• Geomechanics and Engineering
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• 제33권5호
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• pp.519-528
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• 2023

In this paper, we present the results of an experimental study on the effect of polymer support fluid on shaft resistance of offshore bored piles. A series of pullout tests were performed on bored piles installed under various boundary conditions considering different types of grounds and support fluids, and a range of support fluid exposure times. Contrary to previous studies concerning onshore bored piles, a time dependent effect of polymer fluid on shaft resistance was observed in all ground types. The adverse effect of polymer support fluid on the shaft resistance, however, was considerably less than bentonite support fluid for a given exposure time. No significant reduction in shaft resistance was evident when limiting the exposure time of the polymer support fluid to the side wall of the borehole within 2-3 hours. The degree to which the polymer fluid affects shaft resistance seemed to vary with the ground type. A proper consideration should be given to the time dependent effect of polymer fluid on shaft resistance of bored piles installed in offshore construction environment to limit its adverse effect on the pile performance. The practical implications of the findings are discussed.

• 한국소음진동공학회논문집
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• 제21권5호
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• pp.422-429
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• 2011

The critical fluid velocity of cantilevered cylindrical shells subjected to internal fluid flow is investigated in this study. The fluid-structure interaction is considered in the analysis. The cantilevered cylindrical shell is supported intermediately at an arbitrary axial position. The intermediate support is simulated by two types of artificial springs: translational and rotational spring. It is assumed that the artificial springs are placed continuously and uniformly on the middle surface of an intermediate support along the circumferential direction. The steady flow of fluid is described by the classical potential flow theory. The motion of shell is represented by the first order shear deformation theory (FSDT) to account for rotary inertia and transverse shear strains. The effect of internal fluid can be considered by imposing a relation between the fluid pressure and the radial displacement of the structure at the interface. Numerical examples are presented and compared with existing results.

• 대한기계학회논문집
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• 제15권6호
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• pp.1799-1806
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• 1991

본 연구에서는 양단이 지지된 단순 모델을 사용하여, 양단 사이의 한 위치에 탄성지지를 할 때 고유진동수 변화를 검토하고 고유진동수를 높이는 방안을 제시하고 자 한다. 또한 분산변수계(distributed parameter system)을 사용하는 경우, 일반적 으로 홀수차항이 있는 미분방정식에서 그 해를 다항식, 고유벡터나 삼각함수의 무한개 의 합 등으로 표시하고 있으나 본 연구에서는 미분 방정식으로 표시하는 방법을 사용 하여 완전해(closed form solution)로 표시하여 구함으로서 오차를 제거하고 계산을 간결하게 하였다.

• 한국소음진동공학회논문집
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• 제18권2호
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• pp.177-184
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• 2008

The dynamic stability of elastically restrained cantilever pipe conveying fluid with crack is investigated in this paper. The pipe, which is fixed at one end, is assumed to rest on an intermediate spring support. Based on the Euler-Bernoulli beam theory, the equation of motion is derived by the energy expressions using extended Hamilton's Principle. The crack section is represented by a local flexibility matrix connecting two undamaged pipe segments. The influence of a crack severity and position, mass ratio and the velocity of fluid flow on the stability of a cantilever pipe by the numerical method are studied. Also, the critical flow velocity for the flutter and divergence due to variation in the support location and the stiffness of the spring support is presented. The stability maps of the pipe system are obtained as a function of mass ratios and effect of crack.

• Nuclear Engineering and Technology
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• 제42권1호
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• pp.97-108
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• 2010

Fluid-elastic instability and turbulence-induced vibration of steam generator U-tubes of a nuclear power plant are studied numerically to investigate the effect of design changes of support structures in the upper region of the tubes. Two steam generator models, Model A and Model B, are considered in this study. The main design features of both models are identical except for the conditions of vertical and horizontal support bars. The location and number of vertical and horizontal support bars at the middle of the U-bend region in Model A differs from that of Model B. The stability ratio and the amplitude of turbulence-induced vibration are calculated by a computer program based on the ASME code. The mode shape with a large modal displacement at the upper region of the U-tube is the key parameter related to the fretting wear between the tube and its support structures, such as vertical, horizontal, and diagonal support bars. Therefore, the location and the number of vertical and horizontal support bars have a great influence on the fretting wear mechanism. The variation in the stability ratios for each vibrational mode is compared with respect to Model A and Model B. Even though both models satisfy the design criteria, Model A shows substantial improvements over Model B, particularly in terms of having greater amplitude margins in the turbulence-excited vibration (especially at the inner region of the tube bundle) and better stability ratios for the fluid-elastic instability.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.67-70
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• 2002

