• Title/Summary/Keyword: negative friction

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Development of a programming logic to estimate the wall friction coefficient in vehicle tunnels with piston effects (교통환기력이 작용하는 터널 내 벽면마찰계수 추정을 위한 프로그램 로직 개발)

  • Kim, Hyo-Gyu;Choi, Pan-Gyu;Ryu, Ji-Oh;Lee, Young-Hoon
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.20 no.1
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    • pp.39-53
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    • 2018
  • Generally, the total ventilation resistance coefficient in a tunnel consists of inlet/outlet loss coefficient, wall friction coefficient, and other loss coefficient caused by sudden expansion and contraction of cross-section, etc. For the tunnel before opening, when the running ventilation fan is stopped, the wind speed in the tunnel is reduced by the total ventilation resistance drag. The velocity decay method is comparatively stable and easy to estimate the wall friction coefficient in the pre-opening tunnel. However, the existing study reported that when the converging wind speed is a negative value after the ventilation fan stops, it is difficult to estimate the wall friction coefficient according to the velocity decay method. On the other hand, for the operating tunnel in which the piston effect acts, a more complex process is performed; however, a reasonable wall friction coefficient can be estimated. This paper aims at suggesting a method to minimize the measurement variables of the piston effect and reviewing a method that can be applied to the operating tunnel. Also, in this study, a new method has been developed, which enables to calculate an variation of the piston effect if the piston effect is constant with a sudden change of external natural wind occurring while the wind speed in the tunnel decreases after the ventilation fan stops, and a programming logic has been also developed, which enables dynamic simulation analysis in order to estimate the wall friction coefficient in a tunnel.

A Case Study of Underpinning for Building Settlement Reduction (건물 침하방지를 위한 Underpinning 사례연구)

  • 박병기;이인모
    • Proceedings of the Korean Geotechical Society Conference
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    • 1993.10a
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    • pp.57-62
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    • 1993
  • Settlements of maximum 23cm have occurred in and Apartment building consturcted on a fill layer with pile foundations. The main reason of the settlements was due to the negative skin friction applied to the pile, and settlement of adjacent ground since most pile tips are acted as a floating foundation founded on the stratum where the SPT N value was mostly less than 30. To underpin this building, the Jumbo Special Pile grouging was adopted, and instrumented data showed little differential settlement after the JSP underpinning.

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Study on the Curve Squeal Noise of Train Wheels (철도차량 곡선부 소음에 대한 발생 메카니즘 규명 관련 연구)

  • Kim, Kwan-Ju;Kim, Beom-Soo;Park, Jin-Kyu;Kim, Jae-Chul
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2005.11b
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    • pp.29-32
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    • 2005
  • This paper presents experimental analysis of a friction-driven wheel that is responsible for wheel squeal. Squeal noise generating mechanism and environment of train u heels has been tried to reproduce under laboratory condition. Scale down size rail and wheel are made and influential parameters to squeal noise are measured, e. g. frictional force, pressure between rail and wheel, creep speed of rail. Negative damping characteristic curve are calculated currently. Necessary relating computational analysis is also carried on.

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유한요소법에 의한 공구인선의 응력분포에 관한 연구

  • Kim, Jeong-Du
    • Journal of the Korean Society for Precision Engineering
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    • v.1 no.1
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    • pp.50-58
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    • 1984
  • In the present paper are calculated and compared the stresses on the normal tools and the restricted tools which have three various rake angles by Least Square Method. The results obtained are summerized as follows. The tool displacement at rake angle .alpha. = 12 .deg. and .alpha. = 0 .deg. is positive value in the principal cutting direction and negative value in the feed direction. At rake angle .alpha. = -12 .deg. the displacement is negative value in both of directions. The principal stress of the restricted and normal tool is maximum at the tip of the tool, the shear stress is maximum after a certain distance from the tip. The result of FEM and P.E method shows that in the range of rapid decreasing of normal stress of the tool edge, the shear stress is maintaining a certain value. This is due to the friction characteristic of the chip.

