• Title/Summary/Keyword: Force equilibrium

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Development of a Durability Estimation System for Horizontal Machining Centers (수평형 머시닝센터의 내구성 예측 시스템 개발)

  • 김기상
    • Proceedings of the Korean Society of Machine Tool Engineers Conference
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    • 1999.10a
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    • pp.3-10
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    • 1999
  • One of the important considerations in designing a machine tool is the durability. In this study, a durability estimation systems for horizontal machining centers is developed to evaluate the effects of structural specification and driving conditions on the durability. All loads such as weights, inertia forces, cutting force and so on, are automatically transferred from the upper elements to the lower elements by the force flows which can be derived from the structural code of horizontal machining centers. And the external loads applied to the motion elements such as bearings, LM guides, ball screws and so on, are determined by the equilibrium conditions of force and moment. Especially, the durability of horizontal machining center is estimated based on the lifes of motion elements operating under the desired driving conditions.

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Response of Spatially Developing Turbulent Boundary Layer to Spanwise Oscillating Electromagnetic Force (횡 방향 진동하는 전자기력에 대한 공간 발달하는 난류 경계층의 반응)

  • Lee, Joung-Ho;Sung, Hyung Jin
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.29 no.11 s.242
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    • pp.1189-1198
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    • 2005
  • Direct numerical simulations were performed to investigate the physics of a spatially developing turbulent boundary layer flow subjected to spanwise oscillating electromagnetic forces in the near wall region. A fully implicit fractional step method was employed to simulate the flow. The mean flow properties and the Reynolds stresses were obtained to analyze the near-wall turbulent structure. It is found that skin friction and turbulent kinetic energy can be reduced by the electromagnetic forces. The decrease in production is responsible fur the reduction of turbulent kinetic energy. Instantaneous flow visualization techniques were used to observe the response of streamwise vortices and streak structures to spanwise oscillating forces. The near-wall vortical structures are affected by spanwise oscillating electromagnetic forces. Following the stopping of the electromagnetic force, the flow eventually relaxes back to a two-dimensional equilibrium boundary layer.

Development of a Durability Estimation System for Turning Centers (터닝센터의 내구성 예측 시스템 개발)

  • 김기상;김석일
    • Proceedings of the Korean Society of Machine Tool Engineers Conference
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    • 2000.10a
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    • pp.460-465
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    • 2000
  • In this study, a durability estimation system of turning centers is developed to systematically evaluate the effects of structural specification and testing condition on the durability. All loads such as weights, inertia forces, cutting force and so on, are automatically transferred from the upper elements to the lower elements by the force flow which can be derived from the structural code of turning center. And the external loads applying to the moving and rolling elements are determined by using the equilibrium conditions of force and moment. Especially, the durability of turning center is estimated based on the lifes of moving and rolling elements under the required testing condition.

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Shear behavior of multi-hole perfobond connectors in steel-concrete structure

  • Xing, Wei;Lin, Xiao;Shiling, Pei
    • Structural Engineering and Mechanics
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    • v.56 no.6
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    • pp.983-1001
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    • 2015
  • This study focuses on the load carrying capacity and the force transfer mechanism of multi-hole perfobond shear connectors in steel-concrete composite structure. The behavior of multi-hole perfobond shear connector is more complicated than single-hole connector cases. 2 groups push-out tests were conducted. Based on the test results, behavior of the connection was analyzed and the failure mechanism was identified. Simplified iterative method and analytic solution were proposed based on force equilibrium for analyzing multi-hole perfobond shear connector performance. Finally, the sensitivity of design parameters of multi-hole perfobond shear connector was investigated. The results of this research showed that shear force distribution curve of multi-hole perfobond shear connector is near catenary. Shear forces distribution were determined by stiffness ratio of steel to concrete member, stiffness ratio of shear connector to steel member, and number of row. Efficiency coefficient was proposed to should be taking into account in different limit state.

Force Majeure and Hardship - Focusing on the UNIDROIT Principles of International Commercial Contracts - (불가항력과 Hardship에 관한 연구 - 국제상사계약에 관한 UNIDROIT원칙을 중심으로 -)

  • Heo, Kwang-Uk
    • Journal of Korea Port Economic Association
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    • v.21 no.3
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    • pp.219-238
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    • 2005
  • The purpose of this study is to analyze the concept, requirement and the effect of Force majeure and Hardship under the UNIDROIT Principles of International Commercial Contract. Under the UNIDROIT Principles Non-performance by a party is excused if that party proves that the non-performance was due to an impediment beyond its control and that it could not reasonably be expected to have taken the impediment into account at the time of the conclusion of the contract or to have avoided or overcome it or its consequence. There is hardship where the occurrence of events fundamentally alters the equilibrium of the contracts and the events occur or become known to the disadvantaged party after the conclusion of the contract; the events could not reasonably have been taken ito account by the disadvantaged party at the time of the conclusion of the contract; the events are beyond the control of the disadvantaged party; and the risk of the events was not assumed by the disadvantaged party.

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Chaotic response of a double pendulum subjected to follower force (종동력을 받는 진동계의 케이오틱 거동 연구)

  • 이재영;장안배
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 1996.10a
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    • pp.295-300
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    • 1996
  • In this study, the dynamic instabilities of a nonlinear elastic system subjected to follower force are investigated. The two-degree-of-freedom double pendulum model with nonlinear geometry, cubic spring, and linear viscous damping is used for the study. The constant and periodic follower forces are considered. The chaotic nature of the system is identified using the standard methods, such as time histories, phase portraits, and Poincare maps, etc.. The responses are chaotic and unpredictable due to the sensitivity to initial conditions. The sensitivities to parameters, such as geometric initial imperfections, magnitude of follower force, and viscous damping, etc. is analysed. The strange attractors in Poincare map have the self-similar fractal geometry. Dynamic buckling loads are computed for various parameters, where the loads are changed drastically for the small change of parameters.

