• Title/Summary/Keyword: Damping force

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A Study on the Wave Drift Damping of Ship in Waves (파랑중 선박의 표류감쇠에 관한 연구)

  • 이호영;박홍식;신현경
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • 2000.04a
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    • pp.7-12
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    • 2000
  • As the offshore oil fields are moved to the deep ocean, the oil production systems of FPSO(Floating production storage and offloading system) are building these days and so it is the most important to estimate the drift motion and damping effects the drift motion importantly. The components of damping consist of viscous, wave radiation effect and wave drift damping. It is need to estimate the wave drift damping exactly among them. The wave drift damping means the change rate of mean wave drift force with respect to the ship and ocean structures speed. In order to calculate this, the 3-Dimensional panel method used to translating and pulsating Green function is adopted. The calculation is carried out for series 60(CB = 0.7) vessel and the results are compared with other theoretical ones.

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A Study on the Wave Drift Damping of a Moored Ship in Waves (파랑중 계류된 선박의 표류감쇠에 관한 연구)

  • 이호영;박홍식;신현경
    • Journal of Ocean Engineering and Technology
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    • v.14 no.4
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    • pp.17-22
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    • 2000
  • As the offshore oil fields are moved to the deep ocean, the oil production system of FPSO(Floating Production Storage and Offloading System) Type are constructed frequently these days. So, it is very important to estimate the drift motion and damping effects due to the drift motion simultaneously. The components of slow drift motion damping consist of viscous, wave radiation effect and wave drift damping. It is needed to estimate the wave drift damping more accurately than others. The wave drift damping signifies the time-rate of mean wave drift force on oscillating ship or ocean structure which constant speed. In order to calculate this, the 3-Dimensional panel method is employed with the translating and pulsating Green function in the frequency domain. The calculation is carried out for a Series 60 ($C_B$/=0.7) and the results are compared with other numerical ones.

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Bending Moment Characteristics of Flexibly Supported Infinite Beam Subjected to an Axial Force and a Moving Load (이동하중(移動荷重)과 축하중(軸荷重)이 작용(作用)하는 유연(柔軟)한 기초(基礎)위에 지지(支持)된 무한(無限)보의 휨모멘트 특성(特性))

  • Hong, Dong Pyo;Kim, Kwang Sic
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.2 no.3
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    • pp.15-22
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    • 1982
  • This paper presents analytic bending moment solution and resonance diagrams for a uniform beam of infinite length subjected to anaxial force and moving transverse load. Solutions are obtained that are time invariant in a coordinate system moving with the load velocity. The supporting foundation includes damping effects. The influences of the axial force, damping coefficient and load velocity on the beam response are studied. The limiting case of no damping and critial damping are also investigated. The profiles of the mement of the beam is shown graphically for several values of the load speed, the axial force and damping parameters.

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Estimation of damping induced by taut mooring lines

  • Xiong, Lingzhi;Lu, Wenyue;Li, Xin;Guo, Xiaoxian
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.12 no.1
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    • pp.810-818
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    • 2020
  • A moored floating structure may exhibit resonant motion responses to low-frequency excitations. Similar to the resonant responses of many vibration systems, the motion amplitude of a moored floating structure is significantly affected by the damping of the entire system. In such cases, the damping contributed by the mooring lines sometimes accounts for as much as 80% of the total damping. While the damping induced by catenary mooring lines is well-investigated, few studies have been conducted on the damping induced by taut mooring lines, especially one partly embedded in soil. The present study develops a simple but accurate model for estimating the damping contributed by mooring lines. A typical type of taut mooring line was used as the reference and the hydrodynamic drag force and soil resistance were taken into consideration. The proposed model was validated by comparing its predictions with those of a previously developed model and experimental measurements obtained by a physical model. Case studies and sensitivity studies were also conducted using the validated model. The damping induced by the soil resistance was found to be considerably smaller than the hydrodynamic damping. The superposition of the wave frequency motion on the low-frequency motion was also observed to significantly amplify the damping induced by the mooring lines.

An Analysis and Test Results of Damping Characteristics of ER Dampers with Two Different Valve Types (ER 댐퍼의 밸브 형상에 따른 감쇠 특성의 해석 및 실험)

  • 장보영;이종민;김창호;박영필
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 1998.04a
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    • pp.608-613
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    • 1998
  • Damping characteristics of ER dampers and flow rates inside ER valve with two different valve types were analyzed and compared with test results. Fluid flow inside ER valves was modeled by Bingham plastic model and Hagen-Poiseulli flow, while the equations of motion of total ER damper system were modeled by flow and hydraulic force balance. A general straight valve case was compared with a bended valve case which is newly tested for a possible improvement of ER damping force. As expected, the bended ER valve generates higher damping force and lower flow rates than the conventional straight ER valve due to additional flow restriction at the bended section. Analytical models of ER valve and ER damper generally predict reasonable performance characteristics of tested results. Therefore, developed analysis can be used for designing new ER dampers and simulation of ER semi-active suspension system as well.