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Understanding Behaviors of Electrolyzed Water in Terms of Its Molecular Orbitals for Controlling Electrostatic Phenomenon in EUV Cleaning (EUV 세정에서 정전기 제어를 위한 전해이온수 거동의 분자궤도 이해)

  • Kim, Hyung-won;Jung, Youn-won;Choi, In-sik;Choi, Byung-sun;Kim, Jae-young;Ryoo, Kun-kul
    • Journal of the Semiconductor & Display Technology
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    • v.21 no.4
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    • pp.6-13
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    • 2022
  • The electrostatic phenomenon seriously issued in extreme ultraviolet semiconductor cleaning was studied in junction with molecular dynamic aspect. It was understood that two lone pairs of electrons in water molecule were subtly different each other in molecular orbital symmetry, existed as two states of large energy difference, and became basis for water clustering through hydron bonds. It was deduced that when hydrogen bond formed by lone pair of higher energy state was broken, two types of [H2O]+ and [H2O]- ions would be instantaneously generated, or that lone pair of higher energy state experiencing reactions such as friction with Teflon surface could cause electrostatic generation. It was specifically observed that, in case of electrolyzed cathode water, negative electrostatic charges by electrons were overlapped with negative oxidation reduction potentials without mutual reaction. Therefore, it seemed that negative electrostatic development could be minimized in cathode water by mutual repulsion of electrons and [OH]- ions, which would be providing excellences on extreme ultraviolet cleaning and electrostatic control as well.

Study on the Improvement of Milling Recovery and Performance (V) -Experimental Study on Rice Whitening Performance of Jet-air Abrasive-Type Whitener - (도정수율(搗精收率)과 성능향상(性能向上)을 위(爲)한 연구(硏究)(V) -분풍(噴風) 연삭식(硏削式) 정미기(精米機)의 정백성능(精白性能)에 관(關)한 실험적(實驗的) 연구(硏究)-)

  • Lee, Sung Bum;Chung, Chang Joo;Noh, Sang Ha
    • Journal of Biosystems Engineering
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    • v.8 no.1
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    • pp.17-29
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    • 1983
  • The milling process is considered as causing one of the greatest grain losses among all the processes in rice post-production. Major source of grain losses in the rice milling is considered as the whitening process. This study was attempted to develop an abrasive-type whitener, the whitening chamber of which being supplied by jet-air evenly and continuously. To investigate the milling performance by the new whitener, three kind of emery-stone grit(#36, #41, and #46), and three levels of rotational speed of emery stone roller (950, 1070, and 1200 rpm) were tested. The jet-air abrasive-type whitener was also compared with the conventional abrasive-type having no jet-air blower in terms of their milling performance. In addition, the effect of different combinations of sequential uses of the abrasive- and friction-type whiteners on the milling performance was also experimentally evaluated. The results of this study are summarized as follows; 1. In general, the whitening system combined with the abrasive type whitener with jet-air supply, which was newly designed, and the existing jet-air friction type whiteners produces more milled- and head-rice by about 0.3% points and 2.8% points, respectively than the system combined with the existing abrasive type without the jet-air supply under the same operational conditions. The former also consumed less electricity by 0.024 KwH per 100kg of milled rice production and gave more milling capacity by about 35 kg/hr. As compared with the conventional whitening system consisting of jet-air friction type whiteners only, the former yielded more milled- and head-rice by 1.5% points and 4.4% points, respectively. 2. The abrasive roller having 46 grit emery was better than the roller having 36 grit in aspects of milling performance and machine efficiency, in general. 3. With regard to the effect of combination method of abrasive type and friction type whiteners, one pass in abrasive type plus three passes in friction type gave better milling performance and energy efficiency than the two passes in abrasive type plus two passes in friction type regardless of the designs of the emery stone rollers. 4. The increase in rotational speed of the emery stone roller from 950 rpm to 1200 rpm presented negative effects on milled and head-rice yields and machine efficiency, but slightly positive effect on milling capacity.