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Fundamentals of Contact Lens Movement (콘택트렌즈 운동의 기초)

  • Kim, Dae Soo
    • Journal of Korean Ophthalmic Optics Society
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    • v.13 no.1
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    • pp.5-13
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    • 2008
  • Purpose: This review article was written to investigate what kind of forces are acting on the contact lens fitted on the cornea and its subsequent motion. Methods: A capillary action-induced force develops in the tear layer between the lens and cornea, which leads to the restoring force due to difference in layer thickness according to lens rotation. The characteristics of the lens movement can be determined by the various factors such as friction between eyelid and lens, acceleration force based on blinking and the restoring force incorporated with the viscous damping force. A mathematical model which consists of the differential equations and their numerical solution was proposed to analyze the damped motion of lenses. The model predicts the time dependence of lenses during and after the blink varying the BC, blink period and eyelid pressure. Results: It was found that both the blink period and lid pressure increases the movement increases because of the enhanced lid friction. As the BC increases the viscous damping reduces due to the lacrimal layer's increase which resulted in the enhanced lens motion. After blink the lens illustrates the damped oscillation because of the restoring force by the increased lacrimal layer thickness and reduced viscous resistance. The time for the lens to return to the equilibrium shortens as the BC increase because of the resistance reduction. Conclusions: The movement of the contact lens is governed by the characteristics of the lacrimal layer between the lens and cornea as well as the lid blink.

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A Study for the Prediction of a Tire Cornering Characteristics using a Finite Element Method (유한요소법을 이용한 타이어 코너링특성 예측에 관한 연구)

  • 김항우;조규종
    • Transactions of the Korean Society of Automotive Engineers
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    • v.6 no.1
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    • pp.151-162
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    • 1998
  • During a straight driving and cornering maneuver by a vehicle various forces and moments are exerted on the tire's footprint. A cornering properties, handling and stability performances of vehicle can be predicted by these forces and moments values. Therefore, on this study, a lateral force and a aligning torque are predicted by these forces and moments values. Therefore, on this study, a lateral force and a aligning torque are predicted using a finite element method. Contact area of the tire between bead and wheel are fixed to simplify of a finite element model. Lateral force is exerted on the rigid surface as a real load with Coulum friction after inflate and load vertically. Then, rotate the tire's axle to simulate a free rolling untill taken the equilibrium of a aligning torque. Also, experimental observations are made to test a reliability of a FE analysis conducted in this study. The finite element analysis said that good agreement was obtained with experimental results of these cornering properties, giving confidence within about one percent. So it os recommended that a finite element analysis can be used as a good tool to predicted the tire cornering properties.

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Force density ratios of flexible borders to membrane in tension fabric structures

  • Asadi, H.;Hariri-Ardebili, M.A.;Mirtaheri, M.;Zandi, A.P.
    • Structural Engineering and Mechanics
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    • v.67 no.6
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    • pp.555-563
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    • 2018
  • Architectural fabrics membranes have not only the structural performance but also act as an efficient cladding to cover large areas. Because of the direct relationship between form and force distribution in tension membrane structures, form-finding procedure is an important issue. Ideally, once the optimal form is found, a uniform pre-stressing is applied to the fabric which takes the form of a minimal surface. The force density method is one of the most efficient computational form-finding techniques to solve the initial equilibrium equations. In this method, the force density ratios of the borders to the membrane is the main parameter for shape-finding. In fact, the shape is evolved and improved with the help of the stress state that is combined with the desired boundary conditions. This paper is evaluated the optimum amount of this ratio considering the curvature of the flexible boarders for structural configurations, i.e., hypar and conic membranes. Results of this study can be used (in the absence of the guidelines) for the fast and optimal design of fabric structures.

Vibration Analysis of 5-DOF Rotor System Supported by Two or More Ball Bearings Considering Centrifugal Force and Gyroscopic Moment of Ball (Waviness가 존재하며 볼의 원심력과 자이로스코픽 모멘트가 작용하는 볼베어링으로 지지된 5 자유도 회전계의 진동해석)

  • 정성원;장건희
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2001.11a
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    • pp.297-303
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    • 2001
  • This research presents an analytical model to characterize the ball bearing vibration due to the waviness in a rigid rotor supported by multi-row ball bearings considering centrifugal force and gyroscopic moment of ball. The effects of centrifugal force and gyroscopic moment are introduced to the kinematic constraints and force equilibrium equations. The waviness of ball and races is modeled by the superposition of sinusoidal function and it is introduced to position vectors of race curvature center to use the Hertzian contact theory in order to calculate the elastic deflection and nonlinear contact force resulting from the waviness while the rotor has translational and angular motion. They can be determined by solving the nonlinear equations of motion with five degrees of freedom by using the Runge-Kutta-Fehlberg algorithm. The accuracy of this research is validated by comparing with the results of the prior researches. It characterizes the vibration frequencies resulting from the various kinds of waviness in rolling elements, the harmonic frequencies resulting from the nonlinear load-deflection characteristics of ball bearing resulting from the waviness interaction.

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