• 제목/요약/키워드: vertical stiffness

검색결과 649건 처리시간 0.027초

Lower Extremity Stiffness Characteristics in Running and Jumping: Methodology and Implications for Athletic Performance

  • Ryu, Joong Hyun
    • 한국운동역학회지
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    • 제28권1호
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    • pp.61-67
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    • 2018
  • Objective: The human body is often modelled as a spring-mass system. Lower extremity stiffness has been considered to be one of key factor in the performance enhancement of running, jumping, and hopping involved sports activities. There are several different classification of lower extremity stiffness consisting of vertical stiffness, leg stiffness, joint stiffness, as well as muscle and tendon stiffness. The primary purpose of this paper was to review the literature and describe different stiffness models and discuss applications of stiffness models while engaging in sports activities. In addition, this paper provided a current update of the lower extremity literature as it investigates the relationships between lower extremity stiffness and both functional performance and injury. Summary: Because various methods for measuring lower extremity stiffness are existing, measurements should always be accompanied by a detailed description including type of stiffness, testing method and calculation method. Moreover, investigator should be cautious when comparing lower extremity stiffness from different methods. Some evidence highlights that optimal degree of lower extremity stiffness is required for successful athletic performance. However, the actual magnitude of stiffness required to optimize performance is relatively unexplored. Direct relationship between lower extremity stiffness and lower extremity injuries has not clearly been established yet. Overall, high stiffness is potentially associate risk factors of lower extremity injuries although some of the evidence is controversial. Prospective injures studies are necessary to confirm this relationship. Moreover, further biomechanical and physiological investigation is needed to identify the optimal regulation of the lower limb stiffness behavior and its impact on athletic performance and lower limb injuries.

축계 진동 저감을 위한 수직형 안내 베어링의 최적 설계 (An Optimal Design of a Vertical Guide Bearing for Vibration Reduction)

  • 하현천;박철현;김형자
    • 동력기계공학회지
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    • 제5권3호
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    • pp.64-72
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    • 2001
  • This paper describes an optimal design technology in a segment type vertical guide bearing for vertical rotating machinery. Segment type vertical guide bearings have widely used for vertical rotating machinery, however bearing problems, such as excessive vibration and temperature rise, frequently take place in the actual machine. Such excessive vibration magnitude and/or abnormal bearing metal temperature rise result in serious damage and economic losses. Thus the segment type vertical guide bearing should be designed to get optimal characteristics in order to maintain stable operation without bearing failure due to abnormal vibration and/or abnormal bearing metal temperature. The preload ratio is the most important parameter in designing the segment type vertical guide bearing. Because adjustment of the bearing preload by changing the bearing clearance could easily control both the bearing stiffness and the cooling effect. In the paper, the influence of the preload effects on the bearing metal temperature and the bearing stiffness has been investigated both theoretically and experimentally in order to find out an optimum preload ratio. Results show that the segment type vertical guide bearing has an optimum preload ratio at which the bearing stiffness reaches a masimum value while the bearing metal temperature is minimized.

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철도차량용 공기 스프링의 정적 특성 시뮬레이션 (Simulation of Static Characteristics of Railway Vehicle's Airspring)

  • 허신;구정서;우창수;김유일
    • 연구논문집
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    • 통권26호
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    • pp.15-24
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    • 1996
  • In this study, we performed the static analysis of a cord-reinforced rubber airspring and generated the three-dimensional half-symmetry model which use the finite-strain shell elements to model the airbag. the three-dimensional hydrostatic fluid elements to model the air-filled cavity, and the rebar elements to model the multi-ply nylon reinforcement of airbag. In addition, a three-dimensional rigid surface is used to define the contact between the airspring and metal bead. The air inside the airspring cavity has been modeled as a compressible fluid satisfying the ideal gas law. The conclusions of this study are as follows. 1) In the pressurization step of analysis, we could predict the change of vertical reaction force, cavity volume and pressure within the airspring. 2) In the second step of analyzing vertical static stiffness, the increase of the vertical load increases the vertical stiffness. 3) In case of changing the angle of nylon cord, the increase the angle of nylon cord increases the vertical stiffness.

