• Title/Summary/Keyword: Load Capacity Coefficient

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Friction Effects on the Performance of Double-Bumped Air Foil Bearings (이중범프포일 공기베어링의 성능에 미치는 마찰효과)

  • Kim, Young-Cheol;Lee, Dong-Hyun;Kim, Kyung-Woong
    • Tribology and Lubricants
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    • v.23 no.4
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    • pp.162-169
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    • 2007
  • This paper deals with friction effects on the performance of double-bumped AFBs. The stiffness and damping coefficients of the double bump vary depending on the external load and its friction coefficient. The double bump can be either in the single or double active region depending on vertical deflection. The equivalent stiffness and damping coefficients of the bump system are derived from the vertical and horizontal deflection of the bump, including the friction effect. A static and dynamic performance analysis is carried out by using the finite difference method and the perturbation technique. The results of the performance analysis for a double-bumped AFB are compared with those obtained for a single-bumped AFB. This paper successfully proves that a double bumped AFB has higher load capacity, stiffness, and damping than a single-bumped AFB in a heavily loaded condition.

An Experimental Study on Performance of Heat Pump System Using Hydrocarbon Refrigerants by Changing Indoor Load (실내 부하 변동에 따른 탄화수소계 냉매를 이용한 히트펌프 성능에 관한 실험적 연구)

  • Kim, Jae-Dol;Seong, Gwang-Hoon;Jeong, Seok-Kwon;Yoon, Jung-In;Lee, Ho-Saeng
    • Journal of Advanced Marine Engineering and Technology
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    • v.30 no.2
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    • pp.204-210
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    • 2006
  • This study presents heat pump system characteristics using hydrocarbon refrigerants as alternative refrigerant for R-22 with respect to the variation of indoor load. Pure R-22 and R-290. R-600a, R-1270 were considered as working fluids The experimental apparatus was constructed to investigate the performance of heat pump using the air as a heat source. The performance were calculated based on compression shaft work. refrigeration capacity. pressure ratio, discharge temperature and COP. The experimental results show that the COP and refrigeration capacity of hydrocarbon refrigerants were higher than that of R-22. Through the above. hydrocarbon refrigerants are good alternatives in the heat pump system for R-22.

Design of Large-scale Drilled Shaft (대구경 현장타설말뚝의 설계 사례)

  • Im, Chul-O;Choi, Young-Seok;Kwak, Ki-Seok;Jang, Hak-Sung
    • Proceedings of the Korean Geotechical Society Conference
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    • 2009.09a
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    • pp.545-553
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    • 2009
  • A lot of long-span marine bridge, which connects land to island or island to island, are being designed and constructed lately in south-west coast in South Korea. In the past, caisson foundations in marine were mainly adopted in construction and stability aspect, however, nowadays with development of pile construction technology, drilled shaft foundations are mainly adopted. As the long span cable stayed bridge and suspension bridge applied with lots of loads are being designed, the scale of pile foundations are getting larger. As the construction cost of substructure including foundation in marine bridges is too high, the appropriate evaluation of the axial bearing capacity of pile becomes a core factor to decide the construction cost of foundation if the drilled shaft is adopted as foundation type of bridge. The evaluation values of skin friction and end bearing capacity of drilled shaft in weathered rock suggested in south Korea are only to introduce the foreign specifications, and most of them are designed in a kind of hard soil layer. Also the allowable load of pile section is less than the expected bearing capacity of pile in the soil condition since the allowable capacity of pile is undervalued. Recently in order to improve this factor the bi-axial hydraulic load test of pile was taken, the data of load transfer analysis of pile, unit of skin friction and end bearing capacity are accumulated. In our country, the design of piles are made with ASD, however, LRFD considering service, strength and extreme state was adopted in Incheon Grand Bridge implemented with BTL, and the research to systematize the resistance coefficient appropriate at home country are being progressed.

