, the result of this study can be a suggestion which is applicable for the field test and the future research.

• 대한전기학회논문지:전력기술부문A
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• 제48권3호
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• pp.278-285
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• 1999

This paper utilizes the method of Q-parameterization control to design a controller which solves the problem of imbalance in magnetic bearing systems. There are two methods to solve this problem using feedback controal. The first method is to compensate for the imbalance forces by generating opposing forces on the bearing surface (imbalance compensation). The second method is to make the rotor rotate around its axis of inertia (automatic balancing);in this case no imbalance forces will be generated. In this paper we deal with only imbalance compensation. The free parameter of the Q-parameterization controller is chosen such that these goals are achieved. After the introduction of a model of the magnetic bearing system, we explain the Q-parameterization controller design of the magnetic bearing system with emphasis on the rejection of sinusoidal disturbance for imbalance compensation design. The design objectives are formulated as a linear equations in the controller free paramete Q. Finally, simulation and experimental results are presented and showed the robustness and effectiveness of the proposed controllers.

• Tribology and Lubricants
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• 제35권1호
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• pp.37-43
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• 2019

This paper presents an optimization method to determine the shoulder height of an angular contact ball bearing by 3D contact analysis using nondimensional-shaped variables. The load analysis of the ball bearing is performed to calculate the internal load distributions and contact angles of each rolling element. From the results of bearing load analysis and the contact geometry between the ball and inner/outer raceway, 3D contact analyses using influence function are conducted. The nondimensional shoulder height and nondimensional load are defined to give the generalized results. The relationship between the shoulder height and radius of curvature of the shoulder under various loading conditions is investigated in order to propose a design method for the two design parameters. Using nondimensional parameters, the critical shoulder heights are optimized with loads, contact angles, and conformity ratios. We also develop contour maps of the critical shoulder height as functions of internal loads and contact angles for the different contact angles using nondimensional parameters. The results show that the dimensionless shoulder height increased as the contact angle and dimensionless load increased. Conversely, when the conformity ratio increased, the critical shoulder height decreased. Therefore, if the contact angle is reduced and the conformity ratio is increased within the allowable range, it will be an efficient design to reduce the shoulder height of ball bearings.

• 한국자동차공학회논문집
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• 제15권5호
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• pp.160-164
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• 2007

An automotive wheel bearing is one of the most important components to guarantee the service life of a passenger car. The endurance life of a bearing is affected by many parameters such as material properties, heat treatment, lubrication conditions, temperature, loading conditions, bearing geometry, internal clearance and so on. Generally, a tapered roller bearing gives longer endurance life than that of an equivalent size ball bearing. Consequently, the application of taper bearing units will be increased for more compact design and extended warranty. In this paper, we derive the relation between loads and deformations of a taper bearing unit. On the basis of that, we calculate the endurance life of the taper bearing unit considering initial axial clearance.

• Tribology and Lubricants
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• 제19권6호
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• pp.342-348
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• 2003

The purpose of the paper is to investigate the noise characteristics of cylindrical roller bearings. For the sake of simplicity, it is assumed that the cylindrical roller bearing is infinitely long, and there is no outside force acting on the bearing. The effects of radial clearance of the bearing, viscosity of the lubricant and number of the roller on the noise of the bearing are also examined. Results show that the fundamental frequency of the bearing noise corresponds to the multiplication of number of the roller and whirling frequency of the roller center or the retainer. The acoustical frequency spectra of the roller bearing are pure tone spectra, containing the fundamental frequency of the bearing and its super­harmonics. The low viscosity of the lubricant, high radial clearance of the bearing, and low number of the roller decrease the bearing noise. The results and discussions of the present paper could aid in the low­noise design of the cylindrical roller bearing.

• 한국지반공학회논문집
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• 제26권8호
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• pp.27-37
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• 2010

해상 매립 간척지와 같은 지반에서는 말뚝기초에서 주변 지반이 말뚝보다 상대적으로 많이 침하함에 따라 하향력이 발생하게 되며, 이 하항력은 말뚝의 침하량과 말뚝재료의 응력을 증가시켜서 기초의 안전 및 상부구조물의 사용성에 영향을 미치게 된다. 현재 국내에서는 부주면마찰력을 고려한 말뚝의 허용압축지지력 공식이 존재하나 그 적용성에 있어서 정확한 기준이 없는 것이 현실이다. 이에 본 연구에서는 수치해석을 실시하여 부주면마찰력이 작용하는 말뚝의 거동 특성을 분석하고 지지력 산정식의 적용성 검토를 수행하였다. 국내 대표적 해양 매립 간척지라고 할 수 있는 연세대 송도국제화복합단지의 지반과 말뚝 조건을 모델링하여 선단지지 여부에 따른 수치해석을 수행하여, 그에 따른 부주면마찰력의 발생 특성에 대한 경향을 파악하였다. 또한 수치해석을 통하여 얻어진 하중-침하 곡선을 통하여 극한하중을 산정하고 그에 따른 두부하중 작용 시 발생하는 부주면마찰력을 고려하여 허용지지력 공식의 적용성을 검토하였다. 그 결과 부주면마찰력 발생이 지반의 지지력에 미치는 영향은 미미하나, 침하량 및 말뚝 재료의 허용응력에는 큰 영향을 미치는 것으로 나타났다. 극한지지력에 안전율 3을 적용해 산정된 허용지지력과 비교시 부마찰력을 고려한 허용지지력산정법에 안전율 3을 사용한 경우 과소평가하는 경향을 보였으나 2를 적용한 경우 말뚝종류에 따라 유사하게 나타났다.

• 한국지반공학회논문집
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• 제35권8호
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• pp.31-42
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• 2019

최근에 시공된 건축현장의 73개 설계 자료를 분석하여 매입 PHC말뚝에 대한 설계 현황을 고찰하였다. 매입 PHC말뚝의 설계에서 사용하고 있는 극한지지력 산정공식에 따라 산정한 전체지지력에 대한 주면마찰력의 분담율(SRF)는 20~53%로 나타났다. 극한주면마찰력이 과소평가되는 지지력 산정공식에 대한 개선이 필요한 것으로 판단되었다. PHC말뚝의 재료 성능에 대한 평균 설계 효율은 약 70%이었으며 지반 지지력에 대한 평균 설계 효율은 약 80%이었다. 즉, 지반의 설계 효율은 PHC말뚝의 설계 효율보다 약간 높은 수준으로 나타나고 있었다. 이는 지반 지지력을 설계하중보다 동등한 수준 또는 그것보다 약간 높은 수준으로 계산하고 있는 설계 현황에 기인한 것으로 판단되었다. 지반의 허용지지력을 PHC말뚝의 허용연직압축하중보다 높은 수준으로 산정하여야 할 것으로 판단되었다. 매입 PHC말뚝의 지지력 산정공식에서는 극한주면마찰력이 극한선단지지력보다 상대적으로 2.2배 정도 낮은 수준으로 계산되었다. 매입 PHC말뚝의 설계에서 적용하고 있는 극한지지력 산정공식들은 모두 국외 지반을 대상으로 개발되었으며 국내 지반에 대한 적용성 검증 없이 도입되어 사용되어 오고 있었다. 매입 PHC말뚝의 설계에서 적용할 지지력 산정공식의 개선이 이루어져야 할 것으로 판단되었다.