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수직증축 공동주택 하부 기존말뚝의 열화를 고려한 축강성 제안 (Proposed Deterioration-induced Axial Stiffness of Existing Piles in Vertical Extension Structures)

  • 정상섬;김도현;조현철
    • 한국지반공학회논문집
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    • 제35권12호
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    • pp.25-33
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    • 2019
  • 본 연구에서는 수직증축 구조물의 기존말뚝의 축강성(Kve)을 이론적인 접근과 현장 계측 결과를 바탕으로 추정하였다. 이론적인 접근에는 Randolph와 Wroth(1978)가 제안한 축강성 공식을 적용하여, 지중에 설치된 강성 및 연성말뚝의 세장비(L/D)에 따른 축강성의 범위를 도출하였다. 여기에, 1995 - 1997년 사이에 설치된 38본 말뚝의 계측된 시공 당시 축강성을 이론적으로 도출한 축강성 범위에 중첩해서 고려하였다. 이를 통하여, 노후화와 열화에 의하여 감소한 기존말뚝의 축강성의 최대값을 세장비에 따라 제안하였고, 도출된 값을 통계적인 기법을 통하여 상위 95% 값을 제안하여 신설 보강말뚝 설계 시 필요한 최소 축강성(Kvr)을 산정하는 데에 활용할 수 있도록 하였다.

건물용 납면진받침의 의존성 평가 실험 (Experimental Study on Dependent Characteristics of Lead Rubber Bearing for Buildings)

  • 정길영;박건록;하동호;김두훈
    • 한국지진공학회:학술대회논문집
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    • 한국지진공학회 2002년도 춘계 학술발표회 논문집
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    • pp.373-382
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    • 2002
  • In this paper, the characteristic dependencies of LRB(lead rubber bearing) were studied by various prototype tests on LRB for buildings. The characteristics of LRB were dependent on displacements, repeated cycles, frequencies, vertical pressures and temperatures. The prototype test showed that the displacement was the most governing factor influencing on characteristics of LRB. The effective stiffness and equivalent damping of LRB were decreased with large displacement, and increased with high frequency. After the repeated cyclic test with 50 cycles, the effective stiffness and equivalent damping of LRB were reduced by approximately 20% compared with those of the 1$^{st}$ cycle. The effective stiffness was decreased with high vertical pressure, while the equivalent damping was increased. In which, the equivalent damping was more dependent on the vertical pressure than the effective stiffness.s.

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수직접합부 강성을 고려한 프리캐스트 콘크리트 대형판구조물의 응력해석 (Stress Analysis of Precast Concrete Large Panel Structures Taking Account of Stiffness of Vertical Joints)

  • 장극관;이한선;신영식;류진호
    • 한국전산구조공학회:학술대회논문집
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    • 한국전산구조공학회 1993년도 가을 학술발표회논문집
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    • pp.149-156
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    • 1993
  • Precast concrete (P.C.) large panel structures have usually weaker stiffness at joints than that of monolithic in-situ reinforced concrete structures. But structural designers do not in general take into account this characteristics of P. C. large panel structures and use the same analytical models as for the monolithic structure. Therefore, the results of analysis obtained by using these models may be quite different from those actually occuring in real P.C. structure. In this study, the change in force and stress distribution and deflections of structure caused by applying lower shear stiffness at vertical joints are investigated through trying several finite element modeling schemes specific for P.C. structures. Finally, for engineers in practice. a simplified model, which takes account of the effect of lower shear stiffness at vertical joints, is proposed with the understanding on possible amount of errors.

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수직증축 공동주택 하부 신설 보강말뚝의 축강성 산정 (Estimation of the Axial Stiffness of Reinforcing Piles in Vertical Extension Structures)

  • 김도현;정상섬;조현철
    • 한국지반공학회논문집
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    • 제35권12호
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    • pp.35-44
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    • 2019
  • 본 연구에서는 수직증축 공동주택 하부 신설 보강말뚝의 축강성(Kvr)을 기존말뚝의 열화를 고려한 이론적인 접근과 수치해석을 통하여 산정하였다. 3차원 유한요소 수치해석을 수행하는 과정에서, 이론적인 접근과 38본의 시험 말뚝계측 결과를 통하여 제안된 열화를 고려한 기존말뚝 축강성(Kve)의 상한 값을 적용하였다. 이를 통해, 수직증축 리모델링으로 인하여 증가된 하중을 안정적으로 지지하기 위한 신설 보강말뚝의 최소 축강성을 산정하였다. 신설 보강말뚝의 축강성 제안은 선단지지 말뚝과 마찰말뚝에 대해 수행하였고, 다양한 세장비(L/D)에 따라 제안하였다. 해석기법은 기존말뚝의 설계 당시의 양호한 상태를 고려한 말뚝지지 전면기초 거동 해석과 열화가 고려된 기존말뚝의 축강성을 적용한 말뚝지지 전면기초 거동 해석을 수행하였다. 두 해석기법에 대한 검증을 수행한 결과 말뚝지지 전면기초 거동해석이 가능한 것으로 확인되었고, 이를 통하여 기존말뚝의 열화가 발생하였을 때 선단지지 신설 보강말뚝 축강성이 44 - 67% 증가되어야 수직증축 구조물의 안정성이 확보됨을 알 수 있었다.