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Post-buckling analysis of piles by perturbation method

  • Zhao, M.H.;He, W.;Li, Q.S.
    • Structural Engineering and Mechanics
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    • v.35 no.2
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    • pp.191-203
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    • 2010
  • To investigate the critical buckling load and post-buckling behavior of an axially loaded pile entirely embedded in soil, the non-linear large deflection differential equation for a pinned pile, based on the Winkler-model and the discretionary distribution function of the foundation coefficient along pile shaft, was established by energy method. Assuming that the deflection function was a power series of some perturbation parameter according to the boundary condition and load in the pile, the non-linear large deflection differential equation was transformed to a series of linear differential equations by using perturbation approach. By taking the perturbation parameter at middle deflection, the higher-order asymptotic solution of load-deflection was then found. Effect of ratios of soil depth to pile length, and ratios of pile stiffness to soil stiffness on the critical buckling load and performance of piles (entirely embedded and partially embedded) after flexural buckling were analyzed. Results show that the buckling load capacity increases as the ratios of pile stiffness to soil stiffness increasing. The pile performance will be more stable when ratios of soil depth to pile length, and soil stiffness to pile stiffness decrease.

Finite Element Analysis of Mechanical Behavior of Bolt Tightened in Plastic Region (소성역 체결 볼트의 기계적 거동 유한요소해석)

  • Cho, Sung-San;Shin, Chun-Se
    • Transactions of the Korean Society of Automotive Engineers
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    • v.18 no.3
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    • pp.37-42
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    • 2010
  • Plastic region tightening is widely used in critical bolted joints in internal combustion engines in order to reduce the engine weight by maximizing the use of load-carrying capacity of bolt. Mechanical behavior of bolt tightened in plastic region under external axial tensile load is investigated for various friction conditions using three dimensional finite element analysis. The behavior of bolt tightened in elastic region as well as that in tensile test are investigated for comparison. Tightening process is simulated by rotating the bolt in order to examine the friction effect realistically. It is revealed that the bolt tightened in plastic region can carry more external load until the joint is opened, and yields at lower bolt load than the bolt tightened in elastic region. The friction coefficient has effect on the yield load, but not on the load-carrying capacity. Moreover, the scatter in the bolt preload due to friction begins with plastic deformation of bolt in the angle tightening control, whereas it begins with the onset of tightening in the torque tightening control. The observations are interpreted with the residual torsional stress in the bolt generated during the tightening.

Characterization of V-Insert Clamp Joint Applied to Automobile Exhaust Pipes (차량 배기관용 V-Insert 클램프의 체결 성능 평가)

  • Hwang, Young-Eun;Yoon, Sung-Ho
    • Journal of the Korean Society for Precision Engineering
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    • v.29 no.2
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    • pp.208-213
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    • 2012
  • In this study, the mechanical joint performance of the V-Insert clamp applied to automobile exhaust pipes was evaluated through the experimental investigation of its axial load capacity. The axial load of the V-Insert clamp was also determined by using theoretical equations presented by Shoghi and compared with the experimental results. As results of the theoretical prediction, the axial load of the V-Insert clamp tended to increase along with smaller angle of the V-Insert segment and the lower friction coefficient between the V-Insert segment and exhaust pipes. The experimental results under tightening effects were similar to the theoretical results and the axial load of the V-Insert clamp presented maximum values in the range of all torques at distance of 2mm between each exhaust pipes. The experimental results under loading effects were similar to the theoretical results in the range of lower torques but deviated from the theoretical results in the range of higher torques. These results would be beneficial to improve the joint and sealing performance of the V-Insert clamp.

A Study on the Load Carrying Capacity and Equivalence Friction Coefficient of a Textured Plane Bearing with Semi-spherical Dimples and Semi-ellipsoidal Dimples (반구형 및 반타원형으로 텍스처링된 평면 베어링의 부하지지능력과 등가마찰계수에 대한 해석)

  • Lee, Soo-Young;Kim, Pil-Kee;Seok, Jong-Hyuk;Seok, Jong-Won
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.21 no.5
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    • pp.741-746
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    • 2012
  • The increase of energetic efficiency in plane bearing is getting more important in the transfer mechanism of semi-conductor and display panel manufacturing processes. To accomplish this objective, the technique of surface texturing on bearing surface has recently emerged as one of the most effective candidates. In this study, the effects of various pattern parameters on two bearing performance indices(load carrying capacity and effective friction coefficient) are investigated through a semi-analytic method, i.e., the 2-dimensional Reynolds equation incorporated into the finite difference scheme. Here, cavitation effect is also taken into account by employing an appropriate numerical scheme. In this study, the patterns in the textured surface are composed of a series of semi-spheres or semi-ellipsoids in shape. The effects of their size and number density on the performance indices are examined through the performance of various numerical experiments. Also, the effects of the anisotropy of the semi-ellipsoidal pattern on the bearing's lubrication characteristics are investigated and discussed.