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The Influence of Negative Skin Friction on Piles in Groups Connected to a Cap (부마찰력이 작용하는 기초판으로 연결된 군말뚝의 거동)

  • Lee, Cheol-Ju;Park, Byung-Soo
    • Journal of the Korean Geotechnical Society
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    • v.22 no.8
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    • pp.25-31
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    • 2006
  • Over the years the investigation of behaviour of piles in groups connected to a cap in consolidating soil has attracted far less attention than the study of isolated piles in groups. In this paper, a series of three-dimensional numerical simulations have been performed to study the behaviour of pile groups connected to a cap in consolidating ground. Both elastic no-slip and elasto-plastic slip analyses were considered. Based on the analysis results, when piles were connected to a cap, tensile forces were developed near the pile head at the outer piles. Elastic solution and no-slip analysis over-predicted the tensile force near the pile head for outer piles. Relatively speaking, the number of piles in a group is more important than the pile spacing in terms of the influence of negative skin friction on the pile behaviour. The issue on the development of tensile forces on the pile head at the outer piles is perhaps needed to be carefully considered in the pile design to prevent the damages of the pile-cap connection.

Analysis of a Bi-directional Load Test Result on tong PHC Piles in Consideration of Residual Load (잔류하중을 고려한 장대 PHC 말뚝의 양방향 재하시험 결과해석)

  • Kim, Sung-Ryul;Chung, Sung-Gyo;Lee, Bong-Yeol
    • Journal of the Korean Geotechnical Society
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    • v.24 no.6
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    • pp.85-93
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    • 2008
  • For long piles driven in deep clay deposits, it is difficult to estimate the ultimate bearing capacity due to large resistance induced by long embedded depth, and also the load transfer curve due to large residual load induced by negative skin friction, even with the performance of pile load tests. In this research, a hi-directional load test on a PHC pile driven in deep soft deposit was performed in order to evaluate the tip and shaft resistances separately, which are feasible to estimate the ultimate bearing capacity of the pile. Residual load of the pile was determined by continuous monitoring of pile strains after the pile installation. The true resistance and true load-movement curve of the pile were properly estimated by taking account of the residual load. A model far behavior of the shaft resistance vs. movement was also proposed, which includes the effects of residual load based on the experiment. Consequently, it was proved that the residual load should be taken into consideration for correctly analyzing load test results of piles in deep clay deposits.

A Study on the Improvement of Trolling Equipment for Spanish Mackerel and Yellow Tail in the Coast of Jeju island (제주 연근해 삼치·방어용 끌낚시의 조업 장비 개발)

  • Park, Young-Seok;Kim, Byung-Yeob;Lee, Chang-Heon
    • Journal of Fisheries and Marine Sciences Education
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    • v.27 no.2
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    • pp.422-429
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    • 2015
  • The purpose of this study is the improvement of the existing trolling hauler, which has only one wheel to wind a main line, for saving man power around the coast of Jeju island. The trolling hauler manufactured for a test performance consisted of the wheel part of a main line and the roller part of a leader line including labor-saving devices comprised of a friction clutch, a fastener and springs. Even though this existing electric hauler system is convenient to control the wheel speed and the winding direction, it is apt to cost high and to corrode quickly at sea. Therefore, to remove these negative elements and to operate rollers for hoisting a leader line of the trolling, hydraulic motors were used separately. As a result, according to using of labor-saving devices, the towing tension occurred in operating in fishing ground could be selected moderately without breaking of lines and the operating efficiency of the trolling hauler was verified.

Unsaturated shear strength characteristics of Nak-dong River silty-sand (낙동강 실트질 모래의 불포화 전단강도특성)

  • Cha, Bong-Geun;Kim, Young-Su;Park, Sung-Sik;Shin, Ji-Seop
    • Proceedings of the Korean Geotechical Society Conference
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    • 2010.09b
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    • pp.53-60
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    • 2010
  • The natural soils are classified in saturated soils and unsaturated soils according to level of ground water but the research for only saturated soils has been conducted by this time. However, there are many proble.ms which are not solved by using the concept and principle of saturated soils on the natural soils. In fact, it is known that unsaturated soils represent the behavior characteristic unlike completely saturated soils because of the adhesion under the influence of negative pore water pressure, the high angle of friction and the low water permeability by the air entry. So it needs to conduct the various researches on insufficient unsaturated soils. In this paper, unsaturated triaxial compressive tests are conducted in order to do research on shear strength characteristic on sands and silty sands of Nakdong river. As a result of the tests, the cohesion is increased in non-linear type according to the change of the matric suction, but the angle of internal friction is not changed much.

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