재사용율이 높은 시스템 동바리의 수직재와 수평재 연결부 회전강성 평가 (Evaluation of the Rotational Stiffness of Connections between Vertical and Horizontal Members for the Highly Reusable System Supports)

  • 박지선;송태협
    • 한국건설순환자원학회논문집
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    • 제11권4호
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    • pp.517-526
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    • 2023
  • 현장에서 재사용율이 높은 시스템 동바리를 대상으로 임의 설계와 과도한 가재새 보강을 지양하고자 성능평가를 근거로한 시스템 동바리의 수직재와 수평재의 연결부에 대한 연결 조건을 제시하고자 하였다. 이를 위하여 국내에 가설현장에 널리 사용되는 대표적인 연결재 유형인 디스크형과 포켓형을 대상을 하중방향(수직, 수평)과 가력방법(단조, 반복)에 대하여 회전강성을 평가하였다. 평가결과 현행 설계기준에서 연결재에 대하여 회전강성을 "0"으로 규정한 것과 달리 모든 시편에서 회전강성 값을 확인할 수 있었으며, 최대 회전강성은 디스크형 연결재를 사용하여 수직방향으로 반복 가력한 시편에서 회전강성값이 19.624 kNm/rad로 확인되었다.

철도교량용 고무패드의 특성 및 강성 추정기법 (The Characteristics and Estimated Stiffness of Rubber Pads for Railway Bridges)

  • 최은수;김현민;오지택;김성일
    • 한국철도학회:학술대회논문집
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    • 한국철도학회 2005년도 춘계학술대회 논문집
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    • pp.115-122
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    • 2005
  • This study analyzed the characteristics of four kinds of bridge rubber pads and suggested how to determine the stiffness the pads. The stiffness of rubber pads can be estimated by a direct static test. In the procedure to estimate the stiffness of a pad, the dead load(preload) of a bridge and live load of a vehicle are considered. The polyurethane rubber pads have larger hardness than natural and chloroprene rubber pads and thus carry larger load bearing capacity. In addition, they showed higher stiffness with the same shape factor than the others and thus are more avaliable as for bridge bearings. Although natural and chloroprene rubber pads are elongated to large deformation in horizontal direction due to vertical loads, polyurethane rubber pads almost do not generate horizontal deformation due to vertical loads regardless to the thickness and hardness of the pads. Therefore, they do not need reinforced plate to restrict horizontal deformation.

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수직 하중에 따른 목재 짜맞춤 접합부의 강성도 평가 (Evaluation of Stiffness Ratio of Wooden Mortise and Tenon Joint on Vertical Loading)

  • 박천영;이전제;김광철
    • 한국가구학회지
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    • 제23권3호
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    • pp.290-297
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    • 2012
  • Recently, interest in wooden construction have been growing by increasing needs and demands for eco-friendly and traditional wooden building(Hanok). Especially, Hanok has the technical development in manufacturing the mortise-tenon joint without fasteners(precut), so it could be called to modernization, industrialization and popularization. But the structural design and analysis of the structure were not regulated and had the difficulty to consider the variation of wooden member and to conduct the difficulty in the structural analysis and the design of the joint. In this study, the stiffness ratio of wooden mortise and tenon joint was evaluated according to the vertical loading, lintel and loading speed. The joint was distinguished in semi-rigid joint regardless of their factors. The stiffness ratio was 0.40 in vertical loading, 0.50 without vertical loading and 0.44 in horizontal loading with high speed. This study would be utilized to the structural analysis and design with structural analysis and design program.

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