A Study on the Limited Rate Power Capacity for Applications for Precision Passive Devices Based on Carbon Nanotube Materials (탄소나노튜브 소재의 정밀 수동소자 적용을 위한 한계 정격전력 용량에 관한 연구)

  • Lee, Sunwoo
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.35 no.3
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    • pp.269-274
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    • 2022
  • We prepared carbon nanotube (CNT) paper by a vacuum filtration method for the use of a chip-typed resistor as a precision passive device with a constant resistance. Hybrid resistor composed of the CNT resistor with a negative temperature coefficient of resistance (T.C.R) and a metal alloy resistor with a positive T.C.R could lead to a constant resistance, because the resistance increase owing to the temperature increase at the metal alloy and decrease at the CNT could counterbalance each other. The constant resistance for the precision passive devices should be maintained even when a heat was generated by a current flow resulting in resistance change. Performance reliabilities of the CNT resistor for the precision passive device applications such as electrical load limit, environmental load limit, and life limit specified in IEC 60115-1 must be ensured. In this study, therefore, the rated power determination and T.C.R tests of the CNT paper were conducted. -900~-700 ppm/℃ of TCR, 0.1~0.2 A of the carrying current capacity, and 0.0625~0.125 W of the rated power limit were obtained from the CNT paper. Consequently, we confirmed that the application of CNT materials for the precision hybrid passive devices with a metal alloy could result in a better performance reliability with a zero tolerance.

Studies on the Development of Bearing Capacity Reinforcement for the Foundation of Soil (기초지반의 지지력보강공법에 관한 연구)

  • 유동환;최예환;유연택
    • Magazine of the Korean Society of Agricultural Engineers
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    • v.30 no.1
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    • pp.38-49
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    • 1988
  • This paper presented as follows results of laboratory model tests with various shaped footings on soil bed reinforced with the strips on the base of behaviour of soil structure according to the loads and triaxial test results reinforced with geotextiles. Their parameters studied were the effects on the bearing capacity of a footing of the first layer of reinforcement, horizontal and vertical spacing of layers, number of layers, tensile strength of reinforcement and iclination load to the vertical 1.Depending on the strip arrangement, ultimate bearing capacity values could be more improved than urreinforced soil and the failure of soil was that the soil structure was transfered from the macrospace to microspase and its arrangement, from edge to edge to face to face. 2.The reinforcement was produced the reinforcing effects due to controlling the value of factor of one and permeable reinforcement was never a barrier of drainage condition. 3.Strength ratio was decreased as a linear shape according to increment of saturation degree of soil used even though at the lower strength ratio, the value of M-factor was rot influenced on the strength ratio but impermeable reinforcement decreased the strength of bearing capacity. 4.Ultimate bearing capacity under the plane-strain condition was appeared a little larger than triaxial or the other theoretical formulars and the circular footing more effective. 5.The maximum reinforcing effects were obtained at U I B=o.5, B / B=3 and N=3, when over that limit only acting as a anchor, and same strength of fabric appeared larger reinforcing effects compared to the thinner one. 6.As the LDR increased, more and more BCR occurred and there was appeared a block action below Z / B=O.5, but over the value, decrement of BCR was shown linear relation, and no effects above one. 7.The coefficient of the inclination was shown of minimum at the three layers of fabrics, but the value of H / B related to the ultimate load was decreased as increment of inclination degree, even though over the value of 4.5 there wasn't expected to the reinforcing effects As a consequence of the effects on load inclination, the degree of inclination of 15 per cent was decreased the bearing capacity of 70 per cent but irnproved the effects of 45 per cent through the insertion of geotextile.

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