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An Experimental Study on Performances of Leaf Spring Pad Air Bearing (판 스프링 패드 공기베어링 성능에 관한 실험적 연구)

  • 이희락;제양규
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2003.05a
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    • pp.94-99
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    • 2003
  • As the rotating speed of rotors is increased, the instability and power loss become serious problems. Gas bearings are introduced as a good solution to those problems. But in the development of gas bearings, high load capacity and high damping force to vibrations are required. In this study a new air bearing using leaf spring pad is introduced to improve load capacity and damping force. The experimental results of the leaf spring pad air bearings show high load capacity and high damping forces. And the results show that leaf spring pad air bearings can be simultaneously acted as radial and thrust bearings

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Dynamic Characteristics of Eddy Current Damper (와전류 댐퍼의 동적특성)

  • Kwag, Dong-Gi;Hwang, Jai-Hyuk;Bae, Jae-Sung
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2007.05a
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    • pp.947-951
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    • 2007
  • This paper is concerned with a new concept for the damper without neither a coil spring nor fluid. The new damper concept consists of the permanent magnets and the cylinder of the conducting material. The opposite pole magnets produces the repulsive forces and this is substituted for the coil spring. The relative motion between the magnets and conducting cylinder produces eddy currents thus resulting in the electromagnetic force, which turns out to be the damping force thus and is substituted for a damping fluid. This damper is called the eddy current damper(ECD). The important advantage of the proposed ECD is that it does not require the damping fluid and any external power and is non-contacting and relatively insensitive to temperature. In the present study, the proposed ECD was constructed and experiments were performed to investigate its dynamic characteristics. The experiments shows that the proposed ECD has the excellent damping ability.

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Effects of damping on the linear stability of a free-free beam subjected to follower and transversal forces

  • Kavianipour, O.;Sadati, S.H.
    • Structural Engineering and Mechanics
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    • v.33 no.6
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    • pp.709-724
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    • 2009
  • In this paper a free-free uniform beam with damping effects subjected to follower and transversal forces at its end is considered as a model for a space structure. The effect of damping on the stability of the system is first investigated and the effects of the follower and transversal forces on the vibration of the beam are shown next. Proportional damping model is used in this work, hence, the effects of both internal (material) and external (viscous fluid) damping on the system are noted. In order to derive the frequency of the system, the Ritz method has been used. The mode shapes of the system must therefore be extracted. The Newmark method is utilized in the study of the system vibration. The results show that an increase in the follower and transversal forces leads to an increase of the vibrational motion of the beam which is not desirable.

A Parametric Study on the Shear-deformation Effect for Beck's Column under Follower Force (비보존력을 받는 Beck 기둥의 전단변형효과에 관한 매개변수적 고찰)

  • Lee Jun-Seok;Kim Nam-Il;Kim Moon-Young
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 2006.04a
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    • pp.985-991
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    • 2006
  • For a shear-deformable beam-column element subjected to non-conservative forces. equations of motion and a finite element formulation are presented applying extended Hamilton's principle. The influence of non-conservative force's direction parameter. internal and external damping forces, and shear deformation and rotary inertia effects on divergence and flutter loads of Beck's columns are intensively investigated based on element stiffness. damping and mass matrixes derived for the non-conservative system.

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Numerical Analysis on Hydrodynamic Forces Acting on Side-by-Side Arranged Two-Dimensional Floating Bodies in Viscous Flows (점성유동장에 병렬배치된 2차원 부유체에 작용하는 유체력에 관한 수치해석)

  • Heo, Jae-Kyung;Park, Jong-Chun
    • Journal of the Society of Naval Architects of Korea
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    • v.49 no.5
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    • pp.425-432
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    • 2012
  • Viscous flow fields of side-by-side arranged two-dimensional floating bodies are numerically simulated by a Navier-Stokes equation solver. Two identical bodies with a narrow gap are forced to heave and sway motions. Square and rounded bilge hull forms are compared to find out the effects of vortex shedding on damping force. Wave height, force RAOs, added mass and damping coefficients including non-diagonal cross coefficients are calculated and a similarity between the wave height and force RAOs is discussed. CFD which can take into account of viscous damping and vortex shedding shows better results than linear potential theory.