This paper presents the property of the Squeeze Film Damper (SFD) using Magneto-Rheological fluid (MR fluid). The damping property of a SFD for a flexible rotor system varied according to vibration mode. MR fluid is known as a functional fluid with controllable apparent viscosity of the fluid by applied magnetic field strength. When the MR fluid is applied in the SFD, the SFD using MR fluid can effectively reduce vibrations of the flexible rotor in a wide range of rotating speed by control of the applied magnetic field strength. To investigate in detail the SFD using MR fluid, the SFD to support one mass was constructed and its performance was experimentally investigated in the present study. The damping property of the SFD using MR fluid has viscous damping by Newtonian fluid, but not Coulomb friction by Bingham fluid. Therefore, The system damped by the SFD can be considered as a linear system.

• 한국소음진동공학회논문집
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• 제19권6호
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• pp.569-574
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• 2009

The paper presents the influences of the external damping and the tip mass on dynamic stability of a vertical cantilevered pipe conveying fluid. In general, real pipe systems may have some valves and attached mechanical parts, which can be regarded as attached lumped masses and support-dampers. The support-dampers can be assumed as viscous dampers. The equations of motion are derived by energy expressions using extended Hamilton's principle, and some numerical results using Galerkin's method are presented. Critical flow velocities and stability maps of the pipe with external dampers and tip mass are obtained for various tip mass ratios, external damping coefficients and positions of the viscous dampers.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.465-468
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• 2005

The paper deals with the influences of external damping and tip mass on dynamic stability of a vertical cantilevered pipe conveying fluid. In general, real pipe systems may have some valves and attached parts, which can be regarded as attached lumped masses and support-dampers. The support-dampers can be assumed as viscous dampers. The equations of motion are derived by energy expressions using extended Hamilton's principle, and some numerical results using Galerkin's method are presented. Critical flow velocities and stability maps of the pipe with external dampers and tip mass are obtained for various tip mass ratios, external damping coefficients and positions of the viscous dampers.

• 대한간호학회지
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• 제45권5호
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• pp.773-782
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• 2015

Purpose: The purpose of this study was to explore the experience of fluid management in hemodialysis patients by describing how they manage fluid intake and what affects fluid management. Methods: Purposive sampling yielded 11 patients who have received hemodialysis for one year or longer in one general hospital. Data were collected through in-depth interviews and analysed using Giorgi's phenomenological method. Data collection and analysis were performed concurrently. Results: The findings regarding how hemodialysis patients manage fluid intake were classified into four constituents: 'recognizing the need for fluid control', 'observing the status of fluid accumulation', 'controlling fluid intake and output', 'getting used to fluid management'. The factors that affect fluid management of hemodialysis patients were revealed as 'willpower', 'change in the mindset', 'support system', and 'emotional state'. Conclusion: The study results show that hemodialysis patients manage fluid intake through food and exercise as well as interpersonal relationships. These findings suggest that strategies in the development of nursing interventions for hemodialysis patients should be directed at assisting them in familiarization with fluid management based on an understanding of their sociocultural contexts.

• 한국소음진동공학회논문집
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• 제22권5호
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• pp.407-412
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• 2012

The dynamic instability and natural frequency of an axially moving pipe conveying fluid are investigated. Thus, the effects of fluid velocity and moving speed on the stability of the system are studied. The governing equation of motion of the moving pipe conveying fluid is derived from the extended Hamilton's principle. The eigenvalues are investigated for the pipe system via the Galerkin method under the simple support boundary. Numerical examples show the effects of the fluid velocity and moving speed on the stability of system. Moreover, the lowest critical moving speeds for the simply supported ends